Characterizing the blood stage antimalarial activity of pyronaridine in healthy volunteers experimentally infected with Plasmodium falciparum

Although pyronaridine has been used to successfully treat malaria for many years, its antimalarial activity in humans has not been completely characterized. This volunteer infection study aimed to determine the pharmacokinetic/pharmacodynamic (PK/PD) relationship of pyronaridine in healthy malaria naive adults. Volunteers were inoculated with Plasmodium falciparum 3D7-infected erythrocytes on day 0 and different single oral doses of pyronaridine were administered on day 8. Parasitemia, and concentrations of pyronaridine in whole blood were measured and standard safety assessments performed. Curative artemether-lumefantrine therapy was administered if parasite regrowth occurred, or on day 47{+/-}2. Outcomes were parasite clearance kinetics, PK and PK/PD parameters from modelling. Ten participants were inoculated and administered 360 mg (n=4), 540 mg (n=4), or 720 mg (n=1) pyronaridine. One participant was withdrawn without receiving pyronaridine. Time to maximum pyronaridine concentration after dosing was 1-2 hours and the elimination half-life was 8-9 days. A parasite clearance half-life of approximately 5 hours was calculated for all dose levels. Parasite regrowth occurred after dosing with 360 mg (4/4 participants) and 540 mg (2/4 participants). Key efficacy parameters of pyronaridine including the minimum inhibitory concentration (MIC: 5.5 ng/mL) and minimum parasiticidal concentration that leads to 90% of maximum effect (MPC90: 8 ng/mL) were derived from the final PK/PD model. Adverse events considered related to pyronaridine were predominantly mild to moderate gastrointestinal symptoms. There were no serious adverse events. Data obtained in this study will support the use of pyronaridine in new antimalarial combination therapies by informing partner drug selection and dosing considerations.