Polypeptides are a class of antibiotics Overview of Antibiotics Antibiotics are drugs used to treat bacterial infections. They are not effective against viral infections and most other infections. Antibiotics either kill bacteria or stop them from reproducing... read more used to treat several types of infections. Polypeptides include the following:
Most 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 this wall in some bacteria. As a result, the bacteria die.
Bacitracin is used mainly to treat superficial skin infections Overview of Bacterial Skin Infections The skin provides a remarkably good barrier against bacterial infections. Although many bacteria come in contact with or reside on the skin, they are normally unable to establish an infection... read more caused by Staphylococcus aureus. It is applied directly to the skin (topically).
Colistin and polymyxin B commonly cause kidney damage, so they are used only for serious infections in which bacteria are resistant to all other antibiotics and no safer alternatives are available. When colistin or polymyxin B is used, it is given by vein (intravenously). In some cases, colistin may be inhaled through a nebulizer.
Some Potential Side Effects
Ear, eye, or skin infections
Bladder infections (polymyxin B may be used for bladder irrigation)
Serious infections caused by susceptible bacteria that are very resistant to many other antibiotics (colistin and polymyxin B given by injection)
Kidney and nerve damage (when given by injection)*
* Polypeptide antibiotics are usually applied directly to the ears, skin, or eyes, but colistin and polymyxin B are sometimes given by injection when bacteria are resistant to all other antibiotics and no safer alternatives are available. Bacitracin is not available for injection.
(See also Overview of Antibiotics Overview of Antibiotics Antibiotics are drugs used to treat bacterial infections. They are not effective against viral infections and most other infections. Antibiotics either kill bacteria or stop them from reproducing... read more .)
Use of Polypeptides During Pregnancy and Breastfeeding
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 Drug Absorption Drug absorption is the movement of a drug into the bloodstream after administration. (See also Introduction to Administration and Kinetics of Drugs.) Absorption affects bioavailability—how quickly... read more into the bloodstream. However, its safety has not been established. The same is true for polymyxin B and colistin when they are applied topically.
Polymyxin B and colistin should be taken by injection 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. (See also Drug Use During Pregnancy Drug Use During Pregnancy More than 50% of pregnant women take prescription or nonprescription (over-the-counter) drugs or use social drugs (such as tobacco and alcohol) or illicit drugs at some time during pregnancy... read more .)
Whether use of polymyxin B or colistin by injection during breastfeeding is safe is unknown. (See also Drug Use During Breastfeeding Drug Use During Breastfeeding When mothers who are breastfeeding have to take a drug, they wonder whether they should stop breastfeeding. The answer depends on the following: How much of the drug passes into the milk Whether... read more .)