Redeveloping old polymyxins Increasing multidrug-resistance in Gram-negative superbugs,in particular Pseudomonas aeruginosa,Acinetobacter baumannii and Klebsiella pneumoniae,is presenting a global medical challenge.There is no novel candidate in the antibiotic development pipeline for these superbugs and no new anti-Gram-negative antibiotic will be clinically available in the next 9-11 years.Limited therapeutic options have forced infectious disease clinicians and microbiologists to reappraise the clinical application ofpolymyxins (i.e.colistin and polymyxin B),antibiotics discovered 50 years ago.This presentation summarizes recent progress in understanding of the complex chemistry,pharmacokinetics and pharmacodynamics of colistin and polymyxin B,the interplay between these three aspects and their impact on the clinical use of these two important antibiotics.Recent clinical findings are reviewed,focusing on evaluation of efficacy,emerging resistance,potential toxicities and combination therapy.In addition,development of novel polymyxins will be reviewed.In the battle against rapidly emerging bacterial resistance we can no longer rely entirely on the discovery of new antibiotics; we must also pursue rational approaches to the use of older antibiotics such as polymyxins.