Tobramycin is frequently used in premature infants but little is known about its pharmacokinetics in identical twins during the newborn period. We studied 6 twin infants (gestational age 29-31 weeks; postnatal age 3-4 days; birth weight 1.0-1.3 kg) receiving tobramycin 2.5 mg/kg i.v. over 20 min every 12-18 h. Steady-state peak and trough serum concentrations of tobramycin were in the range of 5.3-8.4 and 1.2-2.0 μg/ml, respectively. Total clearance (Cl(T)) ranged from 0.74 to 1.19 ml/min/kg, distribution volume (V) from 0.74 to 0.94 liter/kg, and elimination half-life (t1/2) from 8.2 to 12.8 h. Comparison of data between infants in three identical twin pairs showed that despite a similar infusion method: (a) the time to achieve peak serum concentration ranged from 0.5 to 2.0 h; (b) the peak and trough concentrations normalized for dose varied from 0 to 50%, and (c) the Cl(T), V and t1/2 varied from 3 to 20%. These data should be considered in therapeutic drug monitoring of tobramycin in premature, identical twins during the newborn period.

Keywords:
Tobramycin, Pharmacokinetics, Premature, identical twins, Newborn period
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1986
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