Modulation of the intestinal microflora by the non-absorbable antibiotic vancomycin leads to a reduction of the tumor load in liver and spleen in a leukemic rat model.

Based on previous studies where it was shown that non-absorbable antibiotics can influence the normal hematopoiesis via changes in factors related to the intestinal microflora, the influence of vancomycin on the progression of acute myeloid leukemia was investigated in the BNML rat model. Oral vancomycin, which selectively reduces Gram-positive bacteria in the gut, leads to diminution of the leukemic load in liver and spleen by 30-60%. This 'antileukemic effect' is not dependent on Gram-negative bacteria as source for endotoxin. The presumed mechanism is a decrease of the leukemic growth fraction caused by alterations in the absorption of substances from intestinal Gram-positive bacteria.