Notes & Sources

• Volume of distribution uses the published relationship Vd = 3.84 × weight + 3.12 × CrCl, which accounts for the reduction in distribution seen in renal impairment.
• Use lean or ideal body weight. Digoxin distributes poorly into adipose tissue, so actual body weight over-estimates the loading dose in obesity.
• Target concentrations differ by indication — around 0.5-0.9 ng/mL in heart failure, with higher targets sometimes used for rate control in atrial fibrillation. Higher concentrations in heart failure have been associated with worse outcomes.
• Loading is conventionally given in divided doses, commonly half the total followed by two quarters at 6 to 8 hour intervals, with reassessment between doses.
• Correct hypokalaemia and hypomagnesaemia first — both potentiate digoxin toxicity at concentrations that would otherwise be tolerated. A level drawn less than 6 hours after a dose reflects distribution, not steady state, and will mislead.