Tretinoin/isotretinoin interconversion A problem in preparing pharmaceutical formulations

Maio, V. M. ria Dos Passos; Froehlich, P. E. uardo; Bergold, A. M. ria

Tretinoin is applied topically in the treatment of acne. Isotretinoin, its isomer, inhibits keratinization and it is used orally. Both are light sensitive. The aim of the present work is to evaluate the purity of tretinoin (raw material) used in local pharmacies for pharmaceutical preparations. Analysis was carried out according to official codes. Tretinoin sample was found to be out of pharmacopeial specifications. Methanolic solutions of both isomers were also analysed by HPLC, in order to evaluate their photostability. After 25 minutes less than 30% of original substance remained in the solutions. Tretinoin is the main degradation product of isotretinoin and vice-versa.