Allergenic Extracts, Grass Pollen

The allergic state is initiated by an immune response inducing B cells to produce IgE antibodies to specific allergens. IgE antibodies bind to surface receptors on mast cells and basophils. When antigens gain access to the immune system they react with the bound IgE. The reacting antigen to the surface bound IgE stimulates a number of chemical mediators to be released from the mast cells and basophils. These include histamine, Eosinophil Chemotactic Factor (ECF-A) and leukotrienes. These chemical mediators are pharmacologically active at low concentrations and are partially responsible for the biological manifestations of the allergic response. (3) 

The mechanism by which immunotherapy achieves hyposensitization is not completely understood. There is an increase in "blocking antibody" (lgG) titer and in some patients a decrease in specific IgE, a decrease in histamine release to specific allergen and an increase in suppressor celI population to specific allergen. These changes may occur only after prolonged therapy. (4)

Clinical data from the Center for Biologics Evaluation and Research is shown in the following tables

GENERAL:

      The dosage should be reduced 50-75% from the previous dose when starting a patient on a new lot of standardized grass extract from the same manufacturer or from a different manufacturer. Table A in the Clinical Pharmacology section of this insert can be used for guidance when changing from a non-standardized grass extract to a standardized grass extract. The table shows the similarity in potency of two Iots of the non-standardized grass extracts with respect to the 10,000 BAU/ml standardized extracts. Comparative skin testing can be used to determine the dose.

      A separate sterile tuberculin type syringe should be used with each patient to prevent cross contamination of extracts. This will also prevent transmission of disease such as hepatitis, AIDS and other infectious diseases. Aseptic technique should always be used when injections of allergenic extracts are administered.

INFORMATION FOR PATIENTS:

      Because most serious reactions following the administration of allergenic extracts occur within 30 minutes of the injection, the patient should remain under observation for this period of time. The size of the local reaction should be recorded, because increasingly large local reaction may precede a subsequent systemic reaction with increasing dosage. The patient should be instructed to report any unusual reactions to the attention of the physician. In particular, this includes swelling and/or tenderness at the injection site or reactions such as rhinorrhea, sneezing, coughing, wheezing, shortness of breath, nausea, dizziness or faintness.

DRUG INTERACTIONS:

      Patients who are taking non-selective beta blockers may be more reactive to skin tests and may be unresponsive to the usual doses of epinephrine used to treat allergic reactions. Antihistamines can significantly inhibit the immediate skin test reactions. If long acting antihistamines have been taken recently, it is recommended that they should be stopped for the following minimum intervals before skin testing is performed: at least 1 month for astemizole; 1 week for hydroxyzine or cetirizine; 4 to 7 days for Ioratadine; 3 to 4 days for terfenadine or fexofenadine; and 24 to 48 hours for other sustained release antihistamines. (6)

CARCINOGENESIS, MUTAGENESIS, IMPAIRMENT OF FERTILITY:

      Long term studies with extracts have not been conducted in animals to determine their potential for carcinogenesis, mutagenesis, or impairment of fertility.

PREGNANCY:

      Pregnancy Category C. Animal reproduction studies have not been conducted with allergenic extracts. It is also not known whether allergenic extracts can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Allergenic extracts should be given to a pregnant woman only if clearly needed.

      Controlled studies of hyposensitization with moderate to high doses of allergenic extracts in pregnant women have failed to demonstrate any risk to the mother or fetus. (7)

      Initiation of effective immunotherapy may be beneficial if it allows a pregnant patient to forego medications during the first trimester when the fetus is more vulnerable to teratogenic agents, or if it contributes to better control of asthma so the fetus has less likelihood of being damaged by hypoxemia.

      However, with histamines known ability to contract uterine muscles any reaction which would release significant amounts of histamine such as hyposensitization overdose should be avoided. The physician must weigh the benefits of immunotherapy against the risk of anaphylactic reactions that could result in harm to the mother and/or fetus.

      Hyposensitization should be used during pregnancy only if clearly necessary and administered cautiously. If a woman is on maintenance dose the occurrence of pregnancy is not an indication to stop injection therapy.

NURSING MOTHERS:

      It is not known if allergenic extracts are excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when extracts are administered to nursing women.

PEDIATRIC USE

      Standardized grass pollen extract has not been studied in children, so the safety in children has not been established. The extracts may cause some pain or discomfort when injected, as well as systemic, adverse reactions (see Warnings and Adverse Reactions). The maximum tolerated dose may be less than the adult dose due to the smaller size of the child. Therefore, the volume of the dose may need to be adjusted from the adult schedules provided.

DIAGNOSTIC SKIN TESTING: These products are used to determine a patient's sensitivity to specific antigens and aid in the diagnosis and treatment of atopic diseases. After a thorough history, a decision can be made as to which allergens will be appropriate to use for testing. The recommended procedure is to initially perform puncture tests, then follow with intradermal tests. For enhanced safety, scratch or puncture test with 10,000 BAU/ml before testing with 100,000 BAU/ml. See recommended dosage below:

FREQUENCY OF ADMINISTRATION:

      The number of skin tests applied at one time will depend on the particular patient and their allergic history. These tests should be performed and observed in 15 to 20 minutes. Additional tests may be applied in sequence. Perform tests on the anterolateral aspect of the upper arm on an area that permits the effective application of a tourniquet proximal to the site of the test. The skin at the site of injection should be disinfected with rubbing alcohol before testing.

      Puncture testing: Apply one drop of extract to the skin. Pierce the drop of extract and skin using a sterile hypodermic needle or vaccinating needle. Maintain the needle perpendicular to the skin surface and rock the needle back and forth to produce a small hole without bleeding. Do not rotate or gouge the needle. Remove needle from skin and wipe excess extract from skin surface.

      Scratch testing: Using a scarifier or needle, make a scratch 1/16 inch long on the epidermis penetrating the outer cornified area but being careful not to draw blood. Apply one drop of extract to the scratch.

      Intradermal testing: Use a separate sterile syringe (tuberculin type equipped with a 27 gauge by 3/8 inch needle with intradermal bevel) for each antigen. The tests are made by injecting 0.02ml of allergen into the epidermis. If the test has been performed properly, the solution should raise a bleb 2 to 3mm in diameter. If the bleb does not appear, the injection was made too deeply.

      A negative control consisting of the same solution that the extract was prepared in, should be applied to one of the sites in the same manner as the tests being performed. For example, the negative intradermal control should contain 0.5% (v/v) glycerin, if a 100 BAU/ml concentration grass is used for intradermal testing. Histamine phosphate should be used as a positive control for evaluation of skin testing. Histamine phosphate is available from other manufacturers. See their directions for use, for recommended dosage and interpretation of results.

      A positive reaction usually develops in 15 to 20 minutes. The positive response is a wheal and flare reaction that is larger than the negative control and judged on the size of the reaction. Scratch or puncture tests may not elicit as large and well defined reaction as the intradermal. (5)

The following grading system for intradermal testing is recommended (9):

IMMUNOTHERAPY:

The following are two methods of injection therapy:

      1. Pre-seasonal in which treatment is begun three months before seasonal difficulty begins and brought to maintenance dose by injections 4 to 7 days apart and discontinued after that season ends.

      2. Perennial treatment is the recommended mode of therapy in which the patient is, by injection therapy, brought up to tolerated maintenance dose and remains at that dose until amelioration of allergic symptoms occurs. Injections may be given at intervals of 4 to 7 days.

      Allergenic extracts must be diluted before use. Normally immunotherapy can be started with a 1 BAU/ml dilution. If a patient appears to be extremely sensitive, based on skin testing results, dilutions of the extract can further be made before injections are started. See Table B for additional information. The following are suggested procedures for making a proper dilution series. Recommended diluents contain 0.9% sodium chloride and 0.4% phenol as a preservative. Dlluents with HSA (Human Serum Albumin) as a stabilizer can also be used. Allergenic extracts should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.

      Perennial treatment may be started using the following dosage and dilution schedule. (Modified from Reference 10) This schedule is only illustrative and may not be applicable to all patients, since the degree of sensitivity to grass allergens differs among individuals. The dose administered must be adjusted based on the patient's sensitivity and tolerance. Initial dose can be based on end point titration using a dose that elicits a 1-2+ reaction. Maintenance dose is based on patient tolerance.

Gradually increase the dose as outlined in the schedule. If you give a dose that causes a mild local reaction (manifested by warmth or redness) repeat the same dose. If the reaction is severe or systemic (manifested as hives, asthma, or hay fever) drop back a dose in schedule and build again. If a severe local reaction or a systemic reaction is again encountered, this should be considered more than the maximum tolerance for this patient. The maintenance dose is the largest dose that relieves symptoms without producing local reactions. The size and interval of doses will vary and can be adjusted as necessary. The normal interval between doses is 4 to 7 days. The usual duration of treatment has not been established. A period of two or three years of injection therapy constitutes an average minimum course of treatment.