My Husbands Creatine Level Is 2.9, He Is A Diabetic,

My husbands creatine level is 2.9, he is a diabetic, has hypertension and has been referred to a nephrologist on May 14th. He has allergies tonight and wondered if it was safe to take a Benadryl. His internist has checked him for cancer and obstructions and the test were negative so he's referred him. Just needs something for allergies tonight. Thanks in advance.