Article Title

On the characteristics of the FDA's similarity factor for comparison of drug dissolution


The characteristics of FDA's similarity factor (f2) are investigated and compared with those of the time-series approach proposed by Chow and Ki for the comparison of dissolution profiles. The results indicate FDA's similarity factor simply reflects the overall average difference in percent dissolved of drug, regardless of the different pattern of dissolution. It should be noted, however, that the percent dissolved data in the profile are highly correlated time-series data; they are not the independent variables that the FDA's method assumed. Moreover, the asymptote is usually reached within 45 minutes of dissolution for most of the immediate release solid dosage form products. A high f2 value can be manipulated if one includes several more data points at the asymptote to overcome the large differences observed in 15 to 45 minutes dissolution. Thus, the true difference in dissolution characteristics of the two products may be distorted. Although the f2 method has the advantage of simplicity, it lacks strict statistical justification. On the other hand, the time-series approach proposed by Chow and Ki is much more powerful in discerning differences in dissolution pattern between two drug products. However, Chow and Ki's method does not consider cases with a declined cumulative dissolution profile.

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