Adverse Reactions to Medications Adverse Reactions to Medications
American academy of Allergy, Asthma and Immunology

What is a non-allergic reaction to medication?
What is an allergic reaction to medication?
What are common drugs that cause an allergic reaction?
How are drug allergies diagnosed?
What treatments are available for drug allergies?
When should someone see an allergist/immunologist?

Medications are given to help people, but nearly all can have side effects. Adverse reactions to medications are experienced by most individuals at some point in their lives, and the consequences can sometimes be severe. In fact, there are an estimated 106,000 deaths each year related to serious drug allergies.

What is a non-allergic reaction to medication?
Most adverse reactions to drugs are non-allergic. Medicines have a therapeutic window; too little does not work, too much causes problems. When patients take the wrong amount of a drug for their size, age, gender or specific body chemistry, there is a greater chance for an adverse reaction to develop.

Reactions can be severe, such as vomiting and hair loss with cancer chemotherapy, or they can be mild, such as an upset stomach from aspirin and diarrhea from antibiotics. Almost any drug can trigger a reaction in someone, but most are not signs of a drug allergy. Because non-allergic reactions can be unpredictable, it is important to describe your symptoms to the doctor.

Remember to accurately follow instructions given with prescription medications. If you are unclear on how to take a drug, or if you need to know if the effect you are experiencing is severe, contact the physician who wrote your prescription or the Pharmacist who prepared the medication.

What is an allergic reaction to medication?
Most drugs can occasionally cause allergic reactions. However, only about 5% to 10% of adverse reactions to commonly used drugs are allergic, which means that a patient’s immune system overreacts to the drug.

An allergy occurs when a patient’s immune system responds to modified or unusual proteins as a foreign substance. Small molecules tend to bind to proteins and the combinations of these can cause a reaction. The most frequent types of allergic symptoms to medications include:

Skin rashes, particularly hives
Respiratory problems
Swelling of areas of the body that have fat tissue, such as the face

However, a more severe reaction, called anaphylaxis, can result from drug allergies. This occurs when an allergic patient’s immune system produces the allergic antibody called IgE (immunoglobulin E) in response to a drug. Symptoms of anaphylaxis should be carefully monitored because they can result in death. Anaphylaxis requires emergency attention, including an immediate intra-muscular injection of epinephrine (adrenaline). The most common symptoms of anaphylaxis are:

A sense of warmth or flushing
Swelling in the throat or wheezing
Nausea or vomiting
Abdominal cramping
Shock, loss of consciousness, or death in the most severe cases

What are common drugs that cause an allergic reaction?
Although almost all drugs can occasionally cause an adverse reaction, certain medications are more likely to produce allergic reactions than others, due to their chemical structure. These include:
Antibiotics – such as penicillin
Anticonvulsants and hormones – such as insulin
Certain medicines used in anesthesia – such as neuromuscular blockers
Vaccines and biotechnology-produced proteins – such as Herceptin

The chances of developing an allergic reaction may be increased if the drug is given frequently, or by skin application or injection rather than by mouth. Inherited genetic tendencies of the immune system to develop allergies may also be important. Contrary to popular belief, however, a family history of reaction to a specific drug does not mean that a patient has an increased chance of reacting to the same drug.

How are drug allergies diagnosed?
Adverse drug reactions can be subtle and difficult to recognize because they mimic other conditions. Currently, only limited tests are available to diagnose specific medication allergy. Allergy skin testing to determine the presence of IgE antibody is available for therapeutic proteins such as insulin, some biotechnology products and a few others.

If a drug hypersensitivity is suspected, your physician may recommend that you see an allergist/immunologist. If you believe you are having an adverse reaction to a medication, be sure to note the circumstances. Your physician will want to know the details of the situation, including:

When the medication was taken
When symptoms began
How long the symptoms lasted
A description of the symptoms
Any other medications taken during this time, including over-the-counter drugs

Useful tips
Consider keeping a written record of the reaction and providing it to your physician. This information will be helpful in determining diagnosis and management. If possible, bring the suspected medication with you to your medical appointment. An allergist/immunologist will usually perform a physical exam looking for different signs of an allergic reaction, noting any symptoms of a reaction that you still have.

Keep a list of the medications you take regularly so your physician can identify which drugs may potentially be sources of hypersensitivity. This will also help your physician determine which medications should be avoided and if there are alternative medications that would be acceptable.

What treatments are available for drug allergies?
When an adverse reaction to a medication is minimal, treatment is limited to discontinuation of that drug. However, if there is a more severe reaction that is ongoing, an allergist/immunologist may provide antihistamines, corticosteroids and other medications, including an EpiPen (epinephrine) for emergency situations. Antihistamines block the effects of histamine, which usually initiate an allergic response, and corticosteroids reduce swelling and inflammation.

In most cases, patients with a drug allergy can be safely given an alternative medication. However, when there is no alternative available and the medication is essential, a desensitization to the medication will be recommended. This involves gradually introducing the medication in small doses until the therapeutic dose is achieved.

When should someone see an allergist/immunologist?
The AAAAI’s How the Allergist/Immunologist Can Help: Consultation and Referral Guidelines Citing the Evidence provide information to assist patients and health care professionals in determining when a patient may need consultation or ongoing specialty care by the allergist/immunologist. Patients should see an allergist/immunologist if they:

Have had a severe allergic reaction that could have been due to a medication (anaphylaxis without an obvious or previously defined trigger).
Have a history of penicillin allergy and likely will need antibiotics in the future.
Have a history of penicillin allergy and have an infection with no effective alternative therapeutic options, except for a penicillin class antibiotic.
Have a history of multiple drug allergies or intolerance.
May be allergic to protein based bio-therapeutics and require uses of these materials.
Have a history of an adverse reaction to a non-steroidal anti-inflammatory drug (NSAID) and require aspirin or other NSAID.
Require chemotherapy medication for cancer or other severe conditions and have experienced a prior hypersensitivity reaction to those medications.
Have a history of possible allergic reactions to local anesthetics.
Are HIV-infected patients with a history of adverse reactions to trimethoprim-sulfamethoxazole (TM-S) and need this therapy.