Microsampling with dried blood spots and mass spectrometry enables PK/PD profiling of responses to praziquantel in a Schistosoma haematobium- exposed Zimbabwean population.

Introduction: Praziquantel (PZQ) is commonly used to treat schistosomiasis; however, there is considerable interindividual variability in its efficacy, partly because of genetic variation. Data on this relationship is scarce across Africa - where schistosomiasis is prevalent. This study aimed to investigate the pharmacokinetic/pharmacodynamic and pharmacogenetic relationship between PZQ and its metabolites in a Zimbabwean population infected with Schistosoma haematobium by leveraging dried blood spots (DBS) and mass spectrometry (MS).

Methods: DBS were obtained from 38 Zimbabwean participants on PZQ treatment at four-time points (0.5, 1.5, 2.5, and 4 h). We compared two extraction methods for recovering PZQ and its metabolites from the DBS cards and performed MS analysis to determine the concentrations. A random forest model was used to determine whether CYP1A2 , CYP2C9 , CYP2C19 , CYP2D6 , CYP3A4 , and CYP3A5 known variants were predictive of PZQ efficacy. The relationships between PZQ/metabolite concentration, metabolite ratio, and drug exposure with genotype were determined using a one-way analysis of variance.

Results: An acetonitrile and water (4 : 1) mixture was determined to be optimal for recovering PZQ and its metabolites from the DBS cards. Subsequent MS analysis identified PZQ and six metabolite compounds - including phase 1 metabolites (-2H)-O-PZQ, O2-PZQ, and 4-OH-PZQ. Pooled MS sampling was comparable to individual MS sampling for determining pharmacokinetic profiles at the 2.5 and 4-h time points. The (-2H)-O-PZQ and O2-PZQ metabolites had significantly higher concentrations in participants with CYP2C9*1/*9 and *9/*9 versus those with CYP2C9*1/*1. CYP1A2 rs2069514-A (formerly *1C ) and rs762551-A ( CYP1A2*30 ; formerly *1F ) were observed to alter PZQ pharmacokinetic profiles; however, differences in analyte concentrations across the corresponding genotypes were NS.

Conclusion: We show that low-cost microsampling using DBS and MS is feasible for detecting and quantifying PZQ and its metabolites. Furthermore, our pharmacogenetics analysis elucidates the impact of known cytochrome P450 variants on PZQ drug response in an African setting.