Hi there. I am so sorry to hear about your father's lung issues. When I had pseudomonas, I too was put on tobramycin, 28 days on 28 days off for several years. The pseudomonas was gone after the first month, but I was instructed to stay on it for a long period to get it good and gone. If you Google the indications for taking this med; all sites say it needs to be a 28 day course at a time. You may want to look into that and have him ask his dr why he is being prescribed differently. Also, what has helped myself and many others in this group is using the nebulized saline. I use the 7% strength. This saline solution helps to clean out your lungs by thinning the mucous, and irritating your lungs into coughing. The coughing is good because it brings up a bunch of gunk out of your lungs. Is your dad using this already by any chance?