Icatibant
HOE 140, JE 049, icatibant acetate, D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin
Icatibant is a synthetic decapeptide that blocks the bradykinin B2 receptor. It is licensed for treating acute attacks of hereditary angioedema, the swelling disorder caused by C1-inhibitor deficiency, where uncontrolled bradykinin release makes blood vessels leak. Half its residues are non-natural amino acids, which is what allows a peptide to survive subcutaneous injection and act within hours.
Mechanism
Icatibant is a competitive, highly selective antagonist at the bradykinin B2 receptor, with an affinity in the low nanomolar range and no meaningful activity at the inducible B1 receptor.
The pathophysiology it targets is unusually well defined. In hereditary angioedema types I and II, C1-esterase inhibitor is deficient or dysfunctional. C1-inhibitor is the principal brake on plasma kallikrein and on activated factor XII, so its loss allows unrestrained kallikrein activity, which cleaves high-molecular-weight kininogen and liberates bradykinin. Bradykinin acting on endothelial B2 receptors triggers nitric oxide and prostacyclin release and, critically, disassembly of VE-cadherin at endothelial junctions. The adherens junctions open, plasma leaks into the interstitium, and the result is the non-histaminergic, non-pruritic, non-urticarial swelling characteristic of hereditary angioedema. This is why antihistamines, adrenaline and corticosteroids, which work for mast-cell-mediated angioedema, are ineffective here. Icatibant blocks the final receptor step, so the mediator is generated but cannot act.
The structural design is what makes it viable as a drug. Native bradykinin is destroyed within seconds by ACE and other kininases. Icatibant retains the essential recognition elements while replacing five of the ten residues with non-proteinogenic amino acids: trans-4-hydroxyproline, β-(2-thienyl)alanine, D-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid and octahydroindole-2-carboxylic acid, plus a D-arginine at the N-terminus. These substitutions block peptidase recognition and lock the C-terminal region into an antagonist conformation, giving a half-life of about 1.4 hours and near-complete subcutaneous bioavailability.
What the research shows
The FAST programme comprised three phase 3 trials. FAST-1 (56 patients) compared icatibant with placebo in cutaneous and abdominal attacks and found a median time to clinically significant symptom relief of 2.5 hours versus 4.6 hours, a difference that did not reach statistical significance (p=0.14). FAST-2 (74 patients), run in parallel against tranexamic acid, was clearly positive: 2.0 hours versus 12.0 hours (p<0.001). The investigators attributed the FAST-1 near-miss to early use of rescue medication in the placebo arm, which obscured the comparison.
FAST-3 was designed to settle the placebo question. In 88 patients with moderate to very severe cutaneous or abdominal attacks (43 icatibant, 45 placebo), icatibant reduced the median time to at least 50% reduction in symptom severity from 19.8 hours to 2.0 hours, the median time to onset of primary symptom relief from 18.5 hours to 1.5 hours, and time to almost complete relief from 36.0 to 8.0 hours. No icatibant-treated patient required rescue medication before symptom relief. Adverse event incidence was similar to placebo, though every icatibant-treated patient had an injection site reaction. Additional cohorts within FAST-3 addressed laryngeal attacks, including an open-label arm for severe laryngeal involvement.
A clear negative result deserves equal prominence. ACE inhibitors cause angioedema through the same bradykinin pathway (by blocking bradykinin degradation rather than accelerating its production), so icatibant was an obvious candidate. Sinert and colleagues randomised 121 patients with at least moderately severe ACE-inhibitor-induced upper airway angioedema to icatibant or placebo and found no difference whatever in time to meeting discharge criteria (median 4.0 hours in each group). The conclusion was unambiguous: icatibant was no more efficacious than placebo in this setting. Mechanistic plausibility did not survive contact with a randomised trial, and icatibant is not indicated for ACE-inhibitor angioedema.
Evidence assessment
High-quality evidence
Icatibant holds MHRA, EMA and FDA marketing authorisations for acute hereditary angioedema attacks, supported by three phase 3 randomised controlled trials (FAST-1, FAST-2 and FAST-3), of which FAST-2 and FAST-3 were clearly positive against tranexamic acid and placebo respectively. All three cited papers were verified against PubMed with matching titles, PMIDs, DOIs, journals, years, sample sizes and effect estimates. It is recommended in international hereditary angioedema guidelines and generic products now exist. That is replicated randomised evidence plus regulator-approved labelling. Worth noting alongside: the evidence is strong specifically for hereditary angioedema, and just as clearly negative for ACE-inhibitor-induced angioedema, where a 121-patient randomised trial found no benefit over placebo.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Icatibant, a new bradykinin-receptor antagonist, in hereditary angioedema Preclinical only
FAST-2 was positive: median time to clinically significant relief 2.0 hours with icatibant versus 12.0 hours with tranexamic acid (p<0.001). FAST-1 showed 2.5 versus 4.6 hours but did not reach significance (p=0.14), which the investigators attributed to early rescue medication use in the placebo arm. No serious adverse events related to icatibant were reported.
Randomized placebo-controlled trial of the bradykinin B2 receptor antagonist icatibant for the treatment of acute attacks of hereditary angioedema: the FAST-3 trial Preclinical only
Icatibant significantly reduced median time to at least 50% reduction in symptom severity (2.0 versus 19.8 hours, p<0.001), time to onset of primary symptom relief (1.5 versus 18.5 hours) and time to almost complete relief (8.0 versus 36.0 hours). No icatibant patient needed rescue medication before relief. Adverse event incidence was similar between groups; injection site reactions occurred in all treated subjects.
Randomized trial of icatibant for angiotensin-converting enzyme inhibitor-induced upper airway angioedema Preclinical only
Negative result. There was no difference in time to meeting discharge criteria between groups (median 4.0 hours in each), nor in time to onset of symptom relief or any secondary endpoint. The authors concluded that icatibant was no more efficacious than placebo in at least moderately severe ACE-inhibitor-induced angioedema of the upper airway.
Safety
Icatibant is generally well tolerated. Injection site reactions (erythema, swelling, burning, itching and pain at the subcutaneous site) occur in essentially all treated patients and are usually mild and short-lived. Beyond that, adverse event rates in the phase 3 trials were comparable to placebo. Reported effects include dizziness, headache, nausea, pyrexia and transient elevation of transaminases.
A theoretical concern follows from the mechanism: bradykinin acting at B2 receptors contributes to coronary vasodilation and to the cardioprotective effects of ACE inhibition, so B2 blockade could in principle worsen myocardial ischaemia. Clinical experience has not confirmed a problem, but caution is advised in acute ischaemic heart disease and in the weeks after a stroke. Icatibant may reduce the antihypertensive effect of ACE inhibitors, which act partly through bradykinin accumulation.
Because laryngeal attacks in hereditary angioedema can be fatal, patients treating a laryngeal attack with icatibant are advised to seek immediate medical attention regardless of response. The drug is intended for episodic treatment of acute attacks, not for prophylaxis. Prevention of attacks uses entirely different agents. This is a specialist-prescribed medicine for a rare inherited disease; it has no application in ordinary allergic swelling, urticaria or anaphylaxis, all of which are histamine-mediated and require adrenaline and antihistamines instead.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | Prescription-only medicine (POM). Licensed by the MHRA for symptomatic treatment of acute attacks of hereditary angioedema in adults, adolescents and children aged 2 years and older with C1-esterase inhibitor deficiency. Originally authorised centrally in the EU in July 2008, with the paediatric extension added later; generic icatibant products are now available in Great Britain. Supplied for self-administration by trained patients under specialist supervision. |
| United States | FDA-approved (August 2011) for the treatment of acute attacks of hereditary angioedema in adults 18 years and older, by subcutaneous injection. Generic versions are approved. |
| WADA (sport) | Not listed on the WADA Prohibited List. Bradykinin receptor antagonists are not named in any prohibited class. |
Questions
Because the swelling is not histamine-mediated. In hereditary angioedema, C1-inhibitor deficiency allows plasma kallikrein to run unchecked, releasing bradykinin, which opens endothelial junctions directly. Mast cells are not involved, so there is no urticaria and no itch, and antihistamines, corticosteroids and adrenaline have nothing to act on. Icatibant works because it blocks the actual mediator's receptor.
Native bradykinin is destroyed within seconds by angiotensin-converting enzyme and other kininases, so an ordinary peptide antagonist would never survive long enough to work. Five of icatibant's ten residues are non-natural (including hydroxyproline, a thienylalanine, a tetrahydroisoquinoline carboxylic acid and an octahydroindole carboxylic acid), and these both block peptidase cleavage and lock the molecule into an antagonist rather than agonist conformation. The result is a peptide with a 1.4-hour half-life and near-total absorption after subcutaneous injection.
No. Despite an identical bradykinin mechanism (ACE inhibitors block bradykinin breakdown rather than boosting its production), a randomised placebo-controlled trial in 121 patients with at least moderately severe ACE-inhibitor-induced upper airway angioedema found no difference in time to discharge criteria (median 4.0 hours in both arms). It is a good example of mechanistic reasoning failing when tested properly, and icatibant is not licensed for this indication.
No. It is an on-demand treatment for acute attacks only. Long-term prophylaxis in hereditary angioedema uses entirely different agents: C1-inhibitor concentrates, the kallikrein inhibitor lanadelumab, or the oral kallikrein inhibitor berotralstat. Which approach suits a given patient is a specialist decision made in an immunology or allergy service.