Parenteral drug products should be inspected visually for particular matter and discoloration prior to administration whenever solution and container permit.
When diluting bulk extracts, use of Sterile Diluent for Allergenic Extracts or Sterile Diluent for Allergenic Extracts Normal Saline with Human Serum Albumin (HSA) are recommended. Dilutions should be made with sterile disposable syringes using aseptic technique. Commonly 10 fold dilutions are used to achieve a desired concentration for intradermal testing or initiation and continuation of immunotherapy. For example, transferring 0.5 mL of a 10,000 AU/mL extract into 4.5 mL of diluent will yield 5 mL of extract @ 1,000 AU/mL. Prepare as many additional serial dilutions as necessary to reach the appropriate concentration.
Care should be exercised to avoid cross contamination with other allergens if mixing with other allergenic extracts. The use of separate syringes for each allergen and diluent is mandated when compounding patient mixes.
Diagnosis – In diagnosing the sensitive individual, the symptom history must be associated with exposure to the allergen. Skin testing is used in conjunction with a definitive history for diagnosing individual sensitivities.
An excellent method of recording results is to cover the skin reaction with transparent tape, outline the erythema first then the wheal with an indelible pen, then remove the tape and transfer it to the patient’s permanent record. For preferred results, it is recommended that the actual measurement of the extent of both responses be recorded. This can be accomplished by measuring the longest erythema diameter, then selecting the mid-point of that line and measuring at a 90o angle to that line to determine the orthogonal diameter. The sum of these two measurements is the sum of erythema (∑E); the sum of wheal diameters is determined in a similar manner.
Patient’s response is graded on the basis of the size of erythema and/or wheal.
Percutaneous (prick/scratch/puncture) test:
Prick, scratch, or puncture skin tests should be performed initially using an extract specially made for this purpose.
In a skin test study of 12 patients who were determined to be allergic to cat, the mean puncture test (using a bifurcated needle) to a Cat Pelt extract containing 10,000 BAU/mL had a sum of erythema of 71 mm (range 52 – 90 mm) and a sum of wheal of 15 mm (range 4 – 25 mm).
What follows are general guidelines for percutaneous testing13. Different devices and/or techniques influence the size of the reaction; therefore it is important to refer to the device manufacturer’s or distributor’s instructions when grading reactions. As a negative control, the diluent should be tested and included in the interpretation in the skin test reactions. Use of a positive control such as histamine base at 1 mg/mL should be used to assess skin test reactivity.
On the forearm or upper outer aspect of the arm, using a 26 – 27 gauge, short bevel needle, inject intradermally 0.05 mL of the intradermal test solution. Skin whealing responses should be observed 10 – 20 minutes after administering the test.
In a skin test study of the 12 cat puncture reactive patients described previously, the mean intradermal dose for ∑E = 50 mm was 0.03 BAU/mL (range = 1.5 to <0.002 BAU/mL).
Intradermal testing should start with a dilute solution, usually in the range of 0.1 BAU/mL or less.
Glycerinated extracts diluted for intradermal testing may be diluted at least 25 fold to less than 2% glycerin (by volume) as glycerin above this level can cause false positive intradermal skin tests.
A negative skin test is one where the sum of erythema was 0 or equal to the sum of the wheal. As a negative control, the diluent should be tested and included in the interpretation of the skin reactions. What follows are general guidelines for intradermal tests13.
Immunotherapy – Starting dose for immunotherapy is related directly to a patient’s sensitivity as determined by carefully executed skin testing. Degree of sensitivity can be established by determination of D50 (the intradermal dose, base three, that produces a SE = 50 mm).1
A general rule is to begin at 1/10 of the dose that produces sum of erythema of 50 mm (approximately a 2+ positive skin test reaction). For example, if a patient exhibits a 2+ intradermal reaction to 1 BAU/mL, the first dose should be no higher than 0.05 mL of 0.1 BAU/mL. Dosage may be increased by 0.05 mL each time until 0.5 mL is reached, at which time the next 10-fold more concentrated dilution can be used, beginning with 0.05 mL, if no untoward reaction is observed. (See beginning of DOSAGE AND ADMINISTRATION section for instructions in preparing dilutions of concentrates).
If a tolerated dose of allergenic extract has been established, the initial dose from the new extract should be reduced by 75% of the previously well tolerated dose (see also Precautions).
Interval between doses in the early stages of immunotherapy is no more than once to twice a week, and may gradually be increased to once every two weeks. Generally, maintenance injections may be given as infrequently as once every two weeks to once a month. The progress of patients on immunotherapy should be closely monitored. If improvement is realized a usual course of treatment may be from 3 to 5 yeas. If progress is unsatisfactory for a year or more discontinuation of immunotherapy should be considered.
Injections are given subcutaneously preferably in the arm. It is advantageous to give injections in alternate arms and routinely in the same area. In some patients, a local tolerance to the allergen may develop thus preventing a possible severe local reaction.
After inserting the needle, but before injecting the dose, pull plunger of the syringe slightly, if blood returns in the syringe, discard the syringe and contents and repeat injection at another site.
Bulk concentrated extracts must be diluted for initial therapy and intradermal skin testing. For recommended diluent, refer to DOSAGE AND ADMINISTRATION section.
Withhold allergenic extracts temporarily or reduce the dose in patients with any one of the following conditions:
– severe rhinitis or asthma symptoms
– infection or flu accompanied by fever
– exposure to excessive amounts of clinically relevant allergen prior to therapy
Allergenic extracts slowly become less potent with age. During the course of treatment, it may be necessary to continue therapy with a vial of extract bearing a later expiration date. The initial dose of the extract bearing the later expiration date should be lowered to a safe non-reaction-eliciting level. When switching one standardized extract with another, at least 75% reduction in dose is suggested.
Use standard aseptic precautions when making dilutions. The first dose of the new extract should be reduced at least 50% – 75% of the amount of the dosage from the previous extract.
Stability studies for diluted and undiluted forms of this product are not complete. Indications are the undiluted product will retain its potency under recommended storage conditions at least until the expiration date on the vial label is reached. It is recommended that minimal amounts of the concentrate be diluted so that the diluted product is used up within a relatively short period of time, i.e. preferably not more than four weeks.