Ex vivo evaluation of the stability, safety and antibacterial efficacy of an extemporaneous povidone‐iodine preparation for ophthalmic applications

Efficacy and Safety of Keratosept Eye Drops in Patients with Punctate Keratitis: Clinical and Microbiological Evaluation on 50 Eyes

We evaluated the efficacy and safety of eye drops with antiseptic and re-epithelizing properties (Keratosept®, Bruschettini, Genova, Italy) on 50 eyes affected by punctate keratitis of suspected microbial origin. A biomicroscopic examination, fluorescein dye staining test (Fluotest), tear break-up time test (TBUT), and the ocular surface disease Index (OSDI) questionnaire were used to assess treatment efficacy. Treatment success was defined as a negative Fluotest and an OSDI score <12 on the 15th day of treatment. According to this definition, Keratosept®, either alone or in combination with antibiotics, was effective in over 80% of microbial and nonmicrobial forms. Conjunctival swabs were taken from all patients for culture examination with an antibiogram and sensitivity test for Keratosept®; 32/43 (74.4%) forms with positive culture for the bacteria were sensitive to Keratosept®. A total of 35/38 (92%) eyes treated with this product alone achieved full treatment success without any apparent adverse effects. These results suggest the use of Keratosept® eye drops in punctate keratitis as an alternative or in combination with established antibiotic therapies. Further studies are needed to evaluate its efficacy in different infectious forms and identify other indications for using this product.

Pickering emulsions stabilised with oligoglycine-functionalised nanodiamond as a model system for ocular drug delivery applications

Oil-in-water emulsions, stabilised with conventional surfactants, are commonly used in eye drops for ocular drug delivery. However, the presence of surfactants can sometimes irritate tissues. Furthermore, conventional emulsions often have poor retention on ocular tissue. Pickering emulsions stabilised with nanoparticles have been gaining attention in recent years for a range of biomedical applications because of their biocompatibility. Here, Pickering emulsions were evaluated for the first time for the confinement of organic components for potential application in ocular drug delivery. For a model system, we used nanodiamond (ND) nanoparticles functionalised with covalently-bonded two-tail (2T) oligoglycine C10(NGly4)2 to make Pickering oil-in-water emulsions, which were stable over three months of storage under neutral pH. We proved the non-toxicity of ND-2T Pickering emulsions, comparable to buffer solution, via an ex vivo bovine corneal permeability and opacity test. The retention of the oil phase in the ND-2T stabilised emulsions on corneal tissue is significantly increased because of the mucoadhesive properties arising from the positively-charged terminal amino groups of 2T. Our formulated emulsions have a surface tension, pH and salt concentration comparable to that of tear fluid. The high retention of the ND-2T-stabilised emulsions on the corneal surface, in combination with their non-toxicity, gives them distinct advantages for ocular drug delivery. The principles of this model system could be applied in the future design of a range of formulations for drug delivery.

The Use of Animal Models to Assess Engineered Corneal Tissue

Tissue-engineered corneal constructs offer the potential of readily available corneal substitutes for transplantation. As with all medical devices and implants, these constructs require rigorous safety assessments, combined with well-described analyses of the implant's physical and biological characteristics. Although the constructs are developed in vitro, such studies are currently unable to fully emulate the complex biomechanical and biochemical conditions within living tissue, as well as the interplay between this environment and immunological factors. For these reasons, animal models remain essential to characterize such interactions. They form a stage where corneal implants can be tested for utility and survival in a living location to assess their ability to provide vision and avoid adverse event. Here, we examine the surgical considerations of animal models and we describe how the rabbit can be used for this purpose. This animal has been the routine model for ophthalmological studies and we set out methods to implant corneal constructs with this species.

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

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.