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Microbiological Tests of Transdermal Therapeutic Systems

Validation of the Pharm. Eur. method for microbiological purity

Holger Stockem a and Karl Heinz Meyer b

Gesellschaft für Produktionshygiene und Sterilisationssicherheit, Aachen (Germany) a , and LTS Lohmann Therapie Systeme, Andernach (Germany) b

Microbiological purity is not only important for topical dosage forms but also for transdermal patches as well. The criteria of microbiological purity of those pharmaceutical formulations are stated in the Europeian Pharmacopeia, chapter 51.4, category II. Due to the special nature of transdermal patches, i.e. with their sticking surface, the standard microbiological test procedures cannot be used. For this reason, the microbiological test method of the European Pharmacopeia was modified by Fels so that it can be applied for transdermal patches. In order to be able to validate this method it was necessary to find a possibility to inoculate the patches and to dry the microorganisms, however, avoiding the cell death by dryness. Following this procedure the acceptance criteria for the recovery rate, the linearity, the precision, the limit of detection and the limit of quantification were fixed. The validation run showed that most of those acceptance criteria were fulfilled by means of this method. But concerning the precision of the distribution of microbial data it does not follow a Gaussian distribution and, therefore, the variation coefficient, as determined in validation of chemical analytical methods is misleading.

Key words Microbiological tests, European Pharmacopeia method · Microbiological purity · Transdermal patches