As most of us already know, healthcare in the United States is really costly. Sick people and preppers alike have been known to stock up on fish antibiotics because they are a fraction of the cost that they would spend on getting a conventional prescription. It’s important to remember that if you have a Penicillin allergy, you should not take Fish Penicillin, Mox, or Fish Ampicillin. Cephalexin is in a different drug family than Penicillin, but is quoted as having a 10% cross-reactivity rate with Penicillin.