Simple Pharmanotes: Sterilization by Radiation.

Introduction:

Definition: Sterilization is defined as complete removal of microorganisms from an object, surface or a product.
Sterilization by radiation uses radiations for sterilization.
This method is also called “Cold Sterilization” as there is very negligible amount of heat production during the process.
It is further divided into Ionizing and Nonionizing Radiations.

X-ray and gamma rays are the commonly used ionizing radiation for sterilization.
These are high energy radiation which causes ionization of various substances along with water.
The ionization results in the formation of a large number of toxic O2 metabolites like hydroxyl radical, superoxide ion, and H2O2 through ionization of water.
These metabolites are highly oxidizing agents and kill microorganisms by oxidizing various cellular components.
With ionizing radiation, microbial resistance decreases with the presence of moisture or dissolved oxygen (as a result of increased free radical production) and also with elevated temperatures.
Radiation sterilization is generally exposed to items in the dried state which include surgical instruments, sutures, prostheses, unit-dose ointments, plastic syringes, and dry pharmaceutical products.

Ultraviolet radiation includes light rays from 150-3900 Å, of which 2600 Å has the highest bactericidal effect.
Non-ionizing waves have a very little penetration power, so microorganisms only on the surface are killed.
Upon exposure, these waves are absorbed by many materials, particularly nucleic acids.
The waves, as a result, cause the formation of pyrimidine dimers which bring error in DNA replication and cause the death of microbes by mutation.
UV radiation owing to its poor penetrability of conventional packaging materials is unsuitable for sterilization of pharmaceutical dosage forms.
It is, however, applied in the sterilization of air, for the surface sterilization of aseptic work areas, and the treatment of manufacturing-grade water.