Phase I

Phase I trials are the first-stage of testing in human subjects. Normally a small (20-80) group of healthy volunteers will be selected. This phase includes trials designed to assess the safety (Pharmacovigilance), tolerability, pharmacokinetics, and pharmacodynamics of a therapy. These trials are almost always conducted in an inpatient clinic, where the subject can be observed by full-time medical staff. The subject is usually observed until several half-lives of the drug have passed. Phase I trials also normally include dose-ranging studies so that doses for clinical use can be refined. The tested range of doses will usually be a small fraction of the dose that causes harm in animal testing. Phase I trials most often include healthy volunteers, however there are some circumstances when patients are used, such as with oncology (cancer) and HIV drug trials. In Phase I trials of new cancer drugs, for example, patients with advanced (metastatic) cancer are used. These trials are usually offered to patients who have had other types of therapy and who have few, if any, other treatment choices.

There are different kinds of Phase I trials:

SAD - Single Ascending Dose studies are those in which small groups of patients are given a single dose of the drug while they are observed and tested for a period of time. 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 patients is then given a higher dose. This is continued until pre-calculated pharmacokinetic safety levels are reached, or intolerable side effects start showing up (at which point the drug is said to have reached the Maximum tolerated dose (MTD) ).

MAD - Multiple Ascending Dose studies are conducted to better understand the pharmacokinetics & pharmacodynamics of multiple doses of the drug. In these studies, a group of patients receives multiple low doses of the drug, whilst samples (of blood, and other fluids) are collected at various time points and analyzed to understand how the drug is processed within the body. The dose is subsequently escalated for further groups, up to a predetermined level.

Food effect - a short trial designed to investigate any differences in absorption caused by eating pre-dose, and its effect on the pharmacokinetic profile. These studies are usually run as a crossover study, with volunteers given two identical doses of the drug on different occasions; one while fasted, and one after being fed.
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