Olanexidine [1-(3,4-dichlorobenzyl)-5-octylbiguanide] (formerly OPB-2045), an antimicrobial agent exhibited antimicrobial activity against a wide range of bacteria, especially Gram-positive bacteria, was synthesized in 1997. To optimize its use as a topical antiseptic, olanexidine was converted to the gluconate salt. The resulting formulation (OPB) had more potent bactericidal activity against methicillin-resistant S. aureus and vancomycin-resistant enterococci in both in vitro and in vivo animal models than chlorhexidine and PVP-I. The mechanism of action was considered to be follows: olanexidine binds to the cell membrane, disrupts membrane integrity, and exerts its bacteriostatic and bactericidal activities by causing the irreversible leakage of intracellular components. At relatively high concentrations, olanexidine aggregates the cells through a protein-denaturing effect.