Drug Allergy Evaluation and Desensitization
The goal of drug allergy evaluation and desensitization is to enable our patients to take a full dose of the recommended medication to treat their disease (whether it is cancer, anemia, infection, aspirin for AERD, anesthesia for surgery, etc.) safely despite a a history of an allergic reaction.
We most commonly evaluate patients who have possible adverse reactions to:
- Chemotherapy: for various forms of cancer (Rituximab, cisplatin, oxaliplatin, and others)
- Antibiotics: for various infectious diseases (Penicillin, sulfa, etc.)
- Aspirin: for Aspirin Exacerbated Respiratory Disease and heart disease
- Anesthetic agents (Lidocaine, carbocaine, mepivacaine etc.)
- Intravenous iron for anemia
What are the symptoms of a Drug Allergy?
People with drug allergies may experience symptoms regardless of whether their medicine comes in liquid, pill or injectable form.
Reactions can occur in any part of your body. 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:
- Skin rash or hives
- Wheezing or other breathing problems
- Feeling dizzy or light-headed
- Anaphylaxis, a potentially life-threatening reaction that can impair breathing and send the body into shock; reactions may simultaneously affect two or more organ systems (for example, when there is both a rash and difficulty breathing)
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.
What to Expect During Your Visit
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.
As part of your evaluation, we will need the following information:
- What drug do you suspect caused your reaction?
- When did you start taking it, and have you stopped taking it?
- How long after you took the drug did you notice symptoms, and what did you experience?
- How long did your symptoms last, and what did you do to relieve them?
- What other medications, both prescription and over-the-counter, do you take?
- Do you consume herbal medications or take vitamin or mineral supplements? If so, which ones?
- Have you had reactions to any other drugs? What kind and when did they occur?
If you can, bring the suspected drug with you. This will help your physician recommend alternatives as needed.
During a physical examination, our physicians 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, we 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 a 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, the challenge may have to be performed in an intensive care setting.
If you are diagnosed with a drug allergy:
Make sure all of your doctors are aware of your allergy and the symptoms you experienced.
Ask about related drugs that you should avoid.
Ask about alternatives to the drug that caused your allergic reaction.
Wear an emergency medical alert bracelet or necklace that identifies your allergy.
If there is no suitable alternative to the medication that you are allergic to, you may need to undergo drug desensitization. This involves taking the drug in small increasing amounts until you can tolerate the needed dose with minimal side effects. This procedure must be performed in a closely monitored setting in a medical office or hospital where 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 each time if you need the drug again.
What Happens when you have an Allergic Drug Reaction?
Allergic reactions to medications are the result of a chain reaction that starts in the immune system. Your immune system controls how your body defends itself. For instance, if you have an allergy to a particular medication, your immune system identifies that drug as an invader or allergen. Your immune system may react to medications in several ways. One type of immune reaction is due to production of antibodies called Immunoglobulin E (IgE) specific to the drug. These antibodies travel to cells that release chemicals, triggering an immediate allergic reaction. This reaction causes symptoms in the nose, lungs, throat, sinuses, ears, lining of the stomach or on the skin and usually occurs within minutes to a few hours of taking the drug.
The most common immune response to a drug is due to the expansion of T cells, a type of white blood cell that recognize the drug as foreign. These T cells orchestrate a delayed immune response that most often affects the skin, causing itchy rashes, and occurs days to weeks after exposure to the drug.
Most allergic reactions occur within hours to two weeks after taking the medication and most people react to medications to which they have been exposed in the past. This process is called “sensitization.” However, rashes may develop up to six weeks after starting certain types of medications.
The most severe form of immediate allergic reactions is anaphylaxis (an-a-fi-LAK-sis). Symptoms of anaphylaxis include hives, facial or throat swelling, wheezing, light-headedness, vomiting and shock.
Most anaphylactic reactions occur within one hour of taking a medication or receiving an injection of the medication, but sometimes the reaction may start several hours later. Anaphylaxis can result in death, so it is important to seek immediate medical attention if you experience these symptoms.
Antibiotics are the most common culprit of anaphylaxis, but more recently, chemotherapy drugs and monoclonal antibodies have also been shown to induce anaphylaxis.
The most severe form of delayed drug reactions not only cause rashes but may also involve other organs including the liver, kidneys, lungs, and heart. Blisters may be a sign of serious drug reactions called Stevens-Johnson Syndrome and Toxic epidermal necrolysis (TEN), where the surfaces of your eye, lips, mouth and genital region may be eroded.
You should seek medical help immediately if you experience any of these. Many medications can cause these severe delayed reactions including antibiotics, medications for epilepsy (seizures), depression and gout.
However, not all drug allergic reactions involve a specific immune reaction. Some people experience flushing, itching or a drop in blood pressure from intravenous dyes used in x-rays or CT scans. If you take angiotensin converting enzyme (ACE) inhibitors for high blood pressure, you may develop a cough or facial and tongue swelling.
A number of factors influence your chances of having an adverse reaction to a medication. These include: genetics, body chemistry, frequent drug exposure or the presence of an underlying disease. Also, having an allergy to one drug predisposes an individual to have an allergy to another unrelated drug. Contrary to popular myth, a family history of a reaction to a specific drug typically does not increase your chance of reacting to the same drug.
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).
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.
Penicillin Allergy Symptoms
Mild to moderate allergic reactions to penicillin are common, and symptoms may include any of the following:
- Hives (raised, extremely itchy spots that come and go over a period of hours)
- Tissue swelling under the skin, typically around the face (also known as angioedema)
- Throat tightness
- Trouble breathing
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:
- Tightness in the chest and difficulty breathing
- Swelling of the tongue, throat, nose and lips
- Dizziness and fainting or loss of consciousness, which can lead to shock and heart failure
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
Our allergy specialists can help you evaluate the safety of taking penicillin.
In addition to assessing your detailed history about a prior allergic reaction to penicillin, our allergist will 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.