Efudex (fluorouracil) reaction of the skin.

Fluorouracil or 5-FU is a pyrimidine analog which is used in the treatment of cancer. It is a suicide inhibitor and works through irreversible inhibition of thymidylate synthase. When applied topically, it selectively kills UV-damaged skin cells. It is used primarily to treat actinic keratoses. A patient handout is available.

4% fluorouricil in peanut oil once daily for 2 weeks in one study was as efficacious with slightly fewer side effects compared with 5% BID [J Drugs Dermatol 2016;15(10):1218].

A combination of 5-FU 0.5%/salicylic acid 10% used once daily for 12 weeks is being studied [Dermatol Ther (Heidelb). 2017;7:81-96].

Side Effects

Obviously, skin crusting, inflammation and pain are expected side effects when 5-FU is applied topically. Occasionally patients are allergic to 5-FU. The redness and inflammation with ACD is confluent and not patchy or reticulate as with the usual skin inflammation.

Acute Cerebellar Syndrome

A man in his 60's developed unsteadiness on his feet, altered coordination in gait and dizziness 3.5 weeks into the use of 5-FU BID on the scalp. Cessation of the medication resolved the symptoms within 8 hours [AD 2017;153;831].

Additional Pictures

Efudex (fluorouracil) reaction of the skin. Efudex (fluorouracil) reaction of the skin. Efudex (fluorouracil) reaction of the skin.

Topical 5-FU can induce melanosis of the nail. This child was treated with topical 5-FU for periungual warts and developed nail pigmentation near the proximal nail fold. The pigment has grown out now over several months and will soon be shed.
Nail pigmentation from fluorouracil or 5-FU


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