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Confirmation of the Sterility of Medical Devices and Changes in the Characteristics of Polymers Upon Sterilization

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Confirmation of the Sterility of Medical Devices and Changes in the Characteristics of Polymers Upon Sterilization Biocontrol Science, 2001, Vol.6, No.2, 63-68 Minireview Confirmation of the Sterility of Medical Devices and Changes in the Characteristics of Polymers upon Sterilization HIDEHARU SHINTANI National Institute of Health Sciences, 1-18-1, Kamiyoga, Setagaya, Tokyo 151-0041, Japan Received 15 November 2000/Accepted 20 November 2000 Key words : Sterility/Sterilization/Medical Devices. STERILITY be sterile complies with the requirements set forth in the individual monograph with respect to the test for Medical devices may be sold and used in two differ- sterility. In view of the possibility that positive results ent conditions in terms of their bioburden (that is, the may be due to faulty aseptic techniques or environ- number of viable microorganisms present on the de- mental contamination during testing, provisions are in- vice) : sterile or nonsterile. If they are intended to be cluded under the interpretation of sterility test results used in the sterile condition, the actual act of steriliza- for two stages of testing. tion may be either performed by the manufacturer or Alternative procedures may be employed to demon- by the user (though the latter is commonly the case strate that an article is sterile, provided the results ob- only for reusable devices and instruments, such as tained are equivalent or greater reliability. When a surgical instruments at a health care facility). If the difference appears or dispute occurs, evidence of mi- manufacturer has sterilized the instruments, then this crobial contamination must be confirmed by the vali- is specified in the Device Master File (and in product dated procedure. The result so obtained is conclusive related literature), along with the means for having of the failure of the article to meet the requirements of achieved a suitable degree of sterilization and specifi- the test. Similarly, failure to demonstrate microbial cation of a program to assure proper performance of contamination by the validated procedure is evidence the process. that the article meets the requirements of the test. The sterility assurance level (SAL) is the statistical The following considerations apply to sterilized de- probability that a device is not sterile even after going vices manufactured in lots, each consisting of a num- through an established sterilization process. Residual ber of units. Special considerations apply to sterile microorganisms are usually measured as colony devices manufactured in small lots or in individual forming units (CFUs), with the amount of sterilization units where the destructive nature of the sterility test required to reduce the number of CFUs by an order of renders such conventional sterility tests impractica- magnitude for a specific device being termed the ble. For these articles, validated modifications to the D10 (the sterilization period or radiation dose or pe- sterility tests must be made. riod to produce a tenfold reduction in bioburden). For articles of such size and shape as to permit D10 here is both a concentration (or, for radiation, a complete immersion in not more than 1000 ml of cul- power level) and the time interval the device (or ma- ture medium, test the intact article, using the validated terial) is exposed to that dose (Prince and Rubino, media, and incubate for a validated incubation period. 1984). For devices having hollow tubes, such as transfu- sion or infusion assemblies, or where the size of an Sterility tests item makes immersion impracticable and where only The following procedures are applicable for deter- the fluid pathway must be sterile, flush each lumen of mining whether a pharmacopeial article purporting to 20 units with a sufficient quantity of fluid thioglycollate medium and each lumen of the same 20 units with a Corresponding author. Tel : +81-3-3700-9268, Fax: +81- sufficient quantity of soybean-casein digest (SCD) 3-3707-6950. medium to yield a recovery of not less than 15 ml of 64 H. SHINTANI each medium. Then, incubate not less than 100 ml of test a validated number of units. each of the two media as directed under the validated procedure. For devices in which the lumen is so small INTERPRETATION OF STERILITY TEST that the fluid thioglycollate medium will not pass RESULTS through, substitute an alternative thioglycollate me- dium for fluid thioglycollate medium, but incubate the At the prescribed intervals during and at the conclu- validated medium anaerobically. sion of the incubation period, examine the contents of Where the entire intact article, because of its size all of the vessels for evidence of microbial growth, and shape, cannot be tested for sterility by immersion such as the development of turbidity and/or surface in not more than 1000 ml of culture medium, expose growth. If no growth is observed, the article tested that part of the article most difficult to sterilize and test meets the requirements of the test for sterility. that part, or where possible, remove two or more parts When microbial growth is found, but a review of the each from the innermost part of the article. Aseptically sterility testing facility of the monitoring, materials transfer these article parts to the specified number of used, testing procedure, and negative controls indi- vessels of validated media in a volume of not more cates that inadequate or faulty aseptic technique was than 1000 ml and incubate for the validated incuba- used in the test itself, the first stage should be de- tion period. clared invalid and may be repeated. Where the presence of the test specimen in the me- If microbial growth is observed and there is no evi- dium interferes with the test because of bacteriostatic dence invalidating the first stage of the test, proceed or fungistatic action, rinse the article thoroughly with a to the second stage. minimal amount of rinse fluid. Recover the rinse fluid, The minimal number of specimens selected should and test as directed for devices under validated test be double the number tested in the first stage. The minimal volumes tested from each specimen and the procedures using membrane filtration. media and incubation periods are the same as those indicated for the first stage. If no microbial growth is Sterile empty or prefilled syringes found, the article tested meets the requirements of the Sterility testing of prefilled syringes is performed by test for sterility. If, however, it can be demonstrated employing the same techniques used in testing sterile that the second stage was invalid because of faulty or products in vials or ampuls. The direct transfer tech- inadequate aseptic technique in the performance of nique may be employed if the bacteriostasis and the test, the second stage may be repeated. Sterility fungistasis determination has indicated no adverse testing can be used as part of a quality assurance activity under the test conditions. Where appropriate, the membrane filtration procedure may be employed. program for a production lot or batch or as one of the quality control criteria for release of such a lot or For prefilled syringes containing a sterile needle, flush batch. the contained produce through the lumen. For sy- ringes packaged with a separate needle, aseptically STERILIZATION attach the needle, and expel the product into the vali- dated media. There are three major means employed for steriliz- Special attention should be paid toward demon- ing medical instruments (Nair, 1995), each of which strating that the outer area of the attached needle has advantages and drawbacks. (that part which will enter the patient's tissues) is sterile. For empty sterile syringes, take up sterile me- Heat sterilization dium or diluent into the barrel through the needle if at- Heat (steam) is effective and inexpensive but can tached, or, if not attached, through a sterile needle only be used for medical devices of a relatively small attached for the purpose of the test, and then express volume and materials, which are not degraded or de- the contents into the validated media. formed by it. Accordingly, it is typically useful only for Devices that are purported to contain sterile path- smaller metal devices and cannot always be success- ways may be tested for sterility by the membrane fil- fully applied to plastics and such. It is most commonly tration technique as follows. Aseptically pass a used for reusable steel instruments and glassware. sufficient volume of test fluid through each of not less Steam sterilization by autoclaving has traditionally than 20 devices so that not less than 100 ml is recov- been the most widely used method for medical instru- ered from each device. Collect the fluids in aseptic ments. Today, prevacuum, high-temperature steam containers, and filter the entire volume collected sterilization is considered to be the safest and most through membrane filter funnel (s). practical means of sterilizing the majority of surgical Where the devices are large and lot sizes are small, instruments, surgical dressings, fluids, fabrics, and CONFIRMATION OF STERILITY OF MEDICAL 65 other absorbent materials. The process should be PET has shown that oligomers and, in particular, the used with caution while sterilizing polymers and com- cyclic trimer increases on PET with repeated auto- posites as both heat and steam can drastically alter claving. Studies (Nair, 1995) of the PET materials in- their properties. The main deleterious effect from dicated increased values of heat of fusion and steam sterilization of polymeric materials occurs when percent crystallinity, which suggested reorganization hydrolysis of the polymer takes place leading to unde- of the amorphous phase. Generation of new crystal- sirable contaminants. Under prolonged steam auto- line regions was ruled out as there was no increase in claving, a few ppb of 4,4'-methylene dianiline (MDA) the intensity of the infrared peak of 973 cm' which or less has been detected (Shintani, 1989, 1991, indicates crystallinity. Chain scission of amorphous 1992 and 1995) in the aqueous extract of methyl regions, resulting in the formation of new amorphous diisocyanate (MDI)-based polyurethane which was regions, was, therefore, believed to be the reason for attributed to the hydrolysis of the polymer.
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