The emergence of multidrug-resistant gram-negative bacteria and the lack of new
antibiotics to combat them have led to the revival of
polymyxins, an old class of cationic, cyclic
polypeptide antibiotics.
Polymyxin B and
polymyxin E (
colistin) are the 2
polymyxins used in clinical practice. Most of the reintroduction of
polymyxins during the last few years is related to
colistin. The
polymyxins are active against selected gram-negative bacteria, including Acinetobacter species, Pseudomonas aeruginosa, Klebsiella species, and Enterobacter species. These drugs have been used extensively worldwide for decades for local use. However, parenteral use of these drugs was abandoned approximately 20 years ago in most countries, except for treatment of patients with
cystic fibrosis, because of reports of common and serious nephrotoxicity and neurotoxicity. Recent studies of patients who received intravenous
polymyxins for the treatment of serious P. aeruginosa and Acinetobacter baumannii
infections of various types, including
pneumonia,
bacteremia, and
urinary tract infections, have led to the conclusion that these
antibiotics have acceptable effectiveness and considerably less toxicity than was reported in old studies.