DIGOXIN

• See Heart failure and Atrial fibrillation

• Give orally, no advantage to IV

Younger and fitter

• Normal renal function, normal weight, no interacting medicines, not frail / elderly

Loading dose

• Give in 500 micrograms or 250 micrograms doses with a 6 hr interval between each dose
• reassess HR response before next dose
• if HR <100bpm no need for further loading dose, jump directly to maintenance
• Maximum allowed total loading dose: 1mg, occasionally 1.25mg

Maintenance dose

• Initially 125 micrograms od
• assess HR response and consider adjusting dose
• levels only useful in context of suspected toxicity e.g. nausea, bradycardia

Older, frail or reduced renal function

• CKD or CrCl <60ml/min, reduced weight <60kg, interacting medicines, frail/elderly

Loading dose

• Give in 250 micrograms doses with a 6 hr interval between each dose
• reassess HR response before next dose
• if HR <100bpm no need for further loading dose, jump directly to maintenance
• Maximum allowed total loading dose: 750 micrograms

Maintenance dose

• Initially 62.5 micrograms od
• assess HR response and consider adjusting dose
• levels only useful in context of suspected toxicity e.g. nausea, bradycardia

Patients taking digoxin alone for rate control in AF

• Once treatment is established, ventricular rate is the best guide to the appropriate dosage

Care with concurrent medication

• e.g. if amiodarone added, reduce usual dose by half

Digoxin levels

Indications

• To question need for continued treatment in patients with sinus rhythm
• To monitor effect of concurrent disease or drug treatment
• To confirm diagnosis of suspected toxicity (nausea, visual disturbances, bradycardia) and to aid dose reduction
• To investigate suspected treatment failure or non-compliance

Sampling

• Steady state is not achieved until 1–3 weeks after starting therapy or changing the dosage, depending on patient's renal function
• Take samples at least 6 hr post-dose
• often easier to sample immediately before a dose is due

Target range

• 0.8–2.0 microgram/L
• concentrations <0.8 microgram/L have no useful inotropic effect

Interpretation

• Consider the clinical effect of the drug as well as the serum concentration in dosage adjustment
• Sensitivity to digoxin is affected by thyroid function, oxygen saturation, and serum concentrations of potassium and calcium
• increased sensitivity to digoxin if hypothyroidism, hypoxia, hypomagnesaemia, hypokalaemia and hypercalcaemia
• decreased sensitivity to digoxin if hyperthyroidism and hyperkalaemia
• take into account when interpreting individual serum digoxin concentrations in relation to the target range