Managing coumadin and INR

There are no formal protocols or guidelines for adjusting warfarin dosing and many providers practice differently. In my experience, I do not typically initiate warfarin. However, there are several patients already on coumadin you will likely manage as a PCP.  If you do need to initiate, this is a good resource: www.WarfarinDosing.org/Source/Home.aspx. Some patients go to a coumadin clinic to manage or have point of care testing they can use at home; however, many rely on their PCP. When possible, I try to switch patients over to a DOAC like Xarelto or Eliquis because they are easier to manage and have less drug/diet interactions. 

There are many indications for use of warfarin for prophylaxis and treatment, especially prosthetic heart valves and antiphospholipid syndrome. For most patients, a DOAC is preferred but may not be an option due to cost or severe kidney or liver disease. 

Indications for warfarin: 

• A-fib 
• Acute coronary syndrome 
• Heart failure 
• Prosthetic heart valve 
• Stroke 
• DVT
• Pulmonary embolism 

Maintenance dosing 

• Range can vary significantly from patient to patient from <2 to >10 mg/day
• Dose based on INR levels 
• Typical INR target range 2-3 (can be higher around 2.5-3.5 for certain patients, can consult with cardiologist to find the target range they recommend

Monitoring 

• I usually put in a standing INR lab order for a year so patients can get them drawn anytime and I do not have to continue to put in orders every time 
• Frequency of monitoring depends on the patient and stability of INR levels 
• INR goal 2-3 for most patients 
• <2 blood too thick, risk for clots 
• >3 blood too thin, risk for bleeding
• Stable patients- typically every 4 weeks 
• Outside therapeutic range: more frequently, 1 or more times/week 
• It takes at least 2 days for the INR labs to reflect the dose change 

• Add previous 7 days of warfarin dosing (mg of warfarin per week) and use that total to calculate the percentage changes 
• Distribute the increase or decrease in warfarin dose per week over the following week as evenly as possible 
• Example: 30mg warfarin per week with INR 1.8- increase by 10%
• 30mg x 10% = 3mg 
• 30mg + 3mg = 33mg = new weekly dose 
• Distribute throughout the week as 5mg daily 5 days/week and 4mg 2 days/week OR 5mg 6 days/week and 3 mg the remaining day of the week. 

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Allison Sowders, CNP