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.