Stability study of opioids and benzodiazepines in urine samples by liquid chromatography tandem mass spectrometry

Background: The stability of opioids and benzodiazepines was studied in patient urine samples stored at different temperatures over 30 days. Methods: Samples were prepared by solid phase extraction and quantified by liquid chromatography coupled to a tandem triple quadrupole mass spectrometer. Results: Sample storage conditions affected the stability of all drugs investigated. The concentrations of hydromorphone and oxymorphone in urine samples from patients who had taken hydrocodone, morphine, and/or oxycodone increased significantly over 30 days of storage. Conclusions: These data suggest that results from long-term-stored urine samples with opioids and benzodiazepines should be cautiously interpreted. This study indicates that the biotransformation of parent drugs to metabolites still occurs during sample storage at ambient temperatures.