USMLE Step 1 Practice Test 12

A new oral inhibitor of an inflammatory cytokine has completed a dose-escalation study in 40 healthy volunteers, which established its pharmacokinetics and short-term safety. Investigators now enroll 160 patients with moderate plaque psoriasis and randomly assign them to one of three doses of the drug or to placebo for 12 weeks. The main outcome is the proportion of patients in each group with at least 75% improvement in skin lesions, and adverse effects at each dose are recorded to select the dose for later trials. Which of the following best describes this study?