Serial serum digoxin concentrations were measured over a 10-day period in 15 low birth weight infants requiring digoxin therapy. The calculated total body digoxin clearance (TBDC) was found to be highly dependent on gestational age and body weight, with dose-normalized, steady-state digoxin concentrations inversely related to the same factors. Because of the decreased TBDC in low birth weight infants, our data support the recent recommendations in the literaure to reduce maintenance doses of digoxin in these infants. Our study has further demonstrated that the reduction should be proportional to both gestational age and body weight.

Digoxin pharmacokinetics were studied in 13 low-birth-weight infants requiring digoxin therapy. Their weights ranged from 820 to 2,710 g (x̄ = 1,440 g) and gestational ages ranged from 26 to 38 weeks (x̄ = 30.9 weeks). The distribution and elimination of digoxin can be described by an open two-compartment model. Poor correlation between volume of distribution Vdβ (5.7 ± 1.0 liters/kg) and gestational age (GA) or weight (Wt) was observed. Digoxin half-life (47 ± 21 h) was inversely related to GA and Wt (r = 0.69 and 0.66, respectively), but total body digoxin clearance (29.8 ± 14.7 ml/min/1.73 m^2) was found to be highly dependent on these two variables (r = 0.87 and 0.88, respectively). According to the results of this study and our previous investigation, digitalizing and maintenance dosages of digoxin were recommended.

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