Back to the Future: Penicillin-Susceptible Staphylococcus Aureus

All health professionals know and fear antibiotic resistance. A penicillin resistance has been present in Staphylococcus aureus for years due to its widespread usage for bacterial infections. However, penicillin may be making its come back! New data suggests that penicillin may becoming out of a period of antibiotic resistance. A study published by the American Journal of Medicine examined penicillin resistance in methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia.

At the McGill University Health Centre in Montreal, Canada, all adult MSSA bacteremia from April 2010 to April 2015 were reviewed for susceptibility to penicillin, erythromycin, clindamycin, and trimethoprim-sulfamethoxazole.  Out of 324 samples of MSSA bacteremia, 90 were susceptible to penicillin. This means that more than one quarter of patients with MSSA bacterium could use parenteral penicillin for treatment. This returning treatment may possibly have pharmacokinetic advantages over other beta-lactam, such as amoxicillin. Such pharmacokinetic advantages could potentially lead to better outcomes in the treatment of bacterial infections.

While working at a community pharmacy, I often fill prescriptions for amoxicillin, but I have never seen a prescription for penicillin. This new discovery regarding penicillin resistance could lead to a change in prescribing patterns from physicians in the future. I think that this discovery is also valuable at this time because other antibiotic resistances are emerging in our population. Bringing back an old antibiotic would be very useful to combat bacterial infections that are not responding to current top antibiotics. Although it is great to see the renaissance of an old antibiotic, antibiotic resistance is a serious problem and will continue to be a serious problem unless pharmacists step in to provide effective patient counseling and form beneficial interprofessional relationships with prescribers.

Am J Med. Published online February 25, 2016.

Link to article

Good news: you might not have a penicillin allergy

If you have a penicillin allergy, you might be mistaken. A study conducted by the American College of Allergy, Asthma, and Immunology has recently found that those diagnosed with chronic urticaria have a three times higher likelihood of self-reporting a penicillin allergy when compared to the general public. Similarly, those who self-report a penicillin allergy also have a three times greater likelihood of having undiagnosed chronic urticaria compared to the public.

Penicillin is one of most widely reported antibiotic allergies (13.6% of patients), according to Silverman, et al. Conversely, only 5% of people given a penicillin skin test are actually allergic. The discrepancy could be due to a misappropriation of symptoms during concurrent use of penicillin. The symptom in question is rash. It has been found that greater than 1% of patients on penicillin develop a rash. This rash is the tell-tale symptom of urticaria. Those with chronic urticaria and are given penicillin are more likely to experience a rash (20.5%). It has been concluded that the highest misattribution of penicillin allergies can be due to undiagnosed urticaria. It is also hypothesized that penicillin exacerbates the effects of urticaria.

In their study, 11,143 patients were looked at, and 12% of these patients had a diagnosis of urticaria. Of the 11,143, 1,516 (13.6%) reported a penicillin allergy, thus 86.4% did not report a penicillin allergy. Of this 86.4%, 446 (4.6%) had chronic urticaria. The percent of patients without chronic urticaria and a self-reported penicillin allergy was 14.5% meaning that those not diagnosed with chronic urticaria are 3.15 times more likely to report a penicillin allergy than those who are diagnosed.

Looking at this data, it can be seen that there are many people who claim to have penicillin allergies. With antibiotic resistance becoming a health threat, more screenings should be used to differentiate those with an actual allergy from those who simply self-report the allergy. This will help prescribers cut down on the number of different antibiotics a patient will take over the course of their lifetime.

Ann Allergy Asthma Immunol. 2016; 1:4.