Evaluation of antimicrobial efficacy of Psidium guajava L. leaf extract in ketoconazole shampoo

Despite their effectiveness, synthetic preservatives are often associated with adverse health effects, which has led to growing interest in natural alternatives. This study evaluated the antimicrobial activity of an ethanolic extract of Psidium guajava L. leaves incorporated into a shampoo formulation. The ethanolic extract of Psidium guajava L. leaves was tested at concentrations of 0.5%, 2.5%, 5%, 7.5%, and 10% (w/w) under accelerated conditions for three months. Phytochemical screening and HPLC analysis were conducted to identify key bioactive compounds (including phenols, flavonoids, and terpenoids), antimicrobial efficacy testing, and stability testing (such as pH, viscosity, density, and color) were evaluated. At concentration 10%, extract completely inhibited microbial growth over a 28-day period, in comparison with chemical preservatives. Stability testing conducting at accelerated temperatures (40 °C/75% RH) for three months confirmed the physical stability of the formulation and the chemical integrity of ketoconazole. Preservative efficacy tests, performed accordance with USP/BP guidelines against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, and Aspergillus brasiliensis, demonstrated that the extract reduced microbial counts beyond USP/BP acceptance criteria, achieving total inhibition of all strains within 28 days. Chemical and biological tests confirmed formulation stability and efficacy over a three-months period. The findings suggest that P. guajava L. extract is a promising natural preservative; however, further studies are needed to assess its long-term stability.