The present invention is directed to a novel use of pyridone derivatives such as pirfenidone for the prevention and treatment of damages to tissues or organs induced by various cytotoxic agents, such as chemotherapeutic agents, biologics, immunosuppressants and radiation. Such prophylactic and/or therapeutic effects of the pyridone derivatives make it possible to increase therapeutic dosages of the cytotoxic agent, thereby enhancing the therapeutic efficacy of the cytotoxic agent and radiation therapy.