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Drug Allergy

General Physician

Hyderabad | 14 Dec 2023

What is Drug Allergy?

Drug allergy is an exaggerated response of the body’s immune system to a drug or a prescription medication. A drug allergy may be seen after oral, intramuscular, or intravenous administration of drugs.

Alternate names

Adverse Drug Reaction / ADRs

Is this condition a medical emergency?

Drug allergies may sometimes be serious and lead to anaphylaxis and would require immediate medical attention.

Causes of drug allergy

A drug allergy is a result of the body’s immune system mistakenly identifying a drug or its components as a harmful substance and subsequently producing antibodies that target it. This leads to an exaggerated response to subsequent exposure to the drug. Any drug can cause an allergic reaction, but some of the drugs that are commonly associated with drug allergies include:

Antiepileptics or Anti-seizure medications
Antibiotics such as penicillins, etc
Antiretrovirals
NSAIDs
General Anaesthetics
Local Anaesthetics
Chemotherapeutic agents
Medicines used to treat autoimmune diseases

Some drugs causing pseudo-allergic reactions or reactions that are not caused by the activity of the immune system are:

Radiocontrast agents
Opioid analgesics
Aspirin

Risk factors

The risk factors for drug allergies include:

A family history of drug allergies
A history of other allergic diseases such as food or pets
Extensive use of a drug for a prolonged period
Altered immune system due to infections such as HIV or Epstein Barr virus

Symptoms & signs

The symptoms and signs associated with drug allergies usually develop within an hour or so after the administration of the drug, and they may include:

Rash on the skin
Itching
Fever
Hives
Swelling of the face
Shortness of breath

If anaphylaxis develops, the symptoms may include:

Respiratory: Nasal congestion, running nose, swollen tongue, tightening of the throat, wheezing, difficulty breathing, cough, hoarseness of voice.
Cardiac: Dizziness, weakness, fainting, chest pain, palpitations, fall in blood pressure, weak and rapid pulse.
Gastrointestinal: Difficulty swallowing, nausea, vomiting, diarrhea, bloating, abdominal cramps or pain, metallic taste.
Nervous system: Headache, dizziness, blurring of vision, seizures.

Investigations

Investigations to establish a penicillin allergy may include:

Skin Tests
Laboratory tests

Diagnosis

A diagnosis of a drug allergy may be established based on the medical history and the results of the investigations.

Drug allergy treatment options

The management of a drug allergy is aimed at addressing the current symptoms of the allergy and enabling the individual to continue taking the drug if it is essential for the management of another condition.

Medical management

Medical management of the current symptoms of a drug allergy may include the following:

Management of anaphylaxis, if present
Withdrawal of the drug causing the allergy
Antihistamines
Corticosteroids: To reduce inflammation

Management aimed at continuing the usage of the offending drug may include:

Graded challenge: This involves the administration of the drug in multiple doses, starting with a small dose and increasing it to the desired dose.
Sensitization: A small dose of the drug is given, and the dose is kept increasing over a few hours to a few days until there is no reaction from the immune system.

Role of Diet/exercise/lifestyle changes/preventive measures

Keeping a note of medications that are being taken and that have been taken in the past and informing health care workers or doctors of possible allergic reactions in the past or a history of allergies in the family may help to prevent drug allergies.

Complications

Some of the complications of drug allergies include:

Severe anaphylaxis
Kidney damage
Cardiovascular damage: Due to eosinophilic carditis
Serum sickness
Drug-induced anemia
Drug rash with eosinophilia and systemic syndrome (DRESS): Skin rash, high white blood cell count, lymph node swelling, and hepatitis

Prognosis

The prognosis for drug allergy is generally good if identified and managed early. Fatal drug reactions do occur but are not very common.

When to contact the doctor or hospital/How to identify the emergency or complications?

If any of the symptoms of a penicillin allergy or anaphylaxis are seen after taking a medication, it is advisable to seek immediate medical attention.

Indications for hospitalization if required

Hospitalization is not required for most drug allergies unless there is anaphylaxis, which would require hospitalization until the individual is stabilized.