Absorption
Maximum plasma concentrations were generally observed 12 to 15 hours following oral administration.
Food Effect: Plasma tafenoquine AUC increased by 41% and Cmax increased by 31% when administered as an investigational capsule formulation with a high-calorie, high-fat meal (approximately 1,000 calories with 15% protein, 25% carbohydrate, and 60% fat) compared with the fasted state.
Distribution
Protein binding of tafenoquine is >99.5%. The apparent oral volume of distribution is ~1,600 L. Following single- and multiple-oral-dose administration, tafenoquine whole blood concentrations were on average 67% higher than corresponding plasma values.
Elimination
The apparent oral clearance of tafenoquine is approximately 3 L/h. The average terminal half-life is approximately 15 days.
Metabolism: Tafenoquine undergoes slow metabolism. Unchanged tafenoquine represented the only notable drug-related component in human plasma after a single oral dose of tafenoquine.
Excretion: The full excretion profile of tafenoquine in humans is unknown. Over a 6-day collection period, renal elimination of unchanged tafenoquine was low.
Specific Populations
Pharmacokinetics of tafenoquine were not significantly impacted by age, sex, ethnicity, and body weight. The effect of renal or hepatic impairment on tafenoquine pharmacokinetics is unknown.
Drug Interaction Studies
Clinical Studies: No clinically significant effects on tafenoquine pharmacokinetics were observed following coadministration with chloroquine, dihydroartemisinin-piperaquine, or artemether-lumefantrine in healthy subjects.
No clinically significant effects on the pharmacokinetics of dihydroartemisinin, piperaquine, artemether, lumefantrine, or substrates of cytochrome P450 isoenzymes (CYP)1A2 (caffeine), CYP2D6 (desipramine), CYP2C8 (chloroquine), CYP2C9 (flurbiprofen), or CYP3A4 (midazolam, chloroquine) were observed following coadministration of tafenoquine in healthy subjects.
In Vitro Studies Where Drug Interaction Potential Was Not Further Evaluated Clinically: Tafenoquine inhibited metformin transport via human OCT2, MATE-1, and MATE2-K transporters. Clinical drug interaction studies with tafenoquine and OCT2 and MATE substrates have not been conducted [see Drug Interactions (7)].
The effect of tafenoquine on substrates of P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and organic anion transporting polypeptides 1B1/1B3 (OATP1B1/OATP1B3) is unknown.