Stability-Indicating HPLC Method for Simultaneous Determination of Sulfadimethoxine and Ormetoprim in an Oral Solution

Abstract

A stability-indicating HPLC method was developed and validated for the simultaneous determination of sulfadimethoxine (SDM) and ormetoprim (OMP) in an oral solution. Chromatographic separation was achieved on a C18 column using 0.05% (v/v) phosphoric acid in water and methanol as the mobile phase under gradient elution, with diode array detection at 275 nm. Retention time modeling was applied to optimize the separation of the two analytes from the nine degradation products generated during forced degradation studies. Under the optimized chromatographic conditions, the retention times of the OMP and SDM were approximately 14.76 and 21.94 min, respectively. The method was validated in accordance with the ICH guidelines for specificity, linearity, accuracy, precision, and robustness. Average recoveries ranged from 98.62% to 99.87% for OMP and from 99.74% to 101.14% for SDM, and the % RSD values for both analytes were below 2%. All of the evaluated performance characteristics met the predefined acceptance criteria. Forced degradation studies under acidic, alkaline, oxidative, thermal, and photolytic conditions demonstrated that the analyte peaks were well-resolved from degradation products, supporting the stability-indicating capability of the method. GAPI and AGREEprep assessments indicated a moderate greenness profile, with an AGREEprep score of 0.40, while a BAGI score of 72.5 indicated good practical applicability. The method was further applied to a 6-month accelerated stability study of the oral solution. These results support the suitability of the proposed procedure for the simultaneous quantification of SDM and OMP in an oral solution and for stability evaluation under the conditions studied.