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Yes—some tested products formed as antibiotics break down selected for antimicrobial resistance at levels comparable to or higher than their parent drugs. In a 2026 experiment using wastewater-derived microbial communities, several products enriched the resistance-associated gene intI1 during seven-day tests. The result applies to the compounds and experimental systems studied; it does not show that all antibiotic breakdown products act this way or quantify effects on human health.
What the 2026 study found
Lakhey and colleagues’ study, “Antibiotic transformation products exert selective pressure for antimicrobial resistance comparable to parent compounds,” appeared in Nature Water on 8 June 2026. It compared antibiotic transformation products (TPs)—chemicals formed when antibiotics are transformed—with their parent compounds in wastewater-derived microbial communities. The researchers used growth-based assays and seven-day evolution experiments. Read the study in Nature Water.
The work covered fluoroquinolones, sulfonamides, and macrolide–lincosamide–streptogramin antibiotics. Chemistry World reported that the team tested 15 transformation products and collected wastewater samples from treatment plants in Brisbane, Australia, and Falmouth, UK. Chemistry World’s report describes the study and its context.
Some products remained biologically active
Several transformation products had lowest observed effect concentrations only twofold higher than those of their parent antibiotics. Moxifloxacin sulfate and descladinose roxithromycin inhibited growth more strongly than their respective parent drugs. These findings show that transformation does not necessarily remove biological activity, but the effects varied by product.
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Resistance-associated gene enrichment was comparable or greater
In the seven-day experiments, desmethyl ofloxacin, N-acetyl sulfamethoxazole, and desmethyl erythromycin enriched intI1 at levels comparable to or above those observed with their parent compounds. intI1, the class 1 integron gene measured in the study, served as an indicator of AMR-associated change in the bacterial communities. Its enrichment is not a measurement of clinical infections, treatment failure, or patient outcomes.
What “metabolised antibiotics” means here
The study uses the term “transformation products.” These are chemicals produced as antibiotics change through biological or other transformation processes. They are not necessarily metabolites formed inside a person’s body. The word “metabolite” can suggest human or animal metabolism, so “transformation product” is more precise for the environmental compounds discussed in this work.
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As study lead and University of Queensland researcher Pooja Lakhey told Chemistry World, “Most of the time we consider metabolites to be not harmful, or less harmful, than the parent compounds.” The study’s results challenge that assumption for some of the products tested, not for every antibiotic or every product formed from one.
What the results do—and do not—establish
- Established: Some tested transformation products retained biological activity and selected for intI1 enrichment in the experimental wastewater-derived communities.
- Not established: The study does not quantify how much these products contribute to antimicrobial resistance in people or the environment, or estimate any resulting human-health burden.
- Not established: The findings do not show that every antibiotic transformation product behaves like its parent, or that the same effects occur in every wastewater system.
- Not demonstrated: The study does not establish that a particular wastewater treatment process eliminates the selective effect.
Those limits matter when interpreting “just as much.” It describes a comparison for selected compounds under the study’s experimental conditions, based on the measured enrichment of intI1; it is not a general ranking of all antibiotic breakdown products or a population-level risk estimate.
Why wastewater monitoring may need to include transformation products
The authors argue that transformation products should be considered alongside parent antibiotics in antimicrobial-resistance surveillance, treatment evaluation, and environmental risk assessment. If a parent drug changes into a product that still exerts selective pressure, measuring only the original antibiotic could miss part of the biological activity in a wastewater system.
That is a case for evaluating these compounds in environmental monitoring and treatment research—not evidence that household filters or consumer water-test kits prevent or measure the effects described. The study identifies a question for wastewater assessment; it does not validate a consumer intervention.
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Microbiology expert Lena Ciric of University College London told Chemistry World, “These plants are geared towards lots of other things and if they remove some antibiotics, then that’s a bonus, but that’s certainly not an aim.” Molecular microbiologist Holly Tipper of the UK Centre for Ecology and Hydrology said, “It points to a clear need for more research, which I think should include the development of community-level assays to better capture biological effects.”
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Publication correction
A correction published on 30 June 2026 amended co-author William H. Gaze’s name, which had previously been rendered as “Willam H. Gaze.” The correction notice does not report a change to the study’s findings. Read the correction notice.
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