SK is a 77-year-old male who presents to the primary care clinic for a routine follow-up. His past medical history is significant for atrial fibrillation, hypertension, GERD, and depression. Can you identify two important drug interactions in this medication list?
Medication List:
- Diltiazem CD 240 mg once daily
- Apixaban 5 mg BID
- Omeprazole 20 mg once daily
- Citalopram 40 mg once daily
- Hydrochlorothiazide 25 mg daily
- Atorvastatin 20 mg nightly
- Multivitamin daily
Over the last two weeks, SK has reported easy bruising, occasional dizziness, and one episode of lightheadedness after standing up quickly.
There are a couple of major concerns I have in this scenario. The dizziness is obviously a concern, and the risk for falls is problematic given the use of apixaban. Easy bruising is also a concern. I would ideally like to know some labs and vital signs, with hemoglobin, blood pressure, and pulse being high on that priority list.
The first major drug interaction that I’m concerned about is diltiazem and apixaban. Recall that diltiazem can inhibit CYP3A4 and P-glycoprotein. Both of these actions can increase the concentration of apixaban. Potential resolution of this drug interaction involves reducing the dose of apixaban or considering an alternative to diltiazem for rate control.
The other of the two drug interactions to note here is omeprazole and citalopram (excellent one to remember for board exams). With the citalopram-omeprazole interaction, the concentration of citalopram can be increased due to the inhibition of CYP2C19 by omeprazole. Higher concentrations of citalopram could lead to potential adverse effects. Serotonin syndrome and QTc prolongation are two very rare, but obviously serious adverse effects that could happen with this interaction. In this case, I would look to potentially reduce the dose of citalopram to 20 mg daily. Alternatively, changing GERD therapy would also be a consideration.
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