Are you one of the 10 percent of Americans who report being allergic to penicillin? Did you know that less than 1 percent of the population are truly allergic? Did you know that 80 percent of people with true IgE-mediated penicillin allergy lose their sensitivity after ten years? Did you realize that “the use of broad-spectrum antibiotics in patients labeled ‘penicillin-allergic’ is associated with higher healthcare costs, increased risk for antibiotic resistance, and suboptimal antibiotic therapy?”
False Diagnoses
For many years, I thought I was allergic to penicillin. My medical records labeled me as allergic, and I thought I could never take penicillin again. The diagnosis of allergy was based on the fact that I developed a rash while taking penicillin, but I later realized the rash was probably not caused by the drug but by the infection I was taking the drug for. I had no signs of anaphylaxis, such as hives or symptoms in the respiratory, cardiovascular, or gastrointestinal systems. When I developed strep throat years later, I played the odds and got a penicillin injection. As I suspected, I was not truly allergic; I had no adverse reaction of any kind.
At every encounter with a healthcare provider, I am repeatedly asked if I am allergic to any medications. I can now report “no allergies.”
Skin Testing
Skin testing is now available and highly reliable for ruling out allergy; if a negative skin test is followed by a challenge dose, the accuracy is essentially 100 percent. It is essentially useless for diagnosing allergy because of the high rate of false positive results, and many experts now argue against routine use of testing before an oral challenge, especially in children who only had a rash.
Desensitization
I used to assume that patients thought to be allergic to penicillin could never take it again or take related drugs. That’s no longer true. Penicillin is still the drug of choice for syphilis, certain types of endocarditis, strep throat, pneumococcal pneumonia, and some other infections. Other drugs may not be as effective, and there is no therapeutic alternative for syphilis during pregnancy or neurosyphilis. But there is good news for patients who need penicillin but are allergic to it. Desensitization is now available; it can allow them to tolerate penicillin temporarily without provoking an allergic reaction. Desensitization protocols may involve pretreatment with medications thought to reduce risk; this remains controversial. The initial dose is based on the severity of the reaction and may be as small as one-millionth of the therapeutic dose. Gradually increasing doses are given over several hours to a few days until the patient is able to tolerate the full therapeutic dose.
Take-Home Message
If you think you are allergic to penicillin, there’s a good chance you are not. If you are allergic but penicillin is the drug of choice, you can still take it after desensitization.
This article was originally published in Skeptical Inquirer.
