European Journal of Pharmaceutical Sciences 14 (2001) 347–353 www.elsevier.nl / locate / ejps
Novel method to assess gastric emptying in humans: the Pellet Gastric Emptying Test Sally Y. Choe a , Brien L. Neudeck b , Lynda S. Welage b,c , Gregory E. Amidon d , Jeffrey L. Barnett e , b, Gordon L. Amidon * a Pharmaceutical Research Institute, Bristol-Myers Squibb, Princeton, NJ 08543 -4000, USA College of Pharmacy, The University of Michigan, 428 Church Street, Ann Arbor, MI 48109 -1065, USA c Department of Pharmacy Services, University of Michigan Health Systems, Ann Arbor, MI 48109, USA d Drug Delivery Research and Development, Pharmacia, Kalamazoo, MI 49001, USA e School of Medicine, The University of Michigan and the Department of Internal Medicine, University of Michigan Health Systems, Ann Arbor, MI 48109, USA b
Received 15 February 2001; received in revised form 6 August 2001; accepted 6 September 2001
Abstract To further validate the Pellet Gastric Emptying Test (PGET) as a marker of gastric emptying, a randomized, four-way crossover study was conducted with 12 healthy subjects. The study consisted of oral co-administration of enteric coated caffeine (CAFF) and acetaminophen (APAP) pellets in four treatment phases: Same Size (100 kcal), Fasted, Small Liquid Meal (100 kcal), and Standard Meal (847 kcal). The time of first appearance of measurable drug marker in plasma, t initial , was taken as the emptying time for the markers. Co-administration of same size enteric coated pellets of CAFF and APAP (0.7 mm in diameter) revealed no statistically significant differences in t initial values indicating that emptying was dependent only on size and not on chemical make-up of the pellets. Co-administration of different size pellets indicated that the smaller 0.7-mm diameter (CAFF) pellets were emptied and absorbed significantly earlier than the larger 3.6-mm diameter (APAP) pellets with both the Small Liquid Meal (by 35 min) and the Standard Meal (by 33 min) (P,0.05). The differences in emptying of the pellets were not significant in the Fasted Phase. The results suggest that the pellet gastric emptying test could prove useful in monitoring changes in transit times in the fasted and fed states and their impact on drug absorption. 2001 Published by Elsevier Science B.V. Keywords: Size; Gastric emptying; Acetaminophen; Caffeine
1. Introduction Various methods have been developed to assess gastric emptying in humans under normal gravity conditions and include scintigraphy, gastric aspiration, ultrasound, epigastric impedance, and magnetic resonance imaging (MRI) techniques (Malagelada, 1990). Most of these methods, however, are invasive or expensive or time-consuming and tedious that limit their applicability and often, their repeatability. Scintigraphy is a non-invasive procedure currently considered to be the standard method to measure gastric emptying (Stanghellini et al., 2000; Wilding et al., *Corresponding author. Tel.: 11-734-764-2440; fax: 11-734-7636423. E-mail address: glamidon@umich.edu (G.L. Amidon).
2001); the use of gamma radiation, however, limits its repeatability (Malagelada, 1990). Gastric aspiration is an invasive method suitable only in conjunction with liquid meals, and it requires ingestion of a large volume of liquid in order to provide accurate results (Maughan and Leiper, 1996). Ultrasound, while noninvasive, safe, and reproducible, involves time-consuming procedures by a trained operator (Holt et al., 1985). Although epigastric impedance is non-invasive and does not require the use of radiation, it cannot be used with solid meals, semi-solid meals, or liquids with high conductivity, and is also sensitive to body movements (McClelland and Sutton, 1985). MRI is generally too expensive to be accessible for basic clinical research (Maughan and Leiper, 1996). One of the more recent and novel approaches, the [ 13 C]octanoic acid breath test, has been reported to be quite suitable in measuring the
0928-0987 / 01 / $ – see front matter 2001 Published by Elsevier Science B.V. PII: S0928-0987( 01 )00196-8
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gastric emptying of solids (Ghoos et al., 1993). The breath test was found to be as reliable as scintigraphy in estimating gastric emptying of solids in low caloric meals (Kim et al., 2000; Peracchi et al., 2000). In medium caloric meals, however, the accuracy of the [ 13 C]octanoic breath test has been subject to question (Lee et al., 2000; Peracchi et al., 2000). Thus, it is desirable to develop a simple nonradioactive method to monitor gastric emptying that may alleviate some of the shortcomings of the existing methods, particularly for use in space. The Pellet Gastric Emptying Test, PGET, discussed below is the result of an effort to develop a non-invasive method that could provide an alternative and avoid many of the difficulties of the existing methods, and that can be conducted in either gravity or microgravity conditions. Although particle size, particle density and viscosity are important parameters that influence size-differentiated gastric emptying, the individual parameters have been shown to correlate poorly with gastric emptying of nondigestible solids (Sirois et al., 1990). However, a strong correlation between the differential emptying of non-digestible solids has been observed when the parameters are integrated and described by a buoyancy term (Amidon, 1985; Sirois et al., 1990). The hydrodynamic view of gastric emptying offers a rationale for the effect of microgravity on gastric emptying patterns. The basic forces acting on a particle traveling in a fluid are gravity (FG ), buoyancy (FB ) and drag (FD ). These forces can be combined and arranged into the following dimensionless ratio, Nv , of gravitational forces to viscous forces:
larger particles (Horowitz et al., 1994; Mroz and Kelly, 1997). The Pellet Gastric Emptying Test (PGET) was developed based on the principle of size-differentiated gastric emptying and involves the administration of enteric coated caffeine and acetaminophen pellets of 0.7- and 3.6-mm diameter, respectively. In earlier reports, the gastric emptying of pellets of varying sizes administered in humans under controlled conditions of meal viscosity (4000–8000 cP) and caloric value (100 kcal) was examined along with simultaneous monitoring of antral motility (Rhie et al., 1998). The results indicated that the plasma profiles of the drug markers were superimposable upon the underlying motility patterns most strikingly with the 4000 cP meal. The results further validated the supposition that smaller (0.7 mm) caffeine pellets emptied during the fed state and the larger (3.6 mm) APAP pellets emptied during the subsequent fasted state (Rhie et al., 1998). Furthermore, excellent correlations between plasma and saliva data have been reported (Rhie, 1996; Akinyinka et al., 2000; Carrillo et al., 2000), indicating that noninvasive monitoring of drug marker profile time events is possible. In the present report, we describe the results of studies to validate that gastric emptying of pellets is dependent on pellet size and not on the chemical make up of the particles. We also describe results of evaluation of PGET under a variety of gastric conditions to validate our hypothesis that despite variations in the emptying time of enteric-coated pellets as a function of nutrient conditions, size-differentiated gastric emptying would occur consistently.
2
F G* gDr d p Gravitational forces Nv 5 ] 5 ]] 5 ]]]]]] FD 18kn lh Viscous forces
(1)
where F *G represents the combination of FB and FG , g represents the gravitational constant, Dr represents the difference between particle density and fluid density, the product of g and Dr represents particle buoyancy, d p represents particle diameter, kn l represents average flow velocity, and h represents fluid viscosity (Amidon, 1985). Nv can also be viewed as a dimensionless velocity, equal to the Stokes sedimentation velocity divided by the average linear fluid flow velocity, expressed as follows: 2
gDr d p Settling velocity vs Nv 5 ] 5 ]] 5 ]]]]] Flow velocity kvl 18kn lh
(2)
where vs represents Stokes settling velocity (Amidon, 1985). The fundamental importance of Nv has been qualitatively verified in studies with both dogs and humans (Sirois et al., 1990; Amidon et al., 1991). In the absence of gravity, however, the buoyancy of solids is directly altered, and the influence of size and density on emptying patterns may also be significantly altered (Amidon et al., 1991). Thus, when gastric emptying is the rate limiting step for oral absorption, the onset of absorption of relatively smaller particles should occur before that of relatively
2. Materials and methods
2.1. Pellet dose Spherical caffeine (CAFF) pellets of 0.7 mm diameter and spherical acetaminophen (APAP) pellets of 0.7 and 3.6 mm in diameter were manufactured in collaboration with Pharmacia (Kalamazoo, MI) under cGMP guidelines. The pellet formulations contained sucrose non-pareils as the core with several suspension layers of sequentially coated drug (Glatt fluidized bed coater; Glatt Air Technologies; Ramsey, NJ) to achieve the target diameter, drug potency and enteric coat level. The pellets were enteric coated to prevent dissolution in the stomach and allow rapid dissolution in the small intestine. Previous in vitro studies demonstrated that in pH 2.0 media, drug release was not detected for 2 h. At pH 6.0, the onset of drug release was detected within 10 min for the formulations with a release fraction between 0.8 and 1.0 at the 20-min sampling time (Rhie et al., 1998). The pellet diameters determined in earlier studies using pycnometry were 0.6860.004 mm for 0.7-mm CAFF and 3.6260.001 mm for 3.6-mm APAP pellets, respectively (Rhie et al., 1998). The diameter of 0.7-mm APAP pellets measured with a digimatic microme-
S.Y. Choe et al. / European Journal of Pharmaceutical Sciences 14 (2001) 347 – 353
ter (Mitutoyo Digimatic Micrometer, Japan), was found to be 0.6860.03 mm.
2.2. Human protocol Twelve healthy human subjects (eight female and four male), ranging in age from 19 to 40 years (2466.6 years) and each within 20% of their ideal body weight, participated in this randomized four-way crossover trial. Prior to participation, the subjects gave written informed consent to the study that was approved by the Institutional Review Board at the University of Michigan. The subjects were deemed healthy based on medical history, physical examination, serum chemistries and complete blood count. The subjects refrained from medication, including over-thecounter medications, xanthine-containing foods and beverages for at least 72 h prior to the study. The subjects were admitted to the General Clinical Research Center at the University of Michigan Medical Center following an overnight fast. Subsequently, an indwelling venous catheter was placed in the forearm for blood sampling over a 12-h period and 5-ml blood samples were withdrawn and collected in heparinized Vacutainer vials. The sampling time points were: pre-dose and at 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, 180, 195, 210, 225, 240, 300, 360, 420, 480, 600 and 720 min following the administration of pellets. The subjects returned the next day for a 24-h blood sample. Blood samples were centrifuged at 10 000 rpm for 3 min, plasma was harvested and stored at 2208C until assayed. The randomized four-way crossover study consisted of four treatment phases: Same Size, Fasted, Small Liquid Meal, and Standard Meal. The Same Size Phase consisted of the administration of 0.7-mm enteric coated pellets containing 100 mg APAP and 0.7-mm enteric coated pellets containing 100 mg CAFF with 200 ml of a viscous caloric meal (viscosity 4000 cP, 100 kcal). This study was conducted to examine the effects of pellet size and chemical make-up on the in vivo release of APAP and CAFF from enteric coated pellets. The viscous caloric meal consisted of K15 / MP premium hydroxypropyl methylcellulose (HPMC, Dow Chemical, Midland, MI) and 100 kcal of glucose from the incorporation of a glucose tolerance beverage (Trutol 100, Costan Laboratories Inc., Baltimore, MD). The target viscosity of 4000 cP was achieved using the hot / cold dispersion method described in the Methocel Cellulose Esters Technical Handbook (Dow Chemical Company, 1988). The first 150 ml of the meal was ingested over 5 min to induce the fed state. Fifteen minutes later, the remaining 50 ml of the viscous caloric meal was administered along with the entire CAFF and APAP pellet doses. The subject’s mouth was then rinsed with 30 ml of water to ensure that no pellets remained in the oral cavity. The Fasted Phase consisted of the administration of 3.6-mm enteric coated pellets containing 500 mg APAP
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and 0.7-mm enteric coated pellets containing 100 mg CAFF with 240 ml of water following an overnight fast. The subject’s mouth was then rinsed with 30 ml water. The subjects remained fasted for 4 h following the ingestion of the marker compounds. The Small Liquid Meal Phase consisted of the administration of 3.6-mm enteric coated pellets containing 500 mg APAP and 0.7-mm enteric coated pellets containing 100 mg CAFF with 200 ml of viscous caloric meal (viscosity 4000 cP, 100 kcal). The first 150 ml of the meal was ingested over 5 min to induce the fed state. Fifteen minutes later, the remaining 50 ml of the viscous caloric meal was administered along with the entire CAFF and APAP pellet doses. The subject’s mouth was then rinsed with 30 ml of water to ensure that no pellets remained in the oral cavity. The Standard Meal Phase consisted of the administration of 3.6-mm enteric coated pellets containing 500 mg APAP and 0.7-mm enteric coated pellets containing 100 mg CAFF with 180 ml of orange juice 15 min after the administration of a standard high-fat breakfast. (The standard high-fat breakfast consisted of an English muffin with a large fried egg, a piece of ham, a slice of American cheese, one portion of hash browns and 240 ml of whole milk.) The meal had a total caloric value of 847 kcal, 13% of which was from protein, 35% from carbohydrates, and 52% from fat. Following the meal and pellet dose, the subject’s mouth was rinsed with 30 ml of water.
2.3. Drug analysis CAFF and APAP in plasma samples were assayed with HPLC as previously described by Rhie et al. (1998).
2.4. Data analysis Mean maximal plasma concentrations, Cmax and t max , time to Cmax , were determined by visual inspection of the available data points. AUC, the area under the curve, was calculated using the linear trapezoidal rule extrapolated to infinity from the last data point. t 1 / 2 , the elimination half-life, was determined by linear regression analysis of the terminal phase of the log concentration–time profile. t initial is defined as the first time point at which measurable drug marker appears in plasma, and Dt initial is defined as t initial APAP2t initial CAFF. Statistical analysis was performed using two-way analysis of variance, ANOVA, with Microsoft Excel 97. Differences between the means were evaluated using Tukey’s multiple range tests. The level of significance was set at 0.05. All data are reported as the mean6S.D.
3. Results All 12 subjects completed all four phases of the study. The study results of one subject, however, were excluded
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since baseline plasma in this subject showed the presence of acetaminophen in the Same Size, Fasted and Standard Meal Phases, a protocol violation. The mean plasma profiles of APAP and CAFF for the other 11 subjects for the various phases are shown in Fig. 1. The first time points where measurable levels of CAFF and APAP were obtained (t initial values) are listed in Table 1. The t initial values for APAP and CAFF for the Same Size Phase were 86648 and 94647 min, respectively. The differences in t initial values were found to be statistically insignificant (P.0.05). t initial values for both APAP (68623 min) and CAFF (60620 min) in the Fasted Phase were lower than those obtained in the Small Liquid Meal Phase (101635 min for APAP and 65631 min for CAFF, respectively) and Standard Meal Phase (160668 min for APAP and 127654 min for CAFF, respectively). The differences in the t initial values for the two drugs, Dt initial , (t initial for APAP2t initial for CAFF), are shown in Table 1 and plotted in Fig. 2. The t initial values for APAP and CAFF were significantly different from each other for Small Liquid Meal and Standard Meal Phases (P,0.05) and not significant for the Fasted Phase and Same Size Phases (P.0.05). In the Small Liquid Meal, Fasted and Standard Meal Phases, CAFF pellets were emptied and absorbed before APAP pellets. Dt initial values were: 35625 min for the Small Liquid Meal Phase, 8614 min for the Fasted Phase, 33634 min for the Standard Meal Phase, and 28612 min for the Same Size Phase. The negative sign for Dt initial in the Same Size Phase indicates that, on average, the APAP pellets emptied and were absorbed before the CAFF pellets. The pharmacokinetic parameters, t max , Cmax , AUC and t 1 / 2 for APAP and CAFF in the four treatment phases are listed in Table 2. For APAP, t max values were in the order: Fasted Phase (153645 min),Same Size Phase (180637 min),Small Liquid Meal Phase (229644 min),Standard Meal Phase (275681 min). For both Cmax and AUC of APAP, no statistical differences were detected between the Small Liquid Meal, Fasted and Standard Meal Phases (P.0.05). t 1 / 2 for APAP did not exhibit any statistically significant differences in the four Phases. For CAFF, t max values were in the order: Fasted Phase (157636 min), Small Liquid Meal Phase (187631 min),Same Size Phase (243683 min),Standard Meal Phase (3006100 min). For Cmax , AUC and t 1 / 2 of CAFF, however, there were no statistical differences between the four Phases (P.0.05).
4. Discussion The utility of size-differentiated PGET was evaluated under a variety of gastric conditions. The co-administration of same size enteric coated pellets of CAFF and APAP indicated that the t initial values for the two drug markers were similar and the differences statistically insignificant.
The similarity in time for the appearance of measurable marker following administration of same size enteric coated pellets suggests that both the gastric emptying of the pellets and the in vivo release rates of drugs from the pellets are similar. The similarity in t initial values for the two drugs in the Same Size Phase also suggests that any differences in this parameter that is elicited following co-administration of different sizes of the enteric coated pellets can be attributed to size differences alone. The t initial values for both APAP and CAFF displayed slowing of gastric emptying as the caloric intake increased from the Fasted Phase to the Small Liquid Meal Phase (100 kcal viscous meal) to the Standard Meal Phase (847 kcal high fat calorie meal). With APAP, the trend was more evident suggesting that emptying of the larger 3.6-mm pellets may be affected to a greater degree in the fed state. A likely possibility is that emptying of larger particles usually occurs with MMC and thus could be delayed in the fed state. The observed delayed emptying of both CAFF and APAP pellets in the fed state is consistent with previous reports that the gastric emptying rate of food decreases with an increase in the food’s energy density (kcal / ml) without regard to the proportion of fat, carbohydrate, or protein (Hunt, 1980). The time differential in emptying of 0.7-mm enteric coated CAFF pellets and of 3.6-mm enteric coated APAP pellets in the Fasted Phase was found to be statistically insignificant. However, the differences in emptying time of CAFF and APAP pellets were found to be significant in the Small Liquid Meal Phase (100 kcal, Dt initial 535625 min) and in the Standard Meal Phase (847 kcal, Dt initial 533634 min). The lower value of Dt initial for the Fasted Phase compared to the values for the Small Liquid Meal and Standard Meal Phases is of significance. Thus, the emptying of CAFF and APAP pellets appears to be closer to each other in the fasted state than in the fed state. If emptying of APAP is dependent on the MMC phase, albeit phase III, then one would expect that the actual phase of MMC at the time of dosing would determine emptying patterns. Since dosing in the fasted state was carried out without regard to MMC phase, it is likely that MMC effects on emptying of APAP pellets would not be evident under such dosing conditions. The trends in t max values for both APAP and CAFF were similar to those observed with t initial values in the Small Liquid Meal, Fasted and Standard Meal Phases. Finally, the lack of statistically significant differences in pharmacokinetic parameters Cmax , AUC, and t 1 / 2 for both APAP and CAFF for various administration phases suggests that the observed size-differentiated gastric emptying patterns were not due to different gastric conditions (P. 0.05). In summary, the combined results of our studies with co-administration of enteric coated CAFF and APAP pellets suggest that size-differentiated gastric emptying appears to occur in the fed state. The results of the present
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Fig. 1. Mean plasma concentration profiles (expressed as mean6S.D.) of acetaminophen (APAP, s) and of caffeine (CAFF, d) in human subjects following oral administration of enteric coated pellets under various conditions (n511). Inserts show 90-min post-dose mean plasma concentration profiles of APAP and CAFF in linear scale.
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Table 1 Summary of t initial parameters (expressed as mean6S.D.; min) following oral administration of enteric coated acetaminophen (APAP) and caffeine (CAFF) pellets under various treatment conditions (n511) Phase
t initial APAP (min)
t initial CAFF (min)
Dt initial (t initial APAP2t initial CAFF)
Same Size Phase Fasted Phase Small Liquid Meal Phase Standard Meal Phase
86648 68623 101635 160668
94647 60620 65631 127654
28612 8614 35625 33634
Fig. 2. Plots of t initial parameters (expressed as mean6S.D.; min) following oral administration of enteric coated acetaminophen (APAP) and caffeine (CAFF) pellets under various treatment conditions (n511). *Significant difference (P,0.05) between APAP and CAFF.
study taken together with earlier reports on simultaneous motility monitoring following oral administration of the pellets also indicate that gastric emptying patterns of the pellets may closely reflect motility effects on gastric emptying. Thus, the Pellet Gastric Emptying Test (PGET)
may be a convenient method by which to assess the influence of motility patterns on the absorption profiles of orally administered agents. For example, the co-administration of APAP and CAFF pellets as marker drugs along with a potential therapeutic agent can help determine its
Table 2 Summary of pharmacokinetic parameters (expressed as mean6S.D.) following oral administration of enteric coated acetaminophen (APAP) and caffeine (CAFF) pellets under various treatment conditions (n511) Phase
Same Size Meal Fasted Phase Small Liquid Meal Phase Standard Meal Phase a
Acetaminophen (APAP)
Caffeine (CAFF)
t max (min)
Cmax (mg / ml)
AUC (mg min / ml)
t1 / 2 (min)
t max (min)
Cmax (mg / ml)
AUC (mg min / ml)
t1 / 2 (min)
180 (637) 153 (645) 229 (644) 275 (681)
1.19 a (60.36) 3.85 (61.01) 3.13 (60.97) 2.84 (61.31)
285.4 a (696.0) 864.8 (6242.1) 988.1 (6386.6) 1059.0 (6371.9)
128 (638) 137 (635) 152 (646) 233 (6185)
243 (683) 157 (636) 187 (631) 300 (6100)
1.52 (60.37) 1.87 (60.96) 1.37 (60.40) 1.15 (60.39)
901.1 (6461.5) 985.6 (6742.1) 1010.1 (6902.1) 907.3 (6627.9)
371 (6239) 380 (6274) 378 (6194) 502 (6239)
APAP was not normalized to 500-mg dose.
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gastric emptying pattern by simple comparisons of the appropriate t initial values. Further, PGET may also be of aid in determining dosing strategies for drugs that exhibit gastric emptying rate-limited absorption and that require a stratified dosing regimen, as it can delineate the relevant gastric motility phases (e.g. fed vs. fasted) and thereby provide reliable reference times for dosing. As a practical and cost-effective diagnostic tool to assess gastric emptying, the PGET can serve as a preferred clinical asset to routinely aid in management of patients with gastrointestinal complaints. Finally, the excellent correlation between plasma and saliva profiles of the marker drugs observed in a previous study, confers non-invasive attributes to the PGET that may be of vital importance when monitoring patients such as the elderly or the pregnant or those that are recovering from surgery.
Acknowledgements This work was supported by NASA Grant NAG5-3874 and the General Clinical Research Center (GCRC), University of Michigan, funded by a Grant (M01 RR00042) from the National Center for Research Resources, National Institutes of Health, US PHS. The authors would like to thank the Pharmacia Company for its generous donation of resources and materials in the manufacture of the pellets. We thank the nurses at the General Clinic Research Center at the University of Michigan Medical Center for their support and assistance in this study.
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