Urinary false-positive ecstasy screening by Mebeverine Metabolite: a confirmatory study and controlled administration

Urinary immunochromatographic tests (ICTs) are first-line tools for psychoactive substance screening in clinical and forensic settings. Their limited specificity, however, predisposes them to cross-reactive interferences generating false-positive results.We report three consecutive cases of false-positive 3,4-methylenedioxymethamphetamine (MDMA) results on rapid urinary ICT screening attributable to therapeutic mebeverine use, all confirmed by gas chromatography-mass spectrometry (GC-MS). Three patients admitted to emergency and intensive care units were all receiving mebeverine therapeutically.A 12-panel ICT (MDMA cut-off: 500 ng/mL) returned presumptive positive MDMA results in all three specimens. GC-MS confirmatory analysis detected neither MDMA nor its primary metabolite, 3,4-methylenedioxyamphetamine (MDA). Mebeverine O-desmethyl-butanol was consistently identified in all three specimens. A spiking experiment with certified mebeverine hydrochloride at 3000 ng/mL yielded a negative ICT result, excluding the parent compound as the causative agent. A controlled single-dose administration experiment (200 mg oral mebeverine) produced positive MDMA ICT results in all four urine specimens collected between 4 and 13 hours post-ingestion; GC-MS confirmed mebeverine O-desmethyl-butanol as the sole mebeverine-derived compound identified, strongly implicating this metabolite in the observed cross-reactivity.Any positive MDMA immunochromatographic result in a patient receiving mebeverine must be confirmed by GC-MS or LC-MS/MS. Mebeverine and its metabolites should be incorporated into cross-reactivity documentation by ICT manufacturers.