In this episode, I’ll discuss if antibiotic exposure intensity affects the risk of clostridioides difficile infection.
The antibiotic spectrum index (ASI) was developed to classify commonly used antibiotics based on activity against relevant pathogens. In the ASI antibiotics are given points based on the number of unique pathogens they cover with scores ranging from 1 to 13. The highest-ranking antibiotics by ASI are tigecycline, quinolones, and carbapenems, and among the lowest-ranking antibiotics are ampicillin, cefazolin, and azithromycin.
A group of researchers recently investigated whether there was an independent association between intensity of antibiotic therapy, as measured by the antibiotic spectrum index (ASI), and hospital-associated Clostridioides Difficile Infection (HA-CDI). A retrospective cohort analysis was published in Clinical Infectious Diseases of a single center was conducted on over 23,000 patient cases where at least one antibiotic was received during a hospital stay.
In the overall cohort there was an incidence rate for HA-CDI of 4.1 cases per 10,000 patient-days. When this risk was stratified according to ASI per antibiotic day and adjusted for potential confounders, there was a 1.09 increase in the risk of HA-CDI for every unit increase in ASI per antibiotic day. The 95% confidence interval for this increase in risk was quite narrow at 1.06-1.13.
Combining the ASI with traditional metrics like days on therapy to form the metric “ASI per antibiotic day” provides a more nuanced evaluation of the intensity of antibiotic therapy. In addition, this provides a way to quantify antimicrobial stewardship efforts that result not in the discontinuation of antibiotics but the narrowing of spectrum.
Take for example two patients that started on a 7 day course of meropenem. One completed the entire course on meropenem and the other was stepped down to cefepime after 3 days. Both have the same number of days on therapy. Since meropenem has an ASI score of 10 and cefepime has an ASI score of 5, the intensity of the two different regimens can be compared in a more detailed way that simply looking at days of therapy does not allow for.
Hopefully this research suggesting a strong association of ASI per antibiotic day and risk of HA-CDI will be used to design prospective studies to further evaluate the usefulness of this tool.
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