In Vivo Dissolution and Systemic Absorption of Immediate Release Ibuprofen in Human Gastrointestinal Tract under Fed and Fasted Conditions

Abstract

In vivo drug dissolution in the gastrointestinal (GI) tract is largely unmeasured. The purpose of this clinical study was to evaluate the in vivo drug dissolution and systemic absorption of the BCS class IIa drug ibuprofen under fed and fasted conditions by direct sampling of stomach and small intestinal luminal content. Expanding current knowledge of drug dissolution in vivo will help to establish physiologically relevant in vitro models predictive of drug dissolution. A multilumen GI catheter was orally inserted into the GI tract of healthy human subjects. Subjects received a single oral dose of ibuprofen (800 mg tablet) with 250 mL of water under fasting and fed conditions. The GI catheter facilitated collection of GI fluid from the stomach, duodenum, and jejunum. Ibuprofen concentration in GI fluid supernatant and plasma was determined by LC–MS/MS. A total of 23 subjects completed the study, with 11 subjects returning for an additional study visit (a total of 34 completed study visits). The subjects were primarily white (61%) and male (65%) with an average age of 30 years. The subjects had a median [min, max] weight of 79 [52, 123] kg and body mass index of 25.7 [19.4, 37.7] kg/m². Ibuprofen plasma levels were higher under fasted conditions and remained detectable for 28 h under both conditions. The AUC_0–24 and C_max were lower in fed subjects vs fasted subjects, and T_max was delayed in fed subjects vs fasted subjects. Ibuprofen was detected immediately after ingestion in the stomach under fasting and fed conditions until 7 h after dosing. Higher levels of ibuprofen were detected in the small intestine soon after dosing in fasted subjects compared to fed. In contrast to plasma drug concentration, overall gastric concentrations remained higher under fed conditions due to increased gastric pH vs fasting condition. The gastric pH increased to near neutrality after feeding before decreasing to acidic levels after 7 h. Induction of the fed state reduced systemic levels but increased gastric levels of ibuprofen, which suggest that slow gastric emptying and transit dominate the effect for plasma drug concentration. The finding of high levels of ibuprofen in stomach and small intestine 7 h post dosing was unexpected. Future work is needed to better understand the role of various GI parameters, such as motility and gastric emptying, on systemic ibuprofen levels in order to improve in vitro predictive models.

Graphical Abstract

INTRODUCTION

Designing oral drug formulations with predictable gastrointestinal (GI) absorption profiles is a major objective during drug development. Understanding the dissolution properties of oral formulations using in vitro systems can support this endeavor. Current in vitro models are useful for in vivo prediction of absorption of high solubility drugs. In contrast the absorption of low solubility drugs with high GI permeability, referred to as biopharmaceutical classification system (BCS) II drugs, are especially difficult to predict.^1,2 This prediction problem arises from the inability to optimally mimic the dynamic physiologic parameters such as pH, buffering conditions, and shifting GI volumes that impart changes to dissolution and absorption of BCS II drugs in the GI tract. Designing a predictive model that is able to address this complex drug–GI behavior may play a major role in drug development. Importantly, such a system has the potential to help qualify waivers of bioavailability and bioequivalence studies for BCS II drugs during generic drug development.

Currently there are very limited data available analyzing in vivo BCS II drug dissolution and dosage form performance in the GI tract; however, recent studies by Hens et al. and Van Den Abeele et al. have begun to shed fight on drug dissolution and absorption of weakly acidic BCS II drugs.^3–5 Drug absorption in the GI tract is a complex process that remains to be fully elucidated. Constructing a comprehensive translational model requires clinical measurement of GI variables such as pH, buffer capacity, motility, etc. in order to develop better in vitro models. The goal of this clinical study was to obtain in vivo drug dissolution of BCS class IIa drug ibuprofen in the GI tract in fed and fasted conditions and correlate with systemic drug concentration. We chose to evaluate a model BCS IIa drug, ibuprofen, one of the most commonly used nonsteroidal anti-inflammatory drug (NSAIDs) to treat acute pain, fever, and inflammation.⁶

The potential benefits of ibuprofen are hampered by side effects.⁷ Specifically, the chronic use of NSAIDs like ibuprofen is associated with GI adverse events such as gastroduodenal ulceration.⁸ This adverse event occurs due to topical epithelial irritant effects, suppression of GI prostaglandin synthesis, alteration of local GI blood flow, and interference of injury repair mechanisms. To improve GI tolerability, ibuprofen is often taken with food.⁹ Food can delay the rate of ibuprofen absorption and lower its pharmacological effects.¹⁰ While we understand the effect food has on plasma levels, we have yet to understand the effect of food on local GI ibuprofen concentrations.

In this study a novel multilumen GI catheter was orally placed into the stomach and small intestine of healthy human volunteers to obtain in vivo samples of the GI tract after dosage of an ibuprofen tablet. This study was performed in volunteers under both fed and fasted conditions in order to characterize in vivo drug disintegration and dissolution under each condition. Corresponding plasma samples and GI fluid samples were collected for 7 h following study drug administration. The concentration of ibuprofen in plasma and GI fluid supernatant was determined via LC–MS/MS and correlated with the human physiology data (such as pH) to better understand the effect of food on drug absorption. Correlating in vivo drug concentrations with GI physiology data under fasting and fed conditions from healthy subjects will help support mechanistic absorption model development in the future. This information may also be helpful to improve our understanding of local ibuprofen concentrations that may influence gastroduodenal ulceration with NSAID use.

METHODS

Ethics Statement.

Samples collected in this study were part of clinical trial NCT02806869. The institutional review boards at the University of Michigan (IRBMED, protocol number HUM00085066) and the Department of Health and Human Services, Food and Drug Administration (Research Involving Human Subjects Committee/RIHSC, protocol number14-029D) both approved the study protocol. All subjects provided written informed consent in order to participate. The study was carried out accordance with the protocol, International Conference on Harmonization Good Clinical Practice guidelines, and applicable local regulatory requirements.

Ibuprofen Formulation.

Ibuprofen tablets (800 mg) were purchased from Dr. Reddy’s Laboratories (Shreveport, LA). The ibuprofen tablet was administered with approximately 250 mL of water; actual volumes of water consumed for each subject is fisted in Table S1. The study drug was dispensed by the Investigational Drug Service (IDS) at the University of Michigan.

Catheter Design.

A customized multilumen catheter was manufactured by Mui Scientific (Mississauga, ON, Canada). The catheter was 292 cm long and consisted of four independent aspiration ports located 30–20 cm apart and 16 manometry ports located proximal to the aspiration ports. The outer diameter of the catheter was 3.3 mm while the single lumen tubes used for aspiration had an inner diameter of 1.2 mm. Additionally, the catheter had a channel to fit a guidewire (0.035 in. × 450 cm, Boston Scientific, Marlborough, MA) as well as a channel connected to a balloon that could be filled with 7 mL of water to assist in catheter placement. Finally, the end of the catheter was weighted with 7.75 g of tungsten weights.

Inclusion and Exclusion Criteria for the Study.

Male and female healthy human volunteers between the ages of 18 and 55 were eligible for inclusion in the study. All subjects completed a physical exam and had their previous medical history reviewed by the study physician to confirm that the subjects were healthy volunteers able to participate in the study. All subjects enrolled in the study had normal values for the following laboratory tests: vital signs, electrocardiogram (ECG), urine drug screen, serum pregnancy test (for women of child-bearing potential), comprehensive metabolic panel, complete blood count with platelet and differential, and lactate dehydrogenase. There were no exclusionary criteria in regard to BMI; however, all tests fisted above had to be in normal range and the subject had to overall be deemed healthy by the study physician.

Exclusionary criteria for the study were as follows: Adults unable to consent for themselves or mentally incapacitated; prisoners; significant clinical illness within 3 weeks prior to screening; use of concomitant medications within 2 weeks prior to receiving study drug, including but not limited to prescription drugs, herbal and dietary supplements, over the counter medications, and vitamins (oral contraceptive was permitted); received an investigational drug within 60 days prior to receiving the study drug; history of gastrointestinal surgery; surgery within the past 3 months; history of allergy to ibuprofen or other nonsteroidal anti-inflammatory drugs (NSAIDs); pregnant or lactating females; history of severe allergic diseases including drug allergies, with the exception of seasonal allergies; history of drug addiction or alcohol abuse within the past 12 months; any clinically significant abnormal lab values during screening; any other factor, condition, or disease, including, but not limited to, cardiovascular, renal, hepatic, or gastrointestinal disorders that may, in the opinion of the investigator, jeopardize the safety of the patient or impact the validity of the study results.

Study Procedure.

All clinical procedures were performed at the Michigan Clinical Research Unit (MCRU) or the Medical Procedures Unit (MPU) in the University of Michigan hospital. The subjects were instructed to fast beginning 13 h prior to dosing and to avoid consuming water for 10 h prior to dosing. Upon arrival a physical exam was performed by the study doctor to ensure the health of the subject prior to the GI catheter insertion procedure. The multilumen GI catheter was orally inserted into the GI tract of the subject under the supervision of the study doctor. Lubricating jelly was applied to the GI catheter prior to insertion. To lessen the gag reflex, subjects received a topical anesthetic (1 mL of 4% lidocaine) before the catheter insertion. Once the catheter was swallowed, catheter placement was continued under abdominal fluoroscopy to ensure proper positioning in the GI tract. When catheter placement was completed, the GI catheter was secured to the cheek of the subject using medical tape. The subject remained in bed for 1 h while the GI tube was equilibrated to the manometry instrument, then for 3–5 h while baseline GI motility data was collected. Additionally, GI motility was measured continuously for 7 h following study drug administration. The rate of water perfused into the subject to measure motility was approximately 100 mL per hour for the 11–13 h that motility was recorded.

Prior to study drug administration, an intravenous (iv) catheter was placed and was kept open with saline solution throughout the study visit. A blood sample and a GI sample were collected immediately prior to study drug administration and food consumption. The study subjects were randomized to one of two arms for this study: the study drug dosed in the fasting state or the study drug dosed immediately after consuming up to 710 calories (473 mL) of a 55% fat liquid meal to induce the fed state (Pulmocare (pH 6.6), Abbott Nutrition, Lake Forest, IL). Randomization was performed using Research Randomizer software version 4.0. The maximum time allowed to consume the liquid meal was 15 min, and then the subjects were immediately dosed with ibuprofen.

The subject was given an 800 mg tablet of ibuprofen to be swallowed with 250 mL of water. After administration of the study drug, the subjects did not consume any additional food or water. The study drug, water, and/or Pulmocare were swallowed by the subject and were not administered via the GI catheter. Blood samples were collected at 0 (immediately prior to food consumption and/or study drug administration), 10, 20, 30, and 45 min, then at 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, 11 or 12, and approximately 28 h following study drug administration. Blood samples were added to venous blood collection tubes (K₂ EDTA (spray-dried), 7.2 mg), and plasma was separated from blood samples by centrifugation and stored at −80 °C.

GI fluid samples were collected from available ports by aspiration from individual tubes within the GI catheter. Before collection the contents in the GI catheter remaining from the previous aspiration were collected and discarded. This volume ranged from 3.2 mL for the most distal (jejunal) tube to 1.7 mL for the most proximal (stomach) tube. If the tube was filled with air bubbles, then at least 30 cm³ of the air/fluid mixture (containing no more than 3.2 mL of liquid) was collected and discarded. Collection times included 0 (immediately prior to food consumption and/or study drug administration), 15, 30, and 45 min, then 1, 1.5, 2, 2.5, 3, 4, 5, 6, and 7 h following study drug administration. Immediately after collection, the pH of the samples was determined using a calibrated micro pH electrode (Thermo Scientific Orion pH probe 9810BN). Then the GI fluid samples were centrifuged at 21000g for 5 min, and the supernatant was collected and stored at −80 °C.

At 7 h following study drug administration, the GI catheter was removed orally from the GI tract and the subject was served a meal. Following the 8 h blood draw, the iv catheter was removed, and the remaining blood draws were performed with a butterfly needle and syringe. The subject then returned approximately 28 h post dosing for the final blood draw.

To gain an understanding of intrasubject variability, each subject was asked to complete two GI catheter insertion procedures under the same conditions, either fasting state or fed state. A minimum of 7 days separated each GI catheter insertion procedure. The screening visit was repeated prior to the second study visit if scheduled more than 4 weeks after the first study visit to ensure the subject remained eligible for inclusion in the study.

LC–MS/MS Analysis of Ibuprofen in GI Fluid and Plasma.

All samples were analyzed by the Pharmacokinetics Core at the University of Michigan. LC–MS/MS analyses was performed using a Shimadzu HPLC system interfaced to an AB SCIEX QTRAP 5500 mass spectrometer by a TurboV electrospray ionization (ESI) source (Applied Biosystems/MDS Sciex, Toronto, Canada). Ibuprofen-d₃ was used as an internal standard (IS) to normalize variation during sample preparation and LC–MS/MS analyses. Chromatographic separation was achieved using a 2.1 × 50 mm, 3.5 μm Agilent ZORBAX Extend-C18 column. The injection volume was 5 μL, and the flow rate was kept constantly at 0.4 mL/min. Mobile phases A and B were water and acetonitrile, respectively. Both water and acetonitrile contained 0.1% acetic acid (v/v). The flow gradient was initially 98:2 v/v of A:B for 0.5 min, linearly ramped to 5:95 A:B over 1 min. To completely wash the column, the gradient was held at 5:95 A:B for 2 min and then returned to 98:2 over 0.5 min. This condition was held for 3 min prior to the injection of another sample. The mass spectrometer was operated at ESI negative ion mode, and multiple reaction monitoring (MRM) was used for monitoring the transitions of m/z 205.1 → 159.1 and m/z 208.2 → 161.2 for ibuprofen and ibuprofen-d₃ (IS), respectively.

Protein precipitation with methanol was used to extract ibuprofen from the human plasma. 60 μL of each plasma sample was mixed with 180 μL of methanol containing 500 ng/mL ibuprofen-d₃ in a 96-well plate. The mixture was vortexed for 60 s at a high speed. The 96-well plate was centrifuged at 3000g for 20 min to precipitate proteins at 4 °C. The clear supernatants were collected, and 5 μL of the supernatant was injected for LC–MS/MS analysis.

Sample preparation of GI fluid was similar to the plasma samples. Due to the inadequate amount of blank GI fluid for preparation of calibration standards and QC samples, the plasma calibration curve was used to quantify ibuprofen in GI fluid. In order to reduce matrix effect, all of the GI fluid samples were diluted 10-fold with blank human plasma before protein precipitation in methanol containing 500 ng/mL ibuprofen-d₃.

Stock solutions of ibuprofen (2 mg/mL) were prepared in methanol. An ibuprofen-d₃ (IS) stock solution (5 mg/mL) was prepared in dimethyl sulfoxide. To prepare the calibration standards, the 2 mg/mL ibuprofen stock solution was diluted to 500 μg/mL using methanol, which was spiked with blank human plasma to provide a final ibuprofen plasma concentration of 10 μg/mL. Then serial dilution with the blank human plasma was carried out to provide a series of calibration standards from 2.5 to 10,000 ng/mL. Quality control (QC) plasma solutions at 5,25,250,5000, and 10000 ng/mL were prepared similarly using separately weighed methanol stock solutions of ibuprofen (2 mg/mL). Methanol was used to further dilute the stock ibuprofen-d₃ solution to 500 ng/mL for protein precipitation during sample preparation, also to minimize the variation.

According to Food and Drug Administration (FDA) guidelines, validation procedures were performed in human plasma and GI fluid diluted with human plasma. These procedures included the following: (A) specificity and selectivity; (B) recovery and matrix effects at low (0.015 μg/mL), medium (0.1 and 10 μg/mL), and high (35 μg/mL) concentrations; (C) calibration curve with a correlation coefficient (r) of more than 0.98; (D) precision and accuracy, with the intraday and interday assay precision and accuracy estimated by analyzing six replicates at three QC levels; (E) stability, with all stability studies conducted at three concentration levels in the biomatrix at room temperature, 4 °C, −20 °C, and −80 °C; and (F) dilution integrity, with experiments carried out with blank biomatrix.

Pharmacokinetic Analysis and Data Presentation.

Given the intensive plasma sampling procedure (up to 17 samples/subject), plasma pharmacokinetics were characterized by non-compartmental analyses. These analyses included computation of the area under the curve from time zero to 24 h (AUC_0–24) based on the linear–logarithm trapezoidal rule, maximum concentration (C_max), and time to C_max (T_max). Statistical comparisons of these between group comparisons of pharmacokinetic parameters were performed using the Kruskal–Wallis test. Matched comparisons by subjects who had repeated measures was performed using the Wilcoxon signed-rank test. A p value of <0.05 was qualified as statistically significant. Pharmacokinetic and statistical analyses were performed using StataIC version 14.2 (StataCorp, College Station, TX) . All figures were generated with the R 3.2.3 software package utilizing ggplot2 or with Prism 6 (GraphPad Software, Inc.). Average values are shown with the standard error of the mean (SEM). Significance was determined using nonparametric statistical tests.

RESULTS

Study Enrollment Numbers and Demographics.

To determine eligibility for this study, 65 subjects were screened and 46 met eligibility criteria. These 46 subjects participated in 60 GI catheter placement procedures. Of these 60 catheter placement studies, 24 were discontinued. There was 1 study visit that was discontinued after study drug administration due to discomfort from the GI catheter. There were 23 study visits that were discontinued prior to study drug administration due to the following reasons: inability to advance the GI catheter (n = 1), vomiting (n = 2), or discomfort caused by the GI catheter after insertion (n = 20). One subject experienced an adverse event during the study visit. The subject became hypotensive and reported feeling hot and was clammy to the touch during the study procedures. The subject was immediately placed into the Trendelenburg position while cooling the forehead and neck with ice packs. The subject’s blood pressure returned to baseline after 8 min and remained at that level throughout the remainder of the study.

The plasma concentration–time information from all 25 subjects that completed the study were reviewed individually and revealed two subjects as extreme values. One subject had a rising concentration time profile over the 8 to 28 h period with concentrations at the last time point that were 2-fold higher than at the midpoint. Nonadherence with the study protocol such as self-administration of another dose of ibuprofen was assumed, and as a precaution samples collected from this subject were not included in subsequent analysis. The second subject had plasma concentrations that were approximately 10-fold lower on two study visits (fed conditions) than values measured in comparable subjects with no reasonable explanation for these observations. Given the small sample size, inclusion of these extreme value data from this subject would contribute to a larger difference in the central tendency estimates of ibuprofen exposure in fed compared to fasted subjects (detailed in next section). As a precaution we removed this subject from subsequent data analyses to not skew the effects of food on ibuprofen dissolution and absorption.

Details regarding study participants, whose data were included in our analysis, are shown in Table 1. There were a total of 23 subjects with 11 subjects returning for an additional study visit (a total of 34 study visits) in our analysis. The subjects were primarily white (61%) and male (65%) with an average age of 30 years. The subjects had a median [min, max] weight of 79 [52, 123] kg and body mass index of 25.7 [19.4, 37.7] kg/m².

Table 1.

Demographics of Study Subjects

		mean ± SD (min–max)		sex		race			ethnicity
study arm	N a	age (years)	BMIb	male	female	Caucasian	African-American	Asian	not Hispanic or Latino	Hispanic or Latino
total	23	30 ± 9 (18–54)	26.2 ± 4.6 (19.4–37.7)	15	8	14	7	2	22	1
fed	10	32 ± 9 (22–49)	27.0 ± 4.5 (21.6–35.9)	6	4	6	4	0	9	1
fasted	13	29 ± 9 (18–54)	25.7 ± 4.7 (19.4–35.8)	9	4	8	3	2	13	0

^aNumber of subjects.

^bBody mass index.

Plasma Concentration after Administration of Ibuprofen.

The mean and standard deviation concentration time profiles from the 23 included subjects are displayed in Figure 1 as a semilogarithm plot and as absolute values by fasted and fed states. Individual concentration–time profiles of subjects by fasted and fed conditions are shown in Figure 2. In both the fasted and fed conditions ibuprofen was detected in the plasma 10 min after administration of ibuprofen. As shown in Figures 1 and 2, the C_max was lower and T_max longer in the fed versus fasted state.

Figure 1.

Average plasma concentration vs time profiles of ibuprofen. Fasted (n = 20, green line) and fed (n = 14, black line) conditions plotted in (A) logarithmic and (B) linear scale. Error bars indicate the standard error of the mean (SEM). Data from fasted subjects (n = 20) and fed subjects (n = 14) are shown.

Figure 2.

Individual plasma concentration vs time profiles of ibuprofen under (A) fasted and (B) fed conditions. Each line represents an individual subject.

Fed subjects had a significantly (p = 0.020) lower AUC_0–24 value than those in the fasted condition, though this difference was a mean of 5.42% lower. In contrast, the difference in C_max was 35.2% lower (p = 0.025) in the fed versus fasted conditions. This lower C_max was also associated with a longer T_max that was a mean of 1.71 h longer in the fed condition. The specific values and statistical comparison of these parameters are provided in Table 2. To quantify intrasubject variability, we analyzed the AUC_0–24 from the 11 subjects that completed two separate study visits under the same treatment conditions. The geometric mean [90% confidence interval] plasma AUC_0–24 ratio was 1.056 [0.929, 1.193].

Table 2.

Plasma Pharmacokinetic Parameters of Ibuprofen (Mean ± Standard Deviation), Including Area under the Curve from Time Zero to 24 h (AUC_0–24), Maximum Concentration (C_max), and Time to C_max (T_max)^a

study arm	no. of observations	AUC0–24 (μg·h/mL)	Cmax (μg/mL)	Tmax(h)
fasted	20	241.888 ± 88.907	58.247 ± 18.400	2.980 ± 1.613
fed	14	229.452 ± 76.879	43.051 ± 14.312	4.694 ± 1.994
statistical significance		p = 0.020	p = 0.025	p = 0.010

^aSignificance was determined using the nonparametric Kruskal–Wallis equality-of-populations rank test.

GI pH Values in the GI Tract.

The average pH values in the GI tract are shown in Figure 3. Immediately after feeding, the gastric pH increased from acidic values (2.3 ± 0.3) closer to neutrality (4.6 ± 0.58). The pH levels gradually decreased until the final measurement 7 h post dosing, returning to values seen prior to feeding (2.8 ± 0.64). After feeding, the pH of the small intestine increased from approximately 5 to 6. Fasted subjects had a relatively stable pH compared to the fed subjects throughout the study. The pH values from each subject are shown in Figure 4. Regardless of fed or fasted conditions, the pH in the jejunum showed much less variability than that in the duodenum and stomach. Both of these regions exhibited large variably between subjects.

Figure 3.

Average pH value vs time profiles throughout the GI tract. (A) Fasted and (B) fed study visits are shown. Mid jejunum (black line), proximal jejunum (red line), duodenum (green line), and stomach (blue line). Error bars indicate the standard error of the mean (SEM). Data from fasted subjects (stomach, n = 15; duodenum, n = 16; proximal jejunum, n = 10; mid jejunum, n = 12) and fed subjects (stomach, n = 13; duodenum, n = 11; proximal jejunum, n = 6; mid jejunum, n = 7) are shown.

Figure 4.

Individual pH values vs time profiles for each subject throughout the GI trace. Each line represents an individual subject.

In Vivo GI Concentration of Ibuprofen in the GI Tract.

The average concentration of ibuprofen detected in the GI tract is shown in Figure 5 while the ibuprofen concentration in the GI tract for each individual study visit is shown in Figure 6. GI fluid was aspirated 15 min post dosing and continued at specified intervals until 7 h post dosing. As shown in Figure 5, initial samples had a higher concentration of ibuprofen in the stomach for fed subjects while fasted subjects had a higher concentration of ibuprofen in the small intestine. All subjects still had high levels of ibuprofen throughout the GI tract until the last sampling time point, 7 h post dosing.

Figure 5.

Average concentration of ibuprofen in luminal GI fluid supernatant throughout the GI tract. (A) Fasted and (B) fed conditions. Mid jejunum (black line), proximal jejunum (red line), duodenum (green line), and stomach (blue line). Error bars indicate the standard error of the mean (SEM). Data from fasted subjects (stomach, n = 15; duodenum, n = 16; proximal jejunum, n = 10; mid jejunum, n = 12) and fed subjects (stomach, n = 13; duodenum, n = 11; proximal jejunum, n = 6; mid jejunum, n = 6) are shown.

Figure 6.

Individual ibuprofen concentrations in plasma and luminal GI fluid supernatant. Each line represents an individual subject.

Figure 7 shows the ibuprofen concentration profiles broken down into each site of the stomach and small intestine. In the stomach under fasted condition, the ibuprofen concentration (19,442 ng/mL) was detected at 15 min post dosing. Surprisingly, the high ibuprofen concentration in stomach remained for 7 h after dosing (20,055 ng/mL). In the stomach under fed condition, the ibuprofen concentration (90,637 ng/mL) was detected at 15 min post dosing. This was 4.7-fold higher than that of fasted condition, and this increase of ibuprofen dissolution in the stomach may be due to the higher pH under fed condition.

Figure 7.

Site comparison of the average concentration of ibuprofen in luminal GI fluid supernatant in fed and fasting conditions. (A) Stomach, (B) duodenum, (C) proximal jejunum, and (D) mid jejunum. Error bars indicate the standard error of the mean (SEM). Data from fasted subjects (stomach, n = 15; duodenum, n = 16; proximal jejunum, n = 10; mid jejunum, n = 12) and fed subjects (stomach, n = 13; duodenum, n = 11; proximal jejunum, n = 6; mid jejunum, n = 6) are shown.

It is worth noting that although ibuprofen has higher dissolution in the stomach under fed condition (due to higher pH), the ibuprofen concentration in the duodenum is delayed (due to slow gastric emptying and transit). This delay resulted in lower plasma ibuprofen concentration. These data strongly suggest that the gastric emptying and transit (at fed state) is dominant to determine the plasma drug concentration.

DISCUSSION

The goal of this clinical study was to directly measure drug dissolution in the stomach and small intestine of healthy humans in order to better understand the in vivo conditions that affect drug disintegration and dissolution. We chose to evaluate the in vivo drug dissolution and systemic absorption of the BCS class IIa drug ibuprofen by in vivo sampling of stomach and small intestinal luminal content of fasted and fed subjects. In this study we were able to characterize in vivo the dissolution pattern of ibuprofen through to the mid jejunum. In addition, this study was to determine influence of gastric pH and a fed state on dissolution. These in vivo findings improved our understanding of the luminal profile of this poorly soluble drug and can help to support future models of agents within this class.

The effect of food on the pharmacokinetics of immediate release NSAIDs has recently been reviewed.¹⁰ Having increased plasma levels of ibuprofen results in increased analgesic effect of the drug;¹¹ however, consumption of food can decrease plasma levels of ibuprofen.¹⁰ Ibuprofen is generally taken with food to improve tolerability; therefore, we sought to understand the effect of food on in vivo drug disintegration and dissolution of ibuprofen. Our results were consistent with previous studies¹⁰ showing an overall decrease in the C_max, delay of the T_max, and overall decrease in the AUC_0–24 in the plasma of fed subjects compared to fasted subjects. By utilizing direct in vivo sampling of the GI tract we were able to detect ibuprofen 15 min after dosing in both fed and fasted conditions. In fasted subjects ibuprofen was readily detected in the small intestine, which was reflected in higher plasma concentrations compared to fed subjects. There were high concentrations of ibuprofen in the stomachs of fed subjects compared to fasted subjects. The increase in pH increased drug dissolution in the stomach; however, that did not increase the rate of systemic drug absorption. Ibuprofen is thought to be poorly absorbed in the stomach of humans, with the small intestine being the main site of absorption.¹² Our data suggests that feeding increases the stomach pH, which in turn increases drug dissolution; however, this does not result in higher plasma concentrations. The fed condition likely delayed gastric emptying and transit of drug from stomach to duodenum, which correlated with lower C_max, lower AUC_0–24, and longer T_max. These data strongly suggest that the GI transit is a major determinant for lower plasma drug concentration under fed state.

Our results, as well as results from others,^13,14 show that there is remarkable intersubject variability in the pH of the gastrointestinal tract. The low pH in the stomach below the pK_a of 4.4 for ibuprofen^15,16 correlates with low measurable concentrations in this part of the GI tract. Consumption of food that leads to an initial increase in stomach pH also leads to measurable stomach concentrations of ibuprofen. However, food slows the rate of absorption, leading to a lower C_max and longer T_max, but marginally alters the extent of absorption (as indicated by a similar AUC_0–24). This alteration in the concentration–time profile is relevant for ibuprofen because the analgesic effects of this drug are related to increased plasma levels of the drug.¹¹ The observed extension in the T_max by approximately 1.7 h also implies an expected delay in the therapeutic effects of this drug.

A major unexpected finding of this work was the prolonged high levels of ibuprofen in the GI tract. Our results show that ibuprofen was detected in the GI tract over the course of the 7 h of sampling. Although this was limited to 7 h based on our sampling schema, it is likely that some subjects may have local concentrations in the GI tract for longer periods of time. The implications of prolonged GI retention of ibuprofen have not been previously characterized. Previously, the transit in stomach was estimated from 30 min to 2 h and transit time in small intestine was an average of 3 h, and these estimates were used in drug absorption model prediction. The high drug concentration in the stomach and small intestine for 7 h may challenge these previous assumptions in drug absorption prediction. Better models may need to be developed for better in vitro and in vivo correlation and oral absorption prediction.

In addition, it is known that prolonged use of NSAIDs is associated with an increase in gastroduodenal ulceration. From a theoretical perspective, sustained exposure of local GI tissue to ibuprofen may contribute to the peptic ulcer disease associated with this drug. Our results suggest that there is prolonged exposure to ibuprofen in the GI tract, especially after taking ibuprofen with food. Additionally, food increases the initial ibuprofen concentration approximately 5-fold compared to fasted subjects 15 min after dosing. Our findings suggest we may need to reconsider taking ibuprofen with food. While taking with food might alleviate acute symptoms of GI discomfort, it may lead to long-term consequences by delaying gastric emptying and leading to prolonged exposure of the stomach lining to ibuprofen.

One potential limitation for this study is that with any aspiration catheter going past the pylorus in the stomach there is a possibility of altering gastric emptying by altering how the pylorus opens and closes. Additionally, the presence of a catheter could have an effect on duodenogastric reflux and this in turn could affect drug dissolution and absorption. However, this was examined in work by Muller-Lissner et al. using a catheter of similar size (3.0 mm compared to our 3.3 mm catheter diameter).¹⁷ They found no effect on gastric emptying or duodenogastric reflux when the catheter was placed past the pylorus. No effect of the catheter was found in both fed and fasted conditions. Therefore, the method of using an aspiration catheter to study drug dissolution and absorption should be similar compared to the catheter not being present.

Another potential limitation is that the use of aspiration catheters can be considered uncomfortable to the subject due to the presence of a foreign object placed down the subject’s throat. This caused generalized anxiety and uncomfortable feeling in the subject’s throat. We did have 36 out of 60 subjects complete the entire study that had the tube placed for approximately 15 h. This success rate was similar to a previous study using a similar multilumen catheter where the tube was placed for a similar length of time.¹⁴ While the success rate is lower than that for other studies,⁵ this could be due to the length of time the tube was placed. For example, work from Hens et al. had a higher success rate for the study, but the tube was in place for much less time (approximately 4 h).⁵ The generalized anxiety of having the tube placed for 15 h in our study may have decreased the success rate. However, having the tube placed for this long allowed us to obtain manometry data as well as aspirate fluid for 7 h after dosing, which resulted in a very large data set.

The use of aspiration catheters allows us to better understand the in vivo conditions involved in studying drug dissolution and absorption. In this study we presented the data obtained for the gastric and small intestinal pH as well as the concentrations of ibuprofen in the GI tract and plasma. Further analysis of the data set obtained in this clinical study is described in the manuscript by Hens et al.¹⁸ In this work, Hens et al. further described how ibuprofen concentration in the stomach and small intestine correlate to buffer capacity as well as motility. Additionally Hens et al. looked at the effect of pH and drug dissolution by analyzing the levels of undissolved ibuprofen in the GI tract.

The ability to directly sample small intestinal luminal samples allowed us to follow drug dissolution in vivo. The use of multilumen catheters to aspirate GI fluid to study drug dissolution was pioneered over 30 years ago; however, relatively few studies have been performed since¹⁹ (reviewed by Hens²⁰ and Brouwers²¹). In the past few years multiple groups have begun to utilize this technique to aspirate samples from the stomach and GI tract.^5,14,20,22 Because of this we are beginning to get a better understanding of the complex GI physiological parameters involved in drug dissolution and absorption. A multilumen GI catheter is a powerful tool to be able to independently sample multiple sites in the GI tract to compare regional and temporal drug disintegration and dissolution. Future work is needed to connect motility, gastric emptying, buffer capacity, and viscosity to better understand in vivo drug dissolution and absorption. We hope that the in vivo results obtained in this study can be used to validate in vitro dissolution methodologies in order to support future computational and mathematical modeling efforts. This will aid in the development of an oral drug product optimization process that can be applied to future drugs in order to maximize oral drug safety and efficacy.

CONCLUSION

In this study we used a novel multilumen catheter with the ability to aspirate luminal GI fluid from the stomach and small intestine. Using this catheter, we were able to identify that ibuprofen remains in stomach and small intestine for 7 h. The fed state delayed transit of ibuprofen into the duodenum (presumably due to a delay in gastric emptying) compared to the fasted state. The fed state increased drug dissolution in stomach (presumably due to increase of pH in the fed state) compared to the fasted state; however, this did not result in an overall increase in plasma levels of ibuprofen.

ABBREVIATIONS USED

GI

gastrointestinal

BCS

biopharmaceutical classification system

NSAIDs

nonsteroidal anti-inflammatory drug

FDA

Food and Drug Administration