Polypeptide antibiotics are a group of antibiotics which is used in the treatment of eye, ear, and bladder infections in addition to aminoglycosides. Since they are toxic, polypeptides are not suitable for systemic administration. They are only administered topically on the skin. They are usually applied directly to the eye or inhaled into the lungs. It is not given by injection. Their mechanism of action is protein inhibition, but is largely unknown.
Polypeptide antibiotics adverse effects are kidney and nerve damage when administered by injection. Polypeptides include actinomycin, bacitracin, colistin, polymyxin B.