- Email: [email protected]
Pharmacokinetic and pharmacodynamic characteristics of a new S-amlodipine formulation in healthy Korean male subjects: A randomized, open-label, two-period, comparative, crossover study
formulation (3.1 [0.6] ng/mL, 139.7 [40.3] ng- h/mL, and 161.7 [43.8] ng • h/mL, respectively). The calculated 90% CIs for the corresponding ratios of logtransformed Cmax, AUC0~ , and AUClast were 97.56% to 112.51%, 86.31% to 98.74%, and 83.46% to 100.04%, respectively, which met the predetermined criteria for pharmacokinetic equivalence. Despite the single administration, significant changes in maximal blood pressure and heart rate were observed after drug administration for both formulations, compared with baseline values (all, P < 0.001). However, no significant differences were observed between the 2 formulations in terms of pharmacodynamic profiles, and no clinically relevant changes were observed for either formulation with respect to physical examination, hematology, biochemistry, electrocardiography, or urinalysis. Neither formulation caused any serious adverse events. Conclusions: Two amlodipine formulations were found to be equivalent in terms of the pharmacokinetics of S-amlodipine. The newly developed formulation, comprised of only S-amlodipine, had pharmacodynamic profiles comparable to those of the conventional racemic amlodipine formulation in these healthy Korean male subjects. Both formulations were well tolerated. (Clin Ther. 2006;28:1837-1847) Copyright © 2006 Excerpta Medica, Inc. Key words: amlodipine, S-amlodipine, chiral switching, enantiomer, chiral drug.
INTRODUCTION Amlodipine, a third-generation dihydropyridine calcium channel antagonist, is prescribed for the management of angina and hypertension. 1,2 Its pharmacokinetic profile differs from those of other dihydropyridine calcium channel antagonists (eg, verapamil and nifedipine). In particular, amlodipine is well absorbed and has greater bioavailability (60%-65%). 1-3 Also, because amlodipine has high tissue affinity, it is taken up by hepatic tissue and released to the systemic circulation, 4,5 resulting in a longer Tmax (6-12 hours) and longer elimination tl/2 (30-50 hours) than other dihydropyridine calcium antagonists, which facilitates QD administration. 1,2,6 Enantiomeric drugs have become increasingly important over the last 20 to 30 years. 7 Currently, - 5 6 % of the drugs in use are chiral compounds, and 88% of those are administered as racemic mixtures. The individual enantiomers present in such mixtures frequent-
ly differ in terms of their pharmacodynamic and pharmacokinetic profiles as a result of stereochemical discriminations in their interactions with chiral biological macromolecules. Drugs composed of a single enantiomer have several potential advantages, which include improved therapeutic indexes due to increased potency and selectivity, improved onset and duration of effect, decreased potential for drug-drug interactions, decreased interindividual variability in responses, and reduced adverse events (AEs). 7-9 Therefore, research interest has focused on the issue of "chiral switching," the term given to the replacement of a racemate by the active enantiomer drug. 8-1° Levalbuterol, levobupivacaine, S-ibuprofen, escitalopram, and esomeprazole are just a few examples of drugs that have been developed by chiral switching from a racemic mixture, and are now licensed and available clinically.8, 9 Amlodipine is used therapeutically as a racemic mixture, 8,1°,11 although its enantiomers have markedly different pharmacologic activities. Essentially, the calcium channel-blocking effect is confined to the S-amlodipine, 12,13 whereas the R-amlodipine has 1000-fold lower calcium channel-blocking activity. 14 Thus, the antihypertensive and antianginal effects of amlodipine by the calcium channel-blocking effect are attributed to S-amlodipine, whereas R-amlodipine is regarded as an impurity that might be inactive or might have undesirable activities. 7 Considering that an available conventional amlodipine formulation contains the R- and S-amlodipine in a 1:1 ratio and only S-amlodipine possesses the desirable activity, the successful development of an amlodipine formulation composed of only S-amlodipine might have been anticipated. A 2002 study 14 reported that R-amlodipine releases nitric oxide (NO) in a concentration-dependent manner by kinin-mediated mechanisms, whereas S-amlodipine does not. Therefore, it is believed that R-amlodipine, which composes half of the conventional amlodipine formulation, causes NO-mediated venodilation and is responsible for the AEs commonly associated with amlodipine (eg, peripheral edema, skin erythema, and facial flushing), is Therefore, to accomplish the chiral switching of amlodipine, a newly developed amlodipine formulation composed wholly of S-amlodipine (LodienTM,Hanlim Pharmaceutical Co., Seoul, Korea) has been developed. Preclinical studies have suggested that there was no difference between Lodien and amlodipine besylate in terms of disso-
J.-Y. Park et al. reference formulation in the first study period, followed by a single dose of the test formulation in the second period. The order of the sequence of administration with the 2 formulations was determined by the randomization schedule generated by the use of the statistical package SAS version 9.0 (SAS Institute Inc., Cary, North Carolina) just prior to the beginning of the study. Laboratory testing included hematology, biochemistry, urinalysis, and ECG. Tests were performed by the site staff in fasting subjects over 10 hours at baseline and after study period 2. All study subjects were admitted to the clinical trial center during the evening prior to the day of initial drug administration. The following morning, subjects were administered a single PO dose of either the reference or test formulation. An angiocatheter with a normal saline lock was inserted into an antecubital vein. Blood samples were collected immediately before drug administration (baseline) and then at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 12 hours after drug administration. Before each blood sample was drawn, the line was flushed with saline to ensure patency and 1 mL of blood was drawn and discarded so as not to obtain blood samples diluted by saline in the angiocatheter. Blood samples at 24, 48, 72, 96, 120, 144, and 168 hours after drug administration were collected by venipuncture from both arms. Eight milliliters of blood was collected in heparinized tubes (Vacutainer, Becton Dickinson, Franklin Lakes, New Jersey). Plasma was separated by centrifugation at 3000 rpm at 4°C for 15 minutes within 30 minutes of collection and stored at -70°C for <_12 weeks before assay.
lution profiles, m vitro toxmlties, pharmacokinetics, and blood pressure-lowering effects in animals. The present study was designed to assess and compare the pharmacokinetic and pharmacodynamic characteristics of the new S-amlodipine formulation with those of a conventional racemate in healthy male subjects.
SUBJECTS AND METHODS Study Design This study was conducted as a single center, randomized, open-label, 2-period, comparative, crossover study at the Gil Medical Center and Gachon Medical School, Incheon, Korea. The study was approved by the institutional review board (IRB) and conducted in accordance with the principles of the Declaration of Helsinki 16 and the guidelines of Good Clinical Practice. 17 Compensation for participation in the study was approved by the IRB.
Study Population Male volunteers aged between 20 and 50 years were eligible to participate in this study if their weight was within 20% of ideal body weight and they were judged by physicians to be healthy based on the results of a detailed physical examination, 12-lead electrocardiography (ECG), serum biochemistry, hematology, and urinalysis. Sample size was calculated assuming an intrasubject CV for AUC and the plasma Cma× of about 20% to detect a 20% difference in the pharmacokinetic parameters between the 2 formulations, with a study power of 80% and an 0c error of 0.05.18'19 Subjects were not eligible if they had: a history or evidence of a hepatic, renal, gastrointestinal, or hematologic abnormality; a hepatitis B, hepatitis C, or HIV infection revealed on examination; any other acute or chronic disease; or an allergy to any drug.
Pharmacodynamic Assessments The primary variables measured in this study were systolic and diastolic blood pressure (SBP and DBP, respectively) and heart rate (HR). Before administration of each formulation, baseline blood pressure (BP) and HR were measured 3 times with the subjects in a sitting position; the mean values were used as the baseline value. After administration of each formulation, BP and H R were measured just before each blood sampling at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 24, 48, and 72 hours in the same arm by the same investigator using an automatic BP monitor with a validated oscillometer (Model UA-768, A&D Company, Ltd., Tokyo, Japan). 18,z° Before measurements were begun, each subject was resting seated for >5 minutes, with his or her arm supported at heart level. The cuff was placed on the upper arm. A built-in automatic
Study Procedures All study subjects were administered a single PO dose, under the supervision of a physician (J.-Y.P.), of the reference formulation (racemate, 10 mg) and the test formulation (S-amlodipine, 5 rag) separated by a 3-week washout period in a crossover manner. Subjects were randomly assigned in a 1:1 ratio to 1 of 2 treatment sequences: (1) a single dose of the test amlodipine formulation (S-enantiomer amlodipine 5 mg PO) in the first study period, followed by a single dose of the reference amlodipine formulation (racemate 10 mg PO) in the second study period, or (2) a single dose of the
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compressor provided gradual, adoptive compression of the cuff, and the constant-air-release valve system produced an appropriately stable rate of deflation.
Determination of $-Amlodipine in Plasma Samples Plasma amlodipine concentrations were analyzed by BioCore Company (Seoul, Korea) using a newly developed and validated high-performance liquid chromatography coupled to tandem mass spectrometry method (LCIMS/MS) (Thermo Electron Co., Yokahama City, Japan). Briefly, plasma samples (1 mL) were added to 10-mL glass tubes containing the internal standard (100 ilL of terazocin 100 ng/mL), and 100 IuL of 1 M sodium hydroxide and 6 mL of tert-butylmethylether were then added. After shaking for 30 minutes, the mixture was centrifuged for 5 minutes at 1000 rpm. The organic phase was then transferred to a clean glass tube and evaporated to dryness under a flow of nitrogen gas at 40°C. The dry residue obtained was reconstituted with 125 pL of mobile phase, and a 10-pL aliquot of this solution was injected onto the LC/MS/MS equipped with a chiral alpha(1)-acid glycoprotein column (5 lam, 2.0 × 150 mm, ChromTeck Ltd., Cheshire, United Kingdom). The mobile phase was composed of 10 mM ammonium formate (pH 4.0) and n-propanol (99:1, v/v). Quantification was performed with the multiple reaction monitoring mode, which produced the following transitions: m/z 409--+238 for R- and S-amlodipine; and m/z 388-9290 for the internal standard. Retention times for R-amlodipine, S-amlodipine, and internal standard were 8.4, 11.5, and 2.8 minutes, respectively. We were unable to find any evidence of the conversion of S-amlodipine into R-amlodipine in plasma samples. After administration of the reference formulation, both R- and S-amlodipine were found in plasma samples whereas, after administration of test formulation, only S-amlodipine was detected. A linearity calibration curve over the range 0.2 to 20 ng/mL was established for S-amlodipine (r2 -- 0.9964). Intraday CV was 4.4%, 4.4%, 8.8%, and 7.9% for S-amlodipine at concentrations of 0.2, 1.0, 5.0, and 20.0 ng/mL, respectively; the interday CV was 12.2%, 2.9%, 5.4%, and 8.1%, respectively. The limit of quantification was 0.2 ng/mL.
Safety Profile The investigators monitored ECGs, performed physical examinations, and recorded all observed or
spontaneously reported AEs throughout the study. Onset, duration, severity (mild, moderate, severe), treatment required, and investigators' assessments of AEs and their possible relation to the study drugs were noted. Treatment-emergent AEs were defined as events that were not present at baseline but occurred after administration of the study drug. The following clinical laboratory properties were measured at baseline and at the end of the study: blood hematology--hemoglobin, hematocrit, erythrocyte count, leukocyte count, platelet count, and differential counts; urinalysis--specific gravity, ketone bodies, pH, protein, glucose, urobilinogen, bilirubin, blood, red blood cell/high-power field, white blood cell/high-power field, and casts/low-power field; and serum chemistry--albumin, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, blood urea nitrogen, creatinine, cholesterol, glucose, lactate dehydrogenase, total bilirubin, total protein, creatine phosphokinase, uric acid, calcium, chloride, sodium, potassium, and phosphorus. All laboratory tests were performed at an accredited laboratory (Department of Laboratory Medicine, Gil Medical Center and Gachon Medical School). The quality assurance of the laboratory tests was accredited by both the Korean Society for Laboratory Medicine and the Korean Association of Quality Assurance for Clinical Laboratory. Each ECG was reviewed by a qualified physician (cardiologist) at Gil Medical Center to detect any clinically significant findings.
Statistical Analysis The pharmacokinetic parameters of S-amlodipine were estimated using noncompartmental methods. C .... and Tmax were estimated directly from observed plasma concentration-time data. AUC from time 0 to the last available measurement (AUClast) was calculated using the linear trapezoidal rule. AUC from time 0 to infinity (AUC0~) was calculated using the following formula: AUC0~ = AUC~ast+ Ct/ke, where Ct is the last plasma concentration measured and k e is the elimination rate constant, determined using linear regression analysis of the linear portion of the log plasma concentration-time curve. The tl/2 of S-amlodipine was calculated using the formula tl/2 = In 2/ke, and the oral clearance (CL/F) of S-amlodipine was calculated as CL/F -- dose/AUC0_~. For hemodynamic measures, AUC of effect-time from 0 to 24 hours (AUEC0_e4) was calculated for individual subjects using the linear trapezoidal method.
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Maximum changes (Amax) in SBP, DBP, and H R were also determined for individual subjects. Pharmacokinetic and pharmacodynamic analyses were performed with WinNonlin software version 5.01 (Pharsight Corporation, Mountain View, California). To determine whether the 2 amlodipine formulations were pharmacokinetically equivalent with respect to S-amlodipine, we compared individual Cma×, AUClast, and AUC0~ values and their ratios (test/reference) using log-transformed data; means and 90% CIs were analyzed using a parametric variance analysis method. These were considered the primary end points. Twoway analysis of variance (ANOVA) was used for assessing the effects of formulation, period, and sequence on the pharmacokinetic parameters. 21 Due to the nature of normal-theory CIs, this was equivalent to carrying out two 1-sided tests at the 5% level of significance. 22 Drugs were considered bioequivalent if the difference between compared properties of the 2 formulations was statistically nonsignificant (P > 0.05) and the 90% CI fell within the range of 0.8 to 1.25 for log-transformed data. All statistical analysis was performed with SAS version 9.0 (SAS Institute Inc., Cary, North Carolina).
RES U LTS Demographic Characteristics Twenty-six healthy Korean male volunteers were screened and 18 subjects (mean age [SD], 23.4 [1.5] years [range, 21-26 years]; mean height [SD], 176.1 [4.6] cm [range, 167-184 cm]; mean body weight [SD], 69.3 [6.8] kg [range, 60-88 kg]) were enrolled in this study. Results of hematology, biochemistry, and urinalysis at baseline and at study end are shown in Table I.
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S-amlodipine for the 2 formulations are presented in Table II. The equivalence statistics of the pharmacokinetic parameters of S-amlodipine, including Cmax, AUClast , and AUC0_~, for the 2 formulations are summarized in Table III. The mean log-transformed ratios of these parameters and their 90% CIs all fell within the predefined bioequivalence range of 80% to 125%. There was no effect associated with period, sequence, or formulation. Intrasubject CVs (derived from the mean square errors of the ANOVA) of Cmax, AUC0_~, and AUClastwere 12.2%, 11.6%, and 15.6%, respectively.
Pharmacodynamic Assessment Changes in SBP, DBP, and HR were evaluated after administration of a single dose of the reference or test formulation. Compared with baseline values, mean (SD) SBP decreased significantly during the 4- to 10-hour period following the administration of the reference (A, -15.4 [4.4] mm Hg) and test (A, -14.9 [3.6] mm Hg; both, P < 0.001) formulations (Figure 2). DBP also was decreased significantly during the 5- to 12-hour period following administration of the reference (A, -14.1 [4.7] mm Hg; P < 0.001) and test (A. . . . -13.8 [4.3] mm Hg; P < 0.001) formulations. HR increased significantly during the 5- to 10-hour period following administration of the reference (A, +12.5 [4.6] bpm; P < 0.001) and test (A, +13.4 [4.3] bpm; P < 0.001) formulations. However, SBP, DBP, and HR profiles versus time were comparable for the 2 formulations. In addition, no significant between-formulation differences were found in terms of Areax from baseline or AUEC0_24 for SBP, DBP, and HR. The pharmacodynamic parameters for SBP, DBP, and HR are presented in Table IV.
Pharmacokinetic Analysis Figure 1 shows the mean plasma concentrationtime profiles of S-amlodipine after administration of the reference or test formulation. No significant betweenformulation difference was observed in the mean (SD) AUC0~ values; 175.3 (45.1) ng• h/mL for the reference formulation and 161.7 (43.8) ng • h/mL for the test formulation. Also, no significant betweenformulation difference was observed in the mean (SD) CL/F values of S-amlodipine: 30.6 (9.1) and 33.2 (8.2) L/h for the reference and test formulations, respectively. The mean (SD) Cmax values of the reference and test formulations were 3.0 (0.6) and 3.1 (0.6) ng/mL, respectively; Tmax was reached at 6.2 and 5.7 hours, respectively. The pharmacokinetic parameters of iNovembef:2006
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Safety Profiles Because of the cardiovascular events associated with amlodipine, changes in BP and H R were observed, but no serious AEs occurred during the study period. A total of 5 treatment-emergent AEs were reported: 2 patients reported headache (1 in the reference group and 1 in the test group), 1 reported headache and facial flushing (reference), and 2 reported fatigue (1 reference and 1 test). No clinically meaningful changes in physical, biochemical, hematologic, or urinalysis variables were observed between the screening visit and the end of the study (Table I). Overall ECG assessments were normal in all subjects at baseline and at the end of the study. ii
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Table I. Results of hematology, biochemistry, and urinalysis testing at baseline and at study end in subjects who received a single dose of amlodipine racemate lO-mg or S-amlodipine 5-rag formulations (N = 18). Baseline, Mean (SD)
End of Study, Mean (SD)
Normal Range
Hematology Red blood cell count, cells x 106/L Hematocrit, % Hemoglobin, g/dL White blood cell count, cells x 103/L Platelet count, cells x 103/laL
5.0 45.6 15.4 6.0 264.4
(0.3) (2.7) (1.0) (1.0) (39.8)
5.0 (0.2) 45.7(1.9) 15.6(0.6) 6.5 (0.8) 286.4 (43.5)
4.4-5.9 39-51 13-17 4-10 150-450
Biochemistry Alanine aminotransferase, U/L Alkaline phosphatase, U/L Aspartate aminotransferase, U/L Bilirubin, total, mg/dL Blood urea nitrogen, mg/dL Calcium, mg/dL Chloride, mmol/L Cholesterol, mg/dL Creatine phosphokinase, IU/L Creatinine, mg/dL Glucose, mg/dL Lactate dehydrogenase, U/L Phosphorus, mg/dL Potassium, mmol/L Sodium, mmol/L Uric acid, mg/dL
15.5 165.6 17.5 0.9 11.9 9.0 104.2 151.9 116.4 1.0 97.3 302.3 3.6 4.5 142.6 6.3
(5.7) (37.4) (3.2) (0.2) (2.4) (0.4) (1.8) (20.4) (45.8) (0.1) (6.9) (38.2) (0.5) (0.3) (1.5) (1.0)
20.3 (14.2) 144.0 (21.7) 20.4 (7.1) 0.6(0.2) 13.0 (1.56) 9.1 (0.2) 102.3 (1.6) 170.0 (20.4) 87.3 (23.9) 1.0(0.1) 92.3 (6.9) 296.9 (42.1) 4.1 (0.5) 4.5 (0.3) 141.9 (1.2) 6.2 (1.1)
5-40 70-290 0-40 0.2-1.2 8-22 8.2-10.8 95-110 120-250 26-200 0.6-1.2 70-120 120-520 2.5-4.7 3.5-5.5 135-145 2.5-8.3
Urinalysis pH Specific gravity, g/mL
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tween the 2 amlodipine formulations might be associated with the presence or absence of R-amlodipine; both contain the same amount of S-amlodipine. If the pharmacokinetic characteristics of S-amlodipine had been different in the 2 formulations, the differences might have been attributed to the presence of R-amlodipine. However, as we did not observe any difference between the 2 formulations in terms of the pharmacokinetics of S-amlodipine, we suggest that R-amlodipine does not affect the pharmacokinetics of S-amlodipine in humans. AUC is an accepted indicator of the extent of absorption, whereas Cmax and Tmax are determined by both the rate of absorption and the rate of elimination. 24 Considering that pharmacokinetic parameters for S-amlodipine were similar between the 2 formu-
DISCUSSION The results of the present study suggest that the 2 amlodipine formulations were comparable in terms of their pharmacokinetic and pharmacodynamic characteristics in humans. Cm~X values of S-amlodipine for the 2 formulations were similar (3.0 ng/mL for the reference group vs 3.1 ng/mL for the test group). In addition, Tm~x occurred between 4 and 10 hours for the test formulation, which was similar to the corresponding values for the reference formulations. These findings suggest that both formulations have similar absorption patterns for S-amlodipine. This is consistent with data previously reported by Vincent et a123 in a placebo-controlled, open-label, randomized, 4-way crossover study using single doses of amlodipine 10 mg in healthy men. In fact, any differences observed be-
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Time (h) Figure 1. Mean (SD) plasma 5-amlodipine concentrations after the administration of a single oral dose of amlodipine racemate 10-mg or 5-amlodipine 5-mg formulations in 18 healthy Korean male subjects.
Table II. Pharmacokinetic properties of S-amlodipine in study subjects (N = 18) after the administration of a single dose of amlodipine racemate 10-rag (reference) or S-amlodipine 5-mg (test) formulations. Values are expressed as mean (SD) unless otherwise indicated. Parameter
Reference
AUCo_~, ng" h/mL AUCfa~t, ng" h/mL CL/F, L/h C . . . . ng/mL ke, h -1 tl/2, h Tmax, h
175.3 151.4 30.6 3.0 0.014 53.3 6.2
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(45.1) (35.7) (9.1) (0.6) (0.004) (11.3) (1.4)
P*
161.7 139.7 33.2 3.1 0.014
(43.8) (40.3) (8.2) (0.6) (0.004) 55.0 (18.6) 5.7 (1.1)
0.15 0.20 0.11 0.33 0.80 0.70 0.19
AUC0_~ = AUC from time 0 to infinity; A U C l a s t = AUC from time 0 t O the last available measurement; CL/F = oral clearance bioavailability; ke = elimination rate constant. *No significant between-treatment differences were found for S-amlodipine.
lations, we suggest that their rates and extents of absorption are similar. Moreover, when 2 formulations of a single drug are bioequivalent in terms of rate and extent of absorption, it is suggested that they are therapeutically equivalent. 24 Two internationally recognized organizations (the US Food and Drug Administration [FDA] 25 and the European Medicines Agency26) and the Korean FDA 27 have proposed that bioequivalence can be as-
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sumed only when the characteristic parameters of bioavailability including Cmax and AUC show no more than a defined difference between 0.8 and 1.25 for logtransformed data. It is generally accepted that the AUC and Cmax of a test formulation should lie within 20% of those of the corresponding reference formulation, and thus, the 90% Cls of the AUC and Cmax ratios should lie between 0.8 and 1.25 for log-transformed data. 28,29
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Table III. Bioequivalence statistics: Treatment ratios of the log-transformed geometric mean pharmacokinetic parameters of the amIodipine racemate lO-mg or S-amlodipine 5-mg formulations (N = 18). Parameter Cmax AUC 0 ~ AUCl~st
Ratio, %
90% CI
105.0 92.5 91.8
97.56-112.51 86.31-98.74 83.46-100.04
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Based on accepted regulatory requirements, 23-25 the current study suggests that the test formulation was bioequivalent to the reference formulation with respect to S-amlodipine absorption and elimination. The 90% CIs of Cmax, AUClast, and AUC0_~ for the 2 for-
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mulations were all found to be in the stipulated range (0.80-1.25), suggesting the pharmacokinetic equivalence of these 2 drugs. In this study, intrasubject CV of the primary pharmacokinetic parameters (ie, Cmax, AUClast, and AUC0~ ) were all <16%, which was lower than the anticipated 20%. 18,19 This meant that a smaller sample size would have been enough to prove pharmacokinetic bioequivalence and that the power of the study exceeded the anticipated power of 80% based on 18 subjects. In this study, we found that both formulations caused marked hemodynamic changes in BP and HR, despite the fact that only a single dose was administered to the participants. And, although the amount of test formulation administered was only half that of the reference formulation, the test formulation had a comparable pharmacodynamic profile. These results suggest that S-amlodipine, and not R-amlodipine, is the cause of the hemodynamic effects associated with racemic amlodipine, which is consistent with previous
Table IV. Pharmacodynamic properties obtained from study subjects after a single oral dose ofamlodipine racemate
10-mg or S-amlodipine 5-mg formulations (N = 18). Values are presented as mean (SD) unless otherwise indicated. Parameter
Reference
SBP Baseline, mm Hg¢ A AUEC 0 24, mm Hg/h A Mean SBP, mm Hg Amax, mm Hg T Amax, h DBP Baseline, mm Hgt A AUEC0_24, mm Hg/h A Mean DBP, mm Hg Amax, mm Hg T Amax, h HR Baseline, bpmf A AUEC 0 24, bpm/h A Mean HR, bpm A .... bpm T A .... h
Test
P*
120.5 123.2 5.1 15.4 8.3
(5.2) (43.8) (1.8) (4.4)~ (1.8)
121.4 114.8 4.8 14.9 7.5
(5.3) (46.7) (1.9) (3.6)# (1.5)
0.25 0.48 0.48 0.70 0.20
72.0 108.0 4.5 14.1 7.4
(5.6) (39.0) (1.6) (4.7)# (2.4)
72.4 115.7 4.8 13.8 7.4
(5.4) (45.1) (1.9) (4.3)t (1.9)
0.70 0.48 0.48 0.78 1.00
70.9 89.3 3.7 12.5 6.7
(6.9) (51.4) (2.1) (4.6)t (2.4)
70.5 103.5 4.3 13.4 7.1
(5.8) (63.5) (2.6) (4.3)* (1.8)
0.75 0.45 0.45 0.50 0.58
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findings. 12-14 R-Amlodipine has been associated with a 1000-fold lower calcium channel-blocking effect than S-amlodipine and thus considered an inactive compound. However, studies have suggested that R-amlodipine is linked with the AEs of amlodipine. 14,is As with any clinical trial, the current study had some limitations that should be considered. This was an open-label study, so it might not address objectively the effectiveness and safety profiles of the formulations tested. Because the data we obtained were from healthy male subjects who were administered a single dose, the pharmacokinetic and pharmacodynamic characteristics of amlodipine might differ in target populations. Because of the limited data, we are unable to predict the response of the drug at any time following alternative doses and/or administration interval with the present data set. Further study is needed to determine whether the test formulation has similar or increased efficacy and/or tolerability in the patient groups, considering the comparable pharmacokinetic and pharmacodynamic profiles of 2 formulations. Based on our findings, it is likely that the therapeutic effects are similar in patient groups.
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8. 9.
10. 11. 12.
CONCLUSIONS In this small study, a test amlodipine formulation, comprised of only S-amlodipine, was found to be bioequivalent with a reference formulation, amlodipine racemate, in terms of both the rate and extent of absorption, in these Korean healthy volunteers. The treatment ratios (test/reference) of the geometric means and 90% CIs of C...... A U C l a s t , and AUC0~ were all within the predetermined range of 0.8 to 1.25 for pharmacokinetic bioequivalence. Both formulations suggested similar pharmacodynamic characteristics, which included their effects on SBP, DBP, and HR. Both formulations were well tolerated.
13.
14.
1`5. 16.
ACKNOWLEDGMENT
This study was funded by Hanlim Pharmaceutical Company (Seoul, Korea).
17.
REFERENCES 1. Abernethy DR. The pharmacokinetic profile of amlodipine. Am HeartJ. 1989;118:1100-1103. 2. Meredith PA, Elliott HL. Clinical pharmacokinetics of amlodipine. Clin Pkarmacokinet. 1992;22:22-31. 3. Haria M, Wagstaff AJ. Amlodipine. A reappraisal of its pharmacological properties and therapeutic use in car-
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diovascular disease [published correction appears in Drugs. 1995;50:896]. Drugs. 1995;50:560-586. Beresford AP, McGibney D, Humphrey MJ, et al. Metabolism and kinetics ofamlodipine in man. Xenobiotica. 1988; 18:245-254. Walker DK, Humphrey MJ, Smith DA. Importance of metabolic stability and hepatic distribution to the pharmacokinetic profile ofamlodipine. Xenobiotica. 1994;24:243-250. Stopher DA, BeresFord AP, Macrae PV, Humphrey MJ. The metabolism and pharmacokinetics of amladipine in humans and animals. J Cardiovasc Pharmacol. 1988;12 (Suppl 7):$55-$59. Rentsch KM. The importance of" stereoselective determination of drugs in the clinical laboratory.J Biockem Biopkys Metkods. 2002;.54:1-9. Tucker GT. Chiral switches. Lancet. 2000;3.5.5:1085-1087. Agranat I, Caner H, Caldwell J. Putting chirality to work: The strategy of chiral switches. Nat Rev Drug Discov. 2002; 1:753-768. Burke D, Henderson DJ. Chirality: A blueprint for the future. BrJ Anaestk. 2002;88:563-576. Hurt AJ. The development of single-isomer molecules: Why and how. CNSSpectr. 2002;7(Suppl 1 ):14-22. Arrowsmith JE, Campbell SF, Cross PE, et al. Long-acting dihydropyridine calcium antagonists. 1. 2-AIkoxymethyl derivatives incorporating basic substituents. J Med Chem. 1986;29:1696-1702. Goldmann S, Stoltefuss J, Born L. Determination of the absolute configuration of the active amlodipine enantiomer as (-)-S: A correction.J IVied Chem. 1992;3`5:33413344. Zhang XP, Loke KE, Mital S, et al. Paradoxical release of nitric oxide by an L-type calcium channel antagonist, the R+ enantiomer ofamlodipine.J CardiovascPkarmacol. 2002; 39:208-214. Adik-Pathak L. Chiral molecules in hypertension: Focus on S-amlodipine.J Assoc PhysiciansIndia. 2004;52:187-188. World Medical Association Declaration of Helsinki: Recommendations Guiding Medical Doctors in Biomedical Research Involving Human Subjects [WMA Web site]. Ferney-Vottaire, France: WMA; 1989. Available at: http://www.wma.net. Accessed April 1`5, 2006. European Agency for the Evaluation of Medicinal Products, International Conference on Harmonisation-World Health Organization. Guideline for Good Clinical Practice [EMEA Web site]. ICH Topic E6. Geneva, Switzerland: WHO; 2002. Available at: http://www.emea.eu.int. Accessed April 1`5, 2006. Park JY, Kim KA, Lee GS, et al. Randomized, open-label, two-period crossover comparison of the pharmacokinetic and pharmacodynamic properties of two amlodipine formulations in healthy adult male Korean subjects. Clin Tker. 2004;26:71.5-723.
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19. Abad-Santos F, Novalbos J, GalvezMugica MA, et al. Assessment of sex differences in pharmacokinetics and pharmacodynamics of amlodipine in a bioequivalence study. Pkarmacol Res. 2005;51:445-452. 20. Rogoza AN, Pavlova TS, Sergeeva MV. Validation of A&D UA-767 device for the self-measurement of blood pressure. B l o o d Press M o n i t .
2000;5:227-231. 21. Chow SC, LiuJ-P. Design ol: B i o a v a i l a b i l i t y
and
........
i ¸
Food and Drug Administration Web site. Available at: http:llwww.
fda.gov/cder/ob/docs/preface/ ecpreface.htm. Accessed August 12, 2006.
29. Meyer MC. United States Food and Drug Administration requirements for approval of generic drug products.J Clin Psychiatry. 2001 ;62(Suppl 5):4-9, discussion 23-24.
a n d Analysis
Bioequivolence
NewYork, NY: Marcel Dekker, Inc; 1992:48-69. Schuirmann DJ. A comparison of the two one-sided tests procedure and the power approach for assessing the equivalence of average bioavailability. J P h a r m a c o k i n e t Biop h a r m . 1987;15:657-680. VincentJ, Harris SI, Foulds G, et al. Lack of effect of grapefruit juice on the pharmacokinetics and pharmacodynamics of amlodipine. B r J Clin P h a r m a c o l . 2000;50:455-463. Farolfi M, Powers JD, Rescigno A. On the determination of bioequivalence. P h a r m a c o l Res. 1999;39:1-4. Food and Drug Administration. Guidance: Statistical procedure for bioequivalence studies using standard 2-treatment cross-over design: Statement under 21 CFR 10.9. Rockville, Md: US Dept of Health and Human Services; 1992. Committee for Proprietary Medicinal Products (CPMP) Working Party on the Efficacyof Medicinal Products. Note for guidance: Investigation of bioavailability and bioequivalence Studies.
22.
23.
24.
25.
26.
[European Medicines Agency (EMEA) Web site]. London, UK: EMEA, 2001. Available at: http://www.emea. eu.int. Accessed April 15, 2006. 27. Food and Drug Administration of Korea (KFDA). Korea FDA guidelines for bioequivalence test. [KFDA Web site]. Seoul, Korea: KFDA; 1996. Available at: http://www. kfda.go.kr. Accessed April 15, 2006. 28. Approved drug products with therapeutic equivalence evaluations. US
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INTRODUCTION Amlodipine, a third-generation dihydropyridine calcium channel antagonist, is prescribed for the management of angina and hypertension. 1,2 Its pharmacokinetic profile differs from those of other dihydropyridine calcium channel antagonists (eg, verapamil and nifedipine). In particular, amlodipine is well absorbed and has greater bioavailability (60%-65%). 1-3 Also, because amlodipine has high tissue affinity, it is taken up by hepatic tissue and released to the systemic circulation, 4,5 resulting in a longer Tmax (6-12 hours) and longer elimination tl/2 (30-50 hours) than other dihydropyridine calcium antagonists, which facilitates QD administration. 1,2,6 Enantiomeric drugs have become increasingly important over the last 20 to 30 years. 7 Currently, - 5 6 % of the drugs in use are chiral compounds, and 88% of those are administered as racemic mixtures. The individual enantiomers present in such mixtures frequent-
ly differ in terms of their pharmacodynamic and pharmacokinetic profiles as a result of stereochemical discriminations in their interactions with chiral biological macromolecules. Drugs composed of a single enantiomer have several potential advantages, which include improved therapeutic indexes due to increased potency and selectivity, improved onset and duration of effect, decreased potential for drug-drug interactions, decreased interindividual variability in responses, and reduced adverse events (AEs). 7-9 Therefore, research interest has focused on the issue of "chiral switching," the term given to the replacement of a racemate by the active enantiomer drug. 8-1° Levalbuterol, levobupivacaine, S-ibuprofen, escitalopram, and esomeprazole are just a few examples of drugs that have been developed by chiral switching from a racemic mixture, and are now licensed and available clinically.8, 9 Amlodipine is used therapeutically as a racemic mixture, 8,1°,11 although its enantiomers have markedly different pharmacologic activities. Essentially, the calcium channel-blocking effect is confined to the S-amlodipine, 12,13 whereas the R-amlodipine has 1000-fold lower calcium channel-blocking activity. 14 Thus, the antihypertensive and antianginal effects of amlodipine by the calcium channel-blocking effect are attributed to S-amlodipine, whereas R-amlodipine is regarded as an impurity that might be inactive or might have undesirable activities. 7 Considering that an available conventional amlodipine formulation contains the R- and S-amlodipine in a 1:1 ratio and only S-amlodipine possesses the desirable activity, the successful development of an amlodipine formulation composed of only S-amlodipine might have been anticipated. A 2002 study 14 reported that R-amlodipine releases nitric oxide (NO) in a concentration-dependent manner by kinin-mediated mechanisms, whereas S-amlodipine does not. Therefore, it is believed that R-amlodipine, which composes half of the conventional amlodipine formulation, causes NO-mediated venodilation and is responsible for the AEs commonly associated with amlodipine (eg, peripheral edema, skin erythema, and facial flushing), is Therefore, to accomplish the chiral switching of amlodipine, a newly developed amlodipine formulation composed wholly of S-amlodipine (LodienTM,Hanlim Pharmaceutical Co., Seoul, Korea) has been developed. Preclinical studies have suggested that there was no difference between Lodien and amlodipine besylate in terms of disso-
J.-Y. Park et al. reference formulation in the first study period, followed by a single dose of the test formulation in the second period. The order of the sequence of administration with the 2 formulations was determined by the randomization schedule generated by the use of the statistical package SAS version 9.0 (SAS Institute Inc., Cary, North Carolina) just prior to the beginning of the study. Laboratory testing included hematology, biochemistry, urinalysis, and ECG. Tests were performed by the site staff in fasting subjects over 10 hours at baseline and after study period 2. All study subjects were admitted to the clinical trial center during the evening prior to the day of initial drug administration. The following morning, subjects were administered a single PO dose of either the reference or test formulation. An angiocatheter with a normal saline lock was inserted into an antecubital vein. Blood samples were collected immediately before drug administration (baseline) and then at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 12 hours after drug administration. Before each blood sample was drawn, the line was flushed with saline to ensure patency and 1 mL of blood was drawn and discarded so as not to obtain blood samples diluted by saline in the angiocatheter. Blood samples at 24, 48, 72, 96, 120, 144, and 168 hours after drug administration were collected by venipuncture from both arms. Eight milliliters of blood was collected in heparinized tubes (Vacutainer, Becton Dickinson, Franklin Lakes, New Jersey). Plasma was separated by centrifugation at 3000 rpm at 4°C for 15 minutes within 30 minutes of collection and stored at -70°C for <_12 weeks before assay.
lution profiles, m vitro toxmlties, pharmacokinetics, and blood pressure-lowering effects in animals. The present study was designed to assess and compare the pharmacokinetic and pharmacodynamic characteristics of the new S-amlodipine formulation with those of a conventional racemate in healthy male subjects.
SUBJECTS AND METHODS Study Design This study was conducted as a single center, randomized, open-label, 2-period, comparative, crossover study at the Gil Medical Center and Gachon Medical School, Incheon, Korea. The study was approved by the institutional review board (IRB) and conducted in accordance with the principles of the Declaration of Helsinki 16 and the guidelines of Good Clinical Practice. 17 Compensation for participation in the study was approved by the IRB.
Study Population Male volunteers aged between 20 and 50 years were eligible to participate in this study if their weight was within 20% of ideal body weight and they were judged by physicians to be healthy based on the results of a detailed physical examination, 12-lead electrocardiography (ECG), serum biochemistry, hematology, and urinalysis. Sample size was calculated assuming an intrasubject CV for AUC and the plasma Cma× of about 20% to detect a 20% difference in the pharmacokinetic parameters between the 2 formulations, with a study power of 80% and an 0c error of 0.05.18'19 Subjects were not eligible if they had: a history or evidence of a hepatic, renal, gastrointestinal, or hematologic abnormality; a hepatitis B, hepatitis C, or HIV infection revealed on examination; any other acute or chronic disease; or an allergy to any drug.
Pharmacodynamic Assessments The primary variables measured in this study were systolic and diastolic blood pressure (SBP and DBP, respectively) and heart rate (HR). Before administration of each formulation, baseline blood pressure (BP) and HR were measured 3 times with the subjects in a sitting position; the mean values were used as the baseline value. After administration of each formulation, BP and H R were measured just before each blood sampling at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 24, 48, and 72 hours in the same arm by the same investigator using an automatic BP monitor with a validated oscillometer (Model UA-768, A&D Company, Ltd., Tokyo, Japan). 18,z° Before measurements were begun, each subject was resting seated for >5 minutes, with his or her arm supported at heart level. The cuff was placed on the upper arm. A built-in automatic
Study Procedures All study subjects were administered a single PO dose, under the supervision of a physician (J.-Y.P.), of the reference formulation (racemate, 10 mg) and the test formulation (S-amlodipine, 5 rag) separated by a 3-week washout period in a crossover manner. Subjects were randomly assigned in a 1:1 ratio to 1 of 2 treatment sequences: (1) a single dose of the test amlodipine formulation (S-enantiomer amlodipine 5 mg PO) in the first study period, followed by a single dose of the reference amlodipine formulation (racemate 10 mg PO) in the second study period, or (2) a single dose of the
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compressor provided gradual, adoptive compression of the cuff, and the constant-air-release valve system produced an appropriately stable rate of deflation.
Determination of $-Amlodipine in Plasma Samples Plasma amlodipine concentrations were analyzed by BioCore Company (Seoul, Korea) using a newly developed and validated high-performance liquid chromatography coupled to tandem mass spectrometry method (LCIMS/MS) (Thermo Electron Co., Yokahama City, Japan). Briefly, plasma samples (1 mL) were added to 10-mL glass tubes containing the internal standard (100 ilL of terazocin 100 ng/mL), and 100 IuL of 1 M sodium hydroxide and 6 mL of tert-butylmethylether were then added. After shaking for 30 minutes, the mixture was centrifuged for 5 minutes at 1000 rpm. The organic phase was then transferred to a clean glass tube and evaporated to dryness under a flow of nitrogen gas at 40°C. The dry residue obtained was reconstituted with 125 pL of mobile phase, and a 10-pL aliquot of this solution was injected onto the LC/MS/MS equipped with a chiral alpha(1)-acid glycoprotein column (5 lam, 2.0 × 150 mm, ChromTeck Ltd., Cheshire, United Kingdom). The mobile phase was composed of 10 mM ammonium formate (pH 4.0) and n-propanol (99:1, v/v). Quantification was performed with the multiple reaction monitoring mode, which produced the following transitions: m/z 409--+238 for R- and S-amlodipine; and m/z 388-9290 for the internal standard. Retention times for R-amlodipine, S-amlodipine, and internal standard were 8.4, 11.5, and 2.8 minutes, respectively. We were unable to find any evidence of the conversion of S-amlodipine into R-amlodipine in plasma samples. After administration of the reference formulation, both R- and S-amlodipine were found in plasma samples whereas, after administration of test formulation, only S-amlodipine was detected. A linearity calibration curve over the range 0.2 to 20 ng/mL was established for S-amlodipine (r2 -- 0.9964). Intraday CV was 4.4%, 4.4%, 8.8%, and 7.9% for S-amlodipine at concentrations of 0.2, 1.0, 5.0, and 20.0 ng/mL, respectively; the interday CV was 12.2%, 2.9%, 5.4%, and 8.1%, respectively. The limit of quantification was 0.2 ng/mL.
Safety Profile The investigators monitored ECGs, performed physical examinations, and recorded all observed or
spontaneously reported AEs throughout the study. Onset, duration, severity (mild, moderate, severe), treatment required, and investigators' assessments of AEs and their possible relation to the study drugs were noted. Treatment-emergent AEs were defined as events that were not present at baseline but occurred after administration of the study drug. The following clinical laboratory properties were measured at baseline and at the end of the study: blood hematology--hemoglobin, hematocrit, erythrocyte count, leukocyte count, platelet count, and differential counts; urinalysis--specific gravity, ketone bodies, pH, protein, glucose, urobilinogen, bilirubin, blood, red blood cell/high-power field, white blood cell/high-power field, and casts/low-power field; and serum chemistry--albumin, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, blood urea nitrogen, creatinine, cholesterol, glucose, lactate dehydrogenase, total bilirubin, total protein, creatine phosphokinase, uric acid, calcium, chloride, sodium, potassium, and phosphorus. All laboratory tests were performed at an accredited laboratory (Department of Laboratory Medicine, Gil Medical Center and Gachon Medical School). The quality assurance of the laboratory tests was accredited by both the Korean Society for Laboratory Medicine and the Korean Association of Quality Assurance for Clinical Laboratory. Each ECG was reviewed by a qualified physician (cardiologist) at Gil Medical Center to detect any clinically significant findings.
Statistical Analysis The pharmacokinetic parameters of S-amlodipine were estimated using noncompartmental methods. C .... and Tmax were estimated directly from observed plasma concentration-time data. AUC from time 0 to the last available measurement (AUClast) was calculated using the linear trapezoidal rule. AUC from time 0 to infinity (AUC0~) was calculated using the following formula: AUC0~ = AUC~ast+ Ct/ke, where Ct is the last plasma concentration measured and k e is the elimination rate constant, determined using linear regression analysis of the linear portion of the log plasma concentration-time curve. The tl/2 of S-amlodipine was calculated using the formula tl/2 = In 2/ke, and the oral clearance (CL/F) of S-amlodipine was calculated as CL/F -- dose/AUC0_~. For hemodynamic measures, AUC of effect-time from 0 to 24 hours (AUEC0_e4) was calculated for individual subjects using the linear trapezoidal method.
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Maximum changes (Amax) in SBP, DBP, and H R were also determined for individual subjects. Pharmacokinetic and pharmacodynamic analyses were performed with WinNonlin software version 5.01 (Pharsight Corporation, Mountain View, California). To determine whether the 2 amlodipine formulations were pharmacokinetically equivalent with respect to S-amlodipine, we compared individual Cma×, AUClast, and AUC0~ values and their ratios (test/reference) using log-transformed data; means and 90% CIs were analyzed using a parametric variance analysis method. These were considered the primary end points. Twoway analysis of variance (ANOVA) was used for assessing the effects of formulation, period, and sequence on the pharmacokinetic parameters. 21 Due to the nature of normal-theory CIs, this was equivalent to carrying out two 1-sided tests at the 5% level of significance. 22 Drugs were considered bioequivalent if the difference between compared properties of the 2 formulations was statistically nonsignificant (P > 0.05) and the 90% CI fell within the range of 0.8 to 1.25 for log-transformed data. All statistical analysis was performed with SAS version 9.0 (SAS Institute Inc., Cary, North Carolina).
RES U LTS Demographic Characteristics Twenty-six healthy Korean male volunteers were screened and 18 subjects (mean age [SD], 23.4 [1.5] years [range, 21-26 years]; mean height [SD], 176.1 [4.6] cm [range, 167-184 cm]; mean body weight [SD], 69.3 [6.8] kg [range, 60-88 kg]) were enrolled in this study. Results of hematology, biochemistry, and urinalysis at baseline and at study end are shown in Table I.
J.~. Park et aL
S-amlodipine for the 2 formulations are presented in Table II. The equivalence statistics of the pharmacokinetic parameters of S-amlodipine, including Cmax, AUClast , and AUC0_~, for the 2 formulations are summarized in Table III. The mean log-transformed ratios of these parameters and their 90% CIs all fell within the predefined bioequivalence range of 80% to 125%. There was no effect associated with period, sequence, or formulation. Intrasubject CVs (derived from the mean square errors of the ANOVA) of Cmax, AUC0_~, and AUClastwere 12.2%, 11.6%, and 15.6%, respectively.
Pharmacodynamic Assessment Changes in SBP, DBP, and HR were evaluated after administration of a single dose of the reference or test formulation. Compared with baseline values, mean (SD) SBP decreased significantly during the 4- to 10-hour period following the administration of the reference (A, -15.4 [4.4] mm Hg) and test (A, -14.9 [3.6] mm Hg; both, P < 0.001) formulations (Figure 2). DBP also was decreased significantly during the 5- to 12-hour period following administration of the reference (A, -14.1 [4.7] mm Hg; P < 0.001) and test (A. . . . -13.8 [4.3] mm Hg; P < 0.001) formulations. HR increased significantly during the 5- to 10-hour period following administration of the reference (A, +12.5 [4.6] bpm; P < 0.001) and test (A, +13.4 [4.3] bpm; P < 0.001) formulations. However, SBP, DBP, and HR profiles versus time were comparable for the 2 formulations. In addition, no significant between-formulation differences were found in terms of Areax from baseline or AUEC0_24 for SBP, DBP, and HR. The pharmacodynamic parameters for SBP, DBP, and HR are presented in Table IV.
Pharmacokinetic Analysis Figure 1 shows the mean plasma concentrationtime profiles of S-amlodipine after administration of the reference or test formulation. No significant betweenformulation difference was observed in the mean (SD) AUC0~ values; 175.3 (45.1) ng• h/mL for the reference formulation and 161.7 (43.8) ng • h/mL for the test formulation. Also, no significant betweenformulation difference was observed in the mean (SD) CL/F values of S-amlodipine: 30.6 (9.1) and 33.2 (8.2) L/h for the reference and test formulations, respectively. The mean (SD) Cmax values of the reference and test formulations were 3.0 (0.6) and 3.1 (0.6) ng/mL, respectively; Tmax was reached at 6.2 and 5.7 hours, respectively. The pharmacokinetic parameters of iNovembef:2006
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Safety Profiles Because of the cardiovascular events associated with amlodipine, changes in BP and H R were observed, but no serious AEs occurred during the study period. A total of 5 treatment-emergent AEs were reported: 2 patients reported headache (1 in the reference group and 1 in the test group), 1 reported headache and facial flushing (reference), and 2 reported fatigue (1 reference and 1 test). No clinically meaningful changes in physical, biochemical, hematologic, or urinalysis variables were observed between the screening visit and the end of the study (Table I). Overall ECG assessments were normal in all subjects at baseline and at the end of the study. ii
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Table I. Results of hematology, biochemistry, and urinalysis testing at baseline and at study end in subjects who received a single dose of amlodipine racemate lO-mg or S-amlodipine 5-rag formulations (N = 18). Baseline, Mean (SD)
End of Study, Mean (SD)
Normal Range
Hematology Red blood cell count, cells x 106/L Hematocrit, % Hemoglobin, g/dL White blood cell count, cells x 103/L Platelet count, cells x 103/laL
5.0 45.6 15.4 6.0 264.4
(0.3) (2.7) (1.0) (1.0) (39.8)
5.0 (0.2) 45.7(1.9) 15.6(0.6) 6.5 (0.8) 286.4 (43.5)
4.4-5.9 39-51 13-17 4-10 150-450
Biochemistry Alanine aminotransferase, U/L Alkaline phosphatase, U/L Aspartate aminotransferase, U/L Bilirubin, total, mg/dL Blood urea nitrogen, mg/dL Calcium, mg/dL Chloride, mmol/L Cholesterol, mg/dL Creatine phosphokinase, IU/L Creatinine, mg/dL Glucose, mg/dL Lactate dehydrogenase, U/L Phosphorus, mg/dL Potassium, mmol/L Sodium, mmol/L Uric acid, mg/dL
15.5 165.6 17.5 0.9 11.9 9.0 104.2 151.9 116.4 1.0 97.3 302.3 3.6 4.5 142.6 6.3
(5.7) (37.4) (3.2) (0.2) (2.4) (0.4) (1.8) (20.4) (45.8) (0.1) (6.9) (38.2) (0.5) (0.3) (1.5) (1.0)
20.3 (14.2) 144.0 (21.7) 20.4 (7.1) 0.6(0.2) 13.0 (1.56) 9.1 (0.2) 102.3 (1.6) 170.0 (20.4) 87.3 (23.9) 1.0(0.1) 92.3 (6.9) 296.9 (42.1) 4.1 (0.5) 4.5 (0.3) 141.9 (1.2) 6.2 (1.1)
5-40 70-290 0-40 0.2-1.2 8-22 8.2-10.8 95-110 120-250 26-200 0.6-1.2 70-120 120-520 2.5-4.7 3.5-5.5 135-145 2.5-8.3
Urinalysis pH Specific gravity, g/mL
6.0 (0.7) 1.022 (0.007)
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tween the 2 amlodipine formulations might be associated with the presence or absence of R-amlodipine; both contain the same amount of S-amlodipine. If the pharmacokinetic characteristics of S-amlodipine had been different in the 2 formulations, the differences might have been attributed to the presence of R-amlodipine. However, as we did not observe any difference between the 2 formulations in terms of the pharmacokinetics of S-amlodipine, we suggest that R-amlodipine does not affect the pharmacokinetics of S-amlodipine in humans. AUC is an accepted indicator of the extent of absorption, whereas Cmax and Tmax are determined by both the rate of absorption and the rate of elimination. 24 Considering that pharmacokinetic parameters for S-amlodipine were similar between the 2 formu-
DISCUSSION The results of the present study suggest that the 2 amlodipine formulations were comparable in terms of their pharmacokinetic and pharmacodynamic characteristics in humans. Cm~X values of S-amlodipine for the 2 formulations were similar (3.0 ng/mL for the reference group vs 3.1 ng/mL for the test group). In addition, Tm~x occurred between 4 and 10 hours for the test formulation, which was similar to the corresponding values for the reference formulations. These findings suggest that both formulations have similar absorption patterns for S-amlodipine. This is consistent with data previously reported by Vincent et a123 in a placebo-controlled, open-label, randomized, 4-way crossover study using single doses of amlodipine 10 mg in healthy men. In fact, any differences observed be-
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Time (h) Figure 1. Mean (SD) plasma 5-amlodipine concentrations after the administration of a single oral dose of amlodipine racemate 10-mg or 5-amlodipine 5-mg formulations in 18 healthy Korean male subjects.
Table II. Pharmacokinetic properties of S-amlodipine in study subjects (N = 18) after the administration of a single dose of amlodipine racemate 10-rag (reference) or S-amlodipine 5-mg (test) formulations. Values are expressed as mean (SD) unless otherwise indicated. Parameter
Reference
AUCo_~, ng" h/mL AUCfa~t, ng" h/mL CL/F, L/h C . . . . ng/mL ke, h -1 tl/2, h Tmax, h
175.3 151.4 30.6 3.0 0.014 53.3 6.2
Test
(45.1) (35.7) (9.1) (0.6) (0.004) (11.3) (1.4)
P*
161.7 139.7 33.2 3.1 0.014
(43.8) (40.3) (8.2) (0.6) (0.004) 55.0 (18.6) 5.7 (1.1)
0.15 0.20 0.11 0.33 0.80 0.70 0.19
AUC0_~ = AUC from time 0 to infinity; A U C l a s t = AUC from time 0 t O the last available measurement; CL/F = oral clearance bioavailability; ke = elimination rate constant. *No significant between-treatment differences were found for S-amlodipine.
lations, we suggest that their rates and extents of absorption are similar. Moreover, when 2 formulations of a single drug are bioequivalent in terms of rate and extent of absorption, it is suggested that they are therapeutically equivalent. 24 Two internationally recognized organizations (the US Food and Drug Administration [FDA] 25 and the European Medicines Agency26) and the Korean FDA 27 have proposed that bioequivalence can be as-
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sumed only when the characteristic parameters of bioavailability including Cmax and AUC show no more than a defined difference between 0.8 and 1.25 for logtransformed data. It is generally accepted that the AUC and Cmax of a test formulation should lie within 20% of those of the corresponding reference formulation, and thus, the 90% Cls of the AUC and Cmax ratios should lie between 0.8 and 1.25 for log-transformed data. 28,29
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Table III. Bioequivalence statistics: Treatment ratios of the log-transformed geometric mean pharmacokinetic parameters of the amIodipine racemate lO-mg or S-amlodipine 5-mg formulations (N = 18). Parameter Cmax AUC 0 ~ AUCl~st
Ratio, %
90% CI
105.0 92.5 91.8
97.56-112.51 86.31-98.74 83.46-100.04
...........................................................................................................................................................................................................................
i
AUC0_~ = AUC from time 0 to infinity; AUClast = AUC from ii time 0 to the last available measurement, i
Based on accepted regulatory requirements, 23-25 the current study suggests that the test formulation was bioequivalent to the reference formulation with respect to S-amlodipine absorption and elimination. The 90% CIs of Cmax, AUClast, and AUC0_~ for the 2 for-
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mulations were all found to be in the stipulated range (0.80-1.25), suggesting the pharmacokinetic equivalence of these 2 drugs. In this study, intrasubject CV of the primary pharmacokinetic parameters (ie, Cmax, AUClast, and AUC0~ ) were all <16%, which was lower than the anticipated 20%. 18,19 This meant that a smaller sample size would have been enough to prove pharmacokinetic bioequivalence and that the power of the study exceeded the anticipated power of 80% based on 18 subjects. In this study, we found that both formulations caused marked hemodynamic changes in BP and HR, despite the fact that only a single dose was administered to the participants. And, although the amount of test formulation administered was only half that of the reference formulation, the test formulation had a comparable pharmacodynamic profile. These results suggest that S-amlodipine, and not R-amlodipine, is the cause of the hemodynamic effects associated with racemic amlodipine, which is consistent with previous
Table IV. Pharmacodynamic properties obtained from study subjects after a single oral dose ofamlodipine racemate
10-mg or S-amlodipine 5-mg formulations (N = 18). Values are presented as mean (SD) unless otherwise indicated. Parameter
Reference
SBP Baseline, mm Hg¢ A AUEC 0 24, mm Hg/h A Mean SBP, mm Hg Amax, mm Hg T Amax, h DBP Baseline, mm Hgt A AUEC0_24, mm Hg/h A Mean DBP, mm Hg Amax, mm Hg T Amax, h HR Baseline, bpmf A AUEC 0 24, bpm/h A Mean HR, bpm A .... bpm T A .... h
Test
P*
120.5 123.2 5.1 15.4 8.3
(5.2) (43.8) (1.8) (4.4)~ (1.8)
121.4 114.8 4.8 14.9 7.5
(5.3) (46.7) (1.9) (3.6)# (1.5)
0.25 0.48 0.48 0.70 0.20
72.0 108.0 4.5 14.1 7.4
(5.6) (39.0) (1.6) (4.7)# (2.4)
72.4 115.7 4.8 13.8 7.4
(5.4) (45.1) (1.9) (4.3)t (1.9)
0.70 0.48 0.48 0.78 1.00
70.9 89.3 3.7 12.5 6.7
(6.9) (51.4) (2.1) (4.6)t (2.4)
70.5 103.5 4.3 13.4 7.1
(5.8) (63.5) (2.6) (4.3)* (1.8)
0.75 0.45 0.45 0.50 0.58
..................................................................................................................................................................................................................
i
SBP = systolic blood pressure; A AUEC 0 24 = change in area under the effect-time curve from 0 to 24 hours; Ama× = maximal change; T Areax = time to Amax; DBP = diastolic blood pressure; HR = heart rate. i *No significant between-treatment differences were found. f Value is the mean of 3 measurements taken before amlodipine administration. $P < 0.001 versus baseline, i ...........................................................................................................................................................................................................................
1844
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Amlodipine racemate 10 mg -0- S-Amlopidine 5 mg
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-5 Time (h) Figure 2. Mean (SD) changes in (A) systolic blood pressure (SBP), (B) diastolic blood pressure (DBP), and (C) heart rate (H R) after the administration of a single oral dose of amlodipine racemate I 0-mg or S-amlodipine S-mg formulations in 18 healthy Korean male subjects. No significant between-treatment differences were found.
findings. 12-14 R-Amlodipine has been associated with a 1000-fold lower calcium channel-blocking effect than S-amlodipine and thus considered an inactive compound. However, studies have suggested that R-amlodipine is linked with the AEs of amlodipine. 14,is As with any clinical trial, the current study had some limitations that should be considered. This was an open-label study, so it might not address objectively the effectiveness and safety profiles of the formulations tested. Because the data we obtained were from healthy male subjects who were administered a single dose, the pharmacokinetic and pharmacodynamic characteristics of amlodipine might differ in target populations. Because of the limited data, we are unable to predict the response of the drug at any time following alternative doses and/or administration interval with the present data set. Further study is needed to determine whether the test formulation has similar or increased efficacy and/or tolerability in the patient groups, considering the comparable pharmacokinetic and pharmacodynamic profiles of 2 formulations. Based on our findings, it is likely that the therapeutic effects are similar in patient groups.
4.
5.
6.
7.
8. 9.
10. 11. 12.
CONCLUSIONS In this small study, a test amlodipine formulation, comprised of only S-amlodipine, was found to be bioequivalent with a reference formulation, amlodipine racemate, in terms of both the rate and extent of absorption, in these Korean healthy volunteers. The treatment ratios (test/reference) of the geometric means and 90% CIs of C...... A U C l a s t , and AUC0~ were all within the predetermined range of 0.8 to 1.25 for pharmacokinetic bioequivalence. Both formulations suggested similar pharmacodynamic characteristics, which included their effects on SBP, DBP, and HR. Both formulations were well tolerated.
13.
14.
1`5. 16.
ACKNOWLEDGMENT
This study was funded by Hanlim Pharmaceutical Company (Seoul, Korea).
17.
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Volume ~8 N u r n ~ i{i i
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19. Abad-Santos F, Novalbos J, GalvezMugica MA, et al. Assessment of sex differences in pharmacokinetics and pharmacodynamics of amlodipine in a bioequivalence study. Pkarmacol Res. 2005;51:445-452. 20. Rogoza AN, Pavlova TS, Sergeeva MV. Validation of A&D UA-767 device for the self-measurement of blood pressure. B l o o d Press M o n i t .
2000;5:227-231. 21. Chow SC, LiuJ-P. Design ol: B i o a v a i l a b i l i t y
and
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i ¸
Food and Drug Administration Web site. Available at: http:llwww.
fda.gov/cder/ob/docs/preface/ ecpreface.htm. Accessed August 12, 2006.
29. Meyer MC. United States Food and Drug Administration requirements for approval of generic drug products.J Clin Psychiatry. 2001 ;62(Suppl 5):4-9, discussion 23-24.
a n d Analysis
Bioequivolence
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[European Medicines Agency (EMEA) Web site]. London, UK: EMEA, 2001. Available at: http://www.emea. eu.int. Accessed April 15, 2006. 27. Food and Drug Administration of Korea (KFDA). Korea FDA guidelines for bioequivalence test. [KFDA Web site]. Seoul, Korea: KFDA; 1996. Available at: http://www. kfda.go.kr. Accessed April 15, 2006. 28. Approved drug products with therapeutic equivalence evaluations. US
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Address correspondence to: Ji-Young Park, M D , PhD, Department of Clinical Pharmacology and Toxicology, A n a m Hospital, Korea University College of Medicine, 126-1, Anam-dong 5-ga, Sungbuk-gu, Seoul 136-705, Korea. E-mail: [email protected]
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