CAN DRUGS CAUSE ALLERGY?

About 15% of the population report adverse reactions to medication, but only 5% are truly allergic reactions. Of these, 0.1% are fatal*.
Reactions can be divided into 3 groups:
· Those not related to the drug but coincidental and due to factors other than the drug. For example, rashes or nausea associated with the disease and not the medication.
· Toxic effects from taking an overdose, those due to known side effects and those due to interactions with other medication taken at the same time.
· Then there are allergic reactions and these adverse reactions usually involve the immune system.
Any drug can cause an adverse drug reaction, which can range from a mild rash or hives to a life-threatening allergic reaction. There is a difference between being allergic to a drug and having a side effect from a drug. Prescription and over-the-counter medications provide instructions that should always be read and followed regarding proper use and side effect warnings. Some mild reactions to drugs are considered an adverse drug reaction, but are not considered a drug allergy. If you experience any drug-related symptoms, report them to your healthcare provider.

What are the symptoms?
Most reactions occur within one hour and involve measles-like itchy rashes or urticaria. A severe form may even blister (Stevens - Johnson syndrome). The reaction may progress to life threatening anaphylaxis.
Delayed reactions can develop days after drug exposurewith generalised dermatitis and damage to organs such as the kidneys, liver, lungs and blood cells.

What are the causes?
These may be due to direct anaphylactic immune reactions such as seen with Penicillin, Vaccines, blood transfusions, Insulin and intravenous fluids.
Other medicines can trigger histamine release in the body by non-immune mechanisms and for which no diagnostic blood tests are available. Triggers include aspirin and anti-inflammatory drugs, morphine and the opiates, local anaesthetics and some intravenous xray-contrast fluids.
Drugs that cause allergic reactions:
· Antibiotics: Penicillin, Sulphonamides, Chloramphenicol and Cephalosporins.
· Heart drugs such as ACE inhibitors, Quinidine, Amiodarone, Methyldopa.
· Anaesthetic drugs: Muscle relaxants, Thiopentone, Halothane.
· Morphine derivatives such as Morphine, Pethidine and Codeine.
· Aspirin-like drugs such as Diclofenac, Ibuprofen, Indomethacin.
· Cancer chemotherapy drugs: Cisplatin, Cyclophosphamide, Methotrexate.
· Antiseptics: Chlorhexidine, Iodine.
· Vaccines such as Tetanus Toxoid and Diphtheria vaccine.
· Preservatives such as Parabens and Benzakonium chloride.
· Anti-convulsant, Anti-tuberculosis medication. Streptokinase, Insulin. Enzymes and Latex.
Some people are allergic to antibiotics. The most common is penicillin, which belongs to the family of beta-lactam antibiotics. No one is born allergic to penicillin, nor can it be inherited. However, anyone can develop an allergy to penicillin after exposure to it. Most often the reaction is either hives or rashes that are itchy or irritating and that occur within 2-3 days of starting the medication. Sometimes a delayed reaction can occur after several weeks. Having an allergy to penicillin does not mean you are allergic to all antibiotics. If a penicillin allergy is suspected, the best way to confirm it is with a skin test.

How to diagnose?

DIAGNOSIS of drug allergy is based mostly on patient history. This requires that the healthcare provider be told of every drug that was taken at the time of a reaction, including prescription, over-the-counter, and herbal medicines. Once the drug that caused the reaction is identified, future use of that drug should be avoided. If an adverse drug reaction occurs while in the hospital, blood tests can be done to identify the drug causing the reaction. Following a drug allergy reaction, a provider may recommend that an allergist, a doctor who specializes in allergies, be seen.

What is the treatment?
Treatment involves immediate withdrawal of the implicated drug, followed by antihistamine medication. In cases of anaphylaxis, the prompt use of adrenaline and corticosteroids is life saving.
A blood test for Tryptase release will confirm an allergic reaction has taken place. Unfortunately only Penicillin, Amoxycillin, Sulphonamide and Cephalosporin allergy can be reliably confirmed on RAST testing. If any other drug is suspected then intradermal skin testing, followed by challenge tests in a hospital will be needed. Using Patch tests on the skin can test allergy to certain drugs such as Neomycin and the Paraben preservatives.
What can be done to prevent drug allergies?
· If allergic to one member of a drug family such as penicillin or aspirin, then all other members of the family should be avoided unless negative skin or challenge tests have been performed.
· If allergic to Penicillin, rather use the Erythromycin family of antibiotics, if allergic to anti-inflammatory medication such as ibuprofen, then rather only use Paracetamol.
· It is possible to have an allergic reaction to almost any drug - including Paracetamol. So only use medication if absolutely necessary or if it has been specifically prescribed to you.
· Never use someone else's medication unless you have taken medical advice and are sure it is safe to use.