What Is Drug Hypersensitivity?

Drug hypersensitivity is an allergic syndrome that occurs after a drug has been introduced into the body. The syndrome can begin up to two months after exposure to the drug, but some patients present with symptoms in one to three days. The body can react in varying degrees to a substance that it deems foreign. The response exhibited in cases where there is significant immune system involvement can lead to death from organ failure or anaphylactic shock if not addressed promptly. Common symptoms of the syndrome are a high fever, swollen lymph nodes, and body rash.

The least severe form of drug hypersensitivity is drug intolerance. Drug intolerance accounts for almost 90 percent of cases and is characterized by the patient exhibiting expected toxic side effects at very low doses of the drug. Drug intolerance can be treated by discontinuing the drug and treating any symptoms that linger after discontinuation. The mechanism of drug intolerance is not well-understood, but is suspected by some researchers to be caused by an enzyme deficiency, most likely partly genetic in origin.

The most serious form of drug hypersensitivity is sometimes called serum sickness and is mediated by an extensive immune response inside the body. This reaction constitutes 6 to 10 percent of drug hypersensitivity cases, and some common associated drugs include penicillin, sulfa drugs, and anti-seizure medication. When this type of hypersensitivity develops, the nature of the symptoms depends on which part of the immune system fights against the substance. The most serious cases that can potentially lead to anaphylaxis and organ failure occur when the body produces the IgE antibody in response to the drug. IgE antibodies bind to mast cells and trigger the release of chemicals, like histamine, that lead to the severe reaction.

Drug hypersensitivity can occur at any time throughout a person’s life. Even if the person has not shown any signs of hypersensitivity throughout childhood or as a young adult, serious reactions can begin later in life. Sometimes repeated exposure to a potentially irritating drug causes the body to slowly form a dangerous allergy. The chance of developing serious drug hypersensitivity increases if a drug is taken by injection rather than orally, and if the dose of the drug is large or given frequently. Research indicates strongly that there is a genetic tendency toward specific drug hypersensitivity, and that people with immediate family who have a known allergy should use caution when beginning the regimen themselves.