WARFARIN Tablet Ref.[8408] Active ingredients: Warfarin

Posology

Adults and elderly patients

The typical induction dose of warfarin is 10 mg daily for 2 days, but this should be tailored to individual requirements. Baseline prothrombin measurements (PT) should be taken before beginning therapy with warfarin.

The daily maintenance dose of warfarin is usually 3 to 9 mg taken at the same time each day. The exact maintenance dose for an individual is dependent on the prothrombin time or other appropriate coagulation tests.

The maintenance dose is omitted if the prothrombin time is excessively prolonged. Once the maintenance dose is stabilised in the therapeutic range, it is rarely necessary to alter it.

In emergencies, anticoagulant therapy should be initiated with heparin and warfarin together. Where there is less urgency, as in patients disposed to or at special risk of thromboembolism, anticoagulant therapy may be initiated with warfarin alone.

Concomitant heparin therapy affects the results of control tests and should be discontinued at least six hours before the first test is carried out.

Control is established with INR monitoring at regular intervals and subsequent warfarin maintenance dosage further adjusted according to the results obtained.

Paediatric population

No data are available.

Method of administration

Warfarin Tablets are for oral use

The benefit of gastric decontamination is uncertain. If the patient presents within 1 hour of ingestion of more than 0.25 mg/kg or more than the patient’s therapeutic dose, consider activated charcoal (50 g for adults; 1g/kg for children)

In cases of life-threatening haemorrhage

Stop warfarin treatment, give prothrombin complex concentrate (factors II, VII, IX, and X) 30-50 units/kg or (if no concentrate available) fresh frozen plasma 15 mL/kg. Discuss with local haematologist or National Poisons Information Service or both.

Non-life threatening haemorrhage

Where anticoagulation can be suspended, give slow intravenous injection of phytomenadione (vitamin K₁) 10-20 mg for adults (250 micrograms/kg for a child);

Where rapid re-anticoagulation is desirable (e.g. valve replacements) give prothrombin complex concentrate (factors II, VII, IX, and X) 30–50 units/kg or (if no concentrate available) fresh frozen plasma 15 mL/kg.

Monitor INR to determine when to restart normal therapy. Monitor INR for at least 48 hours post overdose.

For patients on long-term warfarin therapy without major haemorrhage

• INR>8.0, no bleeding or minor bleeding—stop warfarin, and give phytomenadione (vitamin K₁) 0.5-1 mg for adults, 0.015-0.030 mg/kg (15-30 micrograms/kg) for children by slow intravenous injection or 5 mg by mouth (for partial reversal of anticoagulation give smaller oral doses of phytomenadione e.g. 0.5–2.5 mg using the intravenous preparation orally); repeat dose of phytomenadione if INR still too high after 24 hours. Large doses of phytomenadione may completely reverse the effects of warfarin and make reestablishment of anticoagulation difficult.
• INR 6.0–8.0, no bleeding or minor bleeding—stop warfarin, restart when INR <5.0
• INR <6.0 but more than 0.5 units above target value—reduce dose or stop warfarin, restart when INR <5.0

For patients NOT on long term anticoagulants without major haemorrhage

Measure the INR (prothrombin time) at presentation and sequentially every 24-48 hours after ingestion depending on the initial dose and initial INR.

• If the INR remains normal for 24-48 hours and there is no evidence of bleeding, there should be no further monitoring necessary.
• Give vitamin K1 (phytomenadione) if:

a) there is no active bleeding and the patient has ingested more than 0.25 mg/kg;

OR

b) the prothrombin time is already significantly prolonged (INR >4.0).

The adult dose of vitamin K1 is 10-20 mg orally (250 micrograms/kg body weight for a child). Delay oral vitamin K1 at least 4 hours after any activated charcoal has been given. Repeat INR at 24 hours and consider further vitamin K1.

Shelf life: 3 years.

Do not store above 25°C. Store in the original package in order to protect from light.

HDPE bottle with polyester wad and child resistant polypropylene cap.

Contents: 21, 28, 50, 56, 100, 112, 200 or 500 tablets.

PVC/PVDC-aluminium foil or Aclar/aluminium foil blisters.

Contents: 21, 28, 50, 56, 100, 112, 200 or 500 tablets.

Not all pack sizes may be marketed.

No special requirements for disposal.