Q: I have atrial fibrillation and take Coumadin to prevent a stroke. I have not had any problem with it. But I wonder if I should switch to one of the newer drugs instead of Coumadin. What's your opinion?

A: For 50 years, warfarin (Coumadin) was the only choice for people that needed to take an oral anticoagulant drug. While warfarin is inexpensive, it has downsides. People taking it require regular blood testing to be sure the dose is correct. The blood test, called an INR, needs to fall into a predetermined range. A result within the proper range means the person's blood is "thin" enough not to clot easily but not "too thin" to cause a high bleeding risk.

Studies have shown that many people on warfarin frequently have an INR out of the desired range. This makes their blood clot prevention ineffective or puts them at risk for significant bleeding. Taking the wrong dose and missing doses clearly affect the INR test result. But even when a person takes the dose exactly as prescribed, dietary changes and interactions with other medications can change the INR dramatically.

Now new oral anticoagulants are available that are just as effective as warfarin at preventing a stroke in people with atrial fibrillation and normal heart valves. These drugs are known as direct oral anticoagulants (DOACs). The advantages of DOACs; they don't require regular blood tests, have no food restrictions and have fewer drug interactions. The downside: they are much more expensive than warfarin.

To consider switching to a DOAC, you need to have adequate kidney function. This is determined by a blood test for creatinine and glomerular filtration rate (GFR). People with a very lower GRF cannot safely take these new drugs.

Here's what I discuss with patients like you who are thinking of making a switch from warfarin to a DOAC.

Let's make sure you can afford it. This may take some investigation by you to determine if insurance covers a DOAC or you can get the drug at a substantial discount.

If your insurance only covers dabigatran (Pradaxa) and apixaban (Eliquis), it means you need to faithfully take the drug twice per day rather once a day for warfarin. The other DOACs, rivaroxaban (Xarelto) and edoxaban (Savaysa), are once-a-day drugs. Missing a dose puts you at risk of stroke.

The DOACs are short acting drugs, while warfarin keeps acting for well over 24 hours. So if you tend to miss doses of your medications often, you probably want to stick with warfarin.

Staying on warfarin is fine option if your INR blood tests stay in the desired range (2.0 to 3.0) at least 70 percent of the time, meaning you don't need frequent dose adjustments and getting regular blood tests is not a hassle.

(Howard LeWine, M.D., is an internist at Brigham and Women's Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit www.health.harvard.edu.)

(c) 2019 PRESIDENT AND FELLOWS OF HARVARD COLLEGE. ALL RIGHTS RESERVED. DISTRIBUTED BY TRIBUNE CONTENT AGENCY, LLC.