Recombinant clotting factor IX Pregnancy: Animal reproduction studies have not been conducted with factor IX and, because haemophilia B occurs rarely in women, experience of use during pregnancy and breast-feeding is not available — factor IX should be used during pregnancy and lactation only if clearly indicated.

Factor IX (Specialist drug)

Brand names: BeneFIX, Alprolix, Idelvion, Refixia

Factor IX concentrate is a clotting factor replacement product used to treat and prevent bleeding in haemophilia B (factor IX deficiency).

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Individualised and weight-based. On-demand treatment: required units = body weight (kg) x desired factor IX rise (%) or (IU/dl) x 0.85, based on the empirical finding that 1 IU of factor IX per kg body weight raises plasma factor IX activity by 1.16% of normal. Long-term prophylaxis in severe haemophilia B: usually 20 to 40 IU of factor IX per kg body weight at intervals of 3 to 4 days.

Route: Intravenous use, after reconstitution, at a rate not exceeding 3 ml per minute

Frequency: Determined by the bleeding episode or procedure (see notes for the target-level table); for long-term prophylaxis, every 3 to 4 days — in some cases, especially in younger patients, shorter intervals or higher doses may be necessary

PRESCRIBING CONTEXT: treatment should be under the supervision of a physician experienced in the treatment of haemophilia. Dose and duration depend on the severity of the factor IX deficiency, the location and extent of bleeding, and the patient's clinical condition; the amount and frequency should always be guided by clinical effectiveness in the individual case. TARGET FACTOR IX LEVELS AND DOSING FREQUENCY (factor IX activity should not fall below the level given for the period stated) — Haemorrhage: early haemarthrosis, muscle bleeding or oral bleeding, target 20-40% (IU/dl), repeat every 24 hours for at least 1 day until the bleeding episode as indicated by pain is resolved or healing is achieved; more extensive haemarthrosis, muscle bleeding or haematoma, target 30-60%, repeat every 24 hours for 3 to 4 days or more until pain and acute disability resolve; life-threatening haemorrhage, target 60-100%, repeat every 8 to 24 hours until the threat is resolved. Surgery: minor surgery including tooth extraction, target 30-60%, every 24 hours for at least 1 day until healing; major surgery, target 80-100% pre- and post-operatively, repeat every 8 to 24 hours until adequate wound healing, then continue therapy for at least another 7 days to maintain factor IX activity of 30-60% (IU/dl). CONTINUOUS INFUSION: before surgery, perform a pharmacokinetic analysis to estimate clearance; initial infusion rate (IU/kg/hr) = clearance x desired steady state level. After the first 24 hours of continuous infusion, recalculate clearance daily using the steady state equation with the measured level and the known infusion rate. MONITORING: determine factor IX levels during treatment to guide dose and frequency; individual patients vary in half-life and recovery, and weight-based doses may need adjustment in underweight or overweight patients. Precise monitoring by coagulation analysis (plasma factor IX activity) is indispensable for major surgery. When using an aPTT-based one-stage clotting assay, results can be significantly affected by the aPTT reagent and reference standard used — important when changing laboratory or reagents. PAEDIATRIC: the recommended dose and dosing frequency in adolescents aged 12-17 years are as recommended for adults; there are limited data on use in children under 12 years. PRODUCT-SPECIFICITY WARNING: this draft is from the UK SPC for Replenine-VF 50 IU/ml (a plasma-derived human coagulation factor IX). Factor IX dosing is product-specific — recombinant, extended half-life and glycoPEGylated factor IX products (the US label in this bundle is for a different product, REBINYN) use different fixed IU/kg regimens and dosing intervals. Do not transfer this regimen to another factor IX product; always dose from the SPC of the specific product in use.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients

Side effects

Headache (common)
Injection site reaction (common)
Hypersensitivity or allergic reactions (rare) — may include angioedema, burning and stinging at the infusion site, chills, flushing, generalised urticaria, hives, hypotension, lethargy, nausea, restlessness, tachycardia, tightness of the chest, tingling, vomiting and wheezing; in some cases progressing to severe anaphylaxis including shock
Development of neutralising antibodies (inhibitors) to factor IX, manifesting as an insufficient clinical response — closely associated in time with allergic reactions; patients with inhibitors may be at increased risk of anaphylaxis on subsequent challenge
Nephrotic syndrome reported following attempted immune tolerance induction in haemophilia B patients with inhibitors and a history of allergic reaction
Thromboembolic episodes — a potential risk following factor IX administration, with higher risk for low-purity preparations (myocardial infarction, disseminated intravascular coagulation, venous thrombosis and pulmonary embolism); rarely associated with high-purity factor IX

Clinical monograph

How it works

It replaces deficient factor IX, restoring its role in the intrinsic coagulation pathway and enabling normal thrombin and fibrin generation.

Prescribing in practice

Hypersensitivity reactions and development of inhibitory antibodies to factor IX can occur, and inhibitor formation may be associated with allergic reactions, so patients should be observed and assessed for inhibitors.
Thromboembolic events are a recognised risk, particularly with some products and in patients with risk factors, so it should be used at the lowest effective level.
The product brand and batch number should be recorded for each administration for traceability.

Monitoring

Monitor factor IX activity and clinical response, and test for inhibitor development if the expected response is not achieved.

Counselling the patient

Report any rash, wheeze or swelling during or after an infusion, as allergic reactions can occur.
Keep a record of the product name and batch used for each treatment.

Evidence & guidelines

Factor IX replacement is the standard of care for haemophilia B and is delivered through specialist haemophilia services.

Reference: UKHCDO guidelines; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways