Drug Allergy

Do you suffer from skin irritations such as itchiness, rashes and hives, but have no idea what is causing them after taking certain medications?

Unbeknownst to many, the underlying causes of allergies differ from individual to individual. The three most common allergies are contact allergy, food allergy and drug allergy.

What is Drug Allergy?

A drug allergy is the reaction of the body’s immune system to a particular medicine. When this happens, the immune system treats the drug as a threat to the body, releasing chemicals that induce symptoms of an allergic reaction.

All types of medicine, whether prescribed or herbal, can cause a drug allergy. Some medicines are more prone to causing drug allergies.

Common causes of Drug Allergy in Singapore?

Consuming certain drugs can trigger allergies in some individuals. Common drugs that cause allergies include:

  • Drugs prescribed to treat seizures
  • Antibiotics (especially penicillins)
  • Nonsteroidal anti-inflammatory drugs (NSAID) like voltaren, aspirin
  • Medications containing sulfur
  • Chemotherapy drugs

What are the symptoms of Drug Allergy?

The symptoms of drug allergy vary from each individual, and can occur immediately or after a few weeks. These are some common symptoms:

  • Itchy and red eyes
  • Skin rashes or hives
  • Mouth and skin ulcers
  • Wheezing and congestion of the nasal passages
  • Shortness of breath
  • Abdominal cramps, nausea and vomiting

Drug allergies can also trigger a serious allergic reaction called anaphylaxis. This requires urgent medical attention. These are the symptoms of anaphylaxis:

  • Tightening of airways
  • Swollen throat and difficulty breathing
  • Severe drop in blood pressure and rapid pulse
  • Feeling dizzy, lightheaded or losing consciousness

Are Drug Allergies serious?

Drug allergies can be serious and life-threatening. They usually manifest as hives, fever, and rashes, leading to inflammation and redness. However, occasionally they can cause serious illnesses requiring intensive care stay in the hospital. They can be life threatening when the airway is compromised and patients cannot breathe properly.

Who is at risk of Drug Allergy in Singapore?

While anyone can develop a drug allergy at any age, there are some factors that put you at a higher risk.

  • Increasing age
  • A personal or family history of drug allergies or other allergies
  • Having illnesses such as asthma, human immunodeficiency virus (HIV), Epstein-Barr virus (EBV), and cancer
  • Repetitive use of a particular drug especially in increasing doses
  • Administration of a drug (topical or intravenous)

How are Drug Allergies diagnosed?

Drug allergies may be diagnosed based on your symptoms alone, or your dermatologist may suggest tests to determine the source (or sources) of your allergy.

  • Skin prick test - A tiny amount of the suspected drug is placed on your skin, and then your doctor will prick the skin with a needle to enable the substance to enter the surface of your skin. If you develop a bump or irritation, it indicates an allergy to the drug.
  • Blood test - Blood samples may be taken to rule out other illnesses that may be causing the allergic reaction.

What are the treatment options for Drug Allergy in Singapore?

Treatment options for drug allergies in Singapore vary, as it depends on how severe your reactions are and how important the drug is to your well being. Once the drug allergy has been identified, you should avoid the culprit drug to prevent further allergic reactions and look for suitable alternatives. Always inform your healthcare providers and doctors if you have a diagnosed drug allergy.

These are some common treatment options for drug allergy:

  • Withdrawal of the drug that is causing the allergy
  • Antihistamines
  • Medication to treat anaphylaxis
  • Corticosteroids - either oral or topical


What’s the most common allergic reaction to a drug?
Skin irritations and reactions such as rashes and itching are the most common symptoms of an allergic drug reaction.
What’s the difference between a drug allergy and side effects?
Side effects are expected reactions to a certain drug and occur in most patients. However, drug allergy is unexpected and doctors cannot always predict who will get an allergic reaction. In most cases, side effects of a drug are mild and cause symptoms such as stomach pain and drowsiness. Side effects usually disappear after stopping the drug, but drug allergies can linger for several weeks.
Can you overcome a drug allergy?
In some cases, if you must take the drug and there are no alternative options, overcoming an allergy is possible with drug desensitization. This involves reintroduction of a drug in stages starting with small doses, then working up to higher doses if reactions don’t occur.
What can I do if I suspect I’m having a drug allergy?
First and foremost, stop the offending drug and look for alternatives if possible. If the drug cannot be stopped then speak to the prescribing doctor regarding your suspicion. Then consider undergoing skin prick test or blood tests to confirm the suspicion.



Dr Uma Alagappan is a MOH accredited consultant dermatologist in private with more than 15 years experience as a medical doctor. She sub-specialises in paediatric dermatology, women’s dermatology and general dermatology. Dr Uma’s interests include chronic eczema, food allergy and immunodermatology. She is also well versed with the use of lasers for treating paediatric and adult patients.
Dr Uma completed her dermatology training in Changi General Hospital and National Skin Centre in 2015. She joined KKH Dermatology Service to subspecialize in paediatric dermatology in 2017. She was awarded the Ministry of Health Manpower Development Plan Award in 2019 to pursue paediatric immunodermatology and allergo-dermatology in the renowned Boston Children’s Hospital, Massachusetts, USA. Upon her return, she spearheaded a number of clinics at KKH including the food allergy eczema clinic for the paediatric eczema patients, immunodermatology clinics and the psychology eczema multi-disciplinary clinics.
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