FOLLICULAR CONCENTRATIONS OF AZELAIC ACID AFTER A SINGLE TOPICAL APPLICATION

Follicular concentrations of azelaic acid (AzA) were determined in viv o using a rapid. non-invasive method, after a single topical applicati on of 20% (w/w) AzA cream, in order to establish whether the in vitro antimicrobial effects observed in previous studies are relevant in viv o. Preweighed amounts of 20% (w/w) AzA cream were applied over demarca ted areas on the forehead and back of nine young adults, and samples w ere taken over a period of 5 h. AzA was removed from the skin surface by washing with acetone, and follicular casts were collected using cya nacrylate gel. The samples were centrifuged to remove particulate matt er, and the supernatants derivatized for analysis by HPLC. Although th e results showed wide-ranging variability, the follicular concentratio n increased as the amount present on the surface declined, The maximum follicular concentrations of AzA attained ranged from 7.5 to 52.5 ng (mug of follicular casts)-1 and 0.5 to 23.4 ng (mug of follicular cast s)-1 in samples taken from the back and forehead, respectively. Assumi ng an average density of follicular material of 0.9 g ml-1, the mean m aximum follicular concentration attained on the back was between 36 an d 251 mmol/l, and on the forehead was between 2 and 112 mmol/l, and in dicates that the concentration of AzA attained in follicular casts aft er a single topical application is comparable with the concentration r equired to inhibit the growth of Propionibacterium acnes and Staphyloc occus epidermidis, in vitro.