Thermal stability of bimatoprost, latanoprost, and travoprost under simulated daily use.

PURPOSE: To determine the stability of bimatoprost, latanoprost, and travoprost under conditions of simulated daily use and varying degrees of thermal stress.
METHODS: Commercially available bimatoprost, latanoprost, and travoprost were obtained in their original bottles as distributed by the manufacturers. Bottles were stored in calibrated, nonhumidified, light-free incubators maintained at 27°C, 37°C, or 50°C for 3, 9, 15, or 30 days. Capped bottles were inverted and left uncapped for 1  min daily to simulate patient use; no drops were expelled. Bimatoprost concentration was analyzed using liquid chromatography with ultraviolet detection at 210  nm. Latanoprost and travoprost concentrations were analyzed by liquid chromatography/tandem mass spectrometry (MS/MS) using selected reaction monitoring.
RESULTS: Off-the-shelf control bottles of bimatoprost contained 102% of the labeled concentration. In all combinations of stress temperature and duration, mean bimatoprost concentration ranged from 100% to 116% of the labeled concentration with no measurable degradation. Off-the-shelf control bottles of latanoprost contained 115% of the labeled concentration. Mean latanoprost concentration ranged from 97% to 120% of the labeled concentration. Latanoprost was stable at 27°C. When stressed at 37°C or 50°C, latanoprost degraded at a rate of 0.15 or 0.29  μg/mL/day, respectively. Off-the-shelf control bottles of travoprost contained 120% of the labeled concentration. Mean travoprost concentration ranged from 83% to 142% of the labeled concentration. Travoprost was stable at 27°C and 37°C, although concentration measurements at 37°C exhibited high variability. When stressed at 50°C, travoprost degraded at a rate of 0.46  μg/mL/day.
CONCLUSIONS: Higher than expected concentrations for stressed drug samples are likely a result of evaporation. Under the conditions of thermal stress tested in this study, bimatoprost remained stable for all conditions tested. Latanoprost degradation was measurable only in samples stressed at 37°C and 50°C, whereas travoprost degradation was statistically significant only in samples stressed at 50°C.