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Allergies to medications

by John H. Vandergrift (aka the Rock Doc)

This is a rather big topic! Allergy to medications is really a situation that is individualized for each person. Allergies are not predictable, unfortunately. There is a slight inheritable tendency, however just because a relative has a medication allergy, one is not doomed to also acquire that allergy.

Allergies are a reaction to a "foreign substance" (foreign to your body) that elicit an immune response with the release of histamine (thus treated with *anti*histamines) and other factors. Not all of these "factors" are well known. Regardless, one never has an allergic reaction on the first exposure to a substance. What *may* happen is that exposure to a "foreign substance" *may* cause a person to become "sensitized" (the condition where one has become allergic--where antibodies are initially developed). Thereafter, when exposed to that substance, one will express an allergic reaction to it. This is a rather generic explanation, and is the case with any type of sensitization, whether to medications or to any other environmental allergen (a substance that elicits an allergic response), such as pollen or poison ivy.

Allergic reactions are not very predictable. They are not always does-dependent--meaning that it is not always true that a larger dose of the allergen will elicit a more vigorous response. There is a tendency for subsequent responses to similar exposures (such as the same drug in the same doses) to elicit a more vigorous response, but that does not always have to happen. (That's why allergic reactions are not all that predictable.)

Allergy, or sensitivity, to one substance does not necessarily predict sensitivity to other substances. However, there can be some cross-sensitivities, especially in medications. Often times, if a person is allergic to one medication, other medicines in the same drug category will also produce an allergic reaction. For example, a penicillin allergy will also cause a person to be allergic to amoxicillin and Augmentin--both of which are penicillin based antibiotics. An allergy to Cipro will also likely leave someone allergic to Levaquin, Avelox or Tequin--all of these are fluoroquinolone antibiotics. *However*, that is not *always* the case--some people can be allergic to Cipro, yet have no problems with Levaquin. Again, not totally predictable.

Add to this the fact that what many people describe as an "allergy" is really a drug intolerance, but not a true allergic reaction. For example, many people will say they are allergic to codeine when they develop stomach upset with it. That is *not* an allergic reaction, but an intolerance. A true allergic reaction will manifest as a rash at the least severe end of the spectrum, and anaphyllactic shock at the other end. (Anaphyllactic shock is a condition best thought of as severe dilation of blood vessels throughout the entire body--thus the rash of hives on the skin as well as the lungs. This leads to excess secretions and impaired gas exchange in the lungs--like oxygen and carbon dioxide. With diffuse blood vessel dilation, the blood pressure falls--thus the shock state. This is a truly life-threatening process and requires emergency medical attention. Fortunately, it is also rare.)

Your allergy to penicillin gives you lots of company. Penicillin is the antibiotic to which most people will have an allergy, and also the most common drug allergy overall. Much of this is due to the fact that penicillin is derived from a mold (a fungus, not the thing you use for Jello ), and molds are substances that many people will have allergies to.

Add to this that some people are described as "atopic", which means that they have lots of allergies. They tend to have fair skin, often asthma, and also often will have eczema as well. These are the people who are most happy that Claritin is finally available without a prescription these days!

Regarding self medication, the short answer is *don't do it*!! Medications must be individually selected and doses proper for the individual. This is not totally necessary with all medicines, but with antibiotics in particular, this is quite important. A prescriber must be cognizant of allergies as well as the person's weight and age in prescribing a medication, antibiotics in particular. Also, accurate diagnosis is important for proper medication selection. Antibiotics are absolutely useless in most childhood infections, because they are viral and not bacterial. As I often tell people, we have a plethora of antibiotics from which to choose to treat bacterial infections, but we have antibiotics for only 2 viral illnesses: herpes and HIV--and the common cold is not caused by either one of those! Because of very technical reasons, viruses are not very amenable to antibiotic treatment--simply because the chemicals we have found that reliably kill viruses kill people in the process. Although this is effective, it is not very desirable ! OTOH, viral illnesses for the most part make you uncomfortable, but won't kill you. Bacterial infections are by far the more severe ones, and they *can* kill--bit those are the ones I can treat.

When taking antibiotics I would repeat the advice I'm sure all have heard many times before--be sure to take *all* the medicine prescribed until it is finished. The expression of disease symptoms (what you feel) will go away before the infection is totally gone, and if you stop the antibiotics before the course is completed, you may become ill again. At that point, you have selected for resistant germs, and the next course of antibiotics may not be effective--which will require either another course of a more expen$ive antibiotic, or worse, possible hospitalization for IV antibiotics--which is a *LOT* more expensive!! Not all bacteria are responsive to the same antibiotics, so the antibiotic you did not finish 6 months ago for your pneumonia may not be effective against the urinary tract infection you have now. Also, the dosage of the antibiotic you used for your 60 pound 8 year old daughter 3 months ago is probably not appropriate for your 25 pound 3 year old son's current infection.

Remember, your RV is a very expensive investment and you wouldn't want to have some dilletant do a cheap job repairing it. However, the RV *can* be replaced if necessary. You can't replace the body God gave you, and you don't want an amateur "repairing" the only body you have--or ever *will* have! Health matters are not ones to do on the cheap side, and medical issues can be very complex. Remember that medical education spans 11-15 years past high school for a reason! Get proper medical advice, and pay attention to it. Your health and life can literally hang in the balance!

I hope this dissertation is helpful!

John Vandergrift, "Rock Doc"