The relationship between age and morphine infusion rate in children


  • Section Editor: Per-Arne Lonnqvist

Brian Anderson, C/- PICU, Auckland Children’s Hospital, Park Road, Auckland, New Zealand


Aim:  We performed a retrospective audit of intravenous morphine infusion administered to children in an effort to characterize the relationship between dose and age.

Methods:  A retrospective audit of morphine infusions was reviewed for a 24-months period and included all children who received continuous intravenous nurse-controlled morphine infusions and patient-controlled analgesia; a population undergoing acute and elective surgical procedures, as well as medical and oncological treatments. The relationship between age and infusion rate was investigated using nonlinear mixed effects models.

Results:  There were 886 children whose data were acceptable for review. Morphine dose increased with age from 9.97 (CV 28%) μg·kg−1 per h in neonates. The Hill equation with an exponential of 1.5 best described these changes. Morphine rate reached 90% of its mean final rate of 22.5 (CV 167%) μg·kg−1 per h, observed in teenagers, at approximately 5 years of age. There was considerable uncertainty of this age–morphine rate profile, and the maturation half-life of this profile was 20 months of age (CV 632%). An increase in dosing variability was observed with increasing age.

Conclusions:  Morphine infusions at steady-state did not mirror clearance maturation in children nursed in our hospital. We suggest that initial infusion rates in children are started at 10 μg·kg−1 per h in neonates, 15 μg·kg−1 per h in toddlers and 25 μg·kg−1 per h in children above the age of 5 years. The large variability associated with infusion rates means that subsequent infusion rates will depend on feedback from pain scores, adjuvant medications and adverse effects.