some can be extracted from plants digoxin lanoxin

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Unformatted text preview: art Failure Cardiac Glycosides Cardiac Some Background on Cardiac Glycosides: • Structure of Chemical Group – All have sugar structural group (glycoside) – Attach various other chemical groups (aldehyde, hydroxyl, etc.) – 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) Cardiac • Actions: – 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 - Chronotropic - Dromotropic May cause therapeutic and side effects Cardiac Glycosides: Therapeutic Uses Cardiac • 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 Cardiac 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.

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