Category: Formulation and Quality
Purpose: Fungal keratitis (keratomycosis) is a fungal infection of the cornea, the incidence being between 6-20% of all microbial keratitis cases depending on the geographic location. It primarily affects the corneal epithelium and stroma, although the endothelium and anterior chamber of the eye may get involved in more severe cases. Natamycin (NT) is a commercially available antifungal drug used for the treatment of fungal keratitis. It is potent against Aspergillus and Fusarium species apart from Candida species. Currently, NT is available commercially as a 5% w/v topical ophthalmic suspension. NT has low retention at the ocular surface which requires it to be frequently administered. The main objective of the present investigation was to develop and evaluate the NT loaded nanosuspension (NT-NS), as well as it’s corresponding in-situ gel formulation (NT-NS-GG), for the treatment of fungal keratitis.
Methods: NT-NS formulations were prepared using varying drug loads and combinations of surfactants, while keeping the stabilizer concentration (0.1%) constant. NT-NS formulations were prepared using homogenization technique with the aid of a T25 digital Ultra-TurrexTM homogenizer at 16,000 rpm for 5 minutes. NT-NS formulation was optimized based on particle size, PDI, zeta potential (ZP) and assay. Differential scanning calorimetry (DSC) studies were used for the drug and excipients compatibility testing. The stability of an optimized NT-NS formulation was evaluated at refrigerator and room temperature conditions. Further, optimized NT-NS was modified into an in-situ gel (NT-NS-GG) with the addition of varying concentrations (0.2-0.3% w/v) of gellan gum as a gelling agent. The NT-NS-GG formulations prepared were evaluated for gelling time, gel retention time, viscosity and optimized. In vitro release and trans-corneal permeation studies of optimized NT-NS and NT-NS-GG were performed through dialysis membranes and corneas separated from whole rabbits' eye, respectively.
Results: NT-NS formulation was developed using lecithin and poloxamer as surfactants, tyloxapol as the stabilizing agent. An increase in the drug concentration (0.3-1% w/v) caused an increase in the particle size and PDI of the NT-NS formulation. Therefore, a 0.3% w/v drug load was selected for the NT-NS formulation development. Particle size, PDI, ZP and assay of an optimized NT-NS formulation (LP1) was 586 ± 61.3 nm, 0.447 ± 0.129 -38.97 mV and 107 ± 0.6%, respectively. LP1 formulation (aqueous dispersion) was stable for up to 4 weeks under refrigerated and room temperature conditions. NT-NS-GG prepared with 0.2% gellan gum showed satisfactory rheological properties and immediate gelling characteristics upon addition of simulated tear fluid. Prolonged drug release and high permeation through the rabbit corneas were observed from in vitro release and trans-corneal permeation studies. DSC studies showed no interaction between the drug and other excipients being formulated into a NS.
Conclusion: NT-NS and NT-NS-GG formulations were successfully developed with desirable physicochemical properties. The results suggest that NT loaded NS could be an alternative topical ocular dosage form for the treatment of fungal keratitis.
Arun Butreddy– Graduate Research Assistant, University of Mississippi, Oxford, Mississippi
Corinne Sweeney– Graduate student, University of Mississippi, Ocford, Mississippi
Akash Patil– PhD Candidate, University of Mississippi, Oxford, Mississippi
Narendar Dudhipala– Postdoctoral research fellow, University of Mississippi, University, Mississippi
Soumyajit Majumdar– Professor and Associate Dean, Department of Pharmaceutics and Drug Delivery, School of Pharmacy, The University of Mississippi. Oxford, MS, University, Mississippi