Pharmacology · Coagulation factor replacement and haemophilia agents

Coagulation factor IX !

Plasma-derived or recombinant factor IX infused to prevent and treat bleeding in haemophilia B.

Updated 2026-11-01

Class: Coagulation factor replacement and haemophilia agents
Enzyme: Factor IX itself (the serine protease of the tenase complex)
ATC code: B02BD04
WHO Model List of Essential Medicines

Factor IX itself (the serine protease of the tenase complex)Coagulation factor IX

The figure shows activated human factor IX (factor IXa); the small molecule in the crystal is p-aminobenzamidine, a laboratory inhibitor in the active site, not the drug.

Target in 3D: Factor IX itself (the serine protease of the tenase complex). PDB structure 1RFN (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Factor IX is a vitamin K-dependent zymogen. Activated by factor XIa or by tissue factor–VIIa, factor IXa, together with factor VIIIa, activates factor X. In haemophilia B, infused factor IX restores this step and allows thrombin to form.

Infused factor IX replaces the missing zymogen
It is activated to factor IXa
IXa with VIIIa activates factor X
Thrombin generation is restored

Pharmacokinetics

Half-life: Extended half-life products allow less frequent infusions

Indications

Haemophilia B (Christmas disease): prophylaxis, treatment of bleeds and surgery Haemophilia A and B →

Adverse effects

Common

Infusion reactions
Headache, nausea

Contraindications

Known severe allergy to the product

Key interactions

Antifibrinolytics (tranexamic acid, aminocaproic acid): With factor IX complex concentrates the risk of thrombosis increases

What is monitored

Factor IX activity levels
Inhibitor testing and allergy during early exposures
Clinical response

Administration and safety

Intravenous infusion after reconstitution; home infusion is common
Pure factor IX is not the same as prothrombin complex concentrate; check the product before preparing it

Nursing care

Record the product name and lot number of every infusion
Watch for allergic reactions during and after the infusion
Teach the family to recognise joint and muscle bleeds early and to treat them quickly
Report bleeding that does not respond as usual: it may mean an inhibitor

Pregnancy and breastfeeding

Haemophilia B is rare in women; carriers with low levels may need it around delivery.

Test yourself

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

Which haemophilia is treated with factor IX?

Haemophilia B.

Is factor IX vitamin K-dependent?

Yes, like factors II, VII and X.

Which drug interaction raises thrombosis risk with factor IX complex?

Antifibrinolytics such as tranexamic acid.

Add to my cards (3)

Haemophilia A and B

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

Sources: Treatment of Hemophilia | Hemophilia | CDC (Centers for Disease Control and Prevention, 2026); Farmacología básica y clínica (Katzung), 16.ª ed., cap. 34 (McGraw Hill, 2025); DailyMed - TRANEXAMIC ACID injection, solution (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.