Nitrates and Angina Management: Detailed Notes
Anti-Anginal Drugs
- Three main groups of drugs to treat angina:
- Nitrates
- Calcium channel blockers
- Beta-adrenergic blockers
The Cardiovascular System
- Vasculature is a system of interconnected tubes (arteries, veins, capillaries) that moves blood throughout the body.
- Functions:
- Circulates blood to provide oxygen and nutrients
- Assists in dispose of metabolic wastes
Functions of the Heart
- Generates blood pressure
- Routes blood
- Ensures one-way blood flow
- Regulates blood supply
Understanding Angina
- Definition: Angina is a type of chest pain or discomfort due to insufficient oxygen supply to the heart.
- It occurs when there is an imbalance between the oxygen demand of the heart and the oxygen supplied by coronary vessels.
Types of Angina
- Classic Angina:
- Caused by vessel occlusion (atherosclerosis).
- Chest pain not experienced at rest because myocardial oxygen supply remains balanced.
- Vasospastic/Prinzmetal's Angina:
- Occurs due to artery spasm leading to constricted blood flow.
- Spasms can be unpredictable and unrelated to activity.
- Silent Angina:
- Occurs without experiencing chest pain.
- Unstable Angina:
- Occurs when a plaque in the coronary artery ruptures, forming a thrombus and possibly blocking the artery.
Risk Factors for Angina
- Atherosclerosis
- Cigarette smoking
- Diabetes
- Hypercholesterolemia
- Hypertension
- Heredity
- Age
- Inactive lifestyle
- Obesity
Drug Therapy for Angina
- Aimed at restoring the balance between myocardial oxygen supply and demand.
Nitrates in Angina Treatment
- Mechanism: Nitrates exert vasodilatory effects.
- Main Effect: Dilation of veins decreases blood returning to the heart.
- Pathway:
- Nitric oxide stimulates guanylyl cyclase → increases cGMP → leads to vasodilation of veins and arteries.
- In vasospastic angina, nitrates can relax spasms, allowing more oxygen to reach the myocardium.
Classification of Nitrates
- Rapidly Acting Nitrates:
- Nitroglycerin: Available as sublingual tablet/spray, oral sustained-release, and transdermal.
- Long-Acting Nitrates:
- Isosorbide dinitrate & Isosorbide mononitrate
Key Nitrate Preparations and Their Effects
| Preparation | Onset of Action | Duration of Action |
|---|
| Nitroglycerin (sublingual) | 1-3 min | 30 min |
| Isosorbide dinitrate (sublingual) | 5 min | 30-60 min |
| Isosorbide mononitrate (oral) | 30 min | 12-24 h |
Heart Failure
- Definition: Progressive inability of the heart to supply adequate blood flow.
- Symptoms include coughing, tiredness, shortness of breath, swelling in abdomen, ankles, and legs due to fluid accumulation (edema).
Mechanisms of Action of Drugs for Heart Failure
- Adrenergic blockers: Slow heart rate (B₁) and decrease blood pressure (alpha).
- Cardiac glycosides: Increase force of myocardial contraction.
- Vasodilators: Dilate vessels, reducing preload.
- Diuretics: Reduce fluid volume, decreasing blood pressure.
Treatment of Heart Failure with Nitrates
- Example: Isosorbide dinitrate relaxes blood vessels and lowers blood pressure but is not very effective as monotherapy.
Side Effects of Nitrates
- Headache
- Dizziness
- Nausea
- Flushing
- Low blood pressure
Contraindications for Nitrates
- Patients with hypotension
- Closed-angle glaucoma
- Increased intracranial pressure
- Hyperthyroidism
Drug Interactions
- Nitrates may interact with PDE5 inhibitors (e.g., Sildenafil, Vardenafil, Tadalafil) as they can enhance vasodilation effects.