Long-term storage of authentic postmortem forensic blood samples at -20°C: measured concentrations of benzodiazepines, central stimulants, opioids and certain medicinal drugs before and after storage for 16-18 years.

The long-term stability of benzodiazepines, opioids, central stimulants and medicinal drugs in authentic postmortem blood samples was studied. All together, 73 samples were reanalyzed after storage at -20°C for 16-18 years. At reanalysis samples containing diazepam, nordiazepam and flunitrazepam demonstrated only small changes during long-term storage when mean and median drug concentrations were compared, while clonazepam concentrations tended to decrease. Samples containing amphetamine, morphine, codeine and 'acidic' medicinal drugs as paracetamol and meprobamate also showed small changes over 16-18 years in mean and median drug concentrations at a group level. For many drugs, however, single samples could demonstrate marked concentration changes, both increases and decreases during storage. For 'alkaline' medicinal drugs, concentration losses were observed in most cases.