Old antibiotics for multidrug-resistant pathogens: from in vitro activity to clinical outcomes.

Antimicrobial resistance is a major and emerging threat worldwide. New antimicrobials have been unable to meet the resistance challenge, and treatment options are limited for a growing number of resistant pathogens. More and more clinicians are relying on older antimicrobials for the treatment of multidrug-resistant (MDR) bacteria. Some older antimicrobials have maintained excellent in vitro activity against highly resistant pathogens. In some instances, use of older agents is limited by unfavourable pharmacokinetic/pharmacodynamic characteristics and/or toxicities. In general, clinical data pertaining to the use of older agents for the treatment of MDR pathogens are scarce. Research efforts should be focused on the evaluation of older agents for the treatment of MDR pathogens as well as evaluating how these agents perform in complex patient populations with various and multiple co-morbid conditions.