Phenoxymethylpenicillin (penicillin V) and breastfeeding

All penicillin antibiotics can be used during breastfeeding with precautionary infant monitoring (1):

• flucloxacillin, phenoxymethylpenicillin (penicillin V) and the broad-spectrum penicillins, such as amoxicillin and ampicillin, are the preferred choices, as there is more evidence and experience to support their use
• pharmacokinetic properties and characteristics of all the penicillins are very similar
• although protein binding and bioavailability vary between the different penicillins, they are all acidic in nature and therefore only negligible quantities pass into milk
  • drugs cross membranes in an un-ionised form (2)
    • milk is generally slightly more acidic (pH 7.2) than the mother’s plasma (pH 7.4), so it attracts weak organic bases such as oxycodone and codeine
      • such drugs become ionised and ‘trapped’ in the milk
      • conversely, weak organic acids such as penicillin tend to be ionised and held in maternal plasma
  • occasionally disruption of the infant's gastrointestinal flora, resulting in diarrhoea or thrush, has been reported with penicillins, but these effects have not been adequately evaluated (3)
  • there has been the occasional case report of rash, nausea, irritability and drowsiness; these were usually mild and self-limiting, and could be attributable to other causes (1)
• treatment choice should be primarily based on clinical indications and in line with national and local antimicrobial policy, with suitability in breastfeeding as a secondary consideration (1)
  • ideally treatment should be at the lowest therapeutic dose for the shortest duration of time

Use of combination penicillin preparations during breastfeeding

• some penicillins are combined with beta-lactamase inhibitors such as clavulanic acid (co-amoxiclav) or tazobactam (combined with piperacillin as Tazocin®), which help to minimise the risk of antimicrobial resistance
  • there is no information on how much passes into breast milk - however, studies have not identified any concerns for their use in breastfeeding (1)

Breast-milk levels

• is limited published evidence of use in breastfeeding (1)
  • studies for amoxicillin, ampicillin, benzylpenicillin (penicillin G), flucloxacillin, phenoxymethylpenicillin (penicillin V) and piperacillin show negligible levels in breast milk
  • there is no published information for pivmecillinam or temocillin - however, breast milk levels are expected to be low

Infant monitoring

• as a precaution, monitor for gastro-intestinal disturbances, oral candida infection, hypersensitivity reactions (including rashes or breathing problems), nausea, irritability, and drowsiness
  • precautionary infant monitoring will quickly pick up any potential issues
  • further investigation is usually required before any issues or side effects can be attributed to the medicine (1)
• is a theoretical risk of hypersensitivity in the infant after exposure to penicillins through breast milk (1)
  • • foetal exposure to antibiotics through the placenta may cause sensitisation
    • further exposure may result in allergic reactions, even from the negligible quantities seen in breast milk
  • therefore, as a precaution, the infant should be monitored for signs of hypersensitivity, which include rashes and breathing problems

Treatment of infant infections with penicillin-based antibiotic if breastfeeding mother also on penicillin

• if the infant needs treatment themselves with a penicillin or other antibiotic, they should receive the appropriate infant therapeutic dose, regardless of concomitant exposure through breast milk (1)

References:

1. NHS Specialist Pharmacy Service (February 16th 2024). Using penicillin antibiotics during breastfeeding.
2. Hotham N, Hotham E. Drugs in breastfeeding. Aust Prescr. 2015 Oct;38(5):156-9. doi: 10.18773/austprescr.2015.056. Epub 2015 Oct 1. Erratum in: Aust Prescr. 2016 Feb;39(1):27.
3. Drugs and Lactation Database (LactMed®) [Internet]. Bethesda (MD): National Institute of Child Health and Human Development; 2006-. Penicillin V. [Updated 2021 Feb 15]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK501062/.