Quality

Sterility Testing For Medical Devices

- Dr. Nishodh Saxena, Scientist, B.V. Patel Pharamceutical Education Research Centre (PERD), Ahmedabad, Gujarat, India.

Test for sterility :

Intended for detecting the presence of viable forms  of    microorganisms    in     on       Pharmacopoeial preparations  and articles. The following procedures are    applicable    for    determining    whether   a Pharmacopoeial article  purporting   to   be   sterile complies  with  the   requirements  set  forth  in  the individual monograph with respect  to  the  test  for sterility.

Principle:  

The tests are based upon the principle that if microorganisms are placed in a medium which provides nutritive material and water and kept at a favourable temperature, the organisms will grow and their presence can be indicated by a turbidity in the originally clear medium.

Design and Precautions:

Designed to avoid accidental contamination of the product during the test. Precautions taken for this purpose should not adversely affect any microorganisms which should be revealed in the test.

The working conditions in which the tests are performed should be monitored regularly by carrying out control tests.

Batch:

A homogeneous collection of sealed containers prepared in such a manner that the risk of contamination is same for each of the unit in it.

Limitations:

• Within the strictest definition of sterility, a specimen would be deemed sterile only when there is complete absence of viable microorganisms from it. However this absolute definition can not currently be applied to an entire lot of finished compendial articles because of limitations in testing.  

• Absolute sterility can not be practically demonstrated without complete destruction of every finished article. The sterility of a lot purported to be sterile is therefore defined in probabilistic terms, where the likelihood of a contaminated unit or article is acceptably remote.

• Such a state of sterility assurance can be established only through the use of adequate sterilization cycles and subsequent aseptic processing, if any, under appropriate current good manufacturing practice, and not by reliance solely on sterility testing.

• The probability of detecting viable microorganisms in the tests for sterility increases with the number present in a given amount of the preparation being examined and varies according to the species of microorganism present.  

• Very low levels of contamination can not be detected on the basis of random sampling of a batch.  

• If contamination is not uniform throughout the batch, random sampling can not detect contamination with certainty.  

Guidelines for the selection of minimum number of items recommended to be tested in a batch.

Culture Media:

Media for the tests may be prepared as given below or dehydrated mixtures yielding similar formulations may be used provided that when reconstituted as directed by the manufacturer, they have growth promoting properties equal to or superior to those from the formulae given below.

Fluid thioglycollate medium  

Distribute into suitable vessels which provide a ratio of surface to depth of medium such that not more than the upper half of the medium has undergone a colour change, indicative of oxygen uptake at the end of the incubating period.

• Sterilize in an autoclave at 121°C for 20 minutes. Cool promptly to 25°C and store at 20-30°C, avoiding excess of light. Medium can be used within 3 weeks only.

• Use fluid thioglycollate medium by incubating it at 30-35°C under aerobic conditions.

Alternative thioglycollate medium:

For use with turbid and viscid products and for devices having tubes with small lumina.  

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