I have gastroenteritis on the road. i have an old prescription for ciprofloxacin.should i take expired medicine?

Don't treat yourself: Most gastroenteritis is viral and won't get better with antibiotics. Some forms of gastroenteritis can actually get worse with antibiotics. I don't recommend treating yourself with ciprofloxacin, expired or otherwise.

Fyi: The fact that you still have an old prescription also warrants a comment: you should have finished your course of antibiotics as prescribed. Shortening does not make sense since it carries a risk for relapse. Try to stick to prescribed durations of therapy in the future. And yes. Dont self-medicate with antibiotics unless discussed with your physician.