ABSTRACT
The formation and persistence of desmethyldiazepam in the organism has several important repercussions in clinical practice. The pharmacokinetic profiles of diazepam and desmethyldiazepam after single administration are illustrated. Oxazolam is another benzodiazepine devoid of activity at the benzodiazepine binding site that is metabolised in vivo to desmethyldiazepam. The primary determinant of the efficacy of benzodiazepines is the concentration achieved in the plasma of parent drug and/or active metabolites. For anxiolytic benzodiazepines, rate of absorption is of little importance compared with achieving stable plasma levels after repeated administration. Elimination half-lives are also critical parameters for hypnotic benzodiazepines. The vast majority of benzodiazepines are metabolised in the liver by Type I oxidation involving cytochrome P450 enzymes. Certain benzodiazepines are converted by hepatic metabolism into other species that are responsible for exerting their biological effects. The effects of benzodiazepines can change with the age of the patient to whom they are administered.
