Cleocin (clindamycin) is an antibiotic that fights bacteria in the body. Cleocin is used to treat serious infections caused by bacteria. Clindamycin is an effective antibiotic for a variety of serious infections. Clindamycin has an average rating of 6.8 out of 10 from a total of 25 ratings for the treatment of Sinusitis. 60% of those users who reviewed Clindamycin reported a positive effect, while 28% reported a negative effect.