The second rationale given for taking a full course of antibiotics is that it prevents resistance from emerging after therapy. This feels intuitive to many people—that completing a full course of antibiotic prevents any “leftover” bacteria from becoming resistant, living on to cause an infection from a now harder-to-treat pathogen. However, there is no evidence to support it. Bacterial resistance to antibiotics emerging de novo during therapy is a relatively rare occurrence that requires genetic mutations that lead to resistance, all while the bacteria are being affected by antibiotic therapy. Most mutations do not lead to resistance, and many of them have negative effects on the bacteria. It takes a bit of luck to create a resistance mechanism against an antibiotic through random mutation.
The belief that prolonging antibiotic durations prevents resistance is probably due to a misunderstanding of the effects of antibiotics. With rare exceptions, antibiotics broadly affect bacteria, and each dose prolongs exposure to antibiotics for many species in the human microbiota, not just for a particular pathogenic organism leading to infection.4
This exposure selects for resistant pathogens that colonize patients, and prolonging that exposure increases the likelihood that their dominance will increase. Once antibiotic therapy has selected for resistant organisms, they can exchange genes with susceptible pathogens to further spread antibiotic resistance to new species. We have to remember that antibiotics always affect the ecosystem of the human microbiota and that there are no true targeted antibiotics.
A final reason for prescribing antibiotic courses is psychological. It is known that prescribers are more comfortable overprescribing antibiotics for patients for infections than taking a risk of undertreating them, which removes the burden of understanding when to stop antibiotics from the patient.5
Addressing this is a matter of education, a notion that is problematic when current authorities preach “take all your antibiotics as prescribed.” I hope further studies will solidify the roles of symptom-guided and shorter-course antibiotic regimens. Furthermore, careful education by health care professionals, to patients about appropriate use of antibiotics, will ultimately help all of us as we work to preserve the societal benefits that these important medical resources afford.
Jason C. Gallagher, PharmD, FCCP, FIDSA, BCPS, is a clinical professor at Temple University School of Pharmacy and a clinical pharmacy specialist in infectious diseases at Temple University Hospital, both in Philadelphia. He is also the director of the PGY2 Residency in Infectious Diseases Pharmacy at Temple. He is an active member of SIDP.
- Llewelyn MJ, Fitzpatrick JM, Darwin E, SarahTonkin-Crine, Gorton C, Paul J, et al. The antibiotic course has had its day. BMJ. 2017;358:j3418. doi: 10.1136/bmj.j3418.
- Hoberman A, Paradise JL, Rockette HE, Kearney DH, Bhatnagar S, Shope TR, et al. Shortened antimicrobial treatment for acute otitis media in young children. N Engl J Med. 2016;375(25):2446–2456. doi: 10.1056/NEJMoa1606043.
- Pertel PE, Bernardo P, Fogarty C, Matthews P, Northland R, Benvenuto M, et al. Effects of prior effective therapy on the efficacy of daptomycin and ceftriaxone for the treatment of community-acquired pneumonia. Clin Infect Dis. 2008;46(8):1142–1151. doi: 10.1086/533441.
- Willing BP, Russell SL, Finlay BB. Shifting the balance: antibiotic effects on host–microbiota mutualism. Nat Rev Microbiol. 2011;9(4):233–243. doi: 10.1038/nrmicro2536.
- Teixeira Rodrigues A, Roque F, Falcão A, Figueiras A, Herdeiro MT. Understanding physician antibiotic prescribing behaviour: a systematic review of qualitative studies. Int J Antimicrob Agents. 2013;41(3):203–212. doi: 10.1016/j.ijantimicag.2012.09.003.
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