Effect of Neomycin and Other Antibiotics on Serum Cholesterol Levels and on 7α-Dehydroxylation of Bile Acids by the Fecal Bacterial Flora in Man

Abstract

Fresh feces from 25 patients were homogenized and incubated with labeled cholic or chenodeoxycholic acid. After 24 hours of incubation, the percent change to the 7α-dehydroxylated form was measured. In 11 patients, the oral administration of 2g of neomycin daily significantly reduced the levels of serum cholesterol (from an average of 316 mg/100 ml plasma to 237 mg/100 ml plasma) and markedly inhibited the extent of 7α-dehydroxylation of cholic acid (from 89% to 9%); in 2 patients whose serum cholesterol levels were not lowered, the degradation of cholic acid remained unchanged (control 93%, neomycin 91%). In 5 patients the administration of kanamycin reduced serum cholesterol levels (from 280 mg/100 ml plasma to 252 mg/100 ml plasma) and also inhibited 7α-dehydroxylation of cholic acid (from 92% to 21%); in 3 additional patients this drug failed to lower serum cholesterol concentrations and had no effect on bile acid degradation (control 91%, kanamycin 92%). Similar results were obtained with chloramphenicol in 3 patients, and equivocal results were obtained with chlortetracycline in 3 patients. The correlation coefficient between undegraded cholic acid and percent decrease in serum cholesterol concentrations ( r = 0.732) was statistically significant ( P < 0.001). It is proposed that serum cholesterol levels might be controlled in part by the prevalence of bile acid-degrading bacteria within the gastrointestinal tract.