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Disparities in Antihypertensive Medication Adherence in Persons With Disabilities and Without Disabilities: Results of a Korean Population-Based Study
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ORIGINAL ARTICLE
Disparities in Antihypertensive Medication Adherence in Persons With Disabilities and Without Disabilities: Results of a Korean Population-Based Study Jong Hyock Park, MD, MPH, Jae Hyun Park, MD, PhD, MPH, Sang Yi Lee, MD, PhD, So Young Kim, MD, Youngsoo Shin, MD, DrPH, MPH, Su Young Kim, PhD ABSTRACT. Park JH, Park JH, Lee SY, Kim SY, Shin Y, Kim SY. Disparities in antihypertensive medication adherence in persons with disabilities and without disabilities: results of a Korean population-based study. Arch Phys Med Rehabil 2008;89: 1460-7. Objective: To determine disparities in antihypertensive medication adherence between persons with disabilities and those without disabilities in South Korea. Design: The study compared antihypertensive medication adherence between persons with disabilities and those without disabilities using medical claims data of the National Health Insurance (NHI). Setting: We obtained data from claims submitted to the NHI, which covers almost the entire Korean population. Persons who were prescribed antihypertensive medication during the calendar year 2004 were identified. Participants: The study comprised data from persons with disabilities (n⫽85,098) and persons without disabilities (n⫽2,368,636). Interventions: Not applicable. Main Outcome Measures: A cumulative medication adherence (CMA) greater than or equal to 80% was defined as an appropriate medication adherence. Multiple logistic regression was used to identify differences in antihypertensive medication adherence between persons with disabilities and without disabilities. Estimates were adjusted for demographic characteristics (sex, age), type of medical insurance, insurance contribution a month as a proxy for household income, residential area, and clinical characteristics (medication duration, comorbid conditions). Results: People with disabilities had lower CMAs than those without (median CMA, 83.6% vs 85.7%; appropriate medication adherence, 54.5% vs 57.5%). Results of the multiple logistic regression adjusting other factors indicated that people with disabilities had decreased probabilities of appropriate adherence. Conclusions: Medication adherence is reduced by various types of disability and impairment such as those involving
From the Cancer Policy and Management Branch, National Cancer Center (Jong Park, Jae Park), Department of Preventive Medicine, Cheju University College of Medicine, Cheju, Korea (Lee); Department of Healthcare Industry, Korea Health Industry Development Institute, Seoul, Korea (So Kim); Department of Health Policy and Management, Seoul National University College of Medicine, Seoul, Korea (Shin); and Department of Preventive Medicine, Cheju University College of Medicine, Jeju, Korea (Su Kim). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to Jae Hyun Park, MD, PhD, MPH, National Cancer Center, 809 Madu1-dong, Ilsandong-gu, Goyang-si, Gyeonggi-do, 410-769, Korea, e-mail: [email protected]. 0003-9993/08/8908-00306$34.00/0 doi:10.1016/j.apmr.2007.12.045
Arch Phys Med Rehabil Vol 89, August 2008
mobility and communication. Much effort should be made to investigate how and why these disparities take place and develop health policies to remove these disparities if they exist. Key Words: Antihypertensive agents; Disabled persons; Patient compliance; Rehabilitation. © 2008 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation YPERTENSION IS A MAJOR risk factor for cardiovascular disease, as well as morbidity and mortality caused H by stroke. These diseases can be effectively prevented by 1
controlling hypertension on a daily basis. A recent meta-analysis showed that the odds of good blood pressure control among patients who adhered to their antihypertensive medication regimens versus those who did not were 3.44 (95% CI, 1.60 –7.37).2 Therefore, increasing a patient’s adherence to an antihypertensive medication regimen is an important component of successful hypertension control. However, although many studies have shown that the persons with disabilities were less likely to use appropriate health care services,3-8 studies investigating the relationship between disability and medication adherence have rarely been conducted so far. Nosé et al9 reported in their systematic review of 103 studies that 26% of 23,796 patients with psychoses were not adherent to antipsychotic therapy. However, there have not been any studies that investigated whether various disability types (physical, visual, auditory, internal organ, mental disability) have a negative impact on medication adherence. In addition, understanding the importance of antihypertensive medication adherence on successful hypertension control, it is highly valuable to investigate the relationship between disability and antihypertensive medication adherence. Therefore, this study was attempted to investigate whether there is a gap between the persons with disabilities and those without disabilities regarding adherence to antihypertensive drug therapy by adjusting other factors previously associated with antihypertensive medication adherence; these factors were demographic characteristics such as sex, age, type of medical insurance, insurance contributions a month as a proxy for household income, residential area, and clinical characteristics such as medication duration and comorbid conditions.
List of Abbreviations ADLs AOR CI CMA KDA NHI
activities of daily living adjusted odds ratio confidence interval cumulative medication adherence Korean Disability Act National Health Insurance
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park Table 1: Disablement Characteristics According to the KDA Category
Disabling Condition
External physical disability
Definition
Physical impairment Brain impairment Visual impairment Auditory impairment Linguistic impairment Facial deformity
Internal organ disability
Renal function impairment Heart function impairment Liver function impairment Respiratory function impairment Intestinal and urinary tract function impairment
Mental disability
Epilepsy Mental retardation Developmental disability Mental impairment
Amputation, motor disturbance, joint disability, deformity of limbs, spinal cord injury Brain disability caused by stroke, brain damage, brain palsy Visual power loss, visual field defect Hearing disability, disability of the sense of equilibrium Mogilalia, dysphonia Facial deformity caused by head injury, a burn, cancer surgery Renal impairment with hemodialysis, kidney transplantation Heart impairment with daily life limitation Liver impairment with daily life limitation Respiratory impairment with daily life limitation Intestinal and urinary tract impairment with daily life limitation Epilepsy with daily life limitation Intelligence quotient ⬍70 Autism, developmental impairment Mental diseases with daily life limitation
NOTE. The level of severity for each condition ranges from 1 (severe) to 6 (mild).
METHODS Data Source Analyses were conducted using the NHI database (2004) and the National Disability Database. The latter comprises approximately 77.7% of the population with disabilities registered in the National Social Security System.10 In South Korea, the NHI provides mandatory universal health insurance, offering comprehensive medical care coverage to all South Korean residents. Patients should visit a doctor to obtain a prescription and then visit a pharmacy to fill that prescription, according to the prescription-dispensation separation policy instituted in 2000. The NHI pharmacy claims are generated when a patient uses insurance coverage to fill a prescription. The claims are then entered into the NHI’s claims database. We could not include the information of Medicaid beneficiaries, who account for about 3.1% of all Korean residents, because of the lack of information in the NHI claims database. The Medicaid program is a public assistance scheme to secure the minimum livelihood for low-income households and to provide them with medical services. We used pharmacy claims data and enrollment records from January 1, 2004, to December 31, 2004. The data comprised patients’ disease codes, the dates that prescriptions were generated and filled, and the days’ worth of pills supplied. Enrollment records included patients’ insurance identification numbers and information regarding sex, age, contributions a month, and residential region. These were linked to the pharmacy claims data. Persons with disabilities were identified using the National Disability Registry (2003), which is a voluntary self-report system for persons with disabilities and is linked with the pharmacy claims data. This database is assumed to cover 77.7% of the total population with disabilities.10 It contains social security numbers and information regarding disability characteristics such as disability type and severity. Disabilities are classified into 15 groups, and diagnosis is made by the respective medical specialist. The severity of the disability is graded from 1 to 6, indicating very severe to very mild, on the
basis of functional losses and clinical impairment, as determined by the medical specialist. Diagnostic criteria are specified in the KDA (table 1). The personal identification number used for data linkage was deleted before analysis. In addition, this study was a secondary data analysis. For these reasons, this study was inapplicable to the review from the scientific review panel. Study Population The source population consisted of patients over the age of 20 years who visited a doctor more than once for hypertension (International Classification of Diseases and Related Health Problems–10th Revision), as reported in claims data from January to December 31, 2004. Accordingly, the target population consisted of 2,716,682 subjects. This corresponded to 28.7% of the 9,475,043 NHI beneficiaries who were over 20 years of age. In the target population, patients who filled only 1 prescription for an antihypertensive were excluded because the CMA can be calculated only when a prescription has been filled more than twice. Patients who had been hospitalized during the study period were also excluded because adherence to a medication regimen during hospitalization is enforced by the medical staff and requires no effort on the part of the patient. On the basis of these criteria, the study population comprised 2,453,734 patients, which was 90.3% of the source population. In this group, there were 85,098 persons with disabilities and 2,368,636 persons without disabilities. Outcome Measures Adherence to a medication regimen was measured using the CMA scale, which is based on the pharmacy claims data.11 The CMA is defined as the percentage of days for which the patient has pills available. This proportion is calculated by dividing the total number of days of medication dispensed (excluding the final prescription) by the total number of days between the first and last prescriptions. For example, patients who filled 3 hypertension prescriptions for 30 pills each, with the last preArch Phys Med Rehabil Vol 89, August 2008
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park
scription filled 90 days after the first one, would have a CMA of 67% (ie, 60/90⫻100) because they had 60 pills available during the 90 days between the first and last prescriptions. Pills from the last prescriptions are not included because the number of days taken to consume these pills is unknown. Therefore, theoretically, the denominator or the total number of days between the first and last prescriptions can range from 1 day to 12 months. For the numerator, the total number of days of medication dispensed (excluding the final prescription) can range from 1 day to over 12 months because patients get the prescription before finishing the previous prescription (prescription duplication). Therefore, CMA can range from 0% to over 100% because of prescription duplication. A CMA greater than or equal to 80% was considered appropriate medication adherence because it is a commonly used threshold to define antihypertensive medication adherence.12,13 Haynes et al14 reported that hypertension of those who were adherent over 80% of antihypertensive medication was better controlled than those who were adherent under 80%. Adjustment Factors We reviewed studies that evaluated factors that influence medication adherence, and the appropriate adjustment factors were selected.11-13,15 These factors consisted of patient demographic characteristics such as sex and age; clinical characteristics such as medication duration and comorbid conditions; socioeconomic characteristics such as type of medical insurance (self-employed vs employee) and insurance contributions a month as a proxy for household income; and community factors such as type of residential area (metropolitan city, city, rural area, mostly rural area). In previous studies, sex was reported to be related with medication adherence in some studies, while in other studies, it was not.16-18 As for age, several studies reported the trend of increasing medication adherence with increasing age.17-20 Patients’ socioeconomic level,21 patients’ residential area,22,23 duration of medication,21 and patients’ comorbidity21 were also reported to be related with medication adherence previously. Comorbid conditions were classified into 2 disease groups. Class 1 comprised hypertension-related diseases—for example, diabetes mellitus, obesity, and target organ damage caused by hypertension, as defined by the Joint National Committee.1 Class 2 comprised chronic diseases, which were assumed to increase both the number of pharmacy visits and overall medication adherence. Diseases in this group included migraine and other headache syndromes, chronic lower respiratory diseases, and inflammatory polyarthropathies. Statistical Analysis Because the distribution of CMA was not normative, the median and interquartile range of CMAs and the medication adherence rates of persons with and without disabilities were calculated according to the type and severity of the disability. The type of disability was coded as total disability if study subjects were registered in the National Disability Registry and coded as no disability if study subjects were not. In these processes, various types of disability and disease severity were also coded using information in the National Disability Registry. A severe disability was scored as 1 to 3 and a mild disability as 4 to 6. To determine whether various types of disability and severity of disability have influence on the medication adherence, we used the multiple logistic regression model, adjusting for confounding factors and setting the outcome (ie, appropriate medication adherence defined as CMA ⱖ80%) as a binary variable. Various types of disability and Arch Phys Med Rehabil Vol 89, August 2008
severity of disability were entered in the multiple logistic regression model 1 by 1, adjusting the same confounding factors. Estimates were adjusted for demographic characteristics (sex, age), insurance contributions a month as a proxy for household income, residential area, and clinical characteristics (medication duration, comorbid conditions). All analyses were performed using SAS 81.a Statistical significance was defined as 2-tailed P value less than or equal to .05. RESULTS Characteristics of Persons With Disabilities and Without Disabilities We summarized the general characteristics of the persons with disabilities and those without disabilities (table 2). Of the 2,453,734 persons in the study, those with disabilities accounted for 3.47% (n⫽85,098). Male sex occurred more frequently in the population with disabilities than in those without disabilities (61.1% vs 41.2%). In addition, the proportion of self-employed and the number of people with comorbid conditions were higher in the population with disabilities (66.3% vs 43.6% and 65.2% vs 56.4%, respectively). The household income of people with disabilities was lower than that of those without disabilities. CMAs According to Disability Condition and Severity The median and interquartile range of CMAs were calculated by classifying the population with disabilities according to disability type and severity (table 3). Except for the group with some types of mental and internal organ disability, most people with disability had lower CMAs than those without. Furthermore, people with more severe disability had lower CMAs than those with mild disability for disabilities such as brain impairment, auditory impairment, mental retardation, and epilepsy. Disparity in Antihypertensive Medication Adherence According to Disability Condition and Severity The multiple logistic regression adjusting other demographic and clinical variables (table 4) indicated that disability was associated with a lower CMA (AOR⫽.87; 95% CI, .86 –.88). In addition, people with severe disabilities were more likely to have a lower CMA than those with mild disability. Severe limb (AOR⫽.87; 95% CI, .85–.90), brain (AOR⫽.90; 95% CI, .86 –.94), visual (AOR⫽.88; 95% CI, .81–.95), auditory (AOR⫽.76; 95% CI, .70 –.81), and internal organ (AOR⫽.58; 95% CI, .53–.65) impairments were associated with a lower appropriate medication adherence. Higher disability severity was associated with lower CMA. For subjects disabled with a facial deformity or a linguistic, intellectual, or chronic mental impairment, there were no disparities in medication adherence compared with the population without disabilities. DISCUSSION In this study, we confirmed that there is a disparity in medication adherence between persons with disabilities and without disabilities, adjusting demographic and clinical variables (AOR⫽.87; 95% CI, .86 –.88). In the sense that the odds of good blood pressure control among patients adherent to antihypertensive medications, compared with those who were nonadherent, were 3.44 (95% CI, 1.60 –7.37) in a recent metaanalysis,2 this disparity indicates a great clinical impact and health outcome on the persons with disabilities. Previous studies showed that the relationship between high blood pressure and the risk of cardiovascular disease events is continuous,
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park Table 2: Characteristics of the Persons With and Without Disabilities People Without Disabilities
People With Disabilities
Variable
No.
%
No.
%
Total Sex Men Women Age (y 20–29 30–39 40–49 50–59 60–69 ⱖ70 Type of medical insurance Self-employed Employee Comorbidity None of class 1 or 2 diseases Class 1* Class 2† Both class 1 and 2 diseases Medication duration (mo) ⬍6 6–11 12–17 ⱖ18 Contribution a month (Korean won) ⬍30,000 30,000–70,000 ⬎70,000 Residential area Metropolitan area City Rural Mostly rural
2,368,636
100.00
85,098
100.00
975,452 1,393,184
41.18 58.82
51,985 33,113
61.09 38.91
7554 62,370 327,419 628,774 734,103 608,416
0.32 2.63 13.82 26.55 30.99 25.69
137 1310 8971 22,312 31,526 20,842
0.16 1.54 10.54 26.22 37.05 24.49
1,032,762 1,335,874
43.60 56.40
56,453 28,645
66.34 33.66
1,047,617 911,924 272,785 136,310
44.23 38.50 11.52 5.75
30,165 41,407 8277 5249
35.45 48.66 9.73 6.17
162,808 266,516 275,845 1,663,467
6.87 11.25 11.65 70.23
4829 8479 9392 62,398
5.67 9.96 11.04 73.32
755,849 975,384 637,403
31.91 41.18 26.91
32,986 33,890 18,222
38.76 39.82 21.41
1,119,310 990,661 102,529 156,130
47.26 41.82 4.33 6.59
36,518 37,505 4496 6579
42.91 44.07 5.28 7.73
*Class 1: diabetes mellitus and target organ damage caused by hypertension. † Class 2: chronic disease assumed to increase ambulatory service use.
consistent, and independent of other risk factors. The higher the blood pressure, the greater the chances of heart attack, heart failure, stroke, and kidney diseases.24 This means that persons with disabilities are more vulnerable to the various diseases related to hypertension because of a lower antihypertensive medication adherence rate. A previous study showed with empirical data that subjects with disabilities were significantly more likely than those without disabilities to suffer from chronic health conditions such as high blood pressure and other cardiovascular disease.25 Another study also showed that people with disabilities who had hypertension, apart from their original impairments, are likely to experience secondary functional losses such as cardiovascular diseases, strokes, chronic kidney disease, peripheral arterial disease, and retinopathy.1,3 Uncontrolled hypertension and a high prevalence of hypertension-related diseases may have many causes. However, this study result suggests a potential relationship between low adherence of antihypertensive medication adherence and secondary functional losses such as cardiovascular diseases and strokes among persons with disabilities. In this study, people with limb, brain, visual, auditory, or internal organ impairments had lower CMAs than people without these disabilities. According to the KDA classification, limb impairment includes disability resulting from amputation,
motor disturbance, joint disability, limb deformities, and spinal cord injuries.26 Brain impairment includes disability caused by stroke, brain damage, and brain palsy. In both types of disability, severity is decided mainly by the level of impaired mobility. For example, people with brain impairment who do not have mobility impairment as well are considered to have mild brain impairment, which might be the reason for lack of a statistically significant difference in medication adherence between this population and the persons without disabilities. Conversely, people with limb impairment or severe brain impairment inevitably have some degrees of mobility impairment. Previous studies7,26 reported that people with brain impairment are less able to carry out the ADLs, which include essential activities. Thus, it can be assumed that people with limb impairment and severe brain impairment are less likely to adhere to an antihypertensive medication regimen mainly because of impaired mobility, but also because of problems in performing the ADLs. People with mobility impairments are also confronted with the problem of transportation to seek and obtain medications.25,27-29 The necessary mode of transportation may not be particularly accessible, and other unexpected obstacles may make it difficult to reach a clinic or pharmacy. In Korea, despite the provisions of the KDA, physical barriers to primary care givers still remain.26,30 Similar problems with Arch Phys Med Rehabil Vol 89, August 2008
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park Table 3: CMA by Disabling Condition and Severity Total
Mild Disability
Variable
No.
Median
IQR
ⱖ80% CMA
Persons without disabilities Persons with disabilities External disability Limb impairment Brain impairment Visual impairment Auditory impairment Linguistic impairment Facial deformity Mental disability Mental retardation Developmental disability Mental disease Internal organ disability Renal impairment Heart impairment Respiratory impairment Liver impairment Intestinal and urinary tract impairment Epilepsy
2,368,636 85,098
85.71 83.56
38.34 42.13
57.53 54.54
49,943
50,070 12,014 9846 8564 1833 20
83.45 85.94 83.28 81.68 84.98 85.14
41.52 40.57 42.01 44.43 40.49 34.21
54.63 57.08 54.34 52.01 56.79 60.00
786 10 171
84.94 82.33 87.46
44.69 27.02 43.44
557 782 204 44 178
59.65 82.87 76.16 51.29 84.66
19
56.36
Severe Disability
IQR
ⱖ80% CMA
No.
Median
IQR
ⱖ80% CMA
83.33
⫺ 41.35
54.56
35,155
83.78
⫺ 43.28
54.51
33,155 2764 7529 5311 856 10
83.28 87.51 83.07 82.95 84.55 85.14
41.34 38.26 41.68 43.26 40.11 18.73
54.41 59.23 54.24 53.42 56.66 50.00
16,915 9250 2317 3253 977 10
83.92 85.47 83.57 79.72 85.71 85.14
41.87 41.65 43.06 46.26 40.78 18.73
55.04 56.44 54.64 49.71 56.91 70.00
53.82 50.00 60.23
58 2 3
87.93 78.48 97.92
35.19 0.92 11.48
56.90 0.00 100.00
728 8 168
84.85 85.96 86.75
45.18 39.95 43.77
53.57 62.50 59.52
73.22 49.52 46.31 62.24 41.65
35.73 52.56 45.10 31.82 53.37
68 3 0 6 166
69.83 97.34 — 38.08 84.30
64.40 215.27 — 54.56 41.02
41.18 66.67 — 33.33 53.01
489 779 204 38 12
58.61 82.82 76.16 53.66 88.71
74.89 49.52 46.31 65.82 51.32
34.97 52.50 45.10 31.58 58.33
71.27
26.32
12
58.18
71.22
33.33
7
56.36
44.60
14.29
No.
Median
Abbreviation: IQR, interquartile range.
disability laws have been reported in other countries such as the United States, the United Kingdom, and Australia.31,32 The lower CMAs in people with visual and auditory impairments may be explained by the attendant communication disability, as in cases in which vision is so poor that, even with corrective lenses, the person is unable to read medication consent forms or typical patient education materials; or when hearing is so severely impaired that, despite hearing aids, the person cannot understand shouted speech.33 Even in health care settings, aids to communication may be lacking for patients with altered mental states, impaired vision, or hearing deficits,33,34 all of which result in barriers affecting physicianpatient communication. For the patient, the clinical consequences of communication difficulties may be poor adherence to treatment recommendations.35 Limitations in ADLs caused by internal organ impairments such as impaired renal, heart, respiratory, liver, intestinal, or urinary tract function, or epilepsy resulted in lower CMAs than the controls. Patients with these disabilities had lower CMAs for the antihypertensive drug, even though they were being treated with medications for their impairments and were checked regularly by health care providers. These findings suggest that treatment for hypertension is often neglected in people with internal organ impairments who are receiving focused treatment for the damaged organ. For disabilities involving linguistic impairment, facial deformity, and intellectual disability, there were no disparities in medication adherence between persons with disabilities and without disabilities. The absence of disparities in the first 2 groups may stem from the lack of mobility or communication handicaps, which, by contrast, prevail in people with such disabilities as limb, visual, or auditory impairment. Mental retardation and developmental disabilities become apparent during childhood. Consequently, by the time people with these disabilities become adults, they are likely to be strongly dependent on parents or other caregivers and are thus more likely to adhere to a medication regimen. Arch Phys Med Rehabil Vol 89, August 2008
Interestingly, people with mental diseases did not show lower antihypertensive medication adherence in the present study, although the relationship between psychiatric impairment and poor adherence to antipsychotics is very well established in previous studies.9 The reason for this may be assumed that the persons with mental diseases and hypertension who have never visited a doctor to get antihypertensive drug prescriptions were excluded in this study, which is reflected in the relatively small sample size (n⫽171) compared with the high prevalence of mental diseases. A previous study also reported that antihypertensive medication adherence rates were similar between persons with psychotic disorders (n⫽89) and people without psychiatric diagnoses (n⫽89), with age-matching.36 However, the study also showed that rates of blood pressure control were significantly lower in persons with psychotic disorders than in the comparison subjects.36 As a conclusion, we could not illuminate the impact of mental disorder on antihypertensive medication adherence. In the future, more studies focusing on the mental disease and antihypertensive medication adherence using a larger sample and controlled study design need to be conducted to confirm the facts. In this study, the proportion of appropriate medication adherence rate between the 2 groups was quite small; the appropriate medication adherence rate (CMA ⱖ80%) of persons with disabilities was a little lower than those without disabilities (54.5% vs 57.5%). We suggest that these findings stem from the fact that the persons with disabilities and hypertension who have never visited a doctor to get antihypertensive drug prescriptions were excluded in this study. However, in view of the fact that persons with disabilities have various barriers to access medical services,3-8,26,34,37,38 these study results might have underestimated the true differences that exist between the 2 groups. Our study findings have some limitations because this study was not conducted as a controlled trial. It was deemed unethical to compare subjects with and without disabilities in a controlled clinical setting. Nevertheless, this study confirmed that the various types of disabilities have negative
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park Table 4: AOR and 95% CIs for Logistic Regression of CMA by Disabling Condition and Severity Disabling Condition
No disability Disability (total)
External physical disability Limb impairment
Brain impairment
Visual impairment
Auditory impairment
Linguistic impairment
Facial deformity
Mental disability Intellectual disability
Mental disease Internal organ disability†
Severity
OR
95% CI
AOR*
95% CI*
Severe disability Mild disability Total
1 0.88 0.89 0.89
0.87–0.90 0.87–0.90 0.87–0.90
1 0.86 0.88 0.87
0.84–0.88 0.87–0.90 0.86–0.88
Severe disability Mild disability Total Severe disability Mild disability Total Severe disability Mild disability Total Severe disability Mild disability Total Severe disability Mild disability Total Severe disability Mild disability Total
0.90 0.88 0.89 0.96 1.07 0.98 0.89 0.87 0.88 0.73 0.85 0.80 0.98 0.97 0.97 1.67 0.74 1.11
0.88–0.93 0.86–0.90 0.87–0.91 0.92–0.99 0.99–1.16 0.95–1.02 0.82–0.96 0.84–0.92 0.84–0.91 0.68–0.78 0.80–0.90 0.77–0.84 0.86–1.11 0.84–1.11 0.89–1.06 0.44–6.39 0.21–2.54 0.45–2.71
0.87 0.88 0.88 0.90 0.98 0.92 0.88 0.87 0.87 0.76 0.86 0.82 0.95 0.93 0.93 1.64 0.69 1.04
0.85–0.90 0.86–0.90 0.86–0.89 0.86–0.94 0.91–1.05 0.88–0.95 0.81–0.95 0.83–0.91 0.84–0.91 0.70–0.81 0.81–0.91 0.78–0.85 0.82–1.06 0.81–1.07 0.85–1.03 0.42–6.43 0.20–2.39 0.42–2.57
Severe disability Mild disability Total Total
0.85 0.90 0.89 1.22
0.74–0.99 0.54–1.50 0.55–1.37 0.85–1.59
0.92 0.86 0.91 1.15
0.79–1.07 0.52–1.45 0.72–1.05 0.84–1.57
Severe disability Mild disability Total
0.61 0.70 0.62
0.55–0.68 0.55–0.89 0.57–0.68
0.58 0.71 0.60
0.53–0.65 0.55–0.91 0.55–0.66
*Values were adjusted by sex, age, type of medical insurance, contribution a month, comorbidity, residential area, and duration of medication. Renal function impairment, heart function impairment, liver function impairment, respiratory function impairment, intestinal and urinary tract function impairment, epilepsy.
†
effects on antihypertensive medication adherence when other demographic, clinical, and socioeconomic variables are adjusted. Study Limitations Several limitations of our study should be mentioned. First, the Medicaid beneficiaries, who account for about 3.1% of all Korean residents, were excluded because of the lack of information in the NHI claims database.26 Nonetheless, except for those with mental disabilities, Medicaid beneficiaries account for below 10% of the persons with disabilities. Even in persons with mental disabilities, Medicaid beneficiaries account for below 20%. Therefore, the exclusion of this segment of the population with disabilities may have reduced the study’s representativeness, but these problems could not affect the internal validity of the study results. Another limitation of this study is that the coverage rate of the National Disability Registry is 77.7%, reflective of the fact that it is a voluntary, self-reporting system for people with disabilities. However, it can be assumed that most persons with mobility or functional impairments according to the types of disability were included in the registry, because the government provides various benefits such as income aid and financial aid for medical services. Although the problem of representativeness of the study subjects exists, this study covers persons with every type of disability and severity,
so it could not have affected the internal validity of the study results. Also, we excluded those who had been hospitalized during the study period. This group of subjects accounted for a small fraction compared with the target population, and because the concept of medication adherence is not traditionally considered in hospitalization settings, it could not have affected the study results as a whole. Second, the assessment of adherence was based on pharmacy refill data, which can overestimate adherence because the filling of a prescription does not confirm the actual ingestion of the prescribed medication. Refill adherence therefore identifies the upper boundary of medication consumption. However, because patients with an insufficient number of pills prescribed for a given period cannot fully adhere to their medication regimens, we believe that our method is well suited to identifying suboptimal adherence over time.39,40 A disability may lower the probability of appropriate ingestion of medication, which would widen the disparity in adherence between persons with disabilities and without disabilities. Third, this study could not include other potential confounding factors reported in the previous studies. Side effects of treatment, patients’ knowledge and attitude, and different treatment modalities have been reported to affect medication adherence.41 Last, because of the relatively small sample size in specific disability types (especially mental diseases), there is a possibility that we could not identify true Arch Phys Med Rehabil Vol 89, August 2008
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park
disparities between the 2 groups. In the future, larger and more focused studies dealing with specific disability types should be conducted. The strength of our study is that, in contrast with other adherence-monitoring methods such as self-reporting, pill counts, and electronic monitoring, patients were not aware that adherence was being measured and therefore did not alter their usual behavior during the observation period.31 Thus, disparities in antihypertensive medication adherence between people with disabilities and those without could be evaluated using an objective methodology. CONCLUSIONS Although this study could not show a large proportion of the antihypertensive medication adherence rate present between persons with disabilities and without disabilities, this study has a valuable implication for health care policy-making for the persons with disabilities in the sense that this study confirmed that the various types of disability have negative effects on the antihypertensive medication adherence when other demographic, clinical, and socioeconomic variables are adjusted. In the future, more studies should be performed to investigate how and why this disparity takes place, and there should be more efforts to develop health policy to remove the disparity if it exists. Acknowledgment: We thank Miryung Yun, MS, of iMediwrite for manuscript editing services. References 1. Joint National Committee. The sixth report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. Arch Intern Med 1997;157:2413-46. 2. DiMatteo MR, Giordani PJ, Lepper HS, Croghan TW. Patient adherence and medical treatment outcomes: a meta-analysis. Med Care 2002;40:794-811. 3. DeJong G, Plasbo SE, Beatty PW, Jones GC, Kroll T, Neri MT. The organization and financing of health services for persons with disability. Milbank Q 2002;80:261-301. 4. Sutton JP, Dejong G. Managed care and people with disability: framing the issues. Arch Phys Med Rehabil 1998;79:1312-6. 5. Beatty PW, Hagglund KJ, Neri MT, Dhont KR, Clark MJ, Hilton SA. Access to health care services among people with chronic or disabling conditions: patterns and predictors. Arch Phys Med Rehabil 2003;84:1417-25. 6. Lawthers AG, Pransky GS, Peterson LE, Himmelstein JH. Rethinking quality in the context of persons with disability. Int J Qual Health Care 2003;15:274-99. 7. Iezzoni LI, McCarthy EP, Davis RB, Siebens H. Mobility impairments and use of screening and preventive services. Am J Public Health 2000;90:955-61. 8. Cumella S, Ransford N, Lyons J, Burnham H. Needs for oral care among people with intellectual disability not in contact with community dental services. J Intellect Disabil Res 2000;44:45-52. 9. Nosé M, Barbui C, Tansella M. How often do patients with psychosis fail to adhere to treatment programmes? A systematic review. Psychol Med 2003;33:1149-60. 10. Byun YC, Kim SH, Yun SY, et al. National survey for people with disability in South Korea. Seoul: Korean Institute for Health and Social Affairs; 2006. 11. Steiner JF, Prochazka AV. The assessment of refill compliance using pharmacy records: methods, validity, and applications. J Clin Epidemiol 1997;50:105-16. 12. Rudd P. Clinicians and patients with hypertension: unsettled issues about compliance. Am Heart J 1995;130:572-9. Arch Phys Med Rehabil Vol 89, August 2008
13. Sackett DL, Haynes RB, Gibson ES, et al. Randomised clinical trial of strategies for improving medication compliance in primary hypertension. Lancet 1975;1:1205-7. 14. Haynes RB, Taylor DW, Sackett DL. Compliance in health care. Baltimore: Johns Hopkins Univ Pr; 1979. 15. Eraker SA, Kirscht JP, Becker MH. Understanding and improving patient compliance. Ann Intern Med 1984;100:258-68. 16. Steiner JF, Fihn SD, Blair B, Inui TS. Appropriate reductions in compliance among well-controlled hypertensive patients. J Clin Epidemiol 1991;44:1361-71. 17. Caro JJ, Speckman JL, Salas M, Raggio G, Jackson JD. Persistence with treatment for hypertension in actual practice. CMAJ 1999;160:31-7. 18. Marentette MA, Gerth WC, Billings DK, Zarnke KB. Antihypertensive persistence and drug class. Can J Cardiol 2002;18:649-56. 19. Shea S, Misra D, Ehrlich MH, Field L, Francis CK. Correlates of nonadherence to hypertension treatment in an inner-city minority population. Am J Public Health 1992;82:1607-12. 20. Monane M, Bohn RL, Gurwitz JH, Glynn RJ, Levin R, Avorn J. Compliance with antihypertensive therapy: role of age, gender and race. Am J Public Health 1996;86:1805-9. 21. Grant RW, Singer DE, Meigs JB. Medication adherence before an increase in antihypertensive therapy: a cohort study using pharmacy claims data. Clin Ther 2005;27:773-81. 22. McComhs JS, Nichol MB, Newman CM, Sclar DA. The costs of interrupting antihypertensive drug therapy in a medical population. Med Care 1994;32:214-26. 23. Park JH, Shin Y, Lee SY, Lee SI. Antihypertensive drug medication adherence and its affecting factors in South Korea. Int J Cardiol. In press. 24. Chobanian AV, Bakris GL, Black HR, et al. The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: the JNC 7 report. JAMA 2003;289:2560-72. 25. Havercamp SM, Scandlin D, Roth M. Health disparities among adults with developmental disability, adults with other disability, and adults not reporting disability in North Carolina. Public Health Rep 2004;119:418-26. 26. Park JH, Lee JS, Lee JY, et al. [Factors affecting National Health Insurance mass screening participation in the disabled] [Korean]. J Prev Med Public Health 2006;39:511-9. 27. Dejong G. An overview of the problem: primary care for persons with disability supplement: introduction. Am J Phys Med Rehabil 1997;76:S2-8. 28. Patrick DL. Rethinking prevention for people with disability, part I: a conceptual model for promoting health. Am J Health Promot 1997;11:257-60. 29. Iezzoni LI, Davis RB, Soukup J, O’Day B. Quality dimensions that most concern people with physical and sensory disability. Arch Intern Med 2003;163:2085-92. 30. Eun SJ, Hong JY, Lee JY, et al. [Differences in medical care utilization rates of disabled and the non-disabled with ambulatory care sensitive conditions] [Korean]. J Prev Med Public Health 2006;39:411-8. 31. Grabois EW, Nosek MA, Rossi CD. Accessibility of primary care physicians’ offices for people with disability: an analysis of compliance with the Americans with Disability Act. Arch Fam Med 1999;8:44-51. 32. Denson CR. Public sector transportation for people with disability: a satisfaction survey. J Rehabil 2000;66:29-37. 33. Ebert DA, Heckerling PS. Communication with deaf patients: knowledge, beliefs, and practices of physicians. JAMA 1995;273: 227-9. 34. Ebert DA, Heckerling PS. Communication disability among medical inpatients. N Engl J Med 1998;339:272-3.
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35. Rivadeneyra R, Elderkin-Thompson V, Silver RC, Waitzkin HM. Patient centeredness in medical encounters requiring an interpreter. Am J Med 2000;108:470-4. 36. Dolder CR, Furtek K, Lacro JP, Jeste DV. Antihypertensive medication adherence and blood pressure control in patients with psychotic disorders compared to persons without psychiatric illness. Psychosomatics 2005;46:135-41. 37. Burton WN, Chen CY, Conti DJ, Schultz AB, Edington DW. The association of antidepressant medication adherence with employee disability absences. Am J Manag Care 2007;13:105-12. 38. Lennox N, Chaplin R. The psychiatric care of people with intellectual disability: the perceptions of trainee psychiatrists and psychiatric medical officers. Aust N Z J Psychiatry 1995;29:632-7.
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39. Wandless I, Mucklow JC, Smith A, Prudham D. Compliance with prescribed medicines: a study of elderly patients in the community. J R Coll Gen Pract 1979;29:391-6. 40. Cramer JA, Mattson RH, Prevey ML, Scheyer RD, Ouellette VL. How often is medication taken as prescribed? A novel assessment technique. JAMA 1989;261:3273-7. 41. Krousel-Wood M, Thomas S, Muntner P, Morisky D. Medication adherence: a key factor in achieving blood pressure control and good clinical outcomes in hypertensive patients. Curr Opin Cardiol 2004;19:357-62. Supplier a. Version 8.1; SAS Institute, 100 SAS Campus Dr, Cary, NC 275132414.
Arch Phys Med Rehabil Vol 89, August 2008
ORIGINAL ARTICLE
Disparities in Antihypertensive Medication Adherence in Persons With Disabilities and Without Disabilities: Results of a Korean Population-Based Study Jong Hyock Park, MD, MPH, Jae Hyun Park, MD, PhD, MPH, Sang Yi Lee, MD, PhD, So Young Kim, MD, Youngsoo Shin, MD, DrPH, MPH, Su Young Kim, PhD ABSTRACT. Park JH, Park JH, Lee SY, Kim SY, Shin Y, Kim SY. Disparities in antihypertensive medication adherence in persons with disabilities and without disabilities: results of a Korean population-based study. Arch Phys Med Rehabil 2008;89: 1460-7. Objective: To determine disparities in antihypertensive medication adherence between persons with disabilities and those without disabilities in South Korea. Design: The study compared antihypertensive medication adherence between persons with disabilities and those without disabilities using medical claims data of the National Health Insurance (NHI). Setting: We obtained data from claims submitted to the NHI, which covers almost the entire Korean population. Persons who were prescribed antihypertensive medication during the calendar year 2004 were identified. Participants: The study comprised data from persons with disabilities (n⫽85,098) and persons without disabilities (n⫽2,368,636). Interventions: Not applicable. Main Outcome Measures: A cumulative medication adherence (CMA) greater than or equal to 80% was defined as an appropriate medication adherence. Multiple logistic regression was used to identify differences in antihypertensive medication adherence between persons with disabilities and without disabilities. Estimates were adjusted for demographic characteristics (sex, age), type of medical insurance, insurance contribution a month as a proxy for household income, residential area, and clinical characteristics (medication duration, comorbid conditions). Results: People with disabilities had lower CMAs than those without (median CMA, 83.6% vs 85.7%; appropriate medication adherence, 54.5% vs 57.5%). Results of the multiple logistic regression adjusting other factors indicated that people with disabilities had decreased probabilities of appropriate adherence. Conclusions: Medication adherence is reduced by various types of disability and impairment such as those involving
From the Cancer Policy and Management Branch, National Cancer Center (Jong Park, Jae Park), Department of Preventive Medicine, Cheju University College of Medicine, Cheju, Korea (Lee); Department of Healthcare Industry, Korea Health Industry Development Institute, Seoul, Korea (So Kim); Department of Health Policy and Management, Seoul National University College of Medicine, Seoul, Korea (Shin); and Department of Preventive Medicine, Cheju University College of Medicine, Jeju, Korea (Su Kim). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to Jae Hyun Park, MD, PhD, MPH, National Cancer Center, 809 Madu1-dong, Ilsandong-gu, Goyang-si, Gyeonggi-do, 410-769, Korea, e-mail: [email protected]. 0003-9993/08/8908-00306$34.00/0 doi:10.1016/j.apmr.2007.12.045
Arch Phys Med Rehabil Vol 89, August 2008
mobility and communication. Much effort should be made to investigate how and why these disparities take place and develop health policies to remove these disparities if they exist. Key Words: Antihypertensive agents; Disabled persons; Patient compliance; Rehabilitation. © 2008 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation YPERTENSION IS A MAJOR risk factor for cardiovascular disease, as well as morbidity and mortality caused H by stroke. These diseases can be effectively prevented by 1
controlling hypertension on a daily basis. A recent meta-analysis showed that the odds of good blood pressure control among patients who adhered to their antihypertensive medication regimens versus those who did not were 3.44 (95% CI, 1.60 –7.37).2 Therefore, increasing a patient’s adherence to an antihypertensive medication regimen is an important component of successful hypertension control. However, although many studies have shown that the persons with disabilities were less likely to use appropriate health care services,3-8 studies investigating the relationship between disability and medication adherence have rarely been conducted so far. Nosé et al9 reported in their systematic review of 103 studies that 26% of 23,796 patients with psychoses were not adherent to antipsychotic therapy. However, there have not been any studies that investigated whether various disability types (physical, visual, auditory, internal organ, mental disability) have a negative impact on medication adherence. In addition, understanding the importance of antihypertensive medication adherence on successful hypertension control, it is highly valuable to investigate the relationship between disability and antihypertensive medication adherence. Therefore, this study was attempted to investigate whether there is a gap between the persons with disabilities and those without disabilities regarding adherence to antihypertensive drug therapy by adjusting other factors previously associated with antihypertensive medication adherence; these factors were demographic characteristics such as sex, age, type of medical insurance, insurance contributions a month as a proxy for household income, residential area, and clinical characteristics such as medication duration and comorbid conditions.
List of Abbreviations ADLs AOR CI CMA KDA NHI
activities of daily living adjusted odds ratio confidence interval cumulative medication adherence Korean Disability Act National Health Insurance
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park Table 1: Disablement Characteristics According to the KDA Category
Disabling Condition
External physical disability
Definition
Physical impairment Brain impairment Visual impairment Auditory impairment Linguistic impairment Facial deformity
Internal organ disability
Renal function impairment Heart function impairment Liver function impairment Respiratory function impairment Intestinal and urinary tract function impairment
Mental disability
Epilepsy Mental retardation Developmental disability Mental impairment
Amputation, motor disturbance, joint disability, deformity of limbs, spinal cord injury Brain disability caused by stroke, brain damage, brain palsy Visual power loss, visual field defect Hearing disability, disability of the sense of equilibrium Mogilalia, dysphonia Facial deformity caused by head injury, a burn, cancer surgery Renal impairment with hemodialysis, kidney transplantation Heart impairment with daily life limitation Liver impairment with daily life limitation Respiratory impairment with daily life limitation Intestinal and urinary tract impairment with daily life limitation Epilepsy with daily life limitation Intelligence quotient ⬍70 Autism, developmental impairment Mental diseases with daily life limitation
NOTE. The level of severity for each condition ranges from 1 (severe) to 6 (mild).
METHODS Data Source Analyses were conducted using the NHI database (2004) and the National Disability Database. The latter comprises approximately 77.7% of the population with disabilities registered in the National Social Security System.10 In South Korea, the NHI provides mandatory universal health insurance, offering comprehensive medical care coverage to all South Korean residents. Patients should visit a doctor to obtain a prescription and then visit a pharmacy to fill that prescription, according to the prescription-dispensation separation policy instituted in 2000. The NHI pharmacy claims are generated when a patient uses insurance coverage to fill a prescription. The claims are then entered into the NHI’s claims database. We could not include the information of Medicaid beneficiaries, who account for about 3.1% of all Korean residents, because of the lack of information in the NHI claims database. The Medicaid program is a public assistance scheme to secure the minimum livelihood for low-income households and to provide them with medical services. We used pharmacy claims data and enrollment records from January 1, 2004, to December 31, 2004. The data comprised patients’ disease codes, the dates that prescriptions were generated and filled, and the days’ worth of pills supplied. Enrollment records included patients’ insurance identification numbers and information regarding sex, age, contributions a month, and residential region. These were linked to the pharmacy claims data. Persons with disabilities were identified using the National Disability Registry (2003), which is a voluntary self-report system for persons with disabilities and is linked with the pharmacy claims data. This database is assumed to cover 77.7% of the total population with disabilities.10 It contains social security numbers and information regarding disability characteristics such as disability type and severity. Disabilities are classified into 15 groups, and diagnosis is made by the respective medical specialist. The severity of the disability is graded from 1 to 6, indicating very severe to very mild, on the
basis of functional losses and clinical impairment, as determined by the medical specialist. Diagnostic criteria are specified in the KDA (table 1). The personal identification number used for data linkage was deleted before analysis. In addition, this study was a secondary data analysis. For these reasons, this study was inapplicable to the review from the scientific review panel. Study Population The source population consisted of patients over the age of 20 years who visited a doctor more than once for hypertension (International Classification of Diseases and Related Health Problems–10th Revision), as reported in claims data from January to December 31, 2004. Accordingly, the target population consisted of 2,716,682 subjects. This corresponded to 28.7% of the 9,475,043 NHI beneficiaries who were over 20 years of age. In the target population, patients who filled only 1 prescription for an antihypertensive were excluded because the CMA can be calculated only when a prescription has been filled more than twice. Patients who had been hospitalized during the study period were also excluded because adherence to a medication regimen during hospitalization is enforced by the medical staff and requires no effort on the part of the patient. On the basis of these criteria, the study population comprised 2,453,734 patients, which was 90.3% of the source population. In this group, there were 85,098 persons with disabilities and 2,368,636 persons without disabilities. Outcome Measures Adherence to a medication regimen was measured using the CMA scale, which is based on the pharmacy claims data.11 The CMA is defined as the percentage of days for which the patient has pills available. This proportion is calculated by dividing the total number of days of medication dispensed (excluding the final prescription) by the total number of days between the first and last prescriptions. For example, patients who filled 3 hypertension prescriptions for 30 pills each, with the last preArch Phys Med Rehabil Vol 89, August 2008
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park
scription filled 90 days after the first one, would have a CMA of 67% (ie, 60/90⫻100) because they had 60 pills available during the 90 days between the first and last prescriptions. Pills from the last prescriptions are not included because the number of days taken to consume these pills is unknown. Therefore, theoretically, the denominator or the total number of days between the first and last prescriptions can range from 1 day to 12 months. For the numerator, the total number of days of medication dispensed (excluding the final prescription) can range from 1 day to over 12 months because patients get the prescription before finishing the previous prescription (prescription duplication). Therefore, CMA can range from 0% to over 100% because of prescription duplication. A CMA greater than or equal to 80% was considered appropriate medication adherence because it is a commonly used threshold to define antihypertensive medication adherence.12,13 Haynes et al14 reported that hypertension of those who were adherent over 80% of antihypertensive medication was better controlled than those who were adherent under 80%. Adjustment Factors We reviewed studies that evaluated factors that influence medication adherence, and the appropriate adjustment factors were selected.11-13,15 These factors consisted of patient demographic characteristics such as sex and age; clinical characteristics such as medication duration and comorbid conditions; socioeconomic characteristics such as type of medical insurance (self-employed vs employee) and insurance contributions a month as a proxy for household income; and community factors such as type of residential area (metropolitan city, city, rural area, mostly rural area). In previous studies, sex was reported to be related with medication adherence in some studies, while in other studies, it was not.16-18 As for age, several studies reported the trend of increasing medication adherence with increasing age.17-20 Patients’ socioeconomic level,21 patients’ residential area,22,23 duration of medication,21 and patients’ comorbidity21 were also reported to be related with medication adherence previously. Comorbid conditions were classified into 2 disease groups. Class 1 comprised hypertension-related diseases—for example, diabetes mellitus, obesity, and target organ damage caused by hypertension, as defined by the Joint National Committee.1 Class 2 comprised chronic diseases, which were assumed to increase both the number of pharmacy visits and overall medication adherence. Diseases in this group included migraine and other headache syndromes, chronic lower respiratory diseases, and inflammatory polyarthropathies. Statistical Analysis Because the distribution of CMA was not normative, the median and interquartile range of CMAs and the medication adherence rates of persons with and without disabilities were calculated according to the type and severity of the disability. The type of disability was coded as total disability if study subjects were registered in the National Disability Registry and coded as no disability if study subjects were not. In these processes, various types of disability and disease severity were also coded using information in the National Disability Registry. A severe disability was scored as 1 to 3 and a mild disability as 4 to 6. To determine whether various types of disability and severity of disability have influence on the medication adherence, we used the multiple logistic regression model, adjusting for confounding factors and setting the outcome (ie, appropriate medication adherence defined as CMA ⱖ80%) as a binary variable. Various types of disability and Arch Phys Med Rehabil Vol 89, August 2008
severity of disability were entered in the multiple logistic regression model 1 by 1, adjusting the same confounding factors. Estimates were adjusted for demographic characteristics (sex, age), insurance contributions a month as a proxy for household income, residential area, and clinical characteristics (medication duration, comorbid conditions). All analyses were performed using SAS 81.a Statistical significance was defined as 2-tailed P value less than or equal to .05. RESULTS Characteristics of Persons With Disabilities and Without Disabilities We summarized the general characteristics of the persons with disabilities and those without disabilities (table 2). Of the 2,453,734 persons in the study, those with disabilities accounted for 3.47% (n⫽85,098). Male sex occurred more frequently in the population with disabilities than in those without disabilities (61.1% vs 41.2%). In addition, the proportion of self-employed and the number of people with comorbid conditions were higher in the population with disabilities (66.3% vs 43.6% and 65.2% vs 56.4%, respectively). The household income of people with disabilities was lower than that of those without disabilities. CMAs According to Disability Condition and Severity The median and interquartile range of CMAs were calculated by classifying the population with disabilities according to disability type and severity (table 3). Except for the group with some types of mental and internal organ disability, most people with disability had lower CMAs than those without. Furthermore, people with more severe disability had lower CMAs than those with mild disability for disabilities such as brain impairment, auditory impairment, mental retardation, and epilepsy. Disparity in Antihypertensive Medication Adherence According to Disability Condition and Severity The multiple logistic regression adjusting other demographic and clinical variables (table 4) indicated that disability was associated with a lower CMA (AOR⫽.87; 95% CI, .86 –.88). In addition, people with severe disabilities were more likely to have a lower CMA than those with mild disability. Severe limb (AOR⫽.87; 95% CI, .85–.90), brain (AOR⫽.90; 95% CI, .86 –.94), visual (AOR⫽.88; 95% CI, .81–.95), auditory (AOR⫽.76; 95% CI, .70 –.81), and internal organ (AOR⫽.58; 95% CI, .53–.65) impairments were associated with a lower appropriate medication adherence. Higher disability severity was associated with lower CMA. For subjects disabled with a facial deformity or a linguistic, intellectual, or chronic mental impairment, there were no disparities in medication adherence compared with the population without disabilities. DISCUSSION In this study, we confirmed that there is a disparity in medication adherence between persons with disabilities and without disabilities, adjusting demographic and clinical variables (AOR⫽.87; 95% CI, .86 –.88). In the sense that the odds of good blood pressure control among patients adherent to antihypertensive medications, compared with those who were nonadherent, were 3.44 (95% CI, 1.60 –7.37) in a recent metaanalysis,2 this disparity indicates a great clinical impact and health outcome on the persons with disabilities. Previous studies showed that the relationship between high blood pressure and the risk of cardiovascular disease events is continuous,
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park Table 2: Characteristics of the Persons With and Without Disabilities People Without Disabilities
People With Disabilities
Variable
No.
%
No.
%
Total Sex Men Women Age (y 20–29 30–39 40–49 50–59 60–69 ⱖ70 Type of medical insurance Self-employed Employee Comorbidity None of class 1 or 2 diseases Class 1* Class 2† Both class 1 and 2 diseases Medication duration (mo) ⬍6 6–11 12–17 ⱖ18 Contribution a month (Korean won) ⬍30,000 30,000–70,000 ⬎70,000 Residential area Metropolitan area City Rural Mostly rural
2,368,636
100.00
85,098
100.00
975,452 1,393,184
41.18 58.82
51,985 33,113
61.09 38.91
7554 62,370 327,419 628,774 734,103 608,416
0.32 2.63 13.82 26.55 30.99 25.69
137 1310 8971 22,312 31,526 20,842
0.16 1.54 10.54 26.22 37.05 24.49
1,032,762 1,335,874
43.60 56.40
56,453 28,645
66.34 33.66
1,047,617 911,924 272,785 136,310
44.23 38.50 11.52 5.75
30,165 41,407 8277 5249
35.45 48.66 9.73 6.17
162,808 266,516 275,845 1,663,467
6.87 11.25 11.65 70.23
4829 8479 9392 62,398
5.67 9.96 11.04 73.32
755,849 975,384 637,403
31.91 41.18 26.91
32,986 33,890 18,222
38.76 39.82 21.41
1,119,310 990,661 102,529 156,130
47.26 41.82 4.33 6.59
36,518 37,505 4496 6579
42.91 44.07 5.28 7.73
*Class 1: diabetes mellitus and target organ damage caused by hypertension. † Class 2: chronic disease assumed to increase ambulatory service use.
consistent, and independent of other risk factors. The higher the blood pressure, the greater the chances of heart attack, heart failure, stroke, and kidney diseases.24 This means that persons with disabilities are more vulnerable to the various diseases related to hypertension because of a lower antihypertensive medication adherence rate. A previous study showed with empirical data that subjects with disabilities were significantly more likely than those without disabilities to suffer from chronic health conditions such as high blood pressure and other cardiovascular disease.25 Another study also showed that people with disabilities who had hypertension, apart from their original impairments, are likely to experience secondary functional losses such as cardiovascular diseases, strokes, chronic kidney disease, peripheral arterial disease, and retinopathy.1,3 Uncontrolled hypertension and a high prevalence of hypertension-related diseases may have many causes. However, this study result suggests a potential relationship between low adherence of antihypertensive medication adherence and secondary functional losses such as cardiovascular diseases and strokes among persons with disabilities. In this study, people with limb, brain, visual, auditory, or internal organ impairments had lower CMAs than people without these disabilities. According to the KDA classification, limb impairment includes disability resulting from amputation,
motor disturbance, joint disability, limb deformities, and spinal cord injuries.26 Brain impairment includes disability caused by stroke, brain damage, and brain palsy. In both types of disability, severity is decided mainly by the level of impaired mobility. For example, people with brain impairment who do not have mobility impairment as well are considered to have mild brain impairment, which might be the reason for lack of a statistically significant difference in medication adherence between this population and the persons without disabilities. Conversely, people with limb impairment or severe brain impairment inevitably have some degrees of mobility impairment. Previous studies7,26 reported that people with brain impairment are less able to carry out the ADLs, which include essential activities. Thus, it can be assumed that people with limb impairment and severe brain impairment are less likely to adhere to an antihypertensive medication regimen mainly because of impaired mobility, but also because of problems in performing the ADLs. People with mobility impairments are also confronted with the problem of transportation to seek and obtain medications.25,27-29 The necessary mode of transportation may not be particularly accessible, and other unexpected obstacles may make it difficult to reach a clinic or pharmacy. In Korea, despite the provisions of the KDA, physical barriers to primary care givers still remain.26,30 Similar problems with Arch Phys Med Rehabil Vol 89, August 2008
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park Table 3: CMA by Disabling Condition and Severity Total
Mild Disability
Variable
No.
Median
IQR
ⱖ80% CMA
Persons without disabilities Persons with disabilities External disability Limb impairment Brain impairment Visual impairment Auditory impairment Linguistic impairment Facial deformity Mental disability Mental retardation Developmental disability Mental disease Internal organ disability Renal impairment Heart impairment Respiratory impairment Liver impairment Intestinal and urinary tract impairment Epilepsy
2,368,636 85,098
85.71 83.56
38.34 42.13
57.53 54.54
49,943
50,070 12,014 9846 8564 1833 20
83.45 85.94 83.28 81.68 84.98 85.14
41.52 40.57 42.01 44.43 40.49 34.21
54.63 57.08 54.34 52.01 56.79 60.00
786 10 171
84.94 82.33 87.46
44.69 27.02 43.44
557 782 204 44 178
59.65 82.87 76.16 51.29 84.66
19
56.36
Severe Disability
IQR
ⱖ80% CMA
No.
Median
IQR
ⱖ80% CMA
83.33
⫺ 41.35
54.56
35,155
83.78
⫺ 43.28
54.51
33,155 2764 7529 5311 856 10
83.28 87.51 83.07 82.95 84.55 85.14
41.34 38.26 41.68 43.26 40.11 18.73
54.41 59.23 54.24 53.42 56.66 50.00
16,915 9250 2317 3253 977 10
83.92 85.47 83.57 79.72 85.71 85.14
41.87 41.65 43.06 46.26 40.78 18.73
55.04 56.44 54.64 49.71 56.91 70.00
53.82 50.00 60.23
58 2 3
87.93 78.48 97.92
35.19 0.92 11.48
56.90 0.00 100.00
728 8 168
84.85 85.96 86.75
45.18 39.95 43.77
53.57 62.50 59.52
73.22 49.52 46.31 62.24 41.65
35.73 52.56 45.10 31.82 53.37
68 3 0 6 166
69.83 97.34 — 38.08 84.30
64.40 215.27 — 54.56 41.02
41.18 66.67 — 33.33 53.01
489 779 204 38 12
58.61 82.82 76.16 53.66 88.71
74.89 49.52 46.31 65.82 51.32
34.97 52.50 45.10 31.58 58.33
71.27
26.32
12
58.18
71.22
33.33
7
56.36
44.60
14.29
No.
Median
Abbreviation: IQR, interquartile range.
disability laws have been reported in other countries such as the United States, the United Kingdom, and Australia.31,32 The lower CMAs in people with visual and auditory impairments may be explained by the attendant communication disability, as in cases in which vision is so poor that, even with corrective lenses, the person is unable to read medication consent forms or typical patient education materials; or when hearing is so severely impaired that, despite hearing aids, the person cannot understand shouted speech.33 Even in health care settings, aids to communication may be lacking for patients with altered mental states, impaired vision, or hearing deficits,33,34 all of which result in barriers affecting physicianpatient communication. For the patient, the clinical consequences of communication difficulties may be poor adherence to treatment recommendations.35 Limitations in ADLs caused by internal organ impairments such as impaired renal, heart, respiratory, liver, intestinal, or urinary tract function, or epilepsy resulted in lower CMAs than the controls. Patients with these disabilities had lower CMAs for the antihypertensive drug, even though they were being treated with medications for their impairments and were checked regularly by health care providers. These findings suggest that treatment for hypertension is often neglected in people with internal organ impairments who are receiving focused treatment for the damaged organ. For disabilities involving linguistic impairment, facial deformity, and intellectual disability, there were no disparities in medication adherence between persons with disabilities and without disabilities. The absence of disparities in the first 2 groups may stem from the lack of mobility or communication handicaps, which, by contrast, prevail in people with such disabilities as limb, visual, or auditory impairment. Mental retardation and developmental disabilities become apparent during childhood. Consequently, by the time people with these disabilities become adults, they are likely to be strongly dependent on parents or other caregivers and are thus more likely to adhere to a medication regimen. Arch Phys Med Rehabil Vol 89, August 2008
Interestingly, people with mental diseases did not show lower antihypertensive medication adherence in the present study, although the relationship between psychiatric impairment and poor adherence to antipsychotics is very well established in previous studies.9 The reason for this may be assumed that the persons with mental diseases and hypertension who have never visited a doctor to get antihypertensive drug prescriptions were excluded in this study, which is reflected in the relatively small sample size (n⫽171) compared with the high prevalence of mental diseases. A previous study also reported that antihypertensive medication adherence rates were similar between persons with psychotic disorders (n⫽89) and people without psychiatric diagnoses (n⫽89), with age-matching.36 However, the study also showed that rates of blood pressure control were significantly lower in persons with psychotic disorders than in the comparison subjects.36 As a conclusion, we could not illuminate the impact of mental disorder on antihypertensive medication adherence. In the future, more studies focusing on the mental disease and antihypertensive medication adherence using a larger sample and controlled study design need to be conducted to confirm the facts. In this study, the proportion of appropriate medication adherence rate between the 2 groups was quite small; the appropriate medication adherence rate (CMA ⱖ80%) of persons with disabilities was a little lower than those without disabilities (54.5% vs 57.5%). We suggest that these findings stem from the fact that the persons with disabilities and hypertension who have never visited a doctor to get antihypertensive drug prescriptions were excluded in this study. However, in view of the fact that persons with disabilities have various barriers to access medical services,3-8,26,34,37,38 these study results might have underestimated the true differences that exist between the 2 groups. Our study findings have some limitations because this study was not conducted as a controlled trial. It was deemed unethical to compare subjects with and without disabilities in a controlled clinical setting. Nevertheless, this study confirmed that the various types of disabilities have negative
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ANTIHYPERTENSIVE MEDICATION ADHERENCE, Park Table 4: AOR and 95% CIs for Logistic Regression of CMA by Disabling Condition and Severity Disabling Condition
No disability Disability (total)
External physical disability Limb impairment
Brain impairment
Visual impairment
Auditory impairment
Linguistic impairment
Facial deformity
Mental disability Intellectual disability
Mental disease Internal organ disability†
Severity
OR
95% CI
AOR*
95% CI*
Severe disability Mild disability Total
1 0.88 0.89 0.89
0.87–0.90 0.87–0.90 0.87–0.90
1 0.86 0.88 0.87
0.84–0.88 0.87–0.90 0.86–0.88
Severe disability Mild disability Total Severe disability Mild disability Total Severe disability Mild disability Total Severe disability Mild disability Total Severe disability Mild disability Total Severe disability Mild disability Total
0.90 0.88 0.89 0.96 1.07 0.98 0.89 0.87 0.88 0.73 0.85 0.80 0.98 0.97 0.97 1.67 0.74 1.11
0.88–0.93 0.86–0.90 0.87–0.91 0.92–0.99 0.99–1.16 0.95–1.02 0.82–0.96 0.84–0.92 0.84–0.91 0.68–0.78 0.80–0.90 0.77–0.84 0.86–1.11 0.84–1.11 0.89–1.06 0.44–6.39 0.21–2.54 0.45–2.71
0.87 0.88 0.88 0.90 0.98 0.92 0.88 0.87 0.87 0.76 0.86 0.82 0.95 0.93 0.93 1.64 0.69 1.04
0.85–0.90 0.86–0.90 0.86–0.89 0.86–0.94 0.91–1.05 0.88–0.95 0.81–0.95 0.83–0.91 0.84–0.91 0.70–0.81 0.81–0.91 0.78–0.85 0.82–1.06 0.81–1.07 0.85–1.03 0.42–6.43 0.20–2.39 0.42–2.57
Severe disability Mild disability Total Total
0.85 0.90 0.89 1.22
0.74–0.99 0.54–1.50 0.55–1.37 0.85–1.59
0.92 0.86 0.91 1.15
0.79–1.07 0.52–1.45 0.72–1.05 0.84–1.57
Severe disability Mild disability Total
0.61 0.70 0.62
0.55–0.68 0.55–0.89 0.57–0.68
0.58 0.71 0.60
0.53–0.65 0.55–0.91 0.55–0.66
*Values were adjusted by sex, age, type of medical insurance, contribution a month, comorbidity, residential area, and duration of medication. Renal function impairment, heart function impairment, liver function impairment, respiratory function impairment, intestinal and urinary tract function impairment, epilepsy.
†
effects on antihypertensive medication adherence when other demographic, clinical, and socioeconomic variables are adjusted. Study Limitations Several limitations of our study should be mentioned. First, the Medicaid beneficiaries, who account for about 3.1% of all Korean residents, were excluded because of the lack of information in the NHI claims database.26 Nonetheless, except for those with mental disabilities, Medicaid beneficiaries account for below 10% of the persons with disabilities. Even in persons with mental disabilities, Medicaid beneficiaries account for below 20%. Therefore, the exclusion of this segment of the population with disabilities may have reduced the study’s representativeness, but these problems could not affect the internal validity of the study results. Another limitation of this study is that the coverage rate of the National Disability Registry is 77.7%, reflective of the fact that it is a voluntary, self-reporting system for people with disabilities. However, it can be assumed that most persons with mobility or functional impairments according to the types of disability were included in the registry, because the government provides various benefits such as income aid and financial aid for medical services. Although the problem of representativeness of the study subjects exists, this study covers persons with every type of disability and severity,
so it could not have affected the internal validity of the study results. Also, we excluded those who had been hospitalized during the study period. This group of subjects accounted for a small fraction compared with the target population, and because the concept of medication adherence is not traditionally considered in hospitalization settings, it could not have affected the study results as a whole. Second, the assessment of adherence was based on pharmacy refill data, which can overestimate adherence because the filling of a prescription does not confirm the actual ingestion of the prescribed medication. Refill adherence therefore identifies the upper boundary of medication consumption. However, because patients with an insufficient number of pills prescribed for a given period cannot fully adhere to their medication regimens, we believe that our method is well suited to identifying suboptimal adherence over time.39,40 A disability may lower the probability of appropriate ingestion of medication, which would widen the disparity in adherence between persons with disabilities and without disabilities. Third, this study could not include other potential confounding factors reported in the previous studies. Side effects of treatment, patients’ knowledge and attitude, and different treatment modalities have been reported to affect medication adherence.41 Last, because of the relatively small sample size in specific disability types (especially mental diseases), there is a possibility that we could not identify true Arch Phys Med Rehabil Vol 89, August 2008
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disparities between the 2 groups. In the future, larger and more focused studies dealing with specific disability types should be conducted. The strength of our study is that, in contrast with other adherence-monitoring methods such as self-reporting, pill counts, and electronic monitoring, patients were not aware that adherence was being measured and therefore did not alter their usual behavior during the observation period.31 Thus, disparities in antihypertensive medication adherence between people with disabilities and those without could be evaluated using an objective methodology. CONCLUSIONS Although this study could not show a large proportion of the antihypertensive medication adherence rate present between persons with disabilities and without disabilities, this study has a valuable implication for health care policy-making for the persons with disabilities in the sense that this study confirmed that the various types of disability have negative effects on the antihypertensive medication adherence when other demographic, clinical, and socioeconomic variables are adjusted. In the future, more studies should be performed to investigate how and why this disparity takes place, and there should be more efforts to develop health policy to remove the disparity if it exists. Acknowledgment: We thank Miryung Yun, MS, of iMediwrite for manuscript editing services. References 1. Joint National Committee. The sixth report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. Arch Intern Med 1997;157:2413-46. 2. DiMatteo MR, Giordani PJ, Lepper HS, Croghan TW. Patient adherence and medical treatment outcomes: a meta-analysis. Med Care 2002;40:794-811. 3. DeJong G, Plasbo SE, Beatty PW, Jones GC, Kroll T, Neri MT. The organization and financing of health services for persons with disability. Milbank Q 2002;80:261-301. 4. Sutton JP, Dejong G. Managed care and people with disability: framing the issues. Arch Phys Med Rehabil 1998;79:1312-6. 5. Beatty PW, Hagglund KJ, Neri MT, Dhont KR, Clark MJ, Hilton SA. Access to health care services among people with chronic or disabling conditions: patterns and predictors. Arch Phys Med Rehabil 2003;84:1417-25. 6. Lawthers AG, Pransky GS, Peterson LE, Himmelstein JH. Rethinking quality in the context of persons with disability. Int J Qual Health Care 2003;15:274-99. 7. Iezzoni LI, McCarthy EP, Davis RB, Siebens H. Mobility impairments and use of screening and preventive services. Am J Public Health 2000;90:955-61. 8. Cumella S, Ransford N, Lyons J, Burnham H. Needs for oral care among people with intellectual disability not in contact with community dental services. J Intellect Disabil Res 2000;44:45-52. 9. Nosé M, Barbui C, Tansella M. How often do patients with psychosis fail to adhere to treatment programmes? A systematic review. Psychol Med 2003;33:1149-60. 10. Byun YC, Kim SH, Yun SY, et al. National survey for people with disability in South Korea. Seoul: Korean Institute for Health and Social Affairs; 2006. 11. Steiner JF, Prochazka AV. The assessment of refill compliance using pharmacy records: methods, validity, and applications. J Clin Epidemiol 1997;50:105-16. 12. Rudd P. Clinicians and patients with hypertension: unsettled issues about compliance. Am Heart J 1995;130:572-9. Arch Phys Med Rehabil Vol 89, August 2008
13. Sackett DL, Haynes RB, Gibson ES, et al. Randomised clinical trial of strategies for improving medication compliance in primary hypertension. Lancet 1975;1:1205-7. 14. Haynes RB, Taylor DW, Sackett DL. Compliance in health care. Baltimore: Johns Hopkins Univ Pr; 1979. 15. Eraker SA, Kirscht JP, Becker MH. Understanding and improving patient compliance. Ann Intern Med 1984;100:258-68. 16. Steiner JF, Fihn SD, Blair B, Inui TS. Appropriate reductions in compliance among well-controlled hypertensive patients. J Clin Epidemiol 1991;44:1361-71. 17. Caro JJ, Speckman JL, Salas M, Raggio G, Jackson JD. Persistence with treatment for hypertension in actual practice. CMAJ 1999;160:31-7. 18. Marentette MA, Gerth WC, Billings DK, Zarnke KB. Antihypertensive persistence and drug class. Can J Cardiol 2002;18:649-56. 19. Shea S, Misra D, Ehrlich MH, Field L, Francis CK. Correlates of nonadherence to hypertension treatment in an inner-city minority population. Am J Public Health 1992;82:1607-12. 20. Monane M, Bohn RL, Gurwitz JH, Glynn RJ, Levin R, Avorn J. Compliance with antihypertensive therapy: role of age, gender and race. Am J Public Health 1996;86:1805-9. 21. Grant RW, Singer DE, Meigs JB. Medication adherence before an increase in antihypertensive therapy: a cohort study using pharmacy claims data. Clin Ther 2005;27:773-81. 22. McComhs JS, Nichol MB, Newman CM, Sclar DA. The costs of interrupting antihypertensive drug therapy in a medical population. Med Care 1994;32:214-26. 23. Park JH, Shin Y, Lee SY, Lee SI. Antihypertensive drug medication adherence and its affecting factors in South Korea. Int J Cardiol. In press. 24. Chobanian AV, Bakris GL, Black HR, et al. The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: the JNC 7 report. JAMA 2003;289:2560-72. 25. Havercamp SM, Scandlin D, Roth M. Health disparities among adults with developmental disability, adults with other disability, and adults not reporting disability in North Carolina. Public Health Rep 2004;119:418-26. 26. Park JH, Lee JS, Lee JY, et al. [Factors affecting National Health Insurance mass screening participation in the disabled] [Korean]. J Prev Med Public Health 2006;39:511-9. 27. Dejong G. An overview of the problem: primary care for persons with disability supplement: introduction. Am J Phys Med Rehabil 1997;76:S2-8. 28. Patrick DL. Rethinking prevention for people with disability, part I: a conceptual model for promoting health. Am J Health Promot 1997;11:257-60. 29. Iezzoni LI, Davis RB, Soukup J, O’Day B. Quality dimensions that most concern people with physical and sensory disability. Arch Intern Med 2003;163:2085-92. 30. Eun SJ, Hong JY, Lee JY, et al. [Differences in medical care utilization rates of disabled and the non-disabled with ambulatory care sensitive conditions] [Korean]. J Prev Med Public Health 2006;39:411-8. 31. Grabois EW, Nosek MA, Rossi CD. Accessibility of primary care physicians’ offices for people with disability: an analysis of compliance with the Americans with Disability Act. Arch Fam Med 1999;8:44-51. 32. Denson CR. Public sector transportation for people with disability: a satisfaction survey. J Rehabil 2000;66:29-37. 33. Ebert DA, Heckerling PS. Communication with deaf patients: knowledge, beliefs, and practices of physicians. JAMA 1995;273: 227-9. 34. Ebert DA, Heckerling PS. Communication disability among medical inpatients. N Engl J Med 1998;339:272-3.
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35. Rivadeneyra R, Elderkin-Thompson V, Silver RC, Waitzkin HM. Patient centeredness in medical encounters requiring an interpreter. Am J Med 2000;108:470-4. 36. Dolder CR, Furtek K, Lacro JP, Jeste DV. Antihypertensive medication adherence and blood pressure control in patients with psychotic disorders compared to persons without psychiatric illness. Psychosomatics 2005;46:135-41. 37. Burton WN, Chen CY, Conti DJ, Schultz AB, Edington DW. The association of antidepressant medication adherence with employee disability absences. Am J Manag Care 2007;13:105-12. 38. Lennox N, Chaplin R. The psychiatric care of people with intellectual disability: the perceptions of trainee psychiatrists and psychiatric medical officers. Aust N Z J Psychiatry 1995;29:632-7.
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39. Wandless I, Mucklow JC, Smith A, Prudham D. Compliance with prescribed medicines: a study of elderly patients in the community. J R Coll Gen Pract 1979;29:391-6. 40. Cramer JA, Mattson RH, Prevey ML, Scheyer RD, Ouellette VL. How often is medication taken as prescribed? A novel assessment technique. JAMA 1989;261:3273-7. 41. Krousel-Wood M, Thomas S, Muntner P, Morisky D. Medication adherence: a key factor in achieving blood pressure control and good clinical outcomes in hypertensive patients. Curr Opin Cardiol 2004;19:357-62. Supplier a. Version 8.1; SAS Institute, 100 SAS Campus Dr, Cary, NC 275132414.
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