Validation of a Stability-Indicating RP-HPLC Method for the Simultaneous Determination of Trimethoprim and Sulfadimethoxine Sodium in Oral Liquid Dosage Form

A simple, specific, accurate, and stability-indicating RP-HPLC method was developed and validated for the simultaneous determination of Trimethoprim (TMP) and Sulfadimethoxine sodium (SDMS) in Vetricine® oral solution product. The desired separation was achieved on an ODS column (250×4.6 mm i.d., 5 μm) at room temperature. The optimized mobile phase consisted of an isocratic solvent mixture of water:acetonitrile:triethylamine (700:299:1, v/v/v), adjusted to a pH of 5.7 ± 0.05 with 0.2N acetic acid. The mobile phase was fixed at 0.8 ml/min and the analytes were monitored at 254 nm using a photodiode array detector. The effects of the chromatographic conditions on the peaks USP tailing factor, column efficiency, and resolution were systematically optimized. Forced degradation experiments were carried out by exposing TMP, SDMS standards, and the oral solution formulation to thermal, photolytic, oxidative, and acid-base hydrolytic stress conditions. The degradation products were well-resolved from the main peaks and the excipients, thus proving the reliable stability-indicating method. The method was validated as per ICH and USP guidelines (USP34/NF29) and found to be adequate for the routine quantitative estimation of TMP and SDMS in commercially available Vetricine® oral liquid dosage form.