Overdose of meprobamate: plasma concentration and Glasgow Coma Scale

Pharmacokinetics of meprobamate in overdose treated with continuous venovenous hemodiafiltration (CVVHDF)

We report a case of massive suicidal overdose of meprobamate leading to cardiovascular collapse, respiratory failure, and severe central nervous system depression. We observed first-order elimination kinetics despite significant overdose, and demonstrated effectiveness of continuous venovenous hemodiafiltration (CVVHDF) for extracorporeal removal of meprobamate in this patient. Total body clearance was calculated to be 87 mL/minute, with 64 mL/minute (74%) due to CVVHDF. CVVHDF was stopped after 36 hours, and the patient made an uneventful recovery.

[Severe meprobamate poisoning: description of 146 cases in a French department]

Meprobamate poisoning are serious and sometimes fatal. Faced with a potential stop of marketing, we conducted a multicenter retrospective study to assess the severity criteria presented by patients admitted to the ICU for severe meprobamate poisoning, whether with alone form or in combination with aceprometazine. One hundred fourty-six patients have been enrolled between January 2005 and June 2011: 38 had a single meprobamate poisoning, 104 to meprobamate and aceprometazine and 4 to both forms. At admission, 88% of patients exhibited coma (Glasgow ≤ 7) and half of them a systolic blood pressure ≤ 90 mmHg. Mortality rate was 3%. Our results did not find any significant between-group difference, either in regard of clinical or biological severity criteria. These data argue for a cessation of marketing of all meprobamate-based specialities.

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.