The 24-hour serum digoxin level as a prognosticator of dosage requirement in low-birth-weight (LBW) infants.

Eleven LBW infants were studied to assess the predictability of individual digoxin dosage requirement from a single serum digoxin concentration (SDC) at various times within the first dosing interval. The mean and SD of gestational age, weight and postnatal age were 31.6 +/- 3.5 wk, 1.51 +/- 0.47 kg and 3.7 +/- 2.1 days, respectively. Total body digoxin clearance (TBDC) in each infant was calculated from the computer-fitted biexponential equation describing each first-dose blood level curve. There was no correlation between the TBDC (99.5 +/- 37.0 ml/kg/hr) and the 6-hr SDCs (3.1 +/- 0.6 ng/ml) after the first dose (P greater than 0.20). Significant correlation of both 12- and 24-hr SDCs (2.8 +/- 0.6 and 2.3 +/- 0.5 ng/ml) after first dose with TBDC was found (r = -0.53, P less than 0.05 and r = -0.87, P less than 0.005, respectively). Good correlation (r = 0.88) of 1/dose (where dose = mg/kg/day to achieve a mean steady-state level of 2 ng/ml) with the 24-hr SDCs was also observed (P less than 0.005).