Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
For medical purposes, desensitization is a method to reduce or eliminate an organism's negative reaction to a substance or stimulus.
For example, if a person with diabetes mellitus has a bad allergic reaction to taking a full dose of beef insulin, the doctor gives the person a very small amount of the insulin at first. Over a period of time, larger doses are given until the person is taking the full dose. This is one way to help the body get used to the full dose and to avoid having the allergic reaction to beef-origin insulin. (See Hyposensitization.)
At the cellular level, administration of small doses of toxin produces an IgG response which eventually overrides the hypersensitive IgE response.
In pharmacology, desensitization is the loss of responsiveness to the continuing or increasing dose of a drug. Also termed tachyphylaxis, down-regulation, fade or drug tolerance. This may be an important area to consider for the future design of safer drugs.
- Patients who have a positive skin test to one of the penicillin determinants can be desensitized.
- This is a straightforward, relatively safe procedure that can be performed orally or IV.
- Although the two approaches have not been compared, oral desensitization is regarded as safer and easier to perform.
- Patients should be desensitized in a hospital setting because serious IgE-mediated allergic reactions can occur.
- Desensitization usually can be completed in approximately 4-12 hours, after which time the first dose of penicillin is administered.
- After desensitization, patients must be maintained on penicillin continuously for the duration of the course of therapy.