77 newborns, ranging from 25.5 to 43 weeks gestational age (GA) and
receiving gentamicin, were studied prospectively over 4 months. Peak and trough serum
concentrations were obtained on days 1, 3, and 5 of therapy. Gentamicin, 2.5 mg/kg/dose,
was given at intervals according to GA. 63% of newborns of < 28 weeks on doses of
gentamicin of 2.5 mg/kg every 24 h (q24h), 75% of < 28 weeks on gentamicin q18h, 90%
of newborns of 23-34 weeks (on q18h), and 82 % of those of > 34 weeks GA (on q12h) had
serum gentamicin trough concentrations ≤ 2.0 pg/ml on day 1. By day 3, 5/5 newborns of
< 28 weeks (q18h) had trough concentrations > 2.0 μg/ml, whereas only 20% of those on
the q24h regimen had high trough concentrations (p < 0.05). Possible risk factors associated
with altered gentamicin disposition in neonates are discussed.