Antiarrhythmic –
Vaughan Williams Class V
Other

glycoside derived from the dried leaves of the foxglove

Block Na-K-ATPase pump

used in AF and atrial flutter, SVT and in heart failure

PO: tablets 62.5mcg or 250mcg. IV:25-250mcg/ml.
Narrow therapeutic window. Monitoring necessary - 0.5-2mcg/L(~1)

i) Na/K ATPase inhibition → ↑ intracell Na → ↓ Na-Ca pump → ↑ intracell Ca → inotropy
ii) direct: ↑ AV node ERP, ↓ V ERP
iii) Indirect: Via Vagus – bradycardia, ↓ A refr. Augmentn of direct ↑ AV node ERP

onset / duration Oral: 1-2 hours; I.V.: 5-60 mins / 3-4 days

Thyroid-Vd
Narrow therapeutic window -monitoring - 0.5-2mcg/L(~1)
Toxic > 2.5- arrhythmias, AV block.
anorexia,N/V/D, lethargy. Altered Red green colour perception. ECG: ↑ PR, ST dep, T fl-attening, ↓QT. (may not indicate toxicity)

IV, PO BA 60-80%

prot bind ~25%; uremia- displaced fm pl prot bind sites

6-7 L/kg
thyroid (↑ in hyper, ↓ hypo).

Stomach:Sequential sugar hydrolysis+ redn of lactone ring by intestinal bacteria
min hepatic, most excr unchanged

Urine (50% to 70% unchanged)

36-48 hours

IV/PO.
loading 250-500mcg QID then 62.5-125mcg daily

Level 1

Effects: Inotropy
Direct and indirect effects on refractory period + bradycardia -> treat AF&flutter

Level 3

CVS
- The main action of digoxin is to increase the force of cardiac contraction; automaticity and contractility also increase.
- The heart rate is slowed due to a combination of improved haemodynamics, depression of sinus node discharge, slowing of AV nodal conduction, an increase in the AV nodal refractory period, and an indirect vagotonic effect.
- Rapid intravenous administration of digoxin may cause vasoconstriction, leading to hypertension and decreased coronary blood flow.
- The characteristic ECG changes produced by the drug include prolongation of the PR interval, ST-segment depression, T-wave flattening, and shortening of the QT interval

GIT - Anorexia/N/V/Diarrhoea (especially if therapeutic range exceeded)

CNS
- Headache, confusion, coma (toxicity)
- Visual disturbances (deranged red-green colour perception)

Renal- Mild diuretic effect

Miscellaneous- Rashes, eosinophilia; Gynaecomastia