Impurities in pharmaceuticals: The Detailed Guide

Impurities in pharmaceuticals: The Detailed Guide

Dr. Rashmi Ranjan Mohanty

by Dr. Rashmi Ranjan Mohanty

Impurities are present in every chemical compound. Pharma impurities even more in number. But how do you differentiate between pure chemical and impure material? 

The impurities in pharmaceuticals are unwanted chemicals that remain with the active pharmaceutical ingredients (APIs) or develop during formulation or upon ageing of both API and formulation. The presence of these unwanted chemicals even in trace amounts may influence the efficacy and safety of the pharmaceutical product. The control of impurities is currently a critical issue for the pharmaceutical industry. 

Pharma Impurities need to be removed. Otherwise, they will directly affect the composition of any chemical compound. 

Types of Impurities

The impurities in pharmaceuticals can be of three types:

  1. Impurities closely related to the product and coming from the chemical or from the biosynthetic route itself
  2. Impurities formed due to spontaneous decomposition of the drug during the storage or on exposure to extreme conditions,
  3. The precursors may be present in the final product as impurities.

As per the ICH guidelines, impurities in the drug substance produced by chemical synthesis can broadly be classified into the following three categories

Organic Impurities (Process and Drug-related)

The actual and potential impurities are most likely to arise during the synthesis, purification, and storage of the drug substance. Organic volatile impurities are residual solvents that are used in and are produced during the synthesis of drug substances, or in excipients used in the production of drug formulations.

Inorganic Impurities

Inorganic impurities are normally detected and quantified using Pharmacopeial or other appropriate standards.

Residual Solvents

The third and final type of impurity is the residual solvents. These impurities are the residual solvents in the manufacturing process. The solvents used in pharmaceutical manufacturing are defined by three classes based on their toxicity. 

Class one solvents should be avoided, as they are known to be human carcinogens or environmentally hazardous. Class two solvents should have limited use, as some levels of harmful toxicity may be present. Class three solvents have the low toxic potential for humans and do not need a limit.   

The Adverse Effects of Impurities in Pharmaceuticals

Everybody knows that almost pure substances are very difficult to get. Some or the other form of impurity is always present. Here, we present some of the effects of impurities in pharmaceuticals:

→ Impurities may bring incompatibility with other substances

→ Impurities may lower the shelf life of a substance

→ It may cause difficulties during formulations and the use of substances

→ Sometimes, it changes the physical and chemical properties of the substances

→ Therapeutic effect can be decreased

→ It is injurious when present above a certain limit

→ It may change the odour, colour and taste of the substance.


Most of the impurities in pharmaceuticals occur due to manufacturing processes, degradation, storage conditions, excipients, or contamination. Without identifying and eliminating impurities in pharmaceuticals, the quality, safety, and efficacy of drug products are put at risk.

Hence, let's try to keep safety before everything else. 

Dr. Rashmi Ranjan Mohanty

by Dr. Rashmi Ranjan Mohanty