Cardiac Glycosides & Phosphodiesterase Inhibitors

- Cardiac glycosides are used in patients with heart failure, atrial fibrillation, and atrial flutter

- HF: The heart is incapable of pumping adequately to supply oxygen to the body

- A-Fib: Cardiac dysrhythmias with rapid, uncoordinated contractions of the atrial myocardium

- Atrial flutter: Cardiac dysrhythmias with rapid contractions of 200-300 BPM

- Glycosides have 3 functions to increase contractility and stroke volume while decreasing HR

- Positive inotropic response:

- Increases myocardial contractions

- Inhibition of the sodium-potassium pump allows more sodium and calcium to be stored within cells

- The sodium-calcium pump brings in sodium and releases calcium from the cell but inhibition of the sodium-potassium pump prevents sodium from being released which inhibits the amount of sodium that is taken in/calcium released

- Increased intracellular calcium lowers membrane excitability

- Results in greater contractions

- Negative chronotropic response:

- Decreases HR

- Negative dromotropic response:

- Slows the speed of electrical conduction through the AV node

- Increased contractility increases CO, decreases preload and edema, and promotes fluid excretion

- Fluid retention in the lungs and extremities is decreased

Digoxin

- Digoxin is a secondary drug used for HF

- First-line medications include [[phosphodiesterase inhibitors]] (PDE) inhibitors and IV inotropic agents (dopamine and dobutamine)

- Digoxin is 20-30% protein-bound

- Digoxin can be given intravenously or orally

- The half-life of digoxin is 30-40 hours

- High risk for drug accumulation and digitalis toxicity

- Patients with kidney dysfunction can affect the excretion of digoxin

- Thyroid dysfunction can influence the metabolism of digoxin

- Hyperthyroidism: Increased dose

- Hypothyroidism: Decreased dose

Digitalis (Digoxin) Toxicity

- Cardiotoxicity is an adverse reaction to digoxin and can result in ventricular dysrhythmias

- Older adults are more prone to digitalis toxicity

- Digitalis toxicity may result in 1st, 2nd, or 3rd degree heart block

- Digoxin-immune Fab can be used to treat severe toxicity

- Symptoms of toxicity:

- Rhythm changes

- PVC

- Bradycardia

- GI issues

- Nausea/Vomiting

- Anorexia

- Diarrhea

- Neurological changes

- Blurred vision/Visual illusion

- Confusion/Delirium

- Headaches

Drug Interactions

- Potassium-wasting diuretics increase the effects of digoxin

- Increased risk for toxicity

- Hypokalemia increases the effects of digoxin in myocardial cells

- Cortisone drugs increase the effects of digoxin

- Cortisone preparations promote the reabsorption of sodium and the excretion of potassium, which can lead to hypokalemia

- Patients taking cortisone drugs or potassium-wasting diuretics should have a potassium-rich diet or take supplements

- Antacids decrease the effects of digoxin

- Antacids increase gastric pH and decrease the absorption of digoxin

- Antacid medications and digoxin meds should be staggered to prevent interactions

Phosphodiesterase Inhibitors

- Phosphodiesterase inhibitors (PDE) inhibitors are vasodilators and produce an inotropic response, similarly to cardiac glycosides

- Positive inotropic responses increase the contractility of the heart (increased CO)

- PDE inhibitors are a first-line medication for heart failure

- Using IV PDE inhibitors for more than 48-72 hours can cause severe cardiac dysrhythmias