Phase 0 is useful to eliminate drugs that don't measure up to even the most rudimentary requirements, saving time and money. Likewise it smooths the approval process to move on to the next drug trial phases in order to register a new compound.
The objective of Phase 0 trials is to show whether a drug's pharmacokinetics and pharmacodynamics warrant continued exploration. However, it will not demonstrate any therapeutic effect nor will it replace the dose escalation, safety, and tolerance studies required in Phase I.
In Phase 0 the drug is only given to a very small group of healthy volunteers, usually less than 15 individuals, who are administered a microdose, less than 1% of the therapeutic dose of the drug in question, for no more than seven days.
In Phase I trials, researchers test an experimental drug or treatment in a small group of people, around 20 to 100 people, for the first time. Around 70% of drugs move to the next phase.
The objective is to evaluate the drug's safety, determine a safe dosage range, and identify side effects.
Phase I studies are usually conducted in patients with the disease of interest. The goal here is to determine what the drug's most frequent side effects are and, often, how the drug is metabolized and excreted. The number of subjects typically ranges from 20 to 80.
Phase II studies begin if Phase I studies don't reveal unacceptable toxicity. While the emphasis in Phase I is on safety, the emphasis in Phase II is on effectiveness. Phase II usually lasts months to 2 years, and 33% of drugs move to the next phase.
Phase II aims to obtain preliminary data on whether the drug works in people who have a certain disease or condition. For controlled trials, patients receiving the drug are compared with similar patients receiving a different treatment, usually an inactive substance (placebo), or a different drug. Safety continues to be evaluated, and short-term side effects are studied. Typically, the number of subjects in Phase II studies ranges from a few dozen to about 300.
Phase III studies begin if evidence of effectiveness is shown in Phase II. These studies gather more information about safety and effectiveness, studying different populations and different dosages and using the drug in combination with other drugs. The number of subjects usually ranges from several hundred to about 3,000 volunteers. Phase II usually lasts 1 to 4 years. Only 25-30% of the drugs move to phase IV.
The purpose of Phase III is to evaluate how the new medication works in comparison to existing medications for the same condition.
Comparisons are achieved through double-blind randomization of volunteers into two groups where they receive the novel drug vs the comparison existing medication. Double-blind methodology helps to eliminate bias when interpreting results.
Phase IV trials are post-marketing studies conducted after a drug is approved for use by the FDA. They are usually large studies, including several thousand volunteers with the disease/condition.
The goal of Phase IV trials is to provide additional information including the treatment or drugs risks, benefits, and best use.
These post-marketing requirement and commitment studies are sponsored and conducted after the FDA has approved a product for marketing. The FDA uses these studies to gather additional information about a product's safety, efficacy, or optimal use.
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