Development and validation of an HPLC method for simultaneous determination of trimethoprim and sulfamethoxazole in human plasma.

The combination of trimethoprim (TMP) and sulfamethoxazole (SMX) is used in the treatment of many common infections such as urinary, respiratory and gastrointestinal tract infections. The aim of this study was to determine TMP and SMX simultaneously in human plasma samples by high performance liquid chromatography (HPLC) using antipyrine as the internal standard. Separation of the compounds was achieved on a reverse-phase C8 column packed with 5 microm dimethyl octadecylsilyl bonded amorphous silica (4.