A drug allergy develops when the immune system reacts to a medication as a foreign substance. Immune cells produce proteins called antibodies to "protect" the body from future exposures to the drug. If the drug is taken again, the preformed antibodies interact with the medication, causing an allergic reaction that ranges from mild hives to potentially life-threatening airway swelling and shock. Certain drug allergies prove relatively common in the population.
Penicillin and Related Antibiotics
Allergic reactions to penicillin and other antibiotics in the penicillin family are the most commonly reported drug allergies, note Drs. Linda Vorvick and Paula Busse in the National Library of Medicine's online medical encyclopedia MedlinePlus. The frequency of penicillin and related allergies correlates to the high rate of use of these drugs in the population.
People with a penicillin allergy will generally have an allergic reaction to any antibiotic in the penicillin family, including methicillin, amoxicillin, ampicillin, ticarcillin, nafcillin, piperacillin, cloxacillin and dicloxacillin. A small percentage of patients with penicillin allergy may also react to other types of antibiotics with a similar chemical structure. In a 2001 article published in the "Baylor University Medical Center Proceedings," Christopher James, Pharm.D., and Cheryle Gurk-Turner, R.Ph., report that approximately 45 percent of people with a penicillin drug allergy also react to the antibiotic imipenam.
Importantly, nonallergic side effects can be associated with penicillins, such as nausea or diarrhea. The American Academy of Allergy, Asthma & Immunology points out that only 5 to 10 percent of adverse medication reactions represent drug allergies. Among patients in whom it is unclear whether a previous reaction was a drug allergy or a nonallergic side effect, skin testing can be performed to determine the presence or absence of penicillin allergy.
Sulfonamides
Sulfonamides are another large class of commonly prescribed antibiotics that, by virtue of their prevalent use, are a frequent cause of drug allergy. Susan Morey, Pharm.D., of the New York University School of Medicine reports that approximately 3 percent of people who take a sulfonamide antibiotic experience an allergic drug reaction.
People that react to one antibiotic in the sulfonamide class are likely to react to others in the drug group, which includes sulfamethoxazole, sulfasalazine and sulfisoxazole. Additionally, Dr. James Li of the Mayo Clinic warns that many people with a sulfonamide drug allergy are likely to react to the closely related antibiotic dapsone.
Vaccine Allergies
MayoClinic.com notes that immunizations may cause an allergic drug reaction. In most cases, an ingredient in the vaccine triggers the allergic reaction. Eggs, which are often used in the vaccine production process, can trigger an allergic vaccine reaction in people with an egg allergy. Similarly, the antibiotic neomycin, which is used to prevent bacterial contamination of the vaccine, may provoke an allergic drug reaction.
References
- MedlinePlus: Drug Allergies
- "Baylor University Medical Center Proceedings"; Cross-Reactivity of Beta-Lactam Antibiotics; Christopher W. James, Pharm.D., Cheryle Gurk-Turner, R.Ph.;2001
- American Academy of Allergy, Asthma & Immunology: Medications and Drug Allergic Reactions
- Clinical Correlations: Clinical Pharmacy Corner: Sulfonamide Allergy and Cross-Reactivity
- Mayo Clinic: Sulfa Allergy: Which Medications Should I Avoid?
