The Basics of a Drug Allergy

Facts About Prescription and Over-the-counter Medication Allergies

Apr 9, 2009
Stella Walsh

Drugs Can Cause Allergies - Stella Walsh

When taking prescription or over-the-counter medication, it is essential to be aware of the possibility of an allergic reaction, and what may be involved.

Even though some medications, such as antibiotics, have a higher risk of being allergenic, all drugs have the potential to provoke an allergic response.

What is a Drug Allergy?

It is possible for a single medication to cause several different allergic and pseudoallergic reactions:

Type I - This is an IgE-mediated reaction, which usually starts within minutes to an hour of ingesting the drug. It involves the immune system creating IgE antibodies. These, in turn, activate mast cells, which cause symptoms to develop.
Type II - These are "cytotoxic" drug reactions, in which medications attach to and attack certain cells in the body. They can produce hemolytic anemia by destroying red blood cells.
Type III - These are immune-complex medication reactions which cause serum sickness. This condition produces a fever and flu-like malaise.
Type IV - These reactions tend to occur 10 - 20 days after exposure. They involve activated T-lymphocytes and often cause contact dermatitis. Sometimes delayed drug reactions can affect the lungs or kidneys. These reactions are poorly understood.

Factors Affecting Drug Sensitization

In most cases, an individual does not have an allergic reaction the first time he/she takes a particular medication. It usually takes several days to several weeks to become sensitized after the first exposure. There are several factors to keep in mind:

Sensitization can occur when an individual is exposed to drugs like penicillin in food products.
Once an individual has been sensitized he/she can react to traces of the drug.
Drugs are more likely to cause a reaction if they are taken as several short courses that are repeated in a short time frame. An example would be when an infection comes back.
Injected medications are more likely to cause an allergic response than those taken orally.
People who are prone to other allergies are not more likely to have a drug allergic reaction.
People who are allergic to one medication often have more risk of other drug allergies, even if the drugs are unrelated.

Symptoms of a Drug Allergy

The symptoms of a drug allergy are like those of other allergies. They include rash, hives (possibly large), red skin blotches, flushing, swelling, nausea, nasal congestion, swollen larynx, and difficulty breathing.

Unlike other allergies, a drug allergy can include a fever. It may be alone and become confused with the fever from an illness.

Stevens-Johnson Syndrome is a rare non-allergic skin condition. It is a severe, peeling, blistering, and ulcerating skin condition. It can appear with an allergy and should be treated immediately.

Drug allergies have the potential to be very severe or life-threatening. If one is suspected, it is very important to seek medical attention and advice immediately.

Disclaimer: This article is intended for information purposes only. It is not a substitute for medical attention and supervision.

Sources:

Engel, June. The Complete Allergy Book. Toronto, Canada: Key Porter Books Limited, 1997.

Hospital for Sick Children: The Complete Kid’s Allergy and Asthma Guide: The Parent’s Handbook for Children of All Ages. Ed. Dr. Milton Gold. Toronto, Canada: Robert Rose Inc., 2003.

Berger, William E. And Gordon, Debra L. Allergy and Asthma Relief. New York: The Reader’s Digest Association, Inc., 2004.

Website: American Academy of Allergy, Asthma and Immunology, 2007. Visited April 5, 2009.

For other articles related to allergies see The Basics of Hay Fever, Rare and Serious Exercise-induced Anaphylaxis, and Allergic or Sensitivity Reactions to MSG.