Warfarin
Revision as of 15:54, 22 March 2016 by Ostermayer (talk | contribs) (Text replacement - "Category:Drugs" to "Category:Pharmacology")
General
- Type:
- Dosage Forms:
- Common Trade Names: Coumadin
Adult Dosing
- Day 1: 5 - 7.5 mg oral at bedtime (to ensure absorption on empty stomach)
- Day 2 and beyond: 2.5 - 7.5 mg daily (usually 5 mg)
- 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
Special Populations
- Pregnancy Rating: Contraindicated
- Lactation risk:
- Renal Dosing
- Adult
- Pediatric
- Hepatic Dosing
- Adult
- Pediatric
Contraindications
- Allergy to class/drug
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:
- Metabolism: Liver
- Excretion:
- 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