Symptoms
A skin rash may occur during or a few days after taking the penicillin antibiotic amoxicillin. Other beta-lactam antibiotics may also cause it. The typical drug exanthema occurs over large areas on the trunk, arms, legs, and face. The full-blown appearance develops in one to two days. The appearance may resemble a rash in measles (morbiliform maculopapular exanthema). The reddened patches enlarge at onset, are slightly raised, and flow into each other. Papules also occur, and the rash may be accompanied by pruritus, low-grade fever, and mild swelling. Severely itchy hives (urticaria) with wheals may also develop with amoxicillin. This indicates an allergic reaction. There is a risk of dangerous anaphylaxis with edema, breathing disorders, and a drop in blood pressure. Fortunately, severe and even life-threatening skin reactions occur very rarely. These include:
- Stevens-Johnson syndrome (SJS).
- Toxic epidermal necrolysis (TEN)
- Acute generalized exanthematous pustulosis (AGEP).
- Drug exanthema with eosinophilia and systemic symptoms (DRESS).
Warning signs for a medical emergency and an immediate visit to the doctor in this context are:
- Blister or pustule formation
- Detachment or death of the skin, skin hemorrhage
- Erythroderma (extensive redness of the entire skin).
- Involvement of the mucous membrane
- Poor general condition
- General swelling of the lymph nodes
Causes
Rashes under amoxicillin can be allergic (IgE- or T-cell-mediated) and nonallergic. (Prospective study on this e.g., Caubet et al, 2010). Only a minority of patients react again with a rash when they receive oral therapy again. True allergies are more common in adults than in children. Concomitant viral infections seem to be an important risk factor for the development of the rashes. Allergic workup is recommended (see below). This is critical because otherwise affected individuals will have to avoid penicillins and related antibiotics for the rest of their lives without justification.
Diagnosis
Diagnosis is made under medical treatment on the basis of the patient’s history, physical examination, and appearance. Other causes must be ruled out. Whether an allergy to penicillins is actually present must be proven after one to two months with a skin test and/or an oral provocation test in allergology. If the result is positive, an allergy passport is issued.
Non-drug treatment
After stopping the antibiotic, the rash becomes paler within a few days and eventually disappears on its own. The rash is not contagious.
Drug treatment
Treatment depends on the cause and symptoms. For treatment of measles-like drug rash, itch-relieving and skin-conditioning body lotions, for example, with polidocanol or cardiospermum, can be applied. Systemic antihistamines may be tried.
