When I was younger I was on long term antibiotic treatment for staph and PA. It didn't eradicate the problem either way - in regards to the Staph/MRSA or PA.
I was on one month on of TOBI and then the off month I would take Cipro, Levaquin or Bactrim (one of the three not all three). I did that for over a year. Then I started having problems with TOBI an had to be taken off of it temporarily, after that they had me on Bactrim or Cipro (I developed an allergy to levaquin) alternating as I had with TOBI and the others. I will say that I experienced fewer infections when I was taking the antibiotics long term vs. now when I only take antibiotics when I have an infection (except TOBI). I have had more flareups that are contributed to MRSA/Staph since I stopped the long term treatment. Whereas many/most of the infections I had prior to that involved the PA - even though I was being treated with antibiotics that were effective on both Staph and PA.
In general - by what I have been told by my docs and therapists - PA is a more aggressive bug than Staph. Meaning it multiplies at a faster rate, so that is part of the reason it is such a problem and it is more destructive. The Staph may not multiply and spread as fast, but it is still an issue that needs to be addressed (in my mind anyway). I know people say that Staph can prevent PA from growing - I personally have never been told that or read it anywhere but here. I also have not looked it up as I culture both and have for a long time, so I do not have much of an interest as it doesn't matter for me. I am not saying that it is wrong I am just saying I have not read much about that other than on this site.
I can understand why your docs would want to try and eradicate the probem though.
No matter what bacteria you have in your lungs - or your son has in his lungs - it is going to do damage. So what if Staph being present COULD prevent PA from growing. The Staph will also do damage of its own. They may be hoping to clean him out and hope to keep the lungs clear of bacteria in general ... not just PA. That, to me, makes sense. I am not a big fan of the keep the Staph to prevent PA theory - but that is because I have a form of staph and know how crummy it can make you feel .. just like PA .. and I know it can cause just as much of a problem in the long run.
I would talk to your docs more about the side effects and possible outcomes and what they are hoping to see come from this long term antibiotic treatment. I know that I had been cultured/colonized for some time with PA when they put me on a long term regimine, so I never eradicated the bacteria, but like I said I did feel a bit better while I was taking the meds.
Whatever you and your docs decide I am sure it will be the best option for your son. It is always good to get advice and other people's experiences, but remember YOUR docs are the ones that see your son and treat him. Treatments work differently for each person and effect each person in a different way, so I would get information - but ultimately talk to the doc and present questions you have after reading the info on here. In experiences I have had with docs, they are open to discussing and explaining their decisions if you ask questions without being demanding or insulting (not that you are) or without treating them as though they are wrong. No one on here knows your son's history with CF like you and the docs he sees. There may be an underlying reason that they want to try this treatment. I would ask more questions of them, just because they are the doctors doesn't mean you have to take what they say without questioning it. They should understand that you are asking to better understand not to challenge them, and if they have problems with you asking that is their problem.
I hope it all works out and you guys choose the best treatment path for your son.
Lindsey