Background and importance Large diferences in active ingredient concentrations (AI) in drug patch tests, as a result of the drug source chosen, signify the need for further studies to ensure the quality of the preparations.

Aim and objectives To analyse the variability of the resulting AI concentrations in paediatric patch tests, according to the commercialised forms (CFs) used.

Material and methods A review of the recommendations for drug patch tests preparation was carried out using PubMed.

For the Allergy Department requested compounds, when no pure drug was commercially available, the CFs were used instead. In the latter case, following Spanish Society of Allergy and Clinical Immunology (SEAIC) recommendations, the CF weights were used, rather than their AI content, to obtain the prescribed drug concentration in the compounds. Finally, the actual AI concentration in each compound was calculated.

Results The SEAIC and the European Society of Contact Dermatitis recommendations were followed, whenever possible, using the pure drug, and when this was not available, resorting to the CF. Eight drugs were diluted by the Pharmacy Department at different concentrations in petrolatum. The only drugs whose manufacturers provided the pure drug were amoxicillin and doxycycline. When diluting the content of the capsules of phenoxymethylpenicillin potassium at 10%, the AI concentration obtained was 8%; however, when using the oral powder it was 1.4%. The same thing happened when diluting tablets of cefuroxime at 20%, namely the AI concentration obtained was 11%, while if using the oral powder it was 1.2%. For ampicillin at 5%, using the capsules the AI concentration obtained was 4.25%. When preparing brivaracetam at 30% and rufinamide at 3%, using the available tablets the AI concentrations obtained were 5.34% and 1.63%, respectively. However, when diluting the capsules of ethosuximide at 20%, the AI concentration obtained was 15.8%.

Conclusion and relevance The actual AI concentrations in the compounds vary depending on the CF used.Using the CF with the lowest amount of excipients allows one to obtain AI concentrations closer to those usually proposed by scientific societies. The results obtained demonstrate the need to establish protocols with the Allergy Department in order to standardise the preparation and thereby assure quality and security in paediatric patch testing.

Conflict of interest No conflict of interest