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A drug allergy is an allergic reaction that occurs when the body’s immune system produces antibodies and activates disease-fighting cells in response to a specific drug. In the development of a drug allergy, the immune system is triggered by the first exposure to the medication. A future exposure causes an immune response, including the production of allergic antibodies and release of histamine. So, drug allergy reactions occur after a person has been previously exposed to the drug one or more times without any allergic reaction.
Everyone reacts to medications differently. One person may develop a rash, while another person on the same drug may have no adverse reaction. All medications have the potential to cause side effects, but only about 5% to 10% of adverse reactions to drugs are allergic. Reactions to medications can range from mild to life threatening.
Most allergic reactions occur within one hour of taking the medication, and involve the following signs and symptoms:
- Hives (itchy, slightly red and swollen patches on the skin)
- Skin rash
- Itching of the lips, tongue and/or face
- Sensitivity of the skin to sunlight (an itchy and scaly rash when skin is exposed to sun)
- Low blood pressure, wheezing and other signs, which may indicate a potentially life-threatening reaction known as anaphylaxis
Antibiotics are the most common cause of anaphylaxis, but more recently, chemotherapy drugs and monoclonal antibodies have also been shown to do so.
Fortunately, at long last, we now have the ability to test for penicillin and penicillin derivatives through a simple skin test. If the history and testing align, the diagnosis is confirmed in about 97% of cases. Diagnosis of other drug allergies is done mostly through a patient’s medical history. Allergists are specifically trained for this.
Drug rashes are the body’s reaction to certain medications. The type of rash that occurs depends on the type of drug that is causing it. Rashes can range from mild to severe.
Rarely, drug rashes may result in blisters. These blisters can be a sign of a more serious condition, so they require medical attention.
Serum sickness is a delayed type of drug allergy that occurs a week or more after exposure to a medication. The immune system misidentifies a protein in the drug as a potentially harmful substance, and it develops an immune response to fight it, causing inflammation and other symptoms.
Symptoms of serum sickness do not develop until seven to 21 days after the first exposure to the drug. However, people may develop symptoms in one to three days if they have previously taken the medication. Within one to two weeks of taking a medication, the following signs and symptoms may be present:
- Fever
- Muscle and joint aches
- Swollen throat glands (lymph nodes)
- Changes in urine color
The first step in treating a drug allergy is to stop the drug that is causing the reaction. Mild allergy symptoms such as hives and itching may be relieved with antihistamines. Topical corticosteroids may also be recommended. If asthma-like symptoms such as cough or wheezing are present, a bronchodilator such as albuterol may be prescribed.
