Allergenic Extract Sterile Diluent

Studies indicate allergic individuals produce immunoglobulins of the IgE class in response to exposure to allergens. Subsequent exposure to the allergen results in a combination of allergen with IgE antibody fixed on mast cells or basophil membranes. This cross-linking results in stimulation of mast cell which leads to release and generation of pharmacologically active substances that produce immediate hypersensitivity reaction.3

The mode of action of immunotherapy with allergenic extracts is still under investigation. Subcutaneous injections of increasing doses of allergenic extract into patients with allergic disease have been shown to result in both humoral and cellular changes including the production of allergen-specific IgG antibodies, the suppression of histamine release from target cells, decrease in circulating levels of antigen specific IgE antibody over long periods of time and suppression of peripheral blood T-lymphocyte cell responses to antigen.10, 14, 15

Allergenic extract is used for diagnostic testing and for the treatment (immunotherapy) of patients whose histories indicate that upon natural exposure to the allergen, they experience allergic symptoms. Confirmation is determined by skin testing. Diagnostic use of allergenic extracts usually begins with direct skin testing. This product is not intended for treatment of patients who do not manifest immediate hypersensitivity reactions to the allergenic extract following skin testing.

Refer to “STORAGE” section for proper storage condition for allergenic extract. Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit. Some allergenic extracts naturally precipitate.

Physicians undertaking immunotherapy should be concerned with patient’s degree of sensitivity. The initial dilution of allergenic extract, starting dose, and progression of dosage must be carefully determined on the basis of the patient’s history and results of skin tests. Strongly positive skin tests may be risk factors for systemic reactions. Less aggressive immunotherapy schedules may be indicated for such patients.

Precaution is necessary when using extract mixture for skin testing. The diluting effect of individual components within a mixture may cause false negative reactions. Patients extremely sensitive to a common allergen in several components of a mixture may be more likely to experience a systemic reaction than when skin tested individually for each component.9

PRICK-PUNCTURE TESTING: To identify highly sensitive individuals and as a safety precaution, it is recommended that a prick-puncture test using a drop of the extract concentrate be performed prior to initiating very dilute intradermal testing. Prick-puncture testing is performed by placing a drop of extract concentrate on the skin and puncturing the skin through the drop with a small needle such as a bifurcated vaccinating needle. The most satisfactory sites on the back for skin testing are from the posterior axillary fold to 2.5 cm from the spinal column, and from the top of the scapula to the lower rib margins. The best areas on the arms are the volar surfaces from the axilla to 2.5 or 5 cm above the wrist, skipping the anticubital space. A positive reaction is approximately 10-15 mm erythema with 2.5 mm wheal. Smaller, less conclusive reactions may be considered positive in conjunction with a definitive history of symptoms on exposure to the allergen. The more sensitive the patient the higher the probability that he/she will have symptoms related to the exposure of the offending allergen. Hence, the importance of a good patient history. Less sensitive individuals can be tested intradermally with an appropriately diluted extract.

A positive control using histamine phosphate identifies patients whose skin may not react due to medications, metabolic or other reasons. A negative control (50% glycerine for prick-puncture testing) would exclude false-positive reactions due to ingredients in diluent or patients who have dermatographism.

SINGLE DILUTION INTRADERMAL TESTING: The surface of the upper and lower arm is the usual location for skin testing. It is important that a new, sterile, disposable syringe and needle be used for each extract tested. Intracutaneous test dilutions, five-fold or ten-fold, may be prepared from stock concentrate using physiologic saline as a diluent. (1) Start testing with the most dilute allergenic extract concentration. (2) A volume of 0.02-0.05 ml should be injected slowly into the superficial skin layers making a small bleb (superficial wheal). (3) For patients without a history of extreme sensitivity, or a negative or weakly reactive prick-puncture test, the initial dilution for skin testing should be a dilution at least 1:12,500 w/v. This initial dilution can be prepared by diluting 1:20 to 1:50 w/v (2%-5%) extracts five-fold to 5-4 or 1:10 w/v (10%) extracts to 5-5. See “Serial Dilutions Titration Test Dilutions” chart on the next page. Dilute 1:10 w/v (10%) extracts to 10-3 if using ten-fold dilutions. (4) Sensitive patients with a positive prick-puncture test require a further dilution to at least 1:312,500 w/v. This dilution can be prepared by diluting 1:20 to 1:50 w/v (2% - 5%) extracts to 5-6 or 1:10 w/v (10%) extracts to 5-7 (five-fold dilutions). Ten-fold dilution to 10-6 of a 1:10 w/v (10%) extract would be a safe starting dilution. Size of reactions are quantitated based on size of wheal and erythema. For interpretation of skin reactions, refer to chart below. If after 20 minutes no skin reaction is observed, continue testing using increasing increments of the concentration until a reaction of 5-10 mm wheal and 11-30 mm erythema is obtained, or a concentration of 5-2 or 10-1 has been tested. A negative control, 50% glycerine diluted with diluent to 5-2 (1:25) or 10-1 (1:10) dilution and a positive control of histamine phosphate, should be tested and included in interpretation of skin reactions.1, 13

INTRADERMAL TESTING-SKIN ENDPOINT TITRATION: The allergenic extracts to which the patient is sensitive, the patient’s degree of sensitivity and the dose of allergen to be used in immunotherapy can be determined through the use of intracutaneous skin tests involving progressive five-fold dilutions of allergenic extracts. Intracutaneously inject 0.01 to 0.02 ml of the test allergen to form a 4 mm diameter superficial skin wheal. For patients demonstrating a negative or weakly reactive prick-puncture skin test, an initial screening dilution of 1:12,500 w/v is safe. For patients demonstrating a positive prick-puncture skin test, an initial screening dilution of 1:312,500 w/v is safe. (See “Serial Dilution Titration Test Dilutions” chart below.) When a sequence of five-fold or ten-fold dilutions of an allergen are injected, the endpoint is determined by noting the dilution that first produces a wheal and erythema (15 minutes after injection) that is 2 mm larger than wheals with erythema produced by weaker, non-reacting dilutions (5 mm negative wheal). The endpoint dilution is used as a starting dose concentration for immunotherapy. An endpoint dose of 0.15 ml is a safe initial dose to be followed by escalation to the optimal maximum tolerated dose for each individual.

Injections should never be given intravenously. A 5/8 inch, 25 gauge needle on a sterile syringe will allow deep subcutaneous injection.

IMMUNOTHERAPY: If the first injection of the initial dilution of extract is tolerated without significant local reaction, increasing doses by 5-20% increments of that dilution may be administered. The rate of increase in dosage in the early stages of treatment with highly diluted extracts is usually more rapid than the rate of increase possible with more concentrated extracts. This schedule is intended only as a guide and must be modified according to the reactivity of the individual patient. Needless to say, the physician must proceed cautiously in the treatment of the highly sensitive patient who develops large local or systemic reactions.6

Some patients may tolerate larger doses of the allergenic extract depending on patient response.7 Because diluted extract tends to lose activity in storage, the first dose from a more concentrated vial should be the same, or less than, the previous dose.8, 12

Dosages progressively increase according to the tolerance of the patient at intervals of one to seven days until, (1) the patient achieves relief from symptoms, (2) induration at the site of injection is no larger than 50 mm in 36 to 48 hours, (3) a maintenance dose is reached (the largest dose tolerated by the patient that relieves symptoms without undesirable local or systemic reactions). This maintenance dose may be continued at regular intervals perennially. It may be necessary to adjust the progression of dosage downward to avoid local and constitutional reactions.

The usual duration of treatment has not been established. A period of two or three years on immunotherapy constitutes an average minimum course of treatment.

Stock concentrates are available in concentrations of 2-10% or weight/volume (w/v) of 1:50, 1:33, 1:20 or 1:10. Some juicy or liquid foods are available at 1:1 volume/volume (v/v) extraction ratio. Fresh egg white extract is available at 1:9 v/v extraction ratio.

Antigen E content of ragweed mixtures ranges from 46-166 U/ml for Ragweed Mixture (Short/Giant/Western/Southern Ragweed), 47-239 U/ml for Short/Giant/Western Ragweed Mixture, and 106-256 U/ml for Short/Giant Ragweed Mixture. Refer to container label for actual Antigen E content.

Extract (stock concentrate) is supplied in 10, 30 and 50 ml containers. Extracts in 5 ml dropper bottles are available for prick-puncture testing. To insure maximum potency for the entire dating period, all stock concentrates contain 50% glycerine v/v.

Store all stock concentrates and dilutions at 2-8° C. Keep at this temperature during office use. The expiration date of the allergenic extracts is listed on the container label. Dilutions of the allergenic extracts containing less than 50% glycerine are less stable. If loss of potency is suspected, potency can be checked using side by side skin testing with freshly prepared dilutions of equal concentration on individuals with known sensitivity to the allergen.