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Unformatted text preview: art Failure Cardiac Glycosides
Some Background on Cardiac Glycosides: • Structure of Chemical Group
– All have sugar structural group (glycoside)
– Attach various other chemical groups (aldehyde, hydroxyl,
– Some can be extracted from plants
• Digoxin (Lanoxin®) - from white foxglove
– (caution: renal failure) • Digitoxin - from purple foxglove (Digitalis purpura)
– Note that the different cardiac glycosides have
different pharmacokinetics and should not be used
interchangeably. Dosages, durations etc. differ. Cardiac Glycosides (digitalis)
– Positive inotropic action (strength of contraction)
– Negative dromotropic effect in the heart
– Negative chronotropic action • Mechanism:
– Increases Ca++ release within cardiac muscle (stronger)
– Moves calcium into muscle (with slower conduction)
– Increases vagal tone.
• This is a significant feature in later discussions + Inotropic
May cause therapeutic
and side effects Cardiac Glycosides: Therapeutic Uses
• Congestive heart failure - heart fails to pump
adequate amount of blood
– Mechanism of action: positive inotropic effect
• Supportive treatment: decreased weight, physical activity,
and Na intake, and treat hypertension if present
• Result: heart size decreased to normal, lower H.R.,
diuresis • Atrial flutter (200-300 beats/minute) or
Fibrillation (more than 300 beats/minute) or
Paroxysmal tachycardia (irregular beats)
– Usually requires higher dose than treating CHF.
– Mechanism of action (Protect Ventricles):
• Depresses electrical conduction in atria and AV node
• Increased refractory period Cardiac Glycosides Can Be Dangerous
Issues to Consider:
• Commonly prescribed yet poor margin of safety
– Low therapeutic index. • Order of appearance unpredictable.
• Dose must be carefully adjusted for each patient.
• Very small dose required
– Errors are significant. • Poisoning usually due to “cumulative effect“
• Digitalizing" Dose = pri...
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This document was uploaded on 02/07/2014.
- Spring '14