Knowing about drug allergies could save your life!

Allergic reactions occur as an immune response of our body to a foreign substance. When the allergic reaction is due to a drug, new or old, it is said to be a drug allergy. Adverse drug reactions can occur with any class of drugs, but more so in case of antibiotics followed by anti-tumor drugs.

Symptoms of drug allergy

Symptoms of drug allergy are the same for any type of allergy. Common ones are skin rash, hives, and itching of the skin or eyes. These are not very serious symptoms. These reactions are usually treated by substituting the current drug with another.

However, severe reactions after taking the medication include swelling or tightening of the airways, dizziness or lightheadedness, rapid pulse, or even loss of consciousness. Seek emergency treatment since these are anaphylactic symptoms that are potentially life threatening.

Who can get drug allergy

Anyone and everyone can be allergic to one or the other drug. Generally children and middle aged people are more prone to drug allergy than others. Female gender is also a risk factor for allergic reactions to a drug. You may also have an allergic reaction if

• you have a past allergic reaction to any drug
• you are allergic to penicillin then you may be allergic to some other antibiotics as well
• you have a weakened immune system as in AIDS /HIV
• you have a history of other allergies
• you have asthma, high blood pressure or heart disease.

Common drug allergies

You can have an allergic reaction to any drug. But some are more common than others. Here's a list of the most common drug allergies.

• Penicillin and related antibiotics such as cephalosporins, sulfonamides (sulpha drugs), and aminoglycosides are the most common cause of drug allergies. However, the different classes of antibiotics vary in respect of their mechanism of actions and adverse effects.
• Anticonvulsants such as carbamazepine, lithium salts, divalproex sodium, oxcarbazepine, and others used for seizures and other mental illnesses can cause allergic reactions.
• Insulin, especially animal sources of insulin, is a common example of drug allergic reactions.
• Radiocontrast agents or X-ray contrast dyes containing iodine can also cause allergic reactions. Sometimes, they can cause anaphylactic reactions that can be life threatening. The incidence of reactions appears to be lower with non-ionic agents as compared with ionic agents. Oral corticosteroids and H1-antihistamines are generally used to treat such allergies.
• Sulpha drugs, another common cause of drug allergy, can be both antibiotic as well as non-antibiotic. You can have an allergic reaction to either or both these categories. Sulfonamides antibiotics are often associated with more severe drug reactions such as Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) characterized by fever and extensive necrosis (premature cell death). People with HIV are at an increased risk of sulphonamide allergy. Non-antibiotic sulpha drugs such as acetazolamide, frusemide, hydrochlorothiazide, chlopropramide, sulfasalazine, dapsone, etc, are thought to be less likely to cause severe allergic reactions.
• Aspirin and nonsteroidal anti-inflammatory drugs, too can cause allergy in some people. 'If you have an aspirin allergy or sensitivity, you may also have a reaction to nonsteroidal anti-inflammatory drugs (NSAIDs), including ibuprofen (Advil, Motrin IB, others) and naproxen (Aleve, others)', says Mayo Clinic asthma and allergy specialist James T C Li. The allergy can range from mild to severe and the reaction can occur within a few hours of taking the medication.
• Vaccines have been found to cause allergic reactions in some people. Serum sickness is a delayed type of drug allergy that occurs a week or more after you are exposed to a medication or vaccine.

How to identify a drug allergy

It is very difficult to identify a drug allergy. And that is because there are very few good laboratory tests that can be helpful in diagnosing them. What happens is, generally the original form of medication does not cause the allergic reaction. It is the modified form of the drug or the metabolite of the drug that the immune system responds to. However, the skin test for penicillin is very effective because all of the important metabolites of penicillin have been identified. So much so, the test can correctly identify not only who is allergic to penicillin but also who is not allergic. There are a few tests to diagnose drug allergy and these include

Blood test Allergy to some antibiotics, muscle relaxants and insulin can be diagnosed through blood test.

Skin test Skin test may be required for certain antibiotics. A small amount of the drug is injected into the skin. If you're allergic to the drug being tested, you will develop a reaction.

Drug provocation test This test is resorted to when the other two tests are inconclusive. In this test, you will be given gradually increasing doses of the offending drug. If there is a reaction, sensitivity to the drug is indicated; if not, then it could be considered a safe treatment option.

Since lab tests or skin tests are not always helpful, allergists have to depend on a detailed and accurate history of all your current and past medication to identify which drug is responsible.

'First of all, the most important test of a drug allergy is not a laboratory test or a skin test at all, but a careful history of what happened when the allergic reaction occurred previously. That tells an allergist, more than any testing that is done, whether or not the drug reaction was due to an allergic mechanism, allergic cause, and also gives some estimate of whether or not that type of allergy is likely to persist over time. So a good careful history is the most important tool that we have to determine who is allergic to a particular drug', says N. Franklin Adkinson, M.D., Prof., Div. of Allergy and Clinical Immunology, Johns Hopkins University. 'For many other drugs, including other antibiotics, we don't have a validated skin test, and we have to rely on that crucial historical information to tell us, to give us an assessment of how likely it is that a drug allergy exists'.

Practical tips

1. Whenever and every time you visit a doctor, discuss with them your current medications and supplements, and describe all prior adverse reactions to medications. Share this information with your pharamacist too. Sometimes if the prescribed medicine is not available, they tend to give a substitute medicine.
2. For new medications, ask questions regarding possible drug-drug reactions and read the drug inserts included in the medication.
3. Do not take short acting antihistamines (like Benadryl or diphenyhydramine) for 2 days prior to your skin test, and longer acting antihistamines (like cetirizine, fexofenadene [Allergra], loratadine [Claritin, Alavert], or desloaratadine [Clarinex]) for 3-4 days, because they might interfere with the test. However, if you need to take antihistamines, do so, but re-schedule your skin test appointment.
4. Always keep with you an identifying-card that mentions your drug allergies or chronic conditions.
5. Notify your doctor immediately if you notice adverse reaction to any drug you are taking. Your doctor will make the decision for further action, viz. stopping the drug, etc.

Reference:

https://www.ncbi.nlm.nih.gov/pubmed/12592301

https://www.mayoclinic.org/diseases-conditions/drug-allergy/symptoms-causes/syc-20371835

http://aacijournal.biomedcentral.com/articles/10.1186/1710-1492-7-S1-S10

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