Icatibant

In plain language

Icatibant is a self-injected treatment for hereditary angioedema attacks, sold as Firazyr. It is a chain of ten amino acids, some of them mirror-image or unusual forms, that blocks the receptor for bradykinin.

Because HAE patients can carry it as a prefilled syringe and inject themselves at the first sign of an attack, treatment no longer depends on reaching a hospital. Its most common side effect is redness and swelling at the injection site.

For students

Icatibant is a decapeptide bradykinin B2 receptor antagonist (about 1,305 Da) with several non-proteinogenic residues: D-arginine at position 1, hydroxyproline, thienylalanine, D-tic (tetrahydroisoquinoline-3-carboxylic acid) and octahydroindole-2-carboxylic acid, substitutions that confer metabolic stability and antagonist pharmacology. It blocks the B2 receptor (constitutively expressed) rather than B1 (injury-induced).

The FAST-1 and FAST-2 trials (n=56 and 74) showed significant reduction in symptom severity at 3 hours versus placebo and tranexamic acid, with onset of relief within 1-2 hours. Self-administration became the defining clinical feature, cutting median time-to-treatment from hours to under 30 minutes and reducing laryngeal attack morbidity. Local injection-site reactions occur in nearly all patients but are mild; resistance to bradykinin-mediated vasodilation makes concurrent ACE inhibitor use a caution rather than a contraindication.

For researchers and instructors

Biochemistry. A peptidomimetic built from non-standard residues is the structural lesson: the molecule retains bradykinin's receptor-binding geometry while eliminating agonist activity and protease lability, an early demonstration that peptides could be engineered into stable receptor blockers.

Pharmacology. 30 mg subcutaneous injection into the abdominal wall, repeatable at 6 hours (max 3/24 hours); approved for self-administration after training; no dose adjustment for renal or hepatic impairment.

Human evidence. FAST-1 and FAST-2 (n=130 combined) are the pivotal randomized trials; real-world registries (e.g., Icatibant Outcome Survey) extend the evidence to thousands of attacks.

Teaching point. A model of how route-of-administration innovation (self-injection) transforms outcomes in a rare disease, and a contrast case to ecallantide's supervised model.