Single ascending dose studies are those in which small groups of subjects are given a single dose of the drug while they are observed and tested for a period of time. Typically, a small number of participants, usually three, are entered sequentially at a particular dose. If they do not exhibit any adverse side effects, and the pharmacokinetic data is roughly in line with predicted safe values, the dose is escalated, and a new group of subjects is then given a higher dose. If unacceptable toxicity is observed in any of the three participants, an additional number of participants, usually three, are treated at the same dose. This is continued until pre-calculated pharmacokinetic safety levels are reached, or side effects start showing up at which point the drug is said to have reached the maximum tolerated dose. If an additional unacceptable toxicity is observed, then the dose escalation is terminated and that dose is declared to be the maximally tolerated dose.
Multiple ascending dose studies are conducted to better understand the pharmacokinetics and pharmacodynamics of multiple doses of the drug. In these studies, a group of patients receives multiple low doses of the drug, while samples (of blood and other fluids) are collected at various time points and analyzed to acquire information on how the drug is processed within the body. The dose is subsequently escalated for further groups, up to a predetermined level.