Page 80 - Quality control of pharmaceuticals (07-PA 704)

INORGANIC IMPURITIES
Inorganic impurities may also derive from the manufacturing processes used for
bulk drugs. They are normally known and identified and include the following:

a) Reagents, ligands and catalysts
b) Heavy metals

The main sources of heavy metals are the reactors (if stainless steel reactors are
used), where acidification or acid hydrolysis takes place and water used in the
processes. These impurities of heavy metals can easily be avoided using
demineralized water and glass-lined reactors.

RESIDUAL SOLVENTS
Resident solvents are organic volatile chemical that are used or produced in the
manufacture of drug substances or excipients, or the preparation of drug products.
They are potentially undesirable substances which either hazardous to human health
or modify the properties of certain compounds.
The residual solvents also affect physicochemical properties like crystalline of bulk
drug, which affect the dissolution properties, color changes in finished products.

Impurities forms during formulation
Impurities formed during formulation are defined as number of impurities in a drug
product can arise out of inert ingredients used to formulate a drug substance.
These impurities may arise during the process of the formulation of the dosage form
due to exposure to high temperature, light, humidity or during sterilization.
Dosage form related
Although the pharmaceutical companies perform pre-formulation studies, including
a stability study, before marketing the products, sometimes the dosage form factors
that influence drug stability force the company to recall the product.