Pharmacokinetics of benzodiazepines. Short-acting versus long-acting.

Among the various benzodiazepines large differences exist with regard to their pharmacokinetic properties and metabolism in man. Some are eliminated from the body at a relatively slow rate (e. g. diazepam), others are metabolized rather rapidly (e. g. oxazepam, temazepam, triazolam). Several benzodiazepines have the long-acting metabolite N-desmethyldiazepam in common (diazepam, fosazepam, prazepam, clorazepate). Such differences may be very important clinically because pharmacokinetic factors will determine the duration of drug effect and pharmacokinetic parameters constitute the basis for a rational dosage regimen. For the various clinical indications of benzodiazepines the required duration of drug action differs quite fundamentally. In anticonvulsant and anti-anxiety treatment continuous treatment is pursued, so that compounds with long elimination half-lives of parent drug or active metabolites are of advantage. If on the other hand a benzodiazepine is taken as a hypnotic, the duration of action should be restricted to the night, hence a compound with a short elimination half-life is to be preferred. A review is given of the pharmacokinetics of the major benzodiazepines presently available.