Christel, Everyone is different with antibiotics. I can have Biaxin (clarithromycin) with no problems but some people cannot. It's the same "family" of drugs as the Z-Pak (Azirthromycin). DO NOT EVER take Ketek (Telithromycin)!!!
Any of the cephalosporins should work. Augmentin might be okay for you. Quinolones have a new warning for MGers to not take them (and for anyone else really).
Check out the drug list here. I think they still have it there.
www.myasthenia.org
Make sure both your doctor and your pharmacy knows of problem drugs for you. Also, do you have any seasonal allergies? Sometimes they can lead to sinus infections and bronchitis.
Annie