ISTA reports preliminary results for investigational drop

Irvine, CA

-ISTA Pharmaceuticals has announced preliminary results from two recently completed studies of its investigational eye drop, prednisolone acetate 1.0% and tobramycin 0.3% (T-Pred).

The company is developing the drop as a treatment for inflammatory ocular conditions for which a corticosteroid is indicated and where bacterial ocular infection exists, or a risk of bacterial infection is present, according to a prepared statement.

In the first study, the antimicrobial equivalence between the eye drop and a tobramycin-containing reference product were evaluated. In vitro tests were conducted to compare the kill rate of the drop 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 FDA. The company said it successfully demonstrated the antimicrobial bioequivalence of the investigational drop to the reference product in each of the 26 required tests.

The second study was a phase III clinical trial designed to determine the bioequivalence of prednisolone concentrations between the drop and a reference product containing prednisolone acetate 1.0%. The multicenter, 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 solution prior to cataract extraction. Aqueous humor sampling was performed at one of four assigned time points. To demonstrate the bioequivalence of the two products, the ratio of calculated prednisolone values in aqueous humor needed to fall between 80% and 125%, with a 90% confidence interval for the ratios during all time points measured.

Although the investigational drop’s prednisolone concentrations in this study were similar to those of the reference product, bioequivalence was not demonstrated. 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, according to the release.

ISTA said it 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.