Adrenoceptor Antagonists

Question 1

Phenoxybenzamine (Dibenzyline*)

Answer 1

Alpha receptor antagonist

Irreversibly blocks alpha 1 &alpha 2; indirect baroreflex activation

Effects: decrease BP, increase HR due to baroreflex activation

Clinical use: pheochromocytoma, high catecholamine states

Toxicity: T1/2>1 day; orthostatic hypotension, tachycardia, MI

Question 2

Prazosin (Minipress*)
Doxazosin
Terazosin

Answer 2

Alpha receptor antagonist

Block alpha 1 but not alpha 2

Effects: lowers BP

Clinical use: hypertension, benign prostatic hyperplasia

Toxicity: larger depressor effect with 1st dose may cause orthostatic hypotension

Question 3

Tamsulosin (Flomax*)

Answer 3

Alpha receptor antagonist

slightly selective for alpha 1a

Effects: alpha 1a blockade may relax prostatic smooth muscles more than vascular smooth muscle

Clinical use: benign prostatic hyperplasia

Toxicity: orthostatic hypotension may be less common with this subtype

Question 4

Yohimbine
Rauwoscine
Torazoline

Answer 4

Alpha receptor antagonist

Blocks alpha 2, increases central sympathetic activity–>increase NE release

Effects: raises BP and HR

Clinical use: male erectile dysfunction, hypotension

Toxicity: anxiety, excess pressor effect if NET1 is blocked

Question 5

Labetalol

Answer 5

Alpha receptor antagonist

Beta>alpha 1 block

Effects: lowers BP with limited HR increase

Clinical use: hypertension

Toxicity: less tachycardia

Question 6

Propranolol
Nadolol
Timolol
Pindolol

Answer 6

Beta-adrenoceptor antagonists

1st generation, non-selective, Beta 1=Beta 2
Pindolol= intrinsic sympathomimetic activity (ISA)

Effects: (-) inotropic, (-) chronotropic–>decrease BP in pts w/ hypertension; decrease myocardial O2 consumption; decrease renin release;
Beta 2 blockade–> increase airway resistance–>undesirable in asthma/ COPD; No beta blocker is completely free of Beta 2-blocking effect;
decrease aqueous humor production–>decrease intraocular pressure
inhibits lipolysis, decrease glucagon release, increase VLDL, decrease HDL

Clinical use: hypertension, ischemic heart disease, cardiac arrhythmias, heart failure, glaucoma, hyperthyroidism, neurologic diseases

Choice of Beta blockers based on: cardioselectivity, intrinsic sympathomimetic activity, lipid solubility

Adverse effects: fatigue, worsening peripheral vascular disease, worsening bronchospasm, decreased sexual functions, increased incidence of diabetes, masking of symptoms of hypoglycemia

Question 7

Atenolol
Metoprolol
Esmolol
Betaxolol 
Acebutolol
Celiprolol

Answer 7

Beta-adrenoceptor antagonists

2nd generation, Beta 1» Beta 2
Acebutolol= intrinsic sympathomimetic activity

Effects: (-) inotropic, (-) chronotropic–>decrease BP in pts w/ hypertension; decrease myocardial O2 consumption; decrease renin release;
Beta 2 blockade–> increase airway resistance–>undesirable in asthma/ COPD; No beta blocker is completely free of Beta 2-blocking effect;
decrease aqueous humor production–>decrease intraocular pressure
inhibits lipolysis, decrease glucagon release, increase VLDL, decrease HDL

Clinical use: hypertension, ischemic heart disease, cardiac arrhythmias, heart failure, glaucoma, hyperthyroidism, neurologic diseases

Choice of Beta blockers based on: cardioselectivity, intrinsic sympathomimetic activity, lipid solubility

Adverse effects: fatigue, worsening peripheral vascular disease, worsening bronchospasm, decreased sexual functions, increased incidence of diabetes, masking of symptoms of hypoglycemia

Question 8

Labetalol

Carvedilol

Answer 8

Mixed alpha-beta antagonist

3rd generation, vasodilatory, Beta 1=Beta 2>alpha 1>alpha 2

Effects: (-) inotropic, (-) chronotropic–>decrease BP in pts w/ hypertension; decrease myocardial O2 consumption; decrease renin release;
Beta 2 blockade–> increase airway resistance–>undesirable in asthma/ COPD; No beta blocker is completely free of Beta 2-blocking effect;
decrease aqueous humor production–>decrease intraocular pressure
inhibits lipolysis, decrease glucagon release, increase VLDL, decrease HDL

Clinical use: hypertension, ischemic heart disease, cardiac arrhythmias, heart failure, glaucoma, hyperthyroidism, neurologic diseases

Choice of Beta blockers based on: cardioselectivity, intrinsic sympathomimetic activity, lipid solubility

Adverse effects: fatigue, worsening peripheral vascular disease, worsening bronchospasm, decreased sexual functions, increased incidence of diabetes, masking of symptoms of hypoglycemia

Question 9

Phentolamine

Answer 9

Alpha adrenoceptor antagonist

Alpha 1= alpha 2

Effects: decrease BP, orthostatic hypotension, tachycardia, reverse pressor effects of alpha and Beta agonists, miosis, nasal stuffiness, decrease resistance to urine flow

Clinical use: pehochromocytoma, hypertensive emergencies, chronic hypertension, peripheral vascular diseases, urinary obstruction, erectile dysfunction