Polypeptide antibiotics disrupt bacterial cell walls (see Table 15: Bacteria and Antibacterial Drugs: Polypeptides).
Bacitracin is a polypeptide antibiotic that inhibits cell wall synthesis and is active against gram-positive bacteria.
Colistin (polymyxin E) and polymyxin B are cationic polypeptide antibiotics that disrupt the outer bacterial cell membrane by binding to the anionic outer membrane, which contains lipopolysaccharide (endotoxin), and thereby neutralizing the bacteria's toxicity.
Colistin methane sulfonate (colistimethate sodium [CMS]) is a parenteral preparation of a prodrug that is transformed in blood and urine to colistin. CMS is less toxic than colistin.
Polypeptides are usually used topically; systemic absorption is negligible.
Polymyxin B and colistin have rapid concentration-dependent bactericidal activity against
These drugs are not active against Proteus, Providencia, Burkholderia, and
Serratia spp and some obligate anaerobes, including Bacteroides fragilis and gram-positive bacteria. Development of resistance is uncommon.
Polypeptides are used for several types of infections (see Table 16: Bacteria and Antibacterial Drugs: Some Clinical Uses of Polypeptides).
All polypeptides are contraindicated in patients who have had an allergic reaction to them. CMS and polymyxin B should not be given simultaneously with drugs that block neuromuscular transmission or are nephrotoxic (eg, aminoglycosides, curare-like drugs).
Use During Pregnancy and Breastfeeding
Bacitracin may pose minimal risk during pregnancy and breastfeeding because systemic absorption is minimal; however, safety has not been established.
Polymyxin B is in pregnancy category B (animal studies show no risk and human evidence is incomplete, or animal studies show risk but human studies do not).
Colistin is in pregnancy category C (animal studies show some risk, evidence in human studies is inadequate, but clinical benefit sometimes outweighs risk); this drug crosses the placenta. Whether use during breastfeeding is safe is unknown.
Adverse effects include
Polymyxins are nephrotoxic. CMS and polymyxin B may cause circumoral and extremity paresthesias, vertigo, slurred speech, and muscle weakness and respiratory difficulty due to neuromuscular blockade, especially in patients with renal insufficiency.
Last full review/revision July 2009 by Matthew E. Levison, MD