Ten neonates 0 to 28 days old (gestation: 37-42 weeks; birth weight: 2,160-3,640 g) received 20 mg/kg CTRX (8 cases) or 10 mg/kg (2 cases) by intravenous bolus injection, while 9 infants 35 days to 9 months old (gestation: 37-43 weeks; birth weight: 2,800-3,560 g) received 20 mg/kg by intravenous bolus injection, and their blood drug concentrations and urinary drug excretions were examined. Average blood levels of CTRX in the 20 mg/kg dosage group were 114 +/- 14.6 micrograms/ml at 30 minutes, 109 +/- 12.8 micrograms/ml at 1 hour, 100 +/- 12.6 micrograms/ml at 2 hours, 87.9 +/- 15.8 micrograms/ml at 4 hours, 72.8 +/- 15.3 micrograms/ml at 6 hours, and 50.1 +/- 12.3 micrograms/ml at 12 hours in the neonates; and 113 +/- 20.0 micrograms/ml at 30 minutes, 101 +/- 14.7 micrograms/ml at 1 hour, 83.6 +/- 9.3 micrograms/ml at 2 hours, 70.3 +/- 10.7 micrograms/ml at 4 hours, 56.9 +/- 8.6 micrograms/ml at 6 hours, and 35.7 +/- 9.2 micrograms/ml at 12 hours in the infants. Average half-lives of CTRX in blood were 10.3 +/- 4.5 hours in the neonates, and 6.6 +/- 1.9 hours in the infants. Average blood concentrations of CTRX in the 10 mg/kg dosage neonate group were 63.8 +/- 6.0 micrograms/ml at 30 minutes, 57.8 +/- 2.5 micrograms/ml at 1 hour, 53.5 +/- 0.7 micrograms/ml at 2 hours, 41.8 +/- 7.4 micrograms/ml at 4 hours, 32.4 +/- 5.9 micrograms/ml at 6 hours, and 20.8 +/- 1.1 micrograms/ml at 12 hours, and the half-life was 7.2 +/- 0.4 hours. These results suggest that blood concentrations are apparently dose-related in the neonate period; that the peak levels of the neonate and infant groups were similar (the levels at 30 minutes) not showing a relationship to age, gestation period or to birth weight; and that the higher the age was the shorter the half-life became with the half-life in the one week old group was 1.5 times as long as that in the older infant group. The half-life in the younger infant group, however, was similar to that in the older infant group. Urinary excretion was examined in 4 neonates and 2 infants. Average urinary recovery rates in 12 hours after intravenous injection were 40.8 +/- 8.3% in the neonate group and 44.8 +/- 12.8% in the infant group, showing that CTRX is excreted well even in the neonate period.(ABSTRACT TRUNCATED AT 400 WORDS)
