Penicillin Allergy

What is Penicillin Allergy?

Alexander Flemming discovered penicillin, an antibiotic, in 1928. It came into widespread use by 1942 to tackle different bacterial infections caused by staphylococcus and streptococcus bacteria. Even today, penicillin is one of the most common prescriptions for antibiotics. Interestingly, penicillin is the cause of many reported medication allergies too.

The penicillin antibiotic family includes variations like ampicillin, amoxicillin, and also includes groups like cephalosporins, monobactams, carbapenems, and beta-lactamase inhibitors. Though all these antibiotics share a common base structure, they differ in other parts attached to this base, just like a tree with a common trunk but different branches.

It is essential to correctly identify whether a patient is truly allergic to penicillin. This is because the majority (approximately 80-90%) of people who were once thought to be allergic to penicillin can actually tolerate it. Being able to use penicillin reduces the need for antibiotics that treat a wide range of bacteria, thus limiting the chance of creating “superbugs” that are resistant to multiple drugs.

What Causes Penicillin Allergy?

Penicillin is a type of antibiotic that falls under the category of beta-lactam antibiotics. This family includes various forms such as penicillin G and V, procaine penicillin, benzathine penicillin, and over 15 other related compounds known for their broad antibacterial properties. They work to fight off a wide range of bacterial infections.

However, some people might experience allergic reactions to penicillin, most commonly deriving from type 1 and type 4 hypersensitivity reactions. Severe allergies to penicillin are typically type 1, caused by an immune system substance called IgE. Higher chances for such reactions occur if penicillin is given in high doses, administered through a vein or muscle (parenteral administration), or used frequently.

These severe reactions commonly take place between the ages of 20 and 49. In the past, doctors would avoid prescribing certain antibiotics related to penicillin, such as cephalosporins, because they were worried about cross-reactivity. This means if you’re allergic to penicillin, you might also be allergic to related antibiotics.

However, recent studies show that the potential for cross-reactivity depends on the similarities in the chemical structures of certain parts of these drugs, called R-side chains. This understanding now allows doctors to use some antibiotics they previously avoided due to concerns over potential allergic reactions. Particularly, amoxicillin, a type of penicillin, is the most common to cause cross-reactivity.

Risk Factors and Frequency for Penicillin Allergy

About 10% of patients claim they’re allergic to penicillin, but this is often inaccurate and up to 90% of them don’t have a real allergy. The chance of having a severe allergic reaction, anaphylaxis, is very low, ranging from 0.02% to 0.04%. The most common reaction is a skin rash. The immune system response that causes the allergy gradually reduces over time. Therefore, if you’ve tested positive for a penicillin allergy in the past, each year there’s a 10% decrease in the chance you’ll test positive again. This means that if you stay away from penicillin, after about 10 years, between 80% to 100% of people will test negative for the allergy.

Another important thing to know is that sometimes the symptoms that were thought to be penicillin allergies were actually due to a coinciding bacterial or viral infection. For instance, a skin rash could be mistaken as an allergy, but it was actually caused by the Epstein-Barr virus.

Penicillin is similar to other medications in its family, which has led to people avoiding these drugs due to fear of an allergic reaction. For example, cephalosporins, which are a type of antibiotic, were initially suspected of causing similar allergic reactions. Early studies might have overestimated this “cross-reactivity” because the early versions of cephalosporins could have been contaminated with tiny amounts of penicillin. Penicillin and cephalosporins are structurally different, and it is more likely to have cross-reactivity with the older versions of cephalosporin rather than the new ones. The newer versions of cephalosporins are therefore safer for people with a confirmed penicillin allergy. Overall, the risk of cross-reactivity is:

Less than 2% for aminopenicillins,
Less than 1% for carbapenems,
Less than 3% for cephalosporins,
Monobactams show no significant cross-reactivity.

Signs and Symptoms of Penicillin Allergy

When someone has an allergic reaction to penicillin, it’s crucial to find out when the drug was given and how it was taken. Details about the when the symptoms started and what they included – such as breathing problems, stomach issues, changes in mental state, skin symptoms or a sudden drop in blood pressure – are also important. For people who have had reactions to penicillin in the past, it’s helpful to know when that happened, how the medicine was taken, how they reacted to other similar drugs, and what was done to treat their allergic reaction. If they were given medicines to treat allergy symptoms and these were effective, this suggests they were certainly allergic to penicillin.

For patients coming in who are currently having an allergic reaction to penicillin, it’s critical to first check for life-threatening issues with their airway, breathing, and circulation. Further examination would involve checking for swelling of the lips, tongue or throat, and any difficulty with swallowing or dealing with saliva. The heart and lungs should also be listened to, for irregular heartbeat, or unusual sounds when breathing, like wheezing or harsh sounds. Confusion and belly pain can also be signs of a severe allergic reaction. Many people with allergic reactions will have skin symptoms like hives, redness, itching and swelling, however, these symptoms might be absent in 10% to 20% of allergic reactions.

Testing for Penicillin Allergy

To confirm if the patient has a certain type of penicillin allergy (known as an IgE mediated penicillin allergy), a penicillin skin test is conducted. This is the only confirmed test for this purpose currently used in the United States. A specially trained allergist should perform the test. This test involves pricking the skin and applying specific substances known as major and minor determinants, as well as a control substance.

About 15 minutes after application, the skin is checked. If a small raised area (known as a wheel) appears that is at least 3 mm in size, along with a redness of the skin (called erythema), the test is considered positive. It’s important to note that this test shouldn’t be performed if you’ve had a severe reaction to penicillin that wasn’t caused by the IgE mechanism.

If the skin test doesn’t show a reaction, another test called the intradermal test may be carried out using the same substances. This involves injecting the substances into the skin instead of just applying them to the surface. Just like the skin test, a positive result is seen if a 3mm or larger raised area and redness appear at the injection site. Readings are taken at around 15 minutes if there was a history of an immediate reaction, and at 48 and 72 hours for a history of a delayed response. In some cases, patients may need to wait up to 6 weeks after the initial test before having the intradermal test.

If both skin tests come up negative, another type of test called a graded-dose challenge may be performed. In this test, the patient is given a very small dose of penicillin (from 1/100th if the initial reaction was severe, to 1/10th of a normal dose), with increasingly larger doses given afterward. After each dose, the patient is observed for 30 to 60 minutes to see if any reaction occurs. If there’s no reaction, the patient is then given a full dose, followed by another period of observation. This test should only be done by a trained allergist and should ideally be conducted at least 4 to 6 weeks after an acute reaction, after using steroids or antihistamines, or if there are any signs of a skin condition like asthma or hives. Keep in mind that the graded-dose challenge shouldn’t be performed if the initial penicillin reaction was severe and was not caused by the IgE mechanism, like in conditions such as Stevens-Johnson syndrome or toxic epidermal necrolysis.

Treatment Options for Penicillin Allergy

If you have a severe allergic reaction (known as an acute IgE mediated reaction) to penicillin, this should be treated promptly based on how serious it is. In the event of a severe allergic reaction known as anaphylaxis, immediate medical attention is required. During this time, you might receive a medication called epinephrine via an injection into your muscle. You may also get additional medications like antihistamines and glucocorticoids, which are types of drugs that help your body deal with the allergic reaction. Treatments of inhaled medicine like albuterol may also be needed if you’re having trouble breathing.

If severe, you will need to be constantly monitored for changes in your heart activity and given fluids through a vein. It’s important to note that anyone having a severe allergic reaction like anaphylaxis should be admitted to the hospital.

If your reaction to penicillin is mild and only involves skin symptoms, then treatment with an antihistamine may be all you need. Antihistamines are medications that can help reduce allergy symptoms like itching and hives.

It’s crucial to remember that if you have a confirmed allergic reaction to penicillin, you should avoid this medication in the future. Another type of antibiotic will be selected for your treatment. If another equally effective antibiotic isn’t available, you might need to undergo a process called drug desensitization.

With drug desensitization, you slowly receive higher amounts of the medication that causes your allergy. This careful approach allows your body to build tolerance for the drug. For those with a history of severe allergic reactions, the initial drug dose should be very small. Desensitization has been very successful in helping patients tolerate drugs they were previously allergic to. However, please note that this approach should not be used for severe non-IgE-mediated reactions, which are other types of serious drug reactions.

There are several skin conditions that can be confused with each other due to similar symptoms. These include:

Acute urticaria (acute hives)
Allergic contact dermatitis (skin irritation from contact with an allergen)
Chronic urticaria (long-term hives)
Erythema multiforme (a type of hypersensitive skin reaction)
Erythema nodosum (red, painful lumps on the lower legs)
Erythroderma (redness and scaling of the skin)
Hypersensitivity vasculitis (inflammation of small blood vessels)
Irritant contact dermatitis (skin irritation from contact with a non-allergenic substance)
Lichen planus (a rash caused by an immune response)
Sweet syndrome (a rare skin condition with fever and painful skin lesions)

Frequently asked questions

Penicillin allergy refers to an allergic reaction to penicillin, which is an antibiotic.

About 10% of patients claim they're allergic to penicillin, but this is often inaccurate and up to 90% of them don't have a real allergy.

Signs and symptoms of Penicillin Allergy include: - Breathing problems - Stomach issues - Changes in mental state - Skin symptoms such as hives, redness, itching, and swelling - Sudden drop in blood pressure - Swelling of the lips, tongue, or throat - Difficulty with swallowing or dealing with saliva - Irregular heartbeat - Unusual sounds when breathing, like wheezing or harsh sounds - Confusion - Belly pain It is important to note that while many people with penicillin allergies will have skin symptoms, these symptoms might be absent in 10% to 20% of allergic reactions.

Some people might experience allergic reactions to penicillin, most commonly deriving from type 1 and type 4 hypersensitivity reactions. Severe allergies to penicillin are typically type 1, caused by an immune system substance called IgE. Higher chances for such reactions occur if penicillin is given in high doses, administered through a vein or muscle (parenteral administration), or used frequently.

Acute urticaria, allergic contact dermatitis, chronic urticaria, erythema multiforme, erythema nodosum, erythroderma, hypersensitivity vasculitis, irritant contact dermatitis, lichen planus, and Sweet syndrome.

The types of tests needed for Penicillin Allergy include: 1. Penicillin Skin Test: This test involves pricking the skin and applying specific substances known as major and minor determinants, as well as a control substance. A positive result is indicated by the appearance of a raised area (wheel) of at least 3 mm in size and redness (erythema) after 15 minutes. 2. Intradermal Test: If the skin test is negative, an intradermal test may be performed. This involves injecting the substances into the skin instead of just applying them to the surface. A positive result is indicated by the appearance of a raised area and redness at the injection site. 3. Graded-Dose Challenge: If both skin tests are negative, a graded-dose challenge may be performed. This involves giving the patient a small dose of penicillin, followed by increasingly larger doses. The patient is observed for any reaction after each dose. It's important to note that these tests should be performed by a trained allergist and should not be done if there was a severe reaction to penicillin that wasn't caused by the IgE mechanism.

The treatment for a severe allergic reaction to penicillin, known as an acute IgE mediated reaction, involves prompt medical attention. In cases of severe allergic reactions like anaphylaxis, immediate medical attention is required, and medications such as epinephrine, antihistamines, glucocorticoids, and inhaled medicine like albuterol may be administered. Constant monitoring of heart activity and fluid administration through a vein may also be necessary. It is important to note that anyone experiencing a severe allergic reaction should be admitted to the hospital. For mild reactions that only involve skin symptoms, treatment with an antihistamine may be sufficient. It is crucial to avoid penicillin in the future if a confirmed allergic reaction has occurred, and an alternative antibiotic will be selected. In cases where no equally effective alternative is available, drug desensitization may be considered, where the patient gradually receives higher amounts of the medication to build tolerance. However, this approach is not suitable for severe non-IgE-mediated reactions.

When treating a penicillin allergy, there can be side effects from the medications used. Some potential side effects include: - Injection of epinephrine: possible side effects include increased heart rate, increased blood pressure, anxiety, and tremors. - Antihistamines: possible side effects include drowsiness, dry mouth, and dizziness. - Glucocorticoids: possible side effects include increased appetite, weight gain, and mood changes. - Inhaled medicine like albuterol: possible side effects include increased heart rate, tremors, and headache. It's important to note that these side effects can vary depending on the individual and the specific medications used. It's always best to consult with a healthcare professional for personalized advice and guidance.

If a patient has tested positive for a penicillin allergy in the past, there is a 10% decrease in the chance of testing positive again each year. This means that after about 10 years, between 80% to 100% of people will test negative for the allergy. The most common reaction to penicillin allergy is a skin rash, and the chance of having a severe allergic reaction, anaphylaxis, is very low, ranging from 0.02% to 0.04%.

A specially trained allergist.