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Comparison of pH and motility of the small intestine of healthy subjects and patients with symptomatic constipation using the wireless motility capsule
Accepted Manuscript Comparison of pH and motility of the small intestine of healthy subjects and patients with symptomatic constipation using the wireless motility capsule A. Aburub, M. Fischer, M. Camilleri, J.R. Semler, H.M. Fadda PII: DOI: Reference:
S0378-5173(18)30248-5 https://doi.org/10.1016/j.ijpharm.2018.04.031 IJP 17438
To appear in:
International Journal of Pharmaceutics
Received Date: Revised Date: Accepted Date:
31 January 2018 6 April 2018 16 April 2018
Please cite this article as: A. Aburub, M. Fischer, M. Camilleri, J.R. Semler, H.M. Fadda, Comparison of pH and motility of the small intestine of healthy subjects and patients with symptomatic constipation using the wireless motility capsule, International Journal of Pharmaceutics (2018), doi: https://doi.org/10.1016/j.ijpharm.2018.04.031
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Comparison of pH and motility of the small intestine of healthy subjects and patients with symptomatic constipation using the wireless motility capsule A. Aburub†, M. Fischer‡, M. Camilleri§, J.R. Semler¶, H.M. Fadda*
†
Small Molecule Design and Development, Lilly Research Labs, Eli Lilly & Company, Indianapolis, IN ‡
Division of Gastroenterology and Hepatology, Indiana University, Indianapolis, IN
§
Clinical Enteric Neuroscience Translational and Epidemiological Research (CENTER), Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, MN ¶
Medtronic, Minneapolis, MN
*
Department of Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Butler University, Indianapolis, IN
*Corresponding author: Hala M. Fadda Department of Pharmaceutical Sciences College of Pharmacy and Health Sciences, Butler University 4600 Sunset Ave, Indianapolis, IN 46208 E-mail: [email protected] Tel. +1-317-940-8574
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ABSTRACT Gastrointestinal luminal pH shows a rise from the duodenum to the terminal ileum in healthy individuals. Our objectives were to compare the pH in the proximal small intestine (SI) (first 60 min of small intestinal transit) lumen of human volunteers and patients with symptomatic constipation; to quantify contractile pressure profiles of the proximal SI, and to assess the relationship between luminally-recorded contractile pressure and small intestinal transit times (SITT) of a non-disintegrating capsule that measures pH and pressure activity (wireless motility capsule). We used previously acquired records from 39 healthy subjects and 41 patients with symptomatic constipation. Mean pH (±SD) of the proximal SI was similar in healthy subjects and patients with constipation at 6.2 (± 0.6) and 6.3 (± 0.4), respectively. In 13 of the healthy subjects, pH did not rise uniformly in the proximal SI though the pHmedian was 6.0 (5th, 95th percentiles 3.09, 7.06) and the pH fluctuated over a mean period of 28 min. Large inter-individual variability in frequency of pressure activity (Ct) and AUC (area under pressure curve) were observed in the proximal SI of healthy subjects and patients with constipation. Median AUC was 3996 mmHg s-1 (5th, 95th percentiles 948, 16866 mmHg s-1) in these two populations combined. Ct and AUC showed a strong direct linear correlation at r = 0.91, p < 1 x 10-6. An inverse correlation (suggesting longer SITT with lower pressure activity) was observed between Ct/AUC and SITT in both healthy subjects and patients with symptomatic constipation. The pooled results for both groups showed: AUC and SITT correlation at r = -0.49, p < 1 x 10-6. We concluded that both the frequency and amplitude of contractions in the proximal SI are important for the propagation of non-disintegrating capsules. The observed pH fluctuations in the proximal SI may impact supersaturation and precipitation of weakly basic drugs.
Keywords: Absorption, bioavailability, enteric, modified release, dissolution, disintegration 2
1. Introduction Small intestinal transit times (SITT) show large inter-individual variability (Fischer and Fadda, 2016) which can have implications on the absorption of poorly soluble drugs and explain the variability in bioavailability observed from some modified release preparations. We have previously shown that video capsule endoscopy provides accurate and reliable measurements of SITT and a good assessment of the time single, non-disintegrating dosage forms spend in the small intestine (SI) (Fischer and Fadda, 2016). It also provides a sensitive tool to investigate SITT in different patient populations (Fischer et al., 2017). The wireless motility capsule (WMC) (SmartPill™, Medtronic, Minneapolis, MN) is of similar dimensions to the video capsule endoscope and can therefore also provide a good reflection of small intestinal transit time of a single, non-disintegrating dosage form. The WMC is 26.8-mm long and 11.7 mm in diameter and has a battery life of a minimum of 5 days (Hasler, 2014). It houses sensors that provide real-time measurements of temperature, pressure and pH of its immediate environment. Location of the WMC in different regions of the gastrointestinal (GI) tract can be determined by the WMC based on luminal pH changes. The WMC has been approved by the US Food and Drug administration for evaluation of suspected gastroparesis and colonic transit in patients with chronic idiopathic constipation. The American and European Neurogastroenterology and Motility societies have also recommended the WMC as a standardized method for assessment of small intestinal transit time, as an aid to detection of small intestinal dysfunction in patients with generalized motility disorders (Rao et al., 2011). Prior studies also showed that small intestinal and colonic transit times of WMC are highly correlated with the transit profile of radiopaque markers of average 5 mm diameter (Camilleri et al., 2010). Small intestinal pH has been extensively investigated and recently reviewed in a meta-analysis by Abuhelwa et al. (2016). The reported meta-mean pH values are 6.1 for the duodenum, rising to 7.1 in 3
the mid SI and reaching 7.4 in the distal SI. However we are interested in determining whether this pH increase from duodenum to distal SI occurs uniformly, and to appraise the magnitude of any pH fluctuations both within and between healthy subjects and patients with symptomatic constipation using the WMC. Such pH levels and fluctuations are of particular importance in the proximal SI as this is the site where the supersaturation and precipitation of weakly basic drugs is observed (Mitra and Fadda, 2014). The majority of drugs on the market are weakly basic and duodenal pH is critical in determining the extent of supersaturation/precipitation and therefore the amount of drug available for absorption. Preliminary studies have shown patients with prolonged SITT to have lower frequency of pressure activity (Ct) and area under pressure curve (AUC) of the proximal SI compared to healthy subjects (Brun et al., 2011). Luminal pressure influences hydrodynamics which is therefore likely to impact dissolution and/or erosion of modified release (MR) dosage forms. Subjecting the hydrophilic matrix of MR tablets to different mechanical stresses was found to alter drug release rates, probably through changes in gel structure and erosion of the tablets (Takieddin and Fassihi, 2015).
Intraluminal pressures and
contractions in the intestinal wall are also likely to influence drug absorption through mixing at the periphery of the lumen and affecting mass transfer gradients. This may impact drug diffusion gradients which are implicated in drug release from matrix and reservoir MR systems. Our objectives were to compare the pH profile including fluctuations of pH in the proximal SI lumen of human volunteers and patients with symptomatic constipation; to quantify contractile pressure profiles of the proximal SI (first 60 min of small intestinal transit), and to assess the relationship between luminally-recorded contractile pressure and SITT of a non-disintegrating capsule that measures pH and pressure activity (WMC). An improved understanding of GI luminal pressure will also improve GI pressure simulations in biorelevant in vitro dissolution testing, and thus enhance in vitro in vivo correlations.
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2. Methods This was a retrospective study and the study population comprised healthy volunteers who underwent a WMC test during the period March 2005 to March 2007 and patients with symptoms of constipation who underwent a WMC test from April 2009 to June 2009. The data was primarily derived from two multi-center studies in the USA and data was supplied by Medtronic (JRS) (Kuo et al., 2008, Camilleri et al., 2010). The respective Institutional Review Boards at the participating sites approved all the studies included and each subject gave informed consent before enrolment.
2.1 Inclusion criteria/exclusion criteria Both sexes between ages 18 – 80 years were eligible. Healthy subjects were screened with the Mayo GI Disease screening questionnaire (Locke et al., 1994). Males and females with no GI disease and an average bowel movement of at least one per 48 h were recruited as healthy volunteers. For patients with symptomatic constipation, inclusion criteria were patients with functional constipation for at least one year; self-reported hard stool at least 25% of the time with at least one of the six symptoms of functional constipation as defined by Rome III criteria (such as self-reported bowel movement frequency of <3 bowel movements/week for at least 3 of the last 6 months) (Rome Foundation).
Additional exclusion criteria for both healthy subjects and patients with symptomatic constipation were prior GI surgery (except for cholecystectomy and/or appendectomy); cardiovascular, endocrine, renal or other chronic disease likely to affect motility, no pregnancy, diverticulitis, tobacco use within 8 h before
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and after capsule ingestion, alcohol use 8 h before capsule ingestion and throughout the monitoring period, and use of prescription or over-the-counter medicines that can influence GI motility including anticholinergics, 5-HT3 antagonists, anti-emetics, narcotic analgesics.
2.2 Study protocol After an overnight fast, subjects reported to the study center. The studies utilized two different protocols with meals of virtually identical calorie and macronutrient contents. Protocol 1: Healthy Subjects ingested the WMC with 50 ml of water followed by a standardized egg meal (Egg Beaters®, Conagra). The meal comprises scrambled egg substitute (egg beater), 2 slices of bread, strawberry jam and water with caloric value of 255 kcal (72% carbohydrate, 24% protein, 2% fat and 2% fiber) (Tougas et al., 2000). Protocol 2: Subjects with symptomatic constipation ingested a 262 kcal nutrient bar (SmartBar, Medtronic), an FDA approved replacement for the egg beater meal, comprising 75% carbohydrate, 21% protein, 3% fat and 3% fiber) with 50 ml water followed by the WMC.
While the testing protocol was previously shown to influence gastric emptying times and pH, it was not found to significantly alter small intestinal transit times or pH (Wang et al., 2015). Subjects were observed for 6 hours after capsule ingestion and at 6 hrs received a nutrient drink (250 cm3 Ensure, Abbott Laboratories, Abbott Park, IL, USA). Water was consumed ad libitum. Subjects then left the study center and were encouraged to resume normal daily activities and food consumption. After ingestion of the WMC, the radiofrequency signals emitted were detected by a receiver (SmartPill™ motility recorder, Medtronic) that was worn continuously for 5 days or until the capsule was expelled by defecation. Subjects then returned to the study center with the data receiver and a diary of food intake, bowel movements, and any GI symptoms.
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2.3 Regional transit times Capsule ingestion (CI) is defined by the rapid rise in temperature from ambient to body temperature (Figure 1). Capsule emptying from the stomach into the duodenum (gastric emptying time, GE) was defined as the point at which the pH abruptly rose by at least 2 pH units from gastric baseline to at least a pH of 4 and did not decrease to a value below 4 for more than 10 min at any later time in the recording. Capsule passage through the ileocecal junction (ICJ) was determined when an abrupt drop in pH by at least 1.0 unit was observed at least 30 min after gastric emptying and maintained for at least 10 min. (Hasler et al., 2009). Small intestinal transit time (SITT) is defined as the time from which the capsule empties from the stomach to its passage through the ICJ. Capsule expulsion (CE) by defecation is defined by drastic drop in temperature.
2.4 Regional pH and contractile pressure The proximal SI was considered as the region where the capsule was located in the first 60 min of WMC transit along the small intestine. The distal SI was considered as the region where the capsule was located during the last 60 min of capsule transit through the small intestine. The number of contractions (Ct) and area under pressure curve (AUC) were quantified for the proximal SI. Pressure peaks exceeding 10 mmHg but less than 300 mmHg were included in the analyses. Median pH was determined for the proximal and distal small intestine in each subject. In subjects in which fluctuations in pH were observed in the duodenum, these were further analyzed by the pH median and interquartile range determined over the period where fluctuating pH was observed (Figure 2a) and raw pH data were plotted as box7
whisker plots for each individual subject. This analysis was performed using GIMS software (Given Imaging). This further pH analysis only included subjects with duodenal pH fluctuations that exceeded the typical variations in pH that were observed throughout the GI tract in order to understand the magnitude or range of pH fluctuations, which could be conceivably encountered and therefore provide bio-relevant data for in vitro simulations in future studies of drug dissolution. Therefore this analysis did not include data from subjects in whom the pH uniformly rose along the SI (Figure 2b).
2.5 Statistical analysis Pearson correlation coefficient was used to evaluate the correlation between Ct/AUC and SITT. Wilcoxon rank sum test was used to compare contractile pressure for healthy subjects and patients with symptomatic constipation and the student t-test was used to compare pH. A significance level of 0.05 was used in all testing. All figures were plotted and statistical analysis conducted using Origin Pro 9.1 software (Origin-Lab Corporation, Northampton, MA).
2.6 Wireless motility capsule WMC pressure readings are in the range of 0-350 mmHg and accurate to ± 5 mmHg for values < 100 mmHg and accurate to ± 10% for pressure > 100 mmHg. Pressure peaks exceeding 10 mmHg but less than 300 mmHg were included in the analyses as these were considered ‘true’ contractions and not extra-enteric artifacts due to body movements (Benson et al., 1993, Gielkens et al., 1998). pH readings by the WMC are in the range of 0.05 - 9.0 with a sensitivity of ± 0.5 units. During the first 24 hrs, pH readings are quantified every 5 s and pressure measurements every 0.5 s. Smartpill employs ion
senstitive field effect transistor (ISFET) pH sensor technology. This is the most sensitive and 8
accurate pH sensor technology available other than pH glass electrodes. The Smartpill Capsule pH specification is rated at ± 0.5 pH units. This pH accuracy was demonstrated in bench testing over the range of pH 1 to pH 9 and on transition from acidic pH to neutral pH and from neutral to acidic conditions. pH accuracy was submitted to the FDA as part of the 510k regulatory submission K053547, for commercial release. A study comparing glass and ISFET pH electrodes for long term ambulatory pH monitoring in man found that they both had comparable in vitro and in vivo performance (Duroux et al. 1991). Both types of electrodes showed a response time of less than 1 second when transferred from acid to neutral or from neutral to acid buffers. The mean sensitivity of the glass electrode was 54.5 mV/pH and that of the ISFET electrode was 57.7 mV/pH. Prior to ingestion, the capsule is calibrated and activated. The signals are transmitted from the GI lumen and captured by receiving antenna incorporated in a portable external data recorder worn by patient during the study. At the end of the study, the data is downloaded, displayed and analyzed using GIMS software (Medtronic).
3. Results 3.1 pH in the proximal small intestine Mean pH (±SD) of the proximal SI is 6.2 (± 0.6) and 6.3 (± 0.4) in healthy subjects and patients with constipation, respectively. pH then gradually rises reaching a mean maximum pH of 7.5 (± 0.6) and 7.49 (± 0.5) in the distal SI of healthy subjects and patients with constipation, respectively. No significant differences in either proximal or distal small intestinal pH were found between healthy subjects and patients with symptomatic constipation.
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In 13 of the 39 healthy subjects, pH did not rise uniformly in the proximal SI though the pHmedian was 6.0 (5th, 95th percentiles 3.09, 7.06) and the pH fluctuated over a mean period of 28 min (Figure 3). The remaining 26 of 39 subjects were not considered to have true pH fluctuations that exceeded the typical variations or ‘noise’ observed throughout the GI tract. In 4 o
f the 41 patients with symptomatic constipation, pH did not rise uniformly in the proximal SI
though the pHmedian was 5.7 (5th, 95th percentiles 3.8, 7.1), duration of pH fluctuation 31 min.
3.2 Contractile pressure in the proximal small intestine Motility (AUC and Ct) of the proximal SI as well as small intestinal transit times (SITT) were not found to be statistically different in healthy subjects to patients with symptomatic constipation. Therefore the pressure activity for these two populations were pooled. Large inter-individual variability in Ct and AUC was observed in the proximal SI of healthy subjects and patients with symptomatic constipation. Median AUC in these two populations was 3996 mmHg s-1 (5th, 95th percentiles 948, 16866 mmHg s-1). Ct and AUC showed a strong direct linear correlation at r = 0.91, p < 1x10-6 (Figure 4). Since there is a strong correlation between Ct and AUC, all further analysis was performed with AUC. An inverse correlation was observed between AUC and SITT at r = - 0.49, p < 1 x 10-6 (Figure 5), that is a moderate correlation suggesting longer SITT with lower pressure activity.
4. Discussion
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Our findings illustrate that in some healthy subjects and patients with symptomatic constipation, pH in the proximal SI is not uniform but it is characterized by large fluctuations. pH fluctuations between pH 7 and 2 during phase II of the migrating motor complex (MMC) have previously been reported by (Itoh and Sekiguchi, 1983). This can be explained by the presence of gastric acid and pancreaticobiliary secretions which go through cyclical variations in phase with the MMC. Gastric acid secretion is slow during phase I and early phase II, starts to increase during late phase II and reaches its maximum during phase III of the MMC which is responsible for the intraduodenal pH fluctuations in phase II. Shortly before the start of phase III, bursts of pancreatic and biliary secretions (Vantrappen et al., 1979, Sjovall, 2011) and an increase in duodenal bicarbonate secretion take place (Jarbur et al., 2003). These explain the alkalinization of the duodenum and its rise to near-neutral pH during duodenal phase III (Woodtli and Owyang, 1995). pH fluctuations are likely be observed and more apparent in recordings of WMCs with extended dwell in the proximal duodenum. These fluctuations in pH are pertinent to the supersaturation and precipitation behavior of weakly basic drugs. Weakly basic drugs display much higher solubility in the acidic gastric environment compared to the near-neutral pH of the duodenum. Upon transition from the stomach to the duodenum, weakly basic poorly soluble drugs exist in the supersaturated state. The supersaturated state is thermodynamically unstable and drug precipitation occurs in the proximal SI; thus, drug precipitation is a function of gastric emptying patterns, luminal fluid composition and intraluminal pH (Mitra and Fadda, 2014). Drug precipitation contributes to reduced bioavailability and the large intra- and inter- individual variability in absorption of some poorly soluble drugs. Elevated gastric pH due to the concomitant administration of proton pump inhibitors or high protein meals can lead to reduced drug dissolution and absorption as has been shown with antifungal drugs such as posaconazole, and oncology drugs such as dasatinib and gefitinib (Walravens et al., 2011, Budha et al., 2012). The pH, buffer composition and buffer capacity of GI luminal fluids are important in determining the solubility of ionizable drugs (Fadda 11
et al., 2010). While the mean pH in the proximal SI of health subjects is 6.2; this pH in the SI is not always uniformly rising, and in some subjects fluctuates for the first 30 min in the proximal SI (5th, 95th percentiles 3.09, 7.06). These periods of lower pH may hinder the precipitation kinetics of weakly basic drugs in the proximal SI, therefore increasing the amount of drug available for absorption. This may be one of the reasons why in vitro models utilized to study drug supersaturation appear to over-predict precipitation of weakly basic drugs (Carlert et al., 2012, Carlert et al., 2010). Kostewicz et al. (2004) showed that simulated intestinal fluid at lower pH reduced the precipitation of weakly basic drugs. pH fluctuations will likely have the greatest impact on absorption of weakly basic drugs with solubility limited absorption from biopharmaceutics classification system (BCS) class II and class IV. However the in vivo significance of this needs to be confirmed with pharmacokinetic studies. It is also plausible that these pH fluctuations not only affect luminal pH, but also the microenvironmental pH in the immediate vicinity of dissolving drug particles. This fluctuating pH will also have ramifications on drug release from enteric coated tablets. While enteric coated products are intended to rapidly disintegrate in the proximal SI and provide a fast onset of action, this is often not the case. Wilding et al. (1992) showed enteric coated naproxen tablets to have a mean disintegration time of 87 min postgastric emptying. While Liu and Basit (2010) found the mean disintegration time of prednisolone tablets coated with Eudragit L 30D- 55 (pH dissolution threshold > 5.5) coated tablets to be 66 ± 22 min post gastric emptying and disintegration site primarily in the mid to distal SI. The pH fluctuations in the proximal SI may partially explain this delayed disintegration of enteric coated products. These spikes and troughs in proximal small intestinal pH need to be simulated in in vitro models investigating drug dissolution as well as drug supersaturation and precipitation. This will provide a better prediction of the in vivo behavior of ionizable drugs and delivery systems. The direct and strong linear correlation of Ct and AUC shows that the greater the frequency of pressure activity, the higher the area under the pressure curve. This also suggests that with more frequent 12
pressure activity, there is a greater abundance of high intensity motility. The inter-individual variations in small intestinal pressure activity may have implications on the disintegration/dissolution of oral modified release (MR) dosage forms. Koziolek et al. (2014) have shown that the application of different pressure waves in bio-relevant dissolution testing alters the drug release profile of bilayer tablets of immediate release and hydrophilic matrix MR tablets. Irregular drug absorption profiles from MR preparations have also been attributed to peristaltic stress giving rise to irregular drug release (Garbacz et al., 2008). Through improved simulation of small intestinal pressure and mechanical stresses utilizing in vitro dissolution tests, improved in vitro in vivo correlation for drug release from MR systems can be attained. Motility measurements in both healthy subjects and patients with asymptomatic constipation demonstrate outliers in pressure that may explain dose dumping of MR tablets. Our results show that both the frequency and intensity of pressure activity in the proximal SI are important for the propagation of non-disintegrating capsules. The greater the pressure activity in the proximal SI the faster the capsule propagation, despite that motility patterns have different propagation velocities and some occur in stationary clusters. The two main types of contractions in the SI are peristaltic and segmenting. Peristaltic contractions propagate aborally over variable distances. Segmenting contractions are stationary, allowing intestinal contents to mix with secretions and brings them into contact with the absorptive mucosal surface (Grundy, 1985); the presence of segmenting contractions may explain the moderate correlation of Ct/AUC with SITT. The single pressure sensor in WMC precludes differentiation of peristaltic vs. segmenting contractions. Human interdigestive motility plays an important role in the transit of small intestinal content. It is characterized by the MMC which is a cyclic motor pattern comprised of three phases. The MMCs can originate in the stomach or SI and the cycle has a median duration of 100 min. MMC Phase I (40 – 60% of the cycle) is characterized by near quiescence phase where no contractions are seen, phase II (20 30% of the cycle) is composed of irregular contractions which are weaker than phase III. Phase II 13
contractions occur in stationary clusters or propagate rapidly over short distances (Thomas et al., 2004). Phase III is
5 – 10 min of intense, rhythmic contractions known as the housekeeper waves
which serve to clear the gut of any debris and bacteria and have also been found to be largely responsible for the gastric emptying of large, non-disintegrating capsules such as the WMC (Cassilly et al., 2008). Phase III consists of propagating, strong contractile activity. The phase III propagation velocity is 7.2 cm/min and the length of the duodenum traversed by a phase III complex is 40-60 cm (Wilmer et al., 1997). While the propagation velocity of phase II complex is 1.6 cm/min and only 11.3% of duodenal phase II contractions are propagating (Wilmer et al., 1997). Rapid propulsion of small intestinal content is also seen on transition from phase II to phase III (Hasler, 2009). This supports our results which illustrate that intensity of motility patterns are important for transit of small intestinal content. It is noteworthy that we do not see an association between small intestinal transit and pressure activity over the entire SI. This may be because the MMCs migrate slowly along the SI. About 50% of the MMCs migrate beyond the mid-jejunum and only 10% make it to the distal ileum. Those that make it this far die out before reaching the ileocecal valve (Sjovall, 2011). High intensity motility patterns also take place during the gastro-enteric response, whereby propagating contractile clusters sweep digesta along the length of the SI thus accelerating the transit of nondisintegrating solid dosage forms that are present in the proximal SI at the time of food ingestion (Fadda et al., 2009). However retrograde pressure waves also take place during the postprandial period (Castedal et al., 1998). During the first 30 min, 30% of the pressure waves in the immediate juxtapyloric area were antegrade, 40% were retrograde and 30% were simultaneous antegrade and retrograde pressure waves. Retrograde contractions also take place in phase III of the housekeeper waves. These retrograde contractions may further explain the moderate association we are observing between pressure activity and small intestinal transit.
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The objective of future work is to characterize intra-subject variability of pH and motility. With more data on these trends, specifically pH fluctuations, multi-analysis algorithms can be developed to better predict drug dissolution of weakly basic drugs and modified release systems.
5. Conclusions Luminal pH does not necessarily rise uniformly in the SI; fluctuations are sometimes observed over a period of 30 min in the proximal SI. Over the course of these pH fluctuations, periods of high and low pH are observed. These pH changes can have implications on the supersaturation and precipitation of weakly basic drugs in the duodenum. Large inter-individual variability in the frequency of pressure activity (Ct) and area under the pressure curve (AUC) is observed in the proximal SI. An inverse correlation exists between AUC and SITT of non-disintegrating oral solid dosage forms, suggesting longer SITT with lower pressure activity. This improved understanding of GI pH and pressure activities can be utilized in in silico and in vitro drug release and absorption models for oral modified release systems.
References Abuhelwa, A. Y., Foster, D. J.,Upton, R. N. 2016. A Quantitative Review and Meta-Models of the Variability and Factors Affecting Oral Drug Absorption-Part I: Gastrointestinal pH. AAPS J, 18, 1309-21. Benson, M. J., Castillo, F. D., Wingate, D. L., Demetrakopoulos, J.,Spyrou, N. M. 1993. The computer as referee in the analysis of human small bowel motility. Am J Physiol, 264, G645-54. Brun, M., Michalek, W., Surjanhata, B.,Kuo, B. 2011. Small bowel transit times (SBTT) by wireless motility capsule (WMC): normal values and analysis of pressure profiles in different subgroups of patients with slow SBTT. Gastroenterology, 140, S-865. Budha, N. R., Frymoyer, A., Smelick, G. S., Jin, J. Y., Yago, M. R., Dresser, M. J., Holden, S. N., Benet, L. Z.,Ware, J. A. 2012. Drug absorption interactions between oral targeted anticancer agents and PPIs: is pH-dependent solubility the Achilles heel of targeted therapy? Clin Pharmacol Ther, 92, 203-13. Camilleri, M., Thorne, N. K., Ringel, Y., Hasler, W. L., Kuo, B., Esfandyari, T., Gupta, A., Scott, S. M., Mccallum, R. W., Parkman, H. P., Soffer, E., Wilding, G. E., Semler, J. R.,Rao, S. S. 2010. Wireless
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pH-motility capsule for colonic transit: prospective comparison with radiopaque markers in chronic constipation. Neurogastroenterol Motil, 22, 874-82, e233. Carlert, S., Akesson, P., Jerndal, G., Lindfors, L., Lennernas, H.,Abrahamsson, B. 2012. In vivo dog intestinal precipitation of mebendazole: a basic BCS class II drug. Mol Pharm, 9, 2903-11. Carlert, S., Palsson, A., Hanisch, G., Von Corswant, C., Nilsson, C., Lindfors, L., Lennernas, H.,Abrahamsson, B. 2010. Predicting intestinal precipitation--a case example for a basic BCS class II drug. Pharm Res, 27, 2119-30. Cassilly, D., Kantor, S., Knight, L. C., Maurer, A. H., Fisher, R. S., Semler, J.,Parkman, H. P. 2008. Gastric emptying of a non-digestible solid: assessment with simultaneous SmartPill pH and pressure capsule, antroduodenal manometry, gastric emptying scintigraphy. Neurogastroenterol Motil, 20, 311-9. Castedal, M., Bjornsson, E.,Abrahamsson, H. 1998. Postprandial peristalsis in the human duodenum. Neurogastroenterol Motil, 10, 227-33. Duroux, P.H. Emde, C., Bauerfein, P., Francis, C., Grisel, A., Thybaud, L., Armstrong, D., Depeursinge, C., Blum. A.L. 1999. The ion sensitive field effect transistor (ISFET) pH e;ectrode: a new sensor for long term ambulatory pH monitoring, Gut, 1991, 32, 240-45 Fadda, H. M., Mcconnell, E. L., Short, M. D.,Basit, A. W. 2009. Meal-induced acceleration of tablet transit through the human small intestine. Pharm Res, 26, 356-60. Fadda, H. M., Sousa, T., Carlsson, A. S., Abrahamsson, B., Williams, J. G., Kumar, D.,Basit, A. W. 2010. Drug solubility in luminal fluids from different regions of the small and large intestine of humans. Mol Pharm, 7, 1527-32. Fischer, M.,Fadda, H. M. 2016. The Effect of Sex and Age on Small Intestinal Transit Times in Humans. J Pharm Sci. Fischer, M., Siva, S., Wo, J. M.,Fadda, H. M. 2017. Assessment of Small Intestinal Transit Times in Ulcerative Colitis and Crohn's Disease Patients with Different Disease Activity Using Video Capsule Endoscopy. AAPS PharmSciTech, 18, 404-409. Garbacz, G., Wedemeyer, R. S., Nagel, S., Giessmann, T., Monnikes, H., Wilson, C. G., Siegmund, W.,Weitschies, W. 2008. Irregular absorption profiles observed from diclofenac extended release tablets can be predicted using a dissolution test apparatus that mimics in vivo physical stresses. Eur J Pharm Biopharm, 70, 421-8. Gielkens, H. A., Nieuwenhuizen, A., Biemond, I., Lamers, C. B.,Masclee, A. A. 1998. Interdigestive antroduodenal motility and gastric acid secretion. Aliment Pharmacol Ther, 12, 27-33. Grundy, D. 1985. The small intestine. Gastrointestinal motility: The integration of physiological mechanisms. Lancaster, England: MTP Press Limited. Hasler, W. L. 2009. Motility of the small intestine and colon. In: YAMADA, T., ALPERS, D. H., KALLOO, A. N., KAPLOWITZ, N., OWYANG, C. & POWELL, D. W. (eds.) Textbook of Gastroenterology. 5th ed.: Wiley-Blackwell. Hasler, W. L. 2014. The use of SmartPill for gastric monitoring. Expert Rev Gastroenterol Hepatol, 8, 587600. Hasler, W. L., Saad, R. J., Rao, S. S., Wilding, G. E., Parkman, H. P., Koch, K. L., Mccallum, R. W., Kuo, B., Sarosiek, I., Sitrin, M. D., Semler, J. R.,Chey, W. D. 2009. Heightened colon motor activity measured by a wireless capsule in patients with constipation: relation to colon transit and IBS. Am J Physiol Gastrointest Liver Physiol, 297, G1107-14. Itoh, Z.,Sekiguchi, T. 1983. Interdigestive motor activity in health and disease. Scand J Gastroenterol Suppl, 82, 121-34. Jarbur, K., Dalenback, J.,Sjovall, H. 2003. Quantitative assessment of motility-associated changes in gastric and duodenal luminal pH in humans. Scand J Gastroenterol, 38, 392-8.
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Kostewicz, E. S., Wunderlich, M., Brauns, U., Becker, R., Bock, T.,Dressman, J. B. 2004. Predicting the precipitation of poorly soluble weak bases upon entry in the small intestine. J Pharm Pharmacol, 56, 43-51. Koziolek, M., Gorke, K., Neumann, M., Garbacz, G.,Weitschies, W. 2014. Development of a bio-relevant dissolution test device simulating mechanical aspects present in the fed stomach. Eur J Pharm Sci, 57, 250-6. Kuo, B., Mccallum, R. W., Koch, K. L., Sitrin, M. D., Wo, J. M., Chey, W. D., Hasler, W. L., Lackner, J. M., Katz, L. A., Semler, J. R., Wilding, G. E.,Parkman, H. P. 2008. Comparison of gastric emptying of a nondigestible capsule to a radio-labelled meal in healthy and gastroparetic subjects. Aliment Pharmacol Ther, 27, 186-96. Liu, F.,Basit, A. W. 2010. A paradigm shift in enteric coating: achieving rapid release in the proximal small intestine of man. J Control Release, 147, 242-5. Locke, G. R., Talley, N. J., Weaver, A. L.,Zinsmeister, A. R. 1994. A new questionnaire for gastroesophageal reflux disease. Mayo Clin Proc, 69, 539-47. Mitra, A.,Fadda, H. M. 2014. Effect of surfactants, gastric emptying, and dosage form on supersaturation of dipyridamole in an in vitro model simulating the stomach and duodenum. Mol Pharm, 11, 2835-44. Rao, S. S., Camilleri, M., Hasler, W. L., Maurer, A. H., Parkman, H. P., Saad, R., Scott, M. S., Simren, M., Soffer, E.,Szarka, L. 2011. Evaluation of gastrointestinal transit in clinical practice: position paper of the American and European Neurogastroenterology and Motility Societies. Neurogastroenterol Motil, 23, 8-23. Rome Foundation. Rome III diagnostic criteria for functional gastrointestinal disorders. Available: www.theromefoundation.org. Sjovall, H. 2011. Meaningful or redundant complexity - mechanisms behind cyclic changes in gastroduodenal pH in the fasting state. Acta Physiol (Oxf), 201, 127-31. Takieddin, M.,Fassihi, R. 2015. A novel approach in distinguishing between role of hydrodynamics and mechanical stresses similar to contraction forces of GI tract on drug release from modified release dosage forms. AAPS PharmSciTech, 16, 278-83. Thomas, E. A., Sjovall, H.,Bornstein, J. C. 2004. Computational model of the migrating motor complex of the small intestine. Am J Physiol Gastrointest Liver Physiol, 286, G564-72. Tougas, G., Eaker, E. Y., Abell, T. L., Abrahamsson, H., Boivin, M., Chen, J., Hocking, M. P., Quigley, E. M., Koch, K. L., Tokayer, A. Z., Stanghellini, V., Chen, Y., Huizinga, J. D., Ryden, J., Bourgeois, I.,Mccallum, R. W. 2000. Assessment of gastric emptying using a low fat meal: establishment of international control values. Am J Gastroenterol, 95, 1456-62. Vantrappen, G. R., Peeters, T. L.,Janssens, J. 1979. The secretory component of the interdigestive migrating motor complex in man. Scand J Gastroenterol, 14, 663-7. Walravens, J., Brouwers, J., Spriet, I., Tack, J., Annaert, P.,Augustijns, P. 2011. Effect of pH and comedication on gastrointestinal absorption of posaconazole: monitoring of intraluminal and plasma drug concentrations. Clin Pharmacokinet, 50, 725-34. Wang, Y. T., Mohammed, S. D., Farmer, A. D., Wang, D., Zarate, N., Hobson, A. R., Hellstrom, P. M., Semler, J. R., Kuo, B., Rao, S. S., Hasler, W. L., Camilleri, M.,Scott, S. M. 2015. Regional gastrointestinal transit and pH studied in 215 healthy volunteers using the wireless motility capsule: influence of age, gender, study country and testing protocol. Aliment Pharmacol Ther, 42, 761-72. Wilding, I. R., Hardy, J. G., Sparrow, R. A., Davis, S. S., Daly, P. B.,English, J. R. 1992. In vivo evaluation of enteric-coated naproxen tablets using gamma scintigraphy. Pharm Res, 9, 1436-41.
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Wilmer, A., Andrioli, A., Coremans, G., Tack, J.,Janssens, J. 1997. Ambulatory small intestinal manometry. Detailed comparison of duodenal and jejunal motor activity in healthy man. Dig Dis Sci, 42, 1618-27. Woodtli, W.,Owyang, C. 1995. Duodenal pH governs interdigestive motility in humans. Am J Physiol, 268, G146-52.
Figure captions Figure 1.
pH, pressure
and temperature
readings
from
the wireless motility
capsule.
GRT: gastric residence time; SITT: small intestinal transit times; CTT: colon transit time; CI: capsule ingestion; GE: gastric emptying; ICJ: ileocecal junction; CE: capsule expulsion. Figure 2a. pH fluctuations in the duodenum. GE: gastric emptying; SITT: small intestinal transit time; ICJ: ileocecal junction Figure 2b. Uniform pH rise along the small intestine GE: gastric emptying; SITT: small intestinal transit time; ICJ: ileocecal junction Figure 3. Box and Whisker plots of pH in the proximal small intestine of each individual subject (sub) experiencing pH fluctuations in this region (n=13). Medians are shown as the line within the box, the box boundaries are the 25th and 75th percentiles. 5th and 95% percentiles are depicted by the whiskers. Figure 4. Correlation of AUC and Ct in healthy subjects and patients with symptomatic constipation (n= 80) at r = 0.91, p < 1x10-6. Figure 5. Inverse correlation of area under pressure curve (AUC) in the proximal small intestine to small intestinal transit times (SITT) in healthy subjects and patients with symptomatic constipation (n=80) at r = -0.49, p < 1 x 10-6. Graph represents a 2-parameter hyperbolic decay: y = ab/(b + x).
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GRT
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ICJ
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pH
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Temperature (˚C)
ICI
CE
pH
Pressure (mmHg)
CTT
SITT
SITT Duration of pH fluctuation
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Min pH
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S0378-5173(18)30248-5 https://doi.org/10.1016/j.ijpharm.2018.04.031 IJP 17438
To appear in:
International Journal of Pharmaceutics
Received Date: Revised Date: Accepted Date:
31 January 2018 6 April 2018 16 April 2018
Please cite this article as: A. Aburub, M. Fischer, M. Camilleri, J.R. Semler, H.M. Fadda, Comparison of pH and motility of the small intestine of healthy subjects and patients with symptomatic constipation using the wireless motility capsule, International Journal of Pharmaceutics (2018), doi: https://doi.org/10.1016/j.ijpharm.2018.04.031
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Comparison of pH and motility of the small intestine of healthy subjects and patients with symptomatic constipation using the wireless motility capsule A. Aburub†, M. Fischer‡, M. Camilleri§, J.R. Semler¶, H.M. Fadda*
†
Small Molecule Design and Development, Lilly Research Labs, Eli Lilly & Company, Indianapolis, IN ‡
Division of Gastroenterology and Hepatology, Indiana University, Indianapolis, IN
§
Clinical Enteric Neuroscience Translational and Epidemiological Research (CENTER), Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, MN ¶
Medtronic, Minneapolis, MN
*
Department of Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Butler University, Indianapolis, IN
*Corresponding author: Hala M. Fadda Department of Pharmaceutical Sciences College of Pharmacy and Health Sciences, Butler University 4600 Sunset Ave, Indianapolis, IN 46208 E-mail: [email protected] Tel. +1-317-940-8574
1
ABSTRACT Gastrointestinal luminal pH shows a rise from the duodenum to the terminal ileum in healthy individuals. Our objectives were to compare the pH in the proximal small intestine (SI) (first 60 min of small intestinal transit) lumen of human volunteers and patients with symptomatic constipation; to quantify contractile pressure profiles of the proximal SI, and to assess the relationship between luminally-recorded contractile pressure and small intestinal transit times (SITT) of a non-disintegrating capsule that measures pH and pressure activity (wireless motility capsule). We used previously acquired records from 39 healthy subjects and 41 patients with symptomatic constipation. Mean pH (±SD) of the proximal SI was similar in healthy subjects and patients with constipation at 6.2 (± 0.6) and 6.3 (± 0.4), respectively. In 13 of the healthy subjects, pH did not rise uniformly in the proximal SI though the pHmedian was 6.0 (5th, 95th percentiles 3.09, 7.06) and the pH fluctuated over a mean period of 28 min. Large inter-individual variability in frequency of pressure activity (Ct) and AUC (area under pressure curve) were observed in the proximal SI of healthy subjects and patients with constipation. Median AUC was 3996 mmHg s-1 (5th, 95th percentiles 948, 16866 mmHg s-1) in these two populations combined. Ct and AUC showed a strong direct linear correlation at r = 0.91, p < 1 x 10-6. An inverse correlation (suggesting longer SITT with lower pressure activity) was observed between Ct/AUC and SITT in both healthy subjects and patients with symptomatic constipation. The pooled results for both groups showed: AUC and SITT correlation at r = -0.49, p < 1 x 10-6. We concluded that both the frequency and amplitude of contractions in the proximal SI are important for the propagation of non-disintegrating capsules. The observed pH fluctuations in the proximal SI may impact supersaturation and precipitation of weakly basic drugs.
Keywords: Absorption, bioavailability, enteric, modified release, dissolution, disintegration 2
1. Introduction Small intestinal transit times (SITT) show large inter-individual variability (Fischer and Fadda, 2016) which can have implications on the absorption of poorly soluble drugs and explain the variability in bioavailability observed from some modified release preparations. We have previously shown that video capsule endoscopy provides accurate and reliable measurements of SITT and a good assessment of the time single, non-disintegrating dosage forms spend in the small intestine (SI) (Fischer and Fadda, 2016). It also provides a sensitive tool to investigate SITT in different patient populations (Fischer et al., 2017). The wireless motility capsule (WMC) (SmartPill™, Medtronic, Minneapolis, MN) is of similar dimensions to the video capsule endoscope and can therefore also provide a good reflection of small intestinal transit time of a single, non-disintegrating dosage form. The WMC is 26.8-mm long and 11.7 mm in diameter and has a battery life of a minimum of 5 days (Hasler, 2014). It houses sensors that provide real-time measurements of temperature, pressure and pH of its immediate environment. Location of the WMC in different regions of the gastrointestinal (GI) tract can be determined by the WMC based on luminal pH changes. The WMC has been approved by the US Food and Drug administration for evaluation of suspected gastroparesis and colonic transit in patients with chronic idiopathic constipation. The American and European Neurogastroenterology and Motility societies have also recommended the WMC as a standardized method for assessment of small intestinal transit time, as an aid to detection of small intestinal dysfunction in patients with generalized motility disorders (Rao et al., 2011). Prior studies also showed that small intestinal and colonic transit times of WMC are highly correlated with the transit profile of radiopaque markers of average 5 mm diameter (Camilleri et al., 2010). Small intestinal pH has been extensively investigated and recently reviewed in a meta-analysis by Abuhelwa et al. (2016). The reported meta-mean pH values are 6.1 for the duodenum, rising to 7.1 in 3
the mid SI and reaching 7.4 in the distal SI. However we are interested in determining whether this pH increase from duodenum to distal SI occurs uniformly, and to appraise the magnitude of any pH fluctuations both within and between healthy subjects and patients with symptomatic constipation using the WMC. Such pH levels and fluctuations are of particular importance in the proximal SI as this is the site where the supersaturation and precipitation of weakly basic drugs is observed (Mitra and Fadda, 2014). The majority of drugs on the market are weakly basic and duodenal pH is critical in determining the extent of supersaturation/precipitation and therefore the amount of drug available for absorption. Preliminary studies have shown patients with prolonged SITT to have lower frequency of pressure activity (Ct) and area under pressure curve (AUC) of the proximal SI compared to healthy subjects (Brun et al., 2011). Luminal pressure influences hydrodynamics which is therefore likely to impact dissolution and/or erosion of modified release (MR) dosage forms. Subjecting the hydrophilic matrix of MR tablets to different mechanical stresses was found to alter drug release rates, probably through changes in gel structure and erosion of the tablets (Takieddin and Fassihi, 2015).
Intraluminal pressures and
contractions in the intestinal wall are also likely to influence drug absorption through mixing at the periphery of the lumen and affecting mass transfer gradients. This may impact drug diffusion gradients which are implicated in drug release from matrix and reservoir MR systems. Our objectives were to compare the pH profile including fluctuations of pH in the proximal SI lumen of human volunteers and patients with symptomatic constipation; to quantify contractile pressure profiles of the proximal SI (first 60 min of small intestinal transit), and to assess the relationship between luminally-recorded contractile pressure and SITT of a non-disintegrating capsule that measures pH and pressure activity (WMC). An improved understanding of GI luminal pressure will also improve GI pressure simulations in biorelevant in vitro dissolution testing, and thus enhance in vitro in vivo correlations.
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2. Methods This was a retrospective study and the study population comprised healthy volunteers who underwent a WMC test during the period March 2005 to March 2007 and patients with symptoms of constipation who underwent a WMC test from April 2009 to June 2009. The data was primarily derived from two multi-center studies in the USA and data was supplied by Medtronic (JRS) (Kuo et al., 2008, Camilleri et al., 2010). The respective Institutional Review Boards at the participating sites approved all the studies included and each subject gave informed consent before enrolment.
2.1 Inclusion criteria/exclusion criteria Both sexes between ages 18 – 80 years were eligible. Healthy subjects were screened with the Mayo GI Disease screening questionnaire (Locke et al., 1994). Males and females with no GI disease and an average bowel movement of at least one per 48 h were recruited as healthy volunteers. For patients with symptomatic constipation, inclusion criteria were patients with functional constipation for at least one year; self-reported hard stool at least 25% of the time with at least one of the six symptoms of functional constipation as defined by Rome III criteria (such as self-reported bowel movement frequency of <3 bowel movements/week for at least 3 of the last 6 months) (Rome Foundation).
Additional exclusion criteria for both healthy subjects and patients with symptomatic constipation were prior GI surgery (except for cholecystectomy and/or appendectomy); cardiovascular, endocrine, renal or other chronic disease likely to affect motility, no pregnancy, diverticulitis, tobacco use within 8 h before
5
and after capsule ingestion, alcohol use 8 h before capsule ingestion and throughout the monitoring period, and use of prescription or over-the-counter medicines that can influence GI motility including anticholinergics, 5-HT3 antagonists, anti-emetics, narcotic analgesics.
2.2 Study protocol After an overnight fast, subjects reported to the study center. The studies utilized two different protocols with meals of virtually identical calorie and macronutrient contents. Protocol 1: Healthy Subjects ingested the WMC with 50 ml of water followed by a standardized egg meal (Egg Beaters®, Conagra). The meal comprises scrambled egg substitute (egg beater), 2 slices of bread, strawberry jam and water with caloric value of 255 kcal (72% carbohydrate, 24% protein, 2% fat and 2% fiber) (Tougas et al., 2000). Protocol 2: Subjects with symptomatic constipation ingested a 262 kcal nutrient bar (SmartBar, Medtronic), an FDA approved replacement for the egg beater meal, comprising 75% carbohydrate, 21% protein, 3% fat and 3% fiber) with 50 ml water followed by the WMC.
While the testing protocol was previously shown to influence gastric emptying times and pH, it was not found to significantly alter small intestinal transit times or pH (Wang et al., 2015). Subjects were observed for 6 hours after capsule ingestion and at 6 hrs received a nutrient drink (250 cm3 Ensure, Abbott Laboratories, Abbott Park, IL, USA). Water was consumed ad libitum. Subjects then left the study center and were encouraged to resume normal daily activities and food consumption. After ingestion of the WMC, the radiofrequency signals emitted were detected by a receiver (SmartPill™ motility recorder, Medtronic) that was worn continuously for 5 days or until the capsule was expelled by defecation. Subjects then returned to the study center with the data receiver and a diary of food intake, bowel movements, and any GI symptoms.
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2.3 Regional transit times Capsule ingestion (CI) is defined by the rapid rise in temperature from ambient to body temperature (Figure 1). Capsule emptying from the stomach into the duodenum (gastric emptying time, GE) was defined as the point at which the pH abruptly rose by at least 2 pH units from gastric baseline to at least a pH of 4 and did not decrease to a value below 4 for more than 10 min at any later time in the recording. Capsule passage through the ileocecal junction (ICJ) was determined when an abrupt drop in pH by at least 1.0 unit was observed at least 30 min after gastric emptying and maintained for at least 10 min. (Hasler et al., 2009). Small intestinal transit time (SITT) is defined as the time from which the capsule empties from the stomach to its passage through the ICJ. Capsule expulsion (CE) by defecation is defined by drastic drop in temperature.
2.4 Regional pH and contractile pressure The proximal SI was considered as the region where the capsule was located in the first 60 min of WMC transit along the small intestine. The distal SI was considered as the region where the capsule was located during the last 60 min of capsule transit through the small intestine. The number of contractions (Ct) and area under pressure curve (AUC) were quantified for the proximal SI. Pressure peaks exceeding 10 mmHg but less than 300 mmHg were included in the analyses. Median pH was determined for the proximal and distal small intestine in each subject. In subjects in which fluctuations in pH were observed in the duodenum, these were further analyzed by the pH median and interquartile range determined over the period where fluctuating pH was observed (Figure 2a) and raw pH data were plotted as box7
whisker plots for each individual subject. This analysis was performed using GIMS software (Given Imaging). This further pH analysis only included subjects with duodenal pH fluctuations that exceeded the typical variations in pH that were observed throughout the GI tract in order to understand the magnitude or range of pH fluctuations, which could be conceivably encountered and therefore provide bio-relevant data for in vitro simulations in future studies of drug dissolution. Therefore this analysis did not include data from subjects in whom the pH uniformly rose along the SI (Figure 2b).
2.5 Statistical analysis Pearson correlation coefficient was used to evaluate the correlation between Ct/AUC and SITT. Wilcoxon rank sum test was used to compare contractile pressure for healthy subjects and patients with symptomatic constipation and the student t-test was used to compare pH. A significance level of 0.05 was used in all testing. All figures were plotted and statistical analysis conducted using Origin Pro 9.1 software (Origin-Lab Corporation, Northampton, MA).
2.6 Wireless motility capsule WMC pressure readings are in the range of 0-350 mmHg and accurate to ± 5 mmHg for values < 100 mmHg and accurate to ± 10% for pressure > 100 mmHg. Pressure peaks exceeding 10 mmHg but less than 300 mmHg were included in the analyses as these were considered ‘true’ contractions and not extra-enteric artifacts due to body movements (Benson et al., 1993, Gielkens et al., 1998). pH readings by the WMC are in the range of 0.05 - 9.0 with a sensitivity of ± 0.5 units. During the first 24 hrs, pH readings are quantified every 5 s and pressure measurements every 0.5 s. Smartpill employs ion
senstitive field effect transistor (ISFET) pH sensor technology. This is the most sensitive and 8
accurate pH sensor technology available other than pH glass electrodes. The Smartpill Capsule pH specification is rated at ± 0.5 pH units. This pH accuracy was demonstrated in bench testing over the range of pH 1 to pH 9 and on transition from acidic pH to neutral pH and from neutral to acidic conditions. pH accuracy was submitted to the FDA as part of the 510k regulatory submission K053547, for commercial release. A study comparing glass and ISFET pH electrodes for long term ambulatory pH monitoring in man found that they both had comparable in vitro and in vivo performance (Duroux et al. 1991). Both types of electrodes showed a response time of less than 1 second when transferred from acid to neutral or from neutral to acid buffers. The mean sensitivity of the glass electrode was 54.5 mV/pH and that of the ISFET electrode was 57.7 mV/pH. Prior to ingestion, the capsule is calibrated and activated. The signals are transmitted from the GI lumen and captured by receiving antenna incorporated in a portable external data recorder worn by patient during the study. At the end of the study, the data is downloaded, displayed and analyzed using GIMS software (Medtronic).
3. Results 3.1 pH in the proximal small intestine Mean pH (±SD) of the proximal SI is 6.2 (± 0.6) and 6.3 (± 0.4) in healthy subjects and patients with constipation, respectively. pH then gradually rises reaching a mean maximum pH of 7.5 (± 0.6) and 7.49 (± 0.5) in the distal SI of healthy subjects and patients with constipation, respectively. No significant differences in either proximal or distal small intestinal pH were found between healthy subjects and patients with symptomatic constipation.
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In 13 of the 39 healthy subjects, pH did not rise uniformly in the proximal SI though the pHmedian was 6.0 (5th, 95th percentiles 3.09, 7.06) and the pH fluctuated over a mean period of 28 min (Figure 3). The remaining 26 of 39 subjects were not considered to have true pH fluctuations that exceeded the typical variations or ‘noise’ observed throughout the GI tract. In 4 o
f the 41 patients with symptomatic constipation, pH did not rise uniformly in the proximal SI
though the pHmedian was 5.7 (5th, 95th percentiles 3.8, 7.1), duration of pH fluctuation 31 min.
3.2 Contractile pressure in the proximal small intestine Motility (AUC and Ct) of the proximal SI as well as small intestinal transit times (SITT) were not found to be statistically different in healthy subjects to patients with symptomatic constipation. Therefore the pressure activity for these two populations were pooled. Large inter-individual variability in Ct and AUC was observed in the proximal SI of healthy subjects and patients with symptomatic constipation. Median AUC in these two populations was 3996 mmHg s-1 (5th, 95th percentiles 948, 16866 mmHg s-1). Ct and AUC showed a strong direct linear correlation at r = 0.91, p < 1x10-6 (Figure 4). Since there is a strong correlation between Ct and AUC, all further analysis was performed with AUC. An inverse correlation was observed between AUC and SITT at r = - 0.49, p < 1 x 10-6 (Figure 5), that is a moderate correlation suggesting longer SITT with lower pressure activity.
4. Discussion
10
Our findings illustrate that in some healthy subjects and patients with symptomatic constipation, pH in the proximal SI is not uniform but it is characterized by large fluctuations. pH fluctuations between pH 7 and 2 during phase II of the migrating motor complex (MMC) have previously been reported by (Itoh and Sekiguchi, 1983). This can be explained by the presence of gastric acid and pancreaticobiliary secretions which go through cyclical variations in phase with the MMC. Gastric acid secretion is slow during phase I and early phase II, starts to increase during late phase II and reaches its maximum during phase III of the MMC which is responsible for the intraduodenal pH fluctuations in phase II. Shortly before the start of phase III, bursts of pancreatic and biliary secretions (Vantrappen et al., 1979, Sjovall, 2011) and an increase in duodenal bicarbonate secretion take place (Jarbur et al., 2003). These explain the alkalinization of the duodenum and its rise to near-neutral pH during duodenal phase III (Woodtli and Owyang, 1995). pH fluctuations are likely be observed and more apparent in recordings of WMCs with extended dwell in the proximal duodenum. These fluctuations in pH are pertinent to the supersaturation and precipitation behavior of weakly basic drugs. Weakly basic drugs display much higher solubility in the acidic gastric environment compared to the near-neutral pH of the duodenum. Upon transition from the stomach to the duodenum, weakly basic poorly soluble drugs exist in the supersaturated state. The supersaturated state is thermodynamically unstable and drug precipitation occurs in the proximal SI; thus, drug precipitation is a function of gastric emptying patterns, luminal fluid composition and intraluminal pH (Mitra and Fadda, 2014). Drug precipitation contributes to reduced bioavailability and the large intra- and inter- individual variability in absorption of some poorly soluble drugs. Elevated gastric pH due to the concomitant administration of proton pump inhibitors or high protein meals can lead to reduced drug dissolution and absorption as has been shown with antifungal drugs such as posaconazole, and oncology drugs such as dasatinib and gefitinib (Walravens et al., 2011, Budha et al., 2012). The pH, buffer composition and buffer capacity of GI luminal fluids are important in determining the solubility of ionizable drugs (Fadda 11
et al., 2010). While the mean pH in the proximal SI of health subjects is 6.2; this pH in the SI is not always uniformly rising, and in some subjects fluctuates for the first 30 min in the proximal SI (5th, 95th percentiles 3.09, 7.06). These periods of lower pH may hinder the precipitation kinetics of weakly basic drugs in the proximal SI, therefore increasing the amount of drug available for absorption. This may be one of the reasons why in vitro models utilized to study drug supersaturation appear to over-predict precipitation of weakly basic drugs (Carlert et al., 2012, Carlert et al., 2010). Kostewicz et al. (2004) showed that simulated intestinal fluid at lower pH reduced the precipitation of weakly basic drugs. pH fluctuations will likely have the greatest impact on absorption of weakly basic drugs with solubility limited absorption from biopharmaceutics classification system (BCS) class II and class IV. However the in vivo significance of this needs to be confirmed with pharmacokinetic studies. It is also plausible that these pH fluctuations not only affect luminal pH, but also the microenvironmental pH in the immediate vicinity of dissolving drug particles. This fluctuating pH will also have ramifications on drug release from enteric coated tablets. While enteric coated products are intended to rapidly disintegrate in the proximal SI and provide a fast onset of action, this is often not the case. Wilding et al. (1992) showed enteric coated naproxen tablets to have a mean disintegration time of 87 min postgastric emptying. While Liu and Basit (2010) found the mean disintegration time of prednisolone tablets coated with Eudragit L 30D- 55 (pH dissolution threshold > 5.5) coated tablets to be 66 ± 22 min post gastric emptying and disintegration site primarily in the mid to distal SI. The pH fluctuations in the proximal SI may partially explain this delayed disintegration of enteric coated products. These spikes and troughs in proximal small intestinal pH need to be simulated in in vitro models investigating drug dissolution as well as drug supersaturation and precipitation. This will provide a better prediction of the in vivo behavior of ionizable drugs and delivery systems. The direct and strong linear correlation of Ct and AUC shows that the greater the frequency of pressure activity, the higher the area under the pressure curve. This also suggests that with more frequent 12
pressure activity, there is a greater abundance of high intensity motility. The inter-individual variations in small intestinal pressure activity may have implications on the disintegration/dissolution of oral modified release (MR) dosage forms. Koziolek et al. (2014) have shown that the application of different pressure waves in bio-relevant dissolution testing alters the drug release profile of bilayer tablets of immediate release and hydrophilic matrix MR tablets. Irregular drug absorption profiles from MR preparations have also been attributed to peristaltic stress giving rise to irregular drug release (Garbacz et al., 2008). Through improved simulation of small intestinal pressure and mechanical stresses utilizing in vitro dissolution tests, improved in vitro in vivo correlation for drug release from MR systems can be attained. Motility measurements in both healthy subjects and patients with asymptomatic constipation demonstrate outliers in pressure that may explain dose dumping of MR tablets. Our results show that both the frequency and intensity of pressure activity in the proximal SI are important for the propagation of non-disintegrating capsules. The greater the pressure activity in the proximal SI the faster the capsule propagation, despite that motility patterns have different propagation velocities and some occur in stationary clusters. The two main types of contractions in the SI are peristaltic and segmenting. Peristaltic contractions propagate aborally over variable distances. Segmenting contractions are stationary, allowing intestinal contents to mix with secretions and brings them into contact with the absorptive mucosal surface (Grundy, 1985); the presence of segmenting contractions may explain the moderate correlation of Ct/AUC with SITT. The single pressure sensor in WMC precludes differentiation of peristaltic vs. segmenting contractions. Human interdigestive motility plays an important role in the transit of small intestinal content. It is characterized by the MMC which is a cyclic motor pattern comprised of three phases. The MMCs can originate in the stomach or SI and the cycle has a median duration of 100 min. MMC Phase I (40 – 60% of the cycle) is characterized by near quiescence phase where no contractions are seen, phase II (20 30% of the cycle) is composed of irregular contractions which are weaker than phase III. Phase II 13
contractions occur in stationary clusters or propagate rapidly over short distances (Thomas et al., 2004). Phase III is
5 – 10 min of intense, rhythmic contractions known as the housekeeper waves
which serve to clear the gut of any debris and bacteria and have also been found to be largely responsible for the gastric emptying of large, non-disintegrating capsules such as the WMC (Cassilly et al., 2008). Phase III consists of propagating, strong contractile activity. The phase III propagation velocity is 7.2 cm/min and the length of the duodenum traversed by a phase III complex is 40-60 cm (Wilmer et al., 1997). While the propagation velocity of phase II complex is 1.6 cm/min and only 11.3% of duodenal phase II contractions are propagating (Wilmer et al., 1997). Rapid propulsion of small intestinal content is also seen on transition from phase II to phase III (Hasler, 2009). This supports our results which illustrate that intensity of motility patterns are important for transit of small intestinal content. It is noteworthy that we do not see an association between small intestinal transit and pressure activity over the entire SI. This may be because the MMCs migrate slowly along the SI. About 50% of the MMCs migrate beyond the mid-jejunum and only 10% make it to the distal ileum. Those that make it this far die out before reaching the ileocecal valve (Sjovall, 2011). High intensity motility patterns also take place during the gastro-enteric response, whereby propagating contractile clusters sweep digesta along the length of the SI thus accelerating the transit of nondisintegrating solid dosage forms that are present in the proximal SI at the time of food ingestion (Fadda et al., 2009). However retrograde pressure waves also take place during the postprandial period (Castedal et al., 1998). During the first 30 min, 30% of the pressure waves in the immediate juxtapyloric area were antegrade, 40% were retrograde and 30% were simultaneous antegrade and retrograde pressure waves. Retrograde contractions also take place in phase III of the housekeeper waves. These retrograde contractions may further explain the moderate association we are observing between pressure activity and small intestinal transit.
14
The objective of future work is to characterize intra-subject variability of pH and motility. With more data on these trends, specifically pH fluctuations, multi-analysis algorithms can be developed to better predict drug dissolution of weakly basic drugs and modified release systems.
5. Conclusions Luminal pH does not necessarily rise uniformly in the SI; fluctuations are sometimes observed over a period of 30 min in the proximal SI. Over the course of these pH fluctuations, periods of high and low pH are observed. These pH changes can have implications on the supersaturation and precipitation of weakly basic drugs in the duodenum. Large inter-individual variability in the frequency of pressure activity (Ct) and area under the pressure curve (AUC) is observed in the proximal SI. An inverse correlation exists between AUC and SITT of non-disintegrating oral solid dosage forms, suggesting longer SITT with lower pressure activity. This improved understanding of GI pH and pressure activities can be utilized in in silico and in vitro drug release and absorption models for oral modified release systems.
References Abuhelwa, A. Y., Foster, D. J.,Upton, R. N. 2016. A Quantitative Review and Meta-Models of the Variability and Factors Affecting Oral Drug Absorption-Part I: Gastrointestinal pH. AAPS J, 18, 1309-21. Benson, M. J., Castillo, F. D., Wingate, D. L., Demetrakopoulos, J.,Spyrou, N. M. 1993. The computer as referee in the analysis of human small bowel motility. Am J Physiol, 264, G645-54. Brun, M., Michalek, W., Surjanhata, B.,Kuo, B. 2011. Small bowel transit times (SBTT) by wireless motility capsule (WMC): normal values and analysis of pressure profiles in different subgroups of patients with slow SBTT. Gastroenterology, 140, S-865. Budha, N. R., Frymoyer, A., Smelick, G. S., Jin, J. Y., Yago, M. R., Dresser, M. J., Holden, S. N., Benet, L. Z.,Ware, J. A. 2012. Drug absorption interactions between oral targeted anticancer agents and PPIs: is pH-dependent solubility the Achilles heel of targeted therapy? Clin Pharmacol Ther, 92, 203-13. Camilleri, M., Thorne, N. K., Ringel, Y., Hasler, W. L., Kuo, B., Esfandyari, T., Gupta, A., Scott, S. M., Mccallum, R. W., Parkman, H. P., Soffer, E., Wilding, G. E., Semler, J. R.,Rao, S. S. 2010. Wireless
15
pH-motility capsule for colonic transit: prospective comparison with radiopaque markers in chronic constipation. Neurogastroenterol Motil, 22, 874-82, e233. Carlert, S., Akesson, P., Jerndal, G., Lindfors, L., Lennernas, H.,Abrahamsson, B. 2012. In vivo dog intestinal precipitation of mebendazole: a basic BCS class II drug. Mol Pharm, 9, 2903-11. Carlert, S., Palsson, A., Hanisch, G., Von Corswant, C., Nilsson, C., Lindfors, L., Lennernas, H.,Abrahamsson, B. 2010. Predicting intestinal precipitation--a case example for a basic BCS class II drug. Pharm Res, 27, 2119-30. Cassilly, D., Kantor, S., Knight, L. C., Maurer, A. H., Fisher, R. S., Semler, J.,Parkman, H. P. 2008. Gastric emptying of a non-digestible solid: assessment with simultaneous SmartPill pH and pressure capsule, antroduodenal manometry, gastric emptying scintigraphy. Neurogastroenterol Motil, 20, 311-9. Castedal, M., Bjornsson, E.,Abrahamsson, H. 1998. Postprandial peristalsis in the human duodenum. Neurogastroenterol Motil, 10, 227-33. Duroux, P.H. Emde, C., Bauerfein, P., Francis, C., Grisel, A., Thybaud, L., Armstrong, D., Depeursinge, C., Blum. A.L. 1999. The ion sensitive field effect transistor (ISFET) pH e;ectrode: a new sensor for long term ambulatory pH monitoring, Gut, 1991, 32, 240-45 Fadda, H. M., Mcconnell, E. L., Short, M. D.,Basit, A. W. 2009. Meal-induced acceleration of tablet transit through the human small intestine. Pharm Res, 26, 356-60. Fadda, H. M., Sousa, T., Carlsson, A. S., Abrahamsson, B., Williams, J. G., Kumar, D.,Basit, A. W. 2010. Drug solubility in luminal fluids from different regions of the small and large intestine of humans. Mol Pharm, 7, 1527-32. Fischer, M.,Fadda, H. M. 2016. The Effect of Sex and Age on Small Intestinal Transit Times in Humans. J Pharm Sci. Fischer, M., Siva, S., Wo, J. M.,Fadda, H. M. 2017. Assessment of Small Intestinal Transit Times in Ulcerative Colitis and Crohn's Disease Patients with Different Disease Activity Using Video Capsule Endoscopy. AAPS PharmSciTech, 18, 404-409. Garbacz, G., Wedemeyer, R. S., Nagel, S., Giessmann, T., Monnikes, H., Wilson, C. G., Siegmund, W.,Weitschies, W. 2008. Irregular absorption profiles observed from diclofenac extended release tablets can be predicted using a dissolution test apparatus that mimics in vivo physical stresses. Eur J Pharm Biopharm, 70, 421-8. Gielkens, H. A., Nieuwenhuizen, A., Biemond, I., Lamers, C. B.,Masclee, A. A. 1998. Interdigestive antroduodenal motility and gastric acid secretion. Aliment Pharmacol Ther, 12, 27-33. Grundy, D. 1985. The small intestine. Gastrointestinal motility: The integration of physiological mechanisms. Lancaster, England: MTP Press Limited. Hasler, W. L. 2009. Motility of the small intestine and colon. In: YAMADA, T., ALPERS, D. H., KALLOO, A. N., KAPLOWITZ, N., OWYANG, C. & POWELL, D. W. (eds.) Textbook of Gastroenterology. 5th ed.: Wiley-Blackwell. Hasler, W. L. 2014. The use of SmartPill for gastric monitoring. Expert Rev Gastroenterol Hepatol, 8, 587600. Hasler, W. L., Saad, R. J., Rao, S. S., Wilding, G. E., Parkman, H. P., Koch, K. L., Mccallum, R. W., Kuo, B., Sarosiek, I., Sitrin, M. D., Semler, J. R.,Chey, W. D. 2009. Heightened colon motor activity measured by a wireless capsule in patients with constipation: relation to colon transit and IBS. Am J Physiol Gastrointest Liver Physiol, 297, G1107-14. Itoh, Z.,Sekiguchi, T. 1983. Interdigestive motor activity in health and disease. Scand J Gastroenterol Suppl, 82, 121-34. Jarbur, K., Dalenback, J.,Sjovall, H. 2003. Quantitative assessment of motility-associated changes in gastric and duodenal luminal pH in humans. Scand J Gastroenterol, 38, 392-8.
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Kostewicz, E. S., Wunderlich, M., Brauns, U., Becker, R., Bock, T.,Dressman, J. B. 2004. Predicting the precipitation of poorly soluble weak bases upon entry in the small intestine. J Pharm Pharmacol, 56, 43-51. Koziolek, M., Gorke, K., Neumann, M., Garbacz, G.,Weitschies, W. 2014. Development of a bio-relevant dissolution test device simulating mechanical aspects present in the fed stomach. Eur J Pharm Sci, 57, 250-6. Kuo, B., Mccallum, R. W., Koch, K. L., Sitrin, M. D., Wo, J. M., Chey, W. D., Hasler, W. L., Lackner, J. M., Katz, L. A., Semler, J. R., Wilding, G. E.,Parkman, H. P. 2008. Comparison of gastric emptying of a nondigestible capsule to a radio-labelled meal in healthy and gastroparetic subjects. Aliment Pharmacol Ther, 27, 186-96. Liu, F.,Basit, A. W. 2010. A paradigm shift in enteric coating: achieving rapid release in the proximal small intestine of man. J Control Release, 147, 242-5. Locke, G. R., Talley, N. J., Weaver, A. L.,Zinsmeister, A. R. 1994. A new questionnaire for gastroesophageal reflux disease. Mayo Clin Proc, 69, 539-47. Mitra, A.,Fadda, H. M. 2014. Effect of surfactants, gastric emptying, and dosage form on supersaturation of dipyridamole in an in vitro model simulating the stomach and duodenum. Mol Pharm, 11, 2835-44. Rao, S. S., Camilleri, M., Hasler, W. L., Maurer, A. H., Parkman, H. P., Saad, R., Scott, M. S., Simren, M., Soffer, E.,Szarka, L. 2011. Evaluation of gastrointestinal transit in clinical practice: position paper of the American and European Neurogastroenterology and Motility Societies. Neurogastroenterol Motil, 23, 8-23. Rome Foundation. Rome III diagnostic criteria for functional gastrointestinal disorders. Available: www.theromefoundation.org. Sjovall, H. 2011. Meaningful or redundant complexity - mechanisms behind cyclic changes in gastroduodenal pH in the fasting state. Acta Physiol (Oxf), 201, 127-31. Takieddin, M.,Fassihi, R. 2015. A novel approach in distinguishing between role of hydrodynamics and mechanical stresses similar to contraction forces of GI tract on drug release from modified release dosage forms. AAPS PharmSciTech, 16, 278-83. Thomas, E. A., Sjovall, H.,Bornstein, J. C. 2004. Computational model of the migrating motor complex of the small intestine. Am J Physiol Gastrointest Liver Physiol, 286, G564-72. Tougas, G., Eaker, E. Y., Abell, T. L., Abrahamsson, H., Boivin, M., Chen, J., Hocking, M. P., Quigley, E. M., Koch, K. L., Tokayer, A. Z., Stanghellini, V., Chen, Y., Huizinga, J. D., Ryden, J., Bourgeois, I.,Mccallum, R. W. 2000. Assessment of gastric emptying using a low fat meal: establishment of international control values. Am J Gastroenterol, 95, 1456-62. Vantrappen, G. R., Peeters, T. L.,Janssens, J. 1979. The secretory component of the interdigestive migrating motor complex in man. Scand J Gastroenterol, 14, 663-7. Walravens, J., Brouwers, J., Spriet, I., Tack, J., Annaert, P.,Augustijns, P. 2011. Effect of pH and comedication on gastrointestinal absorption of posaconazole: monitoring of intraluminal and plasma drug concentrations. Clin Pharmacokinet, 50, 725-34. Wang, Y. T., Mohammed, S. D., Farmer, A. D., Wang, D., Zarate, N., Hobson, A. R., Hellstrom, P. M., Semler, J. R., Kuo, B., Rao, S. S., Hasler, W. L., Camilleri, M.,Scott, S. M. 2015. Regional gastrointestinal transit and pH studied in 215 healthy volunteers using the wireless motility capsule: influence of age, gender, study country and testing protocol. Aliment Pharmacol Ther, 42, 761-72. Wilding, I. R., Hardy, J. G., Sparrow, R. A., Davis, S. S., Daly, P. B.,English, J. R. 1992. In vivo evaluation of enteric-coated naproxen tablets using gamma scintigraphy. Pharm Res, 9, 1436-41.
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Wilmer, A., Andrioli, A., Coremans, G., Tack, J.,Janssens, J. 1997. Ambulatory small intestinal manometry. Detailed comparison of duodenal and jejunal motor activity in healthy man. Dig Dis Sci, 42, 1618-27. Woodtli, W.,Owyang, C. 1995. Duodenal pH governs interdigestive motility in humans. Am J Physiol, 268, G146-52.
Figure captions Figure 1.
pH, pressure
and temperature
readings
from
the wireless motility
capsule.
GRT: gastric residence time; SITT: small intestinal transit times; CTT: colon transit time; CI: capsule ingestion; GE: gastric emptying; ICJ: ileocecal junction; CE: capsule expulsion. Figure 2a. pH fluctuations in the duodenum. GE: gastric emptying; SITT: small intestinal transit time; ICJ: ileocecal junction Figure 2b. Uniform pH rise along the small intestine GE: gastric emptying; SITT: small intestinal transit time; ICJ: ileocecal junction Figure 3. Box and Whisker plots of pH in the proximal small intestine of each individual subject (sub) experiencing pH fluctuations in this region (n=13). Medians are shown as the line within the box, the box boundaries are the 25th and 75th percentiles. 5th and 95% percentiles are depicted by the whiskers. Figure 4. Correlation of AUC and Ct in healthy subjects and patients with symptomatic constipation (n= 80) at r = 0.91, p < 1x10-6. Figure 5. Inverse correlation of area under pressure curve (AUC) in the proximal small intestine to small intestinal transit times (SITT) in healthy subjects and patients with symptomatic constipation (n=80) at r = -0.49, p < 1 x 10-6. Graph represents a 2-parameter hyperbolic decay: y = ab/(b + x).
18
GRT
GE GE
ICJ
Temperature
pH
Pressure
Temperature (˚C)
ICI
CE
pH
Pressure (mmHg)
CTT
SITT
SITT Duration of pH fluctuation
Max pH
Min pH
pH
Pressure (mmHg)
GE
ICJ
Pressure (mmHg)
SITT
GE pH
ICJ
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20
21
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