A drug allergy is an allergy to a drug, and is a form of adverse drug reaction.
An allergic reaction does not occur on the first exposure to a substance.
The initial exposure allows the body to create antibodies and memory lymphocyte cells for the antigen.
Drugs often contain many different substances, which could cause allergic reactions, 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.
Common symptoms include:
Shortness of breath due to the constriction of lung airways or longer-term damage to lung tissue
Anaphylaxis, a life-threatening drug reaction
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
Some classes of medications have a higher rate of drug reactions than others: antiepileptics, antibiotics, antiretrovirals, NSAIDs, and general and local anesthetics.
Risk factors for drug allergies are 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.
Personal risk factors include: age, sex, atopy, specific genetic polymorphisms, and inherent predisposition to react to multiple unrelated drugs.
Drug allergies are more likely to develop with large doses and extended exposure.
Patients with immunological diseases HIV and cystic fibrosis,or infection with EBV, CMV, or HHV6, are more susceptible to drug hypersensitivity reactions.
The above conditions lower the threshold for T-cell stimulation.
Two mechanisms exist for a drug allergy to occur: IgE or non-IgE mediated.
In IgE-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.
Drug allergies or hypersensitivities are divided into two types: immediate reactions and delayed reactions.
Immediate reactions take place within an hour of administration and are IgE mediated.
Delayed reactions take place hours to weeks after administration and are T-cell mediated.