Pharmacokinetics of gentamicin in children and adults

Peak concentrations and half-life of gentamicin in serum were measured after 140 intravenous and 13 intramuscular doses in 52 children and 17 adults with normal levels of creatinine in serum. Marked interpatient variation in peak concentrations and half-life of gentamicin was observed, but individual patients tended to have similar values on repeated determinations. Age markedly affected the peak concentrations: a 1-mg/kg dose produced mean peak concentrations of 1.58, 2.03, and 2.81 mug/ml in the one-half to five, five to 10, and greater than 10 year age groups, respectively. This age-related change in dose response was diminished when the dose was calculated on the basis of body surface area. Patients in whom gentamicin had a short half-life, patients with fever, and adults with a high extracellular fluid volume had low peak concentrations. The mean half-life after intravenous administration was 75 min (range, 26-230 min). The mean half-life was 29 min longer after intramuscular dosage (p less than 0.01). A low rate of creatinine clearance was associated with a long half-life; fever and anemia were associated with a short half-life. The dosage of gentamicin necessary to produce mean peak serum concentrations between 4 mug/ml and 6 mug/ml was 60 mg/m2 per dose for all age groups or 2.5 mg/kg per dose for ages one-half to five years, 2.0 mg/kg per dose for ages five to 10 years, and 1.5 mg/kg per dose for ages greater than 10 years.