(M0930-02-07) Using the In Vitro Dissolution Absorption System (IDAS) to Evaluate the Effects of Excipients on the Permeation of Putative Biopharmaceutics Classification System Class III Drugs

Purpose: Currently, the ICH M9 guideline allows biowaivers of in vivo bioequivalence (BE) studies with pharmacokinetic endpoints for Biopharmaceutics Classification System (BCS) Class I drugs (highly soluble and highly permeable) and BCS Class III drugs (high solubility, low permeability). However, the current criteria for excipient similarity for Class III drug products are quite stringent (i.e., Q1 the same and Q2 very similar), which may have led to underutilization of the BCS biowaiver pathway for this class of drugs. In addition, there is a need for a robust, predictive in-vitro testing system for evaluating the effects of excipients on drug permeation. A novel in vitro technology, the in-vitro dissolution absorption system (IDAS), was used to evaluate the effects of common excipients on the permeation of a cassette of five model drugs across Caco-2 cell monolayers. Four of the model drugs (acyclovir, atenolol, cimetidine, and ranitidine) are BCS Class III, and one (minoxidil) is BCS Class I.

Methods: IDAS is comprised of a dissolution vessel and two permeation chambers, with polarized monolayers of Caco-2 cells mounted in the interface between the dissolution and permeation chambers. Caco-2 cells were seeded on collagen-coated, 6-well, polycarbonate membranes in Costar Snapwell^® plates (0.4 µm pore size) and maintained in culture until confluent, polarized cell monolayers were established (21-28 days). Snapwell inserts with Caco-2 cell monolayers were mounted vertically in IDAS permeation chambers. The donor medium (for the dissolution chamber) was fasted-state simulated intestinal fluid (FaSSIF), pH 6.5; the receiver buffer (in the permeation chamber) was Hanks’ balanced salt solution (HBSS) with added glucose, HEPES buffer, pH 7.4, and 4.5% BSA. Each IDAS dissolution chamber was filled with dosing solution, consisting of a cassette of five model drugs with or without excipients. Fifteen excipients, representing all major functional classes, were evaluated across a range of pharmaceutically relevant concentrations. A negative control (no excipients) and a positive control (sodium lauryl sulfate (SLS) at 0.6%, a higher concentration than the range used for SLS as an excipient) were run in parallel with each set of excipient treatments, which were run with n=3 dissolution chambers/6 permeation chambers in a total of 18 separate experiments. Two permeation chambers were lowered into each dissolution chamber to start the permeation experiment. Multiple receiver samples were collected over the course of the 120-minute permeation experiment. The extended exposure time in vitro is necessary to allow measurable amounts of drug to permeate to the receiver side of the cell monolayers and differs from the transient exposure of a given intestinal enterocyte in vivo. Samples were analyzed by LC-MS/MS and apparent permeability (P­_app) values were calculated.

Results: Only a few of the tested excipients produced obvious, dose-dependent effects on the permeation of any of the 5 model drugs, including 4 Class III drugs. Seven of the excipients (hydroxypropyl methylcellulose at two viscosities, microcrystalline cellulose, croscarmellose sodium, talc, mannitol, and silicon dioxide) had no effect on the permeation of any of the Class III model drugs, and another seven (povidone K30, magnesium stearate, lactose, calcium phosphate, pregelatinized starch, PEG-400, and sorbitol) had minor effects, generally not dose-dependent, on only one or two of the model drugs.  Sodium lauryl sulfate (SLS), a known absorption enhancer in vitro, was the only excipient that caused dose-dependent increases in the permeation of all model drugs (BCS Class I and III). Our IDAS results showed that the majority of the tested excipients, within the investigated concentration ranges, did not significantly impact the permeation of the BCS Class III model drugs.

Conclusion: The IDAS appears to be a useful platform for evaluating excipient effects. As the in-vitro study design tests the worst-case scenario of a long exposure to a constant concentration of drug substance and excipient, if the IDAS demonstrates no effect of a given excipient on the permeation of a BCS Class III drug, the excipient may have no impact on in vivo permeation either. The results raise the possibility of extending the biowaiver pathway to BCS Class III generic drug products that are Q1 not the same as, and/or Q2 dissimilar to, the reference product

Acknowledgments:

Funding: FDA BAA contract 75F40119C10127, Expanding BCS Class 3 Waivers for Generic Drugs to Non-Q1/Q2 Formulations

* Both the mean of the treatment and the mean of the negative control were outside the range of two standard deviations of the other