Studies in phlebitis VIII: evaluations of pH solubilized intravenous dexverapamil formulations

Injectable and infusion formulations of dexverapamil are evaluated for their potential to produce phlebitis. The evaluation technique utilizes two independent in vitro methods and two in vivo methods to screen a pH solubilized drug for its potential to induce phlebitis due to precipitation at the injection site. One method is based upon a theoretical calculation that simulates the change of solubility upon dilution. Its predictions are confirmed by the second method which consists of an in vitro precipitation experiment. Thermal and visual evaluations are then obtained from an in vivo rabbit ear injection. Dexverapamil formulations that have low buffering capacity are shown to contribute to the incidence of phlebitis to a greater extent than the properly buffered formulations. The calculation and the in vitro precipitation experiment are found to be useful in formulating pH solubilized parenterals. They enable the formulator to optimize pH, drug concentration, and buffer concentration without the need for animal studies. The results of this study show the importance of selecting a buffer that provides adequate buffer capacity in the formulations.