Warfarin: 7 Ways to Keep Blood Levels in a Safe Range
This blood thinner can be tricky to manage, but these tips can help.
Many Americans take warfarin (brand name Coumadin) every day to make their blood thinner. Some are on the medication for three to nine months, for treatment of a blood clot in the leg veins or the lungs. Others are on the medication indefinitely because of atrial fibrillation, an artificial heart valve, or some other chronic condition linked to a high risk of stroke.
Warfarin is an effective and inexpensive drug, but as anyone who's been on it can tell you, it's tricky to use. It requires frequent blood tests to monitor its effect, it interacts with many common foods and medications, and it can cause serious or even life-threatening bleeding. In fact, warfarin regularly shows up on lists of the top-ten medications to cause hospitalization or serious side effects. Studies have also found that most people on warfarin are within the right range (as measured by the INR, or international normalized ratio) only about 60 percent of the time.
Fortunately, it's possible to greatly reduce one's chance of warfarin-related problems by following certain precautions to maximize the likelihood of being in the right range. Here's what to do:
1. Make sure to get dosing instructions in writing, and follow them carefully.
More than almost any other commonly used medication, warfarin requires individualized dosing that may frequently need adjustment. It's also common for a person to take different doses of warfarin, depending on the day of the week (such as 2 milligrams for five days of the week and 3 mg for two days of the week). Because of this, prescription bottles for warfarin may have vague instructions, such as, "Take as directed." This allows the clinician to change the directions without ordering a new prescription, but it also means that patients and families must be vigilant about understanding the instructions.
What to do:
Make sure any dosage instructions or changes are provided in writing.
Don't skip blood tests or appointments for checking warfarin's effects.
Make sure your doctor provides you with instructions if so-called protime or INR results (the blood tests used to monitor warfarin) are lower or higher than goal. (The goal is usually an INR between 2.0 and 3.0; a higher INR means the blood takes longer to clot.)
If you're a caregiver, make sure your loved one is able to keep up with a complicated dosing regimen, or plan on providing extra help with medications.
2. Pay extra-close attention during the first three months after starting warfarin.
Although everyone on warfarin has an increased chance of bleeding, studies have found that the risk is especially high in the first three months after starting warfarin. This probably occurs because this is when people tend to need more dose adjustments and the most monitoring.
What to do:
- Make sure to attend all INR checks and warfarin appointments, even if they seem to be frequent. Frequent appointments are usually necessary to keep new patients in range.
3. Avoid big changes in intake of leafy greens and other sources of vitamin K.
Warfarin works by interfering with the liver's use of vitamin K to make certain clotting factors. Suddenly eating more leafy greens, such as kale, spinach, and collard greens, will decrease the effectiveness of warfarin. Conversely, suddenly reducing intake of leafy greens will make the warfarin have a stronger effect, increasing the chance of bleeding.
What to do:
You don't have to avoid greens; you just need to have a stable weekly intake.
Notify your doctor if you decide to go on a spinach salad diet or otherwise make a big dietary change. Extra monitoring of your warfarin will be required.