Because of their widespread use as well as their well-known propensities for triggering allergic reactions, aspirin, penicillin, and local anesthetics deserve special mention.
Aspirin
Aspirin and other salicylates are well-known causes of upset stomach, ulcers, easy bruisability, and liver irritations, but they are also associated with a number of immediate problems that appear to be similar to hypersensitivity, including hives, giant hive reactions, and anaphylaxis. In addition, approximately 15 percent of aspirin-sensitive asthmatics are also sensitive to the food and drug coloring agent tartrazine (FD&C #5), which is used to give the yellow-orange color to many drinks, cereals, and medications.
But probably the best-recognized aspirin-related syndrome involves the gradual development of rhinitis and sinusitis, followed by the growth of nasal polyps and the development of severe, difficult-to-control asthma, the so-called rhinitis-sinusitis-polyposis-asthma syndrome. This constellation of problems typically develops in otherwise healthy, middle-aged individuals who have never had trouble with aspirin before. Once the condition develops, however, it generally persists even when aspirin is discontinued. Those with the syndrome must avoid not only aspirin but other nonsteroidal antiinflammatory agents, such as indomethacin, ibuprofen, naproxen, phenylbutazone (such as Indocin, Motrin, Naprosyn, and Butazolidin, respectively). However, both sodium aminosalicylate (Tubasal) and choline magnesium salicylate (Trilisate), despite their chemical similarity to aspirin, as well as acetaminophen (Tylenol) may be substituted for aspirin and other nonsteroidal antiinflammatory agents whenever a medication is needed for pain and or to reduce fever. Obviously, for the reasons given, if you know that you are aspirin-sensitive, you would do well to read all food product labels carefully and to check with your physician or pharmacist before taking any new medication.
Penicillin
From what has already been said, you should not be surprised to learn that penicillin is a leading provoker of adverse drug reactions. In fact, about 2 percent of people are estimated to be allergic to penicillin, and more than six hundred people die each year from penicillin allergy in the United States and Canada alone. While less threatening conditions small hives, giant hives, and other itchy skin rashes make up the bulk of penicillin reactions, death occurs in about one in every one hundred thousand times the drug is administered. As a rule the drug appears to be about twice as likely to provoke allergic reactions when given intramuscularly or intravenously rather than when taken orally.
Unfortunately, the story does not end there. If you are allergic to penicillin, you are also very likely to be allergic to its derivatives. These include amoxicillin, ampicillin, dicloxacillin, and methicillin, all of which are commonly used antibiotics. Furthermore, since there is a known cross-reactivity between the penicillins and another, very popular group of broad-spectrum antibiotics, the cephalosporins (such as Keflex, Ceclor, Velosef, and Duricef), these agents should also be avoided by penicillin-allergic persons or used with special caution.
If you've had an allergic reaction to penicillin in the past, you may take some comfort in knowing that approximately 50 percent of penicillin-allergic people lose their allergy after five years and about 80 percent lose it after ten years. This makes it possible for them once again to take the drug (or its derivatives) if needed. Skin testing is an excellent method for detecting IgE- anti-penicillin antibodies and therefore for determining whether a person who had an adverse reaction earlier is still allergic or has "outgrown" the allergy.
Testing is usually reserved for persons suffering from an infection for which penicillin is the drug of choice and for which there exists no comparably effective substitute. Two penicillin derivatives, peni-cilloyl polylysine (PPL, Pre-pen) and penicillin G (PG), are generally used. Patients are first given a prick test, and if there is no adverse reaction, they are then tested intradermally that is, small amounts of the test materials are introduced under the skin to see if local skin reactions result. Virtually all persons at risk for allergic reactions to penicillin are skin-test positive: They react with redness, itching, and hiving at the test sites.
Desensitization methods (procedures for overcoming penicillin allergy) have been developed for treating allergy-proven individuals who must receive penicillin. Under strict observation, such patients are given (usually orally) increasing doses of penicillin every five to fifteen minutes, starting with very small amounts. The protocol is continued until full therapeutic doses can be tolerated without provoking any allergy symptoms. Unfortunately, desensitization is not uniformly successful.
On a related note, oral desensitization to trimethroprim/sulfa (Septra and Bactrim), another important and widely used antibiotic, was achieved in a small study group of sixty-two HIV-positive patients who had previously developed drug rashes or fever while receiving the drug. These results are of no small importance considering that allergies to the drug occur in about half of all HIV-infected persons and that the medication has been shown to be highly effective for preventing a relatively common, potentially life-threatening form of pneumonia in these individuals. The desensitization protocol involves giving increasing doses of the antibiotic every six hours for eight days until therapeutic levels are achieved without any untoward reaction.
Local Anesthetics
Because they are used so often in dental and ambulatory surgery, local anesthetics are among the most commonly employed drugs in medicine. Anyone who has ever had dental work or stitches for a deep cut knows what pain-eliminating lifesavers these drugs are. At the same time they are also responsible for a variety of adverse nonimmunolog-ic reactions, such as central nervous system and cardiac toxicities, and for a variety of presumed allergic problems, including contact dermatitis, hives, giant hives, and anaphylaxis. Problems arise when the physician is asked to help the surgeon or dentist choose an alternative local anesthetic for a patient who has a history of an allergy to a particular local anesthetic.
For practical purposes, local anesthetics can be divided into two main classes. Group I includes such familiar anesthetics as benzocaine (found in many topical anti-itch and antisunburn preparations), tetracaine, and procaine (Novocain). Group II includes lidocaine (Xylocaine, which is probably the most universally used injectable local anesthetic today), mepivicaine, cyclomethycaine, and dibucaine. If you are allergic to one member of a group, you are likely to be allergic to other members of the same group. Fortunately, however, there is little cross-allergenicity: If you are allergic to Novocain from Group I, your dentist may substitute lidocaine (Xylocaine) from Group II without fear of provoking cross-allergy.
Occasionally, skin testing, using prick and intradermal administration of increasing concentrations, may be needed to determine a person's allergic status to local anesthetics. To accomplish this, the individual is challenged by subcutaneous administration (injections into the fat) of increasing doses of the suspected allergen to see if there is evidence of local reaction. As with penicillin testing, skin testing with anesthetics must be performed under strict medical supervision.
