ISTA Pharmaceuticals, Inc. announced preliminary results from two recently completed studies on its investigational ophthalmic product, T-Pred (prednisolone acetate 1.0% and tobramycin 0.3% ophthalmic suspension). The company is developing T-Pred as a treatment for inflammatory ocular conditions for which a corticosteroid is indicated and where bacterial ocular infection exists, or there is a risk of bacterial infection.
In the first study, ISTA evaluated the antimicrobial equivalence between T-Pred and a tobramycin-containing reference product. In vitro tests were conducted to compare the kill rate of T-Pred with the kill rate of the reference product for each of the micro-organisms listed in the reference product's package insert as well as additional micro-organisms specified by the Food and Drug Administration (FDA). ISTA successfully demonstrated the antimicrobial bioequivalence of T-Pred to the reference product in each of the 26 required tests.
The second study was a phase 3 clinical study designed to determine the bioequivalence of prednisolone concentrations between T-Pred and a reference product containing prednisolone acetate 1.0%. The multi-centre, randomized, double-masked study enrolled 172 patients undergoing bilateral cataract removal. Patients served as their own internal control in this study, receiving one drop of either T-Pred or the prednisolone reference product prior to cataract extraction. Aqueous humour sampling was performed at one of four assigned time points. In order to demonstrate the bioequivalence of the two products, the ratio of calculated prednisolone values in aqueous humour needed to fall between 80% and 125%, with a 90% confidence interval for the ratios during all time points measured. Although T-Pred's prednisolone concentrations in this study were similar to those of the reference product, bioequivalence was not demonstrated. ISTA believes differences in the prednisolone reference product, which included a higher drug concentration in the formulation and a recent change in the reference product commercial product delivery dose, may have contributed to the variations in study results between the two products.
ISTA is discussing the study results with the FDA to determine the best path forward for T-Pred. The Company is working with the FDA to determine the appropriate clinical study or studies to perform in lieu of an additional prednisolone bioequivalence study, although no further clinical studies are planned before 2010.
ISTA Pharmaceuticals is the fourth largest branded ophthalmic pharmaceutical business in the US. ISTA's three marketed products plus its product candidates include therapies for inflammation, ocular pain, glaucoma, allergy, and dry eye.