For External Use. DESCRIPTION. Tradename (clindamycin phosphate gel) topical gel, 1%, a topical antibiotic, contains clindamycin. phosphate, USP, at a concentration equivalent to 10 mg clindamycin per gram in a gel vehicle consisting. of carbomer 941, methylparaben, polyethylene glycol 400, propylene glycol, sodium hydroxide, and. purified water.