Differences and ICH guidelines

  1. What is difference between Assay, potency and Purity?
  2. How to define Residual Solvent as not available in ICH guidelines.

Assay: Assay is the percentage purity. i. e. Amount of purity present in the given sample as compare to Impurity, related substance etc.
Potency: is the drug activity which expressed in terms of amount required to an effect of given intensity.

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Assay is the amount of the drug substance available in specified individual dosage form
Potency is the amount of the drug substance required to perform the pharmacological activity
Purity determines the content of the drug substance available excluding the impurities if that particular drug substance.

Residual solvents are the left over solvents in the drug substance or the drug product that remains intact after completion of the all processing steps as per procedure. Limits and categories are defined in iCh Q3C.