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Drug hypersensitivity reaction is an immune-mediated reaction to a drug. Hypersensitivity reactions may vary in severity from mild to life-threatening. Reactions prompt the discontinuation of the causative drug and replacement with alternative agents that may be less effective, more toxic, or more expensive.

Patients receiving drugs for conditions such as rheumatoid arthritis, cancer, or diabetes may become allergic to first-line therapy following repeated exposure to the causative drug or from cross-reactivity with various allergens. Avoiding the culprit drug may negatively impact disease management, quality of life, and life expectancy.

Drug desensitization has emerged as a therapeutic modality that allows patients with drug allergies to receive the sensitizing drug safely.

When is drug desensitization used?

• There are no better alternative medications to treat a particular condition
• When the benefits of drug desensitization outweigh the risks

Drug desensitization is used to manage both IgE-mediated and non-IgE-mediated drug hypersensitivity reactions.

How is drug desensitization performed?

Drug desensitization involves the introduction, usually within hours to days, of a temporary state of tolerance to a drug which the patient has developed a hypersensitivity reaction to.

Various desensitization protocols allow patients to receive the full dose of the medications to which they have had a prior hypersensitivity reaction.

Before initiating desensitization for probable drug allergy, various tests can be conducted to confirm the presence of a drug allergy.

The initial step involves administering an extremely minute amount (1/10,000 of the usual dose) of the medication.

Gradually, the dose is increased and administered at fixed intervals (eg, every 15 minutes) until the full dose is reached. To maintain the temporary non-allergic state, the medication should be taken regularly. Once the drug administration is interrupted or discontinued, the patient returns to being allergic to it.

Common routes of drug desensitisation include:

• Rapid intravenous desensitisation – Undertaken in patients with immediate hypersensitivity reactions
• Oral routes
• Subcutaneous routes

What are the risks and benefits of desensitization?

Increased use of novel anticancer drugs and monoclonal antibodies in recent years has been associated with an increase in hypersensitivity reactions. Development of desensitization protocols for these life-saving medicines should be initiated following a careful assessment of the potential risks and benefits.

Although drug desensitization is an important procedure in the treatment of drug allergic reactions, it should be completely avoided in certain rare drug allergic reactions, such as Stevens-Johnson syndrome and toxic epidermal necrolysis. In such cases, the culprit drug should be avoided indefinitely.

Drug desensitization protocols should be carried out only by professionals trained to do so. There are highly trained allergists and specialized nurses, who are well experienced in determining the reactions which are manageable by desensitization. They can identify high-risk patients and treat them appropriately.

Efforts to increase awareness of the safety and efficacy of drug desensitization should be initiated, especially among non-allergists. Coordinated teamwork among the various healthcare professionals is needed to develop desensitization programs. The fields of oncology and rheumatology should receive special focus.

Further Reading

• All Drug Desensitization Content
• Drug Desensitization Safety