Journal of analytical toxicology
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Comparative Study Clinical Trial Controlled Clinical Trial
Oxaprozin cross-reactivity in three commercial immunoassays for benzodiazepines in urine.
Immunoassay methods are commonly used to screen for drugs of abuse and some prescription drug classes as part of drug-testing programs in clinical and forensic toxicology. Oxaprozin (Daypro) is a new nonsteroidal anti-inflammatory drug that is widely prescribed in North America and has been reported to cross-react for benzodiazepines in several different immunoassay methods. The first objective of this study was to characterize the immunoreactivity of oxaprozin standards over a wide concentration range when analyzed by the EMIT dau, Abbott FPIA, and BMC CEDIA urine benzodiazepine assays. ⋯ With a 200-ng/mL cutoff for benzodiazepines in these assays, all 36 urine specimens collected from the 12 subjects gave positive results by EMIT and CEDIA, and 35 of 36 urine specimens were positive by FPIA. It was concluded that presumptive positive benzodiazepine results by these immunoassays may be due to the presence of oxaprozin or oxaprozin metabolites. It is recommended that all positive immunoassay screening tests for benzodiazepines be confirmed by another technique based upon a different principle of analysis.