Absorption and sedative effects of diazepam after oral administration and intramuscular administration into the vastus lateralis muscle and the deltoid muscle.

The absorption of diazepam 10 mg after oral administration and intramuscular administration into the vastus lateralis muscle or the deltoid muscle was compared in a double-blind cross-over study in eight healthy subjects. Serum diazepam concentrations were measured, and the presence of tiredness was noted 20, 40, 60, 90 and 150 min after the drug administration. Peak concentrations in serum were 209+/-49, 152+/-60 and 143+/-62 ng/ml ((means+/-SD) at 90, 60 and 60 min after oral, shoulder and thigh administration respectively. Absorption was more rapid after intramuscular than after oral administration, serum mean diazepam concentrations at 20 min after oral administration being only 26% of those after shoulder administration. The rapid rate of absorption from the shoulder was associated with a more rapid feeling of tiredness and a greater sedative effect than after oral or thigh administration. There was no evidence that diazepam induced its own metabolism after one or two administrations. The results suggest that, if rapid preanaesthetic medication with diazepam is needed, shoulder administration might be superior to oral or thigh administration.