A new treatment schedule for administration of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide and other related carboxamide anticancer drugs in which the drug is administered in a divided-dose shedule comprising two or more administrations at frequent intervals, for example every hour. Schedules to produce cyclic peaks/troughs in plasma levels are mentioned. The compounds can be used for circumventing multidrug resistance in cancers and may, for example, be used in combination with other cytotoxic drugs, especially non-topo II inhibitors. Treatment of melanoma and advanced colon cancer is included.