Topical FK506--clinical potential or laboratory curiosity?

Cyclosporine A (CsA) is an immunosuppressant that is efficacious in several inflammatory skin disorders. Its use is, however, limited due to systemic side-effects. Topical forms of CsA have been tried but they do not seem to be effective presumably due to insufficient penetration to skin. Tacrolimus (FK506) is another immunosuppressant that has almost similar effects on the cellular level as CsA. FK506 is 10-100 times more potent than CsA and it has lower molecular weight. Recent studies suggest that topical FK506 penetrates human skin in amounts exceeding those of topical CsA. Topical FK506 also seems to suppress skin inflammation in man. These findings prompt for further clinical studies of efficacy and safety of topical FK506.