Author(s): Rees KA
The distribution of free morphine (FM), codeine and 6-acetylmorphine (6AM) in vitreous humour (VH) and femoral blood (FB) was measured in 70 cases involving heroin/morphine. The relationship between tissue drug concentrations was assessed with respect to case circumstances. Total morphine (TM) concentrations in FB are also reported. The relative concentrations of FM in VH and FB were influenced by survival time. In rapid deaths (<3h after drug intake; n=34) the median FM concentration in VH (0.13 mg/L) was significantly lower than the corresponding result for FB (0.25mg/L; p<.01). In delayed deaths (>3h; n=12) the VH concentration (median 0.15 mg/L) was higher than in FB (0.092 mg/L; p>.05). Free morphine VH/FB ratios were significantly higher in delayed (median 1.3) compared to rapid deaths (0.64). Although these findings indicate a lag in the distribution of morphine into the VH, overlaps were observed in the VH/FB ratio in rapid and delayed death groups which limits the interpretive use of VH/FB ratios. Codeine and 6AM appeared to distribute more rapidly into the VH. Despite the observation that all opiate analytes were correlated between FB and VH (r ≥ 61; p<.01), our results indicate that in the absence of a blood sample, blood concentrations cannot be reliably inferred from that measured in the VH. In the absence of additional toxicological evidence, the use of FM to TM ratios in blood as an indicator of survival time is not advised.