As part of a recent class activity, we asked our students to rank the most important inventions in history. Penicillin was on the list and a surprising number of groups ranked it as unimportant. More than a few commented on how they or someone they knew was allergic to penicillin. How could something so dangerous be important?
Coincidentally, the recent episode of Freakonomics Radio had a lot to say about this revolutionary drug and modern allergies in general. Before listening, I knew the bare minimum about penicillin (Alexander Fleming, serendipitous mold in the petri dish, etc.). Since penicillin was discovered almost 100 years ago, I assumed that it had been surpassed by more modern drugs. But while it's true that there are now many antibiotics available, the class of antibiotics that includes penicillin is still most effective at killing certain strains of bacteria and does so with the fewest side effects. These drugs are also generally cheap, safe for pregnant women, and less likely to cause antibiotic resistance than some alternatives.
The special usefulness of penicillin to modern medicine underscores the main topic of this episode: penicillin allergies. About 10 percent of Americans report being allergic to penicillin but apparently, the actual number is probably below 1 percent. According to an allergist interviewed in the episode, rashes that occur normally with childhood infections are often mistaken for an allergy.
This mismatch is more than a series of incorrect notations in medical charts– a long-term study of the outcomes of 260,000 patients found that those with a penicillin allergy in their medical record had a 14% higher all-cause mortality rate than those without. Researchers hypothesize that antibiotic resistance, longer hospital stays, infections associated with surgery, and the toll more toxic antibiotics can take on the kidneys may be contributing factors. One of the authors of this study posits that actively "clearing" people of their penicillin allergies could save billions of dollars (not to mention death and disease). The Mass General Hospital System is actually attempting this on a limited scale.
The second half of the episode featured interviews with two allergy experts and the conversation turned to allergies generally. One described how food allergies used to be a niche complaint but have become almost ubiquitous. There are environmental and behavioral factors that may explain the increased rate of allergies, which are a real and serious health issue for many people. But there may be other, more esoteric reasons for the skyrocketing allergy rate. For example, 50 - 60% of all blood and skin prick tests for food allergies yield a false positive. Mylan Pharmaceuticals, the leading supplier of EpiPens, spent a fortune to lobby the FDA and state governments to make their product easier to prescribe and more likely to be available in schools (my school just installed several emergency boxes that include bleed kits, NARCAN, and epinephrine). Mylan even worked with Disney to produce a series of children's books featuring allergies. Allergy testing and treatment is big business globally– about $40 billion a year.
Although funds for allergy research are comparatively scarce compared to other areas, there are apparently many researchers working on making penicillin allergy de-labeling easier. Ironically, finding enough people who actually have a verified reaction to penicillin has been one challenge to developing an effective blood test. This work is important because such a test, and more accurate allergy testing generally, could redound to significant benefits for public health.