Comedonal levels of free clindamycin following topical treatment with a 1% solution of clindamycin phosphate.
Comedones were extracted from twenty subjects using topical 1% clindamycin phosphate and were assayed for free clindamycin. Positive specimens were obtained from sixteen subjects at 2 weeks and from eighteen at 4 weeks, with levels of 0.06 to 1.49 micrograms/mg. Mean content was 0.39 +/- 0.08 micrograms/mg and 0.6 +/- 0.11 micrograms/mg, respectively. These values closely match levels previously determined following treatment with clindamycin hydrochloride, which may explain how these two esters can be similarly effective therapeutically. Satisfactory cooperation by the participants was likely obtained because their clinical progress paralleled that reported in other studies. Comedonal material reported as negative could very well contain effective levels of clindamycin, since minimum inhibitory concentrations of that antibiotic for most strains of Propionibacterium acnes are far below those detectable by current bioassay methods.