Background Intravenous gentamicin is frequently prescribed for the treatment of early-onset sepsis to premature neonates. Background infusion rate and flush volume are known to influence gentamicin delivery and we aimed to further quantify these factors.

Methods Intravenous infusions were designed to simulate gentamicin delivery through umbilical venous catheters with a constant background flow rate of 0.5 mL/hr. Doses of gentamicin (2 mg or 5 mg) were administered by bolus injection over 3–5 minutes followed by a flush of 0.9% saline (1 mL or 2 mL). Samples were collected at 5 minute intervals for 1 hour and analysed by high pressure liquid chromatography.

Results Complete recovery of 2 mg and 5 mg doses was observed following administration of both flush volumes. Of the 2.15 mg recovered when a 1 mL flush is used, 85% (standard deviation, SD, 3.1%) was collected by 10 minutes and 93% (SD 1.4%) over the first 30 minutes. When a 2 mL flush is given, 99% (SD 0.5%) of the 1.88 mg administered dose is recovered in 10 minutes. Following a 5 mg intended dose, 93% (SD 3.4%) is recovered at 10 minutes and 97% (SD 2%) in 30 minutes after a 1 mL flush, compared to 99% (SD 0.6%) recovery at 10 minutes with a 2 mL flush.

Conclusion Simulated gentamicin delivery by bolus injection into slow-flowing neonatal central lines resulted in >90% dose recovery at 1 hour. Additionally, discrepancies between intended and actual gentamicin dose, and retrograde flow of dye was observed.