Why is chemo used for ectopic?

Methotrexate. Methotrexate stops rapidly dividing cells by preventing utilization of folic acid. Is has been a known abortofascient drugas for years and will usually negate an ectopic pregancy. Woem who take mtx must wait 2 & 1/2 mo to rid their bodies of traces before retrying to get pregnant.
Kills cells. Chemotherapy drugs are designed to kill or slow down the growth of rapidly dividing cells. Cancer cells are often rapidly growing. Similarly a growing embryo during pregnancy has rapidly growing cells. That is why a chemotherapy drug such as Methotrexate is effective.