Adverse drug reactions are a problem of great importance nowadays, due to the large number of existing drugs and their wide use. In many cases it is important to test for drug allergy, as a suspected allergy may imply the use of more expensive and less effective alternative treatments. Adverse drug reactions can affect 10% of the population and 20% of hospitalized patients, 10% of these being hypersensitivity reactions.
Adverse drug reactions
There are several types of adverse drug reactions, and some of them are called hypersensitivity or allergic reactions.
According to the WHO, an adverse drug reaction is “any harmful and unintended effect produced by a drug that occurs at doses used in humans for the prevention, diagnosis or treatment of disease.”
Non-allergic adverse reactions are those in which an immunological mechanism is not involved, but are related to the drug’s own activity and can affect a large number of patients. They are the most frequent adverse reactions and do not require any analysis by the allergist, such as epigastralgias caused by anti-inflammatory drugs and acetylsalicylic acid, the adverse effects of corticosteroids that can appear with their continued use and many others.
Symptoms of drug allergy
A common query of suspected drug allergy is dizziness after administering a drug intramuscularly. The patient is frequently seen in the doctor’s office after the administration of intramuscular penicillin or because of the dizziness that can occur after dental surgery. In most of these cases, the cause is a drop in pressure due to the pain of the puncture or apprehension on the part of the patient and has nothing to do with allergic reactions.
True allergic reactions may present with different symptoms:
- Immediate allergic reactions: an allergic mechanism involving IgE immunoglobulin is involved. They usually occur within the first hour after administration of the drug. They are not hereditary, so an allergy test is not required for a patient with a family member allergic to the same drug. It can cause symptoms of varying severity such as skin problems (itching, urticaria, angioedema), respiratory (choking), cardiocirculatory (hypotension, tachycardia) and digestive problems. Allergy with involvement of various organs is called anaphylaxis. In some cases it could be very severe and even lead to death of the patient.
- Delayed hypersensitivity reactions: these may also include various types of reactions, some of them severe and involving the patient’s skin.
Diagnosis of drug allergy
The diagnosis or testing for drug allergy depends on the particular drug and the type of reaction. With some drugs a blood test may be useful but in general this is only the first step in the study of allergy. With other drugs skin tests are performed, and in many cases a hospital controlled exposure test with the same drug or alternative drugs is required as a definitive test.
Specific testing is not always required when there is a suspicion of drug allergy. In those cases in which the reaction has been produced by a non-essential drug that can be easily substituted by another and that the patient will not need again, no study will be required.
On the other hand, other drugs that may be essential, such as insulin in a diabetic patient, should always be studied if there is a suspicion of allergy. It may also be advisable to study anti-inflammatory drugs or some antibiotics such as penicillin, since a patient may need them at some point.
Any drug can be responsible for an allergic reaction, although the most frequent are usually antibiotic-lactams (including penicillin), anti-inflammatory drugs and acetylsalicylic acid. Although the excipients that accompany the drugs could be in exceptional cases the cause of an allergic reaction, this is not usual, so if there is a suspicion of drug allergy, all drugs containing the same active ingredient should be avoided, even if they are of different pharmaceutical brands.
It may be the case that the drug is a factor that triggers a food allergy, so sometimes even if there is a suspicion of drug allergy, a food allergy study will also be required.