📋 Clinical Overview

Nitroglycerin is a potent organic nitrate vasodilator, primarily used for the prophylaxis and treatment of angina pectoris. It acts by relaxing vascular smooth muscle, leading to venous and arterial dilation. This reduces preload and afterload, decreasing myocardial oxygen demand and relieving angina. In the Indian context, it is a cornerstone therapy for ischemic heart disease, available in various formulations, with the 5mg strength commonly used in sustained-release oral tablets.

💊 Dosage & Administration

Adult: For prophylaxis of angina (Sustained-Release 5mg): 2.5mg to 6.5mg (typically one 5mg tablet) every 8 to 12 hours. MUST incorporate a nitrate-free interval of 10-12 hours daily (e.g., take last dose no later than 6 PM). Dose must be individualized; start low.

Note: Oral Sustained-Release (SR) Tablet: Swallow whole with a glass of water. Do NOT crush, chew, or break. Can be taken with or without food. To prevent tolerance, dosing schedule should provide a daily drug-free interval (e.g., 7 AM, 3 PM, with no dose after 6 PM).

⚠️ Contraindications

Hypersensitivity to nitrates or any excipient
Concurrent use of phosphodiesterase-5 inhibitors (e.g., Sildenafil, Tadalafil, Vardenafil) due to risk of severe hypotension
Severe anemia
Closed-angle glaucoma (relative, but often listed as absolute due to potential pressure increase)
Increased intracranial pressure
Cardiogenic shock (except under specific monitored conditions)

🔬 Mechanism of Action

Nitroglycerin is a prodrug that undergoes enzymatic conversion to release nitric oxide (NO). NO activates soluble guanylyl cyclase (sGC) in vascular smooth muscle cells, increasing intracellular cyclic guanosine monophosphate (cGMP). Elevated cGMP leads to dephosphorylation of myosin light chains, resulting in smooth muscle relaxation and vasodilation.

🤕 Side Effects

Headache (often throbbing, may diminish with continued use)
Dizziness, lightheadedness
Flushing
Postural hypotension
Reflex tachycardia
Nausea

🤰 Special Populations

Pregnancy: Category C (US FDA). Animal studies show adverse effects. Use only if potential benefit justifies potential risk to the fetus. Not recommended during pregnancy unless for life-threatening conditions.

Driving: May cause dizziness, lightheadedness, or syncope. Patients should not drive or operate machinery until they know how nitroglycerin affects them, especially during initial dose titration.

🔄 Drug Interactions

Sildenafil, Tadalafil, Vardenafil (PDE-5 Inhibitors)	Profound, life-threatening hypotension	Contraindicated
Riociguat (sGC stimulator)	Severe hypotension	Contraindicated
Other Antihypertensives (Beta-blockers, CCBs, ACE inhibitors, Diuretics)	Additive hypotensive effect	Major
Alcohol	Additive vasodilation and hypotension	Major
Heparin	Nitroglycerin may decrease anticoagulant effect of heparin	Moderate
Dihydroergotamine	Nitroglycerin may increase ergot toxicity (vasoconstriction)	Moderate
Aspirin	Increased nitroglycerin bioavailability	Minor

Myocardol