Letters to the Editor
Drugs and breastfeeding
- Elizabeth Barbehenn, Molika In
- Aust Prescr 2005;28:29-33
- 1 April 2005
- DOI: 10.18773/austprescr.2005.027
The information under Carcinogenicity states that pulmonary tumours were found in all six studies done in mice including one with dosing only every fourth week; there were also malignant tumours in the liver and malignant lymphomas. In rats, there were liver and mammary tumours. And finally, the drug is genotoxic - it damages the DNA directly.
Under the heading Nursing Mothers, it says, 'because of the potential for tumorigenicity shown for metronidazole in mouse and rat studies, a decision should be made whether to discontinue nursing or to discontinue the drug'. It further states that, 'metronidazole is secreted in human milk in concentrations similar to those found in plasma'.
Based on this information, I take issue with the reviewer who says that, based on this book, she is reassured that metronidazole 'will do the baby no harm'. On the contrary, there is tremendous potential for harm and the US product information actually says not to nurse when using metronidazole. So much for the usefulness of this book!
Public Citizen's Health Research Group
Washington DC, USA
Molika In, Pharmacy Department, The Royal Women's Hospital, Melbourne, comments:
Prescribing for breastfeeding women is a potentially complex decision. Clinicians are often faced with a dilemma when reading product information, as these documents tend to recommend ceasing breastfeeding whenever medications are required. Weaning a baby may, however, not be practical and immediate treatment may be required. Various resources are available and should be used by clinicians in order to make informed decisions and weigh up the risks and benefits with breastfeeding women requiring treatment.
The product information for metronidazole clearly states a potential mutagenicity and carcinogenicity association in animals but not in humans. Several studies showed this association with short treatment courses of metronidazole as not statistically significant.13 Also, the cytogenic effects occur only when there is a metabolic reduction of metronidazole, as in hypoxic tumour cells.47 Metronidazole has been used therapeutically for more than 40 years and its use in breastfeeding has been reviewed over two decades.89
Metronidazole is excreted in the breast milk, but very few cases of adverse effects have been reported and even then the correlation is questionable. Recent reports show no obvious adverse effects associated with mothers taking metronidazole while breastfeeding.1012 Even more reassuring is the fact that the dose of metronidazole received by a breastfeeding infant is far lower than the dose used for treating neonates, infants or children.13
Current literature and The Royal Women's Hospital Drugs and breastfeeding guide suggests the benefits of continuing breastfeeding outweigh the theoretical potential cancer risk posed by metronidazole.1015
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Research analyst Public, Citizen's Health Research Group Washington DC, USA
Pharmacy Department, The Royal Women's Hospital, Melbourne