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When doctors prescribe drugs and pharmacists fill them, one thing both groups are interested in is the type of sensitivities or allergic reactions people have had to other drugs. Knowing this helps to avoid the specific medicines that have caused problems in the past. From another perspective, having this information is equally important. Sometimes sensitivity to one specific drug means possible reaction to other specific drugs; this is called cross sensitivity.
It would be nearly impossible to list all of the drugs that may provoke cross sensitivity reactions. Some people who display sensitized reactions to medications like non-steroidal anti-inflammatory drugs (NSAIDs) may have trouble taking any drug that belongs to that class. A person who cannot take ibuprofen, might not tolerate naproxen sodium (Aleve®) or medications like Vioxx®. Since most reactions to NSAIDs are not usually anaphylactic, doctors might still try giving another NSAID if necessary, but they could try other medications first to avoid causing cross sensitivity.
Similar issues exist with certain antidepressants, especially when the medications are closely related to each other. Other people can’t take some types of antibiotics if they’ve shown sensitivity to one antibiotic that belongs in that group. Many people, for instance, cannot take any form of Sulfa antibiotic, and this would include medications like Bactrim® and Septra®.
One of the classic examples of cross sensitivity is penicillin. Those allergic to penicillin must not take certain antibiotics for fear of provoking a life-threatening reaction. These medications include but are not limited to amoxicillin, augmentin, which contains amoxicillin, ampicillin, oxacillin, and others. Sometimes, people allergic to penicillin also have allergic reactions to antibiotics called cephalosporins, though new research on this suggests that the likelihood of reaction is about 10%. Cephalosporins include the medications Keflex® and Ceclor®.
The reason cross sensitivity usually occurs is because drugs are often created from each other. They may contain some of the same ingredients, possess a similar chemical structure or be made in a way that is very similar. The idea is that closely related substances are more likely to provoke an allergic or immune response reaction, and it is thus dangerous to risk this, unless there are no other options.
This could be compared to nut allergies. Walnuts and pecans aren’t the same, but if a person is allergic to one type he could be allergic to both because they are similar. Additionally, virtually any nut would have to be suspect as having the potential to trigger an allergic reaction. Thus it would be safer to avoid all of them.
What the idea of cross sensitivity means for the average person may vary. When physicians prescribe medications, they normally have a listing, frequently on their computer, that tells them what they can’t prescribe based on sensitivities. This suggests that people really need to keep a record of what drugs they have had reactions to in the past. Severe allergic reactions like those to penicillin might need additional care. Wearing an emergency bracelet that lists extreme allergies could be useful if a person is ever in a position where he/she can’t give this information by speaking.