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Difficulty: MediumPharmacologic Interventions

A 65-year-old man presents to a primary care clinic with a 4-day history of worsening cough productive of yellow sputum, subjective fevers, and fatigue. He has a past medical history of hypertension, type 2 diabetes mellitus, and hyperlipidemia. His daily medications include lisinopril, metformin, simvastatin, and low-dose aspirin. Vital signs show a temperature of 38.2°C (100.8°F), blood pressure of 134/82 mmHg, heart rate of 92/min, and respiratory rate of 18/min. Pulse oximetry is 96% on room air. Physical examination reveals crackles in the right lower lung base. A chest radiograph demonstrates a right lower lobe infiltrate. The physician diagnoses community-acquired pneumonia. Given the patient's comorbidities, he is prescribed an outpatient oral regimen of amoxicillin-clavulanate and clarithromycin. Which of the following is the most appropriate modification to this patient's chronic medication regimen during his antibiotic therapy?

  1. Temporarily withhold simvastatin for the duration of the antibiotic courseAnswer
  2. B
    Administer clarithromycin and simvastatin at least 12 hours apart
  3. C
    Continue all current medications and check serum creatine kinase in 3 days
  4. D
    Switch simvastatin to atorvastatin for the duration of therapy
  5. E
    Reduce the daily dosage of simvastatin by 50%

Answer

Temporarily withhold simvastatin for the duration of the antibiotic course.
The correct action is to temporarily withhold simvastatin for the duration of the antibiotic course. Clarithromycin is a potent inhibitor of the cytochrome P450 3A4 (CYP3A4) isoenzyme, which is responsible for the hepatic metabolism of simvastatin. Coadministration of these two drugs significantly elevates simvastatin serum concentrations, markedly increasing the risk of severe statin-induced myopathy and life-threatening rhabdomyolysis. Because of this well-established and predictable interaction, the concurrent use of simvastatin (or lovastatin) and clarithromycin is absolutely contraindicated by the FDA. The safest and most practical management strategy for a patient requiring a short course of a strong CYP3A4 inhibitor is to simply pause the statin therapy until the antibiotic course is completed, as a brief interruption in lipid-lowering therapy poses no acute cardiovascular risk.

Step-by-Step Solution

1
Analyze the prescribed antibiotic regimen for potential drug-drug interactions.
Clarithromycin is identified as a potent inhibitor of the cytochrome P450 3A4 (CYP3A4) isoenzyme.
Macrolides (excluding azithromycin) are notorious for causing significant pharmacokinetic interactions by inhibiting hepatic enzymes.
2
Evaluate the patient's chronic medications to identify CYP3A4 substrates.
Simvastatin is identified as a major substrate of CYP3A4.
Inhibition of CYP3A4 drastically decreases the clearance of simvastatin, leading to toxic serum concentrations.
3
Determine the appropriate clinical intervention to mitigate the identified interaction.
The concurrent use of clarithromycin and simvastatin is absolutely contraindicated; the statin must be withheld.
To prevent severe adverse effects such as myopathy and rhabdomyolysis, the offending medication (simvastatin) should be paused during the short course of the antibiotic.

Key Concept

Management of pharmacokinetic interactions between strong CYP3A4 inhibitors (clarithromycin) and CYP3A4 substrates (simvastatin).
Estimated Time:1m 0s
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Topics

Pharmacologic Interventions

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