Different actions of neomychin and metronidazole on breath hydrogen (H2) exhalation

Purpose of this investigation was to characterize the effect of antibiotics as a possible limiting factor for the evaluation of hydrogen (H2) breath analysis tests which depend on bacterial carbohydrate fermentation. Breath H2-excretion following ingestion of the non-absorbable disaccharide lactulose was monitored in healthy subjects before and after pretreatment with the aminoglycoside neomycin or with metronidazole. Metronidazole decreased the amount of hydrogen exhaled by 39 % (p<0.05) and peak H2-excretion by 42.1 % (p<0.01), because it suppresses anaerobe H2 producing microorganisms. Neomycin intensified nonsignificantly the integrated (0-6 hours) breath hydrogen response to lactulose (+43 %) and the maximal H2-concentration by 29.8 %, probably because it interferes with intestinal bacteria which are important for H2-consumption.