Abstract: A method for preventing and treating internal infections, e.g., urinary tract infections, caused by catheters is provided, in particular by reduction in catheter-associated biofilms. A coating composition is used to treat the catheter and applied through the catheter into the bladder or other body urinary tract organ to kill or neutralize microorganisms, including biofilms therein. The composition comprises a humectant and an antimicrobial with the antimicrobial including a monoquaternary ammonium compound or pharmaceutically acceptable salt thereof. The coating layer has antimicrobial cidal or static activity for at least about one hour.