Short Ragweed Recall
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Questions & Answers
Side Effects & Adverse Reactions
Physicians who elect to administer ragweed pollen extract should be familiar with the clinical use of allergenic extracts and have the necessary emergency equipment and medication available to treat systemic allergic reactions.
The injection of ragweed pollen extract may cause severe local and/ or systemic anaphylactic reactions in some individuals. To minimize this potential hazard, the relative sensitivity of the patient must be assessed from the allergic history and from clinical observations. Patients should be informed of this risk prior to skin testing and immunotherapy (see adverse reactions).
The dosage must be reduced when starting a patient on fresh standardized (Antigen E) extract or when transferring a patient from non-standardized to standardized extract, even though the labeled strength of the old and new vials may be the same. This is necessary due to a loss of extract potency during storage in the physician's office. The antigen E content of old and new extract must be compared and adjusted by dosage reduction and/or dilution before new extract is administered. The amount of new extract given from the old vial, assuming both extracts contain comparable amounts of antigen E. Any evidence of a local or generalized reaction requires a reduction in dosage during the initial stages of hyposensitization as well as during maintenance therapy.
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FDA Labeling Changes
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Studies have shown that properly performed an interpreted skin tests with ragweed pollen extract are useful in the diagnosis of allergy to ragweed pollen 7, 8, 20, 21. Immunotherapy with the appropriate dosage of short ragweed pollen extract is effective in reducing symptoms of hay fever and asthma resulting from exposure to short ragweed pollen (9, 10, 11), and it is believed to be effective with extract of giant ragweed, although carefully controlled studies are unavailable. However, clinical observations and known cross reactivity between short and giant ragweed pollens have led to the practice of using a mixture of the two species for skin testing and treatment 22, 23, 24, 25, 26, 27.
This form of treatment is recommended for patients who cannot avoid exposure to pollen and who do not obtain satisfactory relief of symptoms from other medications, such as antihistamines. Immunologic changes resulting from treatment with short ragweed pollen extract are believed to include:
- The induction of specific anti-ragweed IgG antibodies commonly referred to as "blocking antibodies" 12, 13.
- A decrease in the elevation of ragweed specific IgE during and immediately following the ragweed pollen season 14.
- A reduction of circulating anti-ragweed IgE after long-term immunotherapy 15.
- A decrease in skin reactivity to the extract 16 and a decrease in leukocyte sensitivity to histamine release 17 after long-term immunotherapy.
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INGREDIENTS - Allergenic extract of short ragweed pollen is a clear, amber-colored solution prepared from the dry, defatted pollen of Ambrosia elatior. The extract contains the water extractables of the pollen, 0.25% sodium chloride, 0.125% sodium bicarbonate, 0.5% phenol and 50% glycerol by volume. Extract of mixed short-giant ragweed has the same appearance as short ragweed pollen extract and contains the same chemical ingredients. It is prepared from equal gram weights of the pollens of Ambrosia elatior and Ambrosia trifida.
STANDARDIZATION - The potency of ragweed pollen extract is based on antigen E, a protein component which is believed to be the most important allergen of short ragweed pollen. Extracts of short ragweed pollen sold in the U.S. must have a minimum antigen E content of 67.5 units per ml for a 1:20 w/v concentrate. Extracts of mixed short-giant ragweed must have a minimum antigen E content of 33.75 units/ml for a 1:20 w/v concentrate. The importance of antigen E in ragweed allergy is based on the following observations:
- In vitro studies with antigen E have shown that it is capable of causing histamine release from peripheral leukocytes of ragweed sensitive persons 1.
- The antigen E content of short ragweed pollen extract has been found to correlate with extract potency when measured by skin test response in persons allergic to short ragweed pollen 2.
- Immunotherapy with antigen E has been shown to be comparably effective to whole short ragweed pollen extract in reducing symptoms related to ragweed pollen exposure 3.
EXPIRATION DATING - Expiration dating is based on the antigen E content of the extract. Extracts containing 50% glycerol by volume have longer dating periods due to the protective effects of glycerol on antigen E 5, 6. The expiration period of aqueous concentrate and saline dilutions of glycerinated concentrate is approximately one-half that of glycerinated extract containing comparable antigen E content.
Ragweed extract should be kept at 2°C to 8°C during use and office storage to retain potency. Higher temperatures have an adverse affect on antigen E.