Sick neonates with haemodynamic instability often require complex medication regimens, which may result in the connection of a catecholamine infusion distally. This increases the dead volume of the infusion system, extending the time to medication delivery. This study evaluated the effects of body weight, and infusion connection point on the delivery rate of two medications infused through a multi-infusion system at infusion rates suitable for extremely and very low birth weight (ELBW and VLBW) neonates. An infusion system consisting of six infusions was used to investigate time to delivery, drug concentration at time to delivery and quantity of adrenaline and dopamine administered by intravenous infusions at infusion rates suitable for premature neonates. In an ELBW neonate model, the measured adrenaline and dopamine concentration at 12 T was higher than expected (66.7 (7.5)% (mean (SD)) and 68.0 (4.4)%, respectively, P < 0.001). At the calculated time to delivery, neither drug reached target concentration. In a VLBW neonate model, the measured adrenaline and dopamine concentration at 12 T was higher than expected (92.2 (7.1)% and 97.1 (3.1)%, respectively, P < 0.001). Adrenaline reached target concentration at 27 (11) min and dopamine at 56 (12) min, times significantly shorter than calculated. The measured quantity of adrenaline and dopamine delivered was lower (P < 0.001) than calculated in all tested combinations except adrenaline at proximal connection (97.2 (3.4)%, P = 0.097) in the VLBW neonate model. Using the most proximal available infusion connection considerably improves drug delivery times and drug doses delivered, which is critical during the administration of short-acting cardiovascular medications.