Postmortem stability of cocaine and cocaethylene in blood and tissues of humans and rabbits.

A study was conducted to examine the postmortem stability of cocaine and cocaethylene in rabbit blood and tissues, and to determine whether cocaethylene is produced in decomposed human specimens containing cocaine and endogenous ethanol. Heart blood, liver, brain and femoral muscle taken from rabbits 20 min after oral administration of 20 mg/kg cocaine together with 2 g/kg ethanol were kept at 20-25 degrees C for 5 days. Cocaine and cocaethylene concentrations were in the order brain > liver > muscle > blood, and showed very large intersubject variations at the time of death. Cocaine was degraded rapidly in the blood and liver. However, 12.0 +/- 8.5% and 26.2% +/- 19.4% of the original cocaine was still detectable in the brain and muscle, respectively. Cocaethylene was degraded more slowly than cocaine in all of the specimens. The pH of the blood remained around 7.4 during a 5-day period; all the other specimens showed pH values of 6.2-6.7 on and after the first day postmortem. When 10,000 ng/g cocaine was incubated with decomposed human blood, liver, brain and muscle homogenates containing 0.29-0.60 mg/g endogenous ethanol at 20-25 degrees C and 37 degrees C, no change in cocaine concentration was observed during the study period of 24 h, and no cocaethylene was detected. The pH values of the homogenates were within the range 4.2 to 5.2 at the beginning of the experiment. It was found that: 1) cocaethylene was more stable in postmortem specimens than cocaine; 2) muscle as well as brain was specimen of choice for detecting cocaine and cocaethylene postmortem; 3) cocaine was resistant to decomposition under acidic conditions; and 4) putrefactive bacteria had no ability to produce cocaethylene even in the presence of cocaine and endogenous ethanol.