Difference Between Alpha Blockers and Beta Blockers

Main Difference

The main difference between Alpha Blockers and Beta Blockers is that Alpha Blockers occupy Alpha receptors thus inhibiting all the pharmacological actions of Alpha receptor agonists whereas Beta Blockers occupy Beta receptors thus inhibiting all the pharmacological actions of Beta receptor agonists.

Alpha Blockers vs. Beta Blockers

Alpha blockers block all the actions of alpha receptor agonists while Beta blockers block all the actions of the beta receptor agonists. Alpha blockers inhibit vasoconstriction caused by endogenous catecholamines as they relax some muscle so help blood vessels to remain open while beta blockers dilate blood vessels as they cause vascular smooth muscle dilation and some third generation beta blockers also cause vasodilation. Alpha blockers induced fall in blood pressure is opposed by baroreceptors leading to an increase in blood pressure while in the case of Beta-blockers no such phenomena are observed. Alpha blockers never act as “inverse agonist” on the other hand Beta blockers show the property of “inverse agonist.” Alpha blockers keep the hormones of norepinephrine or noradrenaline causing smoother blood flow through open veins Beta blockers, meanwhile, block the hormone called epinephrine/adrenaline so lowers the blood pressure and heart rate.

Alpha blockers are used in preoperative management of Pheochromocytoma patients although its use is controversial while beta blockers are not used for such purpose. Alpha-blockers do not influence bronchial smooth muscles while Beta blockers such as propranolol have bronchial smooth muscle constriction property not significant in normal individuals but threaten the life of COPD patients because of bronchoconstriction induction. Alpha blockers lower the resistance to urine flow while Beta blockers don’t have such an effect.

Comparison Chart

Alpha BlockersBeta Blockers
Alpha blockers inhibit the pharmacological actions of Alpha receptor agonists by blocking Alpha receptors.Beta blockers inhibit the pharmacological actions of Beta receptor agonists by blocking Beta receptors.
Subtypes
· Alpha-1 selective blockers (parazosin)
· Alpha-2 selective blockers (yohimbine)
·Non–selectiveAlpha blockers(phentolamine)
· Beta-1 selective blockers (Metoprolol)
· Beta-2 selective blockers (Albuterol)
· Non-selective Beta blockers (propranolol)
Chronotropic and Ionotropic Effect
Alpha-blockers do not have a chronotropic and ionotropic effect.Beta blockers have a negative chronotropic and ionotropic effect.
Effect on Peripheral Resistance
Alpha blockers decrease peripheral vascular resistance.Long term use of Beta-blockers leads to a decrease in peripheral vascular resistance.
Role in Blood Glucose Level
Alpha blockers have a role in decreasing blood glucose levels.Beta blockers decrease insulin level even when the blood glucose level is high.
Use in Heart Failure and Angina
Alpha blockers have no use in heart failure and angina.Beta blockers are used in heart failure and angina.
Adverse Effects
Dizziness, postural hypotension, nasal congestion, reflex tachycardia, fluid retentionDizziness, cold hands and feet, headache, dry mouth, skin, upset stomach, diarrhea or constipation.
Therapeutic Uses
Hypertension, pheochromocytoma, congestive heart failure, Benign prostatic hyperplasia, erectile dysfunction, Raynaud,s syndromeAngina, Heart attack, Heart failure, Atrial fibrillation, migraine

What are Alpha Blockers

Alpha blockers also called the Alpha antagonists are drugs that act on the Alpha receptors (Gq, Gi-coupled) of the sympathetic system and block the actions performed by Alpha agonists at these receptors (Those drugs that act on the Alpha receptors and activate them). The interaction of Alpha blockers with Alpha receptors can be reversible or irreversible. Reversible Alpha blockers are drugs that dissociate from receptors in the presence of a high concentration of Alpha agonists e.g. phentolamine and prazosin. Irreversible Alpha-blockers do not dissociate from the receptors even in the presence of the high concentration of the Alpha receptor agonists e.g. phenoxybenzamine. Effects of irreversible Alpha-blockers can persist for a long period even after the drug is cleared from plasma. Some Alpha blockers act specifically on Alpha-1-receptors and are called the Alpha-1 blockers e.g. prazosin. Some Alpha blockers act specifically on Alpha-2-receptors and are called the Alpha-2 blockers e.g. yohimbine. Some Alpha blockers act on both receptors and are called the Nonselective Alpha blockers e.g. phentolamine. Some drugs that block Alpha receptors and also act on some other receptors are Indoramin, Ketanserin, Urapidil, Neuroleptic drugs(chlorpromazine, haloperidol, phenothiazine, and Butyrophenones). The main therapeutic use of the Alpha blockers is the treatment of hypertension, prostatic hyperplasia, phaeochromocytoma and these are also effective for Erectile dysfunction.

What are Beta Bblockers

Beta blockers also called the Beta antagonists are drugs that act on the Beta receptors of the sympathetic system and block the actions performed by Beta-agonists at these receptors (Those drugs that act on the Beta receptors and activate them). Those drugs that block just Beta-1 receptors are called Beta-1 selective blockers e.g. Metoprolol, Atenolol. Those drugs that block just Beta-2 receptors are called Beta-2 selective blockers e.g. Those drugs that block both beta 1 and beta two receptors are called non-selective beta receptors e.g. propanolol. Some beta blockers have the property of inverse agonism|. Some beta blockers show the property of local anesthetic or membrane stabilizing activity. Beta blockers are mainly used to treat angina, heart failure, higher heart rate, cardiac arrhythmias, blood pressure.

Key Differences

  1. Alpha Blockers block Alpha receptors of the sympathetic system while Beta Blockers block beta receptors of the sympathetic
  2. Alpha Blockers block Gi, Gq coupled receptors while Beta Blockers block Gi and Gs-coupled
  3. Alpha Blockers do not have a chronotropic and ionotropic effect on the other hand Beta Blockers have profound negative ionotropic and chronotropic effect.
  4. Alpha Blockers are used to treat the Hypertension, but postural hypotension is the adverse effect on the other hand Beta Blockers treat Hypertension but do not lead to postural hypotension.

Conclusion

Alpha and Beta blockers both are blockers of the sympathetic system. Alpha and Beta blockers find their major use in cardiovascular disorders and play a basic role in the treatment of cardiovascular ailments.

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