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Difficulty: MediumMedical History Evaluation

During morning rounds on the medical ward, a physician evaluates a 62-year-old man who was admitted overnight with a 3-day history of profound generalized muscle weakness, severe myalgias, and dark brown urine. The patient has a background of ischemic heart disease, hypertension, and mixed dyslipidemia, which are managed chronically with daily aspirin, metoprolol, ramipril, and simvastatin. Upon reviewing the electronic health record, the physician notes that 10 days prior, the patient visited an out-of-state urgent care clinic for a high fever and productive cough. He was diagnosed with community-acquired pneumonia and completed a 7-day course of an oral antimicrobial agent. Current laboratory studies reveal a serum creatinine of 2.62.6 mg/dL (baseline 1.11.1 mg/dL) and a creatine kinase level of 14,50014,500 U/L. Which of the following antimicrobial agents, if identified during a reconciliation of the patient's recent medical history, most likely precipitated his current clinical condition?

  1. ClarithromycinAnswer
  2. B
    Azithromycin
  3. C
    Levofloxacin
  4. D
    Doxycycline
  5. E
    Amoxicillin-clavulanate

Answer

Clarithromycin
The correct answer is clarithromycin because it is a potent inhibitor of the cytochrome P450 3A4 (CYP3A4) enzyme. Simvastatin is heavily dependent on CYP3A4 for hepatic clearance. When these two medications are taken concurrently, simvastatin metabolism is blocked, leading to toxic serum concentrations. This accumulation causes severe statin-induced myopathy, progressing to frank rhabdomyolysis (evidenced by the markedly elevated creatine kinase). The subsequent release of myoglobin into the bloodstream causes pigment-induced acute kidney injury (evidenced by the elevated creatinine and dark urine). A comprehensive medical history evaluation requires reconciling recent acute prescriptions with chronic maintenance medications to identify such dangerous pharmacokinetic interactions.

Step-by-Step Solution

1
Analyze the patient's presenting symptoms and acute laboratory findings.
The patient exhibits severe muscle weakness, dark urine, grossly elevated creatine kinase (14,500 U/L), and acute kidney injury (creatinine 2.6 mg/dL).
This constellation of findings confirms a diagnosis of acute rhabdomyolysis with secondary pigment-induced acute kidney injury.
2
Review the patient's chronic medication list for potential precipitants of this condition.
The patient is chronically taking simvastatin, an HMG-CoA reductase inhibitor.
Statins carry a known, dose-dependent risk of myopathy and rhabdomyolysis, particularly when their hepatic clearance is impaired.
3
Evaluate the recent medical history for new variables that alter the pharmacokinetics of the chronic medications.
The patient recently completed a course of antibiotics for community-acquired pneumonia. Simvastatin is primarily metabolized by the hepatic cytochrome P450 3A4 (CYP3A4) enzyme.
Connecting the recent acute illness treatment to the chronic medication profile is the core of thorough medical history evaluation.
4
Determine which of the potential antibiotic treatments is a potent CYP3A4 inhibitor.
Clarithromycin is a macrolide antibiotic that strongly inhibits CYP3A4, whereas the other options do not.
Identifying the specific drug-drug interaction explains the sudden toxic accumulation of simvastatin and the resulting clinical disaster.

Key Concept

Patients on CYP3A4-metabolized statins (like simvastatin) are at high risk for severe rhabdomyolysis if prescribed a potent CYP3A4 inhibitor (like clarithromycin).
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Topics

Medical History Evaluation

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