Background: The physicochemical modification of allergen extracts provides a chance for administering higher doses of allergen vaccines.
Objective: To evaluate the safety of a chemically modified (depigmented-glutaraldehyde polymerized) therapeutic vaccine of Phleum pratense administered at doses that are 10 times higher than those used in clinical practice, in comparison with conventional doses of the corresponding non-modified alum-adsorbed vaccine.
Materials and methods: The design of the study was randomized, double-blind, parallel and included two groups of patients. Twenty-three patients were treated weekly during nine visits for the build-up phase, followed by two weekly maintenance doses (a total of 11 injections per patient). Twelve patients received a vaccine containing the standardized unmodified extract, at a maximum concentration of 308.5 mcg of freeze dried material/mL (Group A). Eleven patients received a standardized modified allergen extract (Group B). The maximum dose used was 2400 mcg/mL. Safety was evaluated recording all adverse events. Skin test results and specific antibody levels were evaluated at the beginning and at the end of the study.
Results: Group A patients experienced three local immediate (two clinically irrelevant and one with a diameter>5 cm) and 18 delayed reactions (15 irrelevant and three with a diameter>10 cm), while Group B experienced six local immediate and 12 delayed reactions (all clinically irrelevant). Nine Group A patients experienced 12 systemic reactions (one immediate of grade 1, one of grade 2; and one delayed of grade 1; four of grade 2 and three of grade 3), while Group B patients experienced one immediate systemic reaction of grades 1, and 1 delayed reaction of grade 1.
Conclusions: The modified extract of P. pratense is safe to treat sensitive patients, even at concentrations that are 10 times higher than those regularly administered in clinical practice. The majority of the local reactions were clinically irrelevant. No systemic reactions of grade 2, 3 or 4 were reported using the modified extract.