Copper sulfate-lactic acid combinations exhibit broad-spectrum microbicidal activity against viral and bacterial sexually transmitted pathogens in vitro and in vivo.

Abstract

UNLABELLED: Sexually transmitted infections (STIs) and unintended pregnancy remain critical global public health concerns affecting millions of women worldwide. To support the development of new multipurpose products offering non-hormonal contraception and activity against sexually transmitted pathogens, we evaluated copper sulfate, zinc lactate, L-(+)-lactic acid and their combinations as candidate pharmaceutical actives. We determined virucidal (HIV-1, HSV-2) and bactericidal (Neisseria gonorrhoeae, Chlamydia trachomatis) activity in vitro followed by in vivo efficacy testing against HSV-2, N. gonorrhoeae, and C. trachomatis in mice. In vitro, zinc lactate alone showed no inhibitory activity. In contrast, copper sulfate and lactic acid alone and in combination demonstrated activity against all tested pathogens. Furthermore, these combinations remained potent in the presence of vaginal and seminal fluids. Importantly, the actives - alone or combined - at concentrations that inhibited STI pathogens did not inhibit the growth of Lactobacillus crispatus, bacteria associated with an optimal vaginal microbiota. Further, copper sulfate and lactic acid alone and in combination inhibited vaginal HSV-2 and N. gonorrhoeae infection in mice. The combination conferred limited protection against vaginal C. trachomatis infection. These data demonstrate the advantages of combining copper sulfate and lactic acid and support further evaluation and development of this combination as a multipurpose prevention product. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at https://doi.org/10.1038/s41598-026-65145-9.

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