(M1430-05-28) Assessing Gastric Emptying of Gastro-Resistant Capsules in Pigs: Impact of Capsule Size

Purpose: The translation of emerging therapies from preclinical models to clinical applications remains a crucial aspect of pharmaceutical R&D [1]. While there have been considerable advancements in biopredictive in vitro and in silico tools, preclinical animal models remain essential for evaluating drug mechanisms, efficacy, and safety [2]. The pig, a preclinical model with a digestive system comparable to humans [3], demonstrated limitations as large monolithic capsules experienced significantly prolonged and variable gastric emptying compared to humans [4,5]. A critical knowledge gap remains regarding the impact of clinically relevant gastro-protective dosage forms on gastric emptying in pigs. Prokinetic agents, which promote gastric emptying in humans [6] have been suggested as a potential solution to address the prolonged and variable gastric emptying times in pigs[7]. The present study aimed to address these gaps by assessing the impact of clinically relevant gastro-protective oral formulations on paracetamol pharmacokinetics, thereby evaluating gastric emptying differences in pigs, and investigating the potential of metoclopramide as a prokinetic agent to accelerate gastric clearance. ALICAM® endoscopic capsules were employed to visually monitor the retention and transit of gastro-resistant capsules in the stomach.

Methods: This study investigated gastric emptying of gastro-protective capsules in eight fasted male Landrace pigs, assessed by the absorption profiles of paracetamol and caffeine, marker drugs whose early plasma presence correlates with gastric emptying [7,8]. A non-randomized, four-way crossover design was used, evaluating gastro-protective Capsugel® Enprotect® capsules (see Table 1) filled with paracetamol in three sizes (size 2, size 1, and size 0). A fourth treatment group included pre-treatment with 0.1 mg/kg metoclopramide intramuscularly 30 minutes before dosing a size 1 capsule. Caffeine immediate-release (IR) tablets were administered simultaneously for comparison. Capsule endoscopes (ALICAM®; 11 mm x 33 mm) were orally administered to visually monitor gastro-resistant capsule transit. Blood samples were collected at predefined time points up to 24 hours post-dosing. Paracetamol and caffeine plasma concentrations were determined using liquid-liquid extraction and reversed-phase HPLC methods adapted from [9], with ethyl acetate  as extraction agent and 2-acetamidophenol as internal standard. Pharmacokinetic parameters, including maximum plasma concentration (C_max), time to maximum plasma concentration (T_max), area under the plasma concentration-time curve (AUC), mean residence time (MRT_po), mean absorption time (MAT), bioavailability (F) and cumulative AUC/AUC_total were determined from the corresponding plasma concentration-time profiles, using non-compartmental analysis, or calculated based on porcine iv data [7].

Results: All capsule sizes exhibited similar gastric emptying kinetics. The median MAT, T_max, C_max, AUC_0→8, and cumulative AUC/AUC_total of paracetamol from gastro-protective Capsugel® Enprotect® capsules are presented in Figure 1. While certain trends, as seen in Figures 1B, 1D, and 1E, might indicate a tendency towards accelerated gastric emptying with reduced capsule dimensions, none of the differences in any of the pharmacokinetic parameters were statistically significant (p > 0.05). The T_max values of the IR tablets did not differ significantly from those of the gastro-resistant capsules (p = 0.4765). The T_max of gastro-resistant capsules (3.0 – 10.0 hours) were comparable to that of IR paracetamol tablets reported in previous studies [7,9] and did not differ significantly from the T_max of caffeine (2.0 – 9.0 hours) from IR tablets (p = 0.4765). A comparison with previously published human data [10,11] suggests that gastric emptying is prolonged in pigs for both IR and gastro-resistant formulations. Furthermore, the pre-treatment with metoclopramide did not result in a significant difference in any of the pharmacokinetic parameters (p > 0.05). The respective median MAT, T_max, C_max, AUC_0→8, and cumulative AUC/AUC_total are presented in Figure 2. None of the recovered ALICAM® capsule endoscopes were observed to be emptied from the stomach within the battery life (20 hours) as indicated by the video footage. Although suspected Capsugel® Enprotect® capsules were observed, the images were insufficient to definitively confirm their presence or absence in the stomach due to the camera’s resolution and the frequent loss of visual contact when capsules moved out of the camera’s field of view.

Conclusion: In this study, all capsule sizes exhibited consistent gastric emptying with MAT values of 3.9 to 8.1 hours, demonstrating the suitability of pigs as a preclinical model in studies with clinically relevant oral dosage forms. Gastric emptying in pigs was found to be longer than in humans for both IR and gastro-resistant dosage forms, aligning with prior findings and necessitating careful consideration in human scaling predictions. The administration of metoclopramide did not significantly influence gastric emptying, suggesting that it does not offer substantial benefits. These findings contribute to a more comprehensive understanding of gastric emptying in pigs and underscore their value as a preclinical model in oral delivery.

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Acknowledgements: The study was conducted in compliance with the license granted by the Health Products Regulatory Authority (HPRA) of Ireland under the European Union (Protection of Animals Used for Scientific Purposes) Regulations 2012 (as amended) and Directive 2010/63/EU of the European Parliament (license number AE19130/P202). Ethical approval was obtained from the local university ethics committee. Funding for this work was provided under the GENEGUT (https://genegut.eu/) project funded by the European Commission as a Horizon Europe Research and Innovation Action (RIA) under the call tools and technologies for a healthy society (2021) (HORIZON-HLTH-2021-TOOL-06). Material support was provided by Capsugel France SAS (Colmar, France) by supplying the Capsugel® Enprotect® capsules used in this study. Vincent Jannin discloses an affiliation with Capsugel France SAS (Colmar, France) that encompasses his current employment. There are no other known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.


Table 1. Characteristics of administered formulations: Outer dimensions (in mm), dose of paracetamol (Capsugel® Enprotect® capsules, in mg) or caffeine (PROPLUS® tablets, in mg), and total weight of the filled capsule/tablet (in mg)


Figure 1. A Mean absorption time (MAT, hours), B time to maximum plasma concentration (Tmax, hours), C weight- and dose-adjusted maximal plasma concentration (Cmax, ng/(mL·kg)), and D weight- and dose-adjusted area under the curve (AUC0→8, ng⋅h/(mL⋅kg)) following oral administration of Capsugel® Enprotect® paracetamol capsules of size 0 (●, 350 mg), size 1 (∎, 250 mg), and size 2 (▲, 200 mg) (Median and individual values, N = 5); differences were non-significant (p > 0.05); E Cumulative AUC/AUCtotal (%) over 24 hours (Mean ± SEM, N = 5)


Figure 2. A Mean absorption time (MAT, hours), B time to maximum plasma concentration (Tmax, hours), C weight- and dose-adjusted maximal plasma concentration (Cmax, ng/(mL·kg)), and D weight- and dose-adjusted area under the curve (AUC0→8, ng⋅h/(mL⋅kg)) following oral administration of Capsugel® Enprotect® capsules; E Cumulative AUC/AUCtotal (%) over 24 hours with (●) and without (∎) prior intramuscular injection of 0.5 mg/kg metoclopramide (MCP) (Mean ± SEM, N = 4)