Site-dependent postmortem changes in blood cocaine concentrations

When a forensic toxicologist interprets postmortem blood cocaine findings he usually must make assumptions regarding perimortem drug concentrations. In-vitro studies have shown that cocaine rapidly hydrolyzes in unpreserved blood, particularly at elevated temperatures. However, other studies have demonstrated site-dependent postmortem release of some drugs from tissue stores accompanied by increases in drug concentrations in the blood. This study was undertaken to investigate whether blood cocaine concentrations change in the body during the postmortem interval and, if so, to measure the direction and magnitude of the changes. In medical examiner cases in which scene investigation suggested that the decreased was a cocaine user, blood samples were collected as soon after death as possible. At autopsy, a second set of samples was collected. Analysis of paired samples by gas chromatography/mass spectrometry (GC/MS) revealed dramatic differences in the cocaine concentration. The magnitude and direction of the change appears to be site dependent. Usually, but not invariably, cocaine concentration in subclavian vein blood decreases while that in heart, aorta, and femoral vein blood increases during the interval between death and autopsy. The findings emphasize the danger inherent in attempting to estimate the concentration of cocaine in blood at the time of death from postmortem data.