Table 3.

Measures of Infant Exposure to Enantiomer-Specific Methadone via Breastmilk and Milk-to-Maternal Plasma Ratio

	R-Methadone	S-Methadone	Total methadone
Mean (SD) TID (mg/kg/day)	0.020 (0.022)	0.013 (0.016)	0.033 (0.038)
Range	0.004–0.099	0.002–0.071	0.006–0.170
Mean (SD) RID (%)	2.7 (2.1)	1.6 (1.5)	2.1 (1.8)
Range	0.66–10.1	0.33–7.2	0.52–8.7
Mean (SD) M/P ratio	0.52 (0.28)	0.28 (0.15)	0.40 (0.21)
Range	0.05–1.27	0.02–0.68	0.04–1.0

M/P, milk-to-maternal plasma ratio; RID, relative infant dose; TID, theoretic infant dose.