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The f2 Factor in Sustained-Release Tablets: Method for Similarity Evaluation of Release Profiles
In pharmaceutical quality control, comparing dissolution profiles is essential for ensuring batch consistency and bioequivalence—especially for sustained-release (SR) tablets. One widely accepted method for this comparison is the f2 similarity factor.
What Is the f2 Factor?
The f2 factor (similarity factor) is a statistical metric ranging from 0 to 100:
f2 ≥ 50 indicates similar dissolution profiles
f2 < 50 suggests significant differences
Regulatory bodies like the FDA and EMA accept f2 as a standard tool for comparing drug release behavior between a test and reference product.
Why f2 Matters in Sustained-Release Formulations
Sustained-release tablets are designed for controlled, extended drug release. Matching dissolution profiles across batches or generic versions ensures:
Therapeutic consistency
Reduced risk of adverse effects
Regulatory approval for product changes or generics
How Is f2 Calculated?
To evaluate similarity:
Conduct dissolution tests at multiple time points (at least 3–4, ideally 5+)
Measure % drug released for both test and reference products
Use these values to calculate f2 (no need to show formula here)
The closer the profiles, the higher the f2 value—indicating similar release kinetics.
Best Practices for Using the f2 Factor
Time Points: Spread evenly over the release period
Variability Control: Ensure low RSD (≤20% at early points, ≤10% later)
Replicates: Use at least 12 units per product for robust comparison
Acceptance Range: f2 between 50–100 is generally acceptable
Regulatory Alignment
The f2 method is endorsed by:
FDA (Guidance for Industry on Dissolution Testing)
EMA (Comparative in vitro dissolution studies)
ICH Guidelines
Conclusion
The f2 similarity factor is a simple, reliable, and regulatory-approved method for comparing sustained-release tablet dissolution profiles. Proper application ensures product consistency, supports generic development, and accelerates regulatory approvals.
