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Pharmaceutical Impurities types and impact

2021-08-23

Impurities in medicines can be divided into general impurities and special impurities according to their sources.
General impurities refer to impurities that are widely distributed in nature and are easily introduced during the production and storage of a variety of drugs, such as chlorides, sulfates, heavy metals, arsenic salts, loss on drying, residues on ignition, easy carbonization, pH, Iron salt etc.
Special impurities refer to impurities introduced according to the nature and production process of the drug during the production and storage of the drug, such as free salicylic acid in aspirin, 2-methyl-5-nitroimidazole in metronidazole, etc. . Impurities can also be divided into signal impurities and harmful impurities. The signal impurity itself is generally harmless, but its content can reflect the purity level of the drug. If the content is too large, it indicates that the purity of the drug is poor, indicating that the drug production process is unreasonable or there are problems in production control. Chloride and sulfate are signal impurities. Harmful impurities such as heavy metals, arsenic salts, etc., are toxic to the human body or affect the stability of the drug, and should be strictly controlled in the quality standard to ensure the safety of the drug.

The relationship between drug impurities and drug safety is a complex relationship that is affected by many factors.Usually, most of the impurities in drugs have potential biological activity, and some even interact with drugs to affect the efficacy and safety of drugs. May have toxic effects.
1. Toxic and side effects due to impurities in the drug
For example, the penicillium thiazole protein produced by the action of the β-lactam ring is immunogenic and is an exogenous allergen. During storage, the high molecular polymer formed by the self-polymerization of the „-lactam ring by opening the ring is an endogenous allergen. These are the reasons why β-lactam antibiotics are prone to allergic reactions; in addition, the most common synthetic impurity in heterocyclic drugs is N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can selectively destroy dopaergic neurons of the substantia nigra and globus pallidus, and induce symptoms similar to Parkinson's disease; degradation products in tetracycline cause Fanconi syndrome; byproducts of methotrexate Fever reaction, etc.
2. The effect of optical isomers of chiral compounds on drug safety

Some enantiomers of chiral compounds have the same pharmacological effects but different degrees, and some have complementary effects. However, the optical isomers of most drugs will affect the efficacy of the drugs, and even serious adverse reactions. It has been reported that the effect of the optical isomers of chiral compounds on drug efficacy is mainly manifested in the following aspects: 󰀁 Reduced drug efficacy: For example, the effect of the quinolone antibiotic ofloxacin racemate is only the L racemate The pharmacological effect is opposite: For example, the R-enantiomer of Zacobili is a 5-HT3 receptor antagonist, while the S-enantiomer is a 5-HT3 receptor agonist; 󰀁 produces serious adverse reactions: For example, Thalidomide R-isomer and its two metabolites have strong embryo toxicity and teratogenic effects.

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