Colistin: new lessons on an old antibiotic.

Colistin has been re-introduced into clinical practice for the treatment of carbapenem-resistant Gram-negative bacteria. Studies in the last decade attempted to reconstruct the path that present-day medications undergo prior to clinical use. In this review, we summarize the results of recent clinical studies. Colistin was associated with lower mortality than no effective treatment and higher unadjusted mortality than β-lactams in non-randomized clinical studies. However, it was administered to sicker patients with carabapenem-resistant bacteria. Overall, nephrotoxicity rates were not higher with colistin in these studies, and colistin-induced nephrotoxicity is reversible in most patients. The emergence of colistin resistance has been described in high-use settings. Synergy with carbapenem, rifampin and other antibiotics has been reported in vitro. Randomized controlled trials are ongoing or in planning to assess this and other aspects of colistin use in clinical practice.