Bridging a Pharmacopoeial Gap DoE-Optimized RP-HPLC Assay and Dissolution Method Development & Validation for Cefixime–Ofloxacin Fixed-Dose Combination Tablets

Cefixime (200 mg) and Ofloxacin (200 mg) fixed-dose combination (FDC) tablets have been listed on India's CDSCO-approved formulary since 2010, yet no pharmacopoeia — Indian pharmacopoeia, United State Pharmacopeia, British pharmacopoeia, European pharmacopoeia, or International pharmacopoeia —currently prescribes an official assay or dissolution method for the combination, despite validated methods existing for each drug individually. This work addresses that gap through two linked studies. First, an Analytical Quality by Design (AQbD) approach was used to develop a stability-indicating gradient RP-HPLC assay: an Ishikawa fishbone analysis identified flow rate, column temperature, and buffer pH as critical method parameters, which were optimized using a Box–Behnken Design to achieve baseline resolution (>6.8) of both actives within a 10-minute run. The method was validated per ICH Q2 (R2) — linear (R² = 1.00), accurate (100.0–100.7% recovery), precise (%RSD < 1%), specific, and robust — and successfully applied to 8 marketed FDC brands, all within the 90–110% label-claim window, with an AGREE greenness score of 0.79. Second, a dissolution method was developed by screening five media, two apparatus types, and three agitation speeds against solubility and disintegration behavior of both BCS Class II (Ofloxacin) and Class IV (Cefixime) actives. Phosphate buffer pH 7.2, USP Apparatus 2 (paddle), 100 rpm, and 45-minute sampling were identified as optimal, achieving ~99% release for both drugs. This method was similarly validated per ICH Q2 (R2) and discriminated compliant from marginal batches across eight marketed formulations. Together, these methods provide the first validated compendial-ready assay and dissolution procedures for this widely prescribed FDC.