(Part 6) ANS PHARMACOLOGY: Alpha & Beta blockers


[Mechanism of action]

  • Block alpha-1 receptors located in the body, especially on the arterioles
  • antagonists will cause a decrease in blood pressure and in peripheral resistance



  • Very good for hypertension due its vasodilation effect
  • Helps manage pheochromocytoma (tumor of adrenal medulla that releases high amount of epinephrine) by reducing blood pressure
  •  Helps manage benign prostatic hyperplasia (BPH- give selective a1 blockade b/c it relaxes bladder sphincter)
  • Drugs of choice for hypertension given in combinations: alpha-1 antagonist, beta blocker and diuretic

[Side effects]

  • May cause reflex tachycardia; THEREFORE, give in combination with a BETA blocker to stop the tachycardia
  • The drop in BP will stimulate the renin-angiotensin system to cause salt and water retention; to prevent this, give a DIURETIC



[Mechanism of action]

  • These drugs block both alpha-1 and alpha-2 receptors


  • Phentolamine: competitive inhibitor; acute effect
  • Phenoxybenzamine: noncompetitive inhibitor; used in hypertensive crisis; given IV


  • Yohimbine: treats sexual impotence, and orthostatic hypotension
  • Mirtazapine: used to treat depression
  • MOA: They increase norepinephrine causing an increased BP




Note: the rule is that any beta (olol’s) drug that starts with the letters A-M is BETA-1 selective blocker-except Albuterol which is a beta agonist. Starting with letters P-Z is BETA-2 selective blocker

1.       BETA-1 BLOCKERS

[Mechanism of action]

  • Decreases renin and aqueous secretion)
  • Treat: hypertension, asthmatics
  • Side effects: causes bradycardia
  • Contraindications: Don’t give beta2 blockers to diabetics because it decreases insulin secretion


2.       BETA-2 BLOCKERS

  • Pindolol & propranolol (very sedative; treat tremors and migraine)
  • give TIMOLOL to treat glaucoma
  • Acebutolol and pindolol are partial agonists (therefore you won’t get maximum blockade)
  • Atenololis better to give to depressed patients because it is water soluble; doesn’t depress CNS



[Side effects of b blockers]:

  • Hyperlipidemia (acebutolol and pindolol don’t increase lipids)
  • Hypoglycemia due to decreased insulin release
  • May cause vasospasm or bronchospasm
  • Contraindications: DO NOT GIVE TO ASTHATICS , DIABETICS and vasospastic disorders

4 thoughts on “(Part 6) ANS PHARMACOLOGY: Alpha & Beta blockers

    1. Thankyou for your comment. Agreed! Tons of side effects that’s why it is important to take it with other medications to counteract negative effects or better yet, we must all educate ourselves about the importance of diet.

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