When the NOACs (sometimes referred to as DOACs) first came out they were heavily promoted as having fewer drug interactions compared to warfarin. This is true, but please remember that “fewer drug interactions” doesn’t mean “no drug interactions”! Here’s a scenario of the carbamazepine apixaban interaction and some potential strategies to manage it.
A 72-year-old has a past medical history of atrial fibrillation, hypertension, hypercholesterolemia, osteoarthritis, and painful trigeminal neuralgia. He was recently transitioned off of warfarin to apixaban. The primary reason for this was he was tired of having to do INR’s every month. A secondary reason was the new guideline recommendations regarding preference for NOACs in atrial fibrillation.
The major drug interaction with his medications was the carbamazepine apixaban interaction. Carbamazepine is a strong enzyme inducer and can substantially lower concentrations of apixaban. The same thing can also happen with warfarin, but we can adjust by monitoring INR.
Carbamazepine Apixaban Interaction Management
With this drug interaction, it is recommended to avoid using these medications together. If this is the goal, then your objective is simple. You must change either the carbamazepine or the apixaban to avoid the drug interaction.
Changing the Carbamazepine
In this patient scenario, carbamazepine is being used for the indication of trigeminal neuralgia. Trying to wean off this medication to avoid the carbamazepine apixaban interaction would probably be the ideal strategy. This is totally dependent upon the effectiveness of the drug and the patient’s desire to continue with it. It is essential to consider the patient’s goals, past history, and desires in doing any sort of transition or discontinuation.
While carbamazepine has the best evidence in the setting of trigeminal neuralgia, other options might be considered. Gabapentin and baclofen are two agents that I have seen used in the past.
Going Back to Warfarin
If the carbamazepine has had life-altering benefit and the patient will not go without it, we would be between a rock and a hard place. However, if the only reason that the patient wanted to switch to the apixaban was due to less lab monitoring, they might continue to accept the inconvenience of routine INR’s to continue with the carbamazepine.
Adjusting Doses to Compensate for the Interaction
What about leaving it and adjusting doses? The problem with this strategy is that we aren’t really sure how much apixaban concentrations are going to be affected by the interaction. This could vary greatly due to a whole host of factors like dosing, genetics, adherence, etc. So while we know that concentrations of apixaban will likely be subtherapeutic with carbamazepine on board, we don’t know exactly by how much. Here’s a great case example of a patient on low dose carbamazepine where the concentrations weren’t affected much by this interaction.
A Different NOAC to Avoid the Apixaban Carbamazepine Interaction
The most commonly used NOAC I’m seeing used in practice (with the exception of apixaban) is rivaroxaban. Unfortunately, this has the same interaction risk with carbamazepine as apixaban. This likely is not going to be a great option either.
As you can see, managing drug interactions can be tricky and the approach is going to depend upon a variety of clinical factors.
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