Urinary detection times and excretion patterns of flunitrazepam and its metabolites after a single oral dose

We investigated the excretion profiles of flunitrazepam metabolites in urine after a single dose. Sixteen volunteers received either 0.5 or 2.0 mg flunitrazepam. Urine samples were collected after 2, 4, 6, 8, 12, 24, 48, 72, 96, 120, 240, and 336 h. Samples were screened using CEDIA (300 microg/L cutoff) and quantitated using liquid chromatography-tandem mass spectrometry. The cutoff was 0.5 microg/L for flunitrazepam, N-desmethylflunitrazepam, 7-aminoflunitrazepam, 7-aminodesmethylflunitrazepam, 7-acetamidoflunitrazepam, and 7-acetamidodesmethylflunitrazepam. None of the subjects receiving 0.5 mg were screened positive, and only 23 of 102 samples from the subjects given 2.0 mg were positive with CEDIA. The predominant metabolites were 7-aminoflunitrazepam and 7-aminodesmethylflunitrazepam. For all subjects given the low dose, 7-aminoflunitrazepam was detected up to 120 h, and for two subjects for more than 240 h. Seven subjects given the high dose were positive up to 240 h for 7-aminoflunitrazepam. We conclude that the ratio 7-aminodesmethylflunitrazepam to 7-aminoflunitrazepam increased with time, independent of dose, and may be used to estimate the time of intake. For some low-dose subjects, the metabolite concentrations in the early samples were low and a chromatographic method may fail to detect the intake. We think laboratories should consider this when advising police and hospitals about sampling as well as when they set up strategies for analysis.