Amoxycillin Challenge

I am a fourth year pharmacy student at UniSA. During my placement at HPS Pharmacies, I had a great opportunity to be involved in an antibiotic challenge to treat a child with amoxycillin allergy. The challenge was conducted by Dr Damien Chan, an immunologist consulting at The Memorial Hospital. The hospital has recently started an Allergy Clinic specialising in desensitisation. Dr Chan has had 10 years experience in immunotherapy at the Women’s and Children’s Hospital. The majority of his patients have been successfully treated and become able to take the medicines that they were previously allergic to, without reaction. Desensitisation can be used for patients at all ages, but Dr Chan specialises in children. As it was fascinating, I would like share the experience with you.

Allergic reactions are classified into two categories: immediate and non-immediate reactions.1 The immediate reactions are mediated by specific IgE-antibodies and present within an hour from contact with allergens.1 Symptoms are often serious including angioedema, anaphylactic shock and bronchospasm.1 On the other hand, the mechanisms of the non-immediate reactions are not yet fully understood.1 The non-immediate reactions are normally less serious such as skin rashes developing a few days after contact with the allergen.1 Importantly, some viral infections cause skin rash,5 so it is difficult to determine whether or not it is an allergic reaction.

Desensitisation for allergy is an immunotherapy which induces clinical unresponsiveness to allergens by gradually introducing repeated small amounts of the allergen.2 The challenge has been successfully used to treat various kinds of allergies such as insulin allergy,3 peanut allergy6 and cow’s milk allergy4 in the past. The advantage of desensitising children to their drug antigens is that it allows them to avoid limitations to their future treatments. Particularly in children, infections which are not treated properly can result in serious consequences (e.g. loss of hearing from ear infections).

Children who undergo the challenge are carefully selected according to their allergy history. If they have an immediate allergic reaction to an antibiotic, they are not suitable candidates for desensitisation because the challenge could be life-threatening. In that case, the particular antibiotic and cross reacting antibiotics are avoided for life. However, if it is non-immediate, they could have a skin prick test to evaluate the reactions. The bottom line is that the skin test is not well-tolerated in young children as it is quite invasive. So, the challenge can be useful in both to test if the patients have a true allergy, and to desensitise those patients with an allergy. Once they successfully complete the challenge, they are likely to be desensitised for life.

Our patient was a two year old child with a suspected moderate amoxycillin allergy. The patient had previously experienced skin rash (red and flat but not itchy) developing a few days after he took amoxycillin, indicating that he is likely to have a non-immediate allergy. As discussed, since skin rash can also be caused by viral infections, we cannot be sure that he has a true allergy to amoxycillin. To avoid the trauma of skin testing, he was nominated to undergo the desensitisation process. Dr Chan designed a 5-day course of the challenge for him as shown in Table 1. I reconstituted and diluted a commercial oral amoxycillin (RANMOXY) syrup into the different doses and concentrations required for the protocol under the supervision of Ian Tindall, a compounding pharmacist at HPS – Alexander Avenue. The suspensions were yellow with a fruity flavour, which is designed to improve compliance.

Table 1. Amoxycillin Challenge Protocol.

On day 1, the patient was introduced to the diluted oral amoxycillin suspensions at fixed time intervals under direct supervision by the nurse and doctor. The patient’s mother was with us and the child was observed for three hours in total. His body temperature, pulse and blood pressure were measured and the absence/presence of allergic reactions was checked every 30 minutes. They were all recorded. Treatments including adrenaline, hydrocortisone and oxygen pump are prepared for a potential emergency during the intervention. Fortunately, he did not have any allergic reactions during the testing, so he and his mother went home with a 4-day course of amoxycillin at a normal therapeutic dose to complete. His mother was advised to observe him carefully and report mild allergic reactions to Dr Chan or telephone 000 for an emergency. If there were any reactions, the patient would be diagnosed with amoxycillin allergy for life.

From the parents’ point of view, desensitisation of children’s allergy can be frightening. However, the challenge is well organised and performed by experienced health professionals. The allergy clinic room is child-friendly with a TV and toys; and parent-friendly with comfortable reclining chairs and coffee. In this particular case, the patient looked relaxed and enjoyed playing with the toys during the challenge. His mother looked comfortable and trusted the clinic staff to conduct the challenge on him. She expressed that she was happy to let him undergo another challenge for cephalexin in a few weeks as he has a history of a similar reaction to cephalexin.

I found it interesting that children with drug allergies can be successfully treated with desensitisation. Also, as a pharmacy student, it was such a pleasure to see the good outcomes from our products in their treatment, since compounding pharmacists have few chances to witness patients undergoing their treatments. This opportunity allowed me to realise that pharmacists play an important role in a healthcare team. It was also great to receive feedback from the doctor himself on our preparation and labelling of the preparations. I realised that it is important to ensure that our presentation meets doctor’s and patient’s needs. For instance, we were asked to provide spare suspensions in case there were spills or emesis during administration. The lessons are very useful to improve our preparation in the future.