ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Coagulation Factor Replacement — Haemophilia B Pregnancy: Use as clinically indicated — essential treatment; discuss with haemophilia centre and obstetric team for delivery planning

Factor IX Concentrate

Brand names: BeneFIX, Idelvion, Refixia (extended half-life)

Adult dose

Dose: Prophylaxis: 25–40 IU/kg twice weekly (standard half-life) or 25–50 IU/kg weekly (extended half-life). Bleeding: 50–100 IU/kg depending on severity
Route: IV injection or infusion
Frequency: Prophylaxis: twice weekly or weekly; on-demand: as required
Max: Calculated by target factor IX level: dose (IU) = body weight (kg) × desired rise (IU/dL) × 1.3
Used for haemophilia B (congenital Factor IX deficiency). Extended half-life products (Idelvion — rIX-FP; Refixia — N9-GP) allow weekly or fortnightly dosing. Target trough level ≥1% for prophylaxis (ideally ≥3–5% in modern practice).

Paediatric dose

Dose: 25–50 IU/kg IU/kg
Route: IV
Frequency: Prophylaxis: twice weekly; bleeding: as required
Max: Per haematologist guidance and target Factor IX level
BNFc: children require higher doses per kg than adults due to larger volume of distribution. Dose and frequency per haemophilia centre.

Dose adjustments

Renal

No dose adjustment required

Hepatic

Use with caution in hepatic impairment — liver disease may impair endogenous factor production

Paediatric weight-based calculator

BNFc: children require higher doses per kg than adults due to larger volume of distribution. Dose and frequency per haemophilia centre.

Clinical pearls

  • Haemophilia B: X-linked recessive disorder due to Factor IX deficiency; affects ~1 in 30,000 male births
  • Inhibitor development occurs in ~3% of haemophilia B patients (vs ~30% in haemophilia A) — test annually and after intensive exposure
  • Severity classification: severe <1% FIX (<0.01 IU/mL); moderate 1–5%; mild 5–40%
  • Extended half-life products (Idelvion, Refixia) have transformed care — weekly dosing improves adherence and quality of life
  • For haemophilia B with inhibitors — recombinant Factor VIIa (NovoSeven) or emicizumab (off-label) used as bypass therapy
  • UKHCDO (UK Haemophilia Centre Doctors' Organisation) registers all haemophilia patients — all treatment decisions through haemophilia centre

Contraindications

  • Disseminated intravascular coagulation (DIC)
  • Known hypersensitivity to hamster protein (recombinant products)

Side effects

  • Inhibitor development (neutralising antibodies — less common than in haemophilia A)
  • Allergic reactions
  • Anaphylaxis
  • Thrombosis (high doses)
  • Headache

Interactions

  • No clinically significant drug interactions

Monitoring

  • Factor IX activity levels (peak and trough)
  • Inhibitor screen (annually, post-surgery, after intensive exposure)
  • LFTs
  • Viral serology (hepatitis B/C, HIV)

Reference: BNFc; BNF 90; BNFc; UKHCDO Guidelines; BSH Haemophilia Guidelines 2018; World Federation of Haemophilia. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways