Analysis and bioequivalency study on two tablet formulations of co-trimoxazole

This paper describes an analytical procedure for simultaneous quantification of trimethoprim (TMP) and sulphamethoxazole (SMZ) in serum. Serum samples were rendered alkaline with glycine-sodium hydroxide buffer (pH 9.1) and extracted with ethyl acetate. The reconstituted sample was analysed using reversed-phase C-18 column high-performance chromatography. The mobile phase consisted of 75% triethyl ammonium acetate buffer, 20% methanol and 5% acetonitrile. The analytes were monitored at 289 nm and tetroxoprim was used as an internal standard. The maximum values for intra-day coefficients of variation (CV) for TMP-and SMZ were 5.7 and 2.1%, respectively. Interday CV values were 6.4 and 2.2%, respectively. The method was used to compare the bioavailability of two tablet formulations in terms of their pharmacokinetic parameters following oral administration of the tablets to 18 volunteers.