Pharmacokinetic considerations regarding the treatment of bacterial sexually transmitted infections with azithromycin: a review

Rates of bacterial sexually transmitted infections (STIs) continue to rise, demanding treatments to be highly effective. However, curing infections faces significant challenges due to antimicrobial resistance in Neisseria gonorrhoeae and Mycoplasma genitalium and especially treating STIs at extragenital sites, particularly rectal chlamydia and oropharyngeal gonorrhoea. As no new antimicrobials are entering the market, clinicians must optimize the currently available treatments, but robust data are lacking on how the properties or pharmacokinetics of antimicrobials can be used to inform STI treatment regimens to improve treatment outcomes. This paper provides a detailed overview of the published pharmacokinetics of antimicrobials used to treat STIs and how factors related to the drug (tissue distribution, protein binding and t½), human (pH, inflammation, site of infection, drug side effects and sexual practices) and organism (organism load and antimicrobial resistance) can affect treatment outcomes. As azithromycin is commonly used to treat chlamydia, gonorrhoea and M. genitalium infections, and its pharmacokinetics are well studied, it is the main focus of this review. Suggestions are also provided on possible dosing regimens when using extended and/or higher doses of azithromycin, which appropriately balance efficacy and side effects. The paper also emphasizes the limitations of currently published pharmacokinetic studies including oropharyngeal gonococcal infections, where very limited data exist around ceftriaxone pharmacokinetics and its use in combination with azithromycin. In future, the different anatomical sites of infections may require alternative therapeutic approaches.