If i'm allergic to nitrofurantoin , is it likely i'd be allergic to cipro (ciprofloxacin) also?

Most probably not: There is no interaction between the 2 drugs, nor is their structure similar. However, people who are allergic to one drug, are more likely than others to develop new drug allergies. In short, you should take the Cipro (ciprofloxacin) and not worry about drug allergy if you need the medication. The need should be determined by your physician.

Not likely: The two have no relationship to one another. Some studies in the drug literature have found that people who have an allergic response to one drug are likely to have an allergic response - randomly - to another, even though it's chemically unrelated. But that's just a function of the fact that those individuals have hyperactive/hyperresponsive immune systems. There's no predicting who and which.