DIAGNOSIS. If the extract supplied in this package is concentrated product (w/v 1:20), it should not be used for intradermal testing. Concentrated extract may be used for scratch or prick testing providing the patient is not exposed to high levels of ragweed pollen and experiencing pronounced symptoms of hay fever or asthma at the time of testing. Extract for intradermal testing must be diluted to a strength of 0.25 units of antigen E per ml
7. Skin tests should not be performed if the patient has taken antihistamine within 24 hours prior to testing.
Scratch Test: 1 drop of extract concentrate applied to a small scratch or scarification of the volar surface of the forearm or the flat aspect of the back.
Prick Test: 1 drop of extract concentrate applied to the unbroken skin of the forearm or the back followed by pricking the skin under the drop.
Intradermal Test: 0.05 ml of extract containing 0.25 antigen E units per ml given intradermally on the volar surface of the forearm or outer aspect of the upper arm. This test should not be performed unless the patient is negative to a properly administered and interpreted scratch or prick test. A final intradermal test using 0.05 ml of extract containing 2.5 antigen E units per ml may be used to rule out skin sensitivity to ragweed allergen.
INTERPRETATION OF RESULTS
Scratch and Prick Test
A negative test shows only a slight red area at the site of scarification or prick penetration. Positive tests are scored as follows:
1+ Erythema with 5 mm wheal
2+ Erythema with 5 — 10 mm wheal
3+ Erythema with a 10 — 15 mm wheal
4+ Erythema with a wheal 15 mm (or larger) with pseudopodia
A negative test shows no change in the appearance and size of the 5 mm wheal created by the I.D. injection of 0.05 ml of extract. Positive tests are scored as follows:
1+ Erythema with 10-20 mm with a 5-10 mm wheal
2+ Erythema with 20-30 mm with a 5-10 mm wheal
3+ Erythema with 30-40 mm with a 10-15 mm wheal
4+ Erythema greater than 40 mm with a 15 mm wheal (or larger) with pseudopodia
Concentrated ragweed extract must be diluted before administration to new patients. As a rule, extract containing 0.01 to 0.05 units of antigen E per ml are safe to initiate immunotherapy. An intradermal skin test with the intended starting dose may be done as an additional precaution in evaluating the patient’s sensitivity.
Injections should be given subcutaneously in the outer aspect of the upper arm. Care must be taken to avoid injecting the extract into a blood vessel, because of the potential hazard of anaphylaxis. Concentrated extract is usually administered once every two to four weeks at a maximum dose of 0.2 ml. A mild burning sensation immediately following the injection of concentrated extract is due to the glycerol in the extract. It should not be interpreted as an adverse allergic response. A suggested dosage schedule is shown in the Table below.
Patients who have received allergenic extract for maintenance therapy should not be given the same dose from a fresh vial of extract. The antigen E content of ragweed pollen extract varies from lot to lot. Although the potency of fresh extract can be compared with that of previously administered product and adjusted accordingly, it is advisable to reduce the dosage of fresh extract to one-half the amount give from a previous lot. The antigen E content of ragweed pollen extract diminishes during storage and use in the physician’s office, and, therefore, may be less than that specified on the vial label. In addition, ragweed pollen extract contains other components which may contribute to the overall allergenicity of the product 18.
SUGGESTED DOSAGE SCHEDULE FOR RAGWEED EXTRACT BASED ON ANTIGEN E CONCENTRATION (units per ml)
Concentrated extracts (w/v 1:20) of short ragweed pollen usually contain between 100 and 300 units antigen E per ml. Mixed short-giant ragweed pollen extracts contain approximately one-half these values.
|AgE Units 0.01/ml frequency twice weekly||AgE Units 0.1/ml frequency twice weekly||AgE Units 1.0/ml frequency twice weekly||AgE Units 10/ml frequency twice weekly||AgE Units 100/ml frequency twice weekly|
|No. ml||No. ml||No. ml||No. ml||No. ml|
|1 0.025||1 0.025||1 0.025||1 0.025||1 0.025|
|2 0.05||2 0.05||2 0.05||2 0.05||2 0.05|
|3 0.10||3 0.10||3 0.10||3 0.10||3 0.10|
|4 0.15||4 0.15||4 0.15||4 0.15||4 0.15|
|5 0.20||5 0.20||5 0.20||5 0.20||5 0.20|
|6 0.25||6 0.25||6 0.25||6 0.25||6 0.25|
|7 0.30||7 0.30||7 0.30||7 0.30||7 0.30|
Note: Do not exceed a dose of 0.2 ml if the extract being administered contains 50% glycerol by volume
Studies 10, 11 have shown that the accumulated pre-seasonal dose of short ragweed pollen extract should be in the range of 250 to 1000 units of antigen E to effectively reduce ragweed-related symptoms 3, 19. This dosage of antigen E is contained in 2.5 ml to 10.0 ml of extract containing 100 antigen E units/ml. Treatment with a maximum tolerated dose is recommended for both short ragweed pollen extract and mixed short-giant ragweed extract.
The maintenance dose of ragweed pollen extract is defined as the highest tolerated dose that is consistently well tolerated without undue pain or swelling and which provides maximum relief to symptoms. The interval between maintenance injections should not exceed 4 weeks, since tolerance to the extract may be lost at longer intervals. If the interval exceeds 4 weeks, the dosage should be reduced by one-half for every additional two week period. A reduction in the maintenance dose also may be necessary during the ragweed season, due to the overdosing effects of inhaled allergen combined with injected allergen. As a rule, it is advisable to reduce the dosage by one-half during ragweed pollination and to increase the frequency of injections as needed to provide adequate relief symptoms. The dosage of ragweed pollen extract given to children is the same as the adult dose except for slight modifications due to body size and weight. A child’s dose of 0.2 ml is considered comparable to an adult dose of 0.5 ml of the same dilution. Maintenance injection should be continued for a period of two to three years or longer, depending upon patient tolerance and clinical response.
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