Dissolution f1/f2 Similarity Factor
Also known as: f1, f2, similarity factor
The f1 and f2 factors are dimensionless statistical measures developed by Moore and Flanner to quantify the similarity between two dissolution profiles. Adopted by regulatory agencies (FDA, EMA) as the gold standard for comparing dissolution curves, these factors enable rapid assessment of whether formulation changes significantly impact drug release.
Key highlights
- Simple, objective statistical approach requires no assumptions about model or kinetics
- Internationally recognized and accepted by FDA, EMA, and other regulatory bodies
- Quick to compute and interpret; results easily communicated to regulatory authorities
- Enables formulation optimization without repeated clinical trials if f1/f2 criteria are met
Intuition
This section is available to Pro members. Upgrade to Pro
How it works
This section is available to Pro members. Upgrade to Pro
When to use it
Use f1/f2 comparison whenever evaluating post-approval manufacturing changes (supplier switch, process modification), formulation optimization, or stability-indicating dissolution testing. Regulatory agencies expect f1/f2 analysis before approving changes without bioequivalence studies.
Strengths & limitations
- Simple, objective statistical approach requires no assumptions about model or kinetics
- Internationally recognized and accepted by FDA, EMA, and other regulatory bodies
- Quick to compute and interpret; results easily communicated to regulatory authorities
- Enables formulation optimization without repeated clinical trials if f1/f2 criteria are met
- f1 and f2 criteria (f1 < 15, f2 > 50) are empirically derived; may not always align with bioavailability equivalence
- Method is sensitive to late time points and may be influenced by high variability in dissolution data
- Does not account for shape differences early in profiles; two profiles with different absorption rates may appear similar
- Requires adequate data quality and complete dissolution data (usually to 85% or more)
Common pitfalls
This section is available to Pro members. Upgrade to Pro
Applications
This section is available to Pro members. Upgrade to Pro
Frequently asked
What do f1 and f2 values mean?
f1 measures percentage difference; lower is better (f1 < 15 indicates similarity). f2 measures logarithmic similarity; higher is better (f2 > 50 indicates similarity). Together, they form the acceptance criterion: f1 < 15 AND f2 > 50.
Can I use f1/f2 to avoid bioequivalence studies?
Yes, if dissolution profiles are similar (f1 < 15, f2 > 50) and IVIVC exists or dissolution is known to be rate-limiting. However, f1/f2 alone does not guarantee bioequivalence; regulatory guidance must be consulted.
How many time points do I need for f1/f2?
At least 6-12 time points are recommended, spanning the entire dissolution curve. Time points should be chosen to capture the kinetic profile accurately (e.g., earlier points for fast-dissolving, later for slow-dissolving formulations).
What if my profiles don't meet f1 and f2 criteria?
Profiles outside criteria suggest a potential formulation change that may affect bioavailability. Conduct IVIVC, dissolution IVIVC modeling, or clinical bioequivalence studies to confirm safety and efficacy of the new formulation.
Sources
- 1.Moore, J. W., & Flanner, H. H. (1996). Mathematical comparison of dissolution profiles. Pharmaceutical Technology, 20(6), 64-74.
- 2.Shah, V. P., Tsong, Y., Sathe, P., & Liu, J. P. (1998). In vitro dissolution profile comparison--statistics and analysis of the similarity factor, f2. Pharmaceutical Research, 15(6), 889-896.
You have read it. What now?
Cite this page
ScholarGate. (2026, June 3). Dissolution f1/f2 Similarity. ScholarGate. https://scholargate.app/pharmacology/dissolution-f1-f2-similarity