I’m on my way back from Copenhagen where we had a very productive meeting to update the ISCAID pyelonephritis antimicrobial treatment guidelines for dogs and cats. As the process for developing guidelines like these has matured, it’s no longer about simply getting some very smart people in a room and agreeing on recommendations; it’s now a much more structured, evidence-based process. As part of that, we think about more than just “would this drug work?” We also think about factors like adverse effects, cost, acceptability, feasibility, equity and others. One of the newer consideration is now “planetary health,” which is applicable to a lot of things, including antimicrobial use guidelines.

Antimicrobial production, distribution and use have carbon footprints and require other resources that impact more than the individual who gets treated with the drug. (And yes, I fully recognize the irony of talking about carbon footprints while flying across the Atlantic in a plane, but sometimes in-person meetings are important too.) While we’re not going to dramatically alter our guidelines based on a drug’s carbon footprint, it’s something we need to at least think about for awareness. A side benefit of good antimicrobial stewardship resulting in less antimicrobial use is smaller footprints of this sort. But, are those footprints really relevant? It’s always hard to figure out what the contribution of something like a drug (or a flight) is to the big picture, and individual events have near negligible impacts. But, when we do something over and over and over again, the cumulative impact starts to become more relevant.

What do we know about the ecological impacts of antimicrobials? I’m far from an expert in this, but it’s interesting, so I’ll just toss out a few points – food for thought.

• Human healthcare has been estimated to account for 8.5% of US greenhouse gas emissions; 10% of that is from drugs, with antibiotics accounting for a lot of that. Based on an estimate that 30-50% of antimicrobial prescriptions being unnecessary, and including associated paper and plastic waste, it was estimated that the annual carbon footprint from unnecessary prescriptions in the USaccounts for 1887.374 CO₂e/ton of greenhouse gas emisision (Spivak et al. 2024), the equivalent of driving 4,838,375 miles in an average car.
• Similarly, in the UK, it was estimated that 3 antibiotics alone contributed 15% of drug-associated emissions and that a 20% reduction in use could save 4200 tonnes of CO2 per year (Taylor et al. 2024), the equivalent of removing 29,000 cars from the road.
• Production of methane in freshwater sediment increased up to 94% in the presence of antibiotics (Bollinger et al. 2021). Since antibiotics end up in the environment in massive amounts when used in people or animals (e.g. via excretion in urine and feces), or when they’re applied directly to the environment (e.g. trees, crops), that’s noteworthy.
• Tetracycline treatment of cattle affected the microbes found in their feces (not surprisingly) and in dung beetles (Hammer et al. 2016). Treatment also raised methane fluxes from feces, showing that the complete ecological effects may be even more complex.
• Another study (Ali et al. 2025) examined the impacts of transitioning patients from intravenous (IV) to oral antimicrobials at a single hospital. (In general, there’s lots of unnecessary use of IV antibiotics in healthcare, with associated risks and costs, so this kind of transition is an important antimicrobial stewardship goal.) The researchers found that an intervention to de-escalate to oral treatment resulted in reduction of 107 kg of waste and 261 kg of CO₂. They estimated that the carbon footprint of every prolonged IV use equated to 6.2 km of driving, or running a 10W light bulb for 1200 hours. That may sound small at first, but when it happens a lot, the numbers add up.

That’s a random collection of studies on the topic, and ultimately we don’t really know the full downstream effects of antimicrobial use, but it’s fair to say that these drugs have a big carbon footprint, and we can reduce it through antimicrobial stewardship: using fewer antibiotics, using them better when necessary, and, most importantly, optimizing health so we don’t have sick people or animals to treat in the first place.