Antimicrobial drugs that are contraindicated in patients with myasthenia gravis include three main groups: quinolones such as levofloxacin and ciprofloxacin, macrolides such as erythromycin and azithromycin, and aminoglycosides such as chloramphenicol and tobramycin. These antibacterial drugs have some neuromuscular junction blocking effect and may aggravate the symptoms of myasthenia gravis.