Pharmacokinetic and clinical observations on prolonged administration of flunitrazepam.

Eight patients were given flunitrazepam 2 mg orally, once daily for 28 consecutive days. The time-course of the plasma concentration of unchanged flunitrazepam and its principal metabolites were studied in detail after the first and last doses. Additional blood samples were collected immediately before administration of the tablet on days 4, 7, 11, 14, 18, 21 and 25. Clinically there were not changes during the trial period in the onset of sleep, duration of sleep, depth of sleep measured as number of spontaneous awakenings, or in the patients' condition on awakening. The time-course of the plasma concentration of flunitrazepam could be described by a three-compartment model, assuming that the rate constants remained unchanged during treatment. Maximal plasma concentrations of unchanged flunitrazepam, found two hours after intake, reached 10-15 ng/ml after the first and 15-20 ng/ml after the last dose. The beta-half-life was found to be between 20 and 36 h.