A Study to Determine the Correct Dose of Amikacin Which is Delivered Directly to the Lungs of Ventilated Patients as an Aerosol Via an Investigational Device Called the Pulmonary Delivery Device System (PDDS)

Single daily dose of 400 mg aerosolized amikacin and a single dose of aerosolized placebo on a rotating every 12hr schedule

Daily dose of 800 mg aerosolized amikacin delivered in two divided doses of 400 mg per aerosol treatment every 12hr

Two aerosol treatments per day (one treatment every 12hr)