Pharmacokinetic Properties of Conventional and Double-Dose Sulfadoxine-Pyrimethamine Given as Intermittent Preventive Treatment in Infancy

Intermittent preventive treatment in infancy (IPTi) entails routine administration of antimalarial treatment doses at specified times in at-risk infants. Sulfadoxine-pyrimethamine (SDX/PYR) is a combination that has been used as first-line IPTi. Because of limited pharmacokinetic data and suggestions that higher milligram/kilogram pediatric doses than recommended should be considered, we assessed SDX/PYR disposition, randomized to conventional (25/1.25 mg/kg of body weight) or double (50/2.5 mg/kg) dose, in 70 Papua New Guinean children aged 2 to 13 months. Blood samples were drawn at baseline, 28 days, and three time points randomly selected for each infant at 4 to 8 h or 2, 5, 7, 14, or 21 days. Plasma SDX, PYR, and N-4-acetylsulfadoxine (NSX, the principal metabolite of SDX) were assayed by high-performance liquid chromatography (HPLC). Using population modeling incorporating hepatic maturation and cystatin C-based renal function, two-compartment models provided best fits for PYR and SDX/NSX plasma concentration profiles. The area under the plasma concentration-time curve from 0 h to infinity (AUC(0-infinity)) was greater with the double dose versus the conventional dose of PYR (4,915 versus 2,844 mu g/day/liter) and SDX (2,434 versus 1,460 mg/day/liter). There was a 32% reduction in SDX relative bioavailability with the double dose but no evidence of dose-dependent metabolism. Terminal elimination half-lives (15.6 days for PYR, 9.1 days for SDX) were longer than previously reported. Both doses were well tolerated without changes in hemoglobin or hepatorenal function. Five children in the conventional and three in the double-dose group developed malaria during follow-up. These data support the potential use of double-dose SDX/PYR in infancy, but further studies should examine the influence of hepatorenal maturation in very young infants.