BENZYLPENICILLIN TEST DOSE PROCEDURE

A) Dilute the drug to 10,000 units/mL as shown below:

Material: Penicillin G 600mg/vial (1,000,000u/vial)

Dilution method:

1. Pen G 1 vial + 1ml water for injection = 1,000,000u/ml (Solution A)
2. With 10 ml syringe with needle, dilute 0.1 ml of Solution A with 10 ml water for injection = 100,000 units/ml (Solution B)
3. With 10ml syringe, dilute 1ml of Solution B with 10ml of water for injection= 10,000 units/ml

*This dilution is used for testing (prick and intradermal).

B) Prick or percutaneous testing is done first.

Reagents for prick and intradermal:

1. Negative Control:  Sodium chloride solution without preservative
2. Penicillin G 10,000 U/ml (a minor determinant)

Method:

a)      A drop of the diluted drug (Penicillin G 10,000 U/ml) is placed on the ventral surface of the forearm and the skin pricked through the drop.

b)      Prick-puncture skin testing results are read 15 minutes after application:

Results interpretation
Positive response	Wheal that is ≥3 mm in mean diameter than the negative control.
Negative response	No reaction at the prick site or erythema alone without a wheal.

c) If the prick test is negative, it is followed by the intradermal skin test.

 C) INTRADERMAL SKIN TEST

a)      The forearm is injected 0.02 - 0.03 ml using the same reagents intradermally.

b)      Read the results 15 to 20 minutes after application:

Results interpretation
Positive response	Wheal that has increased in size from the original bleb & is ≥ 3 mm in mean diameter than the negative control.
Negative response	No increase in the size of the original bleb and no wheal greater than the control site.

TEST DOSE CHALLENGE WHEN SKIN TESTING IS NEGATIVE 

Test dose may be given and then observe for 30 minutes, followed by the remaining or full oral dose with monitoring for 30-60 minutes.

References:

1. Beta-lactam antibiotic skin testing and oral challenge. From the ACAAI 2015 Drug Allergy and Anaphylaxis Committee

2. Saniel, Mediadora C., et al. "Antibiotic Skin Testing." Workshop held on February. Vol. 5. 1991.

3. Solley, Graham O. "Testing for drug allergy." Australian Prescriber 17.3 (1994).

4. www.uptodate.com