Drug Allergies – Causes, Signs and symptoms

Drug Allergies

Also called: Medication Allergies


Drug allergies cause a person’s immune system to react adversely to the presence of certain drugs in the body. They are different from a side effect, which does not involve an immune system reaction.  Most drug allergies cause symptoms that are mild, such as a small rash or other irritation. However, in rare cases – such as anaphylaxis – reactions can be life-threatening. As a result, an individual with drug allergies must take them seriously and seek medical attention when they suspect a reaction.

The most common drug allergies include:

  • Penicillin and other antibiotic allergies. Antibiotics are the most common source of drug allergies.

  • Serum sickness. A delayed allergic reaction that can occur a week or more after exposure to a medicine or vaccine.

Other drugs commonly known to trigger allergies include:

  • Painkillers (e.g., aspirin, NSAID, codeine)
  • Sulfa drugs
  • Barbiturates
  • Anticonvulsants
  • Insulin drugs
  • Local anesthetics (e.g., procaine)
  • Iodine

Mild cases of drug-associated allergic reactions often can be treated with antihistamines or topical corticosteroids. However, an immediate injection of epinephrine is the only way to adequately treat the life-threatening reaction associated with anaphylactic shock.

About drug allergies

Drug allergies involve allergic reactions to medications. As with all allergies, a person does not show any symptoms during the initial exposure to a drug. Instead, the body goes through the process of sensitization, where the immune system perceives the drug as a harmful invader upon first encounter and begins producing specific immunoglobulin E (IgE) antibodies to attack the drug the next time it appears in the body.

During this subsequent exposure, the body experiences an allergic reaction, where mast cells and other cells coated with IgE release histamine and other chemicals that attempt to fight off the drug while producing the symptoms associated with the allergy. 

Most drug allergies manifest themselves within minutes, hours, days or weeks of taking a drug. Hives or an itchy rash are typical of many allergic reactions and can be easily treated with medications. However, in rare circumstances a drug will provoke anaphylaxis, an allergic reaction involving two or more body systems. Anaphylaxis can lead to the potentially fatal anaphylactic shock if not treated immediately.

Serum sickness is a drug allergy with symptoms that do not appear until a week or more after exposure to a medication or antiserum. Antiserum is a preparation of serum (the clear fluid portion of blood that contains antibodies) used in immunizations such as tetanus or rabies shots. 

Some people also react to the iodine found in contrast dyes that are used during x-ray procedures.

A person who reacts to a drug is not necessarily allergic to it. Most drug reactions are idiosyncratic, meaning they are simply side effects of the drug that do not involve the formation of antibodies. An uncomfortable side effect of a drug – such as nonallergic Hives – is not necessarily the result of an allergy

Potential causes of drug allergies

Drug allergies are the result of an exaggerated immune system response to a drug or class of drugs. Those who are allergic to a medication are likely to have allergies to other medications of a similar class. For example, those with allergies to penicillin are likely to be allergic to other antibiotics such as cephalosporins.

Drug allergies are more common in adults than in children. Anyone who has a history of allergies – including hay fever and eczema – or asthma is at higher risk of developing a drug allergy. Having a family history of drug allergies is a risk factor as well. Other risk factors for drug allergies include frequent exposure to a drug or taking large doses of the drug.

The method in which a drug is administered is also a factor. Drugs that are given intravenously or through injection are more likely to cause an allergic reaction than those taken orally. This is because drugs that are injected or given by intravenous route are sent directly into the bloodstream. 

Those at risk for allergies to multiple medications include individuals with immune disorders such as AIDS or lupus, and those who receive neutral protamine Hagedorn (NPH) insulin. These reactions are not usually life-threatening. 

Drugs known to trigger allergies include:

  • Beta-lactam antibiotics
    • Penicillin
    • Amoxicillin
    • Ampicillin
    • Dicloxacillin sodium
    • Nafcillin sodium
    • Penicillin V
    • Penicillin G

  • Cephalosporin antibiotics
    • Cephalexin monohydrate
    • Cefprozil
    • Cefixime
    • Cefpodoxime proxetil
    • Cefaclor
    • Cefuroxime axetil

  • Sulfa antibiotics
    • Co-trimoxazole

  • Macrolide antibiotics
    • Erythromycin

  • Anticonvulsants
    • Phenytoin
    • Carbamazepine
    • Valproic acid
    • Lamotrigine

  • Insulins
    • Pork insulin
    • Beef insulin

  • Analgesics
    • Codeine
    • Morphine
    • Aspirin and other NSAIDs (e.g., ibuprofen, indomethacin)

Anyone who suspects that they are allergic to a medication should see a physician. Only a physician is qualified to determine whether allergy symptoms are caused by a medication or an underlying condition.

Related allergies and conditions

Drug allergies can trigger many symptoms generally associated with allergic reactions. Some of these symptoms include:

  • Hives. Red, swollen patches of skin that occur in groups and may burn, sting or itch.
  • Skin rashes. Any change to the color and/or texture of the skin.

  • Wheezing. A whistling or high-pitched sound caused by breathing when the breathing tubes are narrowed.

  • Anaphylaxis. An allergic reaction involving two or more body systems that can lead to the severe and possibly life-threatening anaphylactic shock.

Other disorders which can be triggered by drug allergies include:

  • Lupus, an autoimmune disorder (a disorder that is the result of the immune system reacting against the body’s own cells)

  • Vasculitis, an inflammation of blood vessels

  • Myasthenia gravis, an autoimmune disorder

Signs and symptoms of drug allergies

Symptoms of drug allergies depend on the nature of the reaction. General symptoms include the following:

  • Itching of the skin or eyes
  • Sensitivity to sunlight (Photosensitivity)
  • Skin rash similar to measles
  • Hives
  • Coughing
  • Runny nose
  • Wheezing
  • Swelling in the face, lips, tongue or throat (angioedema)
  • Inflammation of the kidneys

In addition, there are several types of drug-associated allergic reactions that have their own specific symptoms. Serum sickness is a rare condition that affects the entire body and begins six to 21 days after a person takes a medication. Symptoms may include:

  • Fever
  • Weakness and body aches
  • Skin eruptions
  • Joint pain

Autoimmune disorders (disorders that are the result of the immune system reacting against the body’s own cells) can result from drug allergies, though this is rare. Symptoms of these disorders vary depending on the disease, but may include:

  • Fever
  • Malaise (general ill feeling)
  • Achy joints
  • Skin rashes
  • Drooping eyelids
  • Double vision
  • Excessive post-exercise fatigue

Signs and symptoms of anaphylaxis – a reaction involving two or more body systems that can lead to the potentially life-threatening anaphylactic shock – occur within seconds or minutes after a problem drug is taken. They include:

  • Difficulty breathing

  • Wheezing

  • Light-headedness

  • Confusion

  • Severe drop in blood pressure

  • Heart palpitations (an awareness of a strong, fast, irregular, abnormal or “galloping” heartbeat)

  • Nausea and vomiting

  • Diarrhea

  • Cramps

  • Bluish tint to the skin (cyanosis), including lips or nail beds

  • Feeling anxious

  • Rapid or weak pulse

Individuals who suspect that they are having an allergic reaction to a medication should contact a physician. The physician will then determine whether or not the patient should stop using the drug. Those experiencing symptoms of anaphylaxis should seek emergency medical attention immediately.

Diagnosis methods for drug allergies

A physician is likely to first investigate whether or not an individual’s symptoms are the result of a drug’s side effect or of an actual allergic reaction. The physician might inquire about a patient’s medical history and ask for a complete list of medications taken.

Patients should also be prepared to provide their physician with the full details of the reaction, including when the drug was ingested, what symptoms appeared, when symptoms began to appear and how long the symptoms lasted. The physician will then perform a physical examination to determine if any symptoms of an allergic reaction are still present.

An allergy skin test might be recommended if an allergy to penicillin is suspected. During this procedure, a tiny dose of penicillin is introduced to the skin via a scratch/prick or injection. If the skin reacts with a wheal or a raised red bump, it indicates an allergic response to the medication.

It should be noted that there is no licensed penicillin skin test in the United States. Physicians who perform skin testing to penicillin make up their own skin testing materials, and this may not be as accurate as a standardized test. 

In addition, a physician may worry about the risk of a serious allergic reaction to the testing and rule out the procedure as a result. In such cases, the physician will simply prohibit the patient from using the suspected drug.

In rare cases, a RAST (radioallergosorbent test) may be used on people who are too sensitive for a skin test. This type of blood test allows a laboratory to directly test a blood sample from an individual in an attempt to detect antibodies that correspond to a penicillin allergy.

Treatment and prevention for drug allergies

The best approach to preventing drug allergy symptoms is simply to avoid taking the drug and to use an alternative drug that does not cause a reaction. In many cases, this solution is easy to implement. Those who are allergic to an antibiotic such as penicillin, for instance, can be tested for reactions to alternative drugs that also fight infections.

However, in some cases, a patient may have no alternative other than the drug that causes the reaction. In such situations, allergy shots (immunotherapy) may be advised. During this treatment, patients receive periodic, low-dose injections of the offending allergen in the hope that they will become desensitized to the drug and stop reacting to it. This process must be done very carefully under a physician’s monitoring because of the risk of anaphylactic shock. When used for treating drug allergies, this process of immunotherapy is often referred to as drug desensitization therapy.

Individuals who have a history of mild allergic reactions to a drug sometimes can avoid a reaction if they are treated with prescription corticosteroids or antihistamines prior to using the drug. A physician may prescribe an antihistamine to treat symptoms such as hives, rash or itching. In cases of severe or stubborn symptoms, corticosteroids may be prescribed. Creams likely will be tried before oral corticosteroids, which are more powerful and thus more likely to cause side effects.

Patients with a history of drug allergies should disclose this information to a healthcare provider before any medical treatment, including dental visits. Pharmacists should also be informed of any drug allergies.  Those with severe drug allergies should wear a medical alert bracelet or necklace that identifies their allergies. A card that identifies drug allergies can also be carried in the patient’s wallet.

A physician also might recommend an allergy kit that contains a syringe filled with epinephrine, a drug that can immediately reverse the life-threatening symptoms of anaphylaxis. This dose usually is injected into the thigh. Patients should be trained in how to self-administer the drug in an emergency. It is also a good idea to make sure loved ones know how to administer the drug. Parents of children with drug allergies need to inform caregivers of how to administer epinephrine to the child in an emergency.

Patients who use an allergy kit to treat themselves should immediately visit a hospital emergency room, even if symptoms stop. Sometimes, symptoms will reappear later after the initial attack has passed.

Patients who are allergic to several medications should be monitored at a healthcare facility when trying any new medication for the first time, or when taking a medication they have not used in some time.

Questions for your doctor

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about drug allergies:

  1. Do my symptoms suggest a drug allergy?
  2. What methods will you use to determine if I have a drug allergy?
  3. What may have caused me to develop this allergy?
  4. Does this allergy pose a danger to my overall health?
  5. What are my treatment options?
  6. Will I have to completely avoid the drug I am allergic to?
  7. Are there safe alternatives for the drug I am allergic to?
  8. Am I a candidate for drug desensitization therapy?
  9. Is it likely that I am allergic to other drugs as well?
  10. Are my children more likely to develop drug allergies because I have the condition?
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