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A drug allergy is an allergic reaction to a medication or drug taken for another purpose. Allergic reactions or drug allergies are not common but seem to happen with a greater frequency with certain antibiotics, such as sulfa drugs and penicillin. Reactions can be as simple as a rash or itching or can involve anaphylaxis, a severe reaction leading to shortness of breath, low blood pressure and organ damage. Anaphylaxis has the potential to be life threatening and must be treated immediately.

Allergic reactions don't happen the first time you take the antibiotic or other medication because your body needs time to develop an allergic response. This can take a few hours or as much as a week to develop. The next time you take the medication (or other subsequent dose) is when the allergic reaction occurs. If you happen to have an allergic reaction the first time you take a medication, it means you have probably been exposed to it or something like it in the past.

An allergic reaction needs to be differentiated from a drug reaction, which is not allergic in nature. All drugs can have side effects related to the action of the drug on the body. Most effects of drugs are not allergic in nature and only about ten percent of all adverse drug reactions are, by nature, allergic. There can be drug reactions that occur as a result of two or more drugs being given at the same time and there can be drug reactions that occur because the body cannot break down the drug fast enough (or at all).

The cause of a drug allergy is a part of the drug that is believed to be foreign by the body's immune system. The immune system makes antibodies against the whole or part of a drug and an allergic response ensues. This is known as a hypersensitivity reaction and is related to the development of IgE antibodies. Histamine is released as part of the allergic reaction that causes itching, red skin, hives and a lowering of the blood pressure. Histamine is a mediator chemical in the development of an allergic reaction.

Common medications that cause allergic reactions include codeine, NSAIDs, morphine, aspirin and antibiotics. Tetracycline, penicillin and sulfa drugs are the antibiotics most likely to cause an allergic reaction. Anti-seizure medications like Tegretol or Dilantin also commonly cause drug allergies. The rate of allergy depends on how long a person was exposed to the drug and the dosage of the drug. If the drug is given by injection, it has a greater degree of allergic response. If a person has asthma or hay fever, they are more likely to have a drug allergy. If a person is allergic to certain foods, such as shellfish, soy-beans or eggs, they are more likely to develop a drug allergy.

Symptoms of drug allergy depend on the person and, to a degree, on the drug involved in the allergy. Common symptoms of a drug reaction include a rash, similar to measles. There can be full blown hives or welts across the entire body. There can be a photosensitivity reaction, with rash or sunburn only on sun exposed areas. There is a condition called erythema multiforme, which involves a raised, red and itchy rash that sometimes looks like bull's-eye targets. It is accompanied by swelling of the face or of the tongue.

People with drug allergies can have muscle or joint aches, fever, swelling of the lymph nodes or kidney inflammation, which can yield blood in the urine or white cells in the urine. The symptoms, as mentioned, can occur shortly after starting the drug or several weeks after the drug is taken on a regular basis. It sometimes takes several weeks for the antibodies against the drug to develop.

In anaphylaxis, there is a narrowing of the airway and extreme shortness of breath or wheezing. The blood pressure drops and the person can have nausea, vomiting or dizziness. Anaphylaxis can quickly develop into shock and so needs immediate treatment. The hands or face can swell with anaphylaxis and can turn a deep red. Anaphylaxis usually occurs within four to five hours post ingestion of the drug and can occur the first time you take the drug.

The treatment of drug allergy includes taking epinephrine if there is an anaphylactic reaction. Epinephrine is given by IM, subcutaneously or IV in order to block the allergic response. Antihistamines are given in order to correct the immune response and reduce histamine. Prednisone blocks the immune response and is given for more long acting treatment of the drug allergy.

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Medical Negligence Solicitors

Our personal injury solicitors operate a specialist medical negligence compensation service. Our Drug Allergy solicitors deal with claims using a no win no fee arrangement which means that if you don�t win then you don�t pay them their professional costs. If you would like legal advice at no cost with no further obligation just complete the contact form or email our lawyers offices or use the helpline and a Drug Allergy solicitor will review your medical negligence compensation claim and phone you immediately.

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The author of the substantive medical writing on this website is Dr. Christine Traxler MD whose biography can be read here