Inhibition of paclitaxel elimination in the isolated perfused rat liver by Cremophor EL
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Purpose: Cremophor can alter the pharmacokinetics of cytotoxic drugs, including doxorubicin and etoposide. In view of its presence in the formulation of paclitaxel, the aim of this study was to investigate the influence of Cremophor on the hepatobiliary elimination of paclitaxel. Methods: In a recirculating isolated perfused rat-liver system the elimination of 1.7 mg paclitaxel given as a bolus into the perfusate reservoir was monitored in perfusate and bile in controls and after the administration of either 80 or 800 μl Cremophor. The higher dose of Cremophor yields clinically relevant perfusate concentrations. Paclitaxel was measured in perfusate, bile, and liver tissue by high-performance liquid chromatography. Results: Cremophor caused a dose-dependent inhibition of the elimination of paclitaxel, with a statistically significant mean value ± SD, n = 3; (P < 0.05 versus controls Bonferroni t-test) 9-fold increase in AUC (2227±106 versus 245 ± 40 g ml−1min), 9-fold decrease in total clearance (0.8±0.1 versus 7.0±1.1 ml/min), and 5-fold increase in elimination half-life (92±14 versus 18±4 min) being observed after a dose of 800 μl Cremophor. With the addition of Cremophor the amount of paclitaxel remaining after 3 h increased in perfusate from none to 20, increased in liver tissue from 4 to 18, and remained constant in bile at 11–13%. In the control group, 86 of the paclitaxel dose was recovered in bile as five putative metabolites, which were measured in paclitaxel equivalents, with the major metabolite. M3 co-eluting with 3′-p-hydroxypaclitaxel. This decreased to 45 of the dose on the addition of Cremophor, and the ratio of M3 to paclitaxel in bile decreased. Conclusions: Cremophor inhibits the hepatic elimination of paclitaxel in the isolated perfused rat liver, primarily by preventing the drug from reaching sites of metabolism and excretion. The presence of Cremophor in the paclitaxel formulation may therefore contribute to the nonlinear pharmacokinetics and pharmacodynamics of paclitaxel.
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