Treatment of infants with congenital toxoplasmosis: tolerability and plasma concentrations of sulfadiazine and pyrimethamine

The aim was to study the tolerability and plasma concentrations of pyrimethamine and sulfadiazine in children treated for congenital toxoplasmosis. Infants were diagnosed through the Danish Toxoplasma Neonatal Screening Programme, based on detection of toxoplasma-specific IgM- and/or IgA-antibodies on 3 mm blood spots collected from phenylketonuria [PKU cards (Guthrie cards)]. Toxoplasma-infected children received 3 months’ continuous treatment with 50–100 mg/kg per day sulfadiazine in two separate administrations and 1 mg/kg per day pyrimethamine after a 1-day loading dose of 2 mg/kg, and folinic acid 7.5 mg was administered twice weekly. Blood cell counts and body weight were recorded during follow-up. The plasma concentrations of pyrimethamine and sulfadiazine were analysed in a subgroup of seven children, using high performance liquid chromatography with ultraviolet and mass spectrometric detection. Of 48 infants, 41 completed the treatment without change in schedule. Six infants had neutrophil counts below 0.5×10⁹/l, and one infant had an elevated bilirubin value. Twenty-nine children were tested by a series of neutrophil counts during treatment. The neutrophil count was ≤0.5×10⁹/l or lower in 4/29 (13.8%). None of the children had anaemia or thrombocytopenia. The drugs did not affect weight gain. Mean plasma drug concentrations varied between 1.3 μg/ml and 2.2 μg/ml for pyrimethamine and between 60 μg/ml and 86 μg/ml for sulfadiazine. Treatment efficacy is still a concern, since progression of eye lesions was observed in three eyes during the follow-up period. We concluded that the treatment was well tolerated in 86% (25/29) of the children. The drugs did not affect their weight gain. Drugs given in the recommended doses led to concentrations within expected therapeutic limits.