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What is it about ?
Hypersensitivity is an abnormal reaction to a specific substance, in this case a drug. The medicine enters the body through the mouth (tablets and capsules), through the breath (asthma inhalers), through the skin (ointment) or by injection. It can be an allergic or non-allergic reaction. A substance that triggers an allergic reaction is called an “allergen”. In principle, it can be any foreign substance, like a medicine.
In the event of an allergic reaction, the body releases a multitude of antibodies, which are responsible for the allergic symptoms. This reaction will always recur each time you take the medicine. Often the reaction also worsens over time.
If there is a non-allergic reaction, there are also symptoms, but the body does not produce excessive amounts of antibodies. It is then a question of drug intolerance. Sometimes an external factor must be present to trigger the reaction (eg sunlight). In this case, the reaction only occurs if you expose yourself to the sun after taking the medicine (photosensitivity).
All medicines can trigger a hypersensitivity reaction. But the main culprits are antibiotics (penicillin), anti-inflammatory drugs and painkillers, as well as drugs that act on the central nervous system, such as drugs for the treatment of epilepsy.
What is its frequency?
Fifteen percent of people think they are allergic to at least one medicine. Studies give other figures, but they are very variable, ranging from 0.5 to 5%. This difference is explained by the fact that the definition of allergy may differ from one study to another.
How to recognize it?
A hypersensitivity reaction can vary widely, ranging from mild to very serious, to life-threatening. It can occur immediately, a few minutes after taking it, or only after several days or even weeks.
Its main feature is a rash accompanied by itching. The most common forms are red spots or small bumps and hives. But virtually any type of rash is possible: wet blisters, dander (skin dandruff) resembling eczema, and small or large effusions of blood in the skin. A drug or a class of drugs can cause different types of rash. Its appearance alone doesn’t tell us much about its cause.
Allergic symptoms can also occur in the respiratory tract: sneezing, runny nose, wheezing and shortness of breath. Tearing is also possible.
In extreme cases, shock can occur and manifest as palpitations, drop in blood pressure, dizziness, and loss of consciousness.
Usually, the hypersensitivity reaction lasts about 12 hours. But it can sometimes persist for several days and, exceptionally, several weeks.
How is the diagnosis made?
The diagnosis of hypersensitivity to drugs can be very difficult. The symptoms are not specific, so they also occur in many other conditions, such as viral infections. For most drugs, there is also no test capable of proving possible hypersensitivity. In addition, people often take more than one medicine at the same time. It is therefore not always easy to identify which drug is responsible for the reaction. This is why the doctor will ask you very specific questions about the onset of symptoms and the taking of medication. He may also order a blood test to determine the antibodies.
For some drugs, there are skin allergy tests (prick-tests). The procedure involves placing a drop of solution containing the medicine on your skin, then piercing it with a fine needle to force the product into your skin. Based on your reaction to this test, the doctor can determine if it is an allergic reaction (white bump circled in red and itchy). There are also patch tests to use for delayed hypersensitivity reactions. As part of these tests, a patch is glued to the skin on which the drug has been applied. Each of these tests gives a result within a few days. These examinations are carried out by a specialist, usually a dermatologist or an allergist.
If these examinations are not decisive, a drug provocation test is still possible. In this case, the drug is administered under medical supervision, starting with a small dose. If there is no reaction, the dose is gradually increased to a normal effective dose. This test can trigger a serious reaction. That is why it always takes place in the hospital and only in people for whom the drug is absolutely necessary.
What can you do ?
For the doctor, it is very important to have correct information. So carefully write down any relevant information: what exactly did you take? What dose? When ? How long after the dose did the symptoms start? Is this the first time or have you had this type of reaction before? Do you have known hypersensitivity to other drugs?
Once the diagnosis is made, ask your doctor for a chart of the medications that you cannot take. Always carry this form with you and present it at each consultation.
What can your doctor do?
The first step to take is of course to stop the drug. If necessary, it will be replaced with a drug that has the same effect, but a different composition. Mild hypersensitivity reactions usually go away on their own.
In the event of a persistent rash accompanied by severe itching, the doctor may prescribe anti-allergic agents. The local application of a cortisone cream can give you relief. In severe cases, cortisone tablets may be prescribed.
The doctor will note in your patient chart that you are hypersensitive to the medicine in question and describe the reaction to it (eg rash).
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