Penicillin allergy

Introduction

Penicillin and related antibiotics are effective for treating bacterial infections. But if you have a penicillin allergy, taking these drugs can be dangerous.

Penicillin and related antibiotics can cause an allergic reaction in some people. Not all adverse reactions to penicillin are a sign of an allergic reaction. True allergic reactions involve the immune system and can cause signs and symptoms that range from an annoying rash to a life-threatening reaction (anaphylaxis) with low blood pressure and trouble breathing.

It isn't clear why some people develop penicillin allergy while others don't. Treating an allergic reaction may require taking medications or, in the case of a serious reaction, emergency care.

Signs and symptoms

Signs and symptoms of a penicillin allergy include:

• Hives
• Rash
• Itchy skin
• Wheezing
• Swollen lips, tongue or face (angioedema)

Tell your doctor if you notice any of the signs or symptoms of penicillin allergy. He or she can determine if you're having an allergic reaction and may prescribe an alternate antibiotic.

Anaphylactic reactions
The most serious allergic reaction to penicillin is an anaphylactic (an-uh-fuh-LAK-tik) response, which can be life-threatening. Anaphylactic reactions develop immediately after penicillin exposure in highly sensitive people. Anaphylactic reactions cause the airways to constrict and low blood pressure. Signs and symptoms include:

• Constriction of the airways, including wheezing and a swollen tongue or throat, that results in difficulty breathing
• Shock associated with a marked decrease in blood pressure
• Weak and rapid pulse
• Dizziness or fainting
• Hives and itching
• Flushed or pale skin
• Nausea, vomiting or diarrhea

Seek emergency medical care if you think you or someone else is having an anaphylactic reaction.

A drug rash usually starts within two weeks of taking a new medication and begins as discrete red spots that spread, covering large areas of the body.

Causes

Penicillin allergy occurs when your immune system responds to the drug as if it were a harmful substance instead of a helpful remedy. Your immune system creates antibodies to attack the medication. Chemicals released by your immune cells can cause the signs and symptoms associated with an allergic reaction.

Penicillin belongs to a family of drugs called beta-lactam antibiotics. These drugs include penicillin and amoxicillin, which are relatively inexpensive and effective at treating many common bacterial infections. Such infections include skin, ear, sinus and upper respiratory infections.

Taken orally or injected, penicillin works by stopping the growth of bacteria in your body. Several varieties of penicillin exist, and each targets a different infection in a different part of your body. You may have heard of some of the other drugs in the penicillin family, including:

• Amoxicillin
• Ampicillin
• Dicloxacillin
• Nafcillin
• Penicillin V
• Penicillin G

Some people allergic to penicillin may also be allergic to cephalosporins, a class of antibiotics closely related to penicillin. Around 4 percent of those with a known penicillin allergy have an allergic response to these medications.

You aren't born allergic to penicillin, but you can develop penicillin allergy once you've been exposed to the drug. After that, re-exposure to penicillin or related antibiotics can trigger an allergic reaction.

Risk factors

It isn't clear why some people develop penicillin allergies while others don't. However, certain people seem to be at greater risk of developing a penicillin allergy than others are. Heredity may play a role, as well as exposure to multiple medications over time.

While anyone can have an allergic reaction to drugs in the penicillin family, you appear to be at higher risk if:

• You're female
• You have HIV/AIDS
• You have cystic fibrosis
• You've had allergic reactions to penicillin or another drug in the past

When to seek medical advice

Talk to your doctor if you think you're allergic to penicillin or if you experience any signs or symptoms of penicillin allergy. If possible, see your doctor when the allergic reaction is occurring. This will aid in making a diagnosis.

Seek emergency medical treatment if you develop any signs or symptoms of anaphylaxis.

Screening and diagnosis

Your doctor will want to know about your past reactions to penicillin and may examine you to identify or exclude other medical problems. He or she may also recommend a skin test. This test, in which your skin is injected with small amounts of penicillin, can determine your sensitivity to the drug. A small amount of penicillin is injected into the skin of your forearm or back. If you're allergic to the particular substance being tested, you develop a red, raised bump or reaction. Only specialized allergy centers perform skin tests for penicillin allergy.

Treatment

If you're having an allergic reaction after taking penicillin or another drug in the penicillin family, your doctor will have you stop taking the medication. In most cases, penicillin allergy treatment consists of avoiding penicillin and using another antibiotic instead.

Treatment for signs and symptoms depends on what kind of reaction you have.

• Anaphylaxis is the most rare and serious possible allergic drug reaction. It can be life-threatening and requires an injection of epinephrine (adrenaline) and emergency care to maintain blood pressure and support breathing.
• Rashes or hives may improve when treated with an antihistamine such as diphenhydramine (Benadryl, others). More severe reactions may require treatment with oral or injected corticosteroids.

Prevention

The best way to avoid an allergic reaction to penicillin is to avoid penicillin and similar antibiotics altogether. If you're allergic to penicillin, it doesn't mean you're necessarily allergic to all antibiotics. Your doctor may be able to give you an antibiotic that's distantly related to penicillin without causing any problems. A number of antibiotics completely unrelated to penicillin also are available.

For some infections, it may be absolutely necessary for you to take penicillin. In these cases, and if you previously experienced a reaction to penicillin, an allergy skin test may be important. If the skin test reveals that you're sensitive to penicillin, your doctor may recommend desensitization.

During the desensitization process, you receive small but gradually increasing doses of penicillin orally or intravenously. Because desensitization can trigger an allergic reaction, it's attempted only in a controlled setting, usually a hospital — and only when penicillin is absolutely necessary. Your desensitization lasts only as long as you continue taking penicillin. If you stop and then need to take penicillin again later, you'll need to go through the desensitization process again.

The process of desensitization generally takes one to two days. However, it doesn't work in all cases.

Self-care

If you think you've had reactions to penicillin in the past, be sure to tell your doctor and other medical professionals, including your dentist. Let your doctor know about any new reactions you notice when taking your medication. If your doctor determines that you're allergic to penicillin, it's a good idea to wear a medical alert bracelet that describes your allergy. You might also want to carry an alert card in your wallet or purse. These items are available over-the-counter at most drugstores or can be purchased on the Internet.