Is it possible for a person to be allergic to all antihistamines? (not the die but the active ingredients itself, ie cyclizine, meclozine)

Allergy: In medicine, anything is possible. However it would be unusual to be allergic to all antihistamines because there are different drug molecules with antihistaminic action that are different in molecular structure and in mechanism of action. If your question is related to a specific clinical situation see your doctor for a substitute medicine.