Pneumonia and Warfarin

By: Alere Staff
Publication Date: Thu, 01/01/2015

Pneumonia and Warfarin

Pneumonia is an infection in one or both of your lungs that can be caused by bacteria, viruses or fungi. Pneumonia is not a single disease and can have more than 30 different causes. According to the American Lung Association, approximately one-third of the pneumonia cases in the United States each year are caused by different respiratory viruses.1 As we enter into the season well-known for spreading illnesses, it is important to be aware of what pneumonia is and whether or not it can affect your INR levels.

Pneumonia Symptoms

Our bodies are designed to catch bacteria and other germs before they enter our bodies. For example, the hairs in our nose filter germs from the air taken in through breathing.However, germs can sometimes find a way to get past these safeguards, particularly if your immune system is weak or if the sickness you are up against is stronger than usual.

When a germ that causes pneumonia gets through to your lungs, the air sacs in the lungs, called aveoli, will become inflamed and fill up with fluid. This will cause the common symptoms of pneumonia such as coughing, trouble breathing, fever and chills.1 Once a person becomes infected with pneumonia, their body may have trouble getting enough oxygen into their blood. Too little oxygen in your blood can cause more serious issues as your body’s cells will not be able to fully function.1

Who is At Risk for Pneumonia?

Pneumonia has many causes and different germs attribute to its development. The five main causes of pneumonia include: bacteria, viruses, mycoplasmas, infectious agents like fungi and various chemicals. The flu virus itself is the most common cause of viral pneumonia in adults and, when you have viral pneumonia, you are still at risk to get bacterial pneumonia as well.1

While anyone at any age can get pneumonia, there are several risk factors that can make a person more likely. Some risk factors include:1

  • Recent viral respiratory infection
  • Cigarette smoking
  • Age 65 or older
  • Lung disease (like asthma or COPD)
  • Difficulty swallowing (due to stroke, dementia or other neurological conditions)
  • Serious illnesses like diabetes, heart failure or sickle cell anemia
  • Weakened or suppressed immune system


Medications used to treat pneumonia depend on the cause of the disease as well as the severity of the symptoms. For example, pneumonia that is caused by bacteria is treated with antibiotics. If you have an underlying condition such as asthma, your doctor may prescribe an inhaler and even steroids. It is known that most antibiotics used to treat pneumonia can alter the anticoagulant effects of warfarin by increasing warfarin’s effectiveness. Patients who are on warfarin are advised to monitor their INR closely during their antibiotic therapy.2 Any time you start a new medication or become ill, it is important you tell the doctor prescribing your warfarin of the change. With proper treatment, most patients with pneumonia may improve within two weeks.1

While pneumonia is a sickness that can’t always be avoided, your best defense is to stay healthy, active and make sure you get your flu shot before the season begins.


  1. American Lung Association. Understanding Pneumonia. Retrieved December 17, 2014 from the ALA website at
  2. Mills, K PharmD, BCPS et al. Treatment of Nursing-Home Acquired Pneumonia. American Family Physician. 2009 Jun 1; 79(11):976-982.