Ciprofloxacin administration decreases enhanced ethanol elimination in ethanol-fed rats

Many colonic aerobic bacteria possess alcohol dehydrogenase (ADH) activity and are capable of oxidizing ethanol to acetaldehyde. Accordingly, some ingested ethanol can be metabolized in the colon in vivo via the bacteriocolonic pathway for ethanol oxidation. By diminishing the amount of aerobic colonic bacteria with ciprofloxacin treatment, we recently showed that the bacteriocolonic pathway may contribute up to 9% of total ethanol elimination in naive rats. In the current study we evaluated the role of the bacteriocolonic pathway in enhanced ethanol metabolism following chronic alcohol administration by diminishing the amount of gut aerobic flora by ciprofloxacin treatment. We found that ciprofloxacin treatment totally abolished the enhancement in ethanol elimination rate (EER) caused by chronic alcohol administration and significantly diminished the amount of colonic aerobic bacteria and faecal ADH activity. However, ciprofloxacin treatment had no significant effects on the hepatic microsomal ethanol-oxidizing system, hepatic ADH activity or plasma endotoxin level. Our data suggest that the decrease in the amount of the aerobic colonic bacteria and in faecal ADH activity by ciprofloxacin is primarily responsible for the decrease in the enhanced EER in rats fed alcohol chronically. Extrahepatic ethanol metabolism by gastrointestinal bacteria may therefore contribute significantly to enhanced EER.