Larger dose reductions of vancomycin required in neonates with patent ductus arteriosus receiving indomethacin vs. ibuprofen.

Ibuprofen and indomethacin are commonly used to induce ductus arteriosus closure in preterm neonates. Our group previously reported that ibuprofen decreased vancomycin clearance by 16%. In this study, we quantified the impact of indomethacin coadministration on vancomycin clearance by extending our vancomycin population pharmacokinetic model with a data set containing vancomycin concentrations measured in preterm neonates comedicated with indomethacin. The modeling data set includes concentration-time data of vancomycin administered alone or in combination with either ibuprofen or indomethacin collected in the neonatal intensive care units of UZ Leuven (Leuven, Belgium) and Sao Francisco Xavier Hospital (Lisbon, Portugal). The derived vancomycin pharmacokinetic model was subsequently used to propose dose adjustments that yield effective vancomycin exposure (i.e., area under the concentration-time curve from 0 to 24 h [AUC(0-24)] between 300 to 550 mg"h/liter, with a probability of <0.1 of subtherapeutic exposure) in preterm neonates with patent ductus arteriosus. We found that indomethacin co-administration reduced vancomycin clearance by 55%. Model simulations showed that the most recent vancomycin dosing regimen, which was based on an externally validated model, requires 20% and 60% decreases of the loading and maintenance doses of vancomycin, respectively, when aiming for optimized exposure in the neonatal population. By analyzing vancomycin data from preterm neonates comedicated with indomethacin, we found a substantial decrease in vancomycin clearance of 55% versus a previously reported 16% for ibuprofen. This decrease in clearance impacts vancomycin dosing, and we anticipate that other drugs eliminated by glomerular filtration are likely to be affected to a similar extent as vancomycin.