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Tips to Remember: Adverse Reactions to Medications
It is important to recognize allergic reactions because they can be life threatening, causing a reaction called anaphylaxis. This brochure provides information on both non-allergic and allergic drug reactions. Non-allergic reactions Reactions can be severe, like vomiting and hair loss with cancer chemotherapy. They can milder like ringing in the ears and stomach upset from aspirin. They can be idiosyncratic or unpredictable. Almost any drug can trigger a reaction in someone. When the immune system is not involved, some patients may still be able to take a lower dose of the same medicine in the future, though in general drugs that cause serious reactions are avoided unless there is a compelling reason to reuse them. Common examples of non-allergic drug reactions Once a person has one contrast reaction they are at very high risk for more unless treated. The reactions do tend to be worse in people who are dehydrated (dried out) when they are given the contrast in their veins. These reactions are not caused by iodine and are not more common in people with shellfish or any other true allergy. They can be minimized by pretreatment with antihistamines and oral steroids and/or using non-ionic contrast material that, interestingly, still has iodine in it. Many people will have stomachache and diarrhea with antibiotics such as erythromycin. Some antibiotics have a direct irritant effect on the intestinal tract or kill good bacteria in the colon. Coughing is common with certain widely used drugs for high blood pressure called ACE (angiotension converting enzyme) inhibitors. Some people, especially those with asthma or sinus problems, have a sensitivity to aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen. Up to 10% of adult patients with asthma, and up to 40% of those with nasal polyps (sac-like growths in the nose), may have aspirin sensitivity. This sensitivity, like contrast reactions, is caused by a direct drug effect on cells. People with aspirin or NSAID sensitivity may experience symptoms such as nasal congestion and a runny nose; itchy, watery or swollen eyes; cough; difficulty breathing or wheezing; or itchy red bumps called hives (urticaria) on the skin. In rare instances, severe reactions can even result in shock. It is always important that you accurately follow the instructions given with prescription medications. If you are unclear on how to take the medication or if the effect you are experiencing is a serious side effect, contact the physician who gave you the prescription. If your symptoms are severe, seek emergency medical help immediately. Allergic reactions An allergy occurs when a person's immune system responds to the modified or unusual proteins as a foreign substance. Small molecules tend to bind to proteins and the combinations of these can cause a reaction. A severe reaction can occur when an allergic person's immune system produces the allergic antibody called IgE (immunoglobulin E) in response to a drug. When the person's body encounters the drug again, IgE antibody bound to certain cells, called mast cells, can result in an explosive release of histamine and other chemicals. This triggers symptoms of an allergic reaction, which may range from scattered hives to anaphylaxis. This is the same type of reaction that occurs when a bee allergic individual is stung by a bee, or a peanut allergic child eats a peanut. The most severe allergic reaction is anaphylaxis. Symptoms of anaphylaxis include a sense of warmth, flushing, itching, hives (which can occur alone, that is, without progression to anaphylaxis), swelling in the throat, asthma or wheezing, light-headedness from low blood pressure, irregular heart rhythm, nausea or vomiting, abdominal cramping or shock. Anaphylaxis can result in death. These symptoms require emergency attention, including an immediate intra-muscular injection of epinephrine (adrenaline). Most anaphylactic reactions occur within one hour after the patient takes the drug but in up to 20% of cases, the anaphylactic reaction may start up to several hours later. In patients at risk for anaphylaxis, the culprit, IgE antibody, was produced by the immune system in response to a prior exposure to the drug. Rarely, blisters develop in association with a drug rash. This is a sign of a serious complication, called erythema multiforme major (Steven-Johnsons syndrome), and should immediately be reported to your physician. These reactions can cause the skin to peel off and are treated like severe burns. It is very important to tell your doctor about any adverse reactions when you are taking a medication and to make certain that the doctor knows of any prior reaction to a drug being prescribed for you. 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 myth, 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. Adverse Drug Reaction Evaluations
Most allergic reactions to medications occur within hours to two weeks after the initial dose. Drugs that have been tolerated for months are a less common cause of reactions. Currently, only limited tests are available to diagnose specific medication allergy. Allergy skin testing to determine the presence of IgE antibody is available for penicillin, therapeutic proteins such as insulin, some biotechnology products and a few other drugs. If you have had a past reaction to a medication, can you receive it again? In most cases, you should receive an alternate drug in the future. Specific skin testing can detect penicillin allergy, and if the testing is negative, the patient may be able to receive penicillin and its derivatives again. There is currently no test to predict the chance of developing most recurrent rashes. In the case of rashes caused by the antibiotic ampicillin or a sulfa drug, some patients can tolerate re-administration if the drug is necessary, but this must be done carefully. If you have any history of a rash with blisters, you should never be prescribed the drug again. If you have had any reactions to medications in the past, make sure to keep a personal record so any physicians treating you in the future can be well informed. You should discuss with your doctor whether you need to also avoid related drugs and whether you need to wear a Medic-Alert tag to alert others of your drug allergy. Again, the single most important factor is to inform your physician of any unusual reactions you experience while taking a medication. Your allergist/immunologist can provide you with more information on adverse reactions to medications. Tips to Remember are created by the Public Education Committee of the American Academy of Allergy, Asthma and Immunology. This brochure was updated in 2003. The content of this brochure is for informational purposes only. It is not intended to replace evaluation by a physician. If you have questions or medical concerns, please contact your allergist/immunologist. American Academy of Allergy, AAAAI Physician Referral and AAAAI Web site |
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Medicines are given to help people, but all medications can have side effects. About 5% to 10% of adverse reactions to commonly used drugs are allergic, which means that the patient's immune system overreacts to the drug.