According to a recent study published in the Journal of the American Medical Association, there are approximately 550,000 serious allergic reactions to medications per year in hospitals throughout the United States.¹ It is unclear how prevalent drug allergies are among the general population, but allergic reactions to medications cause the highest number of documented deaths from anaphylaxis each year. Penicillin alone is responsible for about 5,440 cases of fatal anaphylaxis each year, which accounts for an estimated 75% of the known annual US anaphylaxis deaths.^2,3 Most deaths occur in people who have no medical history of allergic reactions.³

The most common culprits of medication allergies include penicillin and sulfa antibiotics, but many other medications, even over-the-counter medications, can also cause medication allergies. Physicians can help their patients recognize the symptoms of a medication allergy, which range from rashes to anaphylaxis. If a patient is unsure of their medication sensitivity, they can see a specialist to receive an accurate diagnosis, as well as expert advise on how to prevent and treat a possible allergic reaction.

 
Common Culprits

The medications that cause the most allergic reactions are:

• Penicillin
• Sulfa antibiotics
• Allopurinol
• Muscle relaxants
• Certain post-surgery fluids

Other medications known to cause severe allergic reactions are:

• Vaccines
• Radiocontrast media
• Antihypertensives
• Insulin
• Blood products

For example, radiocontrast media, used in over 10 million radiologic exams a year in the United States, are estimated to cause as many as 900 deaths per year from anaphylactoid reactions.⁴ (Anaphylactoid reactions are nearly identical to anaphylaxis but are not triggered by IgE mediation.) Anaphylactoid reactions are treated in the same manner as anaphylaxis.

 
Symptoms

People can experience a wide range of adverse reactions to medication, from drowsiness and nausea to kidney damage or respiratory distress. The most common allergic response is a measles-like rash that does not occur in conjunction with the production of the antibodies that can cause anaphylaxis.⁴ In contrast, systemic allergic reactions that can cause anaphylaxis are mediated by an immune system response that attacks what the body perceives as a foreign substance. This response can cause symptoms such as:

• Itching
• Hives
• Swelling of the throat
• Asthma
• Drop in blood pressure
• Irregular heart rhythm
• Nausea, vomiting, or abdominal cramping
• Loss of consciousness
• Death

 
Diagnosing Medication Allergy

People should see an allergist at the first sign of an allergic reaction to a medication in order to obtain proper treatment, diagnosis, and medical counsel to avert future reactions (see Find an Allergist for help in locating a qualified specialist near you).

Proper diagnosis may confirm that a patient is allergic to a medication. In this case, physicians will recommend substituting other medications and strictly avoiding the allergenic medication. If no suitable alternative is available, a physician may recommend that a patient undergo desensitization, a process of progressive administration of an allergen intended to reduce reactivity. However, this process offers only temporary desensitization and carries inherent risks of anaphylaxis.

Regardless of the method, there is some risk involved in testing for a medication allergy, which is why diagnostic tests should be performed by a certified allergist-immunologist in an environment that is equipped with epinephrine and emergency resuscitation equipment to handle an anaphylaxis emergency.

Diagnostic methods and their reliability will vary depending on the type of medication suspected of causing a patient's allergic symptoms.

Penicillin and insulin
Standard skin-prick tests are available and can determine with a high degree of accuracy whether a patient is allergic and likely to react to penicillin or insulin. For example, 97% to 99% of people who test negative to penicillin will tolerate the antibiotic even if they have reacted previously. However, a positive skin test in a person who has had allergic symptoms predicts a 50% or greater risk of an immediate reaction to penicillin and indicates that a patient should be given an alternative medication or undergo desensitization.⁴

Aspirin and other NSAIDs, radiocontrast materials, local anesthetics, and other medications
There are no definitive skin-prick or in vitro tests, but conventional skin tests (e.g., intracutaneous) and oral or subcutaneous challenges are sometimes used to help assess a patient's reactivity for most other medications.

 
Prevention and Treatment

Avoidance
Despite the fact that most reactions occur in people with no previous history of reactions to medication, and the fact that most people lose their sensitivity to common anaphylaxis culprits such as penicillin, avoiding medications that trigger allergic reactions is still a mainstay in protecting patients against anaphylaxis.⁷

The key aspects of avoiding medication triggers include:

• Keeping a complete medical history of reactions to medications and the results of diagnostic tests, and sharing these with physicians and pharmacists so they can help ensure that inappropriate medications are not prescribed, dispensed, or administered.
• Wearing a medical identification bracelet to inform medical personnel of his or her allergies in the event that the patient is unable to communicate his or her medical history to them.

Emergency medical care
Even after epinephrine has been administered, emergency medical treatment should be sought at once because severely allergic people who have experienced anaphylaxis may need emergency respiratory or cardiac care, or even to be resuscitated if they stop breathing altogether. More commonly, these patients will need professional care to determine whether additional epinephrine, steroids, antihistamines, or other treatments are required. In any case, follow-up diagnosis and care by medical professionals after the administration of epinephrine is critical for recovery.

Delayed or secondary reactions do occur, and patients should remain under medical supervision for at least 4 hours after an episode of anaphylaxis.⁶

 
References

1. Lazarou J, et al. Incidence of adverse drug reactions in hospitalized patients. JAMA. 1998;279(15):1200-1205.
    
2. Bochner BS, Lichtenstein LM. Anaphylaxis. N Engl J Med. 1991;324:1785.
    
3. Joint Task Force on Practice Parameters, American Academy of Allergy, Asthma and Immunology, American College of Allergy, Asthma & Immunology, and the Joint Council of Allergy, Asthma and Immunology. The diagnosis and management of anaphylaxis. J Allergy Clin Immunol. 1998;101(6 pt 2):S465-S528.
    
4. Shehadi WH, Adverse reactions to intravascularly administered contrast media: a comprehensive study based on PA prospective surgery. Am J Radiology. 1975;124:145.
    
5. AAAAI. The use of epinephrine in the treatment of anaphylaxis. Position statement #26. Available at: www.aaaai.org.
    
6. Wood RA. Anaphylaxis in children. Patient Care. 1997;31(13):161.
    
7. Fact File on Anaphylaxis: Acute Allergic Reactions to Food, Medication, Insect Stings, Latex. Dey; 2000.