Drug Allergy & Allergic Reactions to Medications

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A drug allergy is the abnormal reaction of your immune system to a medication. Any medication — over-the-counter, prescription or herbal — is capable of inducing an allergic reaction. The drugs that cause the most reactions are penicillin and aspirin, affecting up to 10% of the population. Other drugs that trigger allergies include sulfa drugs, anticonvulsants, and chemotherapy drugs.

Allergic reactions to drugs or medications usually do not occur the first time a person takes a specific drug. It could take years to develop a drug allergy after constant exposure. You may also have been exposed to the medication or medication in the same drug class without knowing it. It is important to identify a drug allergy early because the symptoms can be very uncomfortable or even life-threatening. 

Drug Allergy Symptoms

  • Hives or rash
  • Itching
  • Asthma
  • Swelling (of the tongue or lips, for example)
  • Loss of consciousness
  • Anaphylaxis

Many people mistake a drug allergy with a drug side effect. For this reason, it is very important to make sure you tell your NY allergist about all of the medications you have been taking. Common side effects that are not allergic reactions include:

  • Diarrhea
  • Dry mouth
  • Headaches
  • Heartburn
  • Racing heart

It is sometimes difficult to determine if you are experiencing an allergy or a side effect. That’s why we recommend seeking medical attention for any abnormal reactions after taking medications. The allergy physicians at NY Allergy & Sinus Centers will help figure out what is an allergic reaction, as opposed to a side effect of a medication. Allergic reactions can be very dangerous, and we can assist you in identifying the symptoms of allergies.

Drug Allergy Diagnosis

A skin prick test can diagnose a drug allergy; however, it’s not always accurate in detecting all drug allergies. Most often, allergists will use intradermal testing to diagnose your drug allergies. Drugs that are injected can be quickly diagnosed by intradermal testing. During this test, an allergist will introduce the allergen beneath the skin and watch for a reaction. Intradermal testing is more sensitive than skin prick testing, so you may experience uncomfortable reactions. Your doctor will have epinephrine and other allergy medications available to treat any symptoms.

In addition, a drug challenge may be performed. This is only performed in extreme cases when allergy testing cannot confirm a drug allergy. During a drug challenge, a dose of the suspected allergen may be administered in the office under careful observation to confirm the allergy. This is done only as a last option, as some drugs are known to cause severe allergic reactions.

Drug Allergy Treatment

Many drug allergies disappear over time. For those that don’t, desensitization is a treatment option. Desensitization is available for penicillin, aspirin, and some chemotherapeutic drugs. The process involves gradually administering the medication by mouth or as shots to build a tolerance to the drug. This treatment is only necessary for patients with ongoing medical conditions who require certain medications where there aren’t any alternatives.

When possible, avoidance is always the best treatment for allergies. Ask your doctor about alternatives to the drugs you are allergic to. There are usually many options of medications to treat your condition. For example, instead of taking penicillin, you may be prescribed trimethoprim or nitrofurantoin. Be sure to discuss your options with our allergy specialists.

Drug Allergy Frequently Asked Questions

Can A Person Outgrow A Drug Allergy?

In some cases, a patient may become less sensitive to medications over time. However, if you have a drug allergy, you should continue to avoid medications you are allergic to.

Does Desensitization Work for Every Drug?

No, the process is not available for every drug. It is most commonly used for aspirin, penicillin, and other related antibiotics. 

How Do I Know if I’m Allergic to Medication or Just Experiencing a Side Effect?

You should seek medical attention immediately if you experience any physical reaction after taking medication. A board-certified physician can identify an allergic reaction.

How Do You Treat An Allergic Reaction to Medication?

Antihistamines and corticosteroids help to relieve mild symptoms such as rash, hives, and itching. Bronchodilators such as albuterol to reduce asthma-like symptoms (moderate wheezing or cough). Epinephrine is also available to treat anaphylaxis. If you suffer from severe drug allergies, ask us about drug desensitization.

How Long Does Desensitization Last?

The process typically takes 2 days, however, it can take longer for some patients. Desensitization is not offered for every patient. You should discuss this treatment with an allergist to determine if you are a candidate for desensitization. 

How Long Does It Take For An Allergic Reaction to Occur from Medication?

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.

If I Have a Reaction to a Drug Once, Does That Mean I Have to Stop Taking it Completely?

If you have been diagnosed with a drug allergy, you should avoid the drug that caused the reaction. However, you should get allergy tested regularly to determine if your sensitivity has disappeared.

What Are the Most Common Drug Allergies?

Penicillin is the most common drug allergy. Anticonvulsants, aspirin, ibuprofen, and chemotherapy drug allergies are also common. It’s possible to have a reaction to a drug at some point in your life and not suffer a similar reaction in the future.

What Does An Allergic Reaction to Medication Look Like?

Drug rashes can appear as a variety of skin rashes, including pink to red bumps, hives, blisters, red patches, pus-filled bumps (pustules), or sensitivity to sunlight. Drug rashes may involve the entire skin surface, or they may be limited to one or a few body parts. Itching is also common in many drug rashes.