Negative drug reactions

A negative drug reaction is an unintended response by the body to a drug. An allergy is one type of reaction. A negative drug reaction is also called an adverse drug reaction or a hypersensitivity reaction.

Most reactions are type A. They are predictable and depend on the dose and chemistry of a drug, such as having a dry mouth from antihistamines or nausea from a chemotherapy drug.

Less common reactions are type B. They are not predictable and don’t depend on the dose or chemistry. They happen only in a small percentage of people when the immune system reacts to a certain drug with severe or life-threatening effects such as breathing problems.

Types of negative drug reactions include the following:

• An allergic reaction is a reaction caused by the immune system fighting substances that are usually harmless such as dust mites, pollen or a drug.
• An infusion reaction is a reaction to a drug given into a vein (intravenously, or by IV). It may or may not be an allergic reaction.
• A pseudoallergic reaction is a negative reaction to a drug but the response is not caused by the immune system.
• An anaphylactic reaction is a severe, life-threatening allergic reaction that comes on quickly.

Nearly all chemotherapy drugs and immunotherapy drugs can cause a negative drug reaction. Some drugs have a higher risk than others, and several other factors increase the risk, including when:

• A drug is given into a vein.
• High doses of a drug are given.
• An IV drug is given quickly rather than slowly.
• A drug is developed from bacteria.
• Two or more drugs are given at the same time.

Symptoms of a drug reaction can vary depending on the cause and other factors. Symptoms include:

• wheezing
• skin rash or hives
• itching
• flushing of the face
• difficulty breathing
• anemia
• low white blood cell count
• jaundice

Some people also have fever and chills. A severe allergic reaction (anaphylaxis) can also happen and can include swelling of the face, eyes, tongue or throat.

If symptoms get worse or don’t go away, report them to your doctor or healthcare team.

The healthcare team watches closely for adverse drug reactions, especially when someone takes a drug for the first time. If a drug is known to cause a reaction (for example, a chemotherapy drug), then medicine such as an antihistamine or a corticosteroid may be given before the chemotherapy to try to stop a reaction from happening.

If a severe allergic reaction happens, drugs (such as epinephrine) and other treatments (such as oxygen therapy) are given.

For more detailed information on specific drugs, go to sources of drug information.