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Drug Desensitization Video and Transcript

Mariana C. Castells, MD

  • Director, Drug Hypersensitivity and Desensitization Center, Brigham and Women’s Hospital
  • Associate Professor of Medicine, Harvard Medical School

Drug Desensitization: What It Is & How It Works

The definition of drug desensitization is essentially a method in which we can safely reintroduce the drug to which the patient has become allergic. So the key word in desensitization is to have a very allergic patient who may have presented an initial reaction to that medication like hives, flushing, itching, or sometimes more severe.

We know that a patient needs desensitization because, when we do skin testing, we observe a positive response to that skin test. Skin testing is just putting a drop of the drug on the patient’s arm and then proceeding to see if they have a weal and flare reaction. So if a patient develops that reaction, it means that they are sensitized to the medication and every time that the patient is exposed to the drug they actually will react if not desensitized.

There was an unmet need for patients who presented reactions to their first-line therapy -- patients who had cancer and reacted to their chemotherapy, patients who had severe infections and reacted to their antibiotics, patients who had connective tissue disorders-- rheumatoid arthritis, Crohn's disease, and others -- and reacted to their medications. We started a program to allow those patients to be back on their first-line therapies.

We have desensitized patients to all kinds of chemotherapy medications, but also to antibiotics, and also to monoclonal antibodies and small molecules.

Drug Desensitization Process

During the desensitization process we divide the total dose of a patient's medication into bags at different concentrations. One in a hundred solution, one in ten solution, and a straight solution. And we approach the delivery of the medication very, very slowly. So with every step of the desensitization protocol, which typically has three bags and twelve steps, or four bags and sixteen steps, at each step the patient receives a doubling of the dose versus the step before. By this process, the immune system is tricked and inhibited to react. And so patients can very safely receive, in about five to six hours, the whole amount of medication that they need without having the symptoms of allergy or anaphylaxis. Patients might react during the desensitization protocol, in which case we stop the infusion, treat the patient, and continue.

This process has allowed patients with cancer to continue on their cancer medication, to complete their treatment plan, and actually to have increased life spans. We have also done this in patients with rheumatoid arthritis, with Crohn’s disease, and other diseases who require monoclonal antibodies. These patients have continued to have an excellent quality of life because they are able to resume their first therapy. We also have worked with cystic fibrosis patients who are very prone to infections and are also very prone to allergic reactions because they have had exposure to many antibiotics. The more that people are exposed to a medication the more likely that they are to become allergic.

Drug desensitization is available to everybody who has an allergic reaction to a drug. In the past it was recommended that somebody who had a very severe reaction should abandon that medication and not take it again. We have broken that paradigm. In fact, patients who are extremely allergic, who have had anaphylactic reactions to their medication, can be very safely desensitized.


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