Medicament Allergies

Medicament allergies, thus, are infrequent. But like food allergies, they can be quite severe, even fatal, when they do occur. The most notorious allergen among medicaments is penicillin, which accounts for about 75 percent of deaths from anaphylaxis in the United States. Ironically, penicillin is also the greatest lifesaver of the past sixty years. Many other medicaments, especially other antibiotics, are occasionally allergenic.

Adverse reactions

Medicaments, like foods, can cause various kinds of adverse reactions: allergies, intolerances, toxic reactions, and so on. An adverse reaction to a medicament is any untoward reaction or nontherapeutic effect of that medicament. Technically, the broad category of adverse reactions includes effects of an overdose. Side effects, too, are numbered among adverse reactions; they are not as universal and predictable as overdose effects, but they tend to affect significant numbers of those who take any given medicament. Many antihistamines, for example, have the side effect of making most people drowsy. Theophylline, often used to treat asthma, may make your heart race. Antibiotics often cause diarrhea. A side effect that is categorized as common may appear almost invariably or may affect only 1 in 20 people. A side effect that is rare may affect 1 in 10,000, or occur with even less frequency than that.

A medicament intolerance is an exaggerated response to a medicament. For example, people who are extremely sensitive to aspirin may get a ringing in the ears and feel nauseated after taking just one tablet. The average person would experience these unpleasant effects only after taking many aspirin.

There are also so-called idiosyncratic reactions to medicaments. These vary according to the individual, and often are not well understood. It is believed that in some cases enzyme deficiencies may be involved. (An example of an idiosyncratic reaction is the bone marrow failure that occurs, rarely, after use of chloramphenicol, an antibiotic. This occurs in approximately 1 in 30,000 uses.)

Finally, of course, there are allergic reactions to medicaments. About 15 percent of patients treated with medicaments experience adverse reactions, and very often these people wrongly say that they are "allergic" to the medicament that caused the problem. But only a fraction of such adverse reactions are due to allergy.

It is important to know the difference between an allergy and intolerance, because if you mistakenly report having an allergy to a medicament, a doctor may be forced to give you a less effective medication to avoid setting off an allergic reaction. Often patients think that if a medicament gives them diarrhea, they are allergic to it. But diarrhea is a common side effect of antibiotics and other medicaments, caused by changes in the bacterial environment in the intestines. On the other hand, if you are truly allergic to a medicament, the doctor must know this, because that medicament or another in its family could cause you life-threatening difficulty.

True medicament allergies

The key to identifying a medicament allergy is that it resembles other kinds of allergy. For instance, you will not get an allergic reaction the first time you take that medicament. A sensitivity must build up. But that buildup can occur quickly, with the result that allergy symptoms can appear during the initial course of therapy, even though everything went well for the first couple of doses. Moreover, some people are exposed to medicaments inadvertently or without realizing it because some medicaments are present in food we eat. A baby may be exposed to penicillin through breast milk. Penicillin and other medicaments may also be present in cow's milk or in meat from farm animals. In these cases, someone will have built up a sensitivity to the medicament without realizing it.

Assuming a normal exposure to medicaments, medicament allergies often appear in early adulthood, but there are no age limits. Some children have allergic reactions to medicaments. Some elderly people develop medicament allergies even after having taken a medicament many times.

Occurrence

Frequently, an allergic reaction to a medicament occurs within minutes to one hour after taking the medicament. If you are very allergic, even a minuscule dose will produce symptoms. There are also delayed reactions that take hours to two to three days to appear. Rarely, there are reactions that are even more delayed. For example, hives resulting from a sensitivity to ampicillin can occur several weeks after taking the medicament and last up to four months.

As a rule, the more rapidly the symptoms appear, the more dangerous the reaction. Symptoms arising within an hour of taking the medicament are potentially life-threatening. The delayed symptoms are normally less serious, but still require evaluation by a physician.

Major adverse reactions to medicaments

A medicament reaction in the first hour or first few minutes after exposure that includes the following symptoms requires immediate, expert medical attention: swelling (sometimes with hives); difficulty breathing or swallowing; vomiting or stomach cramps; itching; choking; weakness; and a sense of impending doom. These are signs of a dangerous reaction-anaphylaxis. Choking and difficulty breathing are caused by swelling in the throat that is closing off the windpipe. This sounds serious, and it is. That sense of impending doom is appropriate. You might die. If you experience any swelling of the lips, tongue, eyes, fingers, or hands - even without choking or wheezing - call your doctor or an ambulance immediately. Do not take the next dose of the medicament.

Typical symptoms of a medicament allergy are itching associated with hives or a rash, angioedema (swelling), and sometimes a fever. If you are taking a medicament and develop hives or itching, do not take another dose. Contact your doctor immediately. Your doctor will have to assess whether to try to continue the medicament or use another.

Another occasional sign of an allergy reaction is a cyanotic, or bluish, tinge to the skin; in dark-skinned people, this can be seen in the lips, nail beds, palms of the hands, and soles of the feet. Joint aches and fever may also occur. If you develop rash or any of the symptoms mentioned above, report this promptly to your doctor.

Incidentally, one sign of medicament allergy is that the symptoms usually clear up or begin to improve within several days after the medicament is discontinued.

Hives and rashes

Acute hives can be a sign of a dangerous medicament allergy and should be treated as a medical emergency, especially following an injection of a medicament.

A sensitivity to nonsteroidal anti-inflammatory medicaments may cause hives and in some cases be associated with chronic hives, as well as with asthma attacks. This sensitivity is sometimes linked to a sensitivity to the food additive tartrazine, a yellow dye. Unfortunately, the anti-inflammatories involved include some of the most widely used medicines for aches and pains: aspirin and ibuprofen. If you are sensitive to these medicines, your doctor may recommend a substitute, such as choline magnesium trisalicylate (Trilisate).

Rashes are a frequent manifestation of medicament allergy. Commonly they are morbilliform, that is, they resemble a measles rash, with multiple tiny red dots allover the body. The rash is itchy but not severely so.

A morbilliform rash can be the result of a medicament allergy or of a number of viral diseases. There is a distinguishing sign between the two, however; an allergic rash may cover your body, but it will not affect your palms and soles. A viral rash usually does not spare the palms or soles. Sometimes an allergic rash progresses to become thick and very red and itchy. Occasionally, when it is difficult to determine whether a rash is caused by the illness being treated or by the medicament used to treat the illness, diagnosis requires a biopsy of the rash.

Most rashes are relatively harmless, but they may develop into exfoliative dermatitis. This is a condition in which the rash spreads over the entire body and the skin begins to shed. This is similar to what happens as the result of a burn, and, as with burn victims, there is great danger of infection. Some patients afflicted with exfoliative dermatitis, chiefly among the elderly, do not survive. Exfoliative dermatitis can also result as a complication of eczema (atopic dermatitis) or psoriasis.

Almost any medicament can cause a rash, but the medicaments that most commonly do so include sulfa medicaments, amoxicillin, synthetic penicillin (such as dicloxacillin sodium and methicillin sodium), penicillin, cephalosporins (which are chemical cousins of penicillin), and hydantoin.

Patients with mononucleosis have an amazing 9 in 10 chance of developing a measles like rash from ampicillin. Certain leukemias also tend to make one susceptible to developing a rash when taking ampicillin. By and large this kind of allergy is not terribly serious, which is a small favor when one is so sick already. The rashes that follow treatment with penicillin and the cephalosporins are notable for their longevity. They may last up to four months after treatment is stopped.

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