There is no single test to determine hypersensitivity (allergic) reaction to all drugs. Hence you should write down the names of those drugs to which allergy has occured and refrain from giving them again either alone or in combination with other agent since sometimes there can be swelling of the respiratory tract that can lead to serious problem. Certain drugs such as amoxycillin have class (group) allergy. Thus a person who is allergic to amoxycillin will also be allergic to ampicillin or cloxacillin. Similarly Flexon contains diclofenac and paracetamol. Since the patient is known to be allergic to paracetamol (Crocin), then a combination product that contains paracetamol (such as Flexon) cannot be given. Similarly Combiflam should not be taken because it also contains paracetamol. May be the patient is not allergic to diclofenac alone (such as Doflex). Nimesulide is banned the world over in all advanced countries due to its serious adverse effects on liver and hence should never be used. The Indian drug regulator is reviewing whether to take similar action. To determine the hypersenstivity to other medicines, you can try by giving a very minute dose and see if there is any allergic reaction; if not then full dose can be given.