Ex vivo evaluation of the influence of pH on the ophthalmic safety, antibacterial efficacy and storage stability of povidone‐iodine

ABSTRACT

Clinical relevance

The monitoring and controlling of pH is important when preparing solutions for ophthalmic administration. In the case of povidone‐iodine, dilution in an appropriate buffer is needed to improve its ophthalmic safety.

Background

Povidone‐iodine is a broad‐spectrum antiseptic agent that is commonly used in ophthalmic applications due to its cost‐effectiveness and accessibility. However, native povidone‐iodine has a pH of about 4.0 and is known to irritate the ocular surface. This study assessed whether adjusting povidone‐iodine formulation pH would influence its ex vivo ophthalmic safety, alongside its impact on antibacterial efficacy and storage stability.

Methods

One per cent w/v povidone‐iodine was diluted in normal saline, or 0.1-mol/l citrate or phosphate buffers to yield solutions with a pH ranging from 4.0 to 7.0. Ocular irritancy was evaluated using the bovine cornea opacity and permeability assay. Antibacterial efficacy was assessed by evaluating povidone‐iodine minimum inhibitory concentration and minimum bactericidal concentration at varied pH. Storage stability of the preparations was determined over 30-days at room temperature (20–25°C).

Results

Combining povidone‐iodine with phosphate buffer notably decreased ocular irritancy of the antiseptic. Surprisingly, combining povidone‐iodine with citrate buffer potentiated irritant effects of the preparation. Antibacterial efficacy of povidone‐iodine was reduced when formulation pH was increased from 4.0 to 7.0, although its general activity was retained. Finally, povidone‐iodine remained stable in both normal saline and phosphate buffer over 30-days.

Conclusion

Ophthalmic application of povidone‐iodine can be optimised by adjusting the pH of the formulation to 7.0 using phosphate buffer, reducing irritancy while maintaining adequate antibacterial efficacy and storage stability.

KEYWORDS:

• Antibacterial eye drop
• ophthalmic drug delivery
• povidone‐iodine

Acknowledgements

The authors would like to thank the technical staff at the University of Auckland Departments of Pharmacy, Ophthalmology and Molecular Medicine for providing training and maintaining the facilities used for the performed experiments. The project was carried out using teaching and research funds internally available within the university.

Supporting information

Additional supporting information may be found in the online version of this article at the publisher’s website:

Appendix S1. Formulae for the two utilised buffers.