Allergy desensitization is defined by MedicineNet as: stimulation of the immune system with gradually increasing doses of the substances to which a person is allergic, the aim being to modify or stop the allergy "war" (by reducing the strength of the IgE and its effect on the mast cells).
According to the American Academy of Allergy, Asthma, and Immunology, allergies make up approximately 5 to 10 percent of all adverse reactions to medications. Drug allergies can be severe, so when a patient reports an allergy to any medication, they are advised to never take that medication again.
For many years, physicians have been using allergy shots to reduce or even eliminate the symptoms of hay fever. These shots contain small doses of the problem allergen and given in increasing doses until the patient develops a tolerance to it. Drug desensitization is the same concept.
Drug desensitization is performed in the hospital for safety. The patient is given small, diluted doses of the medication and the dose is increased over several hours until the optimal dose is reached. This treatment only works if the patient is taking a daily dose of the medication, so patients that are not on daily doses will have to take the desensitization treatments with each new treatment cycle.
Drug desensitization gives patients a way to receive treatments that would otherwise not be available. There are only a few doctors and hospitals that perform these procedures right now, but new interest is growing.