Previous studies suggest that P-glycoprotein (P-gp) modulates the PK/PD of many compounds including opioid agonists and chemotherapeutic agents. The objective of this study was to assess the P-gp affinity status of oxycodone, the P-gp expression, and the paclitaxel's tissue distribution in oxycodone-treated rats. P-gp ATPase assay, Caco-2 transepithelial permeability studies, and mdr1a/b (-/-) mice were used to assess the P-gp affinity status of oxycodone. P-gp expression was determined by Western blot analysis while [(14)C] paclitaxel's distributions in the liver, kidney, brain, and plasma tissues were determined by liquid scintillation counter. Oxycodone stimulated the P-gp ATPase activity in a concentration-dependant manner. The Caco-2 secretory transport of oxycodone was reduced from 3.64 x 10(-5) to 1.96 x 10(-5) cm/s (p < 0.05) upon preincubation with the P-gp inhibitor, verapamil. The brain levels of oxycodone in mdr1a/b (+/+) were not detectable (<15 ng/mL) while in mdr1a/b (-/-) the average levels were 115 +/- 39 ng/mL. The P-gp protein levels were increased by 1.3-4.0 folds while paclitaxel's tissue distributions were decreased by 38-90% (p < 0.05) in oxycodone-treated rats. These findings display that oxycodone is a P-gp substrate, induces overexpression of P-gp, and affects paclitaxel's tissue distribution in a manner that may influence its chemotherapeutic activity.
(c) 2007 Wiley-Liss, Inc. and the American Pharmacists Association.