Prior to perform the sterility test, one should be aware of its objective and need means why we are doing? What information we will get? How to interpret observable information for our purpose?
Sterility testing1,2 is the process in which we can check whether any microorganism is present in the preparation or on article surface by providing the favorable condition for the growth of microbes on different media and other conditions. If any microorganism(s) present in the formulation, will grow in such favorable conditions and we come to know that our formulation is not completely sterile. This is the main objective of sterility testing.
Requirements for sterility testing
Culture medium is used for the growth of microorganisms artificially. For the growth of microorganism various nutrients and other favourable conditions which ever required can be provided. One important factor includes its sensitivity when one has to consider the medium for sterility testing, so that very small amount of microorganisms if present in formulation/ article can be vigorously grown in culture media for detecting its presence. Several media can be used for sterility testing depend upon the type of microorganism we are expecting like media for aerobes, anaerobes, aerobes and anaerobes, aerobes and lower fungi and sometimes joint media for growing different types of microbes in single medium. Many media are recommended by official books like various Pharmacopoeias, sometimes for detecting specific microorganism, specialized medium can also used which was described in official books.
Now, first thing we should understand that why sampling is required for any quality control test? e.g. we will take 6 tablets for disintegration test and if test pass we will give green signal to that respective batch of tablets for disintegration parameter although batch size may be 1000 or 10000 or more tablets....why? One can consider many examples of such tests. The simple reason behind the sampling is majority of tests whichever we perform to assure the quality of pharmaceutical are destructive in nature (means one cannot use the sample again once it undergoes quality control test because either it lose its physicochemical characters or complete destruction takes place). Thus, sampling procedure one has to follow. Sampling can be defined as procedure by which minimum number of sample should be selected which will satisfactorily represent the overall characteristics of total batch/lot. So, number should be less but sufficient. Although one cannot give complete assurance of 100% sterility of formulation until and unless every sample undergoes sterility testing, but it is practically impossible and if we try to do the same, it is worthless operation where finally nothing will left as test is destructive in nature.
There are many pros and cons of every type of sampling method. Based upon the process by which we sterilized formulation/ article we have to select different samples. E.g. in heat sterilization process samples should be taken from each and every shelf and from part of sterilizer where we are less satisfied with sterilization (like corners of shelf etc). Samples can be taken at two stages one is from bulk of the sample and other from final container according to WHO guidelines. Sampling size also very important, mean how much amount of sample to be taken for test and how much amount of medium is required. This is given in official standards like IP, BP, USP etc. According to the guidelines one has to take the adequate sample size. Neutralization of antimicrobial agents in dosage forms2 There are mainly three methods for doing the same that we see in our next page.
- Remington- The science and practice of pharmacy, Lippincott Williams and Wilkins. Philadelphia. 21st ed, 2005: 776, 802.
- Cooper and Gunn's Dispensing Pharmacy. CBS publisher, New Delhi, 12 th Ed: 541-572. Gupta SP. Elementary statistical methods. S Chand and sons, New Delhi, 15th edition, 2004: 63-80.
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