Development and validation of analytical method for microbiological quality control of ketoconazole shampoo 2%

Introduction. Ketoconazole 2% shampoo is a non-sterile topical pharmaceutical preparation containing 20 mg/g micronized ketoconazole, used in the treatment of Malassezia-associated skin disorders. Microbiological quality control is essential for topical preparations, as microbial contamination may affect both product quality and patient safety. The intrinsic antifungal activity of ketoconazole, together with surfactants, preservatives and other formulation excipients, may interfere with microbial recovery. Therefore, effective matrix neutralization and demonstration of method suitability are essential for reliable determination of TAMC, TYMC and specified microorganisms according to Ph. Eur. requirements. Materials and methods. Pharmacopoeial approach was used following Ph. Eur. 2.6.12 and 2.6.13 with low-level inocula (<100 CFU) and 0.45 µm PVDF membrane filters. Neutralizing system consisted of buffered sodium chloride-peptone diluent with neutralizers. Sample preparation involved 10 mL shampoo with PDN neutralizers. Quantitative method suitability was tested by surface-spread and membrane-filtration methods on TSA and SDA media at specified temperatures and durations. Qualitative method suitability involved parallel enrichment and selective subculturing for specified microorganisms using low-level inocula (<100 CFU) with TSB enrichment at 30–35 °C for 18–24 h. Results. TAMC recovery ranged from 91.37% to 100.80% across the tested microorganisms. TYMC recovery ranged from 89.14% to 96.10% for C. albicans and A. brasiliensis. Recovery and precision results demonstrated effective neutralization of the intrinsic antimicrobial activity of the Ketoconazole 2% shampoo matrix without relevant inhibition of the challenge microorganisms. Conclusion. The developed microbiological method demonstrated adequate recovery, precision, and effective neutralization of the intrinsic antimicrobial activity of Ketoconazole 2% shampoo. The method was suitable for both quantitative enumeration and detection of specified microorganisms and is therefore considered reliable for routine microbiological quality control in accordance with Ph. Eur. requirements. Key messages. Ketoconazole 2% shampoo has intrinsic antimicrobial activity that can interfere with microbial recovery in quality control. Effective neutralization of the shampoo matrix is essential for reliable microbiological testing according to Ph. Eur. standards. The validated method demonstrated adequate recovery and precision for TAMC, TYMC, and specified microorganisms, ensuring reliable routine quality control.