Prescribing in breast-feeding
Breastfeeding mothers who require prescribed medicines, are likely to be concerned about the effects of drugs on their child, hence it is important that you understand the principles of use. This is to ensure that infants are protected from adverse drug reactions from maternal medication, and equally that both necessary maternal medication and breast feeding can continue wherever possible, as the benefits of breastfeeding are widely acknowledged as the best form of nutrition for infants (WHO/UNICEF, 2003). Most drugs pass in to breast milk to some degree, though the overall dose that the infant receives is normally low and normally below a therapeutic level for the infant.
What factors affect infant risk?
There are a number of factors which affect the risk of an infant being exposed to drugs from breast milk.
Milk to plasma ratio
This is the ratio of concentration of a drug in breast milk compared to maternal plasma levels. Drugs pass into milk to a varying degree, governed by various physicochemical properties. Low ionisation, low molecular weight, high lipid solubility, and low protein binding, all lead to greater passage into the milk. Most medicines however have a milk:plasma ratio of less than 1.
Maternal plasma levels
A low milk:plasma ratio does not necessarily suggest that a medicine is safe. More important is the maternal plasma level, as if plasma levels of the drug are low, then the level in breast milk will also be low.
Bioavailability
Some medicines are poorly absorbed, or are metabolised to a large degree by the infant before reaching the systemic circulation (the first pass effect). If this is the case, it is unlikely there will be significant effects even if there is drug present in the breast milk.
Infant maturity
As discussed in the section on paediatrics, neonates and premature infants will not have fully developed kidney and liver function needed for elimination of drugs, and therefore are more at risk of accumulating drugs ingested via breast milk. Drugs that have long half lives and active metabolites may compound this problem.
Adverse drug reaction profile
The side effects of the drug are the main factor when you are assessing risk. Of particular concern are cytotoxic drugs, radionuclides, and iodine containing drugs. Combination therapy with drugs with similar side effects will also be of concern as these effects may be additive, for example antipsychotic therapy and antiepileptics.
What general principles should I follow?
As with use in pregnancy, there are some general principles you should follow to follow to try and minimise exposure to the infant:
- Avoid unnecessary maternal use – in particular avoid herbal products because of a lack of data, and advise mothers to seek advice before purchasing any over the counter (OTC) products
- Assess risk-benefit in individual cases – consider particular risk factors such as infant prematurity and multiple maternal medicines. Consult specialist information sources if necessary (see below)
- Minimise exposure – use the lowest effective dose for the shortest possible time.
- Consider local therapy (e.g. topical/inhaled) which normally results in lower maternal plasma levels and therefore lower passage into milk.
- If the drug has a short half-life, advise taking the dose immediately after feeding to avoid feeding at peak milk concentrations
- Avoid drugs with toxic side effects in adults or children (e.g. cytotoxics)
- Avoid new drugs – older drugs are more likely to have data to guide use in breastfeeding.
- Monitor the infant for adverse effects
Sources of information
As for use in pregnancy, the BNF gives brief information on use in breast milk under individual drug monographs. The SPC for a drug will again tend to err on the side of caution. Your local medicines information service will be able to give you more detailed advice where BNF advice is not definitive.
Copyright eBook 2019, University of Leeds, Leeds Institute of Medical Education.