Warfarin: Difference between revisions
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==General== | ==General== | ||
*Type: | *Type: [[anticoagulant]] | ||
*Dosage Forms: | *Dosage Forms: oral | ||
*Common Trade Names: Coumadin | *Common Trade Names: Coumadin | ||
==Adult Dosing== | ==Adult Dosing== | ||
*Day 1: 5 - 7. | *Day 1: 5 - 7.5mg oral at bedtime (to ensure absorption on empty stomach) | ||
*Day 2 and beyond: 2.5 - 7. | *Day 2 and beyond: 2.5 - 7.5mg daily (usually 5mg) | ||
*INR increase of >0.3 - 0.4 per day requires dose reduction | *INR increase of >0.3 - 0.4 per day requires dose reduction | ||
*Response also influenced by congestive heart failure, liver disease, Vitamin K deficiency, many drugs | *Response also influenced by congestive heart failure, liver disease, Vitamin K deficiency, many drugs | ||
| Line 15: | Line 15: | ||
==Pediatric Dosing== | ==Pediatric Dosing== | ||
''Safety and efficacy not well-established, though it is sometimes used in pediatrics for VTE treatment'' | |||
==Special Populations== | ==Special Populations== | ||
*[[Drug Ratings in Pregnancy|Pregnancy Rating]]: Contraindicated | *[[Drug Ratings in Pregnancy|Pregnancy Rating]]: Contraindicated (Category D) | ||
*[[Lactation risk categories|Lactation risk]]: | *[[Lactation risk categories|Lactation risk]]: infant risk minimal | ||
*Renal Dosing | *Renal Dosing: caution advised | ||
*Hepatic Dosing: consider decreased dose | |||
*Hepatic Dosing | |||
==Contraindications== | ==Contraindications== | ||
*Allergy to class/drug | *Allergy to class/drug | ||
*Active bleeding or tendency to bleed | |||
==Adverse Reactions== | ==Adverse Reactions== | ||
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==Pharmacology== | ==Pharmacology== | ||
*Half-life: | *Half-life: 20-60h (anticoagulant effect) | ||
**Of note, half-life highly variable based on rate of clotting factor catabolism | |||
*Metabolism: Liver | *Metabolism: Liver | ||
*Excretion: | *Excretion: Urine 92%, bile | ||
*Mechanism of Action: | *Mechanism of Action: | ||
**Blocks activation of vitamin K dependent prothrombotic factors II, VII, IX, X | **Blocks activation of vitamin K dependent prothrombotic factors II, VII, IX, X | ||
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==Comments== | ==Comments== | ||
*Because of differing factor half-lives, can cause transient (24-36 hour) prothrombosis at start of therapy | *Because of differing factor half-lives, can cause transient (24-36 hour) prothrombosis at start of therapy | ||
**Bridge with heparin for 1-2 days until INR is in desired range | **Bridge with [[heparin]] for 1-2 days until INR is in desired range | ||
==See Also== | ==See Also== | ||
Latest revision as of 13:58, 25 February 2021
General
- Type: anticoagulant
- Dosage Forms: oral
- Common Trade Names: Coumadin
Adult Dosing
- Day 1: 5 - 7.5mg oral at bedtime (to ensure absorption on empty stomach)
- Day 2 and beyond: 2.5 - 7.5mg daily (usually 5mg)
- INR increase of >0.3 - 0.4 per day requires dose reduction
- Response also influenced by congestive heart failure, liver disease, Vitamin K deficiency, many drugs
Target Range of INR
- 2.5 - 3.5: Mechanical prosthetic valves or recurrent thromboembolism
- 2.0 - 3.0: All other indications
Pediatric Dosing
Safety and efficacy not well-established, though it is sometimes used in pediatrics for VTE treatment
Special Populations
- Pregnancy Rating: Contraindicated (Category D)
- Lactation risk: infant risk minimal
- Renal Dosing: caution advised
- Hepatic Dosing: consider decreased dose
Contraindications
- Allergy to class/drug
- Active bleeding or tendency to bleed
Adverse Reactions
- Bleeding
- Risk increased when INR >3
- Exponential increase when INR >5
- Avoid giving NSAIDs, sulfas, macrolidies (azithromycin ok), fluoroquinolones
- Skin necrosis
- Usually in patient with protein C deficiency
- Occurs 3 - 8 days after starting treatment
- Treatment: see Warfarin (Coumadin) Reversal
Pharmacology
- Half-life: 20-60h (anticoagulant effect)
- Of note, half-life highly variable based on rate of clotting factor catabolism
- Metabolism: Liver
- Excretion: Urine 92%, bile
- Mechanism of Action:
- Blocks activation of vitamin K dependent prothrombotic factors II, VII, IX, X
- Blocks synthesis of vitamin K dependent antithrombotic proteins C and S
- Albumin bound
Comments
- Because of differing factor half-lives, can cause transient (24-36 hour) prothrombosis at start of therapy
- Bridge with heparin for 1-2 days until INR is in desired range