Impurities may bring about incompatibility with other substances. Impurities may lower the shelf life of the substances. Impurities may cause difficulties during formulations and use of the substances. Sometimes Impurities change the physical and chemical properties of the substances. Impurities present in a solid organic compound tend to have 2 effects on the melting point. First, they tend to lower the overall melting point of the compound versus the value for pure material. Second, they tend to increase the range of the melting point values.
Effect of Impurities: We know that almost pure substances are difficult to get, and some amount of impurity is always present in the material. So, the impurities which are present in the substances may have the following effects.
To prevent these impurities many tests such as limit tests are carried out to lower the impurities to make the pharmaceuticals safer.
Once a drug product has been manufactured it is possible that low levels of impurities will remain, but that is not an automatic indicator that a drug product’s quality is bad. The key concerns for manufacturers, regulators and patients, are the type and level of those impurities.
Regulatory agencies and standards-setting organizations like the U.S. Pharmacopeial Convention (USP) spend a great deal of time and effort establishing limits on allowable levels of impurities in medicines to help ensure that they do not pose a threat to public health and that product quality meets or exceeds the public’s expectations.
Medicine has two kinds of quality standards that it must meet before it can be given to patients. Failure to meet either makes it a poor-quality medicine.
The first standard involves Good Manufacturing Practices (GMPs). In the pharmaceutical industry, failure to meet quality standards often occurs in GMP processes. Drugs that fail GMPs may happen to be safe and effective, but the care with which they are manufactured is one good indicator of quality.
Many drugs are manufactured in “lots” of more than a million tablets, and GMPs are intended to ensure that through rigorous manufacturing controls all tablets within a lot are of consistent quality.
The other type of standard defines the chemical and physical properties that each drug substance, excipient and drug product must be able to meet. These are the kind of standards developed by USP. They describe how to measure and ensure that:
While many impurities by themselves are non-toxic, their presence can indicate inadequate concern or control to ensure that other more dangerous impurities have been effectively limited.
Even though toxic impurities are rare, their consequences can be devastating if uncontrolled, and minimizing the potential for even unknown hazards is critical for both the manufacturer as well as the patient.