341 - Adrenergic Drugs

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341 - Adrenergic Drugs
2011-10-10 23:39:39

PHAR 341 - Adrenergic Drugs
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  1. Epinephrine (adrenaline)
    • Non-selective agonist of all adrenoreceptors
    • Given locally or iv
    • Doesn't cross blood-brain barrier
    • Effects: Increased sympathetic effects, fear anxiety restleness tremor headache (indirect effect of feeling heart pound), vasodilation of skeletal muscle (increases systolic pressure but decreases diastolic pressure b/c of dilated skeletal muscle blood vessels), pallor (pale skin because blood gets shunted from skin to skeletal muscle)
    • Reduction of regional blood flow: Used in surgery and local anesthesia because it constricts blood vessels
    • Cardiac Arrest: It increases heart rate and contractions strength
    • Asthma: It dilates bronchioles
    • Anaphylactic Shock: Decreases bronchospasm, mucous membrane congestion, angioedema, hypotension
  2. Norepinephrine (noradrenaline)
    Same effects as epinephrine except it features less dilation of skeletal muscle vessels, less bronchodilation, and an increase in both systolic and diastolic BP
  3. Adrenergic Receptor Subtypes
    • α1: excitatory, Vascular Smooth Muscle - contraction, Pupillary Dilator Muscle - contraction (pupil dilates), Pilomotor Muscle - erects hair, Prostate - contracts, Bladder Sphincter - contracts, Heart - positive inotrope (not too effective)
    • α2: inhibitory (opposes effect of α1 and β), Adrenergic & Cholinergic - inhibits trasmitter release at effector sites, Vascular Smooth Muscle - contraction, GI Smooth Muscle - relax (indirect), Fat Cells - inhibits lipolysis
    • β1: excitatory, Heart - positive chronotrope (heart rate) and inotrope (contraction force)
    • β2: excitatory, Respiratory - relaxation (bronchodilation), Uterine - relaxation, Vascular Smooth Muscle - relaxation (vasodilation), Skeletal Muscle - uptake K+
    • β3: excitatory, Fat Cells - activates lipolysis, Bladder - mediates relaxation of fundus
    • D1: excitatory, Smooth Muscle - relaxation/dilation of renal blood vessels
  4. Dopamine
    Selective agonist of D1 (relaxes kidney vessels), D2 (suppresses norepinephrine release which leads to vasodilation in the kidney), β1 (activates heart which increases blood flow to kidneys)
  5. Doputamine
    • Selective agonist of β1 and activates α1
    • Hypotensive Emergency: preserves cerebral and coronary blood flow
  6. Phenylephrine
    • Pure α agonist
    • Mydriatic (dilates pupils), decongestant, can be used to raise BP
  7. Xylometazoline/oxymetazoline
    • Pure α agonist
    • Topical decongestant and promotes constriction of the nasal mucosa
    • May cause hypotension
  8. Clonidine
    • Selective α2 agonist
    • Decreases BP through actions in the CNS to decrease sympathetic output
    • No direct effect on the baroreceptor reflex
    • Hypertension
    • Alcohol and Nicotine Withdrawal: reduces symptoms because withdrawal makes a patient feel a lot of sympathetic effects (an α2 agonist decreases sympathetic tone via CNS action)
    • Used as an epidural analgesic
    • Side effects: Dry mouth, drowsiness, sedation, constipation.
  9. Isoproterenol
    • Pure β agonist
    • Positive chronotropic and inotropic actions (β1)
    • Potent vasodilator (β2)
    • Raises cardiac outpout with little raise in BP
  10. Salbutamol
    • β2 selective agonist
    • Asthma: it's a bronchodilator
  11. Cyanopindolol
    • β3 selective agonist
    • Currently in testing
  12. Amphetamine/Methamphetamine
    • Indirect Acting Sympathomimetic Drug
    • Works by causing displacement of stored catecholamines from the adrenergic nerve ending
    • Causes higher CNS effects
  13. Tyrasine
    • Indirect Acting Sympathomimetic Drug
    • Works by causing displacement of stored catecholamines from the adrenergic nerve ending
    • It's a byproduct of tyrosine metabolism
  14. Ephedrine
    • Indirect Acting Sympathomimetic Drug
    • Mild stimulant
  15. Cocaine and Tricyclic Antidepressants
    • Indirect Acting Sympathomimetic Drugs
    • Inhibits the reuptake of catecholamines back into the presynaptic cell
    • Slow effect
  16. MAO Inhibitors
    • Indirect Acting Sympathomimetic Drug
    • Ex. selegiline
    • Inhibiting MAO results in more catecholamine in synapse
    • Two Types: MAO-A (high in liver) and MAO-B (high in liver and CNS)
    • Parkinson's Disease and Depression
  17. Reserpine
    • Indirect Acting Sympatholytic Drug
    • Plant alkaloid
    • Works by inactivating storage vessicles so nerve terminals are unable to store catecholamines
    • It's very sedating and causes serious depression
    • It's antihypertensive but takes several weaks and needs to be used with a diuretic because it causes sodium retention
    • In research it's used to differentiate between direct actina gnd indirect acting sympathomimetics
    • Exam type question: You have a drug that shows a sympathomimetic effect. If the drug is direct acting - resperine will affect the drug. If the drug is indirect acting - resperine will have no effect.
  18. Guanethidine and Bretylium
    • Indirect Acting Sympatholytic Drug
    • It prevents the release of noradrenaline and they were used as antihypertensives
    • Bretylium is still used as an antiarrythmic agent
  19. Phentolamine
    • Reversible α Antagonist
    • It can dissociate from α receptors, competitve antagonist
    • Pheochromocytoma (tumor or adrenal tissue resulting in a lot of catecholamine release which leads to high BP), Male Erectile Dysfunction, Reversal of Local Vasoconstriction
    • Side effects: Severe tachychardia (α antagonism increases the effect of epinehphrine on beta receptors)
  20. Phenoxybenzamine
    • Irreversible α1 Antagonist "Suicide Inhibitor"
    • Covalently binds to α1 receptor which results in an irreversible blockade
    • Long duration
    • Pheochromocytoma
    • Side effects: Postural hypotension and tachycardia (less than phentolamine)
  21. Prazosin
    • α1 Selective Antagonist
    • Relaxes areterial and venous smooth muscle
    • Hypertension and Mild Benign Prostatic Hyperplasia (age related enlargement of prostate)
    • Side effects: Little tachycardia, postural hypotension, first dose effect (transient dizziness to syncope in elderly)
  22. α1 Receptor Subtypes
    • α1A: located in smooth muscle of peripheral blood vessels - mainly the prostate and urethra
    • α1B: common in the CNS, spleen and lungs, arteries and veins
    • α1B increases and α1A decreases with age
    • α1D: found in the detrusor muscle of the bladder (sphincter control), also found in blood vessels
  23. Tamsulosin
    • Competitive α1A and α1D Antagonist
    • Effects prostate and bladder sphincter smooth muscle
    • Mild Benign Prostatic Hyperplasia: age-related englargment of the prostate which causes weak urine flow. This drug will partially reverse smooth muscle contraction in the enlarged prostate and bladder base.
    • Side effects: Little effect on BP, causes a lot of dizziness, increased urnation with an increased chance of incontinence
  24. Propranolol
    • Non-Selective β Antagonist
    • Extensive first-pass metabolism in the liver
    • Hypertension, angina, migraine prophylaxis, essential tremor, decrease sudden death after MI, sever hyperthyroidism
    • Side effects: Fatigue, dizzines, depression, nightmares, bradycardia, increases triglyceride levels significantly
  25. Metoprolol
    • Selective β1 Antagonist
    • Hypertension, angina, after MI
    • Use may be preferable in diabetics because β2 receptors in the liver may play a role in recovery from hypoglycemia
    • Side effects: Fatigue, dizziness, bradycardia
  26. Acebutolol
    • β1 selective antagonist with partial β1 agonist properties (activates β1 a little while completely blocking endogenous catecholamine binding)
    • Hypertension and agina
    • Side effects: Fatigue, dizziness, less likely to cause bradycardia, less likely to alter plasma lipids
  27. Labetalol
    • α1 Selective Antagonist, β non-selective Antagonist, and some β2 agonist activity
    • Hypertension including hypertensive emergency during prenancy
    • Side effects: Hypotension induced by labetalol is accompanied by less tachycardia than occurs with α blockers (because it's a β blocker too)