Carisoprodol intoxications: a retrospective study of forensic autopsy material from 1992–2003

Carisoprodol is commonly prescribed as a centrally acting muscle relaxant, but it is also subject to abuse. The literature describing fatal intoxications with the drug is limited to a relatively small number of cases, and there are inconsistencies with regard to which concentration levels that are toxic. We therefore investigated all forensic autopsies at the Norwegian Institute of Public Health during the period 1992–2003 where carisoprodol was detected. The median concentrations of carisoprodol in intoxication with carisoprodol only or with only minor other analytical findings was 36 mg/l (range 8–65 mg/l; n=5). In the rest of the intoxications, the relevance of carisoprodol relative to the other drugs detected was variable (n=93). When the number of intoxications with carisoprodol each year were divided by the number of defined daily doses (DDD) sold, a fatal toxicity index between 5.6 and 6.9 deaths/1 million DDD was obtained. The total number of cases where carisoprodol was detected increased during the period studied, which correlated to sales figures for the drug. We conclude that carisoprodol can be fatal in concentrations below those indicated in some of the previously published literature. There were, however, only a small number of cases where the cause of death can be attributed to use of carisoprodol alone.