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Antibiotic Myths – Use Your Judgement for Better Patient Care

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Jarrod Shapiro, DPM, FACFAS, FACPM, FFPM, RCPS Glasg

Practice Perfect April 16, 2019

Many medical myths are propagated throughout the years. We do something because our mentors and teachers did that thing, not realizing that our teachers did that thing because their teachers before them did that thing, rather than according to the best scientific evidence. There’s a rule of thumb that outdated medical treatments are removed from general practice only after about 10 years. It’s understandable, especially if one considers the sheer volume of medical knowledge today.

One of those myths is the duration of time to prescribe an antibiotic. Historically, most of us have been taught to prescribe an antimicrobial for a specific period of time. We tell our patients to finish the dose, concerned that not doing so will allow antibiotic resistant organisms to surface. For example, a patient in the office with cellulitis of the foot may be prescribed an antibiotic for 7 – 14 days. This practice of taking a medication for a specific number of days has been the standard for about as long as there have been antibiotics.

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The Infectious Disease Society of America (IDSA) recommends “continuing antibiotic therapy until, but not beyond, resolution of findings of infection, but not through complete healing of the wound” and suggests 1-2 weeks of antibiotics for mild infections, and 2-3 weeks for severe infections. All of these recommendations are based on weak, low levels of evidence.⁴

As it turns out, this method of prescribing an antibiotic for a specific time period is a myth.

Let’s take a look into this important topic for further details to help us understand.

It’s important to first recall that there are two major ways for creating antibiotic resistance: target selection and collateral selection.¹

• Target selection generally occurs in professional pathogenic species (organisms that are always pathogenic) when spontaneous mutations occur during treatment, resistance is transmitted before treatment is complete, or emerges after treatment failure. Examples of organisms are HIV and N gonorrhoeae.
• Collateral selection generally occurs when microorganisms become resistant during the treatment of other pathogens. This occurs most commonly in the ESKAPE organisms (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter spp, Pseudomonas spp, Enterobacter spp), all of which are opportunistic pathogens (generally harmless unless entering locations where they don’t normally occur – as in all lower extremity infections).

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When looking at resistance of bacteria, we know that collateral selection is the primary driver in patients today, and the pressures toward collateral selection are increased during longer antibiotic treatment regimens. Prior patient antibiotic exposure then becomes a very important consideration. The medical research has also not born out this fear of resistance after shorter doses. Llewelyn and colleagues argue, “For the opportunist pathogens for which antimicrobial resistance poses the greatest threat, no clinical trials have shown increased risk of resistance among patients taking shorter treatments.”¹

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One suggestion has been to move from a specific course of therapy to more patient-specific factors. One new mantra is personalized duration of antibiotic therapy. Some of the factors used to determine when to discontinue antibiotics include:¹

1. Absence of fever
2. Symptom improvement/resolution
3. Serial procalcitonin measurement
4. C-reactive protein

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Is there any support for shorter duration of therapy in the lower extremity? Gariani and colleagues performed a retrospective cohort analysis of treatment in 1,018 patients with diabetic foot infections.² After a multivariate analysis, duration of antibiotic therapy did not affect the risk of recurrence. Additionally, “neither >3 weeks versus <3 weeks of therapy, nor >1 week versus <1 week of intravenous treatment affected recurrence.” The authors found no threshold for optimal antibiotic duration to prevent recurrence and reiterated that the findings may support shorter durations of therapy.

Similar results were found after a prospective observational cohort study of 606 Spanish patients with cellulitis looking at various factors affecting treatment responses. Antibiotic duration did not affect the success of treatment for cellulitis in these patients.³

Physicians should cease the “standard duration of therapy” antibiotic regimen in favor of a more patient-specific method in which antibiotics are discontinued when clinical symptoms and possibly some serological markers have normalized.

Clearly, more research needs to be done to put this issue to bed. However, the mounting evidence seems reasonably clear: physicians should cease the “standard duration of therapy”antibiotic regimen in favor of a more patient-specific method in which antibiotics are discontinued when clinical symptoms and possibly some serological markers have normalized.

Best wishes.

Jarrod Shapiro, DPM
PRESENT Practice Perfect Editor
[email protected]

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