ABSTRACT
The appropriate dosing of gentamicin in the newborn was evaluated. Gentamicin was
administered intramuscularly to 151 neonates ranging in birthweight from 0.66 to 4.7
kg (gestational age, 26-42 weeks) during a 7-month period. A dosage of 2.5 mg/kg of
birthweight every 12 hours was initiated at birth until gentamicin serum levels could
be determined. These infants were divided into three groups based on birthweight:
1) ≤ 1000 gm; 2) 1001-2000 gm; 3) > 2000 gm. From gentamicin serum level data, these
three groups had significantly different (P < 0.05) gentamicin half-lives. Based on the desirability of maintaining a trough
gentamicin serum level < 2, 100, 95.5, and 39% of infants in groups 1, 2, and 3, respectively,
required initial dosing interval adjustments.
A second group of 74 infants whose birthweight ranged from 0.82 to 3.9 kg (gestational
age, 26-42 weeks) required aminoglycoside therapy and were prospectively placed on
gentamicin 2.5 mg/kg of birthweight on the following schedule: 1) ≤ 1000 gm every
24 hours; 2) 1001-2000 gm every 18 hours; 3) > 2000 gm every 12 hours. Using this
method, only 15, 58, and 33% of infants in groups 1, 2, and 3, respectively, required
dosing interval changes. We conclude that a marked reduction in undesirably high trough
gentamicin serum levels can be affected by a simple change in dosing interval based
on birthweight, although gentamicin serum levels are still required due to a significant
number of infants with high trough levels.
