A DBS method for quantitation of the new oral trypanocidal drug fexinidazole and its active metabolites.

Aim: Fexinidazole (FEX) is a nitroimidazole being developed as a new trypanocide treatment for human African trypanosomiasis/sleeping sickness. Its main metabolites, fexinidazole sulfoxide (M1) and fexinidazole sulfone (M2), show the same in vitro pharmacological activity as FEX.

Methods & Results: An LC-MS/MS assay was developed for quantitation of FEX in DBS, collected via finger-prick from healthy subjects. The DBS assay was specific, accurate and reproducible for FEX, M1 and M2 when validated against the current plasma assay. DBS samples were stable for 24 h at 37°C with 95% relative humidity, and 58 weeks desiccated at room temperature.

Conclusion: DBS finger-prick sampling offers a simple, practical method for determining FEX, M1 and M2 concentrations in clinical studies in Africa.