Studies on the photostability of reserpine in parenteral solutions

The photostability of reserpine in several parenteral formulations has been studied and the effects of some commonly used stabilizers have been evaluated. The kinetic data indicate that the photodegradation of reserpine follows zero order kinetics in all the formulations at pH = 2 and 3. The stability of reserpine appears to be higher at pH = 3 than at pH = 2. 3-dehydroreserpine, isoreserpine and lumireserpine were identified as the major photodegradation products by TLC, suggesting that the photodegradation in acidic solutions occurs initially via an oxidative mechanism. The combined effect of EDTA and PABA on the photostability of reserpine was more significant than their individual effect. The formulations in which benzyl alcohol was used as vehicle were found to be more stable than those having propylene glycol. Polyethylene glycol was found to be a better surfactant than Tween 80. The degree of stabilization in the presence of surface active agents has been explained in terms of micellar theory and the degree of hydration of micelles. A stable formula for parenteral solution of reserpine has been suggested.