P56: Effect of variation in site and time on the level of ethanol and methanol in postmortem blood samples

Abstract

Introduction It is well recognized that postmortem (PM) drug levels in blood may be unstable as a consequence of redistribution artifact. Whereby drugs diffuse from their binding sites of high concentration in tissues and major organs, such as liver and lung, into blood. Also drugs can be expected to diffuse from gastric contents into blood. When measuring drug concentrations after death, it is important to consider the phenomenon of PM drug redistribution. PM drug concentrations may not be a true reflection of the ante mortem one and as a result, wrong conclusions could be made about the cause of death. There is few published evidence for most drugs and poisons to show the important differences in their PM concentrations in blood and tissues according to choice of sampling site, sampling time, handling of samples including containers, preservation and documentation and type of laboratory investigation carried out on PM samples. Aim The present work was carried out to evaluate experimentally in rabbits PM behavior of ethyl and methyl alcohol in relation to their concentration in different blood sampling sites at different time intervals. Furthermore to assess the effect of site blood sampling on the level of ethyl alcohol and methyl alcohol at time of autopsy in human cadavers and compare it with the results from rabbit experiments. Methods The study was conducted on ninety male rabbits as experimental animals, and the human cadavers that were positive on screening to ethanol (n=4) and methanol (n=3) during the period of the study. Rabbits were divided into three groups (30 rabbits each), two groups for each drug, which were given the LD50 of the drug. Blood samples were drawn from right and left sides of the heart and femoral vein from each group of rabbits, immediately, twelve hours and twenty-four hours after death. As regards human cadavers, blood samples (5m1) were drawn from right and left sides of the heart and femoral vein at time of autopsy. Experimental and human blood sample extracts were analyzed by gas chromatography. Results The study showed that ethanol was detected in the control group after 12h PM with increased concentration overtime. The highest mean value recorded was 681 μg/ml in 24h PM. No significant changes could be detected in immediate PM blood ethanol concentration (BEC) from different sampling sites. Though PM BEC increased significantly over time for the three sampling sites, yet up to 24h PM, the femoral (peripheral) BEC was the closest to the immediate PM value. Concerning methanol, the study showed also that no significant changes could be detected in immediate PM blood methanol concentration (BMC) from different sampling sites. Similarly, it increased over time for different sampling sites, where within 12h , femoral (peripheral) blood was the only site that didn’t alter significantly and could be used as a reliable indicator for the immediate PM BMC concentration. The results obtained from the human cases were generally in reasonable agreement with those of rabbit experiments. Conclusion Experimental animal studies, when interpreted carefully, are indicative of the PM drug changes observed in human, denoting that femoral (peripheral) blood is the best site for drug sampling.