Dose
How much of a drug is given, how often, and for how long. Cancer drugs have long been given at the highest dose a patient can stand, and regulators are now pushing for doses chosen for benefit rather than tolerability.
Chemotherapy doses are usually scaled to body surface area (mg/m²) or weight (mg/kg) and given in cycles, typically every one to three weeks, to let bone marrow recover; targeted drugs and antibodies are increasingly given at fixed doses. The traditional phase 1 approach escalates until side effects become dose-limiting and sets the maximum tolerated dose as the dose for later trials, a logic that suits chemotherapy but not targeted drugs, which may saturate their target well below the toxic dose; the FDA's Project Optimus now requires sponsors to compare doses. Dose reductions and interruptions for side effects are common in practice and do not necessarily reduce efficacy, as trials with lower-dose arms have shown for several drugs.