Distribution of R- and S-methadone into human milk during multiple, medium to high oral dosing

Results For immature milk (n=8) the M/PAUC for R-methadone was 0.68 (95% CI 0.48, 0.89) and for S-methadone 0.38 (0.26, 0.50). For mature milk (n=2) the M/PAUCs for R-methadone were 0.39 and 0.54 and for S-methadone 0.24 and 0.30, respectively. The estimated doses of R- and S-methadone that would be received by the infant via immature milk were 3.5% (2.05, 5.03%) and 2.1% (1.3, 2.8%), respectively, of the maternal dose (assuming 50% of each enantiomer in the dose). The relative infant dose for R- plus S-methadone together was 2.8% (1.7, 3.9%). Conclusions Breastfeeding during medium to high dose methadone appears to be ‘safe’ according to conventional criteria because the dosage is <10%. However because the absolute dose received by the infant is dependent on the maternal dose rate, the riskbenefit ratio should be considered for each individual case. The doses of methadone received via milk are unlikely to be sufficient to prevent the neonatal abstinence