H&H Podcast Episode 3 – Yes, you have to take ALL of the antibiotics!
So many people tell me that they stop their course of antibiotics early, or truncate it in some way. Maybe they split the pills in half. Maybe they’re supposed to take it twice a day and they take it once a day. Something like that. I also have pet owners and livestock owners frequently tell me that, as the primary caregiver of their animals, they often do the same thing. I think the explanation that gets me the most upset is “saving some for later.” I’m really, really excited to get into this. This is going to be pretty technical and probably boring to everyone but me, but I think it’s easily the most important thing we are ever going to cover, because every listener either does this or has a family member that does this, and it’s a direct threat to your own health.
Let’s explain why shortening or decreasing your course of antibiotics is tinkering with something you don’t understand. It’s not as simple as just cutting a dose in half or stopping the course a few days early. There are a lot of decisions a doctor has to make every time they write a prescription for antibiotics. A prescription gives explicit instructions that cover several decisions: 1. Which antibiotic is being prescribed? 2. What dosage? This is the amount, or mg, sized pill. 3. What dose? This is how many of those mg pills you take in a single sitting. 4. How frequently? This is how often in a day, so for example twice a day (or every 12 hours). 5. For how long? For example, for 10 days. Each one of these things is based on the way that the particular antibiotic functions inside the body. So let’s break each of these choices down. There’s a lot going on here so pour yourself a cocktail and get ready. Or a cup of coffee.
Kevin: Aren’t all antibiotics the same. Don’t they all kill bacteria?
There are many classes of antibiotics, some as old as penicillin and some that just came onto the market yesterday. Every class of antibiotic is suited to kill a different kind of bacteria. Some antibiotics are broad spectrum, meaning they do a moderately okay job at killing a little bit of everything. Some antibiotics are what we call “big guns”, which means they are specialized killers of a very specific bacteria. And then you’ve got everything in between. Different areas of infection in the body grow different kinds of bacteria, which means that the antibiotic chosen needs to be the kind of antibiotic that’s effective against the particular bacteria growing in that area. It gets a little more complicated than that, too, when you introduce the concept that the antibiotic chosen also has to be able to make it to its intended destination in the body. Every antibiotic is picked up by the body in different ways, spread around in different ways, and has different interactions with all the different types of tissue. This means that not only do we pick the right drug to fight the specific infection you have, but we also need to make sure that drug has the tools (or the pharmaceutical engineering) necessary to make it all the way to the part of the body that’s affected. For example, maybe you’ve got Bacteria A infecting the femur bone after a motorcycle accident. There will be a list, which might be long or might be short, of things that will work against Bacteria A. But which one of those things has the capability to unlock and penetrate into femur bone?
Kevin: So when I go to the doctor and they prescribe me a bunch of tablets, how do they decide which tablet size?
Dosage is based on body weight, and although in human medicine for the most part there are pretty standard pill sizes, we have a huge variety in pill sizes in veterinary medicine. We may walk into an exam room and prescribe 50mg of amoxicillin to a cat, then walk into the next room and prescribe 950 mg of amoxicillin to a Great Dane. But generally speaking, the reason this is based on body weight is because in order for the antibiotic to function, it has to reach a certain concentration inside the body or the body part it’s going to, so there has to be enough of it to go around.
Kevin: Okay then, why are some antibiotics once a day, some twice a day….?
Dose frequency! Okay this is the most important part!! Listen up. We just mentioned how there has to be enough antibiotic to go around so that it can reach a certain concentration inside the body. This is called the “therapeutic level.” So let’s say you’ve got that bladder infection, right? In order for the amoxicillin to infiltrate the bladder, which is where it needs to be, let’s say for discussion purposes it has to reach level 10 concentration in the body. Remember that idea. Level 10. Now, consider the fact that every antibiotic dose will only be effective for a certain amount of time. You take a single dose of medication, and as that dose gets absorbed, you slowly climb up to level 10, and after a certain amount of time, level 10 starts declining because the dose only lasts for so long. The art of dose frequency is to figure out the perfect timing of doses so that you don’t let the level decline too much. Ideally, you want the level to stay a plateau at level 10 so that you know it’s working to its full capabilities. The antibiotic might take 1 hour to reach level 10, or it might take 12 hours to reach level 10, or it might take 100 hours to reach level 10. So if you’re supposed to take something twice a day and you skip a dose, you’re undoing every single dose that happened before the skipped dose, and every dose after it, because you totally blew the drug’s ability to climb up to that level and be maintained at that level.
Kevin: Why should my dog or cat keep taking them if they feel better?
This ties in every single decision we mentioned leading up to this. How LONG to take your antibiotics is based most importantly on how long Level 10 has to stay at level 10 in order to kill all the bacteria in the infection that you’re fighting. For example, for your bladder infection, it might be that the bacteria living in your bladder can fight the antibiotic for 7 days, and after 7 days the troops are dying left and right and the antibiotic has won. What that means for me as a prescriber is that I’m giving you a course of 10 days, because I don’t want any troops limping away from the battlefield. I want the infection completely obliterated, because every single tiny bacteria that survives has the ability to mutate and be resistant to the antibiotic it just got cozy with for 7 days. With bone infections, sometimes it takes antibiotics a full 14 days to even break into the bone to begin with, before they can even start fighting the infection that’s living inside of the bone. Once they get into the bone, it generally takes at least a month to deal with whatever is living there and infecting there, so you’re talking a course of at least 45 days. Can you imagine if you stopped taking your antibiotic on day 21? Your troops just breached the enemy wall for the first time, and you’re pulling them out of the battle. They may not have even reached the right level of concentration to be effective yet. But now you’ve given the enemy a chance to see the troops, familiarize with how they breach a wall, and the tools to be resistant next time, not even just to that antibiotic, but probably to an ENTIRE CLASS of antibiotics.
Soon we will be start uploading our podcast episodes for you to listen to. In this episode we also discussed a couple tidbits on antibiotic usage in animal food products such as dairy and meat, and we covered antibiotic resistance more thoroughly than is discussed in the blog.