Studies on spray dried topical ophthalmic emulsions containing cyclosporin A (0.05% w/w): systematic optimization, in vitro preclinical toxicity and in vivo assessments.

Cyclosporin A (CsA, 0.05% w/w)-loaded positively charged emulsions were prepared based on castor oil, chitosan, poloxamer 188, glycerin and double-distilled water. To augment the shelf/storage-stability of original emulsions, the solid-dry powder for reconstitution was made by spray drying technique. The screening (Taguchi OA) and optimization (face-centered central composite) designs produced the optimized conditions for spray drying: 40 Nm/h aspirator flow rate, 15 ml/min feed rate, 115 °C inlet temperature, 10% mannitol and 1.25% trehalose. The % drug entrapment efficiency values of original and reconstituted emulsions ranged from 73.20 ± 0.13 to 71.55 ± 1.25%. At 20 min post-dissolution, two times higher CsA release was seen from reconstituted emulsions than the original emulsions (85.78 ± 1.14 vs. 42.25 ± 1.84%) in simulated tear fluid. Using MTT assay, the reconstituted emulsions with or without CsA produced 94.512 ± 2.12 to 99.941 ± 1.89% cell viability values in HCE-2 cells. No appreciable change in capillary integrity was visualized in HET CAM following reconstituted emulsions treatment. At equivalent 15 µg drug, the in vitro protein denaturation assay showed augmented inhibition value (~ 85%) for tested CsA emulsions compared to diclofenac reference (68.30 ± 2.05) indicating enhanced anti-inflammatory activity. The CsA concentrations in multiple ocular matrices of rabbit eyes determined by the UPLC-MS/MS method attained the therapeutic drug level of 50-300 ng/ml even at 90 min post-topical instillation of both emulsions. Overall, the CsA emulsion eyedrops can be supplied as a spray dried storable intermediate product for reconstitution.