Topical antimicrobial therapy: Current status and challenges

Abstract

Topically applied antibacterial agents are widely used. Opinions regarding the clinical efficacy of topical antibiotics are conflicting, and for most indications, alternative oral therapies are available. Topical application has many potential advantages over systemic therapy that includes high and sustained concentrations of drug directly at the infected site, low quantity of antibiotic needed, better compliance, fewer systemic side effects and potentially less chance of antimicrobial resistance. Despite these advantages, an important concern has been the difficulty in monitoring antibiotic dosage and duration of therapy. Most topical preparations are applied on sites with pre-existing normal bacterial flora, and the detrimental effect of antibiotic on the 'good' bacteria is difficult to control. Unnecessary exposure of the resident microflora to high drug levels may select drug-resistant phenotypes. The number of antibiotics available and the quality and composition of the formulations recommended for topical drug delivery are improving. Their role in the prevention and treatment of locally invasive infections is established for many clinical conditions. However, there is still a lacuna in the availability of pharmacokinetic (PK) knowledge of these topical preparations and translation of the same to clinical practice. In addition, reporting the clinical outcome following the use of these agents and its analysis considering the recently proposed epidemiological cut-off value-based cut-offs are also areas which merit further research. In this review, we highlight the clinical utility and the PK aspects of topical antimicrobials in various infections. We also discuss the limitations of the current antimicrobial susceptibility testing (AST) protocols and new methods for AMST for topical agents.