Objective: Co-medication unknown to the treating physician, including self-medication, may compromise drug safety by increasing the risk of duplicate therapy, drug interactions and adverse drug reactions that are not recognised as such. The aim of the current study was to estimate exposure to unknown co-medication during hospitalisation by performing an analytical screening for a broad range of drugs and drug classes in urine of patients admitted to a general internal medicine ward.
Methods: Urine samples of 44 patients were analysed with REMEDiHS (high-performance liquid chromatography) and six different immunoassays. Positive results were compared with drug history and documented drug prescription. If appropriate, gas chromatographic-mass spectrometric confirmatory analyses were performed on drugs classified at least once as possible unknown co-medication.
Results: Nine (20%) of the patients tested positive for a compound detected by two independent analytical methods and 18 (41%) for a compound detected by at least one analytical method. Unknown co-medication consisted mostly of analgesics, benzodiazepines or ranitidine.
Conclusion: At least one in five patients exhibits at least once during hospitalisation exposure to drugs not documented in the patient record, which may compromise patient safety.