Is ecallantide FDA-approved, and what does the research show?

What is ecallantide?

Ecallantide is a prescription medicine for sudden attacks of hereditary angioedema, known as HAE ¹. The label calls HAE "a rare genetic disorder," marked by low activity of a protein called C1-esterase inhibitor ¹. An international guideline estimates that the forms of HAE tied to that protein affect 1 in 50,000 people worldwide ³.

People with HAE have attacks of swelling. The published trial describes "acute, intermittent, and potentially life-threatening attacks of edema of the skin and mucosa" ⁴. Edema is swelling, and the mucosa is the moist lining of the mouth, throat and gut. The guideline notes that attacks of the upper airway "can result in asphyxiation," and that abdominal attacks "are painful and debilitating" ³.

The drug itself is "a 60-amino-acid protein produced in Pichia pastoris yeast cells by recombinant DNA technology" ¹. In plain words, yeast cells are given the genetic instructions to build it. Its brand name is Kalbitor ¹.

Ecallantide is not a wellness, weight-loss or performance peptide. Its label names one use, the treatment of sudden attacks of HAE ¹. The label's Medication Guide, the FDA-approved leaflet for patients, says it "is not a cure for HAE" ¹.

Is ecallantide FDA-approved?

Yes, as a prescription medicine for one use. FDA approved Kalbitor (ecallantide) on December 1, 2009, under biologics license application (BLA) 125277 ². A BLA is the application under which FDA licenses a biological product ⁵. Drugs@FDA lists its marketing status as "Prescription" as of November 9, 2026, the date of the record's data ².

The current label gives one indication: Kalbitor "is indicated for treatment of acute attacks of hereditary angioedema (HAE) in patients 12 years of age and older" ¹. An acute attack is a sudden episode of swelling. The Medication Guide says it is "not known if KALBITOR is safe and effective in children under 12 years of age" ¹. The FDA record also lists an efficacy supplement, a later filing that can change a drug's approved uses, approved March 28, 2014 ². FDA's 2009 license covered patients 16 and older ⁵; a 2014 supplement broadened it to patients 12 and older ⁶.

The label's boxed warning says who may give the drug. It reads in part: "Because of the risk of anaphylaxis, KALBITOR should only be administered by a healthcare professional with appropriate medical support to manage anaphylaxis and hereditary angioedema" ¹.

The international guideline, published online April 7, 2022, addresses licensing in other countries ³. It says ecallantide "is licensed only in the United States and a few Latin American countries" ³.

See the FDA status of every peptide, updated weekly.

How does ecallantide work?

This mechanism comes from the FDA label of an approved drug ¹. In a healthy body, C1-esterase inhibitor holds an enzyme called plasma kallikrein in check. The label calls it "a major endogenous inhibitor of plasma kallikrein," endogenous meaning made by the body ¹. Plasma kallikrein cuts a larger blood protein, high-molecular-weight kininogen, and so releases a small messenger called bradykinin ¹.

In HAE that check is missing. The label continues: "During attacks, unregulated activity of plasma kallikrein results in excessive bradykinin generation" ¹. Bradykinin widens blood vessels, and the label says it is "thought by some to be responsible for the characteristic HAE symptoms of localized swelling, inflammation, and pain" ¹.

Ecallantide acts one step before bradykinin is made. The label describes a "selective, reversible inhibitor of plasma kallikrein" that "binds to plasma kallikrein and blocks its binding site" ¹. With the enzyme blocked, less kininogen is converted to bradykinin, which the label says "thereby treats symptoms of the disease during acute episodic attacks of HAE" ¹.

In healthy subjects, the blood level of ecallantide peaked about 2 to 3 hours after a single dose under the skin ¹. It then fell with a mean elimination half-life of 2.0 hours, so about half was gone every two hours ¹. The label says no link has been established between the amount of drug in the blood and its effect on the kallikrein pathway ¹.

One laboratory finding concerns clotting. After an intravenous dose in healthy subjects, a blood-clotting test called aPTT took about twice as long as before and returned to normal by 4 hours ¹. That finding came from dosing into a vein, and the approved route is under the skin ¹.

What does the research show?

Ecallantide is approved by FDA for acute attacks of HAE in patients 12 and older, and the label describes two trials, EDEMA4 and EDEMA3 ¹. Both were randomized, double-blind and placebo-controlled: chance decided who received ecallantide or a dummy injection, and neither patients nor staff knew which ¹. Patients having an attack "at any anatomic location, with at least 1 moderate or severe symptom" received one dose under the skin ¹. The trials randomized 96 and 72 patients, and because some joined both, 143 individual patients took part ¹.

Of the 143, 94 were female, and the mean age was 36, with a range of 11 to 77 ¹. Their attacks were abdominal in 64, peripheral in 55 and laryngeal, of the voice box, in 24 ¹. The guideline gives the hands and feet as examples of peripheral attacks ³.

Both trials used two scores reported by the patients themselves ¹. For the Mean Symptom Complex Severity (MSCS) score, patients rated each symptom from 0 (normal) to 3 (severe), and the ratings were averaged ¹. A fall means improvement, and the largest possible fall is 3 points ¹. For the Treatment Outcome Score (TOS), patients rated their response at each attack site from 100 (significant improvement) to -100 (significant worsening) ¹. A score above 0 means the symptoms improved ¹.

In EDEMA4, 48 patients were assigned to ecallantide and 48 to placebo, and the main measure was the change in MSCS score at 4 hours ¹. The mean score fell by 0.8 points with ecallantide, among 47 patients analyzed, and by 0.4 with placebo, among 42 ¹. The 95 percent confidence intervals, the ranges likely to hold the true values, were -1.0 to -0.6 and -0.6 to -0.1 ¹. The difference was statistically significant, meaning unlikely to be chance (P = 0.010) ¹. The mean TOS at 4 hours was 53 with ecallantide and 8 with placebo (P = 0.003) ¹.

At 24 hours the MSCS score had fallen by 1.5 with ecallantide against 1.1 with placebo (P = 0.04), and the TOS was 89 against 55 (P = 0.03) ¹. Within 24 hours, 16 of the 48 ecallantide patients (33 percent) needed medical intervention for unresolved symptoms ¹. In the placebo group, 24 of 48 (50 percent) did ¹.

EDEMA3 assigned 36 patients to each group, and its main measure was the TOS at 4 hours ¹. The label reports means: a TOS of 63 with ecallantide, among 34 patients analyzed, and 36 with placebo, among 35 (P = 0.045) ¹. The MSCS score fell by 1.1 points against 0.6 (P = 0.041) ¹. Medical intervention within 24 hours was needed by 5 of 36 patients on ecallantide (14 percent) and 13 of 36 on placebo (36 percent) ¹.

EDEMA3's own report, in the New England Journal of Medicine of August 5, 2010, gives medians, the middle values, instead ⁴. The median TOS at 4 hours was 50.0 with ecallantide and 0.0 with placebo (P = 0.004) ⁴. The median change in MSCS score was -1.00 against -0.50 (P = 0.01) ⁴. The estimated time to significant improvement was 165 minutes against more than 240 minutes, a difference that was not statistically significant (P = 0.14) ⁴.

Of the 72 patients, 71 completed the trial, which was funded by Dyax, the company FDA's record lists as the applicant ⁴, ². The label gives means and the paper medians; FDA's 2009 review says the label's EDEMA3 MSCS and TOS results are those without imputation for symptom complexes or medical intervention ⁷.

The label is plain about two limits. Some patients reported improvement after a second dose within 24 hours, "but efficacy was not systematically assessed for the second dose" ¹. Efficacy in patients aged 12 to 15 "is extrapolated from efficacy in patients 16 years of age and older," with support from analyses showing similar drug levels in adults and adolescents ¹.

The 2021 international guideline of the World Allergy Organization and the European Academy of Allergy and Clinical Immunology covers on-demand treatment, the treatment of attacks as they happen ³. Its panel wrote: "We recommend that attacks are treated with either intravenous C1 inhibitor, ecallantide, or icatibant" ³. The recommendation carried 96 percent agreement and "evidence level A," the guideline's own grade for the evidence behind it ³. The guideline defines level A as a "Randomized, double-blind clinical trial of high quality" ³. The label describes no head-to-head comparison of ecallantide with either of the other two ¹.

The label names three limits of its data ¹. The label says no formal drug interaction studies were performed, and that no data exist on how the body handles the drug in liver or kidney impairment ¹. The trials "did not include sufficient numbers of subjects aged 65 and over" to show whether older patients respond differently ¹.

What are the side effects?

The label opens with a boxed warning, headed "WARNING: ANAPHYLAXIS" ¹. It reads in part: "Anaphylaxis has been reported after administration of KALBITOR. Because of the risk of anaphylaxis, KALBITOR should only be administered by a healthcare professional with appropriate medical support to manage anaphylaxis and hereditary angioedema" ¹. The Medication Guide says these allergic reactions "can be life-threatening and usually happen within 1 hour after receiving KALBITOR" ¹.

In clinical studies, 10 of 255 HAE patients treated with ecallantide into a vein or under the skin had anaphylaxis, 4 percent ¹. Among the 187 treated under the skin, the approved route, 5 did, 3 percent ¹. The reactions "occurred within the first hour after dosing" ¹. Their symptoms included chest discomfort, flushing, swelling of the throat, itching, hives, wheezing and low blood pressure ¹.

An attack of HAE and an allergic reaction can look alike. The warning tells professionals to be aware of "the similarity of symptoms between hypersensitivity reactions and hereditary angioedema" and says "patients should be monitored closely" ¹. Hypersensitivity is the label's word for an allergic-type reaction. The label has one contraindication, a circumstance in which the drug must not be given: "Do not administer KALBITOR to a patient who has known clinical hypersensitivity to KALBITOR" ¹.

The 255 patients include those treated into a vein as well as under the skin ¹. Across them, the most common adverse reactions were headache (16 percent), nausea (13 percent), fatigue (12 percent) and diarrhea (11 percent) ¹. Next came upper respiratory tract infection (8 percent), injection site reactions (7 percent), nasopharyngitis, an inflamed nose and throat (6 percent), and vomiting (6 percent) ¹. Itching, upper abdominal pain and fever were each reported by 5 percent ¹.

For the two placebo-controlled trials, the label compares adverse reactions in 100 patients treated with ecallantide and 81 given placebo ¹. FDA's 2009 review explains the counts: 100 patients received ecallantide, including 22 placebo patients given an open-label dose, and 81 received placebo ⁷. Headache was reported by 8 percent with ecallantide and 7 percent with placebo, nausea by 5 percent and 1 percent, and diarrhea by 4 percent in each group ¹. Fever was reported by 4 percent and nasopharyngitis by 3 percent with ecallantide, and by no one with placebo ¹. Injection site reactions were reported by 3 percent against 1 percent ¹.

The EDEMA3 report recorded "no deaths, treatment-related serious adverse events, or withdrawals owing to adverse events" ⁴. In EDEMA4, heart tracings (ECGs) showed "no significant effect on the QTc interval, heart rate, or any other components of the ECG" ¹.

Because ecallantide is a protein, the body can make antibodies against it ¹. The label reports that "20.2% of patients seroconverted to anti-ecallantide antibodies," meaning they developed them, and that the rate rose with exposure over time ¹. Neutralizing antibodies, the kind that can block a drug, were found in 8.8 percent and "were not associated with loss of efficacy" ¹. The label adds: "Patients who seroconvert may be at a higher risk of a hypersensitivity reaction. The long-term effects of antibodies to KALBITOR are not known" ¹.

For pregnancy, the label says the available safety-monitoring data "have not identified a drug-associated risk of major birth defects, miscarriage or adverse maternal or fetal outcomes" ¹. In rats, an intravenous dose about 1.6 times the maximum recommended human dose increased early fetal deaths, alongside toxicity in the mother ¹. The guideline calls use in pregnancy "off label and not recommended as no published experience is available as of now" ³. There are no data on ecallantide in human milk ¹.

In sport

The 2026 Prohibited List of the World Anti-Doping Agency (WADA) does not name ecallantide ⁸. Section S2 of the list covers peptide hormones, growth factors, related substances and mimetics ⁸. Neither that section nor any other names plasma kallikrein inhibitors as a class ⁸.

What JumpstartMD offers

JumpstartMD does not prescribe ecallantide. Our peptide library covers it so you have the facts on its FDA status and the evidence, current as of November 10, 2026.

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Compounded medications are not FDA-approved, and FDA does not review their safety, effectiveness, or quality before they are marketed. A licensed clinician decides after an evaluation whether a peptide is appropriate for you, and not every patient will qualify.