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Polypeptide antibiotics are a chemically diverse class of anti-infective and antitumor antibiotics containing non-protein polypeptide chains. Examples of this class include actinomycin, bacitracin, colistin, and polymyxin B. Actinomycin-D has found use in cancer chemotherapy. Most other polypeptide antibiotics are too toxic for systemic administration, but can safely be administered topically to the skin as an antiseptic for shallow cuts and abrasions.
Actinomycin-D is believed to produce its cytotoxic effects by binding DNA and inhibiting RNA synthesis. The mechanism of action of other polypeptide antibiotics is thought to be directed to bacterial membranes, but the details are largely unknown.
Animal studies have shown actinomycin-D is corrosive to skin, irritating to the eyes and mucous membranes of the respiratory tract and highly toxic by the oral route. It has also been shown to be carcinogenic, mutagenic, embryotoxic and teratogenic. Adverse effects of other polypeptide antibiotics include kidney and nerve damage when given by injection.