Phases of Drug Development in Clinical Trials

The processes involved in a clinical trial can vary greatly depending on which phase of the study is currently active, from the number of people being studied to the length of each phase.

• Early Development
• Phase 1
• Phase 2
• Phase 3
• Phase 4

Early Development - lasts 3-6 years

This phase is intended to study a drug's action and metabolism and to evaluate the drug for obvious toxicities before it is given to people.

• Preclinical development
• Test tube or computer-based discovery
• New agents are tested in animals, typically mice or rats
• Drugs are then tested in larger animals, such as dogs
• Permission to test the drug in humans is then requested from the FDA
• If permission is granted, then the clinical research in humans can begin

Phase 1 - lasts months

• 20-100 healthy volunteers are given increasingly larger amounts of the study drug
• Tests the following for the study drug:
• safety
• tolerability
• pharmacokinetics (how long the drug lasts in the body; details about its distribution, metabolism and excretion)
• pharmacodynamics (details of the drug's activity)

Phase 2 - lasts months to years

• Hundreds of patients are given the study drug
• Patients are generally not very ill, nor do they typically have many other conditions or take many other medications that could interfere with the effects of the study drug
• Sponsor determines effectiveness of drugs for its intended use
• Tries to find the best dose for condition
• May include comparator drugs or a placebo to study the differences in results between the current treatment plan and the drug being studied

Phase 3 - lasts 2-3 years

• Thousands of patients are given the study drugs at multiple study sites.
• Studies the effectiveness and safety of the drug on a larger scale
• Includes more real-world patients who have other medical problems in addition to the one being studied
• Patients receive either the new study drug or medication that is already on the market
• Depending on the study, one group may receive a placebo (fake medication or no treatment)
• Placebos are never given to seriously ill patients if an alternative therapy is available.  To do so would be both unethical and illegal.
• The Data Safety Monitoring Board can halt the trial at any time due to safety concerns or significant results showing one group is responding better to treatment than the other.

Phase 4 - lasts 3-4 years

• Number of patients in study varies
• Marketing driven
• Compares the study drug to major market competitor
• Gathers more safety information
• Attempts to expand the approved uses to other conditions
• Can lead to a change in the drug's status from prescription to over-the-counter
• May target new groups of study participants including different age, sexes or ethnicities
• After a drug is marketing, the safety of the drug is still monitored and can still be pulled from the market or have warnings added if any serious side effects are discovered

Information taken from "Conducting Clinical Research" by Judy Stone, M.D. Copyright 2006.