Apixaban in an Older Adult With a GI Bleed and Strong CYP3A4 Inhibition
An 82-year-old man with atrial fibrillation, heart failure, and chronic kidney disease comes to the pharmacy for a refill of apixaban. His cardiologist started apixaban 5 mg twice daily two weeks ago. Today he reports three days of dark, tarry stools and fatigue. His blood pressure is 138/82 mmHg, heart rate 76 beats/min, and he appears pale. Recent labs: hemoglobin 9.8 g/dL (baseline 13.0), serum creatinine 1.7 mg/dL, weight 58 kg, height 168 cm. His medications include ketoconazole 200 mg daily for a nail infection, diltiazem 120 mg daily, aspirin 81 mg daily, and furosemide 40 mg daily. He says the cardiologist told him apixaban was 'the best blood thinner' and that no dose adjustment was needed. The pharmacy's computer flags a drug interaction but does not specify a dose recommendation. He asks whether he should double the apixaban dose because he missed one dose yesterday.
1. Calculate the patient's creatinine clearance and assess whether the apixaban dose is appropriate.
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Using Cockcroft-Gault:
CrCl = [(140 − age) × weight kg] ÷ (72 × SCr mg/dL) = [(140 − 82) × 58] ÷ (72 × 1.7) = (58 × 58) ÷ 122.4 = 3,364 ÷ 122.4 ≈ 27.5 mL/min.
Apixaban dose reduction is recommended when at least two of the following are present: age ≥80 years, weight ≤60 kg, or serum creatinine ≥1.5 mg/dL. This patient meets all three: age 82, weight 58 kg, SCr 1.7 mg/dL. The appropriate dose is therefore apixaban 2.5 mg twice daily, not 5 mg twice daily.
His CrCl of about 27.5 mL/min also warrants caution, but apixaban can be used in severe renal impairment with clinical judgement and close monitoring. The higher 5 mg twice-daily dose increases bleeding risk in a patient who already has multiple risk factors.
2. How do the interacting drugs and the dark stools change the assessment?
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The dark, tarry stools plus a hemoglobin drop from 13.0 to 9.8 g/dL indicate a probable gastrointestinal bleed until proven otherwise. This is an urgent finding, not a routine refill issue.
Interaction and risk analysis:
- Ketoconazole is a strong CYP3A4 and P-glycoprotein inhibitor. It can substantially increase apixaban exposure and bleeding risk.
- Diltiazem is a moderate CYP3A4/P-gp inhibitor and adds to the interaction burden.
- Aspirin 81 mg adds irreversible platelet inhibition on top of anticoagulation.
- Age, low weight, CKD, and anemia further increase bleeding risk.
Doubling the apixaban dose after a missed dose would be dangerous. A missed dose should generally be taken as soon as remembered on the same day, then the usual schedule resumed; doses should not be doubled. The immediate priority is to hold apixaban, arrange urgent medical evaluation for the GI bleed, check CBC and renal function, and reassess the need for aspirin and ketoconazole.
3. What should the pharmacist recommend to the prescriber, and what counseling is needed after discharge?
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Recommendations to the prescriber:
- Do not continue apixaban 5 mg twice daily. If anticoagulation is resumed after the bleed is evaluated, the reduced dose of 2.5 mg twice daily is appropriate based on age, weight, and SCr.
- Stop ketoconazole or choose a non-interacting antifungal if possible. Continuing a strong CYP3A4/P-gp inhibitor with apixaban markedly increases exposure.
- Reassess aspirin. If there is no clear secondary-prevention indication, deprescribing aspirin reduces bleeding risk.
- Evaluate the GI bleed urgently; transfusion, endoscopy, and reversal strategies may be needed depending on severity.
After discharge, counsel the patient to:
- Take apixaban exactly as prescribed, approximately 12 hours apart; do not double a missed dose.
- Report black stools, vomiting blood, unusual bruising, nosebleeds, or severe headache immediately.
- Avoid NSAIDs and new supplements unless approved; tell every prescriber and dentist about apixaban.
- Keep follow-up labs for hemoglobin, renal function, and signs of bleeding. Confirm the final dose and whether aspirin should be stopped.