The gastric emptying of hard gelatin capsules

Disposition of two highly permeable drugs in the upper gastrointestinal lumen of healthy adults after a standard high-calorie, high-fat meal

OBJECTIVES

To quantify the presence of two model highly permeable drugs, paracetamol and danazol, in the upper gastrointestinal lumen under conditions simulating the situation after disintegration of immediate release dosage forms administered in bioavailability/bioequivalence studies in the fed state. To understand the drug transfer process from the antral contents through the upper small intestine based on luminal drug data.

METHODS

8 healthy male adult volunteers participated in a randomized, single dose, two-phase, crossover study. After evaluating the impact of homogenization on meal's viscosity and particle size, the meal, containing phenol red as non-absorbable marker, was administered to the antrum via the gastric lumen of a naso-gastro-intestinal tube. The drugs were administered in solution form (Phase I) and in suspension form (Phase II) with a glass of tap water to the antrum of the stomach, 30 min after the initiation of meal administration. Samples were aspirated from the antrum and the upper small intestine up to 4 hours post drug administration.

RESULTS

Apparent concentrations in the aqueous contents of the antrum were higher than apparent concentrations in the micellar contents of the upper small intestine for paracetamol; the opposite was observed for danazol. Based on total drug amount per volume data in contents of the upper gastrointestinal lumen, the transfer of paracetamol (aqueous solution or suspension) and danazol (aqueous suspension) through the upper small intestine could be described as an apparent first-order process. Transfer of a long-chain triglyceride solution of danazol was highly variable.

CONCLUSIONS

Concentrations in the aqueous/micellar phase of luminal contents and values of parameters controlling the transfer from bulk gastric contents through the upper small intestine after a high-calorie, high-fat meal, were reported for the first time for highly permeable drugs. Data are expected to enhance the development of biorelevant in vitro and physiologically based biopharmaceutics modelling methodologies.

Gastric emptying of pellets under fasting conditions: a mathematical model

PURPOSE

To develop a mathematical model that would adequately describe human gastric emptying of pellets under fasting conditions of healthy subjects.

METHODS

Scintigraphic profiles representing the gastric emptying of pellets were obtained from the literature. Altogether 19 individual and three mean scintigraphic profiles were collected. Three mathematical models namely; the lag-time exponential (two parameters), the Weibull (two parameters), and the double Weibull (five parameters) model were proposed and fitted to the gastric emptying profiles.

RESULTS

Different patterns of gastric emptying (immediate and rapid, delayed but rapid, delayed and slow, and interruptive emptying) were observed, with the emptying time varied from approximately 15 min to more than 3 h. The best model for fitting to the individual profiles was the double Weibull model. This model also provided an insight into the mechanism of interruptive emptying of pellets, observed for some patients. In addition, mean gastric emptying of pellets was calculated using the Weibull model.

CONCLUSIONS

Mean gastric emptying of pellets was adequately described by the Weibull model (eta = 61.9 min, beta = 0.895), which could be applied in the design of in vitro dissolution experiments for pellet formulations with pH dependent dissolution.

In situ studies of regional absorption of lobucavir and ganciclovir from rabbit intestine and predictions of dose‐limited absorption and associated variability in humans

The regional absorption of lobucavir (LBV), an experimental antiviral agent, and ganciclovir (DHPG) was investigated in rabbit intestine using an in situ single-pass perfusion technique. Duodenal, jejunal, and colonic segments in anesthetized rabbits were perfused with drug solutions in a hypotonic buffer at 0.2 mL/min. Effluent perfusate samples for drug analysis were collected every 10 min for 180 min. To account for water absorption during perfusion, an intestinal absorption model was developed to estimate the absorptive clearance (PeA): PeA=Qavexln((QinxCin)/(QoutxCout)), where Qave is a logarithmic average of the inflow (Qin) and outflow perfusion rate (Qout); Cin and C(out) are drug inflow and outflow concentrations. The PeA of LBV in the duodenum and jejunum was 2.1+/-0.77 and 1.7+/-0.46 microL/min/cm (n=3), respectively, 4.8- and 3.0-fold higher than that of DHPG in the same animals. However, LBV PeA decreased significantly in the colon (0.47+/-0.11 microL/min/cm) and was similar to that of DHPG which exhibited no regional differences in absorption. The interplay between PeA and solubility was studied using a compartmental absorption and transit model, and simulations were performed to investigate dose-limited absorption and the sources of variability in absorption where two compounds differ significantly. The dose range where absorption started to decrease was predicted using the model, with LBV exhibiting the phenomenon at a lower dose than DHPG (450 vs. 750 mg). Furthermore, the intersubject variability in human absorption of both compounds was reproduced when the variability in both PeA and the small intestinal transit time was considered in the model. The variability in the ascending colonic transit time also contributed to the intersubject variability observed for DHPG. The results demonstrate value of integrating in situ studies and modeling in predicting these absorption characteristics.

Gastrointestinal transit of liquids in unfed cynomolgus monkeys

In this study, the gastric emptying rate and oro-caecal transit time of two liquid volumes (20 and 60 ml) were compared in unfed cynomolgus monkeys. First, the acetaminophen method was used to determine the gastric half-emptying time (t(50%)). The mean t(50%) from seven monkeys was 21.2 min for the 20-ml volume and 27.8 min for the 60-ml volume. This mean t(50%) in monkeys is similar to that reported previously in fasting humans. Next, the sulfasalazine-sulfapyridine method was used to determine median oro-caecal transit times for the 2 liquid volumes; these times were 2.5 h for the 20-ml volume and 2.3 h for the 60-ml volume, which are about 1.5 h shorter than previously reported transit times in humans. An increase in volume administered did not significantly change either the t(50%) or oro-caecal transit time. The data also show that variability in both t(50%) and oro-caecal transit time within each monkey is not as great as the large variability between monkeys. Consequently, cynomolgus monkeys are good model animals to use for studies on the gastric emptying of drug-containing liquids after fasting; however, analysis of results from bioavailability studies must compensate for differences in the oro-caecal transit time between monkeys and humans.

The influence of the interdigestive migrating myoelectric complex on the gastric emptying of liquids

It is unknown how the interdigestive migrating motor complex influences the gastric emptying of liquids. Therefore, the gastric emptying rate of 50- and 200-mL volumes of phenol red solution were measured while monitoring contractile activity. Motor activity was recorded using a hydraulic manometric system and expressed as either the proximity of dosing time to time of appearance of phase III or as a motility index, defined as (contractile area)/(sampling interval time). After an initial lag period, emptying was log linear. With a 50-mL oral dose, the mean gastric emptying rate of the log-linear phase was successively faster during phase I (0.018 +/- 0.003 min-1), phase II (0.083 +/- 0.031 min-1), and late phase II/III (0.171 +/- 0.066 min-1) (P less than 0.05). Similarly, the mean lag time decreased successively with phases I, II, and late II/III (19.1 +/- 12.4, 7.6 +/- 5.6, and 3.8 +/- 2.8 minutes, respectively). At a 200-mL oral dose, there was no difference in the emptying rate between phase I and phase II (0.104 +/- 0.0014 vs. 0.110 +/- 0.041 min-1), but the emptying rate during late phase II/III was significantly greater (0.236 +/- 0.069 min-1); lag time was not dependent on phase. There was a statistical difference in the overall mean emptying rate between the 50- and 200-mL volumes. Also, during phase I, the emptying rate was faster for the 200-mL volume. This study shows a strong dependence of liquid gastric emptying rate and lag time on interdigestive antral motility, the emptying of small volumes being more dependent on motility phase than that of large volumes. Phase-related fluctuations in contractile activity can account for much of the reported variability in gastric emptying data. Furthermore, this study suggests that dose volume and interdigestive motor activity at the time of drug administration can affect absorption and onset of therapeutic response for some drugs.

Estimation of gastric residence time of the Heidelberg capsule in humans: effect of varying food composition

In animal and human studies, the gastric emptying of large (greater than 1 mm) indigestible solids is due to the activity of the interdigestive migrating myoelectric complex. The gastric residence time (GRT) of an orally administered, nondigestible, pH-sensitive, radiotelemetric device (Heidelberg capsule) was evaluated in three studies in healthy volunteers. In 6 subjects, the GRT of the Heidelberg capsule was compared with the half-emptying time (t1/2) of diethylenetriaminepentaacetic acid labeled with technetium 99m after a 4-ml/kg liquid fatty meal. The mean (+/-SD) GRT (4.3 +/- 1.4 h) was significantly (p less than 0.001) longer than the mean t1/2 (1.1 +/- 0.3 h); the GRT was prolonged compared with the t1/2 in each subject. In a randomized, crossover trial in 10 subjects, frequent feeding caused a dramatic prolongation in mean GRT of the capsule compared with the fasting state (greater than 14.5 vs. 0.5 h, p less than 0.005). In another crossover study in 6 subjects, the GRT of the capsule was evaluated after an overnight fast, a standard breakfast including solid food, and a liquid meal (i.e., 200 ml of diluted light cream). The mean GRT was 2.6 +/- 0.9 h after the liquid meal vs. 1.2 +/- 0.8 h after fasting (p less than 0.025). The mean GRT after the breakfast was 4.8 +/- 1.5 h, which was significantly greater than that after fasting (p less than 0.001) and after the liquid meal (p less than 0.01). These data suggest that the GRT of the Heidelberg capsule is a marker of the interdigestive migrating myoelectric complex in humans, the interdigestive migrating myoelectric complex can be markedly delayed by frequent feedings with solids, and the interdigestive migrating myoelectric complex is delayed by both liquid and solid meals.

Effect of stress on the gastric emptying of capsules

During a series of experiments on the gastric emptying of capsules, certain subjects were exposed to stress in the form of high noise levels. In the non-fasting condition, these subjects showed a significantly faster gastric emptying than those who were not exposed to the stress.