Chemical Nature and Impurities in Paracetamol and Metronidazole: A Review

Paracetamol and metronidazole are two drugs that are frequently used across the world, one for relieving pain and fever and the other for treating anaerobic and protozoal infections. Like all active pharmaceutical ingredients (APIs), both can carry or generate impurities at different stages such as synthesis, formulation, or storage. Even small amounts of these impurities may influence the drug’s safety, stability, and overall effectiveness. International guidelines, particularly those issued by the ICH, emphasize the need to detect, identify, and control impurities. This review brings together information on the chemical characteristics of paracetamol and metronidazole, highlights the common impurities associated with them, and explains the analytical techniques most often employed, including HPLC, TLC, and different spectroscopic methods. A short discussion on regulatory aspects and the future direction of impurity profiling is also provided.