STABILITY OF NITROBENZODIAZEPINES IN POSTMORTEM BLOOD

Studies were undertaken to determine the stability of nitrobenzodiazep ines and their 7-amino metabolites in water and blood. Ar 22 degrees C nitrazepam and clonazepam were stable in sterile fresh blood containi ng preservative over 28 days, whereas 25% of flunitrazepam was degrade d. At 37 degrees C all three drugs were substantially lost over 9 h (2 9-51%). There was only a small loss observed for the 7-amino metabolit es and no substantial amounts of parent drug and 7-amino metabolite we re degraded in water under these conditions. In the absence of preserv ative substantial amounts (25-50%) of parent drugs were lost in fresh blood over 10 days at 22 degrees C. In bacterially-contaminated postmo rtem blood all three drugs were completely degraded over 8 h at 22 deg rees C with almost all drug completely converted to the respective 7-a mino metabolite. These metabolites were also partially degraded (10-20 degrees C) over 45 h at 22 degrees C. All 3 nitrobenzodiazepines were stable in blood stored for up to 24 months at -20 degrees C, or 4 deg rees C over 10 months. Their respective 7-amino metabolites were, howe ver, relatively unstable at -20 degrees C with a significant loss (29% ) after 2 months. At 4 degrees C a 21% loss occurred after 1 month. Fr eeze/thawing was found not to affect the concentration of nitrobenzodi azepine and 7-amino metabolites. These results show that the nitrobenz odiazepines and their metabolites are unstable chemically and metaboli cally in blood. We advise that blood collected for the purpose of nitr obenzodiazepine determinations should be preserved with sodium fluorid e, stored at -20 degrees C and assayed as soon as practicable, prefera bly within a week of collection.