Re-treatment Studies: Design and Analysis

For some disorders such as irritable bowel syndrome, symptoms may wax and wane with variable periodicity. In clinical practice, treatment is usually targeted at symptom reduction during exacerbations. The management of such patients will likely involve intermittent courses of therapy tailored to the patient's individual symptom pattern instead of chronic, uninterrupted treatment. Three study designs to assess the feasibility and efficacy of repeated drug treatment in patients with irritable bowel syndrome are discussed. The first design is a parallel group design in which patients, after the initial treatment period, may repeatedly receive the same treatment as in the first period (test drug or control). In the second design, patients who respond favorably to initial treatment with a test drug and whose symptoms recur when this treatment is stopped will be randomly assigned to receive the test drug or control in a second period. The third design has in addition a control group in the initial period. The three designs are compared regarding analysis and sample size.