Well, we know that methadone, as most drugs, gets into the milk in only tiny
quantities. If 20 mg results in tiny quantities and 80 mg results in 4 times
the tiny quantity, 4 times a tiny quantity is still usually a tiny quantity
and usually not significant.  So, if you look in Hale, at the dose of 10 mg
per day, the milk concentration was 0.05 mg/L, whereas the milk
concentrations in the milk of the mother taking 80 mg was 0.57 mg/L, still a
tiny amounts.  Hale quotes others studies which show variable amounts, but
still tiny.

It does not follow that 4 times a dose will result in 4 times the milk
concentration, though, and you have to be careful about this.  Some drugs at
larger doses will saturate their binding sites, and the blood levels rise
higher than one would expect with the increase in dosage.  This does not
appear to be the case with the studies on methadone, though.

The other problem is when we have a long acting drug, such as methadone.
The baby may accumulate the drug over time.

However, the evidence presented in Hale suggests that it is not necessary to
stick to "okay to breastfeed only if the mother takes 20 mg or less a day".
Breastfeeding is too important, especially in the situation where the mother
is requiring methadone, to hang decisions on a number.

Besides, if there are questions, the milk and/or baby's blood concentrations
can be followed (good research paper).

Jack Newman, MD, FRCPC

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