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

To determine the stability of bimatoprost, latanoprost, and travoprost under conditions of simulated daily use and varying degrees of thermal stress.

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.

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.

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.