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S. M. Walsman, A. Antes, R. J. Rescigno, D. Lutz, P. J. Lama; What Is in a Drop? Brand versus Generic Prednisolone Acetate Formulations: A Quantitative Analysis. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5825.
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To quantify and compare the concentration of prednisolone with and without shaking in a single drop of brand and generic formulations of prednisolone acetate 1%.
Comparative ELISA quantification of 2 brand name and 2 generic formulations of prednisolone acetate 1%. A single drop of Pred Forte (PF), (Allergan, Irvine Ca), Econopred Plus (EP), (Alcon, Ft Worth, Tx), and generic prednisolone acetate 1%; Falcon (FG) and Pharma (PG) each were deposited in separate assay wells. One assay was run without pre-shaking before drop instillation and another was run with pre-shaking. All bottles used were manufacturer sealed with a volume of 5ml. In the pre-shaken group each bottle was shaken 10 times (1 shake=1 full up and down excursion) in a similar fashion by one investigator. A separate bottle was used for each drop. The contents in each well were then diluted to a concentration of 10-7 and ELISA using an EIA kit (Assay Designs, Ann Arbor, MI) was performed. Quantification of prednisolone in each well was determined by extrapolation from a spectral absorption and generation of a standard curve derived from the known standard. The protocol was performed in duplicate. Pairwise comparisons using one way ANOVA and Tukey tests were used to determined statistical significance between concentrations.
No shake single drop concentrations of prednisolone were lowest with EP (1220.33 pg/ml) and highest with PG (2003.67pg/ml). This difference was statistically significant. However, no shake single drop concentrations between PF, FG, and PG were not statistically significant. After shaking, the concentration of prednisolone increased in all formulations. Though the absolute change in concentration was highest with EP (+583.34pg/ml), the highest total concentration was with PF (2215.33pg/ml) and lowest was still EP.
Pred Forte and both generic formulations of prednisolone acetate 1% , as determined by ELISA, had statistically similar drop concentrations with and without shaking. As expected, shaking significantly increases the concentration of prednisolone in all formulations. In contrast, branded Econopred Plus had the lowest concentration with or without shaking. Thus, different formulations of prednisolone acetate 1% may not necessarily yield the same drop concentration of prednisolone. Clinical evaluation of these agents prospectively will help elucidate the implications of these data.
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