Intestinal Absorption of (–)-Carbovir in the Rat

(–)-Carbovir (CBV) is a carbocyclic nucleoside analogue with in vitro activity against the human immunodeficiency virus. The sites and mechanism of absorption of (–)-CBV from the rat small intestine were studied in the anesthetized male Sprague–Dawley rat. (–)-CBV was perfused through either duodenal, jejunal, or ileal segments at three concentration levels ranging from 1 to 500 µg/mL. The fraction remaining to be absorbed at steady-state and the absorptive clearance were calculated for each experiment. The effect of solvent drag on the absorptive clearance was also investigated. Two-way ANOVA for the absorptive clearance per unit length was not significant for either (–)-CBV concentration or site of perfusion. The fraction remaining to be absorbed at steady-state was found to be 0.804 ± 0.091 (n = 30). A strong correlation was found between the absorptive clearance and the net water absorptive flux. The mechanism of (–)-CBV absorption across the rat small intestine apparently consists of both passive diffusion and convection.