Cotrimoxazole skin rash: what to know

Cotrimoxazole can be followed by a mild itchy rash, but a new eruption may also be an early sign of a more serious medication reaction. Timing, the shape and spread of the rash, fever, skin pain, and involvement of the mouth or eyes help clinicians judge the risk. Other causes such as Atopic Dermatitis, Contact Dermatitis, Heat Rash, Intertrigo, Psoriasis, Ringworm, or Scabies can look similar, so appearance alone cannot identify the cause.

Contact the prescriber or an urgent medical service as soon as you notice a new rash while taking cotrimoxazole. Have the medicine name, dose, start date, other medicines, and photographs of the rash available. Do not take another dose until a clinician or pharmacist gives you a clear plan, unless an emergency clinician has instructed otherwise. Avoid starting leftover creams or another antibiotic to cover the rash.

Keep the skin cool, avoid new fragranced products, and do not scratch areas that are blistering or tender. A clinician may document the reaction and advise whether this medicine should be avoided in future.

Call emergency services immediately for trouble breathing, throat or facial swelling, faintness, or rapidly developing hives. Go to emergency care for blistering, peeling skin, skin pain, fever, purple or dusky spots, or sores involving the mouth, eyes, or genitals. These features can signal a severe drug reaction and need urgent examination.

Could this be a cotrimoxazole reaction, and should the medicine be recorded as an allergy? What symptoms require emergency care? Which medicines or antibiotics should I avoid until the reaction is clarified? How should the infection that led to treatment be managed now?