Antimicrobial Effect of a Single Dose of Amoxicillin on the Oral Microbiota

Abstract Purpose Amoxicillin is commonly used in oral surgery for antimicrobial prophylaxis against surgical‐site infection and bacteremia because of its effect on oral streptococci. The aim of this study was to determine whether amoxicillin reaches the break‐point concentrations in saliva and has any effect on the salivary microbiota, colonizing bacteria on mucosal membranes and on the gingival crevice after a single dose of amoxicillin. Material and Methods Twenty subjects received 2 g of amoxicillin, per os . The facultative and strictly anaerobic microflora, as well as the streptococcal microflora specifically, were followed from baseline and after 1, 4, and 24 hours. Samples were taken for microbial analysis from saliva, the dorsum of the tongue, and the gingival crevice, and were inoculated and cultured. Plasma samples and saliva samples were analyzed for amoxicillin concentrations (free and protein bound) using liquid chromatography and mass‐spectrometry. Results Amoxicillin was detected in concentrations over the break‐point (>2 μg/mL) of amoxicillin in plasma after 1 and 4 hours but not after 24 hours. The dose had a significant effect on the streptococci in the gingival crevice. Conclusion A single dose given as prophylaxis to prevent a surgical‐site infection results in a significant reducing effect on the oral streptococcal microflora in the gingival crevice and may have an impact on bacteria spreading into tissues and the bacteremia of streptococci.