My son is almost 15 yrs old. He was prescribed cloxicillin (antibiotic) by IV drip. Hes been receiving it for 2 days now and has broken out in a extremely itchy rash on back and stomach. He had poision ivy or was bit by something 2 weeks ago and was given an antibiotic that didn't do much and started to get a little rashy on back and tummy . A different Dr said he had a skin infection and he put him on the IV antibiotic that has caused the tummy and back rash to get worse the last 2 days. I stopped the IV antibiotic until we see the Dr in the morning. Can I give him his normal Reactin allergy pill to help this "reaction rash" ? Or will the reactin pill interact with the stopped antibiotic Medicine?

Thank you,