Pharmacological role of efflux transporters: Clinical implications for medication use during breastfeeding

Abstract

The World Health Organisation recommends exclusive breastfeeding for the first six months of an infant’s life and in combination with solid food thereafter. This recommendation was introduced based on research showing numerous health benefits of breastfeeding for both the mother and the infant. However, there is always concern regarding the transfer of medications from mother to their breastfed baby via milk. Pharmacokinetic properties of a drug are usually used to predict its transferability into breast milk. Although most drugs are compatible with breastfeeding, cases of toxic drug exposure have been reported. This is thought to be due to active transport mechanisms whereby efflux transporter proteins expressed in the epithelial cells of the mammary gland actively secrete drugs into milk. An example of such efflux transporters including the breast cancer resistance protein which is strongly induced during lactation and this could result in contamination of milk with the substrates of this transporter which may place the suckling infant at risk of toxicity. Furthermore, there is little known about the substrate specificity of most efflux transporters as we have highlighted in this review. There also exists some degree of contradiction between in vivo and in vitro studies which makes it difficult to conclusively predict outcomes and drug-drug interactions.

Keywords: Active efflux transporters; Lactation; Breastfeeding; Mammary gland; Breast cancer resistance protein; P-glycoprotein; Breast milk; ABC transporters

Core tip: The aim of this review was to analyse the available literature on psychoactive drugs specifically selective serotonin reuptake inhibitors, antipsychotics and antiepileptic drugs that are commonly prescribed during lactation and pregnancy. This review investigated whether these drugs are substrates and/or inhibitors of efflux transporters especially of P-glycoprotein and breast cancer resistance protein and whether this has any effect on adverse outcomes in the breastfed infant of mothers who use these pharmacotherapeutic agents. Current evidence on acute adverse effects in breastfed infants due to the aforementioned drug groups either as sole treatment or their use in combination with other drugs was also explored.