Unexpected variation of the codeine/morphine ratio following fatal heroin overdose

Postmortem samples from 14 cases of suspected heroin overdose were subjected to a preliminary systematic toxicological analysis in order to highlight the presence of unknown exogenous compounds (e.g., drugs of abuse, alcohol) that may have played a role in the mechanism of death. This analysis unveiled histories of poly-drug use in seven of the cases under investigation. Moreover, the concentrations of morphine and codeine in the brain were also investigated, and the results were compared with the data obtained from the blood specimens. The concentration of morphine in blood ranged from 33 to 688 ng/mL, while the concentration of codeine ranged from 0 to 193 ng/mL. However, in the brain, the concentration of morphine was found to be between 85 and 396 ng/g, while the levels of codeine ranged from 11 to 160 ng/g. The codeine/morphine ratio in the blood ranged from 0.043 to 0.619; however, in the brain, the same ratio was found to be between 0.129 and 0.552. In most cases, a significantly higher codeine/morphine ratio was found in the brain, suggesting the accumulation of codeine in brain tissue due its high lipophilicity as compared with morphine.