Stability-indicating RP-HPLC method for analysis of the antibiotic doripenem in pharmaceutical formulation—comparison to UV spectrophotometry and microbiological assay

A stability-indicating liquid chromatographic (LC) method with UV detection was developed for the determination of doripenem in the marketed formulation (Doribax® 500 mg, powder for injection). A forced degradation study was conducted according to available guidelines and main references. Thermal, oxidizing, acidic and basic stress conditions were assayed to show the stability-indicating power of the method. Chromatographic separation was achieved using an isocratic elution method in a reversed-phase system using a mobile phase prepared from phosphate buffer and acetonitrile. Extensive degradation was observed under thermal, oxidative and basic treatment, and the products formed were detected without interference in the analysis of doripenem. To verify the efficiency of chromatographic run, the system suitability was studied. The theoretical plates (N = 5498.3) and tailing factor (tf = 0.951) were constant during repeated injections. The retention time of doripenem was 7.35 min and the method was validated within the concentration range 5–50 μg mL−1 (r = 0.999). Adequate results were obtained that indicate repeatability (RSD % = 1.03–1.37), inter-day precision (RSD % = 0.51) and accuracy. In comparison to spectrophotometric and microbiological methods, statistical analysis showed no significant difference between the obtained results. The proposed method was successfully applied to doripenem quantification, showing it is applicable to determine the antibiotic in the presence of degradation products and also that is a reliable method for routine analysis.