Study of the Physicochemical Stability of a Fortified Eye Drop Based on Vancomycin

Background: Fortified eye drops containing vancomycin are generally not available in a ready-to-use form. As a result, hospital pharmacies are forced to prepare these solutions from injectable formulations, adapted to ophthalmic specificities. This process raises challenges in terms of stability, since injectable formulations are not designed for prolonged topical use or for storage conditions in ophthalmic vials. The stability of these eye drops is thus influenced by various factors such as storage temperature, exposure to light, pH and potential interactions with packaging materials, which can alter their efficacy and safety. The primary objective: In this study, the focus will be on the evaluation of the physicochemical stability of the fortified vancomycin eye drops. This analysis will determine whether the formulation maintains its therapeutic properties over time, taking into account storage factors such as temperature, pH and interaction with packaging material. Methods: The duration of the study was set at 6 weeks (1 month and a half). The samples prepared for the study will be stored at two different temperatures: room temperature and in the refrigerator (2 to 8°C). The parameters controlled are as follows: clarity (by visual inspection), pH and concentration of active ingredient. Samples for analysis are taken on D0, D1, D3, D5, D7, D14, D21, D28, D35 and D42 for each storage temperature. The bottles are then labeled and numbered with even numbers for eye drops to be stored in the refrigerator (2 to 8°C) and odd numbers for eye drops to be stored at room temperature (nearly 25°C). On each sampling date selected, a bottle is taken and analyzed for each storage temperature in accordance with the adopted schedule. Visual inspection, pH measurement and HPLC dosage will be carried out. Results: Our study allowed us to determine the average physicochemical stability of vancomycin-fortified eye drops before opening. This duration is 6 weeks for eye drops stored between 2 and 8°C and 2 weeks for eye drops stored at room temperature. However, with the appearance of crystals in the sixth week of storage in the refrigerator, it would be prudent to limit ourselves to a storage duration of 1 month at 4°C. A more complete study including microbiological control could be considered in order to be able to recommend a more concise storage duration. Conclusion: This stability study could motivate the initiative to upgrade the status of antibiotic-fortified eye drops from magistral preparation to the status of hospital pharmaceutical preparation complying with the rules of good preparation practices, as is now recommended at hospital pharmacy levels throughout the world. Batches of eye drops could therefore be prepared in advance and stored, thus ensuring the permanent availability of the drug and saving time in the preparation phase.