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What is a Phase 2 Clinical Trial?

By Dr Ananya Mandal, MD

A phase 2 clinical trial is conducted to evaluate the effectiveness and safety of a new drug or drug combination for a particular indication.

While a phase 1 trial may recruit healthy volunteers for determining the maximum doses and dose ranges that should be administered, phase 2 is more focused on the therapeutic efficacy in a particular patient population to establish whether or not the drug may ultimately benefit patients and should be studied in a phase 3 trial.

Phase 2 trials are usually randomized, controlled studies evaluating the safety and efficacy of a drug for a particular condition and involve participants selected using narrow criteria, to allow close monitoring of a relatively homogenous patient population.

Although information about safe and well tolerated doses is obtained in earlier phases of drug development, phase 2 trials also assess safety parameters to check for any adverse effects that may have been missed earlier or that may be specific only to a certain patient population.

One of the main goals of phase 2 trials is to determine an appropriate dose and treatment regimen that can be tested in phase 3 trials. Dose response studies may therefore be carried out and confirmed in the phase 2 trial. The doses used in phase 2 are generally less than the highest of those used in phase 1 and the treatment is given to a larger population of people in phase 2, usually 100 to 300 patients.

Phase 2 trials are sometimes further divided into:

  • Phase 2a
  • Phase 2b

Phase 2a is focused specifically on dosing requirements. A small number of patients are administered the drug in different quantities to evaluate whether there is as a dose-response relationship, which is an increase in response that correlates with increasing increments of dose. In addition, the optimal frequency of dose is also explored.

Phase 2b trials are designed specifically to rigorously test the efficacy of the drug in terms of how successful it is in treating, preventing or diagnosing a disease.

Reviewed by , BSc

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Last Updated: Jan 29, 2014

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