Evaluation of the first immunoassay for the semi-quantitative measurement of meprobamate in human whole blood or plasma using biochip array technology.

Background: Meprobamate is a carbamate, and the main metabolite of carisoprodol. It is used as an anxiolytic agent. Overdose of both drugs produces intoxication that is often serious and sometimes life threatening. However there was until now no immunoassay for the diagnosis of this intoxication.
Methods: A chemiluminescent immunoassay for the semi-quantitative measurement of meprobamate in human blood and plasma has recently been developed, using the Evidence Investigator system (Randox®). In this study, the immunoassay was evaluated by testing drug-free (n=10) or spiked whole blood and plasma samples (n=70), and authentic post mortem whole blood samples from deceased patients in which meprobamate was present (n=38) or not (n=10). A previously validated gas chromatography-mass spectrometry (GC-MS) method was used for confirmation and quantification. 97 psychoactive drugs including carisoprodol were analyzed for possible interference.
Results: With a cut-off at 0.5 mg/L, specificity, sensitivity and accuracy were 100%, 97.2% and 97.6%, respectively. All the untreated patients presented results under the cut-off. Meprobamate was not detected in three whole blood samples spiked with concentrations under the therapeutic range. In the authentic patients (n=48), there were no false-negative results. A good correlation was found between the immunoassay and GC-MS (r=0.90). Quantitative results of the immunoassay are approximately two-fold lower than GC-MS results. Only carisoprodol presented a cross-reactivity, 38±6.6% at 10 mg/L, and 26±4.8% at 100mg/L.
Conclusion: The first meprobamate immunoassay has shown very good specificity, selectivity and accuracy, which allow its use in hospital clinical laboratories for rapid diagnosis of meprobamate (or carisoprodol) intoxications.
(Copyright © 2011 Elsevier B.V. All rights reserved.)