Federal drug safety officials have imposed the government's most urgent warning on Cipro and similar antibiotics, citing risks that they can cause tendon ruptures, a serious injury that leaves some patients incapacitated.

The Food and Drug Administration on Tuesday ordered makers of flouroquinolone drugs -- a potent class of antibiotics -- to add a 'black box' warning to their products, which include Cipro, Levaquin, Floxin and other medications.

Patients should immediately stop taking the medications if they develop any tendon pain, swelling or inflammation.