Studies on the stability of injectable solutions of some phenothiazines. Part 1: Effects of pH and buffer systems

The stability of phenothiazines is affected by the pH-value of the solution. At the pH-values of maximum stability, triflupromazine hydrochloride and chlorpromazine hydrochloride are more stable than promazine hydrochloride. The stability of chlorpromazine hydrochloride in the Sörensen's phosphate buffer is slightly higher than that in the McIlvaine's citric acid-phosphate buffer system. On the other hand, the stbility of promazine hydrochloride and triflupromazine hydrochloride in the latter buffer system is slightly higher than that in the former one.