I can't remember the exact one, but ones to definitely avoid are Cipro, Avelox, and levaquin. There may be more than this, but these have a black box warning not to be used if you have mg. (Ask me how I know! 7 days in ICU after taking Levaquin for a urinary tract infection). The website for the Myasthenia Gravis Foundation of America has full lists of which drugs affect mg and how. A good place to check.

Annie is right, this will not be a miracle cure for mg, but it is definitely something you need to get taken care of.