Chlorhexidine-d8 is intended for use as an internal standard for the quantification of chlorhexidine by GC- or LC-MS. Chlorhexidine is a bis(biguanide) antimicrobial disinfectant and antiseptic agent. It inhibits growth of clinical methicillin-resistant S. aureus (MRSA) isolates (MIC90 = 4 μg/ml). It is also active against canine isolates of MRSA, methicillin-susceptible S. aureus (MSSA), methicillin-resistant S. pseudintermedius (MRSP), and methicillin-susceptible S. pseudintermedius (MSSP; MIC90s = 4, 2, 2, and 1 mg/L, respectively). Chlorhexidine inhibits growth of E. faecium strains (MICs = 1.2-19.6 μg/ml) and C. albicans (MIC = 5.15 μg/ml). It generates cations that bind to and destabilize the bacterial cell wall to induce death.6 Chlorhexidine also completely inhibits matrix metalloproteinase-2 (MMP-2) and MMP-9 when used at concentrations of 0.0001 and 0.002%, respectively, in a gelatin degradation assay. Formulations containing chlorhexidine have been used in antisept......