Ecallantide, a recombinant protein that is a selective, highly potent and reversible inhibitor of human plasma kallikrein, is indicated for the treatment of acute attacks of hereditary angioedema (HAE) in patients aged >or=16 years. In the randomized, double-blind, placebo-controlled, multicentre, phase III trial EDEMA3, mean symptom response to treatment at 4 hours (assessed using the Treatment Outcome Score [TOS]; primary endpoint) was significantly greater with a single subcutaneous dose of ecallantide 30 mg than with placebo in patients with acute, moderate to severe attacks of HAE. In addition, the mean change from baseline in symptom severity at 4 hours (assessed using the Mean Symptom Complex Severity [MSCS] scale) was significantly greater with ecallantide than with placebo. At 4 hours in the similarly designed EDEMA4 trial, the mean change from baseline in MSCS score (primary endpoint) and mean TOS were both significantly greater in recipients of a single subcutaneous dose of ecallantide 30 mg than in placebo recipients. Subcutaneous ecallantide 30 mg was generally well tolerated in patients with acute attacks of HAE in the EDEMA3 and EDEMA4 trials. Adverse events were mostly of mild to moderate severity, and no event that was more common in ecallantide than placebo recipients occurred in >10% of patients. [References: 22].