Updated | 31 March 2020 What is drug allergy? Allergy (or hypersensitivity) to medicines is an inappropriate and unpredictable response of our immune system to a drug or medicine . Allergy to a medicine can occur after several doses with no reaction; It does not have to happen the first time a medicine is taken; Even a small amount of a medicine can trigger an allergic reaction. Drug allergy is distinguished from other types of adverse drug reactions . These are related to the drug mode of action and, therefore, are more predictable and often are dose-dependent (for example, side effects). How does drug allergy present? Drug allergy can manifest itself in several ways: Skin and mucous membranes The most frequent symptoms involve the skin and / or mucous membranes and are, for example: Hives, angioedema : It is characterized by the appearance of reddish and itchy (pruritic) skin lesions that are frequently associated with angioedema (swelling), when deeper layers of the skin or mucous membranes are reached. Angioedema often involves the eyelids, lips, mucous membranes and extremities, and resolves more slowly compared to urticaria. Edema of the glottis . Digestive system Allergic reactions to medicines can also have digestive symptoms like: Vomits; Diarrhea; Abdominal pain. Respiratory and cardiovascular system Allergic symptoms associated with the respiratory system can be: Rhinitis; Cough; Wheezing; Difficulty breathing. Related to the cardiovascular system can be: Tachycardia; Hipotension; Lipothymia. Anaphylaxis Anaphylaxis is the most serious form of allergic reaction . It is characterized by symptoms involving two or more organs or systems. Usually, this systemic reaction develops quickly after exposure to the allergen (in this case, the drug) with patient life at risk when not treated immediately and appropriately. What drugs are involved in drug allergy? Any medicine can trigger an allergic reaction, but the drugs most often involved are: Antibiotics, especially from the beta-lactam family; Non-steroidal anti-inflammatory drugs (NSAID). How is drug allergy diagnosed? The medical specialty responsible for the diagnosis, treatment and prevention of drug allergies is immunoallergology . In the immunoallergology consultation, a detailed clinical history is made to: Identify suspicious drugs, Characterize the symtoms of allergy. Subsequently, allergy tests are performed with the suspected medicines in order to confirm or exclude hypersensitivity to it. Sometimes these tests are also performed to find a therapeutic alternative. The type of allergy test to be performed depends on the drug in question, as well as the type of reaction and are: Skin tests Skin tests consist of placing the drugs on the superficial layer of the skin. This can be done through a small prick (prick skin tests), through a small deeper injection (intradermal tests) and / or by contact (contact or epicutaneous tests). Blood tests Provocation tests Provocation tests consist of the administration of the drug, starting with small amounts and progressively increasing up to the therapeutic dose. If an allergic reaction occurs, the test is stopped, and the allergy is confirmed. Provocation tests are usually performed when skin tests or blood tests do not provide conclusive results, or are not possible, as is the case with several medications. How is drug allergy treated? Since an allergic reaction can be serious and potentially fatal, treatment consists of avoiding the responsible drug , identified in the tests performed. At the end of the investigation of drug allergy, written information is delivered indicating the drugs to be avoided, as well as possible therapeutic alternatives. In some cases where there is no therapeutic alternative and where treatment with the drug to which a patient is allergic is imperative, desensitization or induction of drug tolerance may be necessary to make the patient tolerant of the drug in question. Desensitization / tolerance induction consists of the controlled and gradual administration of the drug, starting with minute amounts and progressively increasing up to the predefined therapeutic dose for each patient. Drug allergy tests as well as desensitization / induction of drug tolerance are always carried out under strict medical surveillance , since a severe allergic reaction may be caused. They are usually performed in a day hospital , in specialized centers and always under the supervision of experienced immunoallergologists. The authors of this text are the following allergologists from the Hospital da Luz network: Luís Miguel Borrego, Ana Morais Mendes, Ana Reis Ferreira, Andreia Ferrão, Carlos Braga, Cristina Lopes, Diana Pereira da Silva, Filipa Semedo, Isabel Costa Silva, João Gaspar Marques, Pedro Carreiro Martins, Marta Salgado, Nuno Sousa, Rosa Anita Fernandes, Susana Piedade The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
