How To Determine f1 Difference & f2 Similarity Factors in Dissolution Testing
In dissolution testing, f1 difference and f2 similarity calculations are used to compare one formulation to another or a test batch to a reference batch. This approach is useful to ensure that two formulations have similar bioavailability, which is important for ensuring that the therapeutic effect of the drug product remains consistent. By comparing products side by side, f1 and f2 calculations can provide assurance that both products are suitable for use in clinical trials or final market release.
The difference factor (f1) assesses the relative error between two dissolution curves at any given time point and is calculated as the percentage of discrepancy between them. The similarity factor (f2) is a measurement of the similarity in the percent (%) dissolution between two dissolution curves.
How to determine the difference (f1) and similarity (f2) factors:
1. Determine the dissolution profile of the test and reference products (12 units each).
2. Calculate the difference (f1) and similarity factor (f2) based on the mean dissolution values from both curves using the formulas below:
3. The following recommendations should also be considered:
To ensure accurate comparison, the dissolution measurements for both test and reference batches should be taken in identical conditions. It is essential to use the same time points (e.g. 15, 30, 45, 60 min) throughout the procedure.
Only one measurement after 85% dissolution should be included for both the test and reference batches.
To utilize the mean data, the percent coefficient of variation for earlier time points (ex. 15 minutes) must not exceed 20%, and at the later time points, it should be less than 10%.
Generally, for curves to be considered similar, f1 values should be close to 0 and f2 values should be close to 100. The acceptance range for sameness or equivalence are:
f1 between 0 -15
f2 between 50 - 100
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Related Article: How to Use the f1 and f2 Dissolution Calculator.
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