What Is the Main Idea?

If a patient has an allergy to penicillin, it can complicate the treatment of common bacterial infections, such as tetanus, meningitis, strep throat, pneumonia, food poisoning, and chlamydia. But are penicillin allergies as common as people believe? And do they cause greater mortality in hospital settings? This post refers to the research article “Impact of Penicillin Allergy Label on Length of Stay and Mortality in Hospitalized Patients through a Clinical Administrative National Dataset” published in the journal International Archives of Allergy and Immunology.

What Else Can You Learn?

This post also briefly explains the common classification of bacteria as Gram-positive or Gram-negative and explains why penicillin cannot be used to treat the latter.

A Very Common Antibiotic

Discovered almost 100 years ago, penicillin has been used to treat infections since 1930. It functions by deactivating the enzymes responsible for forming the cell walls of certain bacteria, called Gram-positive bacteria (see below). Penicillin is not effective against all bacteria, but there are derivatives like amoxicillin and ampicillin, which are commonly prescribed against Gram-negative bacteria (see below).

What Are Gram-Positive and Gram-Negative Bacteria?

The Danish scientist Hans Christian Gram developed a method of staining bacteria to aid in their identification. His method divides them into two large groups: Gram-positive bacteria, which stain violet; or Gram-negative bacteria, which stain pink or red. There are some bacteria that stain with a mixture of pink and violet cells, referred to as Gram-intermediate bacteria.

Gram-Positive Bacteria

Common genera of Gram-positive bacteria include Clostridium, Listeria, Staphylococcus, and Streptococcus, which respectively include species causing botulism and tetanus; listeriosis manifesting as sepsis or meningitis; staph-related food poisoning; and strep throat, meningitis, pneumonia, and pink eye. Gram-positive bacteria have a cytoplasmic cell membrane surrounded by a thick peptidoglycan cell wall. They are susceptible to antibacterial agents that target this cell wall, including penicillin.

Gram-Negative Bacteria

Common genera of Gram-negative bacteria include Chlamydia, Escherichia, Pseudomonas, and Salmonella, which respectively include species causing chlamydia; Escherichia coli food poisoning; ventilator-associated pneumonia and sepsis; and salmonella food poisoning. Gram-negative bacteria have a cytoplasmic cell membrane surrounded by a thin peptidoglycan cell wall surrounded by an outer membrane. This outer membrane protects them from a range of antibacterial agents, including penicillin. They also have other protective measures that are different to those of Gram-positive bacteria.

Allergy to Penicillin

If you are allergic to penicillin, you’ve probably encountered issues with getting treatment for some common bacterial infections. Penicillin allergies can manifest as minor to major skin reactions (hives, rashes, or itching); watery eyes and a runny nose; shortness of breath or wheezing; fever; tissue swelling; or in extreme cases, life-threatening anaphylaxis. There are also delayed reactions that can result from penicillin allergies, although these are rare. These can include inflammation of the kidneys, severe blistering and peeling of the skin, and drug-induced anemia.

Around 10% of the U.S. population report having allergies to penicillin, but several studies have found evidence that this number is too high. Some suggest that just 1 or 2% of the population have allergies. One suggests that as few as 0.03% have serious allergies. Nevertheless, since anaphylaxis is possible and potentially fatal, if a patient reports a penicillin allergy, physicians will avoid prescribing it or any of its derivatives. They may also avoid cephalosporins, a group of antibiotics that have a similar structure to penicillins.

In some cases, this can leave very few options for treatment, as alternative antibiotics may be too expensive for the hospital, clinic, or patient to afford. This could mean a longer hospital stay, which is the topic of the research article “Impact of Penicillin Allergy Label on Length of Stay and Mortality in Hospitalized Patients through a Clinical Administrative National Dataset”.

What Does the Paper Describe?

This study of adult patients in the hospital system in Spain compared the lengths of hospital stay and in-hospital mortalities of patients with and without a penicillin allergy. Note that the patients were not admitted because of the allergy: The study focused on whether having an allergy that might complicate the management of disease had a significant effect on hospitalization.

Over a 10-year period, almost a million patients who were admitted to hospital had a penicillin allergy on record. This was just 2.63% of all hospital admissions. The comparison group was a random sample of equivalent size. The study found:

  • If a patient has a penicillin allergy, they are more likely to have a longer stay in hospital.
  • Penicillin allergies are not associated with higher mortality rates in hospital.

What Does that Mean for You?

If you or a family member have a penicillin allergy, you are probably already familiar with the complications that can arise in the treatment of bacterial infections. It may be important to discuss the results of this study with your physician(s) if a hospital stay is coming up. What will happen if you need an antibiotic while in hospital? And do you need to prepare for a potentially longer stay?

Should Physicians Test for Penicillin Allergies?

A few papers published in recent years have suggested testing for penicillin allergies to see if the patient could in fact tolerate the antibiotic. This approach has not entered common practice, but it might also be worth discussing with your physician if there is a suspected allergy. It would be better to know for sure than to have a more difficult experience because of a false assumption.

Note: This post is based on an article that is not open access, i.e., only the abstract is freely available.

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