Reactivity of commercial benzodiazepine immunoassays to phenazepam.

Phenazepam is a long acting benzodiazepine that is not controlled in Canada, the United States or many European countries. The abuse of phenazepam has gained recent attention due to the number of hospitalizations and fatalities resulting from overdose. The compound is relatively potent with recommended doses of 0.5-1.0 mg, or 1/10th the recommended dose of diazepam, and is easy to obtain locally or from international suppliers via the internet. Increased risk of phenazepam overdose is attributed to its potency and the forms in which it is supplied. Individuals without scales or balances are prone to estimate dose amounts of powder visually, which can result in significant errors. The detection of phenazepam has been described using various methods including GC, GC/MS and LC/MS, but no data regarding the sensitivity of commercially available immunoassays exist. In this study, phenazepam-spiked urine samples were analyzed using five commercial instruments and two point of care devices. The concentrations of phenazepam required for detection ranged from 140-462 ng/mL, which is comparable to those of other benzodiazepines. Laboratorians and clinicians should be confident that phenazepam will be detected via most commercial drugs of abuse screens in patients after significant ingestion.