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Pharmacology · patient case question

What is the mechanism of action of the sublingual nitroglycerin she has just been given?

Patient case: Chest Pain During the Appointment

Patient: 64-year-old female

Chief Complaint: “My mouth is hurting on the upper right.”

Background: Hyperlipidemia and hypertension, both reportedly well controlled. Non-smoker. No prior cardiac events.

Medications: Simvastatin 40 mg daily · Carvedilol 12.5 mg twice daily · Aspirin 81 mg daily

Vital Signs: On seating: BP 138/84 mmHg · HR 68 bpm · RR 16 · T 98.4°F

Findings: During the examination she develops crushing substernal chest pain radiating into the left arm, with diaphoresis. Emergency medical services are activated, oxygen is delivered, and a sublingual nitroglycerin tablet is administered. Her panoramic radiograph, taken earlier, incidentally shows diffusely narrowed pulp chambers and canals in multiple posterior teeth.

  1. Releases nitric oxide, which activates guanylyl cyclase and raises cGMP
  2. Inhibits cyclooxygenase and reduces prostaglandin synthesis
  3. Blocks L-type calcium channels in vascular smooth muscle
  4. Increases cAMP through beta-1 adrenergic stimulation
Show answer and explanation

Correct answer: A. Releases nitric oxide, which activates guanylyl cyclase and raises cGMP

  • A. Correct. Nitroglycerin is metabolized to nitric oxide, which activates soluble guanylyl cyclase. The resulting rise in cGMP dephosphorylates myosin light chains and relaxes vascular smooth muscle. Venodilation predominates, reducing preload and therefore myocardial oxygen demand.
  • B. Incorrect. COX inhibition is the mechanism of the aspirin she already takes. Aspirin is critical in acute coronary syndrome for its antiplatelet effect, but that is not how nitroglycerin works.
  • C. Incorrect. Calcium channel blockade describes amlodipine, nifedipine, and diltiazem. These also treat angina, but through a different pathway.
  • D. Incorrect. Beta-1 stimulation with rising cAMP describes dobutamine or epinephrine at the cardiac receptor. It increases oxygen demand, the opposite of what is needed in angina.

Note: Contraindication worth knowing: nitroglycerin must not be given within 24–48 hours of a phosphodiesterase-5 inhibitor such as sildenafil or tadalafil. The combination causes profound, refractory hypotension.

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