Allergy to drugs

Q: Is there any way of ascertaining which drugs one is allergic to? I am allergic to ampicillin and sulpha drugs. I occasionally show allergic reactions to other medicines which I do not know before consuming them. How can I determine which drugs I am allergic to?

A:Unfortunately there is no definitive test for drug allergy. Usually if a person is allergic to ampicillin, then he/she will be allergic to all penicillins. Erythromycin is an alternative to penicillins.