Heparin: Drug Interactions & Contraindications

Instructor: Alexandra Unfried

Alexandra earned her master's degree in nursing education and is currently a hospital supervisor/administrator.

Heparin is an anticoagulant that prevents and treats blood clots. It is also known as a blood thinner. This lesson will discuss the drug interactions and contraindications of heparin.


Becky is a fifty-year-old woman with a history of urinary tract infection and peptic ulcer disease. She is admitted to the hospital for a myocardial infarction (heart attack). Becky is stable, but the doctor is starting her on heparin subcutaneously (SQ) to prevent blood clots from forming. This is a standard approach to treatment, but Becky is wondering what the drug interactions are, and if she has any contraindications to taking heparin.


Heparin is an anticoagulant that is given for many different reasons to treat and prevent blood clots. An anticoagulant is a medication that prevents blood clots by increasing the clotting time of blood. Some of the common conditions for which heparin is used include deep vein thrombosis (DVT), myocardial infarction or acute coronary syndrome (heart attack), atrial fibrillation (heart arrhythmia), pulmonary embolism (PE), embolic stroke, and before surgery. Heparin can be given SQ or intravenously (IV) depending on the diagnosis. With heparin being an anticoagulant, there are risks for bleeding, so it is important to understand the drug interactions and contraindications before taking the medication.

Blood clot in the artery

Heparin Drug Interactions

Heparin has interactions with many other drugs. While the list is vast, the most significant interaction that heparin has with other drugs is increased risk of bleeding. Any medication that has a risk of bleeding as a side effect will also increase the risk when simultaneously taking heparin. Another key interaction is a decreased effectiveness of heparin when taken with other drugs. With this in mind, it is important to discuss any medications already being taken with one's doctor before starting heparin. Even though some drugs interact with heparin, they are still acceptable to take under a doctor's directions. However, there are several drugs that must be avoided due to extreme and life-threatening adverse reactions. Examples of these drugs include:

Drugs that Increase the Risk of Bleeding:

  • Other anticoagulants (ex. Coumadin/warfarin, Lovenox/enoxaparin)
  • Platelet inhibitors (medications that slows down the clotting ability of platelets; ex. Aspirin, Plavix, Persantine)
  • Quinine drugs (anti-parasite medications; ex. Hydroxychloroquine)

Drugs that Decrease the Effectiveness of Heparin:

  • Antihistamines (ex. Allegra, Benadryl)
  • Digoxin (heart medication)
  • Tetracycline antibiotics (broad spectrum antibiotics)

Drugs that Must be Avoided:

  • Corticorelin (diagnostic agent) causes severe low blood pressure and low heart rate.
  • Defibrotide (anticoagulant) decreases clot forming in the blood that can lead to hemorrhage.
  • Mifepristone (synthetic steroid used to terminate pregnancy) increases excessive bleeding/hemorrhage.
  • Prothrombin complex concentrate, human (vitamin K antagonist reversal) increases the risk for bleeding/hemorrhage

Other drugs that interact with heparin are nicotine and alcohol. Smoking may decrease the effectiveness of heparin. Alcohol use may increase the risk of stomach bleeding if used daily. These activities should be avoided while on heparin.

After reviewing the list of drug that have interactions with heparin, Becky tells her doctor that she is taking a tetracycline antibiotic for a urinary tract infection. The doctor tells her that the heparin may not be as effective while taking tetracycline antibiotics. He will look into changing her antibiotic to something else that will treat her urinary tract infection without interacting with the heparin. Now she is wondering about other contraindications she needs to know about.


A contraindication is a situation in which any drug, medication, disease, or treatment should not be used because it may be harmful to the person. For example, any situation that already has a risk for bleeding becomes more risky when heparin is added.

Heparin should not be used in the following situations:

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account