Validation of a New Homogeneous Immunoassay for the Detection of Carisoprodol in Urine

The objective of this project was to validate a new high-throughput homogeneous enzyme immunoassay (HEIA) for the rapid detection of carisoprodol in human urine. Carisoprodol (Soma ® ) and meprobamate are widely prescribed as musculoskeletal pain relief drugs and are listed as one of the 10 most frequently identified drugs associated with DUI cases. Carisoprodol has a short elimination half-life of 1-3 h; however, its major active metabolite, meprobamate, has a longer elimination half-life of 6―17 h. As a result, it is important for an immunoassay to cross-react with both compounds. The advantage of this new assay is that cutoff concentrations can be adjusted between 100 and 500 ng/mL. The reportable range was 25 to 1000 ng/mL for carisoprodol and 50 to 10,000 ng/mL for meprobamate. The intraday coefficient of variation (% CV) for the semi-quantitative assay was less than 1 %. The homogeneous assay was validated with a total of 86 urine samples previously analyzed by liquid chromatography-tandem mass spectrometry with carisoprodol concentrations ranging from 50 to 10,000 ng/mL. The accuracy was found to be 100% when immunoassay cutoff concentrations of carisoprodol and meprobamate were set at 100 and 1000 ng/mL, respectively.