Forensic toxicological analyses of drugs in tissues in formalin solutions and in fixatives

• Psychoactive drug levels were examined with formalin-fixed human tissues.
• Tissues of ante- and post-preservation of multiple terms and fixatives were used.
• Drug levels did not necessarily show further decreases with extended storage.
• Proportion of drugs remained within tissues differed between liver and kidney.
• S-oxide compounds of assayed drugs were generated in formalin storage of liver.

Forensic toxicological drug analyses of human specimens are usually performed immediately after autopsy or on frozen preserved tissues. Occasionally, cases require analysis of drugs from tissues fixed in formalin solution. To improve the estimation of the level of drug in tissues following formalin fixation, we studied drug concentrations in human tissues, liver and kidney, that were collected from a drug-positive autopsy case. Parts of tissues were preserved in formalin solution for 1, 3, 6 and 13 months. Tissues obtained before and after preservation, along with tissue-exposed fixatives, were assayed using gas chromatography–mass spectrometry; all of the samples were assayed for the presence of drugs and changes in the drug concentrations both before and after preservation in formalin. Concentrations of assayed drugs decreased upon fixation in formalin; levels of these drugs did not necessarily show further decreases during subsequent storage in fixative, up to 13 months. Distinct trends in drug levels were found in liver and kidney. In liver, the levels of chlorpromazine, levomepromazine, and promethazine decreased to 23–39% at 1 month after preservation; all 3 of these drugs were detected at all tested time points of preservation. Bromazepam was not detected at 13 months after preservation. Milnacipran was the most unstable after preservation in formalin solution among all of the assayed drugs. In kidney, all assayed drugs exhibited reduced stability during preservation compared to levels in liver. Methamphetamine and methylenedioxymethamphetamine were not detected in any time points of tissues. The proportions of the drugs that remained within the tissues differed between liver and kidney. Also, S-oxide compounds of chlorpromazine and levomepromazine, which were not observed before preservation, were detected in fixed liver tissues and their fixatives at 3, 6 and 13 months of preservation. These results suggest that analyses in formalin-fixed tissues need to include analysis of various organ-tissues and their fixatives at multiple time points for the duration of preservation. These analyses should include detection of chemical degradation/denaturation products, such as S-oxides of chlorpromazine and levomepromazine.