Some patients may experience adverse side effects, such as headache, nausea or dry mouth, after taking drugs. In some rare cases, however, the patient may experience an allergic reaction.
It is important to distinguish between a side effect of a drug and an allergic reaction, since side effects can occur in any person if he or she takes sufficient doses, while allergic reactions occur in a very small percentage of the population. In allergic reactions, also called hypersensitivity reactions, the immune system is involved, which identifies the drug as an aggressive substance and tries to eliminate it. In most cases the organism is sensitized in a previous contact and it is in a subsequent contact with the drug that the allergy symptoms are triggered.
Symptoms of drug allergy
The most common symptoms of an allergic reaction often appear immediately after taking the drug, the most common being:
- Skin wheals, they are itchy and have a reddish color.
- Swelling of the facial region, pharynx and extremities.
- Difficulty in breathing, often with aphonia or wheezing (breathing noises).
- Anaphylaxis: this is the most serious condition, it usually appears a few minutes after taking a drug and is usually accompanied by generalized itching with difficulty in breathing and swallowing. It is usually accompanied by abdominal pain, vomiting, weakness, rapid pulse, dizziness and, in the most severe cases, loss of consciousness.
On rare occasions, the reactions appear days or weeks after starting treatment; these are called late reactions and are the most common:
- Cutaneous rash: rashes similar to measles that spread over a large part of the body, they are not usually very pruritic and are not associated with other symptoms, being in many occasions of mild character.
Other more severe and infrequent processes include:
- Serum sickness: accompanied by fever with skin rash, edema, nausea….
- DRESS syndrome. Associated with skin rash, increased eosinophilic leukocytes (blood cells), generalized edema, enlarged lymph nodes, hepatic involvement…
Drugs causing allergic reactions
Some of the drugs responsible for causing the most common allergic reactions are:
- Antibiotics (especially penicillin and derivatives).
- Aspirin and non-steroidal anti-inflammatory drugs.
- Drugs used in chemotherapy
Drug allergy: When to consult a doctor?
The specialist in Allergology should be consulted if the following symptoms appear after taking a drug:
- Shortness of breath, wheezing.
- Tightness in the chest
- Edema, swelling of the facial region or pharyngeal region.
- Feeling of very intense discomfort
Drug allergy: diagnosis
After a careful clinical history, sometimes other explorations are requested, such as skin tests, which are very useful in the diagnosis of allergic reaction to penicillin or its derivatives (amoxicillin and cephaloporins), although skin tests are not useful for many other groups of drugs.
Another option is to perform blood tests (determination of specific IgE), which are useful in case of allergy to penicillin and its derivatives but of little use for other drugs.
Drug exposure test
If the drug is very important for the cure of a process and there are few alternatives to it or the allergist determines that allergy to a drug is very unlikely, the patient receives small amounts that are increased to confirm the tolerance of the drug.
Most common causes of drug allergy
There are several predisposing causes of drug allergy:
- previous allergic reactions to other drugs
- patients with a high degree of exposure to a drug, either by receiving high doses, by being exposed in very frequent cycles, by its prolonged use…
- previous HIV disease
- family history of allergic reactions to drugs
Treatment of allergic reactions to drugs
In some cases, discontinuation of the drug is sufficient, but in other cases, if the patient presents bothersome symptoms, antihistamines, corticosteroids and in case of anaphylaxis, treatment with adrenaline and other life support measures are required.
Prevention of drug allergy
There are some prevention recommendations to avoid the problems derived from allergic reaction to the drug:
- Inform the healthcare professional doctor or nurse who will be attending you.
- Wear a medical alert such as a bracelet, pendant, or card that specifies the name of the drug you are allergic to