Antibiotic Allergy, When to Test, Challenge or Desensitise

Antibiotics are widely used for treatment of bacterial infections and for prophylaxis during instrumental procedures and in certain conditions such as immunodeficiency and splenectomy. Hypersensitivity (allergic) reactions are unpredictable and can occur in some patients even if they have taken the antibiotic in the past with no reaction. Drug allergy accounts for 11.3% of all adverse drug reactions. Drug allergy drugs can be generally classified (according to the World Allergy Organization) based on timing of symptoms into immediate (Immunoglobulin E (IgE) mediated) occurring within 1 hour and delayed (non IgE mediated) allergic reactions occurring after 1 hour. Many patients are mislabeled with drug allergy especially when the diagnosis is made based on history alone. In such cases, a referral to an allergist is important to confirm or exclude allergy through a detailed clinical history, in vitro and/or in vivo testing, as over diagnosis of drug allergy leads to the unnecessary use of broader spectrum and expensive antibiotics contributing to the emergence of multidrug resistant pathogens. Also, in cases of confirmed drug allergy it is important to establish potential cross reactivity with other drugs. Equally, patients with confirmed drug allergy, who have an absolute requirement for the drug or cross reactive drug (as in penicillin allergic females with syphilis) can undergo a process of desensitization in order to complete their treatment through induction of temporary tolerance of the drug.