Simultaneous spectrophotometric determination of sulfadoxine and pyrimethamine in pharmaceutical formulations.

This study was carried out to simultaneously determine quantitatively sulfadoxine and pyrimethamine in four brands of anti-malarial formulations. The reaction principle was based on the complexation reaction between the drugs (pi-donors) and chloranilic acid (pi-acceptor) giving rise to colour formation. The complexes of sulfadoxine and pyrimethamine absorbed maximally at 500 and 520 nm, respectively. The limits of detection of these complexes were 0.005 mg/ml for pyrimethamine and 0.010 mg/ml for sulfadoxine. Calibration graphs were linear at 0.015 mg/ml for pyrimethamine and 0.020 mg/ml for sulfadoxine. Quantitative recovery experiments gave percentage range between 94.79 +/- RSD 3.85% and 98.04 +/- 2.21% for sulfadoxine and 93.75 +/- RSD 0.89% to 103 +/- 1.04% for pyrimethamine. Analysis by the Official method similarly gave percentages range of between 97.9 +/- 2.3% and 100.1 +/- 3.1% for sulfadoxine; 97.8 +/- 1.9% and 99.6 +/- 2.5% for pyrimethamine. Comparison of the two methods by Students t-test did not reflect any statistical difference (P > 0.05). These figures show that these brands of anti-malarial meet the Pharmacopoeia standard of 95-105%. We found this technique suitable for quality assurance of these drugs. The sensitivity, accuracy, simplicity of this technique also commends it for field studies.