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Difficulty: HardPharmacologic Interventions

A 54-year-old man undergoes evaluation for a 1-week history of progressively worsening pain with swallowing and retrosternal burning. His medical history is notable for a deceased-donor renal transplantation 3 years ago. His daily maintenance immunosuppressive regimen consists of tacrolimus, mycophenolate mofetil, and prednisone. Temperature is 37.2°C (99.0°F), blood pressure is 128/78 mm Hg, and pulse is 76/min. Physical examination reveals easily removable white plaques on the buccal mucosa and soft palate. Upper gastrointestinal endoscopy demonstrates adherent, whitish plaques throughout the middle and distal esophagus. The physician decides to initiate targeted therapy with oral fluconazole. Which of the following is the most appropriate concurrent pharmacologic management step for this patient?

  1. Preemptively decrease the tacrolimus dosageAnswer
  2. B
    Preemptively increase the tacrolimus dosage
  3. C
    Discontinue mycophenolate mofetil during antifungal therapy
  4. D
    Substitute cyclosporine for tacrolimus
  5. E
    Utilize intravenous amphotericin B instead of fluconazole

Answer

Preemptively decrease the tacrolimus dosage
The correct intervention is to preemptively decrease the dosage of the patient's calcineurin inhibitor. Fluconazole is a potent inhibitor of the cytochrome P450 3A4 (CYP3A4) enzyme system. Tacrolimus is heavily dependent on CYP3A4 for its metabolism. Co-administration of fluconazole will significantly decrease tacrolimus clearance, leading to elevated serum drug levels. To prevent severe nephrotoxicity and neurotoxicity, the standard management is to preemptively reduce the tacrolimus dose (often by 30-50%) and closely monitor trough levels when initiating a systemic azole antifungal.

Step-by-Step Solution

1
Identify the patient's diagnosis and the intended treatment.
The patient has esophageal candidiasis and will be treated with oral fluconazole.
Establishing the new medication is necessary to evaluate for potential drug-drug interactions with the patient's baseline regimen.
2
Analyze the pharmacokinetic properties of the intended therapy and the patient's current medications.
Fluconazole is a moderate-to-strong inhibitor of the CYP3A4 enzyme. The patient is taking tacrolimus, which is heavily dependent on CYP3A4 for hepatic and intestinal metabolism.
Identifying shared metabolic pathways predicts how serum drug concentrations will change upon co-administration.
3
Determine the required pharmacologic intervention to prevent adverse effects.
Because fluconazole will inhibit the clearance of tacrolimus, the tacrolimus serum concentration will rise significantly. The dose of tacrolimus must be preemptively decreased.
Preventive dose adjustment and close therapeutic drug monitoring (trough levels) are required to avoid calcineurin inhibitor toxicity, which presents as acute kidney injury and neurotoxicity.

Key Concept

CYP3A4-mediated drug interactions with calcineurin inhibitors
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Topics

Pharmacologic Interventions

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