BACKGROUND: Limited data are available on the pharmacokinetics and optimal dosage of daptomycin, a lipopeptide compound possessing activity against Gram-positive bacteria, in the pediatric population, particularly in neonates and infants. We determined serum levels of daptomycin in hospitalized pediatric patients treated with various dosages of this agent.METHODS: Blood samples were obtained from pediatric patients of all ages with normal renal function who had received daptomycin between May 2009 and December 2010. Serum levels prior ("trough") and 30 min after end of the infusion ("peak") were determined using an ultra-performance liquid chromatography-UV detection method.RESULTS: A total of four daptomycin dosages and four patients were studied. Three patients were infants (gestational age: 29-38 weeks, age at sampling 26-65 days) and the fourth was a 7-year-old boy. A dosage of 6 mg/kg/12 h of daptomycin to the infants resulted in trough concentrations of <4-8.4 mg/l and peak concentrations of 10.9-17.7 mg/l. Comparable levels were observed after one of the infants received a dosage of 11 mg/kg/12 h, while a further dosage increase to 15 mg/kg/12 h yielded peak concentrations of 35.5 mg/l. The 7-year-old child received a daptomycin dosage of 12 mg/kg once daily; trough and peak levels were 4.2 and 103.4 mg/l, respectively.CONCLUSIONS: A dosage of daptomycin 6 mg/kg/12 h in small infants results in lower peak and similar trough concentrations compared with a dosage of 4 mg/kg/day administered to adults. This results suggests that daptomycin dosages of more than 6 mg/kg/12 h may be needed for this pediatric age group to achieve a similar drug exposure as adults.