Warfarin: All Day, Every day!

Posted by Unknown at Saturday, September 05, 2015

It's been 15 weeks and 3 rotations since we started P4 year, which is both incredible and terrifying. My most recent rotation was centered on pharmacy within an ambulatory care setting. I was stationed at an outpatient anticoagulation clinic and the care I was able to provide patients exceeded my expectations. Although I knew going into the rotation that it would be focused on cardiology and blood thinners, I had no idea how immersed in it I would become.

The pharmacists I worked with handle a special, high-risk population of patients who need anticoagulation because they have an LVAD (left ventricular assist device) implanted inside them. These patients need increased monitoring because they are at increased risk to clot. Any foreign substance within the body has the potential to put you at a higher risk for clots as blood will stick to it.

My day usually started by following up with patients who had recently been discharged from the hospital. Although the patient is technically off our service while admitted, we still follow their INRs and report any medication changes. Many times, someone will come home on a new antibiotic that has the potential to affect the INR. About 90% of antibiotics will increase your INR, but nafcillin and rifampin significantly reduce it. In fact, we dealt with a patient who was on a 6 week home course of nafcillin due to MSSA bacteremia. We had to empirically adjust his warfarin dose by doubling it, which is a huge dose change when it comes to warfarin.

I also helped the pharmacist counsel patients who were being started on the new oral anticoagulants termed "DOACs" (direct oral anticoagulant). These include rivaroxaban, apixaban, and dabigatran. They don't need the same kind of monitoring as warfarin does, nor do they require the consistent diet of vitamin K as warfarin, but they are extremely expensive.

Finally, I was able to create "bridging calendars" and provide instructions to patients who had upcoming surgeries. For patients on warfarin, surgeries are tricky as you don't want them to have thin blood during the surgery, but you need to prevent a thromboembolism in the pre-operative period. This is where a low molecular weight heparin such as enoxaparin comes in. They have a much shorter duration of action, which means a patient can take this drug up to the day of surgery while in the interim of stopping the warfarin. Therefore, the warfarin gets out of their system, but they are still protected against clots. The decision if a patient needs bridging is based on their thromboembolism risk classification. High risk patients almost always need bridging and low risk patients almost always don't. However, when it comes to intermediate risk patients, it is based on patient and surgery characteristics. One of my projects while at this rotation was to review the new BRIDGE trial, published in June of 2015 and see how we could apply it at my rotation. Essentially, it showed that bridging for patients with atrial fibrillation in an intermediate risk category is not recommended.

Overall, this rotation taught me a ton about cardiology and pharmacy. I didn't think I was a big cardio girl until I spent all day with it. I know the knowledge I gained about anticoagulants will help me in my future rotations and career.