Nitroglycerin (Glyceryl Trinitrate)

• Nitroglycerin, an organic nitrate, is employed in the management of coronary artery disease and related conditions.
• Acute angina pectoris: rapid relief of chest pain by reducing myocardial oxygen demand.
• Prophylaxis of angina pectoris: prevents episodes of chest discomfort during exertion or stress.
• Management of heart failure (adjunct): improves cardiac output by decreasing preload and afterload.

• After sublingual absorption, glyceryl trinitrate is enzymatically converted to nitric oxide, which activates guanylate cyclase in vascular smooth muscle. The resulting increase in cyclic GMP causes relaxation of both venous and arterial vessels, lowering preload and afterload, and thereby reducing myocardial oxygen consumption and alleviating ischemia.

Nitroglycerin may cause a range of adverse reactions, from mild to severe.

Common Side Effects

• Headache: throbbing pain often triggered by vasodilation.
• Flushing: warmth and redness of the skin, especially on the face.
• Dizziness or light‑headedness due to lowered blood pressure.
• Nausea or mild gastrointestinal upset.

Serious or Rare Side Effects

• Severe hypotension: marked drop in blood pressure that can lead to fainting.
• Syncope: sudden loss of consciousness.
• Methemoglobinemia: abnormal hemoglobin that reduces oxygen delivery.
• Allergic reactions: rash, urticaria, or anaphylaxis in rare cases.
• Cardiogenic shock: extremely low cardiac output, rarely reported.

• Before prescribing nitroglycerin, clinicians should consider several safety measures.
• Assess blood pressure: ensure baseline readings are adequate before administration.
• Avoid concurrent PDE‑5 inhibitors: co‑use with sildenafil, tadalafil, or similar agents can cause profound hypotension.
• Monitor for tolerance: prolonged use may reduce effectiveness, requiring drug‑free intervals.
• Use cautiously in severe anemia or hypovolemia: patients may be more susceptible to hypotensive episodes.
• Educate patients on proper sublingual technique: place tablet under the tongue and avoid swallowing.
• Store at room temperature: keep in the original container, protect from moisture and light.

Nitroglycerin interacts with several drug classes; awareness helps prevent adverse events.

Major Interactions (Avoid)

• Phosphodiesterase‑5 inhibitors (e.g., sildenafil): risk of severe hypotension.
• Other organic nitrates or nitrites: additive vasodilatory effect leading to dangerous blood pressure drops.
• Potent antihypertensives (e.g., ACE inhibitors, ARBs): may cause excessive hypotension.

Moderate Interactions (Monitor Closely)

• Beta‑blockers: may mask reflex tachycardia, complicating assessment.
• Diuretics: can amplify hypotensive response.
• Alcohol: enhances vasodilation and dizziness.
• Calcium channel blockers: may increase the likelihood of low blood pressure.