Cytotoxic chemotherapy drugs work by interfering with the processes involved in cell division. They are sub-classified by their mode of action (Fig. 1). Cytotoxic chemotherapies have their greatest activity in proliferating cells and this provides the rationale for their use in the treatment of cancer. However, they are not specific for cancer cells and the side effects of treatment are largely a result of their antiproliferative actions in normal tissues such as the bone marrow, skin and gut . Other organs, such as the heart, kidney and peripheral nervous system, may also be affected by some cytotoxic drugs.

fig1. Commonly used cytotoxic chemotherapy agents and their mechanisms of action.

The choice of cytotoxic chemotherapy agent, or combination of treatments, is determined by the cancer type. The dosing schedule is determined by the choice of treatments and recovery of normal tissues, usually the bone marrow. For most common cytotoxic chemotherapy regimens the treatment is administered in cycles. A course of treatment may constitute a pre-defined number of cycles, or may continue indefinitely until evidence of disease progression or until limiting side-effects. Supportive therapy is used to enable patients to tolerate therapy and achieve benefit. Nausea and vomiting are common, but with modern antiemetics, regimens such as the combination of dexamethasone and highly selective 5-hydroxytryptamine (5-HT _{3 ,} serotonin) receptor antagonists such as ondansetron, most patients now receive cytotoxic chemo therapy without any significant problems. Myelosuppression is common to almost all cytotoxics and this not only limits the dose of drug but also can cause life-threatening complications. The risk of neutropenia can be reduced with the use of specific growth factors that accelerate the repopulation of myeloid precursor cells. The most commonly employed is G–CSF, which is widely used in conjunction with cytotoxic chemotherapy regimens that induce a high rate of neutropenia.