Cardiac Glycosides Flashcards Preview

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Flashcards in Cardiac Glycosides Deck (11):
1

Cardiac Glycosides

Digoxin, Digitoxin, Digitalis, Ouabain
Used in CHF and AFib
Digoxin used widely due to short half-life and availability of antidote

2

Structure of Cardiac Glycosides

Lactone Ring- functional
Steroid Nucleus- functional
Sugar Residues- PK properties affecting absorption, metabolism and half-life

3

MOA of Digoxin

Inhibits Na/K ATPase which reverses Ca/Na pump
Ca rises in cell and enters SR
Increased contractility at next depolerisation

4

Effects on Myocardium

Increase force of contraction
Increase cardiac automaticity and excitability

5

Effects on Conducting System

Slows Heart Rate
Deceases automaticity of AV node
Prolongs refractory period
Increase automaticity of His-Purkinje system

6

Mechanism of Increased Automaticity/ Excitability

Depolerisation of membrane potential
An increase in slope of phase 4

7

Effects on Autonomic System

Increase Parasympathetic tone: decrease HR, decrease AV node conduction velocity, increase AV node refractory period
Decrease Sympathetic tone: Augments vagal effects on SA and AV node, counteracts vasoconstriction
Sensitises baroreceptors

8

Other Effects

Vessels: Vasoconstriction
CNS: Fatigue, drowsiness, confusion
GI: Anorexia, Nausea, Vomiting

9

Glycoside Interactions

Loop Diuretics and Potassium: In hypokalaemia, Digoxin will be hyperactive- arrhythmia
Calcium: Hypercalcaemia will cause DADs
Chronic Renal Failure: Requires dose adjustment

10

Digoxin Toxicity and Treatment

Therapeutic Window: 1-2ng/ml to 2.5 ng/ml
Signs and Symptoms are similar to CHF: tachyarrhythmia, Conduction Block, fatigue, nausea
Treatment: Reduce Dose, Antidote, Lignocaine(anti-arrhythmatic)

11

Phosphodiesterase Inhibitors

Milrinone
Ionodilator
Inhibits degredation of cAMP and cGMP
Long-term use increases risk of mortality