Breast milk provides appropriate nutrition and protection against infections for babies. Medicines are often prescribed for breastfeeding mothers to treat a range of acute and chronic conditions. Mothers may face difficulties when weighing up the benefits of taking their medicine and breastfeeding their child against the potential for harm in their child via breast milk exposure.

Healthcare professionals play an important role in providing appropriate information to breastfeeding mothers in order to help them make informed decisions about medicine use. Many healthcare professionals will rely heavily on the manufacturer’s approved product information. This information, however, is conservative and may only contain data extrapolated from limited animal studies. Some product information references may suggest measures of avoiding breastfeeding (and discarding breast milk for a period of time); in many cases this may be unwarranted and the potential difficulties with re-establishing milk supply must be considered. Many also list breastfeeding as a contraindication or precaution despite very few medicines which are truly contraindicated in breastfeeding. Reliance on product information could lead to a situation where a mother chooses to delay treatment with a medicine or prematurely discontinues breastfeeding, both of which are undesirable if they can be avoided.

A range of factors must be assessed when considering the safety of medicine use during breastfeeding. These include:

  • Clinical need for treatment in the mother – If the medicine is not deemed sufficiently important, the clinician may advise to delay treatment or consider treatment with a medicine with better known data on safety in breastfeeding.
  • Effect of the medicine on milk production – Some medicines can decrease milk production (e.g. oestrogen-containing contraceptives). In this situation, it may be advisable to consider treatment with an alternative medicine which is known to not reduce milk supply, such as a progesterone only contraceptive.
  • Extent of transfer into breast milk – Many pharmacokinetic and pharmacodynamic properties of the medicine will have an effect on the extent of transfer into breast milk. For example, medicines with a higher molecular weight (e.g. insulin) and those which are highly protein bound (e.g. ibuprofen, sertraline) are less likely to transfer into breast milk.
    The dose consumed will also affect the amount of medicine that transfers into breast milk. For example, topically applied medicines are unlikely to be absorbed systemically in sufficient amounts to enable clinically significant transfer into breast milk. Timing of the dose can also have a significant effect on the quantity of medicine in the breast milk, particularly for medicines with a shorter half-life (those that require multiple doses per day). For these medicines, taking the medicine immediately after a breastfeed can reduce the amount consumed by the infant. It is important to note that the concentration of medicines in breast milk reduce as the plasma levels in the mother decrease via elimination.
  • Extent of absorption by the infant – Many medicines with poor oral bioavailability are unlikely to cause harm for infants. For example, a breastfeeding mother treated with intravenous gentamicin may continue to breastfeed as, even if the baby swallows some gentamicin, not enough will be absorbed by their own gastrointestinal tract to cause significant risk.
    Gestational age also has a bearing; older infants who are on solids will generally be consuming a lower volume of breast milk per kilogram of body weight compared with an exclusively breastfed infant, and therefore have lower exposure via breast milk.
  • Potential for harm for the infant – Where a medicine is likely to transfer into breast milk on theoretical grounds, it may be still be appropriate to breastfeed if it is considered a low risk medicine. In some situations it may be a medicine that is also used to treat conditions in infants directly, and in that case the amount of medicine that is absorbed via breast milk is likely to be significantly less than the typical treatment dose administered.

Resources are available to assist health care professionals provide balanced information to breastfeeding mothers about safety of medicines. These include:

  • The Australian Medicines Handbook: available in print, by electronic download, or online.
  • LactMed, a TOXNET database: a freely available online medicines resource from the US National Library of Medicine. It is updated monthly, peer reviewed and all data is derived from scientific literature and referenced.
  • MotherToBaby: a freely available website provided by the Canadian Organization of Teratology Information Specialists. Covers a wide range of medicines and has useful fact sheets for consumers that address considerations in pregnancy and breastfeeding.
  • NPS Medicinewise: provides a page of links to other medicine resources for health professionals.

To read more about medicines in breastfeeding in the HPS Knowledge Centre, click here.

References:

  1. Hale TW. Medications and mothers’ milk: a manual of lactational pharmacology. 15th ed. Amarillo, Texas: Hale Publishing L.P.; 2012.
  2. Pharmaceutical Society of Australia. Australian Pharmaceutical Formulary and Handbook APF 22, Canberra: PSA; 2012.

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