Warfarin drug interactionsPublished on Anticoagulation Services(https://depts.washington.edu/anticoag/home)

Warfarin drug interactions

Drug Interaction Classification SystemsSignificanceRating (A)

Criteria ManagementRating (B)

Criteria

0 Not listed 0 Not listed1 Severity - Major: The effects are potentially

life-threatening or capable of causing permanentdamage.Documentation: interaction is suspected,probable or established

1 Avoidcombination

2 Severity - Moderate: The effects may causedeterioration in a patient's clinical status.Additional treatment, hospitalization, or anextended hospital stay may be necessary.Documentation: interaction is suspected,probable or established

2 Usually avoidcombination

3 Severity - Minimal: The effects are usually mild;consequences may be bothersome orunnoticeable but should not significantly affect thetherapeutic outcome. Additional treatment isusually not required.Documentation: interaction is suspected,probable or established

3 Minimize risk

4 Severity – Major or ModerateDocumentation: Interaction is possible

4 No actionneeded

5 Severity: MinorDocumention: possibleORSeverity: Major, Moderate or MinorDocumentation: interaction is unlikely

5 No interaction

A. Tatro DS (ed). Drug Interaction Facts. St Louis MO: Wolters Kluwer, 2010B. Hansten P,Horn J. Drug Interactions Analysis and Management. St Louis MO: Wolters Kluwer 2010.

Drug/Drug

ClassEffect on

INRProposed

MechanismSignificance

(A)Managemen

t (B)acarbose increased Unexplained

Mechanisms4 0

acetaminophen

increased Inhibition ofWarfarin

Metabolism

2 3

alcohol(acute use)

increased Inhibition ofWarfarin

4 3

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Metabolismalcohol(chronic

use)

decreased Induction ofWarfarin

Metabolism

4 3

allopurinol increased Inhibition ofWarfarin

Metabolism

4 3

aminoglutethamide

decreased Induction ofWarfarin

Metabolism

2 3

amiodarone increased Inhibition ofWarfarin

Metabolism

1 3

amitriptyline increased Inhibition ofWarfarin

Metabolism

0 4

Androgens increased UnexplainedMechanisms

1 2

aprepitant decreased Induction ofWarfarin

Metabolism

4 3

ascorbicacid

decreased UnexplainedMechanisms

5 3

aspirin/salicylates

no effect IncreasedBleeding

Risk

1 2

azathioprine decreased UnexplainedMechanisms

2 3

azithromycin

increased Inhibition ofWarfarin

Metabolism

1 5

Azole Antifungals

increased Inhibition ofWarfarin

Metabolism

1 3

Barbiturates

decreased Induction ofWarfarin

Metabolism

1 2

bosentan decreased Induction ofWarfarin

Metabolism

2 3

capecitabine

increased Inhibition ofWarfarin

Metabolism

1 3

carbamazepine

decreased Induction ofWarfarin

Metabolism

2 3

carboplatin increased UnexplainedMechanisms

1 0

celecoxib increased Inhibition ofWarfarin

Metabolism

1 4

Cephalosporins

increased DecreasedSynthesis of

ClottingFactors

2 2

chloralhydrate

increased ProteinBinding Disp

lacement

3 3

chloramphe increased Inhibition of 2 0©2014 University of Washington

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nicol WarfarinMetabolism

cholestyramine

decreased ReducedAbsorptionof Warfarin

2 3

cimetidine increased Inhibition ofWarfarin

Metabolism

1 2

ciprofloxacin increased Inhibition ofWarfarin

Metabolism

1 3

clarithromycin

increased Inhibition ofWarfarin

Metabolism

1 3

clofibrate increased UnexplainedMechanisms

1 2

clopidogrel/ticlopidine

no effect IncreasedBleeding

Risk

0 4

colestipol decreased ReducedAbsorptionof Warfarin

2 3

Contraceptives, Oral

decreased IncreasedClotting

Factor Synthesis/Activity

0 2

Corticosteroids

either UnexplainedMechanisms

2 4

cyclophosphamide

increased UnexplainedMechanisms

1 3

cyclosporin decreased UnexplainedMechanisms

4 4

delavirdine increased Inhibition ofWarfarin

Metabolism

4 0

diazoxide increased ProteinBinding Disp

lacement

0 4

dicloxacillin decreased Induction ofWarfarin

Metabolism

2 4

diltiazem increased UnexplainedMechanisms

0 4

DirectThrombin

Inh.

increased Additive AnticoagulantResponse

2 0

disopyramide

increased UnexplainedMechanisms

5 4

disulfiram increased Inhibition ofWarfarin

Metabolism

2 2

efavirenz increased Inhibition ofWarfarin

Metabolism

4 0

erythromycin

increased Inhibition ofWarfarin

Metabolism

1 3

ethacrynic increased Protein 4 4©2014 University of Washington

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acid Binding Displacement

ethcholvynol

decreased Induction ofWarfarin

Metabolism

2 3

etoposide increased UnexplainedMechanisms

1 0

felbamate increased UnexplainedMechanisms

4 4

fenofibrate increased UnexplainedMechanisms

1 3

fluorouracil increased Inhibition ofWarfarin

Metabolism

1 3

fosphenytoina

either Induction orInhibition of

WarfarinMetabolism

2 3

gefitinib increased UnexplainedMechanisms

2 0

gemcitabine increased UnexplainedMechanisms

1 3

gemfibrozil increased UnexplainedMechanisms

1 2

glutethamide

decreased Induction ofWarfarin

Metabolism

2 2

glyburide increased UnexplainedMechanisms

0 3

griseofulvin decreased Induction ofWarfarin

Metabolism

2 3

heparin/LMWHs

increased Additive AnticoagulantResponse

0 3

ifosfamide increased Inhibition ofWarfarin

Metabolism

4 0

influenzavaccine

increased UnexplainedMechanisms

4 4

isoniazide increased Inhibition ofWarfarin

Metabolism

4 3

isotretinoin increased UnexplainedMechanisms

4 4

leflunamide increased Inhibition ofWarfarin

Metabolism

4 0

levofloxacin increased Inhibition ofWarfarin

Metabolism

1 4

lovastatin increased Inhibition ofWarfarin

Metabolism

1 3

mefloquine increased UnexplainedMechanisms

4 3

menthol decreased UnexplainedMechanisms

4 4

mercaptopu decreased Unexplained 2 3©2014 University of Washington

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rine Mechanismsmesalamine increased Unexplained

Mechanisms4 3

methimazole

decreased ReducedCatabolismof Clotting

Factors

1 3

metronidazole

increased Inhibition ofWarfarin

Metabolism

1 2

mineral oil increased UnexplainedMechanisms

5 4

mitotane decreased Induction ofWarfarin

Metabolism

4 3

moxifloxacin increased Inhibition ofWarfarin

Metabolism

1 0

nafcillin decreased Induction ofWarfarin

Metabolism

2 3

nalidixicacid

increased Inhibition ofWarfarin

Metabolism

2 3

neomycin increased ImpairedVitamin KProduction

by Gut Flora

5 3

norfloxacin increased Inhibition ofWarfarin

Metabolism

1 3

NSAIDs no effect IncreasedBleeding

Risk

1 2

ofloxacin increased Inhibition ofWarfarin

Metabolism

1 3

omeprazole increased Inhibition ofWarfarin

Metabolism

4 4

orlistat increased Inhibition ofWarfarin

Metabolism

4 4

paclitaxel increased UnexplainedMechanisms

1 0

phenytoina decreased Induction orInhibition of

WarfarinMetabolism

2 3

prasugrel no effect IncreasedBleeding

Risk

0 0

primidone decreased Induction ofWarfarin

Metabolism

1 2

progestins increased UnexplainedMechanisms

4 4

propafenone increased Inhibition ofWarfarin

4 3

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Metabolismpropoxyphe

neincreased Unexplained

Mechanisms4 3

propranolol increased UnexplainedMechanisms

4 4

propylthiouracil

decreased ReducedCatabolismof Clotting

Factors

1 3

ProteaseInhibitors

decreased UnexplainedMechanisms

4 3

quinidine increased Inhibition ofWarfarin

Metabolism

1 3

quinine increased Inhibition ofWarfarin

Metabolism

1 0

reserpine increased UnexplainedMechanisms

0 4

ribavirin decreased UnexplainedMechanisms

4 3

Rifamycins decreased Induction ofWarfarin

Metabolism

2 2

rofecoxib increased Inhibition ofWarfarin

Metabolism

1 4

simethicone decreased ReducedAbsorptionof Warfarin

0 4

simvastatin increased Inhibition ofWarfarin

Metabolism

1 4

spironolactone

decreased Hemoconcentration of

ClottingFactors

5 4

SSRIs increased Inhibition ofWarfarin

Metabolism

4 3

sucralfate decreased ReducedAbsorptionof Warfarin

5 3

SulfaAntibiotics

increased Inhibition ofWarfarin

Metabolism

1 3

Sulfinpyrazone

increased Inhibition ofWarfarin

Metabolism

1 2

tamoxifen increased UnexplainedMechanisms

4 0

telithromycin

increased Inhibition ofWarfarin

Metabolism

1 4

temafloxacin

increased Inhibition ofWarfarin

Metabolism

1 4

terbinafine decreased Induction ofWarfarin

4 0

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Metabolismtestosterone increased Unexplained

Mechanisms4 0

Tetracyclines

increased ImpairedVitamin KProduction

by Gut Flora

1 3

ThiazideDiuretics

decreased Hemoconcentration of

ClottingFactors

5 4

Thrombolytics

increased Additive AnticoagulantResponse

1 0

ThyroidHormones

increased IncreasedCatabolismof Clotting

Factors

1 3

tolterodine increased UnexplainedMechanisms

4 4

tramadol increased UnexplainedMechanisms

2 0

trazodone decreased UnexplainedMechanisms

2 4

trastuzumab increased UnexplainedMechanisms

4 0

vitamin E increased DecreasedSynthesis of

ClottingFactors

1 3

vitamin K decreased IncreasedClotting

Factor Synthesis/Activity

2 3

zafirlukast increased Inhibition ofWarfarin

Metabolism

0 3

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