PENICILLIN ALLERGYPenicillin allergy is common. Accurate data are not available, but between 1 and 8% of patients report having experienced an allergic reaction to penicillin. Penicillin can cause a variety of skin reactions, involving entirely different mechanisms. Usually, only spots develop, sometimes progressing to a widespread rash. These forms of drug hypersensitivity are bothersome but not dangerous.
However, acute systemic reactions to penicillin, such as hives, shortness of breath, and shock (called anaphylactic shock), are dangerous and a reason to discontinue use of penicillin. Patients with these types of reactions have developed IgE antibodies against penicillin. This type of allergy, also called type I allergy, is much less common, occurring in 0.01 to 0.3% of all patients.HOW IS PENICILLIN ALLERGY DETERMINED?A type 1 allergy to penicillin can be diagnosed with an allergy test. IgE antibodies to penicillin can be detected in the blood. However, this blood test is not sufficiently definitive; a skin test is required. A very small amount of penicillin is injected into the skin, and a reaction (redness and swelling) is observed.HOW GREAT IS THE RISK OF ALLERGIC REACTIONS?If skin tests are negative in patients suspected of having a penicillin allergy, the chance of an acute systemic reaction to penicillin is small (approximately 1.5%).
If skin tests are positive in patients suspected of having a penicillin allergy, the chance of an acute systemic reaction to penicillin is much higher (between 50-70%). This does not mean that all these patients will experience a dangerous reaction. It can range from hives or spots, lightheadedness, mild hoarseness, to general shock with shortness of breath. For safety reasons, this group of patients is advised never to use penicillin again.WHY IS PENICILLIN SOMETIMES GIVEN DESPITE THE ALLERGY?Unfortunately, there are a number of conditions for which penicillin is the only effective treatment. In dermatology, this primarily concerns pregnant patients with lues (syphilis). If syphilis is present during pregnancy, penicillin is the only effective and approved medication during pregnancy. Furthermore, patients may be allergic to all alternative antibiotics, including doxycycline (doxycycline is the alternative antibiotic for treating lues in cases of penicillin allergy).
In these special cases, according to the most recent guidelines, penicillin is administered, with the dosage increased very slowly. Penicillin can be administered through subcutaneous injections, with the dosage increased every 20 minutes, or through an IV. Subcutaneous injections are sensitive and more painful than IV administration, but they allow for better monitoring for any reactions, as these are often already visible around the injection site. If no serious systemic reactions (as mentioned above) occur, the dosage is increased very gradually until the final dose of 2.4 million units of penicillin is reached at the end of the day, which is also the treatment for most forms of syphilis. For neuroleptics, a much longer treatment (10-14 days) is required.HOW DOES PENICILLIN DESENSITIZATION WORK?The type 1 penicillin allergy is caused by special cells in the skin and airways, called mast cells, releasing a substance (histamine), which widens the blood vessels. This causes all the blood to rush to the skin, causing the patient to faint. By initially administering only a very small amount of penicillin (10 units instead of 2.4 million units), a few mast cells will release their histamine. Afterward, these cells are depleted. By gradually increasing the amount of penicillin, eventually all the mast cells will gradually release their histamine and become depleted. The effective dose can then be safely administered at the end of the day.MEASURES TO REDUCE THE RISKGiven the risk of allergic reactions, this type of penicillin desensitization can only be performed in a hospital, where a resuscitation team is always present. The necessary precautions are taken to ensure it can be performed safely. An IV is connected beforehand to allow immediate fluid administration if necessary (if the vessels become dilated, they must be filled more). In addition, blood pressure and pulse are regularly monitored. Medications that can prevent or reduce any allergic reactions are also administered beforehand and, if necessary, during the penicillin administration: prednisone (an anti-inflammatory) and antihistamines (which inhibit the substance histamine responsible for the allergic reaction).INFORMATION AND CONSENT FOR THE TREATMENTGiven the risk of allergic reactions, it is essential that patients are fully informed in advance of what will happen, why it needs to be done, and what the risks are. You are expected to have read and understood this brochure, to be aware of the risks, and to record this in writing and agree to the proposed treatment.DATA THAT MUST BE KNOWN IN ADVANCEBefore treatment, several details must be known. Blood tests (Luesserology) and additional information must clearly indicate that you have active, untreated Lues, requiring penicillin treatment. It must be known whether you are HIV-positive, and, in the case of women, whether there is a possibility of pregnancy. It must also be clear beforehand that there is no infection of the brain or cranial nerves (in which case, there will be neurological symptoms). If there is any doubt about this, a neurologist's examination and a lumbar puncture are necessary. In the event of a brain infection, prolonged (at least 10 days) intravenous penicillin treatment is required immediately after desensitization.AM I NO LONGER ALLERGIC TO PENICILLIN AFTER THIS?Penicillin desensitization doesn't mean you'll be cured of your penicillin allergy. Quite the opposite. It simply involves carefully emptying the mast cells, after which penicillin can be administered. If it needs to be done again later, desensitization will be necessary. A desensitization procedure is only effective for about 12 hours, after which reactions can occur again. Therefore, make sure you don't get another syphilis infection.DESCRIPTION OF THE PROCEDURE- You will be admitted to the hospital. The attending physician will collect your information. If necessary, additional blood tests will be performed, a lung x-ray will be taken, and an ECG (heart tracing) will be performed.
- You must ensure that you have read and understood all information and sign to agree to the treatment.
- You will be given an IV. Only water (0.9% NaCl solution) will be used in the IV.
- Half an hour before the first injection, you will receive 50 mg of prednisone via the IV and an antihistamine (usually in tablet form).
- Your blood pressure and heart rate will be measured.
- You will receive the first injection, a small volume (0.1 ml) containing only 10 units of penicillin, injected just under the skin in your arm or abdomen.
- After 20 minutes, you will receive the next injection, with 20 units. The amount is doubled every 20 minutes. By the end of the day, the dose of one million units will have been reached. Then comes the final dose of 2.4 million. This is also an injection (two injections divided between both buttocks). Afterward, you will remain in the hospital for observation. The next morning, another 25 mg of prednisone will be administered through an IV.
If all goes well, you may go home later that day.LATE COMMENTSLate reactions (spots or bumps on the body) may occur, but these are not significant.
Fever and flu-like symptoms can occur in anyone with syphilis treated with penicillin in the first 24-48 hours. This has nothing to do with a penicillin allergy but is a reaction to the massive breakdown of the bacteria caused by the treatment. |
