Simultaneous determination of tretinoin and clindamycin phosphate and their degradation products in topical formulations by reverse phase HPLC

A new HPLC method based on reverse phase separation and photodiode‐array detection has been developed for the simultaneous determination of tretinoin and clindamycin phosphate, and their degradation products in topical formulations. The method has been shown to be stability indicating, accurate, and precise for two different formulation vehicles. Separation was achieved on a reverse phase C18 column (Lichrospher, RP18, 5 μm, 25 cm×4.6 mm ID, Phenomenex, USA) using a simple gradient with aqueous‐acetonitrile and aqueous‐methanol mobile phases. The method recovery averaged 100.3% for tretinoin and 99.6% for clindamycin phosphate at a concentration range between 80% and 120% of the label claim. The method can be applied to assess the stability of tretinoin and clindamycin phosphate in pharmaceutical formulations containing tretinoin and clindamycin phosphate individually or in combination as active drugs.