Distribution of Butalbital in Postmortem Tissues and Fluids from Non-Overdose Cases

During the investigation of fatal aviation accidents, postmortem samples from the pilots/co.pilots are submitted to the Federal Aviation Administration's (FAA) Civil Aerospace Medical Institute (CAMI) for toxicological analysis. Although therapeutic levels for most drugs are typically reported in the scientific literature for blood and plasma, blood specimens are received in only approximately 70% of our cases. Therefore, it is imperative for an accident investigator and forensic toxicologist to be able to estimate drug concentrations in an aviation accident victim's blood from available tissue drug concentrations. This is exemplified by a recent aviation fatality in which butalbital was identified in the muscle tissue of a pilot. In this case, no blood was available for analysis, but investigators needed to know the approximate butalbital concentration expected in the victim's blood. Certain side effects of butalbital, such as drowsiness, sedation, dizziness, and a feeling of intoxication, could affect pilot performance and become a significant factor in an aviation accident. Thus, our laboratory determined the distribution of butalbital in various postmortem tissues and fluids. The distribution coefficients for butalbital, expressed as specimen/blood ratios, were found to be as follows: 0.66 ± 0.09 (muscle, n = 4), 0.98 ± 0.09 (kidney, n = 4), 0.87 ± 0.06 (lung, n = 4), 0.75 ± 0.03 (spleen, n = 4), 0.96 ± 0.07 (brain, n = 3), 2.22 ± 0.04 (liver, n = 4), and 0.91 ± 0.17 (heart, n = 2). The results obtained from our limited number of cases suggest that muscle, kidney, lung, spleen, brain, liver, and heart could be used, in a cautious and conservative fashion, to estimate butalbital blood concentrations.