Serum diazepam and serum creatine kinase after intra-muscular injection of diazepam in two different vehicles.

Serum diazepam concentration and serum creatine kinase activity (serum CK) were measured in 35 patients (who were divided into three groups (A, B, and C)), over a period of 24 hours after administration of diazepam. An increase in serum CK was regarded as an indication of local muscle injury. In group A, diazepam in a polyethyleneoxydricinolate vehicle was injected intramuscularly; in group B, diazepam in a propyleneglycol-ether alcohol vehicle was injected intramuscularly; and in group C, diazepam was administered orally, combined with intramuscular administration of the vehicle used in group B. The investigation was double-blind and randomized. Serum diazepam absorption expressed as the area under the concentration curve was identical in groups A and C and significantly higher than in group B. Serum CK rose in all groups. The differences among the groups were not significant. There were considerable individual variations in all three groups, and almost half the patients showed no increase in serum CK at all. No negative correlation was found between serum diazepam and serum CK. Thus no effect of muscle injury--if present--on absorption rate could be demonstrated.