Get your patient on House Dust Mite, Dermatophagoides Farinae - House Dust Mite, Dermatophagoides Farinae injection (House Dust Mite, Dermatophagoides Farinae)

Standardized mite extract is indicated for use in the diagnosis of patients with a history of allergy to mites or house dust and for the treatment of patients with a history of mite allergy who have established sensitivity to mites by diagnostic skin testing.

The use of mite extract for the above purposes should be made only by physicians with special familiarity and knowledge of allergy as described in a standard allergy textbook (10).

Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit. The product should be discarded if discoloration or particles are observed.

DIAGNOSTIC USE:

Percutaneous Tests : The skin test concentration of 10,000 AU/mL in dropper vials is used for scratch or prick-puncture testing. Puncture tests performed with D. farinae extract on 5 persons sensitive to mite showed a mean diameter wheal of 8.8 mm ± 1.8 mm and mean diameter erythema of 39.2 mm ± 5.3 mm. Puncture tests with D. pteronyssinus extract on 10 persons sensitive to
mite showed a mean diameter wheal of 7.8 mm ± 4.1 mm and mean erythema of 33.7 mm ± 12.0 mm.

Intradermal Tests : Extract for intradermal testing should be prepared by diluting the 10,000 AU/mL stock concentrate in bulk vials with sterile saline with or without human serum albumin. Intradermal skin tests (0.05 mL) in persons highly sensitive to mite
showed the following results:

Intradermal tests should only be performed after a scratch or prick-puncture test has been administered with a negative result.

Patients who do not react to a valid scratch or prick-puncture test should be tested intradermally with 0.02 to 0.05 mL of a 10 AU/mL (1:1,000 v/v of the 10,000 AU/mL concentrate). If this test is negative, a second intradermal test may be performed using a 100 AU/mL (1:100 v/v dilution of 10,000 AU/mL concentrate).

Skin tests are graded in terms of the wheal and erythema response noted at 15 to 20 minutes. Wheal and erythema size may be recorded by actual measurement of the extent of both responses.

THERAPEUTIC USE: The dosage of mite extract administered by subcutaneous injection is highly individualized and varies according to the degree of sensitivity of the patient, his clinical response and tolerance to the extract administered during the early phases of an injection regimen. In patients who appear to be highly sensitive by history and skin test, the initial dose of the extract should be 0.05 mL of a 0.1 AU/mL dilution or as established by skin test titration. The amount of allergenic extract is increased at each injection by not more than 50% - 100% of the previous amount, and the next increment is governed by the response to the last injection. Large local reactions which persist for longer than 24 hours are generally considered an indication for repeating the previous dose or reducing the dose. Any evidence of systemic reaction is an indication for a significant reduction (at least 50%) in the subsequent dose. The upper limits of dosage have not been established; however, doses larger than 0.2 mL of the concentrate may be painful due to the glycerin content of the extract. The optimal interval between doses of mite extract has not been definitely established. However, as is customarily practiced, injections are given one or two times per week until the maintenance dose of extract is reached. At this time, the injection interval may be increased to 2 weeks, then to 3 weeks and finally to 4 weeks. If the patient does not return for 6 to 8 weeks after the last injection, the dose should be reduced to 25% of the last dose. If longer than 8 weeks, a dose reduction of one, two or three dilutions may be made depending on a consideration of the components and the patient's sensitivity The dosage and the interval between injections may need to be modified according to the clinical response of the patient. When switching patients to fresh extract, the initial dose should be reduced to one-quarter (25%) of the previous dose.

The usual duration of treatment has not been established. A period of three to five years of injection therapy constitutes an average course of treatment.

Children and older age patients appear to tolerate injections of allergenic extract well, and no special recommendations need to be made for these groups.

PREPARING DILUTIONS

To prepare dilutions for intradermal skin tests and therapeutic use as shown in the table below, make a series of ten-fold dilutions starting with the 5,000 AU/mL or 10,000 AU/mL as follows: add 1.0 mL of the concentrate to 9.0 mL of sterile diluent to make the 1:10 dilution; add 1.0 mL of the 1:10 dilution to 9.0 mL of sterile diluent to make the 1:100 dilution. Continue making dilutions as shown in the table below until the highest desired dilution is reached. The number of allergy units per mL in each dilution is shown in the table below.

Injections of mite extract should not be administered in the presence of diseases characterized by a bleeding diathesis. Immunotherapy should not be started in patients until a specific diagnosis of Type I allergy to mite is made by a physician based on skin testing with this product.
Other contraindications include:

EXTREME SENSITIVITY TO MITE: Determined from previous anaphylaxis following skin testing, immunotherapy, or natural exposure.
AUTOIMMUNE DISEASE: Individuals with autoimmune disease maybe at risk, due to the possibility of routine immunizations exacerbating symptoms of the underlying disease.
MYOCARDIAL INFARCTION: Patients who have experienced a recent myocardial infarction may not be able to tolerate immunotherapy. The benefit-to-risk ratio must be carefully evaluated.
CHILDREN WITH NEPHROTIC SYNDROME: Children with nephrotic syndrome require careful consideration and probably should not receive immunotherapy due to a variety of seemingly unrelated events that may cause an exacerbation of nephrotic disease.

Adverse systemic reactions usually occur within minutes and consist primarily of allergic symptoms such as generalized skin erythema, urticaria, pruritus, angioedema, rhinitis, wheezing, laryngeal edema and hypotension. Less commonly, nausea, emesis, abdominal cramps, diarrhea and uterine contractions may occur. Severe reactions may cause shock and loss of consciousness. Fatalities have occurred rarely (11). Systemic reactions occur with varying frequency in different clinics. To some extent, the reaction rate is related to the type and dose of administered extract and to the degree of sensitivity of the patient. Despite all precautions, occasional reactions are unavoidable.

Reports from regulatory authorities in Sweden to the Center for Biologics Evaluation and Research (CBER) indicated that several deaths have been associated with the use of mite extracts. CBER was subsequently informed that these deaths may have been related to use by physicians or other health professionals untrained in the administration of potent allergens, rather than a product defect. It should be noted that anaphylaxis and deaths following the injection of mite and other extracts also have been reported by the British Committee on Safety in Medicine in the British Medical Journal, 293:943, 1986.

Local reactions consisting of erythema, itching, swelling, tenderness and sometimes pain may occur at the injection site. These reactions may appear within a few minutes to hours and persist for several days. Local cold applications and oral antihistamines may be effective treatment. For marked and prolonged local reactions, steroids may be helpful.

The treatment of systemic allergic reactions is somewhat dependent upon the symptom complex. Epinephrine hydrochloride 1:1,000 aqueous, in an adult dose of 0.3 - 0.5 mL (or 0.01 mL per kg. for children) administeredsubcutaneously in the opposite arm is the immediate treatment of choice. A tourniquet should be placed above the site of the extract injection if the injection was done on the extremities. Antihistamines may offer relief of recurrent urticaria, associated skin reactions and gastrointestinal symptoms. Persistent wheezing may necessitate intravenous aminophylline treatment. For profound shock and hypotension, intravenous fluids, vasopressors and oxygen also may be needed. Maintenance of an open airway is critical if upper airway obstruction is present. Corticosteroids may provide benefit if symptoms are prolonged or recurrent.

Mite extract is a sterile solution containing the extractables of mite whole bodies in 0.25% sodium chloride, 0.125% sodium bicarbonate, 50% glycerol by volume and 0.4% phenol as a preservative. The mites are grown on a medium of yeast and pork and are handled and cleaned in a manner to remove more than 99% of the food medium. The medium contains no material of human origin. This extract may be administered by the scratch, prick-puncture, or intradermal methods of skin testing for diagnostic purposes and subcutaneously for therapeutic purposes as directed under Dosage and Administration.

Intradermal skin tests in patients who were puncture test positive (Sum E ≥ 40 mm) to either D. farinae or D. pteronyssinus extract were performed with extracts of the mite food medium obtained from the same supplier. The results, submitted to the FDA by several manufacturers, were as follows: By intradermal testing, there was 1 positive (Sum E ≥ 20 mm) in 44 individuals at an estimated 1% level of medium content (approximately the same as contained in the mite extract). At a ten-fold increase (estimated 10% medium content), 4 positives in 40 individuals were observed. Two of the individuals who were skin test positive to the mite extract and
who also were skin test positive to the medium extract were also skin test positive to an extract of yeast (Saccharomyces sp.) when tested by the puncture method.

The extract is standardized by comparing its relative potency by ELISA competition to a U.S. reference mite extract available from the Center for Biologics Evaluation and Research, U.S. Food and Drug Administration. The U.S. reference extract has been assigned a potency of 10,000 AU/mL based on quantitative skin testing (1).

The mechanism for the pharmacologic action of allergenic extracts used diagnostically is based on the liberation of histamine and other substances when the allergen reacts with IgE antibody attached to mast cells. The mechanism of the therapeutic effect is not well understood and further research is required to substantiate current hypotheses.

Mites belonging to the genus Dermatophagoides are found in approximately 80% of house dust samples throughout the world (2,3). D. farinae is common in much of the United States (3), although D. pteronyssinus is predominant in certain coastal regions and both species are commonly found in homes (4,5).

The diagnosis of mite allergy is established by the allergy history and skin test reactivity (6,7).

Immunotherapy with mite extract has been studied by several investigators. It is generally believed that hyposensitization with this product is helpful in reducing symptoms associated with house dust allergy (8,9).

Extract of D. farinae and D. pteronyssinus containing 5,000 and 10,000 Allergy Units per mL is supplied in 50% glycerol v/v in 10 mL, 30 mL and 50 mL vials. Extract containing 10,000 Allergy Units per mL is supplied in 50% glycerol v/v in dropper vials for scratch or prick-puncture testing. An equal v/v mixture of the two mites is offered in 10, 30 and 50 mL vial sizes at a concentration of 2,500 AU/mL or 5,000 AU/mL for each mite. See DESCRIPTION above for the complete list of the active and inactive ingredients of this product.
Extract of D. farinae and D. pteronyssinus may be diluted in sterile buffered saline containing 0.4% phenol or in sterile buffered saline containing human serum albumin and 0.4% phenol.

STORAGE AND HANDLING

Extract should be stored at 2-8°C since higher temperatures may adversely affect stability. Do not freeze.