Reduction of oral flora with rifampin in healthy volunteers.

The effect of a short course of rifampin on the oral microflora was evaluated in 17 healthy volunteers. Salivary specimens were collected before and after two 600-mg doses of rifampin administered 6 h apart. Salivary bacteria were identified to species, and total quantitative colony counts were determined for each isolate. For all 17 subjects, treatment with rifampin led to a reduction in total bacterial colony counts; the mean inhibitory activity was 85.8% (range, 48.3 to 99.8%). Both aerobic and anaerobic bacteria were inhibited in every case: 45.5 to 99.8% for aerobic bacteria, mean inhibitory activity of 85.8%; 40.9 to 100% inhibition for anaerobic bacteria, mean inhibitory activity of 87.6%. However, total counts were reduced by greater than or equal to 2 logarithms in only 18% of individuals; for aerobes, in 29%; and for anaerobes, in 41%. All classes of bacteria were inhibited, with mean inhibitory activities ranging from 8.4 to 99.9%. However, only streptococci, Haemophilus spp., Bacteroides spp., and aerobic and anaerobic gram-positive nonsporeforming rods were reduced in counts close to 2 logarithms after treatment with rifampin. Clinical studies are needed to clarify the significance of these in vitro data and to delineate a possible role for rifampin in preoperative prophylaxis of patients undergoing head and neck cancer surgery.