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allergic reactions to drugs

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Alternative Names 
drug allergy

A drug allergy, or an allergic reaction to drugs, is an unintended bodily response to a medication. Symptoms can vary from a mild rash to death.

What is going on in the body? 
An allergic reaction occurs when a person's immune system reacts to the presence of a foreign substance in the body. It is an attempt by the body to get rid of the substance. In the case of a drug reaction, this response is harmful, and sometimes causes serious symptoms.

What are the signs and symptoms of the condition? 
Symptoms of an allergic drug reaction can include: Other symptoms may also occur in some cases.

What are the causes and risks of the condition? 
An allergic reaction does not usually occur the first time a person is exposed to the drug. It is only after the body learns to recognise the substance that an immune system reaction is triggered. Almost any drug can cause a reaction. However, allergic reactions are quite rare considering the number of drugs commonly prescribed.

Drug reactions can vary from mild to severe and life threatening. Most of the time, the allergic response takes the form of hives, a skin rash, or breathing difficulties. One type of drug reaction known as serum sickness develops a week or more after exposure to the medication or vaccine.

Drugs that commonly produce adverse reactions include:
  • penicillin and related antibiotics
  • sulphur drugs
  • barbiturates
  • anticonvulsants
  • insulin preparations, particularly from animal sources
  • novocaine and similar anaesthetics
  • iodine
What can be done to prevent the condition? 
There is no way a person can prevent the development of a drug allergy. Once a reaction has occurred, an individual should avoid that particular drug. Rarely, a person will need to take a drug even if he or she is allergic to it. In those cases, the person can be pre-treated with medications that prevent the allergic response from taking place. These medications include steroids, antihistamines, and adrenaline.

How is the condition diagnosed? 
The doctor can often diagnose a drug allergy based on the symptoms a person has. The other clue is the onset of symptoms shortly after taking of a particular drug.

What are the long-term effects of the condition? 
There are few long-term problems associated with drug allergies. In a few cases, the reaction will include severe asthma or shock. However, most people recover quickly.

What are the risks to others? 
There are no risks to others.

What are the treatments for the condition? 
Treatment for drug allergies consists of measures to control the symptoms until the drug is out of the bloodstream. Most often, antihistamines are used to relieve rash, hives, and itching. Prednisone or other steroids are also used to keep symptoms in check. These drugs can be taken orally or applied to the skin. Asthma symptoms can be controlled with asthma medications. Injections of the drug adrenaline are used to treat severe allergic reactions.

Once an individual has had an allergic reaction to a drug, he or she should avoid that medication. Also, an individual should always inform doctors of any drug allergy. People who develop severe reactions or shock from a drug should carry medical alert cards or wear ID bracelets. These devices help inform doctors of the allergy in emergency situations.

What are the side effects of the treatments? 
The drugs used can all have side effects.
  • Antihistamines can cause sleepiness.
  • Prednisone can cause stomach problems, sleep problems, and mood swings. These side effects are generally very mild.
  • Asthma medications can cause shakiness and abnormal heart rate. These, too, tend to be mild.
  • Adrenaline can cause significant anxiety, shakiness, as well as abnormal heart rate. This drug is often administered in the doctor's office or emergency room.
What happens after treatment for the condition? 
The person should avoid the drug that caused the allergic reaction.

How is the condition monitored? 
A person should wear jewellery or a carry a card to identify the allergy in case of an emergency. When receiving any sort of medical treatment, an individual should tell doctors about the allergy.

Author: James Broomfield, MD
Reviewer: eknowhow medical Review Panel
Editor: Dr John Hearne
Last Updated: 18/09/2004
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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