Overview of the Most Common Drug Allergies

Reactions to medication are extremely common with 15 to 30 percent of all hospitalized patients experiencing an unintended reaction as a result of medications. However, true allergic reactions to medications only account for about 1 in 10 of all adverse drug reactions.

People can experience allergic reactions to just about any medication. Most reactions are common and predictable, while others may be unpredictable and may occur only in certain people.

True allergic reactions to medications typically follow certain features:

• The first time you took it there was no reaction.
• The reaction from the medication is different from expected side effects.
• The reaction is suggestive of allergy or anaphylaxis.
• The symptoms of the reaction disappear within a few days after you stop taking it. 

Skin rashes are the most common symptoms of adverse drug reactions. Urticaria and angioedema (hives and swelling) suggest an allergic cause, while blistering, peeling, and sunburn-like reactions suggest non-allergic immunologic causes.

Other non-allergic immunologic symptoms can include:

• Fever
• Kidney failure
• Hepatitis
• Blood problems (such as anemia)

About 1 in every 10 people report a history of an allergic reaction to penicillin, but much less than 10 percent of those who think they are allergic to penicillin actually are. A true allergy to penicillin could cause life-threatening anaphylaxis as a result.

Severe reactions to cephalosporins, a class of antibiotic, are much less common than with penicillins. However, there is a small chance if you have a true penicillin allergy you could also react to cephalosporins.

Non-steroidal anti-inflammatory drugs (NSAIDs) include pain relievers such as aspirin, ibuprofen, and naproxen. Allergies to these medications can cause allergic and non-allergic bouts of hives and swelling, worsen asthma, and cause anaphylaxis. 

The reaction to IV contrast dye is non-allergic but can result in anaphylaxis since the dye's high concentration can cause mast cells to release their contents, mimicking an allergic reaction. However, in most cases, you can take the dye safely by using oral steroids and antihistamines hours before the contrast is given. 

True allergic reactions to local anesthetics (novocaine, lidocaine) are extremely rare, and usually due to other ingredients in the medication, such as preservatives or epinephrine.

Many antiseizure medications used for epilepsy treatment cause non-allergic reactions as a result of certain enzyme deficiencies. Symptoms can include:

• Rash
• Fever
• Body aches
• Hepatitis

If you think you are having an allergic reaction to a medication, you are taking discontinue the medication and call your doctor, or their on-call hotline, to see how you should proceed. If you took a medication and are now having difficulty breathing or any other symptoms that have you concerned, seek medical help immediately. For allergic reactions which cause rashes and hives, your doctor will likely recommend a topical steroid cream which you can purchase over the counter at your local pharmacy. He may also recommend non-prescription antihistamines should symptoms persist or cause discomfort. Reactions can get worse with continued use of a medication, so discontinue the offending medication unless your doctor suggests otherwise.