Feasibility study and preparation of polyethylene glycol (PEG) syringes for allergological skin tests related to COVID vaccination

Background
Following COVID vaccination recommendations, the allergology department requested our assistance in conducting hypersensitivity tests for vaccines. The Summary of Product Characteristics (SmPC) identifies PEG as the only allergenic substance present in the formulation. The French Society of Allergology, the National Professional Council, and the French Federation of Allergology recommend contraindication in cases of a history of immediate reaction to primary vaccination, allergy to PEG or polysorbate through cross-reactivity. They suggest using products containing PEG3350 or 4000, but the presence of other excipients could alter test interpretation.

Objective
Feasibility study and provision of PEG-based syringes for allergological testing.

Materials and methods
The testing protocol involves performing a prick test (PT), and in the absence of a reaction, conducting 3 intradermal reactions (IDRs) with increasing concentrations, followed by a 20-minute reading after each injection. Vaccination can be administered if the tests are negative, with dose split and associated monitoring. The physico-chemical characteristics of the raw material (RM) are studied through the European Pharmacopoeia and a literature review. The availability and the possibility of filtering the non-sterile RM are examined through supplier inquiries and analysis of technical data sheets. This information are collected for the drafting of a preparation operating procedure.

Results
As PEG is highly soluble in water, a stock solution (SS) at 100 mg/mL is prepared from diluted RM in PPI water. Diluted solutions are prepared in different syringes, with sterile filtration of the SS during successive dilutions in a closed system under a sterile environment. For each patient, 2 syringes at 100 mg/mL (PT and IDR), 1 syringe at 10 mg/mL (IDR), and 1 syringe at 1 mg/mL (IDR) are prepared. Due to the lack of stability data, the expiry date was set at 24 hours for same-day injection.
A total of 108 preparations were performed between February 2021 and November 2022, resulting in 27 tests. Five patients did not show up, and 2 patients were not tested due to inappropriate reaction type. Tests were positive in 20% of cases (n=4), indicating contraindication for vaccination and use of PEG-based products, negative in 75% (n=15), and discordant in 1 patient. Among these 15 patients with negative tests, 4 patients were vaccinated without immediate or delayed reaction, and 1 patient chose not to receive the second vaccine dose.

Conclusion
This work adds an additional option for vaccinating the most vulnerable patients through the preparation and availability of magistral preparations. Vaccination data conducted outside the hospital could not be collected, but no reactions were reported afterwards.

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