A swine model was developed to study quantitatively the pharmacokinetics of hepatic extraction and clearance of doxorubicin (DOX). Systemic and hepatic artery infusions of DOX (0.5-9 mg kg-1) were administered to 34 pigs. Pharmacokinetic analysis was simplified by use of a double-balloon catheter in the inferior vena cava to collect hepatic venous effluent. During hepatic artery infusion only, DOX in hepatic venous blood was extracted using activated carbon filters to prevent drug recirculation. Hepatic extraction and clearance of DOX were independent of dose and route of administration. Extraction ratios varied from 0.75 to 0.91 during hepatic artery infusion and from 0.50 to 0.72 during systemic infusion. Clearance results were analogous. After cessation of drug infusions, hepatic extraction and clearance of DOX was negative, suggesting that the liver serves as a drug reservoir during DOX infusion and subsequently is a net source of unmetabolised drug. Liver extraction and clearance of DOX in pigs are substantial. During either systemic or hepatic artery infusion of DOX, the liver serves as a drug reservoir. Subsequent mobilisation of this hepatic pool of DOX may cause prolonged systemic exposure to drug.
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