The Truth About Drug Allergies

in Drug Allergy, Indoor Allergies

drugallergy2.1Photo: Getty
How to tell an allergy to a drug from a side effect, the big offenders, the types of medication reactions, and what to do if you’re busting out in hives.

IT WAS a string of bad luck. First, a fire destroyed Julie Sane’s house and her family was forced to quickly find a temporary place to live. Unfortunately the only place they could find was dusty and moldy, and her daughter Harper began getting sinus infections.

Harper’s doctor prescribed amoxicillin (an antibiotic in the penicillin family) to clear up the infection. But after the third dose, Sane noticed small, red raised bumps on Harper’s arm that spread to her tummy. The girl also developed a sore in her nose. (Sane brought it up with the pediatrician, who was unconcerned.) Harper had two more rounds of amoxicillin in the coming months. Each time, on the third dose, the girl developed a rash and a sore in her nose.

Her mother had a hunch that, with the consistent symptoms, something was going on. While visiting the allergist about Harper’s food allergies, Sane mentioned the strange reactions to the antibiotic. “All it took was a five-minute test,” recalls Sane. Her daughter is allergic to all antibiotics in the penicillin family and should avoid them in the future.

Is It a Drug Allergy?

Allergies to medications can be hard to diagnose because reactions do not all look the same. In fact, there are four different classes of allergic reactions – all involving the immune system, but in quite distinct ways.

Type I: This form of allergic reaction is the most obvious. It involves IgE allergy antibodies and comes on as typical anaphylaxis. Symptoms include hives, difficulty breathing, swelling and closing of the throat, and the patient can be at risk of cardiac arrest and even death.

“Anaphylactic drug reactions can occur very rapidly, often within minutes of exposure,” says Dr. David Stukus, a professor of pediatrics in the allergy section at Nationwide Children’s Hospital and Ohio State University. People can have anaphylactic reactions to any type of medication, but they most commonly occur with anesthesia that’s administered before surgery. Antibiotics are another top culprit.

Type II: This type of reaction is rare, and normally only seen in hospital patients. In a type II reaction, exposure to a certain medication will lead your immune system to form an antibody against itself.

For example, in an allergy to the anti-clotting medication heparin, the body forms antibodies that cause platelet levels to drop to dangerous levels. Other medications that can cause this type of reaction include the heart medication quinidine and the antibiotic vancomycin.

Type III: In a type III response, your immune system creates antibodies against the medication. Then antibody-antigen complexes are deposited throughout the body. “Wherever they get deposited, you get symptoms,” explains Stukus. “In the skin you get a rash, in the blood vessels you get swelling and pain.”

A common type III reaction is called serum sickness, which comes on seven to 10 days after exposure to a medication, such as the antibiotic Cefaclor. Symptoms include joint swelling, fevers and rashes. The person will often feel quite ill, and for some patients, it may take weeks for symptoms to resolve.

Type IV: While anaphylactic reactions come on in a cascade of symptoms, type IV reactions are more “smoldering,” says Dr. Tim Mainardi, a faculty member at New York’s Weill Cornell Medical College and the consultant allergist for Memorial Sloan Kettering Hospital. Mainardi says this type of allergic reaction is the most common for drug allergies. The person will usually get a rash during the course of the medication. It can linger for a few days, even after the patient has stopped taking the medication.

“The vast majority of patients who have a type IV reaction have a mild reaction,” says Mainardi. A fever or other feelings of being unwell may indicate this reaction is becoming more severe. In the more serious cases, organs such as the liver, kidneys and heart can be affected. The most severe form, called Stevens-Johnson syndrome, has a high mortality rate.

The Big Offenders

While it’s possible to be allergic to any type of medication, some are far more likely to cause reactions than others.

Penicillin: Most people take at least one of the antibiotics in the penicillin family at some point in their lives. They are the go-to medications to treat infections such as strep throat and bacterial ear infections. Amoxicillin is the most commonly used penicillin antibiotic today. But if you are allergic to penicillin, you are allergic to all medications in that family. [See also: Are You Sure You’re Penicillin-Allergic?]

Sulfa Drugs: Another class of antibiotics are the sulfonamides, and they are also a common cause of allergic reactions. Sulfa antibiotics, with the brand names Septra and Bactrim, typically cause type IV reactions, rather than anaphylaxis. A typical symptom would be a widespread rash that starts a few days after starting a course of the drugs.

Dr. Roland Solensky is an allergist practicing in Corvallis, Oregon and an internationally recognized expert in drug allergy. He points out that non-antibiotic sulfa medications, such as Imitrex, don’t cross-react with the sulfa antibiotics. “They’re structurally different and there’s no reason to avoid the sulfa non-antibiotic drugs in patients who have a sulfa antibiotic allergy.” (However, it is possible to be allergic to those medications.) It’s also important to note that sulfa drugs are in no way related to sulfites, which are added to some foods as a preservative.

When are NSAIDs an Issue?

Julie Sane and daughterJulie Sane with her daughter, Harper. Sane discovered that Harper is allergic to penicillin after a prescription resulted in symptoms.
NSAIDs: Non-Steroidal Anti-inflammatory Drugs include a host of medications that we use to relieve pain, reduce fever or inflammation. Brands such as Aspirin, Advil, Motrin and Aleve all fall into this category and can cause anaphylaxis in those with the allergy. Some adults with asthma (Solensky estimates in the range of 5 per cent) who also have nasal polyps will get a severe asthma attack, typically within two hours of taking the medication. (This condition is called AERD: aspirin-exacerbated respiratory disease.) For these people, says Solensky, it’s possible to do an aspirin desensitization.

“You can trick the immune system into becoming tolerant,” says Solensky. Patients would then need to keep taking aspirin daily, at which point the aspirin actually starts to help their disease. “They need less prednisone, fewer sinus infection drugs, and there’s a reduced need for nasal surgery,” says Solensky.

People with an AERD reaction to NSAIDs must avoid almost all medications in that category, but those with anaphylaxis to a particular NSAID can usually tolerate other similar medications.

Drug Allergy: What to Do?

If you think you are having an allergic reaction to a medication, doctors advise that you stop taking the medicine immediately and speak to your doctor. (For an anaphylactic reaction, call 911). Your doctor will ask a number of questions to determine what type of reaction you are having, and then prescribe any necessary treatment.

“For delayed-onset allergic reactions, it’s supportive care,” says Stukus. “A doctor can use antihistamines if a person is having itchy rashes. Systemic steroids can be used to help decrease the inflammation. But a lot of times the reactions just have to play themselves out in the system.” What happens next will depend on the medication you were taking, and the type of reaction you had.

Testing: If symptoms indicate a penicillin allergy, an allergist can perform a skin-prick test and then, if the result is negative, follow up with an oral challenge. With other drugs, it’s not that easy. While skin tests can be performed for other medications, they are not as reliable. This is because an allergist can only use what comes out of the bottle to test with, not one of the drug’s broken down “metabolites”.

“A positive skin test for a drug other than penicillin is useful information, but a negative can be difficult to interpret,” says Mainardi. If the patient previously has had a serious type IV reaction, patch testing can be used instead of skin-prick testing.

Dose-Graded Challenge: For other medications, including a suspected NSAID allergy, an allergist can do what’s called a “dose-graded oral challenge.” The doctor gives the patient a small amount of the medication and monitors the person to see if any symptoms develop.

“If nothing occurs, you give them a little bit more and a little bit more until they can tolerate the whole dose,” says Stukus. This only works for people with reactions involving IgE antibodies, as the reaction will need to come on quickly to be observed.

Avoidance: With a confirmed or strongly suspected drug allergy, the patient should avoid the medication and use an alternative, if available. With the exception of aspirin desensitization with AERD, there are no tests or desensitization procedures available for allergic reactions other than type I anaphylactic reactions. In all cases, these medications need to be avoided.

Desensitization: For some people with a type I drug allergy, it may make sense to go through a desensitization process.

“If there are no equally effective structurally unrelated medications available and you’re concerned for an anaphylactic reaction, you can consider a desensitization protocol,” says Stukus. “You generally need to be admitted to the hospital or even the ICU, you receive the medication in a very diluted form in gradually increasing amounts to build a state of tolerance.”

Desensitization would be useful, for example, to treat syphilis during pregnancy with penicillin or for someone who is allergic to chemotherapy drugs. Once a person is desensitized, they have to continue taking the medication daily or they will become allergic once again.

When It’s Not a Drug Allergy

Drug allergies are common, but still don’t occur as often as people think. Studies show between 10 and 20 percent of the population report having a medication allergy. But the real prevalence is considered to be much lower. Studies suggest patients can confuse true allergy with side effects and other conditions.

Side Effects: Stomach pain, nausea and vomiting with some medications may not be allergic responses at all, but rather what doctors call “adverse reactions.” While it’s important to discuss such side effects with your doctor, patients can continue taking these medications in many cases.

Illness: “Why do people get antibiotics?” asks Stukus. “Because they’re sick with an infection. If they’re sick with an infection, that can cause a range of symptoms including itchy rashes, and that may not be due to the antibiotic, it may be from the infection itself.”

Still, in this case you would have to assume that an allergy is possible, and stop taking an antibiotic like penicillin. At a later time, you can be tested for penicillin allergy.

Chronic Hives: Another condition that can be confused with drug allergy is chronic unexplained urticaria. “There are people out there that just get hives, and/or swelling, all the time for no good reason,” says Stukus. “It will drive them insane trying to figure it out, and they will attribute it to every exposure, including medications.”

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Related Reading:
Why Penicillin Allergy is Over-Diagnosed
Are You Sure You’re Penicillin Allergic?