UMEM Educational Pearls

Title: Myth Busters: Antibiotic Edition (Created by Rianna Fedora, PharmD; PGY2 Emergency Medicine Pharmacy Resident)

Category: Pharmacology & Therapeutics

Keywords: Bactrim, skin and soft tissue infections, Streptococcus spp (PubMed Search)

Posted: 3/14/2024 by Wesley Oliver
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MYTH: Bactrim cannot be used as monotherapy for nonpurulent skin and soft tissue infections.

Not True!

Organisms of concern: Streptococcus spp.

Here’s why:

Sulfamethoxazole-Trimethoprim (Bactrim) disrupts folic acid synthesis & utilization.
This prevents the biosynthesis of the nucleic acid thymidine by bacteria and causes them to die.
Some species of Strep, including S. pyogenes, are able to utilize exogenous sources of thymidine to continue their life cycle.
Guess what? The laboratory media that was originally used to test Strep spp. susceptibility to Bactrim contained thymidine - therefore the bacteria were able to use it and did not die!
When tested using thymidine-depleted media, all 370 S. pyogenes isolates tested were highly susceptible to Bactrim!

TRUTH: Bactrim CAN be used as monotherapy for nonpurulent skin and soft tissue infections.

Prepared by Rianna Fedora, PharmD on 2/26/24

Bowen AC et al. “Is Streptococcus pyogenes resistant or susceptible to trimethoprim-sulfamethoxazole?.” Journal of clinical microbiology vol. 50,12 (2012): 4067-72. doi:10.1128/JCM.02195-12.
Coll FP et al. “Exogenous thymidine and reversal of the inhibitory effect of sulfamethoxazole-trimethoprim on streptococci.” European journal of clinical microbiology vol. 3,5 (1984): 424-6. doi:10.1007/BF02017363.
McCreary EK et al. “Antibiotic Myths for the Infectious Diseases Clinician.” Clinical infectious diseases : an official publication of the Infectious Diseases Society of America vol. 77,8 (2023): 1120-1125. doi:10.1093/cid/ciad357.