Drug allergy

Drug allergy
Classification and external resources
Specialty	emergency medicine
ICD-10	T88.7
ICD-9-CM	995.27
MedlinePlus	000819

A drug allergy is an allergy to a drug, most commonly a medication. 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 cells for the antigen. 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, which is often a milder, non-immune-mediated reaction, does not depend on prior exposure. Most people who believe they are allergic to aspirin are actually suffering from a drug intolerance.

Signs and symptoms

Identifying a drug allergy can sometimes be the hardest part. Sometimes drug allergies are confused with nonallergic drug reactions because they both cause somewhat similar reactions. Symptoms of a drug allergy can include, but are not limited to, the following list.^[1]

Hives
Itching
Rash
Fever
Facial swelling
Shortness of breath
Anaphylaxis, a life-threatening drug reaction (produces most of these symptoms as well as low blood pressure)

Causes

When a medication causes an allergic reaction, it is called an allergen. The following is a short list of the most common drug allergens:^[2]

Antibiotics
Analgesics
- Codeine
- Non-steroidal anti-inflammatory drugs (NSAIDs)
Antiseizure
- Phenytoin
- Carbamazepine

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).^[3] A drug allergy is more likely to develop with large doses and extended exposure.

Mechanisms

Drug allergies are attributed to "drug hypersensitivity," otherwise known as objectively reproducible symptoms or signs initiated by exposure to a drug at a dose normally tolerated by non-hypersensitive persons. Drug hypersensitivity reactions are the mediators of a drug allergy.

There are two mechanisms for a drug allergy to occur: IgE or non-IgE mediated. In IgE-mediated reactions, also known as Immunoglobulin E 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.^[4]

References

↑ "Drug Allergy". Mayo Clinic.
↑ "eMedicine". Retrieved 2007-06-08.
↑ "Drug Allergy: An Updated Practice Parameter" (PDF). Retrieved 2013-12-02.
↑ "World Allergy Organization". Retrieved 2013-11-25.

Allergic conditions

Respiratory system	Allergic rhinitis Asthma Hypersensitivity pneumonitis Eosinophilic pneumonia Churg–Strauss syndrome Allergic bronchopulmonary aspergillosis Farmer's lung Laboratory animal allergy

Skin	Angioedema Urticaria Atopic dermatitis Allergic contact dermatitis Hypersensitivity vasculitis

Blood and immune system	Serum sickness

Circulatory system	Anaphylaxis

Digestive system	Coeliac disease Eosinophilic gastroenteritis Eosinophilic esophagitis Food allergy Milk intolerance

Nervous system	Eosinophilic meningitis

Genitourinary system	Acute interstitial nephritis

Other conditions	Drug allergy Allergic conjunctivitis Latex allergy

Consequences of external causes (T66–T78, 990–995)

Temperature/radiation	elevated temperature Hyperthermia Heat syncope reduced temperature Hypothermia Immersion foot syndromes Trench foot Tropical immersion foot Warm water immersion foot Chilblains Frostbite Aerosol burn Cold intolerance Acrocyanosis Erythrocyanosis crurum radiation Radiation poisoning Radiation burn Chronic radiation keratosis Eosinophilic, polymorphic, and pruritic eruption associated with radiotherapy Radiation acne Radiation cancer Radiation recall reaction Radiation-induced erythema multiforme Radiation-induced hypertrophic scar Radiation-induced keloid Radiation-induced morphea

Air	Hypoxia/Asphyxia Barotrauma Aerosinusitis Decompression sickness High altitude Altitude sickness Chronic mountain sickness HAPE HACE

Food	Starvation

Maltreatment	Physical abuse Sexual abuse Psychological abuse

Travel	Motion sickness Seasickness Airsickness Space adaptation syndrome

Adverse effect	Hypersensitivity Anaphylaxis Angioedema Allergy Arthus reaction Adverse drug reaction

Other	Electric shock Drowning Lightning injury

Ungrouped skin conditions resulting from physical factors	Dermatosis neglecta Pinch mark Pseudoverrucous papules and nodules Sclerosing lymphangiitis Tropical anhidrotic asthenia UV-sensitive syndrome environmental skin conditions Electrical burn frictional/traumatic/sports Black heel and palm Equestrian perniosis Jogger's nipple Pulling boat hands Runner's rump Surfer's knots Tennis toe Vibration white finger Weathering nodule of ear Wrestler's ear Coral cut Painful fat herniation Uranium dermatosis iv use Skin pop scar Skin track Slap mark Pseudoacanthosis nigricans Narcotic dermopathy

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