Penetration of topical clindamycin into comedones

Comedones were removed from patients on topical clindamycin and assayed for that antibiotic by of two methods. Prominent levels were found in eight of ten patients by one bioassay method. Once whole comedones from a patient were found to be positive, other comedones were microdissected to separate the external and internal portions. Prominent levels of clindamycin were found in the inner portion as early as 2 weeks. Further, the antibiotic could always be found in the internal portion when it was present in the external layers. Using the more sensitive of two bioassay methods, the whole comedonal level of clindamycin ranged from 0 to 5 microgram/mg of comedonal material, with an average level of 0.824 microgram/mg. The significance of this is discussed.