Is Advair an antihistamine

No. It contains two drugs, one of which reduces inflammation, and the other opens up the airways in the lungs. It's for treating Asthma.

Antihistamines do reduce inflammation caused by Allergies but the inflammation caused by asthma isn't connected with allergies, so Advair cannot be used instead of antihistamines. Some patients have asthma and allergies, but each condition should be treated with the appropriate medication.