ALLERGY: FACTORS ALTERING ONE’S SENSIVITY TO DRUGS
Although no one knows the exact reason why one person develops sensitivity to a drug and another doesn’t, certain recognized factors may alter your vulnerability.
Nature of the Drug. Some drugs, such as milk of magnesia, rarely cause allergic reactions. Others – namely penicillin, aspirin compounds and the sulphonamides – account for 80 to 90 per cent of all allergic drug reactions. Whether or not a drug will cause allergy seems to depend on its ability (or the ability of one of its byproducts) to latch on to a protein. And once you’ve had an allergic response to one drug, you’re open to cross-reactions to chemically similar drugs. Remember, aspirin cross-reacts with other analgesics or the food colouring tartrazine. So anyone who has reacted to one drug is likely to react to new drugs.
How Old You Are. Children don’t react to drugs as often as adults do, possibly because they use less.
Other Allergies. Some evidence suggests that people with allergic diseases (hay fever, eczema, asthma and the like) tend to react more readily to drugs. Other evidence says they don’t. Nevertheless, when allergic people do react to drugs, they seem to react more seriously. For instance, an allergic person is three to ten times more likely to suffer an anaphylactic reaction to a drug than a non-allergic person.
Other Conditions. Doctors say that the risk of reacting is greater among people with a chronic illness. But, they say, that’s probably not because the people are ill but because they take a lot of drugs.
How the Drug Is Taken. Perhaps because the skin is such a sensitive organ, drugs applied topically are more prone to cause reactions than those you swallow. Because of that increased risk, certain drugs, such as penicillin and sulphonamides, are no longer used in salves. Along the same line, you may react to an oral drug if you previously reacted to the drug when it was applied to your skin. For instance, if you once reacted to mercury-containing merthiolate painted on a scratch or cut, you could eventually react to a mercury-containing diuretic.
An injected drug, however, is more likely to cause an immediate and severe reaction, since it enters the system quickly.
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