Penicillins are a group of betalactam antibiotics. Two types of penicillins are in clinical use. One is penicillin G and the other is penicillin V.

Penicillin V is also called phenoxymethylpenicillin. It is given by oral route and used for a number of bacterial infections including strep throat, otitis media and cellulitis. It is contraindicated in people who have shown allergic reaction to any penicillin before.

Penicillin G is also called benzylpenicillin. It is given by IV (intravenous) or IM (intramuscular) route. It is used to treat a number of bacterial infections including strep throat, pneumonia, syphilis, cellulitis, etc.

Penicillin G can cause severe allergic and anaphylactic reactions that can prove fatal. These are type 1 hypersensitivity reactions mediated by IgE antibodies. IgE antibodies cause degranulation of mast cells and release of histamine and other proinflammatory mediators. Such reactions occur only in 0.02 to 0.04% of the people, that means, one out of 2500 or 5000 people. The percentage is very low, however, it is always recommended to perform penicillin allergy test before giving someone penicillin G for the first time.

Let's see how we can do this test. Penicillin allergy test is performed when you are about to give penicillin G to someone for the first time. For this test, mark a circle on the forearm of the patient with a marker or ballpoint pen. Write current time near the circle or note it down on some notebook. Then inject about 1ml of penicillin G just below the skin in the dermis layer of the skin. Do not go too deep into the subcutaneous tissue layer. Remain in the dermis layer of the skin which is only a few millimeters in thickness.

After giving intradermal injection, wait for about 20 minutes. After 20 minutes, check the area where you gave injection. If it is showing signs and symptoms of an allergic reaction, it means allergy test is positive and penicillins should not be given to that patient.

In a positive allergy test, redness and severe itching can occur at the site of injection. Hives may also form. Hives are itchy raised skin lesions which may be red. They are also called urticaria. For example, a mosquito bite usually causes hives to form at the site of bite.

In the video, allergy test was negative. Because no extra redness or itching was present. No hives were formed.

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