The antibiotic development pipeline is drying up. More companies are abandoning the area because antibiotics are expensive to develop and license, but they are low profit drugs that we try to use as little as possible.
This is a big issue for human medicine, and was the focus of a lot of discussion at this week’s Global Leaders Group on Antimicrobial Resistance meeting.
It’s a complex issue. I won’t get into the details here, but there are initiatives to support getting X number of new human antimicrobial products to market by year Y. That leads to the question of how many antimicrobial products we should be aiming to develop for animals, and whether we should aim for completely new “animal only” drugs.
At first glance, having antimicrobials that are only used in animals would be ideal, so that they are distinct from those used in humans, and therefore any resistance that developed in bacteria from use in animals would not impact resistance to the unrelated antimicrobials used in people.
Unfortunately, as with most things about antimicrobial resistance (AMR), it’s not that straightforward. It’s not “drugs” we need to think about, it’s “drug classes.” A new drug that’s just a slightly different version of (and works the same way as) drugs we currently use in people isn’t what we want. We need new drug classes that are different in how they work and how bacteria become resistant to them. That’s a much tougher order.
If I had to characterize a “great animal-only antimicrobial class,” I’d say it should be:
- Effective against a range of bacteria that cause disease (in animals)
- Able to be given orally (vs injectable)
- Low cost
- Safe (in the target species, or ideally in multiple species)
- Not persist in the body for long after treatment (to shorten withdrawal times for meat and milk)
- Not excreted into the environment in urine or feces
And the big one: if resistance develops to our animal-only drug, it doesn’t also confer resistance to human drugs.
That would be great.
However, what else did I just describe? A perfect ‘human-only’ drug.
I’d rather use that drug in people than launch it for use in animals.
So, unless we have a new drug class that fulfills those properties and is toxic in people but not animals OR only works on a pathogen that’s of relevance in animals, we’re not likely to get a completely new useful animal-only drug class that would not impact resistance in people.
That doesn’t mean we shouldn’t keep it in mind and explore new drug classes that have been rejected for use in humans (which is already a prime source of many animal drugs). However, it means our main focus should be saving the drugs we have so we don’t need to worry about finding new drug classes. That’s why we need to focus on better animal health systems to reduce the need for antimicrobials, better education and support systems to optimize antimicrobial use, and more study about what situations contribute to more or less resistance risk. That’s antibiotic stewardship.