Quinupristin is a streptogramin antibiotic that blocks peptide bond formation and peptide extension in bacteria. Quinupristin is usually combined with another streptogramin antibiotic, dalfopristin , to produce quinupristin-dalfopristin complex , known commercially as Synercid. While both quinupristin and dalfopristin have bacteriostatic effects, they act synergistically to kill Gram-positive bacteria, as well as some Gram-negative and anaerobic bacteria.