What is an adverse drug reaction?

Adverse reactions to drugs are common. Most are predictable and are known as side effects. Common examples include diarrhoea caused by antibiotics and drowsiness caused by some anti-histamines.

What is drug allergy?

Although drug allergy is relatively common in adults, it is rare in children. It is not unusual for children to develop rashes with viral infections. They can then be easily confused with allergy to the medicine given when the child is unwell. This is especially the case with antibiotics and pain killers.

Reactions often include a rash, which can come on suddenly or gradually. They may occur after the first dose or many doses of a medication. Drug allergies are generally mild but can also be severe including anaphylaxis.

What will the doctor need to know about the reaction?

It is very important for the doctor to know what drug was taken and what happened. The doctor will also need to know

  • what symptoms developed
  • how quickly did the reaction occur
  • any other illnesses
  • were other drugs taken at the same time
  • has it been taken before
  • why the drug was given

Pictures or videos of a reaction can be very helpful. If possible bring the drug and packaging with you.

How is drug allergy diagnosed?

Allergy tests are often unreliable. Taking a dose of the drug in hospital is the most accurate way of proving an allergic reaction to a drug. This is called a drug challenge.

There are some situations where this will not be done, such as where there is severe blistering of the skin or mouth, or after other very severe reactions.

How is drug allergy managed?

In most children presenting with a possible drug allergy, formal challenge rules out the allergy, allowing the drug to be used in the future if needed. In the rare cases where a drug allergy is diagnosed, avoidance of the drug is usually advised. Your hospital doctor will inform your GP. It is important that you know which drug your child is allergic to. You must tell all health professionals about this allergy, including your dentist.

You should be careful when buying over the counter medicines, receiving medicines from overseas, from friends and family or over the internet.


Allergy alert jewellery is worn by some patients with drug allergy to let doctors and others know.

What if my child gets ill and needs the drug?

In most cases, there are other drugs that can be used. The drug that caused the reaction should be avoided.

If there is no alternative, then your allergist may consider desensitising your child to the drug.

What should I do if I think my child is having a drug reaction?

Stop the drug and tell your doctor.

For rash and swelling an antihistamine should be taken as soon as possible.

If there are severe symptoms:

  • Difficulty breathing (wheezing, noisy breathing, blue colour)
  • Swelling in the throat (noisy breathing, drooling)
  • Feeling faint or dizzy, looking very pale (lie the child down with their legs raised).

Get help straight away and dial 999 stating “anaphylaxis” (ana-fil-ak-sis).