The bleomycins are a group of glycopeptides that are isolated from Streptomyces verticillus. The clinical preparation, bleomycin sulfate (Blenoxane), is a mixture of several components. Bleomycin binds to DNA, in part through an intercalation mechanism, without markedly altering the secondary structure of the nucleic acid. The drug produces both single- and double-strand scission and fragmentation of DNA. It is thought that the bleomycins, which are avid metal-chelating agents, form a bleomycin-Fe ++ complex that can donate electrons to molecular oxygen, thus forming the superoxide and hydroxyl free radicals. It is these highly reactive intermediates that attack DNA and produce DNA strand breakage and maximum cytotoxicity in the late G2 and early M-phases of the cell cycle.
Bleomycin is poorly absorbed orally, but it can be given by various parenteral routes. Its plasma half-life is not affected by renal dysfunction as long as creatinine clearance is greater than 35 mL/minute.
Bleomycin hydrolase, which inactivates bleomycin, is an enzyme that is abundant in liver and kidney but virtually absent in lungs and skin; the latter two organs are the major targets of bleomycin toxicity. It is thought that bleomycin-induced dermal and pulmonary toxici-ties are related to the persistence of relatively high local concentrations of active drug.
Bleomycin, in combination with cisplatin or etopo-side, is important as part of the potentially curative combination chemotherapy of advanced testicular carcinomas. Bleomycin is used in some standard regimens for the treatment of Hodgkin's and non-Hodgkin's lymphomas, and it is useful against squamous cell carcinomas of the head and neck, cervix, and skin.
A potentially fatal lung toxicity occurs in 10 to 20% of patients receiving bleomycin. Patients particularly at risk are those who are over 70 years of age and have had radiation therapy to the chest. Rarely, bleomycin also may cause allergic pneumonitis. Bleomycin skin toxicity is manifested by hyperpigmentation, erythe-matosus rashes, and thickening of the skin over the dorsum of the hands and at dermal pressure points, such as the elbows. Many patients develop a low-grade transient fever within 24 hours of receiving bleomycin. Less common adverse effects include mucositis, alopecia, headache, nausea, and arteritis of the distal extremities.
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