Two simple, sensitive, accurate and economical spectrophotometric methods were developed for the estimation of Trimethoprim and Sulphamethoxazole simultaneously in tablet dosage forms. First method is based on the simultaneous equations and second method is based on Q-analysis (absorbance ratio method). Trimethoprim and Sulphamethoxazole show absorbance maxima at 256 nm and 254 nm in Methanol respectively. The linearity was obtained in the concentration range of 2-10 µg/ml for Trimethorpim and 2-10 µg/ml for Sulphamethoxazole. In the first method, the concentrations of the drugs were determined by using simultaneous equations; and in the second method, the concentrations of the drugs were determined by using ratio of absorbance at isoabsorptive point and at the max of the one drug. The results of analysis have been validated statistically and by recovery studies.
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