# Drugs for Hereditary Angioedema > Hereditary angioedema drugs in MBBS Pharmacology: icatibant, C1-INH concentrate, lanadelumab, danazol, bradykinin logic and C4 testing. - Canonical URL: https://prepelephant.com/topics/mbbs/pharmacology/drugs-hereditary-angioedema - Exam / course: MBBS · Subject: Pharmacology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Drugs for Hereditary Angioedema", PrepElephant, https://prepelephant.com/topics/mbbs/pharmacology/drugs-hereditary-angioedema ## Direct answer Hereditary angioedema swells without itching — and that one missing feature redirects the entire therapeutic logic. The disease is C1-inhibitor deficiency (type 1: low antigenic levels; type 2: dysfunctional protein), leaving bradykinin free to leak vessels; there is no urticaria, no pruritus, and no response to antihistamines, steroids or adrenaline. Screening shows low C4; diagnosis needs C1-INH antigenic and functional levels, with C1q normal in hereditary disease (low C1q suggests the acquired form). Acute attacks take icatibant (bradykinin B2 receptor antagonist, 30 mg subcutaneously), C1-inhibitor concentrate intravenously, or — where concentrates are unavailable, as across much of India — fresh frozen plasma. Long-term prophylaxis runs from lanadelumab (anti-plasma kallikrein, fortnightly) and oral berotralstat to danazol and tranexamic acid; ACE inhibitors are permanently contraindicated. ## What you must remember - **The pathway:** factor XII activation → plasma kallikrein → bradykinin → B2 receptor → vascular leak — this chain explains every drug choice and the ACE inhibitor danger. - **Acute attack:** icatibant 30 mg SC (self-administered in most guidelines), C1-INH concentrate 20 U/kg IV, ecallantide (plasma kallikrein inhibitor, US); FFP is the resource-limited stand-in since it carries C1-INH. - **Prophylaxis, modern:** lanadelumab 300 mg SC every 2 weeks (anti-plasma kallikrein monoclonal), berotralstat (oral daily kallikrein inhibitor), C1-INH subcutaneous. - **Prophylaxis, classic:** danazol 200 mg (range 50–600 mg) daily — an attenuated androgen that raises hepatic C1-INH and C4 synthesis; virilisation, weight gain, hepatic adenomas (LFTs and liver ultrasound for life); tranexamic acid 1 g two-three times daily as the weaker, cheaper alternative. - **Diagnosis ladder:** C4 low during and between attacks (the screening test), C1-INH antigenic low (type 1) or normal antigenic with low function (type 2), C1q normal; family history in about 75%. - **Permanent exclusions:** ACE inhibitors (bradykinin degradation blocked) and oestrogens (worsen attacks) — for life, not just during treatment. - **Procedural cover:** C1-INH concentrate or a danazol boost before dental or surgical work — laryngeal attacks after airway instrumentation are the feared event. - **Indian anchor:** danazol plus FFP remains the affordable backbone; acquired C1-INH deficiency (lymphoproliferative or autoimmune, C1q low) is the differential the C1q level resolves. ## The laryngeal attack and the diagnosis that explains it A 24-year-old woman arrives with lip and tongue swelling and a tightening throat — no wheal, no itch, no response to adrenaline given in the ambulance. That trio is the diagnosis speaking: hereditary angioedema, confirmed later by C4 of 8 mg/dL (low), C1-INH antigenic low, C1q normal. The airway takes precedence — icatibant 30 mg subcutaneously, C1-INH concentrate 20 U/kg IV where available, intubation standby; adrenaline was always going to fail because there is no mast-cell mediator to block. Her triggers get named — minor trauma, dental work, oestrogen-containing pills (she stopped them that day), and an ACE inhibitor her previous doctor prescribed for hypertension, now permanently replaced. Long-term: danazol 200 mg daily, started with a frank conversation about virilisation, weight, and the liver scans she will keep for life; where cost allows, lanadelumab every fortnight offers cleaner chemistry with the same endpoint — no laryngeal attack. Every therapeutic sentence in this story traces back to one biochemistry line: without C1-INH, bradykinin runs unchecked. ## Where students slip The first slip is treating it like allergic angioedema — adrenaline, steroids and antihistamines do nothing here, and recognising their failure is itself diagnostic information; the viva question "why did adrenaline fail?" expects the bradykinin answer. The second is the screening test: C4, low even between attacks, is the cheap first clue, while C1q's level separates hereditary (normal) from acquired (low) disease. Third, ACE inhibitors in HAE are not merely unhelpful — they are contraindicated for life, because ACE degrades bradykinin; the same logic explains why the drug causes acquired angioedema in normal people. Fourth, danazol is quoted without its tax: attenuated androgen, hepatic adenoma risk, virilisation, lifelong monitoring — and pregnancy absolutely contraindicates it, at which point C1-INH concentrate becomes the prophylaxis of choice. Fifth, students forget procedural cover before dental extraction or intubation — the trigger list (trauma, oestrogens, ACE inhibitors, instrumentation) is half the clinical exam. Finally, tranexamic acid's role is antifibrinolytic dampening of the kallikrein-driven cascade — weaker, cheaper, and honest about both. ## Frequently asked questions ### Why do antihistamines and adrenaline fail in hereditary angioedema? The mediator is bradykinin, not histamine — mast-cell-directed drugs have no target, which itself helps distinguish HAE clinically. ### What is the screening test and how is hereditary distinguished from acquired disease? C4 is low in both during and between attacks; C1q is normal in hereditary C1-INH deficiency and low in the acquired form. ### How does icatibant work? It is a selective bradykinin B2 receptor antagonist given 30 mg subcutaneously, blocking the vascular-leak signal at the end of the kallikrein-kinin pathway. ### Why is danazol effective despite being an androgen? Attenuated androgens increase hepatic synthesis of C1-INH and C4, raising functional inhibitor levels — with virilisation and hepatic adenoma risks requiring lifelong monitoring. ### Which drugs are permanently contraindicated in HAE? ACE inhibitors (they block bradykinin degradation) and oestrogens (they worsen attacks) — for life, independent of therapy.