A drug allergy is an

allergy Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derm ...

to a drug, most commonly a

medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...

, and is a form of

adverse drug reaction An adverse drug reaction (ADR) is a harmful, unintended result caused by taking medication. ADRs may occur following a single dose or prolonged administration of a drug or result from the combination of two or more drugs. The meaning of this term ...

. Medical attention should be sought immediately if an allergic reaction is suspected. An allergic reaction will not occur on the first exposure to a substance. The first exposure allows the body to create antibodies and memory

lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...

cells for the

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune respons ...

. However, drugs often contain many different substances, including dyes, which could cause allergic reactions. This can cause an allergic reaction on the first administration of a drug. For example, a person who developed an allergy to a red dye will be allergic to any new drug which contains that red dye. A drug allergy is different from an intolerance. A

drug intolerance Drug intolerance or drug sensitivity refers to an inability to tolerate the adverse effects of a medication, generally at therapeutic or subtherapeutic doses. Conversely, a patient is said to be "tolerating" a drug when they can tolerate its adve ...

, which is often a milder, non-immune-mediated reaction, does not depend on prior exposure.

Signs and symptoms

Symptoms of drug hypersensitivity reactions can be similar to non-allergic

adverse effects An adverse effect is an undesired harmful effect resulting from a medication or other intervention, such as surgery. An adverse effect may be termed a "side effect", when judged to be secondary to a main or therapeutic effect. The term complica ...

. Common symptoms include: * Hives * Itching * Rash * Fever * Facial swelling * Shortness of breath due to the short-term constriction of lung airways or longer-term damage to lung tissue *

Anaphylaxis Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the foll ...

, a life-threatening drug reaction (produces most of these symptoms as well as low blood pressure) * Cardiac symptoms such as chest pain, shortness of breath, fatigue, chest palpitations, light headedness, and syncope due to a rare drug-induced reaction,

eosinophilic myocarditis Eosinophilic myocarditis is inflammation in the heart muscle that is caused by the infiltration and destructive activity of a type of white blood cell, the eosinophil. Typically, the disorder is associated with hypereosinophilia, i.e. an eosinoph ...

Causes

Some classes of medications have a higher rate of drug reactions than others. These include

antiepileptic Anticonvulsants (also known as antiepileptic drugs or recently as antiseizure drugs) are a diverse group of pharmacological agents used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of b ...

s, antibiotics, antiretrovirals,

NSAID Non-steroidal anti-inflammatory drugs (NSAID) are members of a therapeutic drug class which reduces pain, decreases inflammation, decreases fever, and prevents blood clots. Side effects depend on the specific drug, its dose and duration of ...

s, and general and local

anesthetics An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into two ...

Risk factors

Risk factors for drug allergies can be attributed to the drug itself or the characteristics of the patient. Drug-specific risk factors include the dose, route of administration, duration of treatment, repetitive exposure to the drug, and concurrent illnesses. Host risk factors include age, sex, atopy, specific genetic polymorphisms, and inherent predisposition to react to multiple unrelated drugs (multiple drug allergy syndrome). A drug allergy is more likely to develop with large doses and extended exposure. People with immunological diseases, such as

HIV The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...

and cystic fibrosis, or infection with EBV, CMV, or HHV6, are more susceptible to drug hypersensitivity reactions. These conditions lower the threshold for T-cell stimulation.

Mechanisms

There are two broad mechanisms for a drug allergy to occur: IgE or non-IgE mediated. In IgE-mediated reactions, also known as

immunoglobulin E Immunoglobulin E (IgE) is a type of antibody (or immunoglobulin (Ig) " isotype") that has been found only in mammals. IgE is synthesised by plasma cells. Monomers of IgE consist of two heavy chains (ε chain) and two light chains, with the � ...

mediated reactions, drug allergens bind to IgE antibodies, which are attached to mast cells and basophils, resulting in IgE cross-linking, cell activation and release of preformed and newly formed mediators. Most drugs do not cause reactions in themselves, but by the formation of

haptens In immunology, haptens are small molecules that immunogenicity, elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response by itself (in general, only larg ...

Types

Drug allergies or hypersensitivities can be broadly divided into two types: immediate reactions and delayed reactions. Immediate reactions take place within an hour of administration and are IgE mediated, while delayed reactions take place hours to weeks after administration and are

T-cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...

mediated. The first category is mostly mediated through specific IgE, whereas the latter is specifically T-cell mediated.

Management

Management of drug allergy consists principally of avoidance or discontinuation of the causative drug. Treatment is largely supportive and symptomatic. It may consist of

topical A topical medication is a medication that is applied to a particular place on or in the body. Most often topical medication means application to body surfaces such as the skin or mucous membranes to treat ailments via a large range of classes ...

corticosteroids and

oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid **Oral administration of medicines ** Oral examination (also known as an oral exam or or ...

antihistamine Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic (not patented) drug that can be bought without a prescription and provid ...

s for

cutaneous Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different d ...

symptoms such as hives and itching. Mild cutaneous reactions can be managed with antihistamines only. However, antihistamines cannot antagonize activated

histamine Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered ...

that has already been released from

mast cell A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a par ...

s. In severe cases of drug allergy, systemic corticosteroids may be used. Corticosteroids are limited by a delayed

onset of action Onset of action is the duration of time it takes for a drug's effects to come to prominence upon administration. With oral administration, it typically ranges anywhere from 20 minutes to over an hour, depending on the drug in question. Other meth ...

of greater than 45minutes as they act via

gene modulation Regulation of gene expression, or gene regulation, includes a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products (protein or RNA). Sophisticated programs of gene expression are wi ...

. If

anaphylaxis Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the foll ...

occurs,

injectable An injection (often and usually referred to as a "shot" in US English, a "jab" in UK English, or a "jag" in Scottish English and Scots) is the act of administering a liquid, especially a drug, into a person's body using a needle (usually a hypo ...

epinephrine is to be used. If a person is allergic to a drug and no suitable alternative exists, a desensitization procedure with the drug, in which the drug is introduced slowly at very low doses such that tolerance to the drug allergy develops, can be employed.

References

External links

{{Consequences of external causes Allergology Drug safety