[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Hereditary angioedema agents](https://durgical.com/en/pharmacology/classes/hereditary-angioedema-agents/) › C1 esterase inhibitor

# C1 esterase inhibitor

## Hereditary angioedema agents?

Hereditary angioedema agents

A concentrate of the plasma protein missing in hereditary angioedema; it treats acute attacks and prevents them by curbing bradykinin production.

Updated Nov 1, 2026

Also called: C1-INH, C1 inhibitor, plasma derived

## Quick facts

**Group**
[Hereditary angioedema agents](https://durgical.com/en/pharmacology/classes/hereditary-angioedema-agents/)

**Target**
Proteases it inhibits: plasma kallikrein, activated factor XII and complement C1r/C1s

**Used for**
Acute attacks of hereditary angioedema

**Key effects**
Headache · Fever or chills · Runny nose

**Monitor**
Response of attacks · Signs of clots in people

**ATC**
B06AC01

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

✂**Proteases it inhibits: plasma kallikrein, activated factor XII and complement C1r/C1s**C1 esterase inhibitor

ⓘ The figure shows the drug itself: the active form of human C1 inhibitor, a serpin that traps the proteases it controls.

**Target in 3D:** Proteases it inhibits: plasma kallikrein, activated factor XII and complement C1r/C1s. PDB structure 5DU3 (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/5DU3) · Drag to rotate · pinch to zoom

C1 esterase inhibitor is a serine protease inhibitor (serpin) from human plasma. Given to people who lack it, it restrains plasma kallikrein and activated factor XII, so less bradykinin is produced and swelling settles. It also controls the first component of complement.

- The concentrate replaces the missing C1 inhibitor
- It traps plasma kallikrein and activated factor XII
- Less bradykinin is cut from kininogen
- Vessel leak and swelling settle

## Indications

- Acute attacks of hereditary angioedema (intravenous product) [Urticaria and angioedema →](https://durgical.com/en/conditions/urticaria-and-angioedema/)
- Prevention of hereditary angioedema attacks (intravenous or subcutaneous products) [Urticaria and angioedema →](https://durgical.com/en/conditions/urticaria-and-angioedema/)

## Adverse effects

### Common

- Headache, nausea, vomiting, bad taste
- Fever or chills
- Injection-site redness or pain
- Runny nose, sneezing, sore throat, dizziness

### Serious (rare, important)

- Allergic reactions (hives, swelling of face or throat, breathing difficulty), which are very rare
- Blood clots (swollen painful limb, chest pain, one-sided weakness), mainly at very high doses or with other risk factors

## Contraindications

- Previous severe allergic reaction to the product
- Caution with a history of clots, stroke, heart disease, indwelling catheters or long bed rest

## Key interactions

**Oestrogen-containing medicines (including the contraceptive pill) and androgens such as danazol**
Reported before starting: oestrogens can worsen hereditary angioedema and treatment may need adjusting

## What is monitored

- Response of attacks (frequency, severity)
- Signs of clots in people with risk factors
- Allergic reactions during the injection

## Administration and safety

- Powder mixed with its diluent just before use and brought to room temperature
- Intravenous products are given by slow injection; the subcutaneous product goes into the abdomen, avoiding the navel and damaged skin, with sites rotated
- During an acute attack, especially with throat symptoms, emergency care is sought even after a dose
- Plasma-derived and recombinant C1 inhibitors are different products: check which one is prescribed

## Pregnancy and breastfeeding

Pregnancy or breastfeeding is discussed with the treating team before use; a pregnancy during treatment is reported.

## Nursing care

- Check the airway and breathing first in any facial or throat swelling
- Ask about clot history, surgery, dental work and oestrogen use
- Teach mixing and injection technique when home treatment is planned
- Teach the patient to keep an attack diary

## Pharmacokinetics

**Absorption**
Intravenous injection; one product is given subcutaneously for prevention

**Distribution**
Acts in the plasma

## Memory aid

«Replace the brake»: hereditary angioedema lacks C1 inhibitor, the brake on kallikrein; the concentrate puts the brake back.

## Test yourself

Think of the answer, then tap the question to see it.

## Which enzymes does C1 inhibitor restrain to reduce bradykinin?

Plasma kallikrein and activated factor XII.

## Is C1 inhibitor used for attacks, prevention or both?

Both, depending on the product.

## Which rare serious effect is linked to very high doses?

Blood clots (thrombosis).

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/c1-esterase-inhibitor/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 3

- [Icatibant](https://durgical.com/en/pharmacology/icatibant/)
- [Lanadelumab](https://durgical.com/en/pharmacology/lanadelumab/)
- [Berotralstat](https://durgical.com/en/pharmacology/berotralstat/)

## Related conditions 1

- [Urticaria and angioedema](https://durgical.com/en/conditions/urticaria-and-angioedema/)

[← Back to the class: Hereditary angioedema agents](https://durgical.com/en/pharmacology/classes/hereditary-angioedema-agents/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [C1-Esterase Inhibitor Human Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a622016.html) (MedlinePlus (U.S. National Library of Medicine), 2025); [5DU3: Active form of human C1-inhibitor](https://www.rcsb.org/structure/5DU3) (RCSB Protein Data Bank, 2016).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/c1-esterase-inhibitor/