Stability assessment of preservative-free losartan potassium eye drops compounded for ophthalmic use

To evaluate the physicochemical and microbiological stability of preservative-free losartan potassium (LP) eye drops (0.8 mg/mL) prepared using balanced salt solution (BSS), normal saline (NS) or glucose saline (GS) and stored in sterile polypropylene eye drop bottles under different temperature conditions for 30 days.

Three independent batches of each formulation (BSS, NS and GS) were aseptically prepared in a laminar flow cabinet and stored under three conditions: room temperature (25±4°C), refrigeration (4±3°C) and freezing (-20±5°C). Three samples from each batch were analysed for each condition and time point. LP concentrations were measured on days 0, 7, 15, 22 and 30 using high-performance liquid chromatography with photodiode-array detection (HPLC-DAD) and ultraviolet (UV) - visible spectrophotometry. Visual inspection was performed to identify macroscopic changes and physicochemical parameters - including pH, osmolality and refractive index - were evaluated. Microbiological quality was assessed on days 0, 10, 20 and 30.

BSS and NS formulations maintained 90-110% of their initial LP concentration under all storage conditions. The GS formulation remained stable when refrigerated or frozen but showed a marked decline at 25°C, with turbidity and concentrations falling below 50% by day 20. pH, osmolality and refractive index remained within acceptable physiological ranges for ophthalmic solutions. All samples tested negative for microbial growth.

LP eye drops prepared with BSS or NS were stable in closed sterile eye drop bottles for at least 30 days under all tested conditions. Frozen and refrigerated conditions are preferred for storage. Because the formulation does not contain preservatives, its use is recommended for no longer than 7 days after opening. GS-based formulations are not recommended for ophthalmic use. The conducted stability study provides hospital pharmacies with data supporting the safe preparation, storage and use of non-commercial ophthalmic formulations.