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JAMA PATIENT PAGE  | Drug Therapy

BloodThinners

Thereare 2 typesofbloodthinners,anticoagulantsandantiplateletdrugs.

Blood clots cancauseproblemswhenthey preventbloodfromflow-

ing freely, especially to the heart and brain. Sometimes a doctor

may not want a patient’s blood to clot as easily and will prescribe

a blood thinner.

Conditions That May Benefit From an AntiplateletDrug

• Heart disease or prior heart attack

• Blood vessel disease

• Prior stroke or transient ischemic attacks

• Diabetes

• Being overweight or having metabolic syndrome

• Being a smoker

• Taking certain other medications

• Certainoperations, such as angioplasty

Conditions That May Benefit From an Anticoagulant

• Atrial fibrillation (abnormal heart rhythm)

• Prior surgery on a heart valve

• Congenital (since birth) heart defect

• Deep vein thrombosis

• Pulmonary embolism

• Pulmonary hypertension

Typesof Blood Thinners

The2 types ofbloodthinners work indifferentways(Figure).Blood-

thinningdrugs havebeen usedfor manyyears. Newermedications

are now available, but they may be more costly or less convenient

or have other drawbacks compared with older drugs. Some com-

monly used anticoagulants are heparin, enoxaparin or other low-

molecular-weight heparins,fondaparinux,and warfarin; neweran-

ticoagulants are dabigatran, rivaroxaban, and apixaban. Common

antiplatelets include aspirin, aspirin plus extended-release dipyri-

damole, clopidogrel, prasugrel, and the newer drug cangrelor.

Treatment With Blood Thinners

Antiplatelets are usually given orally. Sometimes, the anticoagulant

heparin is given continuously through the veins in the hospital.

Warfarin is started orally while a patient is receiving intravenous

heparinand is continued after theheparin is stopped. Once the INR

(internationalnormalizedratio,atestofbloodclotting)isstable,hep-arinis stoppedand thepatient continues to take warfarin after leav-

ing the hospital. It takes some care to maintain the correct level of 

warfarin. Patients must keep track of foods they eat that contain vi-

tamin K,especiallygreenleafyvegetables.Patientstypicallyhavetheir

bloodtesteddaily,thenmonthly,basedontheINR,whichshowshow

well the warfarin treatment is reducing blood clotting. Some condi-

tions require lifelong treatment with blood thinners.

Insomecircumstances,enoxaparinorfondaparinuxcanbeused

instead of heparin and/or warfarin. Although they require daily in-

 jections, they do not require routine INR testing of blood clotting.

If you are prescribed a blood thinner, be sure to tell your doc-

tor about any other medications you take. And if you are taking a

blood thinner, you need to be cautious about using over-the-

countermedicationsor herbal (dietary)supplements.Althoughsome

new anticoagulants do not interact with vitamin K, their interac-

tion with other substances hasnot been well studied.

Forming blood clot

RE D

BLOOD

CELL

Platelets, a type of blood cell,

stick together when activated

and form a plug.

BLOOD VESSEL

Antiplatelet drugs work by

making platelets less able

to stick together.Anticoagulants work by

interfering with blood-clotting

proteins.

Blood-clotting proteins react

to form a protein network,

trapping the platelets and

strengthening the clot.

FORMOREINFORMATION

• National Library of Medicine

www.nlm.nih.gov/medlineplus/bloodthinners.html 

www.nlm.nih.gov/medlineplus/bloodclots.html 

To findthisand previous JAMA Patient Pages,go to thePatient

Page linkon JAMA’swebsiteat  jama.com. Many areavailable in

English and Spanish.

Author: Deborah TolmachSugerman,MSW

Conflictof InterestDisclosures:Theauthor hascompleted andsubmittedthe

ICMJE FormforDisclosureof PotentialConflictsof Interest andnonewere

reported.

Source: BonowRO etal.Braunwald’sHeart Disease:A Textbookof Cardiovascular 

Medicine . 9th ed. Philadelphia,PA: Elsevier Sanders; 2012:chap87.

Correction: This articlewas correctedfor a typo on August6, 2014.

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