An In Vitro Method for Predicting In Vivo Oral Bioavailability of Novel Immunosuppressive Drugs

Objective: To evaluate an in vitro method for predicting oral availability of novel immunosuppressive drugs, cyclosporine A (CsA) and rapamycin (RAPA). Methods: In this study, we report the development and characterization of an in vitro method to study the influence of vehicle composition on cyclosporine A (CsA) and rapamycin (RAPA) drug efflux across 12 days postconfluent, absorptive human Caco-2 intestinal epithelial cell monolayers. The apical-to-basal (Jab) and the basal-to-apical (Jba) fluxes of 0.5 μCi3H-CsA or 0.05 μCi 14C-RAPA solubilized in a 10 mg/L final drug concentration in vehicle were measured. Results: The Jab CsA flux was found to be dose dependent, temperature sensitive, and highly polarized (Jab> Jba). For CsA the vehicles were NeoralR, SandimmuneR, 95% (v/v) ethanol/ fetal bovine serum (ethanol/FBS); and for RAPA these were polyethylene glycol/dimethylacetamide (PEG/DMA), polysorbate/Phosal PEG, ethanol/FBS. When NeoralR-CsA was tested, the Jab flux of 3H-CsA was the highest and increased almost linearly even after an incubate time of 240 min. The Jab flux of 3H-CsA when SandimmuneR-CsA or ethanol/FBS-CsA were used as vehicle was lower and reached a maximal rate by 120 min. In contrast the Jab flux of 14C-RAPA using either PEG/DMA-RAPA or ethanol/FBS-RAPA as vehicle was highest and reached a maximal rate by 120 min, in contrast to the polysorbate/Phosal PEG-RAPA vehicle, which was significantly lower. Conclusion: These data are consistent with the pharmacokinetics of these ISD reported in vivo in human patients or in rabbits, using the same vehicles in the oral formulation. As an integral part of drug development, the data presented that an in vitro system as described may be useful in predicting the effect of drug vehicle on absorption in vivo.