Drug allergy reactions are common in children and adults. They usually tend to be mild like a drug rash or hives but can be severe as an anaphylaxis. Many a times this situation is clear and the offending medicine is clearly identified. Sometimes, there is a suspected drug allergy which needs to be clarified. At other times the child gets a reaction when lots of drugs have been given. In these situation the offending medicine needs to be identified and hence Drug Challenge are done.
Why is it Important?
This is an important question which parents and patients need to understand.
If you or your child has a proven drug allergy then the offending medicine has to be avoided for ever. But many a times the situation is unclear that whether the reaction is actually caused by the particular medicine or not. Sometimes these are common medicines like antibiotics, fever or pain medicines which the child might require in future. Drug challenge would help clarify this. If no reaction is actually found then the child can take that medicine if needed. If the child actually has an allergy to a particular medicine, we also try and find a safe alternative which he or she might require in future.
The other situation arises when a reaction happens but the child was receiving many medicines at a time. These are children usually admitted in hospital, ICU’s or during surgery. In such situation drug challenge helps to guide which medicines can be taken safely in future since these are key medicine which any one can need during emergency.
How are drug challenge testing done?
Before doing a drug challenge we would take a detailed history and would possibly conduct a Skin Prick Test and Intradermal Test to the offending drugs. This might be followed by a provocation challenge to get a definite answer if required.
The testing process depends on whether the previous reaction was mild or severe and whether the medicine to be tested is an oral medicine or injectable.
The testing is conducted when the child is otherwise well. If the previous reaction was mild then the medicine can be used at home or might need to be in the ward as day care. In case of severe reactions the child would need an IV cannula.
On the day of the Challenge the child would be assessed for baseline observations, including temperature, pulse, respiratory rate, oxygen saturations, blood pressure, and chest auscultation.
Thereafter the child is given the medicine in small doses under observation. If no reaction is noted, we give increased doses of the medicine at 20-30 minute intervals until the top dosage for medicine is reached or a reaction occurs. The child is monitored closely for at least 2 hours. If no reaction is noted during this period then the challenge is said to be negative. If reaction is noted we would take care as per the standard guidelines.