Effect of urine concentration versus tissue concentration of ampicillin and mecillinam on bacterial adherence in the rat bladder.

We investigated the effect of tissue and urine concentrations of ampicillin and mecillinam on bacterial bladder wall adherence in rats. Escherichia coli 02 labeled with 3H-1-leucine was inoculated into the bladder for 2 hr. With the ureters transected bilaterally, antibiotic was instilled into the bladder lumen or administered intravenously only. No bacteria survived after the presence of antibiotic in the bladder lumen for 1.5 hr. After intravenous administration of ampicillin, with no antibiotic in the bladder lumen, measured by viable counts, decreased significantly as compared to controls. Adherence, measured by radioactive counts, decreased significantly after intravenous administration of mecillinam, possibly indicating prevention of tissue invasion. This finding was explained by entrapment of bacterial debris in the bladder lumen and invasion of bacteria into the bladder wall. Our results support the importance of tissue concentrations in the treatment of urinary tract infections.