Glyceryl Trinitrate (Nitroglycerin): An Essential Vasodilator for Angina Management
Glyceryl trinitrate (nitroglycerin) is a potent vasodilator medication primarily used to treat and prevent angina pectoris by dilating blood vessels, reducing cardiac workload, and improving myocardial oxygen supply-demand balance.
Mechanism of Action
Nitroglycerin works through the following mechanisms:
- Forms free radical nitric oxide (NO) which activates guanylate cyclase 1
- Increases cyclic GMP in smooth muscle, leading to vasodilation 1
- Primarily dilates venous capacitance vessels (venodilatation) 2
- Reduces cardiac preload by decreasing ventricular filling pressures 2
- Dilates coronary arteries, particularly in regions of plaque disruption 2
- Improves collateral coronary blood flow 2
- May inhibit platelet aggregation 2
Formulations and Administration
Nitroglycerin is available in multiple formulations:
- Sublingual tablets: 0.3-0.6 mg (up to 1.5 mg), onset 1-7 minutes 2
- Sublingual spray: 0.4 mg as needed, similar onset to tablets 2
- Transdermal patches: 0.2-0.8 mg/hr every 12 hours 2
- Intravenous: 5-200 mcg/min 2
Clinical Uses
1. Acute Angina Management
- Rapidly relieves symptoms during angina attacks 2
- Should be taken at the first sign of chest pain 1
- May be repeated approximately every 5 minutes until pain relief (maximum 3 tablets in 15 minutes) 1
2. Prophylactic Use
- Can be used 5-10 minutes prior to activities that might trigger angina 1
- Increases angina-free walking time and exercise tolerance 3
3. Vasospastic Angina
- Effective in treating coronary artery spasm 2
- Complete normalization of ST-segment elevation after nitroglycerin administration, along with symptom relief, suggests coronary spasm 2
4. Unstable Angina/NSTEMI
- Intravenous nitroglycerin may be initiated at 10 mcg/min and increased by 10 mcg/min every 3-5 minutes until symptom relief or blood pressure response 2
Important Clinical Considerations
Dosing Guidelines
- For sublingual tablets: One tablet dissolved under the tongue at first sign of chest pain 1
- If pain persists after 3 tablets in 15 minutes, seek emergency help 1
- For IV administration: Start at 10 mcg/min, increase by 10 mcg/min every 3-5 minutes until symptom relief 2
Contraindications
Absolute contraindications:
- Recent use of phosphodiesterase inhibitors (sildenafil within 24h, tadalafil within 48h) 2
- Hypotension (SBP <90 mmHg or 30 mmHg below baseline) 2
- Severe bradycardia (<50 bpm) or tachycardia (>100 bpm) without heart failure 2
- Right ventricular infarction 2
Side Effects
- Headache (most common) 2, 1
- Flushing 2
- Postural hypotension 1
- Reflex tachycardia 2
- Burning or tingling sensation in mouth (with sublingual forms) 1
Tolerance
- Develops with continuous use (typically after 24 hours) 2
- For long-term use, a "nitrate-free" interval is recommended to preserve efficacy 2
- For transdermal patches, remove during part of the day or at night 2
Clinical Pearls
Patient positioning: Patients should sit down when taking sublingual nitroglycerin to prevent falls due to potential lightheadedness 1
Storage: Protect from light and moisture; store in original container 1
Warning signs: If angina pain persists after 3 tablets in 15 minutes or feels different than usual, seek emergency help immediately 1
Spray vs. tablets: The sublingual spray formulation may provide faster onset of action and is advantageous for patients with dry mouth 3
Nitrate-free intervals: For chronic use, schedule a daily nitrate-free period (typically at night) to prevent tolerance 2, 4
By understanding the properties and proper use of glyceryl trinitrate, healthcare providers can optimize its effectiveness in managing angina and improving patients' quality of life.