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1. The in vitro sulphoxidation of Albendazole (ABZ) by rat intestinal microsomes has been examined. The results revealed intestinal sulphoxidation of ABZ by intestinal microsomes in a NADPH-dependent enzymatic system. The kinetic constants for sulphoxidase activity were Vmax = 46 pmol/min/mg protein and Michaelis constant Km = 6.8 microM. 2. The possible effect of inducers (Arochlor 1254 and ABZ pretreatment) and inhibitors (erythromycin, methimazole, carbon monoxide and fenbendazole), was also studied. In rat pretreated with Arochlor 1254, Vmax was 52 pmol/min/mg protein, whereas oral administration of ABZ increased the intestinal sulphoxidation of the drug, Vmax being 103 pmol/min/mg protein. 3. Erythromycin did not change the enzymatic bioconversion of ABZ, but methimazole and carbon monoxide inhibited the enzyme activity by approximately 60 and 30% respectively. Fenbendazole (a structural analogue of ABZ) was a competitive inhibitor of the sulphoxidation process, characterized by a Ki or 69 microM. 4. These data demonstrate that the intestinal enzymes contributing to the initial sulphoxidation of ABZ may be similar to the hepatic enzymes involved in the biotransformation process by the P450 and FMO systems, a conclusion that needs to be further established.

The effect of ethanol administration on gastric absorption in rats of two benzimidazole derivatives has been studied. The ethanol administration was carried out as both acute (5%, 10% and 15% w/v of ethanol in the perfusion solution), and chronic (15, 30 and 120 days) forms. Two benzimidazole derivatives were used: albendazole (ABZ) and mebendazole (MBZ). The administration of ethanol did not affect the kinetic mechanism of the absorption process (simple diffusion) but the absorption rate decreased in all treatments except in 5% acute ethanol, presumably due to the improved solubility of the drugs. Plasma, bile and liver levels after gastric perfusion suggest a possible interference of ethanol metabolism with drug hepatic metabolism.

Uptake of albendazole (ABZ) and mebendazole (MBZ) by isolated rat enterocytes was carried out. These drugs, widely used oral anthelmintics, exhibit a scarce water solubility which reduce its absorption by the oral tract. The present study was designed to assess the captation for ABZ and MBZ in different enterocyte populations isolated from upper to crypt villus. The concentration range used for the absorption experiments was within 10-500 microM for both drugs, using DMSO as solvent. The results obtained show the existence of a passive mechanism for the uptake of ABZ and MBZ at concentrations between 10 and 100 microM, with a maximum intake value around 20 microM/mg protein. No differences were found with respect to the cell populations analyzed. The drug uptake levels seem to be higher for MBZ than for ABZ prior to reaching the maximum plateau.

1. A study was carried out to determine the kinetics of the gastric absorption of two wide spectrum benzimidazole anthelmintics, albendazole and mebendazole. 2. The method used was gastric recirculation of solutions containing the drugs in concentrations ranging from 0.5 to 100 mM. 3. The results obtained showed that absorption corresponds to first order kinetics, with diffusion constants of 0.0087 min-1 for albendazole and 0.0077 min-1 for mebendazole. 4. Blood levels of the drugs for the whole range of concentrations were always higher in the case of albendazole.