Imipenem (IMP) and Cilastatin (CILA) are co-formulated β-lactam antibiotics extensively used in the management of severe bacterial infections, requiring reliable analytical methods for simultaneous estimation to ensure quality control and regulatory compliance. A simple, accurate and reproducible reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed and validated for the concurrent quantification of IMP and CILA in bulk and pharmaceutical dosage forms in accordance with ICH Q2(R1) guidelines. Chromatographic separation was performed on a Zodiac Sil RP-C18 column (250 × 4.6 mm, 3.0 µm) using a mobile phase of methanol and phosphate buffer (pH 3.0) in a 70:30 (v/v) ratio at a flow rate of 1.0 mL/min, with UV detection at 240 nm and an injection volume of 10 µL. IMP and CILA were well resolved with retention times of 2.45 and 3.19 min, respectively and a resolution greater than 3.0. The method exhibited excellent linearity in the ranges of 50–250 µg/mL for IMP and 5–25 µg/mL for CILA with correlation coefficients (r²) of 0.999 for both drugs. Accuracy studies demonstrated mean recoveries of 99.54% for IMP and 100.75% for CILA, while intra- and inter-day precision values were within 2% RSD. The method demonstrated high sensitivity with LOD/LOQ values of 2.16/6.62 µg/mL for IMP and 0.037/0.11 µg/mL for CILA. Robustness was confirmed under deliberate variations in flow rate and mobile phase composition. The proposed method is rapid, sensitive and reliable, making it highly suitable for routine quality control and stability testing in pharmaceutical industries.
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