17. ANTI-ANGINAL DRUGS

Introduction

Angina pectoris is chest pain caused by reduced blood flow and oxygen supply to the heart muscle. When the oxygen demand of the heart becomes higher than supply, the patient experiences sudden pressure-like pain that may spread to the neck, jaw, back or arms. It can be triggered by exercise, emotional stress or a heavy meal. Angina is a warning sign of myocardial ischemia and should be treated promptly to prevent heart attack.

Types of

1. Stable (Typical) Angina

  • Triggered by exercise, excitement or heavy meals.
  • Due to atherosclerosis of coronary arteries.
  • Pain lasts for 1–15 minutes.
  • Shows ST-segment depression on ECG.

2. Variant (Prinzmetal) Angina

  • Occurs at rest due to coronary artery spasm.
  • Pain is not related to physical activity or blood pressure.
  • Shows ST-segment elevation on ECG.
  • Responds well to nitrates and calcium channel blockers.
  • Beta blockers are contraindicated.

3. Unstable Angina

  • Occurs due to plaque rupture and platelet aggregation.
  • Lies between stable angina and myocardial infarction.
  • Pain lasts longer and may indicate acute coronary syndrome.

Classification of Anti-Anginal Drugs

  • Nitrates
  • Beta blockers
  • Calcium channel blockers
  • Potassium channel openers

1. Nitrates (Organic Nitrates)

Examples: Nitroglycerin, Isosorbide dinitrate, Isosorbide mononitrate

Mechanism of Action

Nitrates act as nitric oxide (NO) donors. NO activates guanylyl cyclase and increases cGMP levels, leading to smooth muscle relaxation. This results in:

  • Reduced preload due to venodilation.
  • Reduced afterload due to arteriolar dilation.
  • Improved coronary blood flow by dilating large coronary arteries.

Adverse Effects

  • Headache (most common)
  • Postural hypotension
  • Flushing
  • Tachycardia

Drug Interactions

  • Sildenafil and other PDE5 inhibitors increase nitrate effect dangerously → severe hypotension. Combination is contraindicated.

Tolerance and Dependence

  • Tolerance develops rapidly and requires a “nitrate-free interval”.
  • Dependence may occur; sudden withdrawal can cause coronary spasm.

2. Beta Blockers

Examples: Atenolol, Metoprolol, Bisoprolol, Propranolol

Mechanism of Action

They block β1 receptors in the heart resulting in:

  • Decreased heart rate
  • Reduced contractility
  • Reduced cardiac output and oxygen demand
  • Increased perfusion time during diastole

Clinical Use

  • Effective for stable angina (exercise-induced).
  • Not useful in variant (spasm) angina.
  • Used for long-term prophylaxis, not for acute attacks.

Important Notes

  • Cardioselective agents like atenolol and metoprolol are preferred.
  • Avoid drugs with intrinsic sympathomimetic activity such as pindolol.
  • Taper slowly to prevent rebound hypertension or angina.

3. Calcium Channel Blockers (CCBs)

Examples: Amlodipine, Verapamil, Diltiazem, Nifedipine

Mechanism of Action

  • Block calcium entry into cardiac and smooth muscle cells.
  • Cause vasodilation and reduce vascular resistance.
  • Decrease myocardial contractility and oxygen demand.

Types of CCBs

Phenylalkylamines – Verapamil

  • Strong effect on heart conduction.
  • Reduces heart rate, AV conduction and contractility.
  • Avoid combining with beta blockers and digoxin.

Benzothiazepines – Diltiazem

  • Slows SA and AV node conduction.
  • Useful in variant angina due to strong coronary vasodilation.

Dihydropyridines – Nifedipine, Amlodipine

  • Mainly produce arteriolar dilation.
  • Less effect on cardiac conduction.
  • Common side effects include flushing, palpitations, ankle swelling.

4. Potassium Channel Opener

Nicorandil

  • Opens ATP-sensitive potassium channels & causes vasodilation.
  • Has both nitrate-like and potassium channel opening activity.
  • Used in stable and variant angina.

Adverse Effects

  • Flushing
  • Headache
  • Dizziness
  • Palpitations

Why Combinations Are Used?

  • Nitrates + Beta Blockers: beta blockers prevent reflex tachycardia caused by nitrates.
  • Nitrates + CCBs: increase coronary flow and reduce oxygen demand.
  • Beta Blockers + CCBs (non-DHP): avoid this combination due to risk of heart block.

Detailed Notes:

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