This is the second time I have had to be desensitized to an antibiotic to which I am allergic. I don’t understand the medical or biological principle of desensitization. I would like to know why I have to undergo this process every time I need to take the antibiotic. Can you also explain why it has to be done in the intensive care unit?

The principle of desensitization is a phenomenon that is not yet fully understood. What we do know is that when the immune system is exposed to a substance to which the patient is allergic, it produces an allergic reaction involving, among other things, type E antibodies (Immunoglobulin E or IgE). When a person is given a very small dose of a substance to which he or she is allergic, and the dose is subsequently increased grad-ually, the body reacts by developing a different type of immune response that does not involve IgE. The new immune response will therefore not cause an allergic reaction with the ensuing eye irritation, runny nose, nasal congestion, itching, rash, upper airway obstruction, difficulty breathing, low blood pressure and shock.

During the desensitization process, the new harmless immune response will be maintained as long as the drug (including antibiotics) is being administered regularly. But if the drug treatment is interrupted, the patient will once again have a more severe allergic reaction when exposed to a normal dose of the drug. This is why it is necessary to start the desensitization process over again when a patient starts a new treatment.

Desensitization is not risk free and has to be done under the supervision of a doctor specializing in allergies and immunology. Despite all the precautions taken, the process can still provoke allergic reactions with potentially serious consequences, especially in people with cystic fibrosis who have reduced lung function. In most cases, the desensitization process is performed under strict supervision in the intensive care unit so that possible allergic reactions can be detected and treated quickly.

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