(See also Overview of Antibiotics.)
Polypeptides are a class of antibiotics used to treat several types of infections. Polypeptides include the following:
Some bacteria have an outer covering (cell wall) that protects them. Bacitracin works by preventing bacteria from forming this wall. Colistin and polymyxin B work by disrupting the cell membrane underlying the wall. As a result, the bacteria die.
Bacitracin is used mainly to treat superficial skin infections caused by Staphylococcus aureus.
In hospitals, doctors are increasingly using colistin given by vein (intravenously) to treat serious infections caused by bacteria that are very resistant to other antibiotics when no safer alternatives are available.
With bacitracin, the risk to the fetus during pregnancy and to the newborn during breastfeeding is thought to be slight because bacitracin is applied topically and little of the drug is absorbed into the bloodstream. However, its safety has not been established.
Polymyxin B and colistin should be taken during pregnancy only when the benefits of treatment outweigh the risks. With polymyxin B, no harmful effects on the fetus have been observed in animal studies, but no well-designed studies have been done in pregnant women. With colistin, harmful effects on the fetus have been observed in animal studies.
Whether use of polymyxin B or colistin during breastfeeding is safe is unknown.