Impurities are the constituent in a drug product that isn’t the drug substance or an excipient.
Quantification of impurities in drug substances and drug products is achieved by HPLC.
What is Response Factor (RF):
The ratio between the concentration of a composite and its equivalent analytical response.
What is Relative Response Factor (RRF):
As per U.S. Pharmacopoeia (USP), The Relative response factor is the ratio of the responses of equal amounts of the Impurities then the drug substance or its reference standard. Different compounds at the identical concern. gives the variable responses and hence has varied RF values.
Why Relative Response Factor (RRF):
As per the International conference on harmonization (ICH) guidelines the foremost main aim is to estimate the impurities accurately and consistently as per the defined reporting threshold, identification threshold, and quantification threshold.
Quantification of impurity by using external standards is an impeccable method but it was impossible in any respect at the time because of a lack of sufficient amount of impurities. Impurity isolation and synthesis is a difficult task and even should confirm its purity, quality, and integrity by doing periodic assessments.
The relative response factor is convenient for the estimation of impurities when it’s difficult to synthesize, or has very unstable, or in absence of its standard. Probable robustness study of RRF to be performed during method development or validation. Accurately established RRFs are utilized within the strategy of study with acceptable conditions.
References:
- United States Pharmacopeia, <1225> Validation of Compendial Procedures,
- ICH Q2(R1), Harmonised Tripartite Guideline Validation of Analytical Procedures: Text and Methodology
- ICH, Q3A (R2) Impurities in New Drug Substances: Text and Methodology,
- ICH, Q3B (R2) Impurities in New Drug Substances: Text and Methodology.
