Photostabilization of papaverine hydrochloride solutions

Abstract: The stability of aqueous and non-aqueous papaverine hydrochloride solutions exposed to the UV radiation is poor. In order to enhance its photo-stability suitable light absorbers may be used. There werefour photo-protectors considered in this work: 4-aminobenzoic acid, sodium benzoate, methyl 4-hydroxybenzoate and propyl 4-hydroxybenzoate, whose UV absorption spectra characteristics match to some extent with the UV spectrum of papaverine. Approximately 20 mg/mL papaverine chloroform solutions with the above non-toxic additives in the concentrations 0.01; 0.05; 0.10% were exposed to the UV light of 254 nm. High performance capillary electrophoresis was used to determine the papaverine hydrochloride concentration loss as a function of time exposition to the light. It was found that papaverine hydrochloride photolysis proceeds according to the first-order kinetics. Methyl 4-hydroxybenzoate was found to be the best UV radiation-protective agent, and at the concentration 0.10%, the reaction rate constant decreases from 0.143 h(-1) to 0.028 h(-1). Both 4-hydroxybenzoate esters develop a more efficient UV radiation-protective activity than sodium benzoate, because the latter additive molar extinction coefficient is less significant. However, in spite of a high value of 4-aminobenzoic acid molar absorptivity coefficient, it is an unsuitable photo-protector for papaverine hydrochloride solutions, because its UV absorption spectrum does not match with that of papaverine.