Nitrazepam is one of the oldest benzodiazepines and is widely used as an hypnotic throughout the world, except North America, where it is not available. It is a safe hypnotic, with low acute toxicity and minor side effects. Development of tolerance or dependence and withdrawal symptoms are rare and very few known interactions with other drugs exist.The absorption of nitrazepam from the gastrointestinal tract is fairly rapid (tmaxranging 0.5 to 7 hours). The bioavailability after oral intake averages about 80%. Maximum plasma concentrations after a single 5mg dose are of the order of 40ng/ml. As a lipophilic drug, nitrazepam is distributed rapidly in the body. The plasma levels can be fitted to a 2-compartment open model. The &agr;-phase is rather rapid and the elimination phase is characterised by a long half-life of about 30 hours; accumulation with daily use therefore occurs. Marked interindividual variation (up to 10-fold) is found in all pharmacokinetic parameters. Age and immobilising diseases may influence the parameters, evidently increasing Vd&bgr;and t1/2&bgr;.A similar amount of protein-free drug found in the plasma, i.e. 10 to 15% of the total plasma level, is found in the cerebrospinal fluid. In saliva the concentrations are significantly smaller. Nitrazepam penetrates the human placenta. In early pregnancy, the ratio of cord to maternal plasma concentration is about 0.5, 12 hours after drug administration. In late pregnancy, the ratio reaches 1 within a few hours. Breast milk concentrations are about one-half of those in maternal plasma.Nitrazepam has no clinically active metabolites. It is excreted mainly as conjugated and non-conjugated 7-aminonitrazepam and 7-acetamidonitrazepam. Polymorphic acetylation is not likely to be of clinical importance. Enzyme induction or significant loss of efficacy have not been found with long term use.There is no significant correlation between plasma concentrations and clinical effects (or side effects) of nitrazepam. Plasma level monitoring is therefore of no benefit clinically (except for special cases, e.g. in epileptic patients). Increased responsiveness in terms of therapeutic effects and side effects is evident in the elderly. Therefore, small doses not exceeding 5mg daily should be prescribed for geriatric patients.