AGENTS THAT BLOCKS ADRENOCEPTORS -ALSO KNOWN AS SYMPATHOLYTICS

ARENERGIC BLOCKER/SYMPATHOLYTICS

Bind to adrenoreceptors reversibly or irreversibly, preventing its activation by

endogenous catecholamine. 

CLASSIFICATION

α Blockers

Phenoxybenzamine , Phentolamine,

Prazocin, Terazocin, Doxazocin,

Yohimbine, Alfuzosin, Tamsulosin

β Blockers

 Propranolol, Metoprolol, Acebutolol,

Atenolol, Betaxolol, Bisoprolol,

Carteolol,

Carvedilol, Esmolol, Labetalol, Nadolol,

Nebivolol, Penbutolol, Pindolol, Timolol

Inhibiting reuptake or release Guanethidine, Reserpine

Phenoxybenzamine: non-selective, α1 & α2 blocker, irreversible, non-competitive,

MOA:

 covalently block the α1 & α2 adrenoreceptor..action last about 24hrs..body has to

synthesize new receptor to overcome this block..

Actions:

 vasodilation..decreased peripheral resistance provoke Reflex Tachycardia…

Not used in Hypertension b/c its blockade release more nor-epinephrine which stimulate

β receptor….

Epinephrine Reversal b/c by blocking α adrenoreceptor it block Vasoconstriction but

stimulation of β receptors by Epinephrine cause vasodilation (Reverse Action)….Actions

of Nor-Epinephrine not reversed b/c it lacks β receptors

T.E:

 used in Pheochromocytoma (increased release of catechoamine)…..in Raynaud

disease…Frostbite..Arocyanosis... chronic management of catecholamine-tumor

S.E:

postural hypotension.. Reflex tachycardia.. Nasal stuffiness

Contraindicated in Pt. with decreased coronary perfusion

Phentolamine:

 Competitive blocker of α1 & α2 ..4hrs duration

T.E

Short-term managemeent of Pheochromocytoma…prevent Dermal Necrosis

…prvent Extravasation..treat Hypertensive crisis due abrubt withdrawl of Clonidine &

from digesting Tyramine containing food…

used in Impotence produce vasodilation of penile arteries

S.E:

 Postural hypotension…reflex tachycardia

Prazocin, Terazocin, Doxazocin, Tamsulosin, Alfuzosin

Selective competitive blocker of α1 receptor.

Actions= decrease Peripheral resistance & Aterial B.P by relaxation of both venous and

arteries smooth muscle….

T.E= Prazocin, Terazocin, Doxazocin used in Hypertension..Doxazocin long acting

Tamsulosin & Alfuzocin used in Benign Hypertrophy...Tamsulosin found on smooth

muscle of prostate

S.E:

 Orthostatic Hypotension…no reflex tachycardia

Prazocin retain Na+ and fluid so used in Diuretic

Tamsulosin used catiously in” Floopy Iris Syndrome” acondition in which iris billows due to intraoperative surgery

Finasteride & Dutasteride:

 inhibit 5α-reductase, preventing conversion of Testosterone into DiHydroTestosterone…used in Benign Hyperplasia

Yohimbine:

Selective competitive α2 blocker…..obtained from bark of yohimbe tree…

Sexual stimulant…used in Raynaud disease...contraindicated in CNS & CVS disorder b/c it is CNS & CVS stimulant

β-ADRENERGIC BLOCKING AGENTS

Propranolol: Non-selective...Prototype..block β1 & β2 receptors..O.D sustained release

Actions: 

-Ve ionotropic & chronotropic effects (decrease Heart rate & force of

contraction) …Bradycardia...Cardiac output, work , oxygen consumption decreased…

Blockade of β-blocker cause decreased cardiac output..decreased B.P…which causes

reflex peripheral vasoconstriction…reduced blood flow to periphery

Blocking β2 receptors in lungs ..Bronchoconstriction.. contraindicated in COPD &

Asthma

Combine with Diuretic to prevent Na+ retention,

Hypoglycemia due to blockade of β receptors, Block the actions of Isoproterenol

Vd is 4L/kg

T.E:

 used in Glaucoma…in Hypertension…prophylactically in Migraine..in

Hyperthyroidism life-saving by preventing Cardiac Arrythmias….In Angina..in M.I

S.E:

 Bronchoconstriction,,,,Sexual impairment,,,Fasting hypoglycemia,,,,abrupt removal 

cause arrhythmia…..increase LDL(bad cholesterol) & decrease HDL(good cholesterol) 

Timolol & Nadolol:

 β1 & β2 blocker…Timolol in Glaucoma 

Betaxolol & Carteolol also used in open-angle glaucoma.. 

Acebutolol, Atenolol, Metoprolol, Bisoprolol, Betaxolol, Nebivolol, Esmolol

Block β1 receptor…Esmolol has a short half life, used in Cytoscopy & in surgery

All of these used in Hypertension & not contraindicated in Asthma 

S.E:

 coldness of Extremities 

Pindolol & Acebutolol:

 Antagonists with partial Agonist activity..weakly stimulate β1 & β2…..Have intrinsic sympathomimetic activity…used in Hypertension

Labetalol & Carvedilol:

 α & β blocker…produce peripheral vasodilation..decreased B.P 

Carvedilol decrease lipid peroxidation….Labetalol used in elderly/Black hypertensive Pt. 

.Labetalol alternative to METHYLDOPA in treatment of Pregnancy-induced Hypertension 

Drugs Affecting Neurotransmitter release or uptake 

Reserpine= plant alkaloid...Block Mg++/ATP dependent transport of Catecholamine from Cytoplasm to storage vesicle…

Guanethidine= Block the release of Norepinephrine from storage vesicle into synaptic cleft…

S.E= orthostatic hypotension…impair male sexual function

Cocaine= Highly addictive…Block Reuptake of Catecholamine ..prolong the CNS & Peripheral action of these monamines.. 

Prolong Dopaminergic effects in Brain‟s pleasure sys produce intense EUPHORIA ..