Phenytoin has an M/P ratio of about 0.3. Studies of more than 80 milk samples have shown that a fully breastfed infant can get between 0.5 and 5%, with a maximum of 10%, of the maternal weight-related dosage via the mother's milk. This is normally less than 5% of a pediatric phenytoin dosage (10 mg/kg) (survey in Hagg 2000). The phenytoin concentration in the serum of affected children was, at most, 1.5% of the maternal value. The half-life of 10-40 hours docs not appear to be extended in infants when they have already been exposed in utero (Shimoyama 1998, survey in Bennett 1996) With the exception of two case observations, side effects in breastfed babies have not been reported. These two observations described swallowing difficulties and methemoglobinemia, as well as feeding problems and sedation, with anticonvulsive combination therapy using phenytoin plus barbiturates or with carbamazepine in addition (survey in Hagg 2000).
For recommendations, see section 4.8.7.
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For many years, scientists have been playing out the ingredients that make breast milk the perfect food for babies. They've discovered to day over 200 close compounds to fight infection, help the immune system mature, aid in digestion, and support brain growth - nature made properties that science simply cannot copy. The important long term benefits of breast feeding include reduced risk of asthma, allergies, obesity, and some forms of childhood cancer. The more that scientists continue to learn, the better breast milk looks.