Trial results indicated that clindamycin phosphate gel was more effective than a vehicle gel in the treatment of mild to moderate acne vulgaris. The 12-week, multicenter, randomized, vehicle-controlled trial compared clindamycin phosphate topical gel, 1% once daily to a vehicle gel administered once daily.he total mean percent reduction in lesion counts at the end of treatment was 38% for clindamycin phosphate gel and 27% for the vehicle gel. In a contact sensitization trial, four of the 200 subjects appeared to develop suggestive evidence of allergic contact sensitization to clindamycin phosphate gel.