Here is a side effect you may never have considered an antibiotic causing: "Imagine taking an antibiotic like Tequin or Cipro for a bad bacterial infection and then getting tendonitis or a tendon rupture as a side effect. Scary. The Public Citizen consumer watchdog organization filed a petition with the FDA to warn people about this critical side effect." Read More on how Tendon Rupture is Caused by Some Antibiotics.