1. Clinical Overview
Nitroglycerin (Glyceryl Trinitrate) 0.2% w/w is a topical formulation, primarily an ointment, used for the prophylaxis and long-term management of angina pectoris. It is a potent organic nitrate that acts as a vasodilator, primarily affecting venous capacitance vessels, reducing preload and myocardial oxygen demand. In the Indian context, it is a cost-effective option for chronic stable angina management, especially in patients who cannot tolerate or afford other long-acting nitrate formulations.
| Onset | Duration | Bioavailability |
|---|---|---|
| 30 to 60 minutes after topical application. | Approximately 8 to 10 hours. | Highly variable (10-30%) due to skin permeability factors, application site, and surface area. |
2. Mechanism of Action
Nitroglycerin is converted to nitric oxide (NO) within vascular smooth muscle cells. NO activates soluble guanylyl cyclase, increasing intracellular cyclic guanosine monophosphate (cGMP). Elevated cGMP leads to dephosphorylation of myosin light chains, resulting in smooth muscle relaxation and vasodilation.
3. Indications & Uses
- Prophylaxis and long-term management of chronic stable angina pectoris (exertional angina)
- Prevention of angina attacks before anticipated physical or emotional stress
4. Dosage & Administration
Adult Dosage: Apply 1 to 2 inches (2.5 to 5 cm) of ointment, squeezed onto the provided applicator paper, every 8 hours. Start with 0.5 inch, titrate upward based on response and tolerability. Apply to a clean, dry, hairless area of skin (e.g., chest, upper arm, or thigh). Rotate sites to prevent skin irritation.
Administration: 1. Measure the desired length on the applicator paper. 2. Squeeze ointment onto paper. 3. Spread thinly (do not rub in vigorously) over a 6x6 inch area. 4. Cover with plastic wrap if directed to enhance absorption. 5. Wash hands thoroughly after application. 6. Remove previous application before applying a new dose. 7. Maintain a daily nitrate-free interval of 10-12 hours (e.g., overnight).
5. Side Effects
Common side effects may include:
- Headache (often pulsating, may be severe initially, usually diminishes with continued therapy)
- Dizziness, lightheadedness
- Reflex tachycardia
- Flushing
- Hypotension, postural hypotension
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Phosphodiesterase-5 Inhibitors (Sildenafil, Tadalafil, Vardenafil) | Profound, life-threatening hypotension | Contraindicated |
| Other Vasodilators (e.g., ACE inhibitors, ARBs, Calcium channel blockers, Alpha-blockers) | Additive hypotensive effect | Major |
| Antihypertensives | Enhanced blood pressure lowering | Major |
| Heparin | Nitroglycerin may partially antagonize anticoagulant effect of heparin | Moderate |
| Alcohol | Additive vasodilation and hypotension | Major |
| Ergot Alkaloids (e.g., Ergotamine) | May antagonize the antianginal effect of nitrates and increase ergot-induced vasoconstriction | Moderate |
| Triptans (e.g., Sumatriptan) | Theoretical risk of coronary vasospasm; use with caution | Moderate |
7. Patient Counselling
- DO apply the ointment exactly as prescribed, using the measuring paper.
- DO rotate the application site daily to prevent skin irritation.
- DO maintain a daily 'nitrate-free' period of 10-12 hours as directed by your doctor (usually overnight).
- DO wash hands thoroughly after application.
- DO remove old ointment before applying a new dose.
- DONT apply to broken, irritated, or hairy skin.
- DONT rub the ointment in vigorously; spread it thinly.
- DONT suddenly stop using this medication without consulting your doctor.
- DONT use PDE-5 inhibitors (e.g., Viagra, Cialis) while on this therapy.
8. Toxicology & Storage
Overdose: Severe hypotension with throbbing headache, vertigo, palpitations, visual disturbances, flushing, perspiration, syncope, methemoglobinemia (cyanosis, dyspnea, anxiety), nausea, vomiting, diarrhea, reflex tachycardia followed by bradycardia, heart block, cardiovascular collapse, coma, and death.
Storage: Store at controlled room temperature (15°C to 30°C). Keep the tube tightly closed in its original carton to protect from light and moisture. Do not freeze. Keep out of reach of children and pets. Do not use after the expiry date printed on the pack.