Effect of the buffer system on stability of tetracaine hydrochloride 0.5% eyedrops

The effect of the buffer system on the stability of tetracaine hydrochloride in eyedrop formulation was evaluated. Eyedrop formulations containing tetracaine hydrochloride 0.5%(w/v) were prepared using different buffer systems (acetate, phosphate and borate buffer) under a constant pH of 5.4, and a buffer concentration of 0.06M. Long-term tests at 26 o C and accelerated stability tests at elevated temperature (45, 50, 60 oC) over a period of 168 days were carried out by following the macroscopic view, pH, sterility, content of tetracaine hydrochloride and detection of the degradation products. Also, values of the constant of degradation rate at different temperatures and t90% were calculated. The phosphate and acetate buffers provided satisfactorystability of tetracaine hydrochloride eyedrops, while borate buffer was not sufficient to maintain the pH value of the solution