Gentamicin dosage in children: A randomized prospective comparison of body weight and body surface area as dose determinants

Body surface area and body weight were evaluated as gentamicin dose determinants in a randomized prospective study of 35 children with normal renal function. Patients were randomly assigned to receive intravenous gentamicin doses of either 37.5 mg/m 2 (Group I) or 1.25 mg/kg (Group II) administered every six hours, and were studied after their first dose on days one, three, and six of therapy. When the variability in peak concentrations for the two dosage regimens was compared, there was no statistically significant difference ( P=0.45) between the two groups. The gentamicin volume of distribution for all patients correlated only moderately with body weight (r=0.82) and body surface area (r=0.79). The mean volume of distribution on day one was 0.295±0.115 l/kg when expressed as a function of body weight and 7.26±2.62 l/m 2 when expressed as a function of body surface area, and did not change significantly with multiple dosing. The results indicate that the variability in serum concentrations is not significantly reduced when pediatric doses are calculated from body surface area instead of body weight, supporting the need for individualization of doses based on measured serum concentrations.