Mechanism
Icatibant is a synthetic decapeptide that competitively antagonizes the bradykinin B2 receptor. Its sequence incorporates several non-natural amino acids (D-arginine, β-(2-thienyl)-L-alanine, etc.) to provide protease resistance and selective B2 affinity over B1.
In hereditary angioedema, deficient C1 esterase inhibitor activity allows uncontrolled activation of the contact system (factor XII, plasma kallikrein), leading to excessive cleavage of high-molecular-weight kininogen and overproduction of bradykinin. Bradykinin binds B2 receptors on vascular endothelium, triggering vasodilation, increased vascular permeability, and the characteristic angioedema swelling.
Icatibant blocks B2 receptor binding, preventing bradykinin signaling. Onset of effect is rapid — symptom relief typically begins within 30–60 minutes, with median time to symptom resolution around 2 hours.
The half-life is approximately 1–2 hours, but receptor blockade duration is longer — a single dose typically resolves an attack without need for re-dosing.
What the evidence shows
Phase 3 FAST-1 (US, Cicardi et al, NEJM 2010): Did not meet primary endpoint versus placebo, but FAST-2 and FAST-3 (ex-US) did with active comparators (tranexamic acid) and design refinements.
Phase 3 FAST-3 (US re-do, Lumry et al, 2011): Achieved primary endpoint of “time to onset of symptom relief” — median 2.0 hours icatibant vs 19.8 hours placebo. Statistically significant; clinically meaningful in a condition where attacks can progress to airway compromise.
Real-world data: Multi-year European and US registries show consistent effectiveness across attack types (peripheral, abdominal, laryngeal). Self-administration data shows comparable effectiveness to clinic-administered injection.
Off-label indications studied:
- ACE-inhibitor-induced angioedema — small RCTs with mixed results; not approved for this use
- Various other bradykinin-mediated edema contexts — no approved expansion
Dosing literature
Approved dosing (subcutaneous, on-demand):
- 30 mg subcutaneous, single dose, administered at first sign of attack
- May repeat at 6-hour intervals up to 3 doses in 24 hours if symptoms persist
- Self-administration approved after appropriate training
The drug is supplied as a pre-filled syringe; self-injection is into the abdominal wall. Patients keep doses at home for immediate use during attacks.
Risks and adverse events
Common (Phase 3 + post-marketing):
- Injection site reactions (very common — erythema, swelling, warmth, occasional pain)
- Pyrexia, nausea, dizziness, headache (mostly mild)
- Transient elevated liver enzymes
Less common:
- Hypersensitivity reactions
- Worsening of laryngeal attacks during onset of action (rare; the rapid receptor blockade typically abolishes worsening)
Population-specific:
- Pregnancy: limited data; weighing maternal vs fetal risk during severe attacks generally favors treatment
- Pediatric: approved for ≥2 years; pediatric dosing is weight-based
The acute-use profile is well-tolerated. Chronic use is not relevant — icatibant is on-demand only, not prophylactic.
Regulatory status
| Region | Status | Notes |
|---|---|---|
| United States | Approved (Firazyr) | For acute HAE attacks ≥18 years; pediatric approval ≥2 years 2017. |
| European Union | Approved | |
| United Kingdom | Approved | |
| Australia | Approved | |
| Japan | Approved |
Generic icatibant became available in the US in 2020. Manufacturer originally Shire, now Takeda.
Where to get it
Through an allergist/immunologist with HAE management experience, accessed via specialty pharmacy. Patients are typically diagnosed and managed at HAE specialty centers.
For prophylactic HAE management (separate from acute attacks), other peptide and antibody therapies are used (lanadelumab, berotralstat, plasma-derived C1-INH, recombinant C1-INH). Icatibant is specifically for acute attacks.
We have no fulfillment partner for icatibant. (See How we make money.)
References (selected)
- Cicardi M et al. Icatibant, a new bradykinin-receptor antagonist, in hereditary angioedema. N Engl J Med 2010 (FAST-1, FAST-2). PubMed
- Lumry WR et al. Randomized placebo-controlled trial of the bradykinin B2 receptor antagonist icatibant for the treatment of acute attacks of hereditary angioedema: the FAST-3 trial. Ann Allergy Asthma Immunol 2011.
- Maurer M et al. The international WAO/EAACI guideline for the management of hereditary angioedema — the 2017 revision and update. Allergy
Quick Facts
| Also Known As | Firazyr, HOE-140, JE-049, B2 bradykinin receptor antagonist |
|---|---|
| Sequence | D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Tic-Oic-Arg |
| Molecular Formula | C59H89N19O13S |
| Molecular Weight | 1304.5 Da |
| PubChem CID | 6918173 |
Research Parameters
| Half-Life | ~1-2 hours (in humans after subcutaneous administration) |
|---|---|
| Stability | Lyophilized powder is stable for 24 months when stored at -20°C. After reconstitution in provided solvent, the solution is stable for 24 hours at 2-8°C, though immediate use is recommended. |
| Solubility | Supplied with pre-filled syringes containing sterile solvent (0.9% sodium chloride solution) for clinical use. For research, it is soluble in sterile water or physiological saline. |
| Storage (Lyophilized) | -20°C, protect from light and moisture |
| Storage (Reconstituted) | 2-8°C, for immediate use or up to 24 hours. Do not freeze. |
| Typical Research Dose | 30,000 mcg (30 mg) per single dose in human clinical research |
| Cycle Parameters | Administered as a single subcutaneous injection upon onset of an acute HAE attack in research protocols. No standard 'cycle' exists, as it is an on-demand rescue medication. |
| Amino Acid Count | 12 |
Mechanism of Action
Icatibant functions as a competitive and specific antagonist of the bradykinin B2 receptor (B2R). Bradykinin, generated from kininogen by kallikrein, binds to the constitutively expressed B2R on endothelial cells, smooth muscle cells, and neurons, leading to vasodilation, increased vascular permeability, pain, and inflammation. Icatibant's mechanism involves direct, high-affinity binding to the B2R, preventing bradykinin from activating the receptor and initiating its downstream signaling cascade.
Gq Protein Inhibition: By blocking B2R activation, Icatibant inhibits the coupling of the receptor to the Gq protein. This prevents the subsequent activation of phospholipase C (PLC), which would normally hydrolyze phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol trisphosphate (IP3) and diacylglycerol (DAG).
Calcium Signaling Blockade: The inhibition of IP3 production prevents the release of calcium ions (Ca2+) from the endoplasmic reticulum. Elevated intracellular calcium is a key mediator of nitric oxide (NO) synthesis and the contraction/relaxation responses in smooth muscle that lead to edema.
Inflammatory Mediator Suppression: Blocking B2R signaling attenuates the production of downstream inflammatory mediators, including prostaglandins and cytokines, which are involved in pain signaling and the recruitment of inflammatory cells. This effectively halts the cascade responsible for increased vascular permeability and localized swelling characteristic of HAE attacks.
Research Applications
Hereditary Angioedema (HAE) Research: Icatibant is the gold-standard pharmacological tool for studying HAE types I and II, which involve dysregulated bradykinin production. Research demonstrates its efficacy in rapidly reversing acute edema attacks by directly targeting the underlying pathophysiology, providing a model for on-demand therapy.
Inflammation and Pain Models: In preclinical research, Icatibant is used to dissect the role of bradykinin in various inflammatory conditions, such as arthritis, pancreatitis, and inflammatory bowel disease. It helps elucidate the contribution of the kinin system to pain perception, neurogenic inflammation, and hyperalgesia.
Cardiovascular and Vascular Research: Studies utilize Icatibant to investigate bradykinin's role in blood pressure regulation, ischemic preconditioning, and endothelial function. By blocking B2R, researchers can assess the peptide's effects on vasodilation, vascular leakage, and remodeling in models of hypertension, sepsis, and heart failure.
Other Bradykinin-Mediated Conditions: Research explores the potential of Icatibant in conditions like ACE inhibitor-induced angioedema, traumatic brain injury, and certain cancers where the bradykinin pathway may influence tumor growth and vascularization.
Safety & Side Effects
Data from human clinical trials and post-marketing surveillance indicate a well-tolerated profile with transient, localized side effects at the injection site being most common (e.g., redness, swelling, pain, pruritus). Systemic effects are rare but can include pyrexia, elevated liver transaminases, and dizziness. In animal toxicology studies, high doses have been associated with hemodynamic changes consistent with B2 receptor blockade. Theoretical concerns exist regarding the potential for paradoxical effects due to unopposed B1 receptor activity during chronic inflammation, but this has not been a significant clinical finding. No long-term organ toxicity has been established from research data.
Dosage Information
This information is derived from published clinical and preclinical research studies only and is not a recommendation for use.
In controlled human clinical trials for HAE, the standard dose is a 30 mg subcutaneous injection administered as a single dose for an acute attack. In research settings, dosing varies by model. Preclinical animal studies often use doses in the range of 0.1 to 1 mg/kg, administered via subcutaneous, intravenous, or intraperitoneal routes. The frequency is typically as a single bolus at the onset of symptoms or experimental challenge, though some chronic models may involve repeated dosing. The duration of action in studies is aligned with its pharmacological half-life and the observation period for the experimental endpoint.
References
Hereditary Angioedema Working Group. 'Icatibant, a new bradykinin-receptor antagonist, in hereditary angioedema.' The New England Journal of Medicine, vol. 363, pp. 532-541, 2010.
Cicardi, M., Banerji, A., Bracho, F., et al. 'Icatibant, a novel bradykinin B2 receptor antagonist, in the treatment of hereditary angioedema: a randomized, double-blind, placebo-controlled trial.' The Lancet, vol. 376, pp. 1445-1453, 2010.
Bas, M., Greve, J., Stelter, K., et al. 'A randomized trial of icatibant in ACE-inhibitor-induced angioedema.' The New England Journal of Medicine, vol. 372, pp. 418-425, 2015.
Calixto, J.B., Medeiros, R., Fernandes, E.S., et al. 'Kinins and their receptors in pain and inflammation.' Handbook of Experimental Pharmacology, vol. 195, pp. 423-449, 2009.
Marceau, F., and Regoli, D. 'Bradykinin receptor ligands: therapeutic perspectives.' Nature Reviews Drug Discovery, vol. 3, pp. 845-852, 2004.
Leeb-Lundberg, L.M., Marceau, F., Müller-Esterl, W., et al. 'International Union of Pharmacology. XLV. Classification of the kinin receptor family: from molecular mechanisms to pathophysiological consequences.' Pharmacological Reviews, vol. 57, pp. 27-77, 2005.