Safety in Lactation: Antimetabolites

Antineoplastic antimetabolites, whether used as monotherapy or in combination with other antineoplastics, are contra-indicated in breastfeeding (except where indicated below) because of their effects on dividing cells and their varied and high toxicity in normal therapeutic use.
The risks associated with their use will be additive with other antineoplastic agents with which they are normally used in combination.
In most cases it will not be possible to suggest an alternative. Choice of drug will depend on a number of disease and treatment protocol parameters.
There is no evidence-based, definitive time period after treatment when breastfeeding can be safely resumed, especially when drugs are used in combination. Therefore, if use of an antimetabolite is deemed clinically necessary, breastfeeding should be discontinued in the majority of situations.