Background: To provide safety data for efalizumab, a recombinant humanized monoclonal IgG1 antibody, in adults with chronic plaque psoriasis. Methods: A 12-week, Phase IIIb, randomized, double-blind, parallel-group, placebo-controlled trial. At 58 study sites in the USA and Canada, 686 patients with moderate to severe chronic plaque psoriasis received an initial conditioning dose of efalizumab 0.7 mg/kg subcutaneously (SC) followed by either 11 weekly doses of efalizumab 1 mg/kg SC or matching placebo. Main outcome measures were safety and tolerability outcomes (primary) and efficacy outcomes (secondary). Results: During 12 weeks of therapy with efalizumab or placebo, the incidence of clinical adverse events was 82.2% and 72.9%, respectively; the incidence of serious adverse events was 1.8% and 3.4%, respectively; and the incidence of nonserious adverse events leading to withdrawal was 1.8% and 1.7%, respectively. In the efalizumab group, there were no clinically significant changes in vital signs or laboratory parameters and no evidence of end-organ toxicities. A significantly higher proportion of patients receiving efalizumab than those receiving placebo achieved ≥ 75% improvement in the Psoriasis Area and Severity Index (PASI) (P < 0.001), ≥ 50% improvement in PASI (P < 0.001), and a static Physician's Global Assessment rating of Minimal or Clear (P < 0.001). The mean improvement in the Psoriasis Symptom Assessment was significantly greater in the efalizumab group (P < 0.001). Conclusions: Efalizumab treatment SC for 12 weeks was safe, well tolerated, and effective in patients with moderate to severe chronic plaque psoriasis.
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