A dramatic increase in newborn infants with neonatal abstinence syndrome has been observed and these neonates are frequently treated with complex methadone dosing schemes to control their withdrawal symptoms. Despite its abundant use, hardly any data on the pharmacokinetics of methadone is available in preterm neonates. Therefore we investigated developmental pharmacokinetics of methadone and evaluated current dosing strategies and possible simplification in this vulnerable population.
A single center open-label prospective study was performed to collect pharmacokinetic data after a single oral dose of methadone in preterm neonates. A population pharmacokinetic model was built to characterize developmental pharmacokinetics of methadone and to assess the effects of weight and age on clearance and volume of distribution. In addition, simulation techniques were applied to evaluate reported dosing scenarios, investigate methadone exposure levels and examine the feasibility of simplified dosing recommendations.
In total, 121 methadone concentrations were collected from 31 preterm neonates. The median weight and gestational age amounted 1.6 kg and 32 weeks, respectively. A one-compartment model with first order absorption and elimination kinetics best described the data for (R)- and (S)-methadone. Clearance was observed to be higher for the (R)-enantiomer as compared to the (S)-enantiomer (0.244 versus 0.167 L/h). Target exposures, based on simulations, can be maintained with a simplified dosing strategy during the first four days of treatment. It is therefore questionable if there is a need for the currently used more extended dosing regimen of methadone in neonates.
This clinical investigation demonstrates that the clearance of methadone increases with advancing gestational age and higher clearance values and volumes of distribution can be observed for (R)-methadone as compared to (S)-methadone in preterm neonates. Simulations that account for developmental pharmacokinetics indicate that a simplified methadone dosing strategy can maintain target exposure to control withdrawal symptoms in preterm neonates.
Nothing to disclose