Dose-Dependent Inhibition of Transporter-Mediated Hepatic Uptake and Biliary Excretion of Methotrexate by Cyclosporine A in an Isolated Perfused Rat Liver Model

Methotrexate (MTX) and cyclosporine (CyA) are coadministered in a number of diseases. In this study, the effects of CyA on the hepatobiliary disposition of MTX were investigated in an isolated perfused rat liver model. A bolus 5-mg dose of MTX was added to a recirculating perfusate in the absence or presence of a relatively low (0.5 mg) or high (2.5 mg) dose of CyA or vehicle pretreatment, and perfusate, bile, and terminal liver samples were collected for analysis by high-performance liquid chromatography (HPLC). In control and vehicle groups, MTX showed a low hepatic extraction ratio (~ 0.1) and was almost completely eliminated by excretion into the bile. The low-dose CyA significantly reduced (60%) the hepatic extraction ratio and clearance of MTX, without affecting the bile/liver concentration ratio, suggesting inhibition of sinusoidal uptake of MTX only. In contrast, the high-dose CyA significantly reduced both hepatic uptake and Mrp2-mediated biliary excretion of MTX. Isolated rat hepatocyte uptake studies showed significant inhibition of [3H]MTX uptake in the presence of CyA. It is concluded that CyA significantly alters the hepatobiliary disposition of MTX by inhibiting its sinusoidal uptake and/or biliary transport, potentially reducing enterohepatic recirculation of the drug in vivo.