Dosage of digoxin in premature infants

The pharmacokinetics and pharmacodynamics of digoxin in premature infants was studied. During maintenance therapy, after a total digitalizing dose of 30 microgram/kg, the measured digoxin level was related inversely to body weight at birth and to estimated gestational age. The serum digoxin levels found in the immature and smaller infants were two to three times the values usually reported to be toxic in older children. Based on these findings, a second group of premature infants was digitalized with 20 microgram/kg; in this group, the serum digoxin levels were below the toxic range, irrespective of gestational age or birth weight. The cardiac effects of digoxin, i.e., shortened left ventricular pre-ejection period and ejection time as determined by echocardiography, were similar in the two groups. For both groups, the half-life of digoxin in the serum was twice that reported for term infants and children. Since digitalis effect is obtained with lower dose and serum concentration, we recommend that this dose be used in premature infants.