Instrumental evaluation of color of solid dosage forms during stability testing

The principles of color measurement established by the Commission International de I'Eclairage (CIE) have been applied to determine color formation during long-term storage and stability testing of four white commercial solid dosage forms. The products tested were preparations of captopril tablets, flucloxacillin sodium capsules,cefoxitin sodium powder for injection and theophylline controlled release tablets in their original packaging. Different batches of medicines were examined for color formation and chemical stability under ambient conditions and a single batch was monitored on accelerated testing. Only flucloxacillin sodium and cefoxitin sodium showed statistically significant degradation of active drug on ambient storage accompanied by color formation (yellowing) in the latter case. On accelerated testing, linear relationships were observed between color formation and drug content for all formulations except theophylline where color formation occurred without significant drug degradation. The rate of color formation obeyed the Arrhenius equation in every case. Color change can be quantified according to the CIE system and may be useful for potency predictions where a causal relationship between color change and drug decomposition can be established. Even where a causal relationship does not exist, patient confidence in a pharmaceutical product may be undermined by perceptible color change. In this situation, the shelf-life could be specified using the CIE colour system.