Physical stability of 0.02% chlorhexidine digluconate eye drops in 5% glucose or phosphate buffer at refrigerated and room

28 September 2021

Erwin Lenglet1, Manon Gareau1, Léa Savio1, Mathieu Wasiak1, Yassine Bouattour1,2, Valérie Sautou1,2, Philip Chennell1,2
1 : CHU Clermont-Ferrand, Pôle Pharmacie, 63000 Clermont-Ferrand, France
2 : Université Clermont Auvergne, CHU Clermont-Ferrand, CNRS, SIGMA Clermont-Ferrand, ICCF, 63000 Clermont-Ferrand, France

0.02 % chlorhexidine digluconate ophthalmic solutions are an efficient alternative to polyhexamethylene biguanide for the treatment of Acanthamoeba keratitis. However, the very limited data available regarding its stability limits its clinical use. As chlorhexidine precipitates with sodium chloride, the objective of this study was to perform a preliminary investigation of the physical stability of 0.02% chlorhexidine solutions in two alternative diluents: 5% glucose or phosphate buffer.

Two 0.02% chlorhexidine diluents were studied: a 140 mM phosphate buffer adjusted to pH 5.55, and 5% glucose. These solutions were sterilized by filtration and aseptically conditioned in Novelia® eye dropper (Nemera). The units were stored at ambient (22±2°C) or refrigerated temperature (5±3°C) for up to 56 days. The following parameters were measured in triplicate: pH, osmolality, turbidity and subvisible particles count (from 3 to 100 µm). Macroscopic particles and color change were checked by visual examination under day light and under polarized white light. A sterility test was also realized every 28 days.

For both diluents, none of the measured parameters varied by more than 2.02% (pH) and 6.59% (osmolality) from initial values (pH = 5.57±0.03 and 5.13±0.06 and osmolality of 268±2 and 290±5 mOsmol/kg for respectively the phosphate buffer and 5% glucose solution). Turbidity values stayed below 1.3 FNU. Subvisible particles values did not increase for both diluents for a storage at ambient temperature. No color change or macroscopic particles were detected and sterility was preserved.

Discussion - Conclusion
0.02% chlorhexidine digluconate solutions did not present any physical instabilities when stored at ambient or refrigerated temperature in phosphate buffer or 5% glucose for 56 days. This is not unexpected, as neither of these diluents contain chloride anions which are incompatible with chlorhexidine. As glucose solutions are a more favourable media for bacteria growth, the best diluent and storage condition seems to be the phosphate buffer with an ambient storage. This preliminary study would need to be completed by a full physicochemical study before any overall conclusions can be made.

Keywords : Chlorhexidine, eye drops, physical stability, Acanthamoeba keratitis

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