Tafenoquine is not neurotoxic following supertherapeutic dosing in rats

Tafenoquine is a new drug for malaria prevention. The goal of the present work was to conduct a specific neurobehavioral study in rats with histopathological assessment of the brain.

The clinical, hematological, behavioral, motor activity, and neurohistopathologic changes induced by different dose levels of tafenoquine were evaluated following single super-therapeutic dose administration. Toxicokinetic data were generated to allow extrapolation to clinical exposures.

At the highest dose (500 mg/kg), two animals (of 12) died. Surviving animals showed clinical signs of toxicity and had reduced body weight 7-8 days after dosing. Decreases in motor activity were observed on more than one occasion at doses > 9-fold higher than the clinical exposure. No statistically significant changes were observed for other behavioral endpoints. No neurohistopathological changes were noted. Changes in hematological and clinical pathology endpoints were observed at the lowest dose level (125 mg/kg). For context, the human dosing regimen is a 10 mg/kg load followed by 3.3 mg/kg weekly (in a 60 kg person).

As in humans, adverse events other than neurotoxicity were dose-limiting for tafenoquine in rats. This raises the prospect that a new weekly prophylactic, without neurologic liability, may become available in the near future.