ABSTRACT
The identification and quantitation of carisoprodol (Soma) and its chief metabolite meprobamate, which is also a clinically prescribed drug, remains a challenge for forensic toxicology laboratories. Carisoprodol and meprobamate are notable for their widespread use as muscle relaxants and their frequent identification in the blood of impaired drivers. Routine screening is possible in both an acidic/neutral pH screen and a traditional basic screen. An improvement in directed testing quantitations was desirable over the current options of an underivatized acidic/neutral extraction or a basic screen, neither of which used ideal internal standards. A new method was developed that utilized a simple protein precipitation, deuterated internal standards and a short 2-min isocratic liquid chromatography separation, followed by multiple reaction monitoring with tandem mass spectrometry. The linear quantitative range for carisoprodol was determined to be 1-35mg/L and for meprobamate was 0.5-50mg/L. The method was validated for specificity and selectivity, matrix effects, and accuracy and precision.
Subject(s)
Carisoprodol/blood , Chromatography, High Pressure Liquid/methods , Meprobamate/blood , Tandem Mass Spectrometry/methods , Carisoprodol/chemistry , Drug Stability , Female , Forensic Toxicology/methods , Humans , Linear Models , Meprobamate/chemistry , Reproducibility of Results , Sensitivity and Specificity , Substance Abuse Detection/methodsABSTRACT
The objective of this study was to investigate the accuracy of screening postmortem whole blood for oxycodone using the ratio of the oxycodone immunoassay response to the response for the specimen obtained with a general opiate-class immunoassay. Fifty eight specimens which were negative for opiates and 158 postmortem whole blood specimens positive for opiates including 66 specimens known to contain oxycodone were assayed. Specimens were diluted 1:5 with assay buffer and analyzed by both the Neogen Oxymorphone/Oxycodone ELISA and the Neogen Opiate Group ELISA (Neogen Corporation, Lexington KY). The oxycodone equivalents in ng/mL from the Oxymorphone/Oxycodone ELISA were divided by the morphine equivalents in ng/mL from the Opiates ELISA to obtain an Oxycodone/Opiates Response Ratio. This ratio was compared with the GC/MS data for all specimens and for opiate positive specimens. Receiver Operating Characteristic (ROC) analysis suggested that optimum relative response ratio was 2.0. The sensitivity of the ELISA response ratio for the presence of oxycodone at a response ratio cutoff of 2.0 was 89.4% +/- 3.8% and the specificity was 88.1% +/- 3.2%. Specimens with a ratio of 2.0 or higher had a greater than 50% probability (positive predictive value) of containing oxycodone in a population with a greater than 15% prevalence of oxycodone.
