Development and validation of an LC-MS/MS method for the quantification of the anthelmintic drug moxidectin in a volumetric absorptive microsample, blood, and plasma: application to a pharmacokinetic study of adults infected with Strongyloides stercoralis in Laos

Moxidectin is a promising candidate for addition to the lean repertoire of drugs against neglected tropical diseases (NTD) including strongyloidiasis. Pharmacokinetic (PK) and -dynamic studies are required to support its clinical development. Microsampling approaches enable PK studies in the challenging environments where NTDs are most prevalent, due to simplified collection and processing. We developed a liquid chromatography tandem mass spectrometry method for the sensitive quantification of moxidectin in human blood obtained by capillary sampling with the microsampling device Mitra(R) compared to blood and plasma obtained by venous sampling. Sample preparation consisted of protein precipitation, evaporation and reconstitution and also included phospholipid filtration for blood and plasma. Moxidectin was detected by multiple reaction monitoring (640.4 --> 528.5 m/z) using a Luna C8(2) (30 x 2.0 mm, 3 microm particle size, 100 A) analytical column with a gradient program of 6 min duration. Validation was performed with respect to accuracy, precision, sensitivity, selectivity, linearity, stability, recovery, and haematocrit influence with a limit of quantification of 0.5 and 2.5 ng/mL, for venous and capillary blood respectively. Moxidectin was stable up to 2 months at storage condition (blood and plasma: -20 degrees C, microsamples: room temperature), 3 cycles of temperature shift, for at least 4 h on the bench-top and 24 h in the autosampler (4 degrees C). Deviations of inter- and intra-assay accuracy and precision were smaller than 12.6% and recoveries were in the range of 80.7-111.2%. The method was applied to samples obtained from nine Strongyloides stercoralis-infected adults from northern Laos. A good agreement in the time-concentration profiles of moxidectin and a high consistency in PK parameters was found between the different matrixes and sampling strategies: e.g. identical time to reach maximal concentration of 4.0 h and a similar maximal concentration of 83.9-88.5 ng/mL of moxidectin. The simple and practical capillary procedure using Mitra(R) microsampling has been demonstrated to be suitable for PK studies of moxidectin and will pave the way for future PK studies.