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Ecallantide

EvidenceFDA approved

ClassPlasma kallikrein inhibitor

Ecallantide is an FDA-approved plasma kallikrein inhibitor for acute hereditary angioedema attacks. Learn how it works, who gives it, and its boxed warning.

Reviewed by: William Maish, MD MBA MPH, Clinical Product Lead
Published: October 5, 2026
Last updated: October 5, 2026

Key takeaway

Ecallantide (sold as Kalbitor) is a protein that blocks plasma kallikrein, used to treat acute attacks of hereditary angioedema. By stopping kallikrein, it reduces production of the bradykinin that drives the swelling. It has been FDA-approved in the U.S. since 2009, is given by a healthcare professional, and carries a boxed warning for anaphylaxis.

At a glance

What it is	A plasma kallikrein inhibitor (a recombinant Kunitz-domain protein)
Approved for	Acute attacks of hereditary angioedema in patients 12 and older
Key fact	In a pivotal trial it significantly improved symptom scores versus placebo
Route	Subcutaneous injection, administered by a healthcare professional
Evidence strength	FDA approved

What is ecallantide?

Ecallantide, sold under the brand Kalbitor, is a recombinant 60-amino-acid protein that inhibits plasma kallikrein, an enzyme central to the swelling of hereditary angioedema (HAE). It is used to treat acute HAE attacks. Because it can cause anaphylaxis, it is given by a healthcare professional rather than self-administered. It was developed under the code DX-88 and approved in the United States in 2009.

How does ecallantide work?

Ecallantide blocks plasma kallikrein, an enzyme that cleaves a protein called high-molecular-weight kininogen to release bradykinin. Bradykinin is the mediator that causes the blood vessels to leak and the tissues to swell in hereditary angioedema. By inhibiting kallikrein, ecallantide reduces the generation of bradykinin and thereby controls the acute attack.

This upstream action distinguishes it from drugs that block the bradykinin receptor directly. In the EDEMA3 trial, ecallantide significantly improved both symptom-severity and treatment-outcome scores¹ compared with placebo. Because the molecule can provoke severe allergic reactions that may resemble an HAE attack, administration in a supervised setting is required.

Is it FDA-approved?

Yes. Ecallantide is FDA-approved, and its age range has widened since approval:

Year	FDA action	Who it covers
2009	Approved² for acute attacks of hereditary angioedema	Patients 16 and older
2014	Age lowered	Patients 12 and older

It carries a boxed warning for anaphylaxis and must be administered by a healthcare professional equipped to manage anaphylaxis; it is not for self-injection.

What is ecallantide prescribed for?

Ecallantide is prescribed to treat acute attacks of hereditary angioedema in people aged 12 and older. It is given in a clinical setting because of the risk of serious allergic reactions.

What are the side effects?

According to the prescribing information, common side effects include:

Headache
Nausea and diarrhea
Fever
Injection-site reactions and nasopharyngitis

More serious considerations include:

A boxed warning for anaphylaxis, which is why it is administered by a healthcare professional
Allergic reactions that can be hard to distinguish from an HAE attack

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Sources: FDA prescribing information for Kalbitor; the EDEMA3 trial (Cicardi et al., The New England Journal of Medicine, 2010, DOI: 10.1056/NEJMoa0905079¹), indexed on PubMed. This document is educational and does not constitute medical advice.