Adrenergics & Adrenergic Blockers

Adrenergics and Adrenergic Blockers I. Adrenergics/ Sympathomimetics •

mimic effects of NE by stimulating SNS.

A. Effects of Adrenergics at receptor sites Alpha 1 Receptors • vasoconstriction (skin & mucous membrane) • increase BP • pupil dilation • closure of urinary bladder sphincter • thickened salivary secretions • goosebumps • ejaculation

Beta 1 receptors    

Alpha 2 receptors • decrease NE release • decrease BP • decrease GI motility

Beta 2 receptors

increase HR Increase cardiac contraction increase cardiac conduction lipolylis

     

bronchodilation vasodilation (skeletal muscle) relaxation of uterus relaxation of GIT & decrease GI secretions relaxation fo urinary bladder increase blood sugar

B. Inactivation of NE: 1. reuptake of NE back into the neuron. 2. enzymatic degradation - MAO & COMT 3. diffusion away from transmitter C. Classification of Adrenergics/ Sympathomimetics I.

Direct Acting Adrenergic • epinephrine

II.

Indirect Acting Adrenergic • amphetamine

III.

Mixed Acting Adrenergic • ephedrine

A. Nonselective Adrenergics  endogenous catecholamines • epinephrine* • norepinephrine • dopamine  synthetic catecholamine • dobutamine Epinephrine Indications: tx of allergic reaction, anaphylaxis, bronchospasm, cardiac arrest. Mechanism of Action (MOA):  acts on alpha 1 , to increase vasoconstriction & BP  acts on beta 1, to increase heart rate  acts on beta 2, to promote bronchodilation B. Alpha selective- adrenergics  Alpha 1 & 2 adrenergic • phenylephrine*  Alpha 2 adrenergics • clonidine • methyldopa phenylephrine Indications: Tx of cold & allergies, shock MOA: alpha adrenergic that causes vasoconstriction & increase BP C. Beta selective adrenergics  Beta 1 & 2 adrenergics (beta agonists) • Isoproterenol* • ritodrine  Beta 2 selective adrenergics • terbutaline • albuterol Isoproterenol

Indications : tx of congestive heart failure, asthma MOA: beta adrenergic, increases heart rate & contractility & bronchodilation  Common S/E & adverse reactions of adrenergics: • hypertension • tachycardia , palpitations & tremors • dizziness • urinary retention • pallor • nausea & vomiting ( N & V) • blood glucose may increase  Lifethreatening effect: cardiac dysrhythmias

II.

Adrenergic Blockers/ Sympatholytics • block alpha & beta receptors, blocking sympathetic responses

A. Effects of adrenergic blockers at receptor sites: Alpha 1 receptor     

Alpha 2 receptor

vasodilation & decrease BP reflex tachycardia miosis suppress ejaculation reduce contraction of bladder sphincter & prostate gland

Beta 1 receptor

Beta 2 receptor

 decrease HR & contraction

 bronchoconstriction  uterine contraction  decrease blood sugar

C. Classification of Adrenergic Blockers/ Sympatholytics  Direct Acting  Indirect acting A. Alpha & Beta adrenergic Blockers (Nonselective Adrenergic blockers)  carvedilol  labetolol*

indications: tx of hypertension & angina pectoris MOA: blocks alpha & beta receptors in SNS causing decrease BP without reflex tachycardia & decrease renin B. Alpha 1 selective adrenergic blockers  phentolamine*  doxazosin  prazosin Indications: Tx of peripheral vascular disease, pheochromocytoma, acute HPN, benign prostatic hypertrophy MOA: blocks alpha 1, producing vasodilation & decrease BP & decrease contraction of prostate SE/ Adverse effects of alpha blockers: • flush & nasal stuffiness • orthostatic hypotension & dizziness • reflex tachycardia Lifethreatening effect: cardiac dysrhythmias C. Beta 1 and 2 adrenergic blockers (Nonselective beta blockers)  propanolol*  sotalol  timolol  nadolol  pindolol propanolol Indications: Tx of cardiac dysrhythmias, HPN, angina, myocardial infarction (MI) MOA: blocks beta 1 & 2 adrenergic receptors, causes decrease HR & BP as well as bronchoconstriction & uterine contraction S/E & Adverse effects of beta blockers: • bradycardia • hypotension & dizziness • headache • hypoglycemia • visual hallucinations & mood changes • thrombocytopenia Lifethreatening effects: laryngospasm, heart block

D. Beta 1 selective adrenergic blockers  metoprolol*  atenolol  acebutolol  esmolol  bisoprolol  betaxolol  esmolol Indications: Tx of HPN, angina pectoris , myocardial infarction MOA: blocks beta 1, to decrease HR & BP  Alpha blockers (ie prazosin) & beta blockers (ie propanolol, metoprolol, pindolol) • may cause impotence or decrease in libido E. Adrenergic Neuron blockers  guanethidine  guanadrel

Whatsoever you sow, that you shall reap.