The validity of medicines microbial quality testing relies on the adequacy of the test procedure employed. The aim of the study was to analyse factors triggering false results during microbial quality testing of non-sterile medicinal products, as well as to find ways of their elimination. Materials and methods: the study was focused on non-sterile medicinal products tested for microbial quality: N-methylglucamine, L-Malic acid, Xeroform, Fingolimod hydrochloride, Succinic acid, Streptocide, Aripiprazole, Doxazosin, Clopidogrel, Moxonidine, Tilorone, Mycophenolic acid, Folic acid, Gabapentin, Dutasteride, Imatinib, Temozolomide. The study involved the use of the following test strains: Bacillus subtilis, Bacillus cereus, Candida albicans, Escherichia coli, Aspergillus brasiliensis, as well as of reagents and growth media. The methods used were determination of antimicrobial activity under conditions of microbial quality testing, and modified in-depth testing of microbial quality of medicinal products according to the requirements of the State Pharmacopoeia of the Russian Federation, 13th edition. Results: the analysis of literature sources helped reveal the main factors causing false results of microbiological testing and determine ways of their elimination. The article sets forth the results of experimental comparison of two ways of sample preparation for solid formulations: the standard one described in the State Pharmacopoeia of the Russian Federation, 13th edition, and the one involving the use of a laboratory shaker. The article provides experimental data on specific aspects of elimination of antimicrobial activity against B. subtilis and B. cereus and the use of specific inactivators for particular medicinal products. Conclusions: a set of measures aimed at prevention of false-positive and false-negative testing results should include: sterility control of the growth media and reagents used, monitoring of facilities; control of growth promotion properties and selectivity of the growth media; selection of adequate incubation conditions and inoculation procedure with due regard to the dosage form; justification of the amount of sample, diluents and dilution factor used; consideration of the antimicrobial activity of a medicinal product.
