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Adrenergic Drugs

Overview

Mimic the effects of SNS neurotransmitters (catecholamines) Norepinephrine (NE) Epinephrine (EPI) Dopamine

Adrenergic Receptors Alpha 1 Receptors

All vascular smooth muscle, GI & urinary sphincters Dilator muscle of the iris Arrector pili muscle of hair follicles

Alpha 2 Receptors: Located on secretory terminals of

postsynaptic adrenergic neurons.

Adrenergic Receptors Beta 1 Receptors

Cardiac pacemaker Myocardium Salivary gland ducts Eccrine and apocrine sweat glands

Beta 2 Receptors: gastrointestinal tract urinary bladder skeletal muscle arteries bronchial tree some coronary vessels

Beta 3 Receptors: on the smooth muscle cells of the urinary bladder

Beta-Adrenergic Receptors

Dopaminergic Receptors Stimulated by dopamine Causes dilation of the following blood vessels,

resulting in increased blood flow Renal Mesenteric Coronary Cerebral

Dopaminergic Receptors D1 Receptors:

Smooth muscles of pulmonary artery, kidney, smooth muscles of various organs e.g sphincters of stomach., proximal tubule of nephron, brain

D2 receptors: Brain, Substantia nigra, neostraital pathway,

pulmonary artery, kidney D3,D4,D5:

These are primarily present in brain. D4 receptors are expressed in atrial wall. dopamine increases myocardium contractility.

Adrenergic Receptors Activation of alpha 1 and beta 1 receptors

cause stimulatory responses Activation of alpha 2 , beta 2 & B3

receptors cause inhibitory responses

Responses to Stimulation

Mechanism by which stimulation of a nerve fiber results in a physiologic response:

Catecholamines Endogenous substances:

Epinephrine. Norepinephrine. Dopamine.

Exogenous substances:

Dobutamine. Phenylephrine.

1- direct acting sympathomimetics.

2- indirect acting sympathomimetics.

• Inhibit catecholamine breakdown

3- mixed acting sympathomimetics

Direct acting adrenergic agonists Epinephrine. (alpha and beta) Norepinephrine. (alpha and beta) Dopamine. (alpha and beta) Isoproterenol (on beta 1 and beta 2) Dobutamine (beta 1 agonist). Salbutamol (albuterol), terbutaline, salmetrol, and

formetrol (acting on beta 2 only). Oxymetazoline(alpha1 and alpha2) Phenylephrine (alpha 1) Clonidine (alpha2)

Indications Respiratory indications Indications for topical nasal decongestants Ophthalmic indications Cardiovascular indications

Respiratory indications 1- as bronchodilators

Nasal congestion

Indications (cont’d) Treatment of nasal congestion

Alpha1-adrenergic receptors Examples: epinephrine, ephedrine, naphazoline,

oxymetazoline, phenylephrine, and tetrahydrozoline

Ophthalmic indications Reduction of intraocular pressure and dilation of

pupils. (Phenylephrine )

Temporary relief of conjunctival congestion (eyes)

CVS indications Support the cardiovascular system during cardiac

failure or shock.

Common vasoactive adrenergic drugs include dobutamine, dopamine, ephedrine, epinephrine, fenoldopam, midodrine, norepinephrine, and phenylephrine.

Epinephrine/ adrenaline

Dopamine • Dopamine

• At doses < 2 mcg/kg/min, stimulates dopamine receptors, vasodilatation and increase renal perfusion .

• At doses between 5 and 10 mcg/kg/min, stimulates beta-1 adrenergic receptors, resulting in increased cardiac output.

• At doses > 10 mcg/kg/min, dopamine stimulates alpha-adrenergic receptors, leading to vasoconstriction, which increases the systemic vascular resistance and increase BP

Dobutamine • Dobutamine

• Primarily stimulates beta-1 receptors, leading to increased inotropic and chronotropic effects to al lesser extent

• Dobutamine also stimulates beta-2 adrenergic receptors, leading to vasodilatation.

• This combination of effects contributes to increased cardiac output with decreased systemic vascular resistance.

• Dobutamine is typically used for patients with cardiogenic shock.

Nursing Implications (cont’d) • Overuse of topical nasal decongestants may cause

rebound nasal congestion or ulcerations

•Administering two adrenergic drugs together may precipitate severe cardiovascular effects such as tachycardia or hypertension

Nursing Implications (cont’d) • Monitor for therapeutic effects (cardiovascular

uses) – Decreased edema – Increased urinary output – Return to normal vital signs – Improved skin color and temperature