Learning Objective
By the end of this section, the learner should be able to:
- Explain the mechanism of action of nitrates in the management of angina
- Describe their hemodynamic effects on myocardial oxygen demand
- Identify clinical uses, adverse effects, and important drug interactions of nitrate therapy
Mechanism of Action
Nitrates act as: Prodrugs of Nitric Oxide (NO)
Nitric oxide stimulates:
➡️ Guanylate cyclase
➡️ ↑ cGMP levels
➡️ Smooth muscle relaxation
Primary Hemodynamic Effect
- Venodilation
- ↓ Preload
- ↓ Cardiac workload
- ↓ Myocardial oxygen requirement
✔️ This improves the balance between oxygen supply and demand in ischemic myocardium.
Clinical Benefits
- Reduction in infarct size
- Decreased post–myocardial infarction mortality
- Effective in:
- Stable angina
- Vasospastic (Prinzmetal) angina
- Acute anginal attacks
Commonly Used Nitrates
| Drug | Route | Clinical Use |
|---|---|---|
| Nitroglycerin | Sublingual, Transdermal, IV | Acute angina relief |
| Isosorbide | Oral (Extended Release) | Chronic angina prophylaxis |
Adverse Effects
- Headache
- Flushing
- Orthostatic hypotension
- Reflex tachycardia
- Fluid retention
Cautions and Contraindications
⚠️ Tachyphylaxis may occur with continuous or repeated nitrate use. Concurrent use with PDE-5 inhibitors such as:
- Sildenafil
- Vardenafil
- Tadalafil
👉 Severe hypotension due to excessive vasodilation
👉 Risk of myocardial infarction or cardiovascular collapse
Clinical Note
Nitrates—particularly Nitroglycerin—are the:
- Drug of choice for the acute management of stable angina
- Effective in vasospastic angina via direct coronary vasodilation
They are commonly used alongside:
- Antiplatelet agents (e.g., aspirin)
- β-blockers
to improve clinical outcomes in patients with ischemic heart disease.
