Antianginal Drugs: Nitrates and β-Blockers

Organic nitrates are metabolized to release nitric oxide, which activates guanylyl cyclase and increases cGMP production. This triggers relaxation of vascular smooth muscles, causing vasodilation and improving coronary blood flow to the heart. Nitroglycerin is administered sublingually for rapid symptom relief in angina pectoris.

Common side effects of nitroglycerin include headaches, postural hypotension (sudden blood pressure drops when standing), facial flushing, and tachycardia (increased heart rate). These effects result from the drug's vasodilatory action on blood vessels throughout the body, though they typically diminish with continued use.

Beta-blockers like atenolol and metoprolol block adrenaline and noradrenaline at β1-adrenergic receptors in cardiac and vascular muscle cells. By reducing heart rate, myocardial contraction force, and systemic blood pressure, they decrease myocardial oxygen demand, preventing angina episodes. Oral administration produces effects within an hour.

Nitroglycerin is administered sublingually for rapid onset of action, making it ideal for acute angina relief. Beta-blockers are given orally and take approximately one hour to produce therapeutic effects, making them suitable for long-term angina prevention rather than immediate symptom management.

Beta-blockers commonly cause fatigue, cold extremities, hypotension, and bradycardia (slow heart rate). These effects stem from reduced sympathetic nervous system activity and decreased cardiac output. While generally manageable, these side effects may limit use in certain patient populations.

Nitrates work by directly dilating blood vessels through nitric oxide signaling, increasing oxygen supply to the heart. Beta-blockers reduce oxygen demand by decreasing heart rate and contractility. Together, these complementary mechanisms—supply enhancement versus demand reduction—represent different antianginal strategies for managing angina pectoris.

Sublingual administration allows nitroglycerin to bypass hepatic metabolism and enter the bloodstream directly through oral mucosa, producing rapid vasodilation within minutes. This fast onset is critical for acute angina relief. Oral administration would delay absorption and be ineffective for emergency symptom management during anginal episodes.