Pharmacological Actions and Therapeutic Uses of Beta-Blockers and Autonomic Drug...

Pharmacological Actions and Therapeutic Uses of Propranolol and Other Beta-blockers

• Propranolol is well absorbed after oral administration and undergoes extensive first-pass metabolism.
• It has pharmacological actions on the cardiovascular system, kidney, respiratory tract, eyes, CNS, skeletal muscle, and metabolic effects.
• Propranolol is used for hypertension, angina, myocardial infarction, cardiac arrhythmias, migraine, hyperthyroidism, pheochromocytoma, performance anxiety, essential tremors, and glaucoma.
• Adverse effects of Propranolol include CVS effects, respiratory complications, metabolic effects, and other adverse effects.
• Contraindications for Propranolol include asthma, COPD, diabetes, Raynaud’s disease, and Prinzmetal angina.
• Drug interactions with Propranolol include digitalis, verapamil, insulin, oral hypoglycemics, NSAIDs, cimetidine, timolol, and nadolol.
• Beta1-selective antagonists like Atenolol, Esmolol, and Metoprolol have specific pharmacological actions and therapeutic uses.
• Atenolol has lower lipid solubility, less CNS entry, and is excreted unchanged in the urine.
• Metoprolol can be administered orally or intravenously for hypertension, angina, and acute myocardial infarction.
• Esmolol is the shortest-acting beta-blocker and is administered intravenously to treat acute supraventricular tachycardia.
• Beta-blockers with partial agonist activity like Pindolol and Acebutolol have specific pharmacological actions and therapeutic uses.
• Labetalol and Carvedilol are alpha and beta blockers that cause peripheral vasodilation, do not alter serum lipid and glucose levels, and can be used in hypertensive emergencies.

Autonomic Drugs and Their Uses

• Autonomic drugs are used to treat a variety of conditions such as hypertension, ophthalmic hyperemia, hypotension, shock, heart failure, angina, arrhythmias, pheochromocytoma, benign prostatic hyperplasia, nasal congestion, myasthenia gravis, urinary retention, urinary incontinence, glaucoma, asthma, COPD, dry mouth, and sialorrhea.
• Adrenergic blockers are categorized into α blockers (irreversible and reversible) and ß blockers (non-selective, selective ß1, and selective ß2).
• The general effects of α blockade include the blockade of vasoconstriction, causing reflex tachycardia and interfering with postural reflex.
• Other actions of α blockade include relaxation of trigone & sphincter muscles, leading to decreased resistance to urinary outflow, nasal stuffiness, miosis, increased intestinal motility, and a failure of ejaculation.
• Phenoxybenzamine is a non-selective, irreversible α1 and α2 blocker used in Pheochromocytoma to prevent hypertensive crisis through Dale’s vasomotor reversal.
• Dale’s vasomotor reversal occurs when high doses of epinephrine result in a drop in blood pressure instead of a vasopressor effect when α1 blockers are given before epinephrine.
• Phentolamine, a competitive non-selective α blocker, also causes postural hypotension and epinephrine reversal, leading to reflex tachycardia.
• α blockers are only used for acute hypertension in hospitals, opposing catecholamines actions in Pheochromocytoma and treating Raynaud’s disease.
• Adverse effects of α blockers include postural hypotension, nasal stuffiness, sexual dysfunction, tachycardia, and are contraindicated in decreased coronary perfusion.
• α1-selective blockers, such as Prazosin, Terazosin, Doxazosin, and Tamsulosin, are used for conditions like hypertension, Raynaud disease, and benign prostatic hypertrophy.
• Adverse effects of α1 blockers include "first dose" effect, orthostatic hypotension, headache, dizziness, reflex tachycardia, nasal stuffiness, sexual dysfunction, and miosis.
• Yohimbine is a selective α2 blocker used as a sexual stimulant, and Mirtazapine is used as an antidepressant. Both have limited clinical utility.