If you've been avoiding penicillin because of a past allergic reaction to the antibiotic, there's a good chance it may now be safe for you to take it.
Studies at the Johns Hopkins School of Medicine and Good Samaritan Hospital in Baltimore have concluded that 80 percent of the adult patients who have had reactions to penicillin in the past are no longer allergic to it.
Quick, simple skin tests are available to determine whether a patient still has a penicillin allergy.
"This is not a lifelong problem," said Dr. N. Franklin Adkinson, an allergy specialist and assistant professor at Hopkins who led the studies. Patients who show no reaction to penicillin in the skin test, "could safely receive it," he said.
Unfortunately, he said, the tests are rarely done. Portions of the tests remain experimental and must be administered at research hospitals, or by affiliated allergists.
"We feel this data leads to the conclusion that we should be doing much more skin testing than we're doing," Adkinson said. "It would allow the removal of the stigma of penicillin allergy from the patient's medical record."
Fifty years after their introduction, penicillin-based antibiotics remain "the single most valuable group of antibiotics we have," Adkinson told an allergy seminar yesterday at the Hopkins Asthma and Allergy Center. Penicillin drugs are highly effective and rarely toxic.
Penicillin is the drug of choice for use against infectious organisms that cause such problems as brain abscesses, syphilis, meningitis and endocarditis, an inflammation of the interior lining of the heart.
Patients labeled as allergic to penicillin are forced to forgo what may be the most effective treatment, in favor of alternative drugs that cost more and don't work as well.
Nevertheless, allergic reactions to penicillin are not uncommon, and can be serious.
Sixty to 80 percent of all reported allergic drug reactions are attributed to penicillin and related antibiotics. The reactions range from skin rashes to life-threatening anaphylactic shock, in which the patient's blood pressure drops so sharply that the heart can no longer pump blood to the brain and vital organs.
There are 300 to 500 penicillin-related deaths in the United States every year, Adkinson said.
Studies in outpatient clinics and hospitals in Baltimore found that 8.5 to 10 percent of all adult patients surveyed reported they had experienced an allergic reaction attributed to penicillin.
More than a third said they broke out in hives. Smaller numbers reported "measles-like" symptoms, and 7 percent reported anaphylactic symptoms ranging from wheezing to shock.
In their study, Adkinson and his associates performed skin tests on 5,063 people, in which tiny amounts of two penicillin products, or "reagents", were introduced beneath the skin. The researchers then watched for a spreading welt and reddening that indicated an allergic reaction.
Of those patients who reported no prior penicillin allergy, fewer than 2 percent had a positive reaction to the test. This, Adkinson said, is the population at risk for an unexpected allergic reaction to the drug.
But of those who did report a history of penicillin allergy, only 7 percent had allergic reactions to the skin tests.
In a similar study in the mid-1980s of patients who had experienced hives or anaphylactic reactions to penicillin in the past, only 13.2 percent had allergic reactions to the penicillin skin test.
Adkinson said one could conclude from this either that the skins tests aren't very accurate, or "that 87 percent of the patients who've had problems really are no longer allergic. And indeed, that's turned out to be the case."
In subsequent studies, between 2 and 15 percent of patients who tested negative on skins tests later experienced allergic reactions to penicillin. "All of them had very mild reactions. Most did not need treatment," Adkinson said.
On the other hand, of those who tested positive to one penicillin reagent, or skin test, 50 percent later had allergic reactions to the drug. Of those testing positive to a second reagent, 70 percent later had allergic reactions to the drug itself.
It's not clear how long it takes for the penicillin antibodies responsible for the reactions to go away. But Adkinson said other studies suggest that similar antibodies vanish from the system at rates that vary widely among individuals, from months to many years.
Tests with both types of penicillin reagents are needed to determine accurately whether a patient is allergic to the drug, Adkinson said. Unfortunately, only one type -- called PRE-PEN -- is currently licensed by the U.S. Food and Drug Administration.
The second reagent is one of many "orphaned" drugs for which there has been insufficient demand to prompt drug companies to pay the costs of winning FDA approval.
It remains officially experimental and available only through research hospitals like Hopkins and their affiliated doctors. But Adkinson expects it will be fully licensed and available to any allergist within a year.
Adkinson said persons who want to see whether they remain allergic to penicillin can call the Hopkins Asthma and Allergy Center at 550-2300 for more information.