Discuss with your doctor appropriate forms of birth control before starting treatment with fluorouracil topical. It is not known whether fluorouracil topical passes into breast milk. Do not use fluorouracil topical without first talking to your doctor if you are breast-feeding a baby.o not use other prescription or over-the-counter skin products without first talking to your doctor during treatment with fluorouracil topical. They may interfere with treatment or increase irritation to the skin. Drugs other than those listed here may also interact with fluorouracil topical.