Simultaneous determination of pyrimethamine, sulfadiazine and N-acetyl-sulfadiazine in plasma for monitoring infants in treatment of congenital toxoplasmosis

A method for the simultaneous determination of pyrimethamine, sulfadiazine and its metabolite N-acetyl-sulfadiazine in small plasma samples from neonates in treatment for congenital toxoplasmosis has been developed. In this method only 25 μl of plasma is used and a simple sample preparation based on protein precipitation and centrifugation provides highly reliable data as the recovery is about 100% and the precision is good. The analysis is performed using high performance liquid chromatography with UV and mass spectrometric (MS) detection. Pyrimethamine was found to give a linear response using MS detection in the range 0.02-5 μg/ml. Sulfadiazine and its metabolite N-acetyl-sulfadiazine were preferably analysed by UV at 269 nm in the concentration ranges 0.2-200 μg/ml for sulfadiazine and 0.2-50 μg/ml for N-acetyl-sulfadiazine.