Ecallantide (Kalbitor): A plasma kallikrein inhibitor approved for the treatment of acute attacks of hereditary angioedema

Ecallantide 30 mg (3 mL) subcutaneous injection was approved by FDA in December 2009 to treat hereditary angioedema (HAE). HAE is a rare genetic condition caused by a mutation in the C1 esterase-inhibitor (C1-INH) gene, resulting in low levels of the blood protein. C1-INH plays a role in regulating a person's immune system and intrinsic clotting pathways through inhibiting kallikrein, and ultimately, reducing the downstream production of bradykinin (a vasodilator thought to be responsible for HAE symptoms). HAE attacks result in sudden fluid buildup in the face and other parts of the body, and may lead to permanent disfigurement, disability or death. It is estimated that 10,000 people in the United States have HAE. This is the second drug marketed in the United States to treat HAE attacks. Earlier in 2009, FDA approved human blood derived C1-INH (Berinert) to treat facial and abdominal attacks of HAE.

Efficacy. The safety and efficacy of ecallantide was evaluated in 2 randomized, double-blind, placebo-controlled trials (dubbed EDEMA3 and EDEMA4) enrolling 168 patients with HAE. Patients having an attack of HAE, at any anatomic location (abdominal, peripheral or laryngeal), and having at least 1 moderate or severe symptom, were treated with 30 mg subcutaneous injections of ecallantide or placebo. Both trials demonstrated that patients treated with ecallantide had significantly greater reductions in their symptom severity and were more likely to report a positive response to treatment compared with patients receiving placebo.

Safety. The most worrisome side-effect of ecallantide is anaphylaxis. In 255 HAE patients treated with the drug as part of clinical trials, 10 patients (3.9%) experienced anaphylaxis. Anaphylaxis most commonly occurs within the first hour after injection of ecallantide. Because of the risk of anaphylaxis, ecallantide should only be administered by a healthcare professional, in a healthcare setting where serious anaphylactic reactions and HAE can be treated. Other common side-effects of ecallantide use include headache, nausea, fatigue, diarrhea, upper respiratory tract infection, injection site reactions, nasopharyngitis, vomiting, pruritus, upper abdominal pain, and pyrexia.