Concentrations of free-morphine in peripheral blood after recent use of heroin in overdose deaths and in apprehended drivers

The concentration of free-morphine was determined in peripheral (femoral) blood from heroin-related deaths and compared with the concentration in venous blood from impaired drivers. The presence of 6-MAM in blood or urine served as a biomarker for recent use of heroin. Males dominated over females (p < 0.001) in both the autopsy cases (88%) and the drivers (91%), although their mean age was about the same 33–35 y (p > 0.05). Concentrations of free-morphine in blood were not associated with age of heroin users in Sweden (p > 0.05). The median concentration of free-morphine was higher in autopsy cases (0.24 mg/L, N = 766) compared with apprehended drivers with 6-MAM in blood (0.15 mg/L, N = 124, p < 0.05), and appreciably higher than in drivers with 6-MAM in urine but not in blood (0.03 mg/L, N = 1823, p < 0.001). The free-morphine concentration was above 0.20 mg/L in 65% of autopsy cases, 36% of drivers with 6-MAM in blood but only 1.4% of drivers with 6-MAM in urine. Poly-drug deaths had about the same concentrations of free-morphine in blood (0.24 mg/L, N = 703) as heroin-only deaths (0.25 mg/L, N = 63). The concentration of morphine in drug overdose deaths (median 0.25 mg/L, N = 669) was about the same as in traumatic deaths among heroin users (0.23 mg/L, N = 97). However, the concentration of morphine was lower when the deceased had consumed alcohol (0.18 mg/L, N = 104) compared with taking a benzodiazepine (0.32 mg/L, N = 94). The concentration distributions of free-morphine in blood in heroin-related deaths overlapped with the concentrations in impaired drivers, which makes the interpretation of toxicology results difficult without knowledge about tolerance to opiates in any individual case.