Development of a Colorimetric Method for Determination of Piroxicam in Pharmaceutical Formulation Based on Charge Transfer Complex Formation Using Picric Acid

Background: Piroxicam is a non-steroidal anti-inflammatory drug (NSAID) that is used to manage mild to moderate pain, arthritis, and other inflammatory conditions. There is a dearth of simple, cost-effective, and reliable colorimetric methods for the routine determination of piroxicam in pharmaceutical formulations. The study was aimed at developing a colorimetric method for quantifying piroxicam based on charge-transfer complexation between piroxicam and picric acid. Methods: The method is based on the formation of a charge-transfer complex between piroxicam an electron donor and picric acid as the electron acceptor. The yellow coloured product formed was quantified at the absorption maximum of 420 nm. The effect of various experimental conditions (reaction time, solvent type and reagent concentration) on complex formation were also investigated. The method was validated as per ICH guidelines. The accuracy was evaluated using recovery studies while precision was evaluated on intra-day and inter-day basis. The limit of detection (LOD), limit of quantification (LOQ) and molar absorptivity were determined and the method was compared with the official titrimetric assay method for the drug. Results: The optimized conditions for complex formation were found to involve the use of Dichloromethane as solvent, a reaction time of 10 minutes and 2.5 ml of 0.001% picric acid solution. 2 Beer's law was obeyed in the concentration range of 20 – 100 μg/ml (r = 0.994). The method showed good precision with inter-day precision in the range of 0.03 – 0.91 % RSD while intra-day precision was from 0.02 – 0.85 % RSD. A comparison of the proposed method with the official method revealed that they produce comparable analytical results. Conclusion: The developed method was applied successfully to the analysis of piroxicam in capsule formulation with good accuracy and precision and without any interference from the excipients. As such, the newly developed method can serve as a useful technique for the quality assessment of piroxicam.