B-312 Sensitive Homogeneous Enzyme Immunoassay for Carisoprodol Metabolite (Meprobamate)

Background Carisoprodol is a carbamate derivative medication used for musculoskeletal pain. Therapeutic use of carisoprodol produces common side effects such as headache, dizziness, and sleepiness, but more serious side effects include allergic reactions and seizures. Isolated case reports suggest that carisoprodol may have the potential for abuse. Carisoprodol was approved for medical use in the United States in 1959. Its approval in the European Union was withdrawn in 2008 due to the risk of abuse or addiction. In the United States, it is a Schedule IV controlled substance. In humans, carisoprodol primarily metabolizes to meprobamate, an active metabolite, via the polymorphic CYP2C19 enzyme. Meprobamate is also a schedule IV-controlled substance used to treat anxiety and has a noted potential for abuse. ARK Diagnostics has developed a sensitive homogeneous enzyme immunoassay to detect meprobamate and carisoprodol in human urine at a cutoff concentration of 100 ng/mL. Methods The ARK Carisoprodol Metabolite (Meprobamate) Assay is a liquid-stable homogenous enzyme immunoassay consisting of two reagents. The assay has a 100 ng/mL cutoff. The performance characteristics of this assay, including precision, spiked recovery, specificity, and method comparison to LC-MS/MS, were evaluated on the Beckman Coulter AU680 automated clinical analyzer. Results The ARK Carisoprodol Metabolite (Meprobamate) Assay demonstrated acceptable precision, with no overlap between 100 ng/mL cutoff and ± 25% control levels (75 ng/mL and 125 ng/mL) in a histogram overlap analysis, and less than 6.5 % CV in semi-quantitative mode. Spiked meprobamate samples spanning the semi-quantitative assay range of 500 ng/mL were recovered between 91.4% and 103.0% of the spiked levels from 30.0 to 500.0 ng/mL. LLOQ was determined at 20 ng/mL. The prodrug, carisoprodol, at concentrations approximately equivalent to the 100ng/mL cutoff was determined at 100 ng/mL (100% cross-reactivity). In method comparison studies, the ARK Carisoprodol Metabolite (Meprobamate) Assay accurately identified all 230 human urine samples confirmed negative by LC-MS/MS as negative. For the confirmed meprobamate and carisoprodol positive samples, ARK Carisoprodol Metabolite (Meprobamate) Assay showed 95.7 % specificity and 97.7 % sensitivity. Conclusion The ARK Carisoprodol Metabolite (Meprobamate) Assay is applicable to a wide range of clinical chemistry analyzers and performs a sensitive, rapid, and reliable measurement of meprobamate and carisoprodol in human urine.