Concentration ratios of free-morphine to free-codeine in femoral blood in heroin-related poisoning deaths.

The concentrations of free-morphine (Mo), free-codeine (Co) and 6-monoacetyl morphine (6-MAM) were determined in femoral blood in N=747 heroin-related deaths. The opiates were determined by isotope dilution gas chromatography-mass spectrometry after solid-phase extraction. The median blood concentrations of 6-MAM, free-morphine and free-codeine were 0.01 mg/L, 0.24 mg/L and 0.02 mg/L, respectively. The mean and median Mo/Co concentration ratios were 13.2 and 11.0, respectively with a range from 0.2 to 124. Despite the fact that all victims had taken heroin, there were eight cases (1.1%) with a Mo/Co ratio less than one and 18 cases (2.4%) with a ratio less than two. The free-morphine concentration in blood did not depend on the Mo/Co ratio; median 0.29 mg/L (Mo/Co<2.0) and median 0.25mg/L (Mo/Co ratio>2.0). By contrast, the concentration of free-codeine in blood was highly dependent on the Mo/Co ratio; median 0.75 mg/L (Mo/Co<1.0) and median 0.30 mg/L (Mo/Co ratio<2.0). A Mo/Co ratio in post-mortem (PM) femoral blood >1.0 is compelling evidence that the deceased had taken illicit heroin. However, finding a low Mo/Co ratio (<1.0 or <2.0) does not preclude use of heroin because such low ratios are possible if a person had co-ingested heroin along with use or abuse of codeine medication.