Comparison of the subjective effects and plasma concentrations following oral and i.m. administration of flunitrazepam in patients.

The use of flunitrazepam 1 and 1.5 mg was compared as a premedicant with diazepam 10 mg and lorazepam 2.5 mg. Plasma flunitrazepam concentration were measured after oral and i.m. administration. Flunitrazepam and diazepam had a similar onset time and duration of action, both being more rapid in onset and shorter in duration than lorazepam I.m. flunitrazepam had a slightly greater sedative effect than oral flunitrazepam and plasma concentrations correlated well with the onset of the sedative effect by either route of administration. The i.m. injection of flunitrazepam was not as painful as that of diazepam, but slightly more painful than lorzepam. A second peak occurred at about 5 h and flunitrazepam was still detectable at 48 h. The plasma half-life was 3-4 h.