Article date: January 2006
By: Karel Allegaert, Brian J. Anderson, Veerle Cossey, Nicholas H. G. Holford, in Volume 61, Issue 1, pages 39-48
Aim
Identify and quantify factors describing variability of amikacin clearance in preterm neonates at birth.
Methods
Population pharmacokinetics of amikacin were estimated in a cohort of 205 extreme preterm neonates [post conception age (PCA) 27.8, SD 1.8, range 24–30 weeks; weight 1.07, SD 0.34, range 0.45–1.98 kg, postnatal age < 72 h]. Covariate analysis included weight, PCA, Apgar score, prophylactic administration of a nonsteroidal anti‐inflammatory drug (NSAID) to the neonate, maternal indomethacin and betamethasone administration, and chorioamnionitis.
Results
A one‐compartment linear disposition model with zero order input (0.3 h i.v. infusion) and first‐order elimination was used. The population parameter estimate for volume of distribution (V) was 40.2 l per 70 kg. Clearance (CL) increased from 0.486 l h−1 per 70 kg at 24 weeks PCA to 0.940 l h−1 per 70 kg by 30 weeks PCA. The population parameter variability (PPV) for CL and V was 0.336 and 0.451. The use of a NSAID (either aspirin or ibuprofen) in the first day of life reduced amikacin clearance by 22%. Overall 65% of the variability of CL was predictable. Weight explained 48%, PCA 15% and NSAIDs 2%.
Conclusions
Size and post‐conception age are the major contributors to clearance variability in extreme premature neonates (<31 weeks PCA). The large (35% of total) unexplained variability in clearance reinforces the need for target concentration intervention to reduce variability in exposure to a safe and effective range.
DOI: 10.1111/j.1365-2125.2005.02530.x
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