Peptide Schedule
Icatibant (Firazyr)10 residues (approx.)RRPPGSTPPREach bubble = one amino acid. Size = residue mass. Color = chemical class.Uses closest standard amino acids for non-standard residues.Icatibant (Firazyr)
Benefits
About Icatibant (Firazyr)
Icatibant is a synthetic decapeptide containing five non-natural amino acids, designed as a highly selective competitive antagonist of the bradykinin B2 receptor. Developed by Jerini AG (later acquired by Shire, now part of Takeda), it was specifically engineered to block the pathological effects of excessive bradykinin signaling that drives the edema characteristic of hereditary angioedema (HAE). HAE is a rare autosomal dominant disorder caused by deficiency or dysfunction of C1-esterase inhibitor (C1-INH), which leads to uncontrolled activation of the contact system and overproduction of bradykinin. Bradykinin binds the constitutive B2 receptor on vascular endothelial cells, triggering vasodilation and increased vascular permeability that manifests as unpredictable, potentially life-threatening episodes of subcutaneous and submucosal swelling affecting the extremities, face, gastrointestinal tract, and most dangerously, the larynx. Icatibant competes directly with bradykinin for B2 receptor binding with high affinity (Ki ~0.7 nM), effectively blocking the downstream signaling cascade responsible for endothelial gap formation and plasma extravasation. Its incorporation of non-natural amino acids — including D-Arg, hydroxyproline (Hyp), thienylalanine (Thi), D-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (D-Tic), and octahydroindole-2-carboxylic acid (Oic) — confers resistance to enzymatic degradation by ACE and other peptidases, giving it a dramatically longer half-life (~1-2 hours) compared to the natural bradykinin substrate (~15-30 seconds). In the pivotal FAST-3 trial (NCT00912093), icatibant demonstrated statistically significant superiority over placebo in time to onset of symptom relief for cutaneous and abdominal HAE attacks, with a median time to clinically significant relief of approximately 2 hours. The drug has since become a standard of care for acute HAE management alongside C1-INH replacement therapies and kallikrein inhibitors.
Who Should Consider Icatibant (Firazyr)
- Adults 18+ with confirmed hereditary angioedema (HAE) types I and II experiencing acute attacks
- HAE patients seeking on-demand self-injectable treatment for cutaneous, abdominal, or laryngeal attacks
- Patients who prefer a synthetic (non-plasma-derived) option for HAE attack management
- Allergists and immunologists managing HAE patients in clinical practice
- Emergency physicians treating acute angioedema episodes
- Researchers studying bradykinin pathway modulation and kinin receptor pharmacology
How Icatibant (Firazyr) Works
Icatibant functions as a selective, competitive antagonist at the bradykinin B2 receptor (BDKRB2), a G-protein coupled receptor constitutively expressed on vascular endothelial cells, smooth muscle, and sensory neurons. The peptide binds the B2 receptor with high affinity (Ki ~0.7 nM), directly competing with endogenous bradykinin for the orthosteric binding site. By occupying the receptor without activating it, icatibant prevents bradykinin-induced Gαq signaling, thereby blocking phospholipase C (PLC) activation, inositol trisphosphate (IP3)-mediated intracellular calcium release, and the downstream activation of endothelial nitric oxide synthase (eNOS). This cascade inhibition prevents the NO-dependent and prostacyclin-dependent vasodilation and endothelial gap formation responsible for the plasma extravasation and edema of HAE attacks. Icatibant is highly selective for the B2 receptor and has no significant affinity for the inducible B1 receptor. The incorporation of five non-natural amino acids provides substantial resistance to cleavage by ACE/kininase II, aminopeptidase P, and carboxypeptidase N, resulting in a plasma half-life approximately 200-400 times longer than that of bradykinin itself.
What to Expect
Rapid absorption from injection site, reaching peak plasma concentration at approximately 30 minutes. B2 receptor occupancy begins within minutes. Injection site reactions typically appear immediately.
Onset of symptomatic relief for most patients. Reduction in swelling, pain, and edema as bradykinin B2 receptor blockade prevents further vascular permeability.
Continued symptom resolution as tissue edema reabsorbs. If no improvement by 6 hours, a second 30 mg dose may be administered.
Most attacks fully resolved within 12-24 hours. Icatibant largely cleared from plasma. If symptoms recur, additional doses may be given (maximum 3 doses/90 mg per 24 hours).
On-demand use, not prophylactic. No tolerance or tachyphylaxis observed with repeated use. No cumulative adverse effects reported with long-term intermittent use.
Dosing Protocol
| Level | Dose / Injection | Frequency |
|---|---|---|
| Beginner | 30mg | Single dose |
| Moderate | 30mg | Single dose |
| Aggressive | 30mg | Single dose |
Note: Icatibant (Firazyr) is an FDA-approved synthetic decapeptide (H-D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Tic-Oic-Arg-OH) that acts as a selective and competitive antagonist of the bradykinin B2 receptor. It is supplied as a 30 mg/3 mL pre-filled syringe for subcutaneous self-injection during acute hereditary angioedema (HAE) attacks in adults 18 years and older. Icatibant was the first bradykinin B2 receptor antagonist approved for HAE, receiving EMA approval in 2008 and FDA approval in 2011. The recommended dose is 30 mg SC injected in the abdominal area. If symptoms persist or recur, additional 30 mg doses may be administered at intervals of at least 6 hours, with a maximum of 3 injections (90 mg) per 24-hour period. No reconstitution or dilution is required.
How to Inject Icatibant (Firazyr)
Icatibant is supplied as a 30 mg/3 mL (10 mg/mL) clear, colorless solution in a ready-to-use pre-filled syringe with a 25-gauge, 1/2-inch needle. No reconstitution or dilution is required. At the onset of an HAE attack, clean the injection site on the abdomen (at least 2 inches from the navel, avoiding areas of bruising or scarring). Pinch a fold of skin and insert the needle at a 45-90 degree angle. Inject the full 3 mL slowly over approximately 30 seconds. If symptoms are not relieved or recur, a second 30 mg injection may be given no sooner than 6 hours after the first dose, and a third dose no sooner than 6 hours after the second. Do not exceed 3 injections (90 mg) in 24 hours. For laryngeal attacks, administer icatibant immediately and seek emergency medical attention.
Cycling Protocol
Icatibant is used on-demand for acute HAE attacks and is not administered on a scheduled cycling basis. Each attack is treated individually with a single 30 mg SC injection. If symptoms persist or recur, up to 2 additional doses may be given at intervals of at least 6 hours (maximum 3 injections / 90 mg per 24 hours).
Pharmacokinetics
Source: FDA Firazyr label & Schwarz et al., Clin Pharmacokinet, 2014 — terminal half-life ~1-2 hours after SC injection
Loading the interactive decay curve.
Side Effects
Injection site reactions are the most common adverse event, occurring in approximately 97% of patients in clinical trials. These reactions include erythema, swelling, warmth, burning, itching, and pain at the injection site, typically mild to moderate in severity and resolving within a few hours. Less common systemic adverse effects include pyrexia (fever), transaminase elevations, dizziness, and rash. In clinical trials, nausea and headache were reported at rates similar to placebo. Because icatibant blocks B2 receptors, there is a theoretical concern that it could attenuate the cardioprotective vasodilatory effects of bradykinin; however, no clinically significant cardiovascular events attributable to this mechanism have been reported. There is no evidence of tachyphylaxis or antibody formation with repeated use.
Contraindications
- Known hypersensitivity to icatibant or any excipients in the formulation
- Pediatric patients under 18 years of age (safety and efficacy not established)
- Pregnancy — Category C; B2 receptor blockade may theoretically affect uterine contractions and placental blood flow
- Patients with acute ischemic heart disease or unstable angina — theoretical concern about blocking cardioprotective bradykinin effects
- Patients within weeks of an acute stroke — bradykinin may play a role in post-ischemic neuroprotection
Drug Interactions
- ACE inhibitors (enalapril, lisinopril, ramipril) — icatibant may theoretically reduce the antihypertensive effect of ACE inhibitors
- tPA and thrombolytics — bradykinin promotes endogenous tPA release; B2 blockade may modestly reduce endogenous fibrinolytic activity
- Other HAE therapies (C1-INH concentrate, ecallantide, lanadelumab) — can be used sequentially, but concurrent use not formally studied
- Antihypertensives — monitor blood pressure, as the interaction between B2 blockade and other vasodilatory pathways is not fully characterized
Storage & Stability
Molecular Profile
Related Peptides
References
- Icatibant, a new bradykinin-receptor antagonist, in hereditary angioedema (FAST-3 trial)PubMed 22348603
- Efficacy and safety of icatibant for treatment of hereditary angioedema: a meta-analysisPubMed 26272682
- Pharmacokinetics of icatibant in patients with hereditary angioedemaPubMed 24552744
- Firazyr (icatibant) FDA Prescribing InformationFDA Label
- Bradykinin-mediated angioedema: an update of the genetic and pharmacological landscapeReview