Cipro, avelox, and another antibiotic in the same class (I think it begins with a L) can all cause the same tendon problems. I just remembered the other drug is levaquin. My sister has had ongoing Achilles issues after being put on levaquin several times for sinus infections. She eventually had sinus surgery. I had to take my mom to the ER when she was on avelox because the pain in her legs was so bad. It says right on the warning to exercise caution in prescribing it to the elderly.