Studies of allergen extract stability: the effects of dilution and mixing.

BACKGROUND: However potent the allergy extracts provided by manufacturers, they are subject to deterioration with storage, especially after dilution or mixture with other extracts.
OBJECTIVE: This study was performed to assess separately the deterioration during storage in allergen extract potency caused by dilution or by mixture with allergen extracts that have been reported to contain proteases.
METHODS: To assess the effect of dilution, three serial 10-fold dilutions of cat, short ragweed, Bermuda grass, and Dermatophagoides farinae extracts were prepared alone or combined with other extracts. They were stored at 4 degrees C for 3 and 12 months. To assess the effect of mixing with other extracts that have been reported to contain proteases, extracts of timothy grass, Bermuda grass, short ragweed, Russian thistle, white oak, box elder, D. farinae, and cat were stored alone or combined with one or more extracts of American cockroach, Alternaria spp., Cladosporium spp., Penicillium spp., and a house dust mite mix for 3 months at 4 degrees C.
RESULTS: Bermuda grass, cat, and house dust mite extracts incurred significant loss of potency at all dilutions with storage. Short ragweed was stable at all dilutions. Potency of extracts of timothy grass, Bermuda grass, Russian thistle, white oak, box elder, and cat were all reduced by combination with one or more extracts potentially containing proteases. Only short ragweed and D. farinae, which was in a final concentration of 25% glycerin, were resistant. Alternaria extract was most frequently responsible for loss of potency, followed by cockroach and Cladosporium extracts. Combination with extracts of Penicillium and a house dust mite mix did not reduce the potency of any extract.
CONCLUSIONS: Both dilution alone and mixture with extracts reported to contain proteases caused loss of potency of most extracts tested. Ragweed was uniquely resistant under both conditions of storage.