1142 PHARMACOKINETICS AND DOSAGE REGIMEN OF TOBRAMYCIN IN NEWBORN INFANTS BELOW ONE KILOGRAM BIRTH WEIGHT

Abstract

Current dosing recommendation of tobramycin 2 mg/kg/12 hr, in newborn infants does not consider birth weight as a variable. Because of limited data, we studied tobramycin kinetics in eight infants (gestational age 24-30 wk; postnatal age 3-6 d; birth weight 600-970 g) receiving tobramycin, 2.5 mg/kg IV every 18-24 hr for presumed or proven sepsis or meningitis. After 2-4 days of therapy, the blood samples were collected at 0, 0.5, 1, 2, 4, 6, 8, 12, 18 and 24 hr and analyzed by EMIT. Tobramycin peak and trough serum concentration ranged from 6.0 to 8.4 and 1.3 to 2.4 μg/ml, respectively. Trough serum concentration exceeded 2 μg/ml in 75% at 12 hr and 20% patients at 18 hr. Total body clearance ranged from 0.55 to 0.81 (0.69±0.11) ml/min/kg; apparent volume of distribution ranged from 0.44 to 0.71 (0.56±0.12) L/kg; and elimination half-life ranged from 7.7 to 11.7 (9.5±1.4) hr. These data suggest that tobramycin, 2.5 mg/kg every 18-24 hr may be adquate to achieve effective and potentially safe serum concentration in low birth weight infants.