Drug Allergies

Topic Overview

What is a drug allergy?

A drug allergy happens when you have a harmful reaction to a medicine you use. Your body’s immune system fights back by setting off an allergic reaction. Most drug allergies are mild, and the symptoms go away within a few days after you stop using the medicine. But some drug allergies can be very serious.

Some drug allergies go away with time. But after you have an allergic reaction to a drug, you will probably always be allergic to that drug. You can also be allergic to other drugs that are like it.

A drug allergy is one type of harmful, or adverse, drug reaction. Symptoms and treatments of different kinds of adverse reactions vary. So your doctor will want to find out if you have a true drug allergy or if you have another type of bad reaction that isn't as serious.

What are the symptoms?

The symptoms of a drug allergy can range from mild to very serious. They include:

• Hives or welts, a rash, blisters, or a skin problem called eczema. These are the most common symptoms of drug allergies. See a picture of skin reactions caused by drug allergies.
• Coughing, wheezing, a runny nose, and trouble breathing.
• A fever.
• A serious skin condition that makes your skin blister and peel. This problem is called toxic epidermal necrolysis, and it can be deadly if it is not treated.
• Anaphylaxis, which is the most dangerous reaction. It can be deadly, and you will need emergency treatment. Symptoms, such as hives and trouble breathing, usually appear within 1 hour after you take the medicine. Without quick care, you could go into shock.

What medicines commonly cause an allergic reaction?

Any medicine can cause an allergic reaction. A few of the most common culprits are:

• Penicillins (such as nafcillin, ampicillin, or amoxicillin). These types of medicines cause the most drug allergies.
• Sulfa medicines.
• Barbiturates.
• Insulin.
• Vaccines.
• Anticonvulsants.
• Medicines for hyperthyroidism.

If you are allergic to one medicine, you may be allergic to others like it. For example, if you are allergic to penicillin, you may also be allergic to similar medicines such as cephalosporins (cephalexin or cefuroxime, for example).

People with AIDS or lupus may be allergic to many types of medicines. The reactions usually aren't dangerous, but they can make it hard to treat the disease.

Some people—especially those with asthma—have reactions to common pain relievers such as aspirin and ibuprofen. These seem like allergic reactions but they are not, because they do not affect the immune system. But these reactions can be severe in people who have asthma.

How is a drug allergy diagnosed?

Your doctor will diagnose a drug allergy by asking you questions about the medicines you take and about any medicines you have taken in the recent past. Your doctor will also ask about your past health and your symptoms. He or she will do a physical exam.

If this doesn't tell your doctor whether you have a drug allergy, then he or she may do skin tests. Or your doctor may have you take small doses of a medicine to see if you have a reaction. In some cases, you may need a blood test or other type of testing.

How is it treated?

The best thing you can do for a drug allergy is to stop taking the medicine that causes it. Be sure to wear a medical alert bracelet or other jewelry that lists your drug allergies. If you are in an emergency, this can save your life. You also should know what to do if you have an allergic reaction.

• Talk to your doctor to see if you can take another type of medicine.
• If you have an allergic reaction that threatens your life, you may need to give yourself an epinephrine shot and seek emergency medical treatment. Call 911 right away if you have trouble breathing or if you start to get hives. You may also need to take other medicines, such as antihistamines and steroid medicines. A doctor may put these medicines directly into your vein (IV).
• If you have a mild allergic reaction, over-the-counter antihistamines may help your symptoms. You may need prescription medicine if these do not help or if you have problems with side effects, such as drowsiness.

If you can't change your medicine, your doctor may try a method called desensitization. This means that you will start to take small amounts of the medicine that caused your reaction. You will then slowly increase how much you take. This lets your immune system "get used to" the medicine. After this, you may no longer have an allergic reaction.

Frequently Asked Questions

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	Allergies in children: Giving an epinephrine shot to a child
	Allergies: Giving yourself an epinephrine shot

Symptoms

Symptoms of drug allergies can be mild or life-threatening and usually appear within 1 to 72 hours. They include:

• Hives or welts, rash, blisters, or eczema. These are the most common symptoms of drug allergies. See a picture of skin reactions caused by drug allergies.
• Coughing, wheezing, runny nose, and difficulty breathing.
• Fever.
• Toxic epidermal necrolysis, which is a serious life-threatening condition that involves blistering and peeling of the skin.
• Anaphylaxis, which is the most serious reaction. It is life-threatening, and you will need emergency treatment. Symptoms usually appear within 1 hour after you take the medicine and include hives, difficulty breathing, and shock.

A drug allergy can also affect the liver, kidneys, and lymph system. But you usually do not have any symptoms in this case.

Medicines may also cause:

• Serum sickness. This rare condition usually begins 6 to 21 days after you take the offending medicine. Symptoms include fever, weakness and body aches, joint pain, and skin eruptions, such as hives or a rash.
• Medicine fever. Symptoms usually begin 7 to 10 days after you take this medicine. They include high fever and chills and sometimes a skin rash. When you stop taking the medicine, the fever usually drops within 48 to 72 hours.
• Autoimmune disorders. Drug allergies can cause several autoimmune disorders, such as drug-induced lupus, vasculitis, andmyasthenia gravis, although these are rare. See more information on medicines and lupus.
• Destruction of platelets and red blood cells, resulting in thrombocytopenia and hemolytic anemia, respectively. Symptoms of thrombocytopenia include bruising easily, red spots around the feet and ankles, and nosebleeds. Symptoms of hemolytic anemia include fever, chills, shortness of breath, and a rapid heart rate.

When to Call a Doctor

Call 911 or other emergency services right away if:

• You develop hives and have trouble breathing or other symptoms of anaphylaxis. If you have an epinephrine shot, give it to yourself while you have someone else call 911.

See pictures of hives and a skin rash caused by a drug allergy.

Call your doctor if:

• Your face, tongue, or lips are swollen, even if you are not having trouble breathing and the swelling is not getting worse.
• You develop a skin rash, itching, a feeling of warmth, or hives.
• Home treatment does not help and symptoms get worse.

Exams and Tests

Your doctor will diagnose a drug allergy by asking you questions about the medicines you are or have recently been taking, your past health, and your symptoms (medical history) and by doing a physical exam. To find out which medicine is causing your allergic reaction, your doctor will consider:

• Your medicine. Some medicines are more likely to cause an allergic reaction than others.
• Whether you have a drug allergy or another adverse reaction to medication. You have more treatment options if you have an adverse reaction that does not involve the immune system.
• How many medicines you are taking. If you take several medicines, the medicine you began taking most recently is often the cause.

Your doctor probably will ask you to stop taking the medicine that is most likely to be causing the reaction. If this does not help, your doctor may ask you to stop taking other medicines, until you can find which medicine is causing the allergic reaction.

If your doctor cannot find out which medicine is causing the reaction, he or she may suggest a skin test. In a skin test, your doctor will place a small amount of medicine on or under your skin to see if your body reacts to it. But a skin test does not work for all medicines, and you risk having a severe reaction.

Skin tests can diagnose allergies to:

• Penicillin, which is the most common cause of drug allergies.
• Insulin.
• Heterologous serum (used in the prevention or treatment of botulism, diphtheria, severe gangrene, organ transplant rejection, and snake and spider bites).
• Streptokinase (used to dissolve blood clots).
• Chymopapain (used for herniated discs).

Another way to find the cause of your allergic reaction is a medicine challenge. In a medicine challenge, you start by taking small doses of a medicine and slowly increase how much you take to see whether you have an allergic reaction. This challenge is usually done where emergency medical help is available and under the supervision of a health professional.

If you have medicine fever, serum sickness, or other complications, you may need more tests. These tests include a chest X-ray and blood tests to see how well your liver and kidneys are working.

Treatment Overview

Treatment for drug allergies includes understanding what to do if you have a severe allergic reaction, avoiding the medicine that causes the allergy, and using medicines such as antihistamines for mild symptoms.

Emergency treatment

Call 911 or other emergency services immediately if:

• You develop hives and have trouble breathing or other symptoms of anaphylaxis. If you have an epinephrine shot, give it to yourself while you have someone else call 911. See pictures of hives and a skin rash caused by a drug allergy. For more information, see:

Allergies: Giving yourself an epinephrine shot.

Allergies in children: Giving an epinephrine shot to a child.

If you have a severe allergic reaction, your first treatment may occur in an emergency room, or emergency personnel may treat you where the reaction occurs. If you have not already given yourself an epinephrine shot, you may get one to help you breathe. You may also get antihistamines and corticosteroids.

Other treatment

You treat a drug allergy by avoiding the medicine that causes the allergic reaction. When your doctor knows which medicine is causing your reaction, he or she will find another medicine for you to use. If this is not possible, your doctor may suggest desensitization therapy.

In desensitization therapy, you start taking small amounts of the offending medicine and gradually increase how much you take. This lets your immune system "get used to" the medicine, and you may no longer have an allergic reaction to it. Because you may have a severe reaction during this therapy, it is done where emergency medical help is available and under the supervision of a health professional.

If you have a mild allergic reaction, several medicines may help ease symptoms. Prescription or over-the-counter antihistamine tablets or syrup, such as diphenhydramine hydrochloride (for example, Benadryl) or chlorpheniramine maleate (for example, Chlor-Trimeton), may lessen rash, itching, and other symptoms. Your doctor may also suggest corticosteroid medicine to decrease your symptoms. Take these medicines as your doctor tells you.

If you have severe drug allergies:

• Your doctor may give you an allergy kit that contains a shot of epinephrine and antihistamine tablets. Give yourself the epinephrine shot as soon as you feel a reaction starting. Then take the antihistamines. For more information, see:

  Allergies: Giving yourself an epinephrine shot.

  Allergies in children: Giving an epinephrine shot to a child.

• Go to the emergency room every time you have a reaction, even if you are feeling better. Symptoms can develop again even after the epinephrine shot.
• Keep your allergy kit with you at all times. Be sure to check the expiration dates on the medicines and replace them as needed.
• Always wear medical alert jewelry that lists your drug allergies. You can get this type of jewelry at most drugstores or on the Internet.

If you have allergies to many different medicines, be careful when you start any new medicine. The first time you take a new medicine, take it at your doctor's office or at a hospital where you can get immediate treatment if you have a reaction.

What To Think About

People with AIDS or lupus may have more drug allergies than other people. While the reactions are usually not life-threatening, they make treating the disease more difficult.

If you are allergic to one medicine, you may be allergic to other closely related medicines. For example, if you are allergic to penicillin, you may also be allergic to similar antibiotics such as cephalosporins (cephalexin or cefuroxime, for example).

Home Treatment

Home treatment for a drug allergy includes avoiding medicines that can cause an allergic reaction, relieving symptoms, and knowing what to do if you have a severe reaction.

Avoiding allergic reactions

You can help avoid future allergic reactions by knowing which medicines you are taking.

• Keep a list of all the medicines you take, including supplements and over-the-counter medicines. Share this list with your doctor. This will help him or her identify a medicine you may be allergic to.
• Whenever you start a new medicine, ask your doctor if it may cause an allergy. This includes asking about supplements and over-the-counter medicines. You may have to take the medicine for the first time in your doctor's office.
• Do not use someone else's medicine or share yours. A medicine may appear the same but have a part that can cause a reaction.

Relieving symptoms

If you have a mild skin rash, you can take steps to make yourself more comfortable and relieve itching.

• Take cool showers, or apply cool compresses.
• Wear light clothing that doesn't bother your skin.
• Take it easy. Keep your activity level low.
• Use calamine lotion or take over-the-counter antihistamines, such as diphenhydramine (such as Benadryl), chlorpheniramine maleate (such as Chlor-Trimeton), or loratadine (such as Claritin).
• Stay away from strong soaps, detergents, and other chemicals, which can make itching worse.

Other Places To Get Help

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Related Information

• Dealing With Medicine Side Effects and Interactions
• Food Allergies
• Rash, Age 11 and Younger
• Rash, Age 12 and Older
• Swelling

References

Other Works Consulted

• Dykewicz MS, Gray HC (2006). Drug allergies. In DC Dale, DD Federman, eds., ACP Medicine, section 6, chap. 14. New York: WebMD.
• McNeil D (2009). Allergic reactions to drugs. In RE Rakel, ET Bope, eds., Conn's Current Therapy 2009, pp. 781–784. Philadelphia: Saunders Elsevier.
• Anderson JA (2007). Allergic and allergic-like reactions to drugs and other therapeutic agents. In P Lieberman, JA Anderson, eds., Allergic Diseases Diagnosis and Treatment. 3rd ed., pp. 295–318. Totowa, NJ: Humana Press.
• Archer GE, Polk RE (2008). Treatment and prophylaxis of bacterial infections. In AS Fauci et al., eds., Harrison's Principles of Internal Medicine, 17th ed., vol. 1, pp. 851–864. New York: McGraw-Hill.
• Celik G, et al. (2009). Drug allergy. In NF Adkinson Jr et al., eds. Middleton's Allergy Principles and Practice, 7th ed., vol. 1, pp. 1205–1226. Philadelphia: Mosby Elsevier.
• Roujeau J, et al. (2008). Cutaneous drug reactions. In AS Fauci et al., eds., Harrison's Principles of Internal Medicine, 17th ed., vol. 1, pp. 343–349. New York: McGraw-Hill.

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