Not medical advice. Talk to your provider before using any peptide.
Full disclaimer
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.Also known as: Firazyr, HOE 140, JE049
Ninety-seven percent of patients get injection site reactions. That number looks alarming until you realize it means the drug is doing its job. Icatibant (Firazyr) is an FDA-approved bradykinin B2 receptor antagonist, a synthetic decapeptide that blocks the exact molecule driving hereditary angioedema swelling. The FAST-3 trial (n=56) confirmed clinically meaningful relief within about 2 hours. It won't prevent attacks. That's not its role. Icatibant is on-demand rescue therapy for adults with HAE types I and II, delivered through a pre-filled syringe that requires zero mixing, zero reconstitution, and zero IV access.
Thirty milligrams in a pre-filled syringe. That's the entire dosing protocol for icatibant, also sold as Firazyr (CAS 130308-48-4). The drug is a synthetic decapeptide (H-D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Tic-Oic-Arg-OH) containing five non-natural amino acids engineered to resist enzymatic breakdown. Where natural bradykinin survives roughly 15 to 30 seconds in plasma, icatibant holds on for 1 to 2 hours. The mechanism is straightforward competitive antagonism. Bradykinin binds the B2 receptor on vascular endothelial cells, triggering vasodilation and plasma leakage. Icatibant sits in that same binding pocket with high affinity (Ki approximately 0.7 nM) and does nothing, blocking the downstream cascade that produces swelling. Think of it as a lock filled with a blank key. Hereditary angioedema affects roughly 1 in 50,000 people. Attacks hit the extremities, gut, and face; the most dangerous involve the larynx. Before targeted therapies, laryngeal attacks carried real mortality risk. Icatibant earned EMA approval in 2008 and FDA approval in 2011 based on the FAST-3 trial (NCT00912093, n=56 in the icatibant arm). Median time to clinically significant relief landed at approximately 2 hours for cutaneous and abdominal attacks, statistically superior to placebo [1]. The drug is manufactured by Takeda under full GMP standards. No compounded versions exist in the US market. Retail pricing runs $11,147 to $12,302 per syringe, making insurance coverage or patient assistance programs practically mandatory.
Icatibant is a selective, competitive antagonist at the bradykinin B2 receptor (BDKRB2). This is a G-protein coupled receptor expressed on vascular endothelial cells, smooth muscle, and sensory neurons. The peptide binds with high affinity (Ki approximately 0.7 nM), occupying the orthosteric site without activating downstream signaling. By sitting in that binding pocket, icatibant prevents bradykinin from triggering Gq protein activation. The blocked cascade includes phospholipase C (PLC) activation, inositol trisphosphate (IP3)-mediated calcium release, and endothelial nitric oxide synthase (eNOS) activation. Without that cascade firing, the vasodilation and endothelial gap formation responsible for HAE edema simply don't happen. Selectivity matters here. Icatibant has no meaningful affinity for the inducible B1 receptor. It targets the constitutive B2 receptor specifically. The five non-natural amino acids in the sequence (D-Arg, hydroxyproline, thienylalanine, D-Tic, and Oic) give icatibant serious resistance to ACE/kininase II, aminopeptidase P, and carboxypeptidase N. Schwarz and colleagues mapped out the pharmacokinetics: plasma half-life runs approximately 200 to 400 times longer than bradykinin itself [2]. Absolute bioavailability after subcutaneous injection is about 97%, with peak plasma concentration reached at approximately 30 minutes.
FDA-approved (2011) on-demand treatment for acute HAE attacks in adults ≥18. FAST-3 demonstrated statistically significant superiority over placebo in time to onset of symptom relief. Evidence is strong and unambiguous: 30 mg SC per attack is the sole established dose.
FAST-3 trial: Lumry et al., Ann Allergy Asthma Immunol, 2011 (PMID 22123383, n=56 icatibant arm); median time to clinically significant relief ~2 hours vs placebo
All pivotal trials enrolled HAE types I and II only; no RCT data in pediatric patients (<18); efficacy in HAE type III (estrogen-dependent) is not established; limited head-to-head data vs C1-INH concentrate in laryngeal attacks
HAE patients report reliable, rapid attack relief. Community is very small (HAE affects ~1/50,000 people). No off-label or performance use: exclusively medical. Overall positive sentiment with injection-site reactions and cost as primary complaints.
Science and community are fully aligned: 30 mg on-demand is the established dose, onset within 1–2 hours is reproduced in both trials and patient reports, and injection-site reactions are the primary adverse event in both clinical data and community experience. No off-label use exists to create divergence.
| Level | Dose / Injection | Frequency |
|---|---|---|
| Beginner | 30mg | Single dose |
| Moderate | 30mg | Single dose |
| Aggressive | 30mg | Single dose |
Icatibant arrives in a pre-filled syringe. No reconstitution math needed here, which is unusual for this platform. The syringe contains 30 mg in 3 mL (10 mg/mL concentration) with a 25-gauge, half-inch needle already attached. You're injecting the full syringe contents every time. Store below 25 degrees Celsius. Don't freeze it. A frozen syringe is a discarded syringe. Keep it in the original packaging away from light. When traveling, bring at least 2 to 3 syringes; one may not be enough for a severe or recurrent attack. The non-obvious thing most beginners miss: speed of injection matters. Thirty seconds minimum for the full 3 mL. Pushing faster makes the site reaction much worse. Some patients use a timer on their phone. For laryngeal attacks, don't wait to see if the drug works before calling emergency services. Inject AND call simultaneously. Airway compromise can progress faster than icatibant's onset of action. One more practical note: keep your attack frequency log current. If you're reaching for icatibant more than once a month, that's a signal to discuss prophylaxis options (lanadelumab, berotralstat, C1-INH replacement) with your HAE specialist.
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).
Icatibant is on-demand acute rescue therapy, not a cycling compound. There is no scheduled administration: each injection treats an individual HAE attack as it occurs. The concept of "cycling" does not apply. No receptor desensitization, antibody formation, or cumulative pharmacological tolerance has been observed with long-term intermittent use across clinical trial populations.
Or use the universal Peptide Calculator for any peptide.
Expected: Clinically significant symptom relief in the majority of patients within 30 minutes to 2 hours; complete attack resolution within 6–24 hours in most cases
Monitor: Assess symptom status at 1h and 2h post-injection. If no clinically meaningful improvement by 6 hours, a second dose is permitted. For any laryngeal (throat/airway) attack: administer icatibant AND call emergency services simultaneously: do not wait to assess drug response before calling 911.
At the first sign of an HAE attack, retrieve one pre-filled syringe from storage. Check the expiration date. Inspect the solution; it should be clear and colorless. Discard any syringe with particles, cloudiness, or discoloration.
Clean a site on your abdomen at least 2 inches from the navel. Avoid areas with bruising, scarring, or previous injection site reactions that haven't fully resolved.
Insert the 25-gauge needle at a 45 to 90 degree angle.
The syringe delivers 30 mg total (10 mg/mL concentration). Do not rush this step.
Expect injection site redness, warmth, and mild swelling; this is normal and resolves within hours.
Assess symptoms at 1 hour and 2 hours post-injection.
If symptoms persist or recur after 6 hours: administer a second 30 mg syringe using a different abdominal injection site.
If symptoms persist after the second dose: a third 30 mg dose may be given no sooner than 6 hours after Dose 2. Maximum is 3 injections (90 mg) per 24 hours.
For any laryngeal (throat/airway) attack: inject icatibant immediately AND call emergency services. Do not wait to evaluate drug response before calling 911.
Do not recap the needle.
Standard long-term prophylaxis for HAE: plasma kallikrein inhibitor (monoclonal antibody) that prevents attacks; icatibant is used on-demand for breakthrough attacks occurring despite lanadelumab prophylaxis
Lanadelumab 300 mg SC every 2–4 weeks for prevention; icatibant 30 mg SC on-demand for breakthrough acute attacks
Oral prophylaxis for HAE: plasma kallikrein inhibitor taken daily to reduce attack frequency; icatibant used on-demand for breakthrough attacks that occur despite berotralstat prophylaxis
Berotralstat 150 mg orally once daily for prevention; icatibant 30 mg SC on-demand for acute breakthrough attacks
Alternative acute HAE treatment targeting the upstream contact/complement pathway; used when icatibant is unavailable, for patients with C1-INH deficiency as the primary pathology, or sequentially by clinical preference; not typically combined with icatibant for a single attack
Either icatibant OR C1-INH concentrate for acute attack management; Haegarda (SC C1-INH) may serve a prophylaxis role separately
ACE inhibitors act on the bradykinin/kinin system; icatibant B2 receptor blockade may reduce the antihypertensive effect of ACE inhibitors. ACE inhibitors independently cause ACE inhibitor-induced angioedema (a distinct bradykinin-mediated condition) which may be misdiagnosed as HAE, and may respond differently to icatibant. Discuss with prescribing physician before use; FDA label flags this interaction explicitly.
Pricing updated 2026-04-09
Injection site reactions affect approximately 97% of patients in clinical trials. That is not a typo. Erythema, swelling, warmth, burning, itching, and local pain at the abdominal injection site are expected, not exceptional. Most reactions are mild to moderate and resolve within a few hours. The key distinction: these are local pharmacological reactions, not allergic responses. True allergy would present with generalized urticaria, respiratory distress, or cardiovascular instability beyond what the HAE attack itself produces. Injection speed directly affects site reaction severity. The full 3 mL must be delivered slowly over approximately 30 seconds. Patients who rush the injection consistently report worse local reactions. Count to 30 while pushing the plunger. Systemic adverse effects are less common. Clinical trials flagged pyrexia, transaminase elevations, dizziness, and rash at rates modestly above placebo. Nausea and headache occurred at placebo-comparable rates in the FAST-3 and FAST-2 studies [1]. A theoretical cardiovascular concern exists and deserves honest discussion. Bradykinin has cardioprotective vasodilatory properties. Blocking B2 receptors could, in theory, attenuate those benefits. The FDA label calls out patients with acute ischemic heart disease and unstable angina as populations requiring caution. To date, no clinically meaningful cardiovascular events attributable to this mechanism have surfaced in trial data or post-marketing surveillance. But "no signal yet" and "proven safe" are different statements; the population using icatibant is small. Patients taking ACE inhibitors face a specific interaction concern. Both icatibant and ACE inhibitors affect the bradykinin system. B2 receptor blockade may reduce the antihypertensive effect of ACE inhibitors. More importantly, ACE inhibitors can themselves trigger bradykinin-mediated angioedema, a condition that mimics HAE but may respond differently to treatment. Pregnancy carries a Category C designation. B2 receptor blockade could theoretically affect uterine contractions and placental blood flow. No adequate human data exists. When to seek emergency care: if symptoms don't improve after the first dose by 6 hours, if laryngeal swelling is progressing despite treatment, or if three doses in 24 hours haven't resolved the attack. Never rely solely on icatibant during a throat attack; inject AND call emergency services simultaneously.
Verify Icatibant (Firazyr) dosing and safety with a second opinion
Icatibant (Firazyr) is an FDA-approved pharmaceutical product manufactured by Takeda under full GMP standards and distributed exclusively through licensed US specialty pharmacies. No compounded or generic versions are approved or widely commercially available in the United States. Quality risk is minimal compared to research peptides.
| Test | When | Target |
|---|---|---|
| Clinical symptom assessment | 1h, 2h, and 6h after each injection | Clinically significant improvement by 2h; complete or near-complete resolution by 6–12h. Absence of any improvement by 6h warrants emergency care. |
| Blood pressure monitoring | During and after icatibant use in patients on ACE inhibitors or other antihypertensives | — |
| Attack frequency log | Ongoing between attacks (patient-maintained) | — |
Determines whether attack is resolving, stable, or progressing; guides decision on whether a second or third dose is needed, or whether emergency escalation is warranted
Icatibant may reduce the antihypertensive effect of ACE inhibitors via overlapping bradykinin pathway modulation; blood pressure may rise transiently
Icatibant is on-demand rescue therapy only. Increasing attack frequency (>1 attack per month, or any laryngeal attack) is a clinical indicator to reassess prophylaxis adequacy with the treating HAE specialist; does not reflect a limitation of icatibant itself
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.
0 to 30 minutes: Absorption starts fast. Peak plasma concentration hits at roughly 30 minutes after abdominal injection. B2 receptor occupancy begins within minutes. Injection site reactions (redness, burning, swelling) show up almost immediately. Most patients won't feel meaningful symptom relief yet; some describe a subjective sense of the drug working by the 15 to 20 minute mark. 30 minutes to 2 hours: This is where relief begins. The FAST-3 trial pinned median time to clinically meaningful improvement at approximately 2 hours. B2 receptor blockade halts further vascular permeability and stops edema progression. Existing swelling starts to reabsorb. HAE patients commonly report noticeable reduction by 60 to 90 minutes. Abdominal attack sufferers often report faster subjective pain relief than those with cutaneous swelling. Mild dizziness or low-grade fever can occur during this window. 2 to 6 hours: Continued resolution. Tissue edema reabsorbs as bradykinin-mediated extravasation stays blocked. Icatibant plasma levels are declining toward the end of the therapeutic window. Most patients report clear improvement by 4 hours. Cutaneous attacks may take the full 6 hours for visible swelling to fully resolve. A small subset experiences symptom recurrence at 4 to 6 hours. If no improvement by 6 hours, a second 30 mg dose is permitted. 6 to 24 hours: Most attacks resolve completely within 12 to 24 hours. Icatibant is largely cleared from plasma. Per FAST-3 trial data, fewer than 20% of attacks required more than one injection. A second or third dose can be given at 6-hour minimum intervals (maximum 3 doses, 90 mg per 24 hours). Patients who need a second dose consistently report it works as well as the first.
Rapid SC absorption from abdominal fat; B2 receptor occupancy begins within minutes of injection. Peak plasma concentration reached at approximately 45 minutes (FDA label). Injection site reactions (erythema, burning, swelling) appear immediately.
Some patients describe a subjective sense of the drug "working" within 15–20 minutes; others notice the injection site reaction as the first sign. No meaningful symptom relief typically expected this early.
FAST-3 median time to clinically significant relief approximately 2 hours. B2 receptor blockade prevents further bradykinin-mediated vascular permeability and halts edema progression. Existing edema begins reabsorbing.
Majority of HAE patients report noticeable swelling reduction by 60–90 minutes. Abdominal attack patients often report faster subjective pain relief than cutaneous swellers. Some describe relief as "like a valve closing" on the swelling.
Tissue edema reabsorbs progressively as bradykinin-mediated extravasation is blocked. Icatibant plasma concentration declining toward end of therapeutic window. Second dose permitted at 6h if attack not adequately resolving.
Most patients report significant improvement by 4h. Cutaneous attacks may take the full 6h for visible swelling to resolve; abdominal attacks often fully resolved. Small subset reports symptom recurrence at 4–6h requiring a second dose.
Most attacks fully resolved within 12–24 hours. Icatibant largely cleared from plasma. Per trial data, <20% of attacks require more than one dose. A second or third dose may be administered at ≥6-hour intervals if symptoms recur or persist.
Majority of patients report complete resolution within 12h. Patients requiring multiple doses describe the second dose as equally effective as the first with no loss of response.
Source: FDA Firazyr label & Schwarz et al., Clin Pharmacokinet, 2014: terminal half-life ~1-2 hours after SC injection
Loading the interactive decay curve.
Icatibant is FDA-approved (NDA 022150, approved August 2011) for the treatment of acute attacks of hereditary angioedema in adults 18 years and older. The European Medicines Agency approved it in 2008. It is marketed as Firazyr by Takeda (originally developed by Jerini AG, acquired by Shire). Icatibant is a prescription medication available only through licensed US specialty pharmacies. No compounded or generic versions are FDA-approved or commercially available in the United States. WADA status is not applicable; icatibant has no performance-improving profile and no history of athletic misuse. Pediatric use (under 18) is not approved. The FDA label explicitly states safety and efficacy have not been established in patients under 18 years of age. This content is for informational purposes only. It does not constitute medical advice, diagnosis, or treatment. Consult a qualified healthcare provider before using any prescription medication. Hereditary angioedema management should be supervised by an allergist, immunologist, or HAE specialist.
Peptide Schedule Research TeamReviewed Apr 20268 Citations
