DIGOXIN

“LANOXIN”

1) Action

• Cardiotonic glycoside

2) Mechanism

• Inhibits Na+,K+-ATPase [membrane enzyme associated with the sodium pump] resulting in increased intracellular Na+, consequently, intracellular Ca++ rises as normally expel Ca++ from cell into SR or ECF by exchanging with Na+ resulting in increased cardiac contractility [increase inotropic effect]

• Increases vagal tone to heart resulting in depressed AV conduction and slower HR

• Also has a direct effect in reducing AV conduction

3) Indications

• CCF [2° atherosclerosis, hypertension, valvular lesions]

• Atrial fibrillation to reduce ventricular rate

4) Effects on organs—side effects

• In excessive doses, increases excitability of cardiac muscle which results in ectopics

5) Toxic effects/ precautions with administration

• Hypokalaemia sensitises heart to digoxin [caution with diuretics and corticosteroids]

• Bradycardias & almost any type of arrhythmias esp heart blocks & ventricular ectopics

6) Contraindications

• Hypokalaemia; bradycardia

7) Reversal, antagonism or antidote

• Phenytoin/lignocaine/propranolol/procainamide/quinidine/atropine

8) Loading dose, maintenance dose, frequency & method of administration

• Slow IV bolus over 5 min

• 50 mcg/2 ml; 500 mcg/2 ml

9) Drug’s metabolism—Drug’s excretion—Half life (pharmacokinetics)

• Elimination halflife: 40 hr

• % plasma binding: 25