Drug Allergies: Everything You Need to Know

Surely more you've read about the possible risks of an allergic reaction in a medication leaflet at some time. Let's see what is behind it.
Drug Allergies: Everything You Need to Know

Written by Josberth Johan Benitez Colmenares, 03 September, 2021

Last update: 03 September, 2021

Adverse effects are relatively common when people start drug-based therapy. These usually involve nausea, headaches, or gastrointestinal problems. They’re stated in the information leaflet of each medication and, for the most part, don’t cause too many problems. A small percentage of these, however, correspond to drug allergies.

This term describes all the reactions generated by the immune system after contact with certain active compounds. They’re considered very dangerous, not only because of the symptoms they can cause (such as anaphylaxis), but because they create delays in treatment and even the impossibility of treating someone. Today, we’ll explain everything you need to know about the topic.

Characteristics of drug allergies

Drug allergy can have various origins
Although it isn’t a direct cause, people with a personal or family history of allergies are more likely to develop hypersensitivity to certain medications.

Drug allergies are considered a manifestation of adverse drug reactions (ADRs). These are divided into predictable and unpredictable. Allergies are classified as the latter and, according to the World Allergy Organization, they represent less than 10% of all cases of ADRs.

Reactions can be immediate or they can develop a few hours later. Most cases manifest between 1 and 6 hours after ingestion, but it all depends on how quickly the drug is metabolized. These types of episodes are also known as drug hypersensitivity. The exact cause that triggers them is unknown, but the following risk factors have been identified:

  • People diagnosed with multiple allergy syndrome
  • Patients diagnosed with asthma, HIV, or Epstein-Barr virus
  • Long-term exposures to a specific drug
  • Genetic predisposition to hypersensitivity
  • Medical history of allergic reactions
  • Intermittent or poorly controlled treatments of a drug (in terms of dose, frequency, and type of intake)
  • Cross sensitivity
  • Being an older person (due to being exposed to compounds for a longer time)

Although, in theory, any drug can trigger an allergic reaction, UCLA Health cautions that antibiotics, pain relievers, non-steroidal anti-inflammatory drugs, and anticonvulsants are usually the main culprits. In part, this is due to the nature of its composition, and here are some examples:

  • Amoxicillin
  • Ampicillin
  • Aspirin
  • Ibuprofen
  • Naproxen
  • Clobazam
  • Lamotrigine
  • Acetaminophen

This is just a selection of the main ones, as the full list contains a hundred drugs. Drug allergies can be spontaneous, or can even develop permanently in some people. These latter cases are the most dangerous, as they force doctors to look for an alternative medication when conditions that require the use of the active compound appear.

Symptoms of drug allergies

The signs of a drug allergy are the same as any other type of allergy, with the exception that they occur right after you take the drug. According to the American College of Allergy, Asthma & Immunology, you can develop the following:

  • Rashes
  • Urticaria
  • Swelling
  • Wheezing and other breathing problems
  • Itching

In some cases, an anaphylactic reaction may occur. This is very rare and the percentage of episodes that lead to it isn’t even known with certainty. As the American Academy of Allergy, Asthma & Immunology (AAAAI) points out, these conditions require immediate attention as they can be life-threatening.

Symptoms like nausea, vomiting, headache, back pain, and so on aren’t considered to be drug allergies, but rather adverse reactions or side effects. It’s very unlikely that you’ll develop the symptoms if this is the first time you take a medicine, as it takes time for your body to generate the necessary antibodies.

The manifestations don’t always appear in the same group of drugs. For example, you may have a reaction to ibuprofen, but not to naproxen. Skin symptoms are by far the most obvious sign that you’re going through an allergic reaction (common in more than 68% of cases, according to the evidence).

Diagnosis of drug allergies

Although it might seem easy at first, in practice, diagnosing a drug allergy is more difficult than you might think. The specialist has to be 100% sure that the real trigger of the episodes is the active compound of a drug, as many factors can coexist at the moment to produce the same symptoms.

In this way, the researchers suggest performing the following tests to corroborate the reactions in a controlled environment:

  • Tests such as a skin prick, intradermal or drug patch
  • Drug patch test
  • Measurement of histamine and tryptase levels
  • Complete blood count
  • Basophil activation test

The results are analyzed in the context of reviewing the patient’s symptoms, medical history, family history, and possible underlying conditions. In some cases, a direct challenge test may be done, which involves a monitoring team administering the drug and assessing the body’s reaction.

However, this involves several risks. There’s always the possibility of a severe reaction, so these methods will be used only at specific times. Sometimes the patient’s symptoms and history are enough to make the trigger connection.

Treatment options

Drug allergy can be controlled
There’s no definitive cure for drug allergies. However, avoiding exposure is enough to control the situation, and there are treatment alternatives for many diseases.

As with other types of allergies, treatment involves avoiding the catalyst. Patients who have a drug allergy should permanently limit their intake of the drug and opt for alternatives from the same group according to the specialist’s guidelines. He should choose an analog that doesn’t trigger a cross-reaction.

Since the most common groups that develop allergies have several options for intake, this shouldn’t represent a problem when looking for an alternative treatment. However, some patients have reactions to groups whose alternatives are fewer, so they represent a challenge when choosing a therapy to counteract a condition.

Some researchers propose desensitization therapy, which consists of gradually prescribing lower doses of the compound to ensure that it’s tolerated by the body. It’s also suggested that patients wear a bracelet or necklace to identify the condition and communicate with all specialists to look for alternatives that don’t include the compound if a condition is being treated.

If intake is avoided, those diagnosed shouldn’t fear an anaphylactic reaction, so they won’t be required to have an injection of epinephrine as prevention. In any case, you should consult with your doctor to carry out the diagnostic process and rule out other triggers that can cause your allergies.

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  • Abrams EM, Khan DA. Diagnosing and managing drug allergy. 2018 Apr 30;190(17):E532-E538.
  • Castells, M. Desensitization for drug allergy. Current opinion in allergy and clinical immunology. 2006; 6(6), 476-481.
  • Mirakian R, Ewan PW, Durham SR, Youlten LJ, Dugué P, Friedmann PS, English JS, Huber PA, Nasser SM; BSACI. BSACI guidelines for the management of drug allergy. Clin Exp Allergy. 2009 Jan;39(1):43-61.
  • Warrington R, Silviu-Dan F. Drug allergy. Allergy Asthma Clin Immunol. 2011 Nov 10;7 Suppl 1(Suppl 1):S10.