Hives due to antibiotics: what to know and do

Hives are raised, itchy patches that can appear suddenly and move to different areas. They may follow an immune reaction to the antibiotic, but a viral illness or another trigger can also cause them. The timing, appearance and other symptoms help a clinician judge what happened. A suspected reaction should be recorded clearly, including the medicine name, dose, time taken and when the rash began. Do not assume every future antibiotic is unsafe; a clinician may need to distinguish an allergy from another rash and choose alternatives carefully.

Do not take another dose until you have received advice from the prescriber or an urgent-care clinician, unless you have been given a specific action plan. Keep the packaging or a photo of the label. Avoid rubbing the skin, use cool compresses, and wear loose clothing. An antihistamine may help some people, but check with a pharmacist or clinician first, especially for a child, pregnancy, long-term illness or other medicines. Do not restart the antibiotic from an old supply.

Call emergency services immediately for trouble breathing, wheezing, swelling of the lips, tongue or throat, faintness, confusion, or rapidly worsening symptoms. Seek same-day medical advice if hives are widespread, keep returning, or occur with vomiting, dizziness or marked weakness. A rash with blistering, skin peeling, mouth or eye soreness, or fever also needs prompt assessment. Bring the medicine information and describe any previous reactions.

Which antibiotic should I avoid for now? Could this have been a delayed rash rather than an immediate allergy? What should be written in my medical record? Is another treatment needed for the infection? What symptoms would require emergency help if they recur?