(Part 6) ANS PHARMACOLOGY: Alpha & Beta blockers

1.        SELECTIVE ALPHA-1 ANTAGONISTS

[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

Drugs: PRAZOSIN, DOXAZOSIN, TERAZOSIN AND TAMSULOSIN

[Treatment]

• 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

 

2.       NONSELECTIVE ALPHA BLOCKERS

[Mechanism of action]

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

Drugs: PHENTOLAMINE & PHENOXYBENZAMINE

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

 3.       SELECTIVE ALPHA-2 BLOCKERS

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

 

 

BETA BLOCKERS

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