Intravenous neonatal paracetamol dosing: the magic of 10 days.

Intravenous (i.v.) paracetamol (acetaminophen) is gaining increasing use in neonates (1–3), despite an off-label status in some countries. Product information for i.v. paracetamol does not consider the clearance maturation with age in neonates in its dosing recommendations. In Australasia the same dose of 15 mgÆkg 6 h is suggested for neonates over 10 days of age and for infants and children up to 33 kg. A reduced dose of 7.5 mgÆkg 6 h is proposed in term neonates <10 days of age. In Europe there is no labeled use for neonates <10 days of age. The registered dose is 7.5 mgÆkg 6 h for neonates after 10 days of age through to infants of 10 kg. A dose of 15 mgÆkg 6 h (max daily dose 60 mgÆkg) is recommended between 10 and 40 kg. These dosing regimens suggest something magic about 10 days. There are data concerning the pharmacokinetics of this formulation in neonates. Population pharmacokinetics of the i.v. prodrug (propacetamol) have been studied in neonates following single (4,5) and repeat dose administration (6). Parameter estimates from neonates given repeat doses of i.v. paracetamol over a median of 4 days duration are consistent with those estimated using propacetamol (7). Dosing regimens used in some institutions for neonates have been published in Pediatric Anesthesia (2,8), but there are few data validating the safety or effectiveness of these regimens. The idea that a target effect and associated target concentration can be used to make rational individual dose decisions has acceptance (9). A knowledge of neonatal pharmacokinetics assists with dose prediction to achieve the target concentration. There are, however, flaws and constraints of current knowledge that limit implementation of this approach to dosing.