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Difference between Related Substances and Impurities

Q. What is the difference between Related Substances and Impurities?


The "Related Substance" word was first coined by European Pharmacopoeia and is confusing if we look at it in isolation.

EP has defined it as,

"Related substances are known impurities which may be identified or unidentified. They include intermediates and by-products from synthetically produced organic substance, co-extracted substances from natural products and degradation products of the substance.

This definition does not include other Impurities i.e. residual solvent or water/moisture or inorganic impurities or residues from cells and micro-organism or culture media used in a fermentation process.

"Pharmaceutical Impurities" are the unwanted chemicals (known or unknown) that remain with the active pharmaceutical ingredients (APIs), and/or finished products, or dveloped during manufacturing of APIs and/or finished products.

It is correct to say that all related substance are impurities but all impurities are not related substances.

Resource Person: Dr. Shivang Chaudhary

Read also: An Overview of Pharmaceutical Impurities

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