Allergies to medicine are the result of an immune system response that occurs upon exposure to a drug. Drug allergy can occur with any medication including over-the-counter as well as prescription varieties. Drug allergies can be problematic if a patient is allergic to multiple medications or to a medication which he needs to take regularly.
Cause
Allergy to medication occurs when the body falsely recognizes a drug as a harmful attacker. Antibodies known as immunoglobulin E, or IgE, form in response to the medication. When the immune system encounters the medication again, these antibodies recognize it and release chemicals that result in an allergic reaction. Once a reaction to a particular type of medication occurs, an allergic response will occur every time that medication is encountered and in some cases when a similar medication is used.
Common Medications
While an allergic reaction can occur in response to any medication, penicillin and penicillin-related medications are the most common cause of drug allergies. According to the University of Maryland Medical Center, other common culprit medications include sulfa drugs, anticonvulsants and insulin preparations that are derived from animal sources.
Symptoms
The most common symptom of an allergy to a medication is skin rash or hives. This rash may be itchy in nature and typically occurs immediately after starting a medication. Facial or lip swelling may also occur. This allergic reaction can progress to involve nausea or vomiting, shortness of breath, cough and dizziness. These symptoms may represent an anaphylactic reaction that can be life-threatening if not treated promptly.
Nonallergic reactions
Not all adverse reactions to medication represent an allergy. For example, antibiotics may cause symptoms of nausea or diarrhea that are uncomfortable but not related to an allergic response. Some medications can have reactions that are similar to an allergic response but are not mediated by the same immune system pathway. Reactions to X-ray contrast and to aspirin can present in this way. When there is any question of whether an allergic reaction has occurred, an allergist can help with diagnosis.
Diagnosis
For most medications, a diagnosis is obtained by a careful history, or discussion of the events leading up to the reaction. An allergy specialist can often help determine whether it is likely that a medication caused the reaction. For penicillin allergy, standardized skin testing can be performed to confirm the allergy. In this test, a small amount of the allergenic part of penicillin is scratched on the surface of the skin and is injected just underneath the skin. An allergist then measures the reaction to this testing to determine whether a penicillin allergy exists.
Treatment
If there is doubt regarding whether an allergy to a certain medication is likely, the typical strategy is to avoid the medication. If the medication is needed, a desensitization procedure can be performed. This procedure must take place in a monitored setting and involves the administration of small amounts of the medication in incrementally larger doses until a full dose is achieved. The medication course can then be given safely, according to Cleveland Clinic. Unfortunately, this effect only lasts as long as the medication is taken daily. Once the medication has been stopped, the allergy can recur and desensitization has to occur again for the drug to be used. If a severe allergic reaction occurs because of an allergy to medication, injectable epinephrine is given to reverse the reaction.
