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- Alan P. Koterba, M.D., Ph.D., F.A.C.A.A.I., F.A.A.A.A.I.
- Elena E. Perez, M.D., Ph.D., F.A.A.A.A.I.
People with drug allergies may experience symptoms regardless of whether their medicine comes in liquid, pill or injectable form.
Drug Allergy Symptoms
Reactions can occur in any part of your body.
For more information on drug allergy symptoms click here.
Common Triggers of Drug Allergies
Diagnosing Drug Allergies
Drug Allergy Management and Treatment
For more information on drug allergy management and treatment click here.
Symptoms
While you may not experience allergic symptoms the first time you take a drug, your body could be producing antibodies to it. As a result, the next time you take the drug, your immune system may see it as an invader, and you'll develop symptoms as your body releases chemicals to defend against it.
These symptoms may include:
Penicillin causes most allergic drug symptoms. Just because you show allergic symptoms after taking penicillin doesn’t mean that you will react to related drugs, such as amoxicillin, but it’s more likely. Also, just because you had a reaction to penicillin (or any other drug) at one time doesn’t mean you will have the same reaction in the future.
Antibiotics that contain sulfa drugs, such as Septra and Bactrim (sulfamethoxazole-trimethoprim) and Pediazole (erythromycin-sulfisoxazole), occasionally cause allergic reactions. Nonantibiotic drugs containing sulfa are very low-risk.
Diagnosing
Drug allergies can be hard to diagnose. An allergy to penicillin-type drugs is the only one that can be definitively diagnosed through a skin test. Some allergic reactions to drugs - particularly rashes, hives and asthma - can resemble certain diseases.
Your allergist will want to know the answers to these questions:
Your allergist will also want to know whether you have had a reaction to any other drug. If you can, bring the suspected drug with you. This will help the allergist recommend alternatives as needed.
During a physical examination, your allergist will look for problems that are part of the drug reaction, along with nonallergic reasons for the reaction.
Depending on the drug suspected of causing the reaction, your allergist may suggest a skin test or, in limited instances, a blood test. A blood test may be helpful in diagnosing a severe delayed reaction, particularly if your physician is concerned that multiple organ systems may be involved. This rare reaction is known as “drug rash with eosinophilia and systemic symptoms” or, more commonly, “DRESS syndrome.”
If a drug allergy is suspected, your allergist may also recommend an oral drug challenge, in which you will be supervised by medical staff as you take the drug suspected of triggering a reaction. (If your reaction was severe, a drug challenge may be considered too dangerous.)
Management and Treatment
If you have a drug allergy:
Anaphylaxis
Anaphylaxis is a severe, potentially life-threatening reaction that can simultaneously affect two or more organ systems (for instance, when there is both swelling and difficulty breathing, or vomiting and hives). If this occurs, call 911 and seek emergency medical care immediately.
If you are caring for someone who appears to be having a severe reaction to a drug, tell the emergency care team what drug was taken, when it was taken and what the dosage was.
If your allergic reaction to a drug is not life-threatening, your allergist may give you:
Drug desensitization
If there is no suitable alternative to the antibiotic that you are allergic to, you will need to undergo drug desensitization. This involves taking the drug in increasing amounts until you can tolerate the needed dose with minimal side effects. This will most likely be done in a hospital so immediate medical care is available if problems develop.
Desensitization can help only if you are taking the drug every day. Once you stop it — for example, when a chemotherapy cycle ends — you will need to go through desensitization a second time if you need the drug again.
Penicillin Allergy
Nearly everyone knows someone who says they are allergic to penicillin. Up to 10 percent of people report being allergic to this widely used class of antibiotic, making it the most commonly reported drug allergy. Over time, however, the vast majority of people who once had a severe allergic reaction to penicillin lose sensitivity and can be treated safely with the drug (although 10 percent of individuals will remain allergic).
Penicillin, famously discovered by Alexander Fleming in 1928, is prescribed today to treat a variety of conditions, such as strep throat. Despite its efficacy, some people steer clear of penicillin for fear of experiencing an allergic reaction to the medication.
Understanding penicillin allergies is important for a variety of reasons. For certain conditions, penicillin is the best (or only proven) therapy. Some patients need penicillin because they are allergic to other types of antibiotics. Allergists, experts in the treatment and diagnosis of allergies and asthma, may want to know if childhood allergic reactions persist in their adult patients, to establish more complete medical histories and treatment options.
Mild to moderate allergic reactions to penicillin are common, and symptoms may include any of the following:
A less common but more serious, sudden-onset allergic reaction to penicillin is anaphylaxis, which occurs in highly sensitive patients. Anaphylaxis occurs suddenly, can worsen quickly and can be deadly. Symptoms of anaphylaxis might include not only skin symptoms, but also any of the following:
These symptoms require immediate attention at the nearest Emergency Room. Epinephrine, the therapy of choice, will be given in this urgent care setting, but should also be self-administered via autoinjector as soon as possible by patients who have already been prescribed and are wisely carrying this device.
Penicillin Allergy Testing and Diagnosis
An allergist can help you evaluate the safety of taking penicillin.
In addition to assessing your detailed history about a prior allergic reaction to penicillin, allergists administer skin tests to determine if a person is or remains allergic to the medication. These tests, which are conducted in an office or a hospital setting, typically take about two to three hours, including the time needed after testing to watch for reactions.
When safely and properly administered, skin tests involve pricking the skin, injecting a weakened form of the drug, and observing the patients reaction. People who pass penicillin skin tests by reacting negatively to the injection are seen as at low risk for an immediate acute reaction to the medication. The allergist might then give these individuals a single, full-strength oral dose to confirm the absence of a penicillin allergy.
Those with positive allergy skin tests should avoid penicillin and be treated with a different antibiotic. If penicillin is recommended, people in some cases can undergo penicillin desensitization to enable them to receive the medication in a controlled manner under the care of an allergist.
Penicillin Allergy Treatment
Those who have severe reactions to penicillin should seek emergency care, which may include an epinephrine injection and treatment to maintain blood pressure and normal breathing.
Individuals who have milder reactions and suspect that an allergy to penicillin is the cause may be treated with antihistamines or, in some cases, oral or injected corticosteroids, depending on the reaction. Visit an allergist to determine the right course of treatment.
For more medical information, contact an allergist in your area.
Content was based on American College of Allergy, Asthma & Immunology