Antibiotic timing
Also called: antibiotics before immunotherapy.
Last reviewed 2026-09-16. How this works.
Avoiding unnecessary courses around immunotherapy Grade B
Good human evidence, with a limit worth knowing.
Antibiotics given around the start of immunotherapy seem to make it work less well.
Consistent observational evidence, and it already changes practice.
The claim
The claim is that antibiotics taken around the time immunotherapy starts reduce how well it works, by disturbing the gut bacteria the treatment appears to depend on.
What it does
Checkpoint immunotherapy works through the immune system, and the gut microbiome shapes how that system behaves. Antibiotics clear a large part of it indiscriminately.1
The evidence
Antibiotic consumption was associated with poor response to this class of immunotherapy in people with epithelial tumours. Non-responders with lung and kidney cancers had low levels of one particular organism.1
The mouse half of the same work is what raises this above a correlation. Giving that organism back to antibiotic-treated mice restored the response to immunotherapy, which points at a mechanism rather than just an association.1
This entry is graded B rather than higher because the human evidence is observational: nobody has randomised people to receive antibiotics or not, and nobody ever will. It is graded B rather than lower because it is consistent and because it already changes how careful teams sequence treatment.1
What this is not is a reason to decline an antibiotic that is needed. An untreated infection during cancer treatment is a far more immediate danger than a possible reduction in response, and the question is about unnecessary courses.
The studies this rests on
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Antibiotic use and response to PD-1 blockade in epithelial tumours1
An observational study, measured a clinical outcome.
antibiotic consumption associated with poor response to PD-1 blockade.
What is absent
No trial has randomly assigned people to receive antibiotics or not around immunotherapy, and none is likely to, because withholding a needed antibiotic would not be acceptable.
Scope: antibiotic timing around immunotherapy.
Established by trial scope, checked 2026-09-16. Result: the human evidence in this record is observational; the causal element comes from mouse experiments.1
What to ask
If I need an antibiotic while I am on immunotherapy, does the timing of it matter?
The dish-to-person gap
This entry is about the timing of a prescribed treatment rather than about a compound reaching a concentration.
When to call your team — no warning signs are recorded
If this is something you are considering or have already had done, the people treating you can only weigh it if they know about it. That is true when nothing has been written down here, and it is most true then.
The register records no warning signs for this entry. Nothing here is a reason to decline an antibiotic that is needed, and an infection during cancer treatment is itself dangerous.
Interactions
This is the clearest treatment-class interaction in the register, and it runs between two prescribed treatments rather than between a supplement and a drug. Antibiotic use around the start of checkpoint immunotherapy has been associated with poorer response. It is a question for the team prescribing both.1
Antibiotics around the start of checkpoint immunotherapy
Recorded as documented, against Checkpoint immunotherapy.
If I need antibiotics around the time my immunotherapy starts, is the timing something you would weigh?
The whole interaction list, and how to turn it into a pharmacy review request.
Find a trial instead
This is a question about how existing treatments are sequenced, not an intervention to enrol in.
References
Routy B, Le Chatelier E, Derosa L, et al. Gut microbiome influences efficacy of PD-1-based immunotherapy against epithelial tumors. Science 2018;359:91-97.
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 23 note 1. The author string is abbreviated in the source that was read and has not been expanded.