Drug Allergies/Sensitivities Health Article

Definition

A drug allergy is an adverse reaction to a medication, often an antibiotic, that is mediated by the body's immune system. A drug sensitivity is an unusual reaction to a drug that does not involve the immune system.

Description

Adverse reactions to medication may be allergic reactions involving a child's immune system, individual sensitivities to a drug, or side effects of the drug itself. Some children are allergic or sensitive to drugs that are not harmful for most people. Some drugs, such as aspirin and penicillin or related antibiotics, may induce allergic reactions in some children and sensitivities in other children.

Drug allergies

Any drug (either prescription or over-the-counter) can evoke an allergic reaction; however, antibiotics, especially penicillin and related drugs, are the most common cause of drug allergies. Children also frequently (i.e. to these agents more frequently than to other agents) develop allergies to the following:

• aspirin
• sulfa-based drugs
• barbiturates
• anticonvulsants
• insulin preparations, particularly those from animal sources
• dyes that are injected into blood vessels before taking x rays

The symptoms of a drug allergy vary from quite mild to life-threatening anaphylaxis. Unlike other common allergies, drug allergies often affect the entire body. The most common symptoms of a drug allergy are skin conditions including rash, generalized itching, and urticaria (hives; a very itchy rash with red swellings affecting only a small area of skin or the entire body; possibly the early symptom of anaphylaxis). The type of rash depends on the type of allergic response.

Less common symptoms of drug allergies include runny nose, sneezing, and congestion.

Uncommon but more serious symptoms of a drug allergy include the following:

• nausea, vomiting, diarrhea
• abdominal pain or cramps
• fever
• low blood cell count
• wheezing and difficulty breathing
• inflammation of the lungs, kidneys, and joints
• angioedema (a sudden swelling of the mucous membranes and tissues under the skin, anywhere on the body but especially on the face, eyes, lips, neck, throat, and genitals)

Angioedema occurs within a few minutes of exposure to the drug, often in conjunction with urticaria. Angioedema often is asymmetrical: for example, only one side of the lip may be affected. Swelling of the tongue, mouth, and airways can cause difficulty speaking, swallowing, or breathing. Angioedema can become life-threatening if the swelling affects the larynx (voice box) and the air passages become blocked. Emergency symptoms of a drug allergy include obstruction of the throat from swelling, severe asthma attack, and anaphylaxis.

Allergic reactions to drugs are the most common cause of an inflammation of the kidneys called tubulointerstitial nephritis. The allergic reaction and development of this acute condition may occur between five days and five weeks after exposure to penicillin, sulfonamides, diuretics (drugs to increase urination), and aspirin and other NSAIDs.

IGE-MEDIATED ALLERGIES IgE-mediated allergies can be caused by the following:

• penicillin when the allergic reaction is immediate
• blood factors, including antisera
• hormones
• vaccines (usually an allergic reaction to some component of the vaccine such as egg protein, gelatin, or neomycin, an antibiotic)
• very rarely, local anesthetics such as Novocain

The most common symptom of an IgE-mediated drug allergy is a rash that develops after the child has taken the drug for several days and produced antibodies against it.

ANAPHYLAXIS Anaphylaxis is a violent immune system reaction that can occur when a child who has large amounts of drug-specific IgE antibodies is re-exposed to the drug. The antibodies bind to the drug very rapidly causing an immediate, severe response. Anaphylaxis most often is caused by the following:

• penicillin and related antibiotics
• streptomycin
• tetracycline
• insulin

Analphylaxis usually begins within one to 15 minutes following exposure to the drug. Only rarely does the reaction begin an hour or more after exposure. Anaphylaxis can progress very rapidly leading to collapse, seizures, and loss of consciousness within one to two minutes. Without treatment, cessation of breathing, anaphylactic shock, and death can occur within 15 minutes. Any drug that has caused anaphylaxis in a child will probably cause it again on subsequent exposure, unless measures are taken to prevent it.

Symptoms of anaphylaxis include:

• urticaria on various parts of the body
• angioedema
• intense itching
• flushing of the skin
• coughing and sneezing
• nausea, vomiting, diarrhea
• abdominal pain or cramping
• tingling sensations
• ear throbbing
• heart palpitations
• uneasiness or sudden extreme anxiety
• swollen throat and/or constricted air passages causing a hoarse voice, wheezing, and difficulty breathing, the most characteristic symptom of anaphylaxis

Constriction of the air passages in the bronchial tract and/or throat, accompanied by shock, can cause a drastic drop in blood pressure that may lead to the following:

• rapid pulse
• paleness
• weakness
• dizziness, lightheadedness
• slurred speech
• mental confusion
• unconsciousness

OTHER DRUG ALLERGIES Cytotoxic/cytolytic-type drug allergies can be caused by the following:

• penicillin
• sulfonamides
• quinidine
• methyldopa

Cytotoxic/cytolytic-type of drug allergy can result in the following:

• immune hemolytic anemia due to the destruction of red blood cells
• thrombocytopenia from the reduction in blood platelets
• granulocytopenia from a deficiency of a type of white blood cell called a granular leukocyte

Drugs that can cause immune complex reactions, such as serum sickness or drug-induced lupus syndromes, include:

• hydralazine
• procainamide
• isoniazid
• phenytoin

Serum sickness (a delayed type of drug allergy that may take one to three weeks to develop) can be caused by an allergic reaction to penicillin or related antibiotics. Serum sickness also can be an allergic response to animal proteins present in an injected drug. Serum sickness is characterized by the following:

• fever
• aching joints
• swelling of the lymph nodes
• rash
• general body swelling
• skin lesions
• nephritis (an inflammation of the kidneys)
• hepatitis (an inflammation of the liver)

Some drugs, including penicillins and sulfonamides, can cause delayed dermatologic allergic reactions. These are various types of skin reactions, including eczema, that do not occur immediately upon exposure to the drug. These types of allergies are thought to be caused by metabolites formed from the breakdown or further reaction of the drug.

Drug allergies can result in hypersensitivity reactions, which in turn can result in liver disorders. Such damage can be caused by the following:

• sulfonamides
• phenothiazines
• halothane
• phenytoin
• isoniazid

Pulmonary hypersensitivity allergic reactions that affect the lungs and result in rashes and fever may be caused by nitrofurantoin and sulfasalazine.