Good question! I have not tested the Claritan with antibiotics yet because the only antibiotic I have had in the past couple of years (that I know of) has been the penicillin during the allergy test for that. Not sure if they gave me an antibiotics during my rotator cuff surgery last year. But my reactions to food and additive allergies have been much, much less since I began my little "protocol." My allergist has instructor me to take 2 Claritan right before any surgery due to a reaction I had during eye surgery 4 years ago. Have not had an issue since during surgery.