AN IN-VITRO METHOD FOR PREDICTING IN-VIVO ORAL BIOAVAILABILITY OF NOVEL IMMUNOSUPPRESSIVE DRUGS

Objective: To evaluate an in vitro method for predicting oral availabi lity of novel immunosuppressive drugs, cyclosporine A (CsA) and rapamy cin (RAPA). Methods: In this study, we report the development and char acterization of an in vitro method to study the influence of vehicle c omposition on cyclosporine A (CsA) and rapamycin (PAPA) drug efflux ac ross 12 days postconfluent, absorptive human Caco-2 intestinal epithel ial cell monolayers. The apical-to-basal (J(ab)) and the basal-to-apic al (J(ba)) fluxes of 0.5 mu Ci H-3-CsA or 0.05 mu Ci C-14-RAPA solubil ized in a 10 mg/L final drug concentration in vehicle were measured. R esults: The J(ab) CsA flux was found to be dose dependent, temperature sensitive, and highly polarized (J(ab) > J(ba)). For CsA the vehicles were Neoral(R) Sandimmune(R), 95% (v/v) ethanol/fetal bovine serum (e thanol/FBs); and for PAPA these were polyethylene glycol/dimethylaceta mide (PEG/DMA), polysorbate/Phosal PEG, ethanol/FBS. When Neoral(R)-Cs A was tested, the J(ab) flux of H-3-CsA was the highest and increased almost linearly even after an incubate time of 240 min. The J(ab) flux of H-3-CsA when Sandimmune(R)-CsA or ethanol/FBS-CsA were used as veh icle was lower and reached a maximal rate by 120 min. In contrast the J(ab) flux of C-14-RAPA using either PEG/DMA-RAPA or ethanol/FBS-RAPA as vehicle was highest and reached a maximal rate by 120 min, in contr ast to the polysorbate/Phosal PEG-RAPA vehicle, which was significantl y lower. Conclusion: These data are consistent with the pharmacokineti cs of these ISD reported in vivo in human patients or in rabbits, usin g the same vehicles in the oral formulation. As an integral part of dr ug development, the data presented that an in vitro system as describe d may be useful in predicting the effect of drug vehicle on absorption in vivo.