question: I'm taking cephalexin, going to have a tooth pulled in a few days. My dentist suggested breaking open a Benadryl capsule, making a paste to put on my tooth for the pain. It is helping the pain. My concern is this: Will the Benadryl interact badly with the nitrous oxide or laughing gas that he will give me when he pulls my tooth? & will Benadryl interact with the injections he'll give me in my gums to numb them? Also, can I take my antibiotics & Benadryl the day that he pulls my tooth?