Bioequivalence study of three generic formulations of co-trimoxazole tablets in human urine

Many proprietary and generic formulations of co-trimoxazole tablets commercially marketed in Nigeria are mostly from Asian countries. Nigerians buy these products because of their cheaper prices but not confident with regards to therapeutic, quality, safety, and efficacy. Health professionals usually are cautious about drug product selection and substitution during prescription and dispensing. In this paper, the bioequivalence study of three multi-sourced (generic) co-trimoxazole tablets was carried out on the urine of twelve healthy volunteers. The reversed-phase high performance liquid chromatography was employed for the analysis. Sulphadoxine was used as internal standard. The limits of detection were 76.3 ng/mL for trimethoprim, and 61.9 ng/mL for sulphamethoxazole at 0.16 aufs. The linearity (n = 5) for the calibration curve was of the order, 1.0000 for trimethoprim and 0.9998 for sulphamethoxazole; percentage recoveries for trimethoprim and sulphamethoxazole were 89.4 and 87.9% respectively. The relative bioavailabilities of the two generics to the innovator's product were 104.2% (trimethoprim) and 106.8% (sulphamethoxazole); 114.8% (trimethoprim) and 111.8% (sulphamethoxazole) for a product of reputable pharmaceutical company in Nigeria and Indian product respectively. In conclusion, the three generic formulations of co-trimoxazole tablets were biologically equivalent. Interchangeability of drugs in prescription and dispensing may be recommended in this situation.