Hypersensitivity to drugs

When taking medication, it is not uncommon for you to encounter some “inconvenience”. This can be a predictable adverse reaction, linked for example to an overdose of a drug, but also a hypersensitivity reaction, such as an allergy or intolerance. In fact, we speak of hypersensitivity to drugs in case of adverse reactions that manifest themselves with symptoms of an allergic nature.

Types of hypersensitivity reactions

Hypersensitivity reactions account for about 15 percent of all adverse drug reactions. They can have an immunological mechanism, as in the case of real allergies, but also non-immunological mechanism; In this case we speak of pseudoallergies or “intolerances”, which simulate allergy in their manifestations.

In most cases, allergies are mediated by antibodies (IgE) or cells of the immune system (T lymphocytes). The mechanisms underlying drug “intolerances” can be of various kinds and range from the non-specific release of histamine by some cells of the immune system, to the pharmacological action of some substances that induce bronchospasm, with consequent breathing difficulties.

The most common allergies and intolerances

The drugs most often involved in allergies are antibiotics (in particular penicillins and cephalosporins), while non-steroidal anti-inflammatories (NSAIDs) are those most frequently involved in intolerances (or more correctly in non-immune-mediated hypersensitivity reactions). However, this does not exclude that NSAIDs can sometimes be responsible for real allergies.

Symptoms

Antibody-mediated drug allergies and some intolerances, such as those induced by nonsteroidal anti-inflammatory drugs, typically cause immediate reactions, in which symptoms appear within 1-6 hours of taking the medicine.

The most typical symptoms in these cases are urticaria, sudden swelling of an area of the skin or mucous membranes, asthma, gastrointestinal disorders up to, in the most serious cases, anaphylactic shock.

Allergies to drugs mediated by T lymphocytes, on the other hand, more often cause non-immediate reactions that occur at different times starting one hour after the initial administration of the medicine.

In this case, the most characteristic disorders are diffuse skin rashes reminiscent of measles spots, dermatitis more or less extensive up to very serious pictures, such as those of Lyell syndrome and Stevens-Johnson syndrome, with bullous skin lesions and ulcerations of the mucous membranes, which are sometimes associated with problems with other organs (hepatitis, renal failure, pneumonia, hematological changes, etc.).