Therapeutic amoxicillin levels achieved with oral administration in term neonates

The standard treatment of neonatal group B Streptococcus infection is intravenous amoxicillin for 10 days. We investigated whether effective serum amoxicillin concentrations could be reached by switching to oral amoxicillin after 48 h of intravenous administration in full-term neonates with group B Streptococcus infection.

Over 2 years, we included 222 full-term neonates who had early onset group B streptococcal disease responsive to 48 h of intravenous amoxicillin, at which point they were asymptomatic and fed orally. They were switched to oral amoxicillin (300 or 200 mg/kg per day in four divided doses). Steady-state serum amoxicillin concentrations were determined 48 h later by high-performance liquid chromatography; values > or =5 mg/l were considered effective.

Mean gestational age was 39.32 +/- 1.5 weeks ,and mean birth weight was 3,422 +/- 533 g; 29 newborns were bacteremic. Median serum amoxicillin concentration on oral therapy was 31,.15 (range 11-118) and 25.80 (range 5-84.8) with 300 and 200 mg/kg per day, respectively. None of the infants had a concentration <5 mg/l (p < 0.001). Gastrointestinal tolerance was satisfactory; 216 patients were discharged at 5 days of age, and none was readmitted within the 3-month follow-up.

Early switching to the oral route in asymptomatic full-term newborns with early onset group B streptococcal disease maintained serum amoxicillin concentrations within our predefined therapeutic range (error risk<0.001). This strategy may hold potential for reducing treatment invasiveness and shortening hospital length of stay.