Purpose: To determine experimentally the intestinal permeability of the anticancer prodrug irinotecan, and to quantify the amount of its cytotoxic metabolite SN-38 that is intestinally excreted (exsorped) as a predictor of intestinal toxicity, and to assess the effect of p-glycoprotein (p-gp) inhibitors (verapamil as a model) on the permeability and toxicity of irinotecan.
Methods: Single pass intestinal perfusion of rat's whole length small intestines is applied to assess the permeability of the parent drug and quantify the intestinally excreted metabolite. The perfusion solution contained 30μg/ml of irinotecan (control group) without or with verapamil (verapamil group). A simple reversed phase HPLC method with UV detection is developed and validated for simultaneous determination of irinotecan and SN-38 using camptothecin as an internal standard.
Results: HPLC-UV method found to be simple, specific, accurate, and precise. Effective permeability coefficient of irinotecan found to be 4.9±1.7 10-3 mm/min and was doubled in verapamil group (P=0.007). Average cumulative amount of SN-38 exsorped found to be 29 ng/cm over 2 hours perfusion time which was decreased to 15 ng/cm in verapamil group (P=0.016).
Conclusions: in situ intestinal perfusion method was successfully applied to quantify the permeability of irinotecan and the exsorption of SN-38 in the same experiment, in a manner that robustly reflects real in vivo situation. P-gp inhibition using verapamil found to significantly enhance the intestinal permeability of irinotecan and potentially decrease the intestinal toxicity due to SN-38 exposure.