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Difficulty: EasyPharmacologic Interventions

An established clinic patient with ischemic heart disease schedules a visit to discuss new-onset erectile dysfunction. He reports achieving partial erections that are insufficient for intercourse and desires pharmacological assistance. His past medical history includes a myocardial infarction three years prior, hypertension, and hyperlipidemia. His daily medication regimen consists of low-dose aspirin, lisinopril, carvedilol, atorvastatin, and isosorbide mononitrate. He specifically asks for a prescription for sildenafil. The physician explains that this medication cannot be safely prescribed due to an absolute contraindication with his current regimen. Which of the following home medications precludes the use of sildenafil in this patient?

  1. Isosorbide mononitrateAnswer
  2. B
    Carvedilol
  3. C
    Lisinopril
  4. D
    Atorvastatin
  5. E
    Aspirin

Answer

Isosorbide mononitrate
The correct medication is isosorbide mononitrate, which belongs to the class of organic nitrates. Phosphodiesterase-5 (PDE-5) inhibitors, such as sildenafil, inhibit the degradation of cyclic guanosine monophosphate (cGMP). Organic nitrates also increase cGMP production by providing nitric oxide. The concurrent administration of these two classes of medications leads to a massive accumulation of intracellular cGMP, resulting in profound, synergistic systemic vasodilation. This can precipitate life-threatening, refractory hypotension and cardiovascular collapse. Therefore, the use of any PDE-5 inhibitor is an absolute contraindication in patients taking continuous or intermittent organic nitrates.

Step-by-Step Solution

1
Identify the mechanism of the requested drug.
Sildenafil is a phosphodiesterase-5 (PDE-5) inhibitor.
Understanding the drug class is necessary to identify potential interactions.
2
Review the patient's current medication list for dangerous interactions.
The patient takes isosorbide mononitrate, an organic nitrate.
PDE-5 inhibitors and organic nitrates both increase intracellular cGMP, which can lead to life-threatening synergistic vasodilation.
3
Select the contraindicated medication.
Isosorbide mononitrate is the correct answer.
This combination is an absolute contraindication in clinical practice.

Key Concept

Absolute contraindication of combining PDE-5 inhibitors with organic nitrates
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Topics

Pharmacologic Interventions

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