Codeine and Metabolite Concentrations in the Breastfed Neonate

Area of Science:

• Pharmacogenomics
• Neonatal toxicology

Background:

• Codeine's analgesic effect is mediated by its metabolite, morphine, via cytochrome P450 2D6 (CYP2D6) enzyme.
• CYP2D6 gene polymorphism results in varied metabolizer phenotypes (poor, intermediate, normal, ultra-rapid).
• Concerns exist regarding neonatal respiratory depression from morphine transfer via breastmilk in ultra-rapid metabolizer mothers.

Purpose of the Study:

• To evaluate the risk of neonatal opioid toxicity from codeine via breastfeeding.
• To assess predicted neonatal morphine concentrations in breastfed neonates.
• To review current restrictions on codeine use in breastfeeding postpartum women.

Main Methods:

• A pharmacokinetic compartment model was employed to simulate maternal codeine ingestion and neonatal morphine exposure.
• Key factors analyzed included maternal genotype, milk-to-plasma ratio, and neonatal drug metabolism and clearance.
• Predicted neonatal morphine plasma concentrations were calculated.

Main Results:

• The pharmacokinetic model indicated that neonatal opioid toxicity from breastfeeding is implausible.
• Predicted neonatal morphine concentrations were consistently below 1 µg/L, irrespective of maternal CYP2D6 genotype.
• Current bans on codeine for breastfeeding postpartum women may warrant reconsideration.

Conclusions:

• Maternal codeine use during breastfeeding is unlikely to cause neonatal toxicity.
• The current prohibition of codeine for breastfeeding mothers requires review based on pharmacokinetic modeling.
• Similar precautions as with other maternal opioids should be applied, with neonates monitored for adverse effects.