Antibiotics: 5 Myths Debunked

Brad Spellberg, MD


October 20, 2016

In contrast, only one trial found a cidal antibiotic to be superior in efficacy to a static agent. That trial compared tigecycline vs imipenem for the treatment of ventilator-associated pneumonia, and found that tigecycline was inferior.[37] However, pharmacologic analysis determined that the tigecycline dose used in the trial was too low, resulting in inadequate drug levels compared with the susceptibility of bacteria causing the infections[38]; when a subsequent trial was done with double the dose of tigecycline, tigecycline was similar in efficacy to imipenem for the same disease.[31]

Thus, there is no evidence that cidal antibiotics are more clinically effective than static antibiotics. To the contrary, more studies have found a static agent to be superior in efficacy to a cidal agent than the reverse!

Implications of busting this myth. Although clinicians continue to prefer cidal antibiotics, there is no evidence that these result in superior clinical outcomes than static agents, nor that cidal drugs more effectively prevent the emergence of resistance. Whether an antibiotic is static or cidal should not be a factor in determining antibiotic therapy for patients.

What Are the Take-Home Messages for Clinicians?

There is no end to our struggle with bacteria; we will never "win a war" against them, and no "gorilla-cillin" will ever come along to save us from emergence of antibiotic resistance. Resistance is inevitable.

Thus, it is critical that we not waste antibiotics. They must not be prescribed to patients who do not have bacterial infections. When appropriate, prescribe the narrowest-spectrum agent and the shortest duration possible to treat bacterial infections.

Do not instruct patients to take every dose prescribed even after they feel better. Rather, focus on evidenced-based, short-course regimens, and if the patient's symptoms resolve before completing the course of therapy, ask that they call you to discuss whether they should stop the antibiotic course early. Encourage them to stop early when their symptoms resolve.

Do not be falsely reassured by the lack of emergence of resistance at the site of infection. When you prescribe an antibiotic, you are selecting for resistance in the patient's microbiome. The resistant bacteria colonize the patient and can cause future antibiotic-resistant infections.

When choosing an antibiotic regimen, cidal vs static is largely irrelevant.


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