Final answer:
A nurse should advise a breastfeeding client to continue breastfeeding as usual while taking penicillin and to follow the prescribed method of taking the medication, typically on an empty stomach.
Step-by-step explanation:
A nurse should educate a breastfeeding client on taking penicillin by advising her to continue breastfeeding as usual. Penicillin is generally considered safe to use while breastfeeding, as only small amounts of the drug are passed into breast milk and are not likely to harm a nursing infant. It's also important to take penicillin as prescribed, typically on an empty stomach for better absorption, but this does not necessitate stopping breastfeeding. It is not advisable to take it with grapefruit juice, as it can interfere with medication absorption and effectiveness.