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C50 Cardiology and Cardiac Surgery
Common Medications
Toronto Notes 2019
Table 19. Antiarrhythmic* Drugs (Vaughan-Williams Classification)
Class Agent
Ia quinidine procainamide
disopyramide
Ib lidocaine mexiletine
Ic propafenone flecainide
encainide
II propranolol metoprolol, etc.
III amiodarone** sotalol
IV verapamil diltiazem
Indications
SVT, VT
VT
SVT, VT AFib
SVT, AFib
SVT, VT
AFib
SVT, VT, AFib
SVT AFib
Side Effects
Torsades de Pointes (all Ia), diarrhea Lupus-like syndrome Anticholinergic effects
Confusion, stupor, seizures GI upset, tremor
Exacerbation of VT (all Ic) Negative inotropy (all Ic) Bradycardia and heart block (all Ic)
Bronchospasm, negative inotropy, bradycardia, AV block, impotence, fatigue
Amiodarone: Photosensitivity, pulmonary toxicity, hepatotoxicity, thyroid disease, increased INR Amiodarone and Sotalol: Torsades de Pointes, bradycardia, heart block, β-blocker side effects
Bradycardia, AV block Hypotension
**Amiodarone has class I, II, III, and IV properties
Mechanism of Action
Moderate Na+ channel blockade
Slows phase 0 upstroke
Prolongs repolarization, slowing conduction
Mild Na+ channel blockade Shortens phase 3 repolarization
Marked Na+ channel blockade Markedly slows phase 0 upstroke
β-blocker
Decreases phase 4 depolarization
Blocks K+ channel
Prolongs phase 3 repolarization, which prolongs refractory period
Calcium channel blocker
Slows phase 4 spontaneous depolarization, slowing AV node conduction
*All antiarrhythmics have potential to be proarrhythmic
Table 20. Actions of α and β Adrenergic Receptors
Target System Cardiovascular
Respiratory Dermal
Ocular Gastrointestinal
Genitourinary
Metabolic
α RECEPTORS
α1
Constriction of vascular smooth
muscle
Constriction of skin, skeletal muscle, and splanchnic vessels
Increased myocardial contractility Decreased heart rate
Pilomotor smooth muscle contraction
Apocrine constriction
Radial muscle contraction
Inhibition of myenteric plexus Anal sphincter contraction
Pregnant uterine contraction Penile and seminal vesicle ejaculation
Urinary bladder contraction
Stimulate liver gluconeogenesis and glycogenolysis at the liver
α2
Same as α1
Peripherally act to modulate vessel tone
Vasoconstrict and dilate; oppose α1 vasoconstrictor activity
Smooth muscle wall relaxation
Same as α1 Fat cell lipolysis
β RECEPTORS
β1
Increased myocardial
contractility Accelerate SA node Accelerate ectopic pacemakers
Ciliary muscle relaxation
Stimulation of renal renin release
Fat cell lipolysis Glycogenolysis
β2
Decreased vascular
smooth muscle tone
Bronchodilation
Bladder wall relaxation Uterine relaxation
Gluconeogenesis Fat cell lipolysis
β2 Albuterol
Terbutaline Butoxamine
Adapted from the Family Practice Notebook (www.fpnotebook.com/NEU194.htm)
Table 21. Commonly Used Drugs that Act on α and β Adrenergic Receptors
Mechanism of Action
Agonist Antagonist
α RECEPTORS
α1 Phenylephrine
Methoxamine
Prazosin Phenoxybenzamine
α1 and α2 Epinephrine
Norepinephrine Phentolamine
α2 Clonidine
Methyldopa
Yohimbine Mirtazipine
β RECEPTORS
β1 Norepinephrine
Dobutamine
Metoprolol Acebutolol Alprenolol Atenolol Esmolol
β1 and β2 Isoproterenol
Epinephrine
Propranolol Timolol Nadolol Pindolol Carvedilol
Adapted from the Family Practice Notebook (http://www.fpnotebook.com/NEU194.htm)