Transfer of Methamphetamine (MA) into Breast Milk and Urine of Postpartum Women who Smoked MA Tablets during Pregnancy: Implications for Initiation of Breastfeeding

Background: Methamphetamine (MA) use by pregnant women remains a growing problem in South East Asia. After delivery, a negative maternal urine MA assay is assumed to reflect the absence of MA in breast milk and marks breastfeeding initiation. To date, no data exist that describe the relationship between the peripartum and postpartum transfer of MA into breast milk and its urinary excretion in women, following recreational use by smoking. Objective: This study aimed to determine the pharmacokinetic of smoked MA in breast milk and its relationship to urinary MA excretion in postpartum women who tested positive for MA before delivery. Methods: Timed urine and breast milk samples of 33 women who had positive urine drug screens for MA prior to delivery were analyzed for MA using Acquity Ultra Performance Liquid Chromatography (Waters, Milford, Massachusetts, USA) with the ACQUITY UPLC Photodiode Array Detector (Waters). Those participants with 4 or more timed breast milk samples were included for pharmacokinetic calculation using log-linear trapezoidal rule. Results: Pharmacokinetic data from 2 women were analyzed. The half-life values for MA in the breast milk were 11.3 and 40.3 hours. The absolute infant doses were 21.3 and 51.7 μg/kg/day. Methamphetamine disappears from breast milk approximately 1 day before the maternal urine MA becomes negative. Conclusion: Smoked MA shows a similar breast milk pharmacokinetic pattern to previously reported intravenous MA. Breastfeeding can be safely initiated in mothers whose urine MA screen has turned negative for ≥ 24 hours. However, concurrent maternal substance use treatment and screening is necessary for continued promotion of lactation.