A method for determining a therapeutically effective amount of suramin for administering to a patient, who is to receive a cytotoxic agent, which comprises the steps of determining the circulating suramin concentration in the patient administering suramin, if required, to establish a low circulating concentration of suramin in the patient of below about 200 μM and administering the chemotherapeutic agent to the patient when the low circulating concentration of suramin is present in the patient. Conveniently a nomogram can be constructed for use in clinical settings with the suramin.
