What is the best treatment for chronic psuedomonas?

[aprilmay20]

My dad is 81 and has chronic pseudomonas infection in his lungs. He also has COPD. This is his 4th round of getting this infection in 3 years. He just got out of the hospital from a 5 day stay 3 weeks ago and did a 10 day pick line antibiotic. His Dr called today and he still has the infection. They are calling it a 4+ pseudomonas infection. (whatever that means). He has done every antibiotic there is (pill form, nebulizer, inhalers and pick line) for this and nothing is working anymore. Does anyone have any other suggestions?