Penicillin skin testing is the most reliable way to evaluate patients for IgE - mediated penicillin allergy. Skin testing is conducted using benzylpenicilloyl polylysine (major determinant), penicillin G diluted with normal saline to 10,000 units/ml (minor determinant), a positive and negative control. Testingwith both the major and minor determinant of penicillin can identify up to 97% of patients with an immediate hypersensitivity to penicillin.
Penicillin skin testing can be done electively when a patient is well and not in immediate need of antibiotic therapy or alternatively, when a patient is in need of antibiotics and treatment with penicillin is being considered. If done electively, it is important to carefully document the results of the testing (e.g., in the problem list and as an annotation to the drug allergy history). There is lack of agreement regarding the need to perform an elective challenge with penicillin immediately after a negative penicillin skin test result.
Skin testing should be performed in a two-step manner:
Step 1) Puncture or prick test (inner volar aspect of the forearm):
Using a 22-28-gauge needle, apply a small drop of skin test antigen to the test site, then puncture the epidermis using the same needle, do not draw any blood. Using separate needles, follow the same procedure for applying penicillin minor determinant mixture (MDM-penicillin G diluted with normal saline to a concentration of 10,000 units/ml), positive control (histamine base 1.0 mg/ml)) and negative control (normal saline). Read in
15-20 minutes:
a. If change in diameter of wheal is <3 mm than that observed with the negative control, test is
negative, proceed to intradermal test
b. If change in diameter of wheal is >3 mm that that observed with the negative control, test is
positive. As soon as a positive response is observed, the solution should be wiped off the skin.
Patient is NOT to receive penicillin.
c. The positive control (histamine skin test) should be positive to ensure the results are not
falsely negative.
Step 2) Intradermal test
(upper, outer arm, sufficiently below the deltoid muscle or the inner volar aspect of the forearm) conducted only if the puncture or prick test is negative. Using a 26-30 gauge, short bevel needle, withdraw the contents of the ampule and inject a sufficient amount of benzylpenicilloyl polylysine to raise a small intradermal bleb of about 3 mm in diameter; in duplicate at least 2 cm apart. Mark the margins of initial bleb with a pen. Using separate syringes and needles, inject a like amount of penicillin G [MDM-diluted to 10,000 units/ml] in duplicate at least 2 cm apart and a single intradermal test using the negative control, spaced at least 5 cm apart from the antigen test
sites. Read in 20 minutes:
d. If there is no increase in the original bleb and no greater reaction than the negative control
site, test is negative.
e. If bleb or wheal increases >2 mm from its original size or is >2 mm larger than the negative
controls, the test is positive. Patient is NOT to receive penicillin
f. If the negative control (saline) site exhibits a wheal >2-3 cm, repeat the test. If the same
reaction is observed, a provider experienced in allergy skin testing should be consulted.
Step 3) (Optional) Oral penicillin (e.g., amoxicillin 250 mg administered in a monitored setting for
45-60 minutes) challenge if both puncture and intradermal tests are negative. However, this step is considered as optional since these tests are rarely positive after negative skin testing.
Some patients may develop an intense local inflammatory response at the skin test site. In rare cases,
patients may develop systemic allergic reactions from skin testing with benzylpenicilloyl polylysine.
These reactions may manifest as generalized erythema, pruritis, angioedema, and shortness of breath,
hypotension and anaphylaxis. To minimize the risk of systemic reactions, a puncture skin test should
be performed first. Intradermal skin testing should be performed only if the puncture test is entirely
negative.
Because of the risk for systemic allergic reactions, including anaphylaxis, skin testing should be performed in an appropriate healthcare setting supervised by healthcare providers experienced and prepared to manage these types of reactions. When treating a benzylpenicilloyl polylysine induced reaction, it is recommended that a venous occlusion tourniquet be applied proximal to the skin test site and epinephrine be administered. The patient should be kept under observation for several hours
