In the newborn period, the half-life of metronidazole is extended -in premature babies it can be up to 35-74 hours. In adults it is up to 10 hours. Following a single oral dosage of 2g for trichomoniasis, the highest concentration was found in the milk after 2-4 hours. This is on average around 21 mg/1; in a single case it reached 46 mg/I (Erickson 1981). On average, 12°/o (at most up to about 20%) of a weight-related therapeutic child's dosage (15 mg/kg per day) is calculated for a fully breastfed infant when the active metabolites in the milk are considered. In the plasma of breastfed children, 2[ig/ml each of metronidazole and its metabolite hydroxymetron-idazole were detected. Comparable results were found with a 9-day course of 1200 mg/d (Passmore 1988, Heisterberg 1983, Erickson 1981). Specific toxicity via mother's milk has not been described among some 60 mother-child pairs published to date. Used therapeutically in prematures (i.e. for necrotizing enterocolitis), this drug is, in general, well-tolerated.
There has as yet been no indication of experimentally observed mutagenic and carcinogenic effccts of metronidazole in human beings.
With tinidazole, transfer via mother's milk can reach a maximum of 10% of the weight-related maternal dosage administered intravenously (Mannisto 1983)-
The use of nimorazole during breastfeeding has not been studied.
Recommendation. With trichomoniasis, metronidazole should be used in preference to the other nitroimidazoles. A single oral dose of 2 g is preferable to vaginal application spread over several days. This is more effective therapeutically, and limits the exposure for the baby. Whenever possible, the administration of metronidazole should be in the evening after the last breastfeed in order to limit further the exposure during the nightly breastfeeding break.
This also applies to intravenous administration spread over several days in cases where this really is urgently indicated. Weaning or interruption of breastfeeding with substitution of Infant formula no longer seems justifiable based on the available experience.
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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.