Une interférence analytique peut en cacher une autre : l'exemple de l'urapidil, du dépistage de MDMA et de l'identification d'un stimulant de synthèse, la 2-MeOPP

A 53-year-old-man was hospitalized for a stroke. As usually, qualitative urine drug screenings were ordered in the emergency department. Urine immunoassay testing was negative for amphetamines, cannabis, cocaine and opiates, but was very positive for ecstasy using EXTC kit (Siemens®). Then chromatographic analyses were realized to confirm this result or identify a possible analytical interference. A specific assay of ecstasy performed using LC-MS/MS did not allowed confirming the presence of MDA and MDMA, the detection limit of this technique was 1 μg/L. Qualitative urine drug screens were also realized using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-diode array detection (LC-DAD). The screening of urine performed with GC-MS allowed for the identification of a piperazine, the (1,2-methoxyphenyl)-piperazine (2-MeOPP). Piperazine derivatives act as stimulants, these substances being classified as designer drugs. However, the screening performed using LC-DAD revealed the presence of urapidil, a sympathetic antihypertensive drug. More analyses were realized to control these different results. Urines of patients treated with urapidil induced positive results to EXTC kit and presented a signal identified as 2-MeOPP using GC-MS. In this article, two interferences associated with urapidil were shown.