Ecallantide

A 60-amino-acid recombinant plasma kallikrein inhibitor engineered by phage display from a Kunitz domain of tissue factor pathway inhibitor, FDA approved since 2009 as Kalbitor for acute hereditary angioedema attacks, carrying a boxed anaphylaxis warning.

Also referenced as: Kalbitor, DX-88, DX88, FOV2302

Also appears in: Other

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What is Ecallantide?

Ecallantide is a recombinant 60-amino-acid protein (molecular weight about 7,054 Da) that inhibits plasma kallikrein with picomolar affinity. It is a small protein rather than a short peptide: it is a folded Kunitz-type protease inhibitor domain, stabilized by three disulfide bonds and expressed in Pichia pastoris yeast, not a synthesized linear sequence. Dyax’s predecessor, Protein Engineering Corporation, engineered the lineage by displaying the first Kunitz domain of human tissue factor pathway inhibitor (TFPI, then called lipoprotein-associated coagulation inhibitor, LACI) on bacteriophage and selecting variants that converted a weak, broad-spectrum inhibitor into a highly selective plasma kallikrein inhibitor; the clinical candidate, DX-88, differs from the native domain at seven amino acid positions.

It reached the clinic as Kalbitor for the treatment of acute attacks of hereditary angioedema (HAE), and is one of the targeted HAE therapies that displaced fresh frozen plasma and androgens in the late 2000s. The product is now Takeda’s, although the BLA is still held in the name of Dyax Corp. As a yeast-expressed biologic with no synthetic route, ecallantide has essentially no presence in the research-peptide market.

How it works

Hereditary angioedema results from deficient or dysfunctional C1 esterase inhibitor, the main physiological brake on plasma kallikrein. Unchecked kallikrein cleaves high-molecular-weight kininogen to release bradykinin, which acts on B2 receptors to increase vascular permeability and drive the swelling of an attack. Ecallantide intervenes one step upstream of icatibant, blocking bradykinin production rather than bradykinin’s receptor.

• Engineered selectivity. Iterative phage-display optimization of the TFPI first Kunitz domain produced inhibitors with inhibition constants down to 40 pM and high selectivity over related serine proteases, the lineage from which DX-88 was taken (Markland et al., Biochemistry, 1996, 35(24):8058–8067).
• Active-site blockade. As a Kunitz-type inhibitor, ecallantide inserts a reactive loop into the kallikrein active site, so the enzyme cannot convert high-molecular-weight kininogen to bradykinin; the label describes it as a potent, selective, reversible inhibitor with an inhibition constant of 25 pM, and Dyax’s early development rationale for targeting kallikrein in HAE is laid out in Williams and Baird, Transfusion and Apheresis Science, 2003, 29(3):255–258.
• Clinical proof of the kallikrein node. The first placebo-controlled trial of intravenous ecallantide in HAE attacks (EDEMA1) showed symptom relief over placebo, which the authors presented as direct evidence for the critical role of kallikrein in attack pathogenesis (Schneider et al., Journal of Allergy and Clinical Immunology, 2007, 120(2):416–422).
• Short systemic exposure. After a single 30 mg subcutaneous injection in healthy subjects the mean elimination half-life is 2.0 ± 0.5 hours, so the inhibitor covers the acute phase of an attack rather than providing sustained suppression; this contrasts with lanadelumab, the long-acting anti-kallikrein monoclonal antibody later developed by the same company for prophylaxis (half-life from the FDA label; development overview in Lehmann, Expert Opinion on Biological Therapy, 2008, 8(8):1187–1199).

Research status

Ecallantide has a completed Phase 3 program in hereditary angioedema, a US approval, a withdrawn European application, and discontinued development in two other indications.

EDEMA1 and EDEMA2 (early phase). EDEMA1 was a placebo-controlled, ascending-dose trial of intravenous ecallantide (5 to 40 mg/m²) in 49 patients with acute attacks; 72.5% of ecallantide-treated patients versus 25.0% of placebo patients reported significant improvement within 4 hours (P = 0.0169), the first clinical evidence that kallikrein inhibition relieves HAE swelling (Schneider et al., Journal of Allergy and Clinical Immunology, 2007, 120(2):416–422). EDEMA2 (NCT01826916) was an open-label, repeat-dose Phase 2 study in 77 patients that established the subcutaneous route and the dose carried into Phase 3.

EDEMA3 (NCT00262080). Seventy-two patients with a moderate or severe attack were randomized 1:1 to a single 30 mg subcutaneous dose or placebo. The primary endpoint, the patient-reported treatment outcome score at 4 hours, favored ecallantide (median 50.0 versus 0.0, P = 0.004), as did the change in mean symptom complex severity score at 4 hours (−1.00 versus −0.50, P = 0.01); the estimated time to significant improvement (165 minutes versus more than 240 minutes) did not reach significance (P = 0.14). There were no treatment-related serious adverse events (Cicardi et al., New England Journal of Medicine, 2010, 363(6):523–531).

EDEMA4 (NCT00457015). The second placebo-controlled Phase 3 trial randomized 96 patients to the same regimen, with the mean symptom complex severity score change at 4 hours as the primary endpoint (−0.8 with ecallantide versus −0.4 with placebo, P = 0.01) and the treatment outcome score as a secondary endpoint (53.4 versus 8.1, P = 0.003); benefit was evident by 2 hours and maintained through 24 hours, with a similar safety profile between groups (Levy et al., Annals of Allergy, Asthma & Immunology, 2010, 104(6):523–529). An integrated analysis of both trials (168 enrollments, 143 unique patients) confirmed a consistent effect across attack locations (Sheffer et al., Journal of Allergy and Clinical Immunology, 2011, 128(1):153–159.e4). EDEMA3 and EDEMA4 are the two trials in the US label; Kalbitor was approved on December 1, 2009 (BLA 125277, with orphan designation) for patients 16 years and older.

Long-term and pediatric data. The open-label continuation study DX-88/19 (NCT00456508) treated 147 patients for 625 attacks and found no loss of efficacy with repeated dosing; 8 patients (5.4%) had potential hypersensitivity reactions, 6 of them meeting NIAID anaphylaxis criteria (Lumry et al., Allergy and Asthma Proceedings, 2013, 34(2):155–161). A pooled post hoc analysis of 29 patients aged 9 to 17 years from four studies reported efficacy and safety similar to adults (MacGinnitie et al., Pediatrics, 2013, 132(2):e490–e497). On this data the FDA approved an efficacy supplement on March 28, 2014 lowering the age floor to 12 years, with efficacy in the 12-to-15 group extrapolated from older patients. Two planned studies in younger children (NCT01253382, ages 2 to 17 prepubertal; NCT01832896, ages 2 to 16) were withdrawn with no participants enrolled, and the label still states that safety and effectiveness below 12 years have not been established.

Anaphylaxis. In a retrospective characterization of 230 patients who received 1,045 subcutaneous doses in the clinical program, 8 patients (3.5%) had reactions meeting NIAID anaphylaxis criteria; none occurred on first exposure, all began within an hour of dosing, and all resolved with standard treatment, while anti-ecallantide and anti-P. pastoris IgE status did not reliably predict who reacted (Craig et al., Journal of Allergy and Clinical Immunology: In Practice, 2015, 3(2):206–212.e4). A Phase 4 observational safety study required after approval (NCT01059526; completed June 2014) enrolled 81 patients, 44 of whom were treated during follow-up, and recorded anaphylaxis by NIAID criteria in 2 and type 1 hypersensitivity events in 4, with no coagulation-related events.

Europe. Dyax filed for EU authorization but withdrew the application on November 11, 2011, after the CHMP indicated a provisional negative view, citing uncertainty about the effectiveness of the proposed dose in heavier patients and the higher rate of hypersensitivity reactions seen with the drug. Ecallantide has never been approved in the European Union.

ACE-inhibitor angioedema. A multicenter, double-blind, placebo-controlled Phase 2 trial (NCT01343823) randomized 79 emergency-department patients with ACE-inhibitor-induced angioedema to a single 10, 30 or 60 mg dose or placebo on top of conventional therapy; discharge eligibility within 6 hours was met by 72% of placebo recipients versus 85%, 89% and 89% in the ecallantide arms, the trial was halted early after an interim analysis, and the authors concluded that adding ecallantide did not improve outcomes (Lewis et al., Annals of Emergency Medicine, 2015, 65(2):204–213). A smaller investigator-initiated 50-patient Phase 2 study (NCT01036659) found 31% versus 21% meeting discharge criteria within 4 hours, a difference whose confidence interval spanned zero (Bernstein et al., Annals of Allergy, Asthma & Immunology, 2015, 114(3):245–249). No Phase 3 followed.

Cardiac surgery blood loss. Licensed to Cubist Pharmaceuticals as a potential replacement for aprotinin, ecallantide was tested in cardiopulmonary bypass. The Phase 2 CONSERV-2 trial (NCT00888940) randomized 218 high-risk cardiac surgery patients to ecallantide (n = 109) or tranexamic acid (n = 109, high- and low-dose arms); ecallantide patients received more packed red cells in the first 12 hours (median 900 mL versus 300 mL, P < 0.001), and the data safety monitoring board stopped the trial early for higher 30-day mortality in the ecallantide group (12% versus 4%, P = 0.041) (Bokesch et al., Journal of Thoracic and Cardiovascular Surgery, 2012, 143(5):1022–1029). The earlier placebo-controlled KALAHARI-1 study (NCT00448864) had been terminated after 75 patients once it had informed the follow-on design, and the companion dose-ranging CONSERV-1 study (NCT00816023) completed without a follow-on trial. The surgical program was abandoned.

Other and current status. A Phase 1 study of an ophthalmic formulation for retinal vein occlusion macular edema (FOV2302, NCT00969293) was terminated after 11 patients. As of November 2026, ClinicalTrials.gov lists no active or recruiting ecallantide trials. Recent literature is limited to preclinical work, for example an albumin-fusion variant that retained anti-kallikrein activity and cleared more slowly in mice (Al-Adimi et al., Journal of Biotechnology, 2024, 391:11–19), its use as a comparator in a 2025 mouse stroke model, and cross-trial reviews of on-demand HAE therapies. Kalbitor remains licensed: Drugs@FDA lists BLA 125277 with prescription marketing status, the June 2025 label revision did not change the indication, and no discontinuation notice had been issued. No new indication was approved in 2025 or 2026.

Common dosage forms

• Single-dose vial. 10 mg/mL ecallantide in 1 mL of clear, colorless, preservative-free solution for subcutaneous injection, supplied as three vials per carton.
• Intravenous formulation. Used only in the early EDEMA1 dose-ranging trial and the cardiac surgery program; no intravenous product is marketed.
• Ophthalmic formulation. FOV2302 was investigational only; development ended after Phase 1.

Key considerations

• Regulatory status. The FDA Approved status reflects Kalbitor (BLA 125277), approved December 1, 2009 for acute hereditary angioedema attacks. The age floor was lowered to 12 years on March 28, 2014. Development in ACE-inhibitor angioedema, cardiac surgery and prophylaxis ended without an approval, and the European application was withdrawn.
• Boxed anaphylaxis warning. Anaphylaxis occurred in 4% of HAE patients in the clinical program (10 of 255 who received intravenous or subcutaneous drug), never on first exposure in the characterized series and always within an hour of dosing, which is why the label requires administration by a healthcare professional with the means to treat it. That requirement is a major reason usually given for ecallantide losing ground to icatibant and C1-inhibitor products that patients can inject themselves at the onset of an attack.
• Immunogenicity. In the label’s pooled data 20.2% of patients seroconverted to anti-ecallantide antibodies, 8.8% developed neutralizing antibodies, 4.7% had anti-ecallantide IgE and 20.2% had IgE against the P. pastoris host proteins; seroconversion was associated with a higher risk of hypersensitivity reactions, although IgE status alone did not reliably predict anaphylaxis.
• Evidence gaps. The pivotal trials together comprised 168 enrollments from 143 unique patients and used patient-reported 4-hour symptom scores as primary endpoints; time-to-relief endpoints were not consistently significant, no head-to-head trial against icatibant or C1-inhibitor was run, the laryngeal-attack data are observational, and children under 12 were never studied because both pediatric trials were withdrawn before enrollment.
• Naming and identity. Ecallantide, DX-88, Kalbitor and FOV2302 are the same 60-residue protein. It should not be confused with aprotinin, the bovine Kunitz-domain kallikrein inhibitor it was designed to replace in surgery; with lanadelumab, a full-length monoclonal antibody against plasma kallikrein; or with berotralstat and sebetralstat, which are small-molecule kallikrein inhibitors.