Chlorhexidine is a bactericidal antiseptic effective against a large range of vegetative gram positive and gram negative bacteria, but it is more effective against gram positive bacteria. Some species of Pseudomonas and Proteus are relatively less susceptible. Chlorhexidine is most active at a neutral pH; its activity is reduced by organic matter (blood, serum, etc.) and by phospholipids. Chlorhexidine is ineffective against acidfast bacteria, bacterial spores, fungi and viruses.