Predicting Pharmacokinetics of Multisource Acyclovir Oral Products Through Physiologically Based Biopharmaceutics Modeling

An industrial procedure for the intestinal permeability enhancement of acyclovir: in-vitro and histological evidence

Acyclovir, an antiviral drug, has low bioavailability due to its low permeability. Consequently, high drug doses and frequent administration are required. This study investigates the use of span 60, at different concentrations, as a granulating agent to enhance drug permeability using an industrial procedure on a pilot scale. The micromeritics, drug content, drug crystallinity, drug partition coefficient, and drug release of the produced formulations were examined. The findings revealed an enhanced drug partition coefficient, suggesting drug entrapment in the polar portion of span 60. The drug release profiles exhibited rapid and complete drug release. The improvement of the drug permeability was evaluated using a modified non-everted sac technique. Notably, drug permeability through the rabbit intestine significantly improved, as evidenced by various calculated permeation parameters, providing insights into the drug absorption mechanism. The widening of the paracellular pathway was observed through histological examination of the rabbit intestinal segment, which aligns with the drug absorption mechanism. The utilization of a paracellular pathway enhancer as a granulating agent holds promise as a strategy to enhance the oral bioavailability of class III drugs. Overall, this study presents a novel drug delivery approach to enhance drug permeation and bioavailability, with potential implications for other medications.

Novel food drug interaction mechanism involving acyclovir, chitosan and endogenous mucus

Drug absorption from drug products may be affected by pharmaceutical excipients and/or food additives through different mechanisms. Chitosan is a recognized nutraceutical, with potential as an excipient due to its permeability enhancer properties. While chitosan properties have been evaluated in in vitro and pre-clinical models, studies in humans are scarce. Unexpectedly, a controlled clinical trial showed chitosan actually reduced acyclovir bioavailability. The effect seems to be related to an interaction with gastrointestinal mucus that prevents further absorption, although more in depth research is needed to unravel the mechanism. In this paper, we propose a mechanism underlying this excipient effect. The mucus - chitosan interaction was characterized and its effect on acyclovir diffusion, permeation and bioaccessibility was investigated. Further, pharmacokinetic modeling was used to assess the clinical relevance of our findings. Results suggest that in situ coacervation between endogenous mucus and chitosan rapidly entrap 20-30% of acyclovir dissolved dose in the intestinal lumen. This local reduction of acyclovir concentration together with its short absorption window in the small intestine would explain the reduction in acyclovir C_max and AUC. This study highlights the importance of considering mucus in any biorelevant absorption model attempting to anticipate the effect of chitosan on drug absorption.

The Use of Physiologically Based Pharmacokinetic Analyses-in Biopharmaceutics Applications -Regulatory and Industry Perspectives

The use of physiologically based pharmacokinetic (PBPK) modeling to support the drug product quality attributes, also known as physiologically based biopharmaceutics modeling (PBBM) is an evolving field and the interest in using PBBM is increasing. The US-FDA has emphasized on the use of patient centric quality standards and clinically relevant drug product specifications over the years. Establishing an in vitro in vivo link is an important step towards achieving the goal of patient centric quality standard. Such a link can aid in constructing a bioequivalence safe space and establishing clinically relevant drug product specifications. PBBM is an important tool to construct a safe space which can be used during the drug product development and lifecycle management. There are several advantages of using the PBBM approach, though there are also a few challenges, both with in vitro methods and in vivo understanding of drug absorption and disposition, that preclude using this approach and therefore further improvements are needed. In this review we have provided an overview of experience gained so far and the current perspective from regulatory and industry point of view. Collaboration between scientists from regulatory, industry and academic fields can further help to advance this field and deliver on promises that PBBM can offer towards establishing patient centric quality standards.