Allergic reactions to drugs are usually mild or moderately severe – no more than some itching or a few hives. But occasionally a drug reaction can be fatal. That’s why allergic people should learn all they can before they take any drugs, whether prescribed by a doctor or purchased over-the-counter.
Each drug has a number of known side effects – health problems caused by the drug, which doctors have learned to expect. An allergic reaction, on the other hand, is an unexpected reaction which people who respond to a drug with known side effects rarely have. One out of every four adverse reactions to drugs is allergic.
The chemistry behind drug allergies hasn’t been pegged down as an antigen-antibody reaction, or any other identifiable immune reaction. Just the same, the possible symptoms are identical to those of other allergies: skin rashes, asthma, hives, and shock. And reactions occur only after a prior, uneventful exposure to the drug or a chemically related substance. So doctors regard drug sensitivities as allergy in the true sense despite a lack of measurable immunological changes.
But how does your doctor know whether you are experiencing a side effect or an allergic reaction? For one thing, side effects, no matter how numerous and varied, are spelled out either on drug package inserts or in one of several reference books containing drug information, such as The British Formulary of Drugs: A Handbook of Psychoactive Medicines. More important, however, an allergic reaction follows a latent period – usually seven to ten days – after you first take the drug. In other words, your doctor starts you on penicillin today, but you may not react until next week. Then the next time you take penicillin, you may react immediately – and explosively. And if you’re allergic, you’ll react no matter how small the dose.
The skin is the organ most likely to suffer when you swallow a drug or get an injection that doesn’t agree with you. Here is a list of possible symptoms.
Itching. Alone or with other symptoms, itching is so characteristic of drug allergy that if you don’t itch, you probably aren’t really allergic.
Hives. Huge hives all over the body are almost a sure sign of allergy to certain drugs – notably penicillin, aspirin and related compounds (salicylates) or even allergy treatment extracts. Rashes. Drug-induced rashes come in a variety of shapes and hues, from bright red, itchy patches to bumps or scattered spots that resemble measles. Occasionally, the rash takes on a bluish tint. Whatever the form or colour, it usually centers on the trunk.
A mixed bag of eruptions known as erythema multiforme is the ultimate in drug-induced rashes. The blotches vary in size, shape and appearance, are usually distributed on the backs of the legs or forearms, and are frequently accompanied by fever, general discomfort, stomach and abdominal upset and joint pains. It’s reassuring to know that all clears up when the drug is discontinued.
Generalized Swelling (angioedema). This often affects the eyelids, lips, hands and feet. Broken Capillaries (purpura). These red or purple threadlike squiggles beneath the skin surface are less common but occasional signs of drug allergy.
Photosensitivity. Sunlight presumably alters certain drugs so that they readily form allergy-triggering substances in the skin. The resulting flare-up resembles contact dermatitis or eczema, and may not appear until days or months after the sun/drug encounter.
Scaling and Shedding of the Skin (exfoliative dermatitis). Needless to say, this is one of the more drastic symptoms of drug allergy. Sometimes the hair and nails fall out, too. Fever, chills and overall discomfort go along with it. Don’t worry about being taken by surprise, though; this problem doesn’t develop overnight. The trick is to alert your doctor to any patches of scaly skin early on, before things get out of control.
While the skin takes the brunt of our allergic encounters with drugs, the rest of the body is not off limits. Bronchial asthma can be caused by aspirin. (Most people who get this already have regular asthma.) Fever – rarely a consequence of other types of allergy – can develop as part of a drug reaction, and can easily be mistaken for a symptom of the illness that’s being treated. By far, though, anaphylaxis is the most severe and dangerous non-skin drug reaction, and one that’s most commonly caused by penicillin. With little or no warning, blood pressure drops, the pulse weakens, the throat swells closed and the individual collapses – all within minutes or even seconds after getting the drug. Anaphylaxis, by the way, is far more likely to occur after an injection than after oral medication.
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