Polyhexamethylene guanidine hydrochloride as active ingredient for anticariogenic products: studies in vitro and in...

Dental caries is a highly prevalent multifactorial oral disease that can cause both local and systemic lesions. The aim of this study was to evaluate the in vitro antiseptic effect of a topical solution containing polyhexamethylene guanidine hydrochloride (PHMGH) and its possible toxic effects in vivo. PHMGH was tested (0.31-625.0 ppm) against Streptococcus mutans, Streptococcus sanguinis, Streptococcus salivarius, Streptococcus mitis, Streptococcus sobrinus, Lactobacillus casei, and Enterococcus faecalis by determining the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), minimum biofilm inhibitory concentration (MBIC₇₅), fractional inhibitory concentration index (FICI), and bactericidal kinetics. The polymer was effective against all microorganisms, with MIC and MBC ranging from 0.31 to 1.24 ppm; lower values were observed especially against S. mitis and E. faecalis when compared to commercial chlorhexidine digluconate. PHMGH inhibited 75% of the microbial biofilms, including S. mutans, with the MBIC₇₅ of PHMGH and CLX being similar for this microorganism. The combination of the polymer with CLX exerted indifferent effects against the cariogenic microorganisms. Regarding bactericidal kinetics, the polymer caused higher percent reductions in the microorganisms than CLX; at concentrations of 3.000 and 1.000 ppm, with 2 and 4 min of exposure, respectively, inducing 100% bacterial death. Given the promising results, rats received daily oral instillations of four drops of PHMGH at a concentration of 625 ppm for 90 days, mimicking a mouthwash. None exhibited alterations in mucosae or tongue, as well as no body weight and histological changes were observed in the oral mucosa, tongue, esophagus, stomach, and intestine. The toxicological evaluation showed that the treated animals did not present significant alterations in the parameters of hepatotoxicity and nephrotoxicity and DNA damage. Regarding the histopathological analyses of the digestive organs, there were no statistics differences, except for the mononuclear inflammatory infiltrate in the intestinal mucosa, which was significantly higher in treated animals. Under the present experimental conditions, PHMGH exerted in vitro antimicrobial activity against dental caries microorganisms, with no evidence of in vivo toxicity; thus, it becomes a promising and less costly option for the development of oral antiseptic products.