How Does Kenalog And 5-FU Work In Scar Injections?

Q: Dr. Eppley, I have a question regarding injectable scar treatments. What is the difference between 5-FU and Kenalog? What do each of them do to help a scar/scar tissue?

A: There are two types of scar injections that are currently available. The use of steroids, specifically triamcinolone (kenalog), is an historic and classic injectable approach. Triamcinolone is a synthetic corticosteroid that has a significant anti-inflammatory effect. It works on scars by either inhibiting or breaking down the cross-linking of collagen fibers, which is the backbone of scar formation. Dosing and frequency of Kenalog injections is critically important as it can have side effects such as soft tissue atrophy and tissue thinning. For this reason, lower doses are usually used, such as K10 rather than the more concentrated K40, and injections sessions should not be spaced more than 3 or 4 weeks apart.

5-FU is a well-known drug used as a chemotherapy agent against cancer for several decades. It works by inhibiting DNA replication which is important in stopping cancer cells which usually multiply faster than normal cells. In dermatology, 5-FU is most commonly used topically (as a cream) for treating actinic (solar) keratoses and some types of basal cell cancers of the skin. (e.g., Efudex or Carac) It is thought that it works in scar problems because it blocks collagen synthesis which might help to control excessive scar formation. It does not have the side effects of corticosteriods but injections are still done only every month or so, mainly to see how it is working.

I often combine the two, Kenalog and 5-FU, as an injectble combination when either it is a known problematic scar or a scar that has failed to respond to Kenalog injections. It is unknown whether one is superior to the other as a primary scar therapy.

Dr. Barry Eppley