Any time anyone uses something new and they get hives, they should stop all new meds immediately and get to the doctor or ER. Hives is an allergic reaction. Hives are different than just being itchy:
acaai.org/allergies/types/skin-allergies/hives-urticariaWith that said, we do have members that get hives as part of a herx or part of their symptoms when under stress. The best thing to do is to contact your doc.
I wouldn't assume you can have another dose of those meds though - the next time the reaction could be even more severe. Hives shows that there is something very wrong in the body. The last time I had hives, I had just taken penicillin as a kid - and the hives were all over my body, plus they were going down my ears and down my throat. Obviously, I have not had penicillin since, but I also did that when I took Keflex - so I no longer can take either of those meds. I'm not interested in a full on anaphylactic shock.