drug allergies in adults

A drug allergy is an acute or chronic allergic reaction to a drug. In an allergic reaction, the immune system, which fights infections and diseases, reacts to the drug. This reaction can cause symptoms such as rash, itching, malaise, and difficulty breathing. True drug allergy is rare. Less than 5-10% of adverse drug reactions are due to a true drug allergy. The rest is the side effects of the drug. At the same time, it is important to know if there is an allergy to certain medications and what to do about it.

People with drug allergies may experience symptoms regardless of whether their medication is in liquid, tablet, or injectable form. If a person is unsure of their symptoms and which medications are safe to take, temporarily discontinue all medications and see an allergist.

What is allergy

The immune system helps protect the human body from disease. It is evolutionarily designed to fight off alien invaders such as viruses, bacteria, parasites and other dangerous substances. In a drug allergy, the immune system mistakes a drug that has entered your body for one of these invaders. In response to what she considers a threat, the immune system begins to produce antibodies. These are special proteins that are programmed to attack the invader. In this case, they attack the drug.

This immune response leads to increased inflammation, which can cause symptoms such as rash, swelling, redness, or difficulty breathing. An immune response may occur the first time the drug is taken, or it may only occur after the person has taken the drug many times without problems for a while.

Causes of drug allergies in adults

In principle, an allergy can be caused by any drug that is applied to the skin or mucous membranes (taken topically), used for oral administration in various forms (tablets, capsules, syrups or solutions, powders), injected (subcutaneously, intravenously or intramuscularly) .

A drug allergy occurs when the immune system mistakenly identifies a drug as a harmful substance, such as a virus or bacterium. Once your immune system detects a drug as harmful, it produces antibodies specific to that drug. This can happen the first time the medication is taken, but sometimes the allergy does not develop until repeated exposure occurs.

The next time you take a drug, these specific antibodies signal the drug and direct the immune system to it. The chemicals released during this activity cause the signs and symptoms associated with an allergic reaction.

However, you may not be aware of your first exposure to the drug. Some evidence suggests that trace amounts of drugs in food, such as antibiotics, may be enough for the immune system to create antibodies to it.

Allergic reactions may be the result of a slightly different process. Researchers believe that some drugs can directly bind to a specific type of white blood cell in the immune system called T-lymphocytes. This event triggers the release of chemicals that can cause an allergic reaction when the drug is first taken.

Medications commonly causing allergies

While any medication can cause an allergic reaction, some medications are more likely to be associated with allergies:

• antibiotics such as penicillin;
• pain relievers such as aspirin, ibuprofen, and naproxen sodium;
• chemotherapy drugs for cancer treatment;
• medicines for autoimmune diseases such as rheumatoid arthritis;
• antibiotics containing sulfonamides (sulfa drugs);
• anticonvulsants;
• funds for radiopaque diagnostics (especially iodine preparations).

Non-allergic drug reactions

Sometimes a drug reaction can cause signs and symptoms that are almost the same as those of a drug allergy, but the reaction to the drug is not caused by the activity of the immune system. This condition is called a non-allergic hypersensitivity reaction or a pseudo-allergic drug reaction.

Medications that are more commonly associated with this condition include:

• Aspirin;
• dyes used in imaging (radiocontrast media);
• opiates to treat pain;
• local anesthetics.

Risk Factors

Although anyone can have an allergic reaction to a drug, several factors can increase the chance of reactions:

• a history of other allergies, such as food allergies or hay fever;
• a personal or family history of drug allergy;
• increased drug exposure due to high doses, repeated or prolonged use;
• certain diseases that are usually associated with allergic reactions to drugs, such as HIV infection or the Epstein-Barr virus.

Symptoms of drug allergy in adults

The most common signs and symptoms of a drug allergy are hives, rash, or fever. Drug allergies can cause serious reactions, including a life-threatening condition that affects multiple body systems (anaphylaxis). Important! A drug allergy is not the same as a side effect of a drug, a known possible reaction listed on the drug label. Drug allergy is also different from drug toxicity caused by drug overdose.

Signs and symptoms of a serious drug allergy often occur within an hour of taking the medicine. Other reactions, especially a rash, may occur hours, days or weeks later. They may include:

• skin rash;
• urticaria;
• itching;
• high fever;
• swelling at the injection site and swelling throughout the body;
• shortness of breath;
• wheezing;
• coryza;
• itchy, watery eyes.

Anaphylaxis is a rare, life-threatening reaction to a drug allergy that causes widespread dysfunction of body systems.

Other conditions caused by drug allergies

Less common allergic reactions to drugs occur days or weeks after exposure to the drug and may persist for some time after the drug is stopped. These conditions include:

• serum sickness, which can cause fever, joint pain, rash, swelling, and nausea;
• drug-induced anemia, a decrease in the number of red blood cells, which can cause fatigue, an irregular heartbeat, shortness of breath, and other symptoms;
• drug rash with eosinophilia and systemic symptoms (DRESS), which leads to rash, high white blood cell count, general edema, swollen lymph nodes, and recurrence of previously hidden hepatitis;
• inflammation of the kidneys (nephritis), which can cause fever, blood in the urine, general swelling, confusion, and other symptoms.

Treatment of drug allergies in adults

Call 112 or emergency medical services if you have signs of a serious reaction or suspect anaphylaxis after taking the medication. If you have milder drug allergy symptoms, see your doctor as soon as possible.

Diagnostics

An accurate diagnosis is very important. Studies have shown that drug allergies can be overdiagnosed and that patients may report drug allergies that have never been confirmed. A misdiagnosed drug allergy can lead to the use of less suitable or more expensive medications. The doctor will perform a physical examination and ask you questions. Details about the onset of symptoms, when medications were taken, and whether symptoms improved or worsened are important clues to help your doctor make a diagnosis.

Your GP may order additional tests or refer you to an allergy specialist (allergist) for tests. They may include the following.

Skin tests. With a skin test, an allergist or nurse injects a small amount of a suspicious drug into your skin using a tiny needle (scarifier) ​​that scratches the skin, an intradermal injection, or a patch. A positive test reaction will cause a red, itchy, raised bump to appear.

A positive result suggests that you may have a drug allergy.

The negative result is not so unambiguous. For some drugs, a negative test result usually means you are not allergic to the drug. For other drugs, a negative result cannot completely rule out the possibility of a drug allergy.

Blood tests. A doctor may order a blood test to rule out other conditions that may be causing the signs or symptoms. While there are blood tests to screen for allergic reactions to certain drugs, these tests are not commonly used due to relatively limited research on their accuracy. They can be used if there is concern about a serious skin test reaction.

When your doctor analyzes your symptoms and test results, they can usually come to one of the following conclusions:

• you are allergic to medicines;
• you are not allergic to medicines;
• you may have a drug allergy – with varying degrees of certainty.

These insights can help your doctor and you make future treatment decisions.

Modern treatments

Interventions for drug allergies can be divided into two main strategies:

• treatment of existing allergy symptoms;
• treatment that may allow you to take the allergy medication if medically necessary.

Treatment of current symptoms. The following interventions may be used to treat an allergic reaction to a drug:

• discontinuation of the drug – if the doctor determines that you have an allergy to drugs or a probable allergy, stopping the drug is the first step in treatment: in many cases this may be the only intervention needed;
• antihistamines – a specialist may prescribe antihistamines or recommend drugs such as diphenhydramine, which can block immune system chemicals that are activated during an allergic reaction
• corticosteroids – oral or injectable corticosteroids may be used to treat inflammation associated with more severe reactions;
• treatment of anaphylaxis – anaphylaxis requires an immediate injection of epinephrine, as well as hospitalization to maintain blood pressure and support breathing.

Taking medications that cause allergies. If you have a confirmed drug allergy, your doctor will not prescribe medication unless it is necessary. In some cases – if the diagnosis of a drug allergy is unclear or there is no alternative treatment – the doctor may use one of two strategies to administer the suspect drug.

When using any of these strategies, your physician will ensure close monitoring and supportive care services are available to treat the adverse reaction. These interventions are usually avoided if medications have caused severe, life-threatening reactions in the past.

If the diagnosis of a drug allergy is unclear and your doctor thinks an allergy is unlikely, they may recommend dosed drug therapy. During the procedure, you will receive 2 to 5 doses of the drug, starting with a small dose and increasing it to the desired one. If you reach the therapeutic dose without any reaction, your doctor will conclude that you are not allergic to the drug. You will be able to take the drug as directed.

Desensitization with drugs. If you need to take the medicine that caused the allergic reaction, your doctor may recommend a treatment called drug desensitization. With this treatment, you get a very small dose and then gradually increase it every 15 to 30 minutes over several hours or days. If you can reach your desired dosage without any reaction, you may continue with your treatment.

Prevention of drug allergies in adults at home

If you are allergic to medications, the best prevention is not to take problematic medications. Steps you can take to protect yourself include the following:

• tell healthcare providers about allergies – make sure your drug allergy is clearly listed in your medical records, tell other professionals, such as your dentist or any healthcare professional, about allergies;
• wear a bracelet – wear a medical alert bracelet that indicates your drug allergy – this information can ensure proper treatment in an emergency.

Popular questions and answers

We asked questions regarding the development of drug allergies and possible consequences Pathologist, Junior Researcher, National Research Center for Pediatric Hematology, Oncology and Immunology named after N.N. Dmitry Rogachev to Dmitry Abramov.