A principal objective of forensic entomotoxicology is to apply insect specimens for post-mortem toxicological analysis. Successful identification of drugs in necrophagous insects may depend on pharmacokinetic processes occurring in larvae. We thus applied a model system involving Lucilia sericata (Meigen, 1826) (Diptera, Calliphoridae) to investigate pharmacokinetics of diazepam in larvae in vitro, followed by a field experiment with Göttingen Minipigs.
Lucilia sericata larvae were fed one of four diazepam concentrations at constant temperature, sampled regularly, and analysed for diazepam and metabolites by liquid chromatography tandem mass spectrometry (LC-MS/MS). Two Göttingen Minipigs of 60 kg each were euthanised one hour after oral administration of 25 mg/kg diazepam and placed outdoors. While available, samples of peripheral blood, cardiac blood, liver, and fly larvae were collected over 70 days. Extracts from porcine samples and larvae were analysed by LC-MS/MS. Some larvae were bred to adulthood and identified morphologically together with 718 larvae.
Oxazepam was a primary metabolite of diazepam in L. sericata larvae. The most prevalent fly species on minipig carcasses were Lucilia caesar (Linnaeus, 1758) (Diptera, Calliphoridae) and Lucilia illustris (Meigen, 1826) (Diptera, Calliphoridae). Diazepam and metabolites were detected in all larval samples, even weeks after porcine samples were unacquirable due to post-mortem decomposition. Ratios of oxazepam and nordazepam to diazepam concentrations in larvae were significantly higher than in associated porcine samples, confirming metabolism in larvae.
These findings are relevant to forensic casework, as there is potential for misinterpreting that the deceased consumed oxazepam or nordazepam rather than diazepam. This caution may also apply to other drugs that can form through metabolism in larvae.