Clinical pharmacokinetics of acamprosate

Abstract

Acamprosate is a new psychotropic drug used in the treatment of alcohol (ethanol)-dependence. Recent studies suggest that acamprosate inhibits neuronal hyperexcitability by antagonising excitatory amino acids. It is available as a 333 mg enteric-coated tablet, with a recommended dosage of 1.3 g/day for patients with a bodyweight < 60 kg and 2 g/day for patients with a bodyweight > or = 60 kg. Treatment with higher dose strength tablets 2 x 500 mg twice daily is bioequivalent to treatment with the 2 x 333 mg 3 times daily dosage regimen. Acamprosate is absorbed via the paracellular route in the gastrointestinal tract. Absorption is rapid but limited after oral administration. At steady-state, acamprosate has a moderate distribution volume of about 20L. Acamprosate is not protein bound or metabolised. Half of the elimination of acamprosate occurs as unchanged acetyl-homotaurine in urine, the other half might be eliminated by biliary excretion. The administration of the enteric-coated tablets showed a flip-flop mechanism with a terminal elimination half-life 10-fold higher than the 3-hour half-life reported after intravenous infusion. During repeated oral administration of 666 mg 3 times daily, steady-state is reached after 5 to 7 days and leads to plasma concentrations ranging from 370 to 650 micrograms/L. The pharmacokinetics of acamprosate administered as an enteric-coated tablets are time- and dose-independent, and its accumulation ratio is about 2.4 at steady-state. Acamprosate disposition does not differ between males and females. The pharmacokinetics of acamprosate are not modified in patients with hepatic insufficiency or chronic alcoholism. In contrast, renal insufficiency influences the elimination of acamprosate and it is, therefore, contraindicated under such circumstances. Interaction studies have confirmed that when acamprosate is concomitantly administered with food, the amount absorbed is decreased. When combined with diazepam, disulfiram or alcohol, the pharmacokinetic disposition of acamprosate is not modified. Acamprosate does not influence the kinetics of diazepam, alcohol or imipramine and its metabolite desipramine.