High gentamicin trough concentrations in neonates of less than 28 weeks gestational age.

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 less than 28 weeks on doses of gentamicin of 2.5 mg/kg every 24 h (q24h), 75% of less than 28 weeks on gentamicin q18h, 90% of newborns of 23-34 weeks (on q18h), and 82% of those of greater than 34 weeks GA (on q12h) had serum gentamicin trough concentrations less than or equal to 2.0 micrograms/ml on day 1. By day 3, 5/5 newborns of less than 28 weeks (q18h) had trough concentrations greater than 2.0 micrograms/ml, whereas only 20% of those on the q24h regimen had high trough concentrations (p less than 0.05). Possible risk factors associated with altered gentamicin disposition in neonates are discussed.