Formulary
Warfarin sodium: Indications, Dosing, Side Effects and Interactions
Warfarin sodium clinical drug profile including indications, dosing, side effects, cautions and interactions.
MedNext Academy | 5 min read
Warfarin sodium: Indications, Dosing, Side Effects and Interactions
Warfarin sodium clinical drug profile including indications, dosing, side effects, cautions and interactions.
Indications and dose
**Prophylaxis of embolisation in rheumatic heart disease and atrial fibrillation,Prophylaxis after insertion of prosthetic heart valve,Prophylaxis and treatment of venous thrombosis and pulmonary embolism,Transient ischaemic attacks**
- **Adult** (By Mouth): Initially 5-10 mg, to be taken on day 1; subsequent doses dependent on the prothrombin time, reported as INR (international normalised ratio), a lower induction dose can be given over 3-4 weeks in patients who do not require rapid anticoagulation, elderly patients to be given a lower induction dose; maintenance 3-9 mg daily, to be taken at the same time each day.
**Treatment and prophylaxis of thrombotic episodes (induction) for warfarin sodium**
- **Neonate (initiated under specialist supervision)** (By mouth): Initially 200 micrograms/kg for 1 dose on day 1, then reduced to 100 micrograms/kg once daily for the following 3 days, subsequent doses dependent on INR levels, induction dose may need to be altered according to condition (e.g. abnormal liver function tests, cardiac failure), concomitant interacting drugs, and if baseline INR above 1.3.
- **Child** (By mouth): Initially 200 micrograms/kg (max. per dose 10 mg) for 1 dose on day 1, then reduced to 100 micrograms/kg once daily (max. per dose 5 mg) for the following 3 days, subsequent doses adjusted according to INR levels, induction dose may need to be altered according to condition (e.g. abnormal liver function tests, cardiac failure), concomitant interacting drugs, and if baseline INR above 1.3.
**Treatment and prophylaxis of thrombotic episodes following induction dose (if INR still below 1.4) for warfarin sodium**
- **Neonate (under expert supervision)** (By mouth): 200 micrograms/kg once daily.
- **Child** (By mouth): 200 micrograms/kg once daily (max. per dose 10 mg).
**Treatment and prophylaxis of thrombotic episodes following induction dose (if INR above 3.0) for warfarin sodium**
- **Neonate (under expert supervision)** (By mouth): 50 micrograms/kg once daily.
- **Child** (By mouth): 50 micrograms/kg once daily (max. per dose 2.5 mg).
**Treatment and prophylaxis of thrombotic episodes following induction dose (if INR above 3.5) for warfarin sodium**
- **Neonate (under expert supervision)** (By mouth): Dose to be omitted.
- **Child** (By mouth): Dose to be omitted.
**Treatment and prophylaxis of thrombotic episodes (usual maintenance) for warfarin sodium**
- **Neonate (under expert supervision)** (By mouth): Maintenance 100-300 micrograms/kg once daily, doses up to 400 micrograms/kg once daily may be required especially if bottle fed, to be adjusted according to INR.
- **Child** (By mouth): Maintenance 100-300 micrograms/kg once daily, doses up to 400 micrograms/kg once daily may be required especially if bottle fed, to be adjusted according to INR.
Cautions
K antagonists Bacterial endocarditis (use only if warfarin otherwise indicated); conditions in which risk of bleeding is increased; history of gastro-intestinal bleeding; hyperthyroidism; hypothyroidism; peptic ulcer; recent ischaemic stroke; recent surgery; uncontrolled hypertension Cautions, further information Elderly Screening Tool of Older Persons' potentially inappropriate Prescriptions (STOPP) criteria to aid medication reviews (see Prescribing in the elderly for information). Potentially inappropriate: with concurrent significant bleeding risk, such as uncontrolled severe hypertension, bleeding diathesis, or recent non-trivial spontaneous bleeding (high risk of bleeding) as part of dual therapy with an antiplatelet agent in patients with stable coronary, cerebrovascular, or peripheral arterial disease, without a clear indication for anticoagulant therapy (no added benefit) for first deep venous thrombosis without continuing provoking risk factors (e.g. thrombophilia) for longer than 6 months (no proven added benefit) for first pulmonary embolus without continuing provoking risk factors for longer than 12 months (no proven added benefit) Cautions For warfarin sodium Postpartum (delay warfarin until risk of haemorrhage is low-usually 5-7 days after delivery)
Contraindications
K antagonists Avoid use within 48 hours postpartum; haemorrhagic stroke; significant bleeding
Side effects
K antagonists Common or very common Haemorrhage Rare or very rare Alopecia; nausea; vomiting Frequency not known Blue toe syndrome; CNS haemorrhage; diarrhoea; fever; haemothorax; jaundice; pancreatitis; skin necrosis (increased risk in patients with protein C or protein S deficiency); skin reactions Side-effects For warfarin sodium Frequency not known Calciphylaxis; hepatic function abnormal
Interactions
**Severe interactions:**
- Listed below are drugs which are known to interact with warfarin in a clinically significant way.
**Other interactions (27):**
- Warfarin has a narrow therapeutic range and care is required with all concomitant therapy.
- The individual product information for any new concomitant therapy should be consulted for specific guidance on warfarin dose adjustment and therapeutic monitoring.
- Drugs which should be avoided if possible The following examples should be avoided, or administered with caution with increased clinical and laboratory monitoring: Clopidogrel NSAIDs (including...
- Warfarin may initially be given with a heparin in the initial treatment of thrombosis, until the INR is in the correct range.
- Metabolic interactions Warfarin is a mixture of enantiomers which are metabolised by different CYPP450 cytochromes.
- R-warfarin is metabolised primarily by CYP1A2 and CYP3A4.
Pregnancy
K antagonists Should not be given in the first trimester of pregnancy. Warfarin, acenocoumarol, and phenindione cross the placenta with risk of congenital malformations, and placental, fetal, or neonatal haemorrhage, especially during the last few weeks of pregnancy and at delivery. Therefore, if at all possible, they should be avoided in pregnancy, especially in the first and third trimesters (difficult decisions may have to be made, particularly in women with prosthetic heart valves, atrial fibrillation, or with a history of recurrent venous thrombosis or pulmonary embolism). Stopping these drugs before the sixth week of gestation may largely avoid the risk of fetal abnormality. Pregnancy For warfarin sodium Babies of mothers taking warfarin at the time of delivery need to be offered immediate prophylaxis with intramuscular phytomenadione (vitamin K 1 ).
Breast feeding
Not present in milk in significant amounts and appears safe. Risk of haemorrhage which is increased by vitamin K deficiency.
Hepatic impairment
K antagonists In general, manufacturers advise caution in mild to moderate impairment; avoid in severe impairment.
Renal impairment
Use with caution in mild to moderate impairment. Monitoring In severe renal impairment, monitor INR more frequently.
Medicinal forms
Solution,Tablet,Suspension
Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
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