I'm sorry but all bacteria have the capability of resistence, esp. the pathogenic ones, the ones causing you the trouble in the first place, and causing you to put the medication there. Most bacterial infections of the nasal cavaties are gram negative, and correlate with what is also in your mouth and throat. Just like in your mouth, the ones in your throat and nose, are also capable of making biofilms. So all the medication in the world won't get at the real problem. Hence the chronic sinusitis. Have your doc get you an intra-nasal mucinase (dextranase is phenomenal) in addition to your med cocktail.
About those containing gentamicin. There are two purposes for adding gentamicin to a mix. One is the broad spectrum coverage of gram positives, as any broad spectrum gram negative med can then allow the gram positives to proliferate. And vice versa. The second is that it is a powerful toxin binder.
I dislike having to contradict someone, but this is something I am very familiar with. My very best to you all...
LaurieL