Ivermectin is great for parasitic infections in dogs. Ivermectin as a cancer treatment? Not so much.
Caller Debbie has gotten her dog with lymphoma through chemo, and he is in remission. But she has some questions after someone recommended that she put her dog on ivermectin as a follow-up to chemo.
Oncologist Brooke Britton weighs in with the issues with the limited research on ivermectin and cancer, plus the very real risks of giving this drug for extended periods of time or at high doses.
[00:00:00] >> Dr. Brooke Britton: No medication is benign. If your dog doesn’t have a parasitic infection for which ivermectin would otherwise be warranted, I would not recommend using it as a maintenance after chemotherapy.
[00:00:12] >> Announcer: Welcome to Dog Cancer Answers, where we help you help your dog with cancer.
[00:00:19] >> Molly Jacobson: Hello, friend. Thank you for joining us. Today we’ve got a caller, Debbie from South Carolina who has a question about ivermectin. And to join us to answer is Dr. Brooke Britton. Thank you so much for joining us today.
[00:00:33] >> Dr. Brooke Britton: Thank you so much for having me.
[00:00:35] >> Molly Jacobson: Let’s listen to Debbie’s question.
[00:00:37] >> Debbie: Hello, my name is Debbie. I’m calling from South Carolina. My dog has cancer, 14 year old Lab Retriever Husky mix, has lymphoma type B and is blind from a secondary infection as a result of the cancer. He just finished his chemo protocol, and I have a question regarding ivermectin, which is suggested by a holistic veterinarian that I know, uh, suggests to give ivermectin in doses of 200 micrograms per kilogram of weight for at least 30 days.
And after that, suggested to give the dog a break to avoid toxicity. My question is, how will I know how much of ivermectin to give my dog before it could possibly become toxic? Should I take him to my regular veterinarian for blood work? What should the veterinarian look for in the blood work to see if there’s toxicity as a result of ivermectin in my dog’s system? Ivermectin is a new therapy, just groundbreaking for use in cancer for dogs as well as humans, therefore, not a lot of information is out there about it, but that is my question, and thank you very much.
[00:01:51] >> Molly Jacobson: So, Dr. Brooke Britton, let’s wade into the murky waters of ivermectin use in cancer, which certainly has been a topic as of late.
[00:02:02] >> Dr. Brooke Britton: Okay. Yes. Definitely ivermectin has come more to the forefront and I’m starting to get more questions about ivermectin again from an anti-cancer perspective and with COVID. So there have been a lot of people doing research on ivermectin. And I’m sorry to hear about your dog, Debbie, and I’m glad that your dog sounds like they’re doing well and went through a chemotherapy protocol and we’re now done. So that’s a huge milestone completed. So congratulations on that.
As for ivermectin, the reason that there’s not a lot of, if any, information out about ivermectin with regard to lymphoma is that we don’t have any data to support using it in dogs with lymphoma. Ivermectin, as you likely know, is an anti parasitic drug, so it’s used to treat dogs that have parasitic infections including heartworm.
From an anti-cancer perspective, we have no proof that ivermectin is operational or effective as an anti-cancer drug. There is some more recent data in people for carcinoma cells, which is a different type of tumor, in the Petri dish, what we call in vitro, that says that very high concentrations of ivermectin can kill some of those cells.
But when you look at those studies, the concentrations that you would need to have in the body of ivermectin to have the same effect in the body would cause significant toxicity in a human or in a dog, for example. And so we don’t give ivermectin at those very high doses because it can have significant toxicity.
In addition, there is no data to suggest that ivermectin would be effective at any dose for lymphoma cells. Lymphoma is a very different type of cancer, it’s a type of immune system cancer, and ivermectin is not known to be effective against lymphoma or have any type of anti-cancer benefit for dogs with lymphoma.
We also do not suggest using anything, really, any drug as a maintenance, quote unquote, "maintenance" therapy for lymphoma. If your dog has gone through and completed chemotherapy protocol that is standard of care such as CHOP, for example, which is the most common type of chemo protocol that we use in dogs with lymphoma, there’s no need to do a maintenance therapy.
And so in answer to your questions, I would not recommend a maintenance with ivermectin, and I would not – it’s not that the dose that your veterinarian recommended is not appropriate for treating as an anti-parasitic, but if your dog does not have evidence of parasitic infection that requires ivermectin treatment, there’s no added anti-cancer benefit.
[00:04:54] >> Molly Jacobson: Wow. Okay. That was pretty clear. We’re going to take a brief break, but when we come back I’d like to ask you more about ivermectin toxicity.
And we’re back with Dr. Brooke Britton. Did I hear you correctly, ivermectin can be toxic to dogs?
[00:05:12] >> Dr. Brooke Britton: From a toxicity perspective, we can actually see very serious toxicities with ivermectin, usually at very high doses, but in some dogs, and some breeds that are predisposed to toxicity at lower doses, and those can be very serious. They’re usually neurologic in nature. Usually dilated pupils, unsteadiness when walking, seizures, and in some severe cases, death. So no medication is benign. If your dog doesn’t have a parasitic infection for which ivermectin would otherwise be warranted, I would not recommend using it as a maintenance after chemotherapy.
[00:05:49] >> Molly Jacobson: So is that dose of 200 micrograms per kilogram of weight, is that the dose that you would give for a parasitic infection?
[00:05:56] >> Dr. Brooke Britton: That’s in the range, but I would hesitate to say if that’s an appropriate dose, even for a parasitic infection in this dog, because I don’t know this dog’s weight, I don’t know this dog’s medical history, and so I would not, you know, give advice on dosing for Debbie’s particular dog even for a, a parasitic infection. But I don’t think it is warranted for maintenance treatment after a chemo protocol with lymphoma. There’s no data to suggest that that provides benefit, and it could be toxic over time.
[00:06:29] >> Molly Jacobson: It just doesn’t sound – like it’s not that this dose is too high, like high enough to actually have an effect possibly in sarcoma, it’s that no dose is safe at that for 30 days. You wouldn’t do that for a dog, it sounds to me like you’re saying.
[00:06:45] >> Dr. Brooke Britton: Well, and the question is, you know, it sort of begs the question, where is the data to support using it? And then even if we were saying in the Petri dish it had an effect against some type of cancer, we don’t know, even for carcinomas – which that is what data is out there for this different cancer type, not lymphoma – but we don’t know exactly what dose is appropriate in the body translated from the Petri dish, and then for how long to give it.
And there aren’t comparison studies looking at standard of care treatment where we have a wealth of data out there to know what we get with the treatments that currently exist and are accepted versus adding this drug. But it is not an appropriate therapy for anti-cancer benefit at this time. It does not have anti-cancer benefit in dogs that we have shown, and certainly not for lymphoma.
[00:07:40] >> Molly Jacobson: Not for lymphoma. And is the data that’s out there enough – ’cause I know that typically, the way that science works, it’s sort of like a game of getting a lot of things wrong and, and less wrong and less wrong and less wrong until you get something right. Right.? Like so a small trial study at the beginning just to see like, what does this thing do in the lab? Then if it does well enough, then they move into bigger studies that have maybe an, a live animal, a mouse or another animal that they can test on.
[00:08:10] >> Dr. Brooke Britton: Mm-hmm.
[00:08:10] >> Molly Jacobson: And there’s more participants and they can do more things, they could find out more things. And then those lead to more questions: oh, well if this is safe, what’s the best dose for efficacy, as well as safety? And then, well, how do dogs do compared to the gold standard treatment? So there’s-
[00:08:26] >> Dr. Brooke Britton: That’s right.
[00:08:27] >> Molly Jacobson: -like lots of trials. And from my understanding, as a layperson who writes about science, most things start off with a lot of promise in the pilot trials. And then as they go through more trials, they fail.
[00:08:41] >> Dr. Brooke Britton: That’s right.
[00:08:41] >> Molly Jacobson: The things that start out with a lot of promise don’t end up being treatments. ‘Cause there’s a lot of things that kill cancer cells in Petri dishes, right?
[00:08:49] >> Dr. Brooke Britton: That’s exactly right.
[00:08:51] >> Molly Jacobson: But they’re not gonna kill cells in the body.
[00:08:52] >> Dr. Brooke Britton: Yeah. You can put mostly anything in a Petri dish and it’ll, and it will kill cells, including cancer cells. So a lot of things, a lot of things can kill cells and cancer cells included in a Petri dish, but translating that into the body or what we call in vivo, and understanding how a drug is absorbed in the body, what is the most appropriate dose and the safe dose. And do we know or think that it has any benefit at that safe dose, and efficacy.
You know, if we know giving a drug is safe, it doesn’t mean it does anything for a particular condition. And ivermectin can have some very serious toxicities. So it’s not something that I would recommend giving even just to see, you know, it’s, it’s not a benign therapy. It’s not like giving a sugar pill, you know, it can have some real serious neurological and other toxicities, and those may be severe enough that they could be life threatening.
So it is not something that we should just try because, you know, well, we wanna do everything we can. You know, with standard of care chemo, like in Debbie’s dog, especially with lymphoma, we know very well what we get with those drugs, the types of response rates, the types of outcomes in those dogs.
And so throwing in a, a drug at the end as a maintenance with no data to back it up is not ideal because of the potential for toxicity. We did well with chemo, we received standard of care, and I think that’s great and I think we would be tempting fate to do something like ivermectin. It’s just not recommended.
[00:10:31] >> Molly Jacobson: It’s too dangerous a substance to give on an ongoing basis without a medical reason for it, and lymphoma is not a medical reason for ivermectin. A parasitic infection would be.
[00:10:43] >> Dr. Brooke Britton: That’s correct.
[00:10:44] >> Molly Jacobson: But then it’s a short, right? I mean, that’s a short course of treatment for parasites. That’s not 30 days.
[00:10:50] >> Dr. Brooke Britton: That’s right. We wouldn’t do it for a month or months on end, even if it were a parasitic infection that we were treating. So I, I would not recommend it.
[00:10:58] >> Molly Jacobson: Yeah. Those side effects sound really disturbing. Not being able to walk, having seizures, that does not sound like a, a happy dog. That does not sound like quality of life to me.
[00:11:09] >> Dr. Brooke Britton: They can be really, um, effective to the quality of life and affecting to the quality of life and they can be extremely serious or life-threatening. So it is not something that’s recommended. And to Debbie’s other point, it is not a new treatment, you know, ivermectin is a really old drug. And so when we see it coming up and around again, it’s what’s called repurposed.
It means that we are looking at using it for a purpose other than which it was originally FDA approved. It doesn’t mean that that doesn’t happen for some drugs and that that’s not appropriate. We do find that-
[00:11:44] >> Molly Jacobson: Sure.
[00:11:44] >> Dr. Brooke Britton: -we originally approve a drug for this reason, and then we find out it’s effective against something else. And then it has to go through trials though for it to be formally approved for that something else through the FDA.
Sometimes we can use drugs off-label without a specific approval if there’s enough evidence to suggest that it is appropriate for another purpose. But in this case, ivermectin should not be used off-label to treat cancer in dogs if and until we have more firm data that supports that it’s effective and we know the dose that’s safe for them for anti-cancer purposes, if it even is there.
[00:12:23] >> Molly Jacobson: Right. What’s that saying? The dose makes the poison. And anything can be poisonous.
[00:12:30] >> Dr. Brooke Britton: Yes. Yeah, some of these drugs have a very narrow, narrow safety profile or narrow side effect profile. And sometimes we have a wide variety of what different dogs will tolerate. Just like in people, you know, what dose is good for your friend or your mom isn’t necessarily the dose that you are going to tolerate, which is why, as tempting as it is, doctors say don’t take your friend’s drugs.
If we have an antibiotic or, you know, a pain medicine, or a sedative or anything like that, you know, we don’t know how as an individual each dog is going to respond. That’s why there are dose ranges. But some of these dogs can be very severely affected even at lower doses with side effects. There are some dogs that have, for ivermectin, a specific mutation called an MDR mutation, which can predispose them to sensitivity. And that can be very, very severe, even at very low doses of ivermectin.
And in those dogs we say we can’t even treat, there’s the saying "white feet don’t treat" for ivermectin. So, it’s just very important to, um, understand that nothing is a truly benign treatment, especially not ivermectin. So that’s the reason why I’m so strong with my wording. I would not recommend it.
[00:13:48] >> Molly Jacobson: I’ve never heard you say that before. I’ve never heard you say that you just categorically would not recommend something. You usually are very careful to say this might be useful in some cases, right? Or your veterinarian might have a reason for using this, but that’s not what you’re saying here about ivermectin. You’re saying this is a serious medication that has toxicity associated with it, even when it’s used for its normal purpose.
And the evidence for lymphoma is not there and you’re really concerned about using it in dogs with cancer in general, ’cause we don’t know that it would help and it could very much hurt the dog. Am I summarizing you correctly?
[00:14:28] >> Dr. Brooke Britton: Absolutely. And it is used all the time. You know, it’s a drug that’s used all the time as a preventative, as an anti-parasitic in some of the very common prescription anti-parasitics, you know, heartworm preventative that lots of GPs dispense-
[00:14:44] >> Molly Jacobson: Yeah.
[00:14:44] >> Dr. Brooke Britton: -you know, once a year. So I’m not saying that it’s a horribly dangerous drug that shouldn’t be used.
[00:14:49] >> Molly Jacobson: No.
[00:14:49] >> Dr. Brooke Britton: I’m just saying in this particular instance, with lymphoma, the risks of using it outweigh the benefits of which we do not know of any benefits for lymphoma for this drug at this time. So if and until the studies come along that show that, I would not recommend it for Debbie’s dog. But I do think she’s already done a tremendous amount for her dog with taking that dog through a chemo protocol, and my hope is that she won’t have to, you know, suffer through a relapse with her dog down the line, or if she does, it’s a long time coming.
But there are options aside from ivermectin if relapse happens. So.
[00:15:29] >> Molly Jacobson: Yeah.
[00:15:29] >> Dr. Brooke Britton: That’s a whole other podcast.
[00:15:31] >> Molly Jacobson: Right, right.
[00:15:33] >> Dr. Brooke Britton: Uh, not ivermectin, I’m sorry to say.
[00:15:36] >> Molly Jacobson: Yeah. And yes, of course, Debbie is doing what she knows best to do for her dog, and she’s getting guidance from her veterinarian about this and very specific information and dosing recommendations. So she’s obviously a caring, loving dog owner who’s doing really beautifully by her dog and clearly, I mean, he’s gone through chemo protocols and he is 14.
[00:16:05] >> Dr. Brooke Britton: Yeah.
[00:16:05] >> Molly Jacobson: So he’s doing really, really well.
[00:16:07] >> Dr. Brooke Britton: Absolutely.
[00:16:08] >> Molly Jacobson: And she’s doing a great job. So any forcefulness that I’ve had in my tone or you’ve had in your tone has nothing to do with Debbie and how much she loves her dog. It has to do with wanting to make sure that people know this is a really serious choice-
[00:16:22] >> Dr. Brooke Britton: Yeah.
[00:16:23] >> Molly Jacobson: -that we all have to face of, is this truly going to benefit my dog? Like, are the risks associated with this worth the possible benefits. That’s a calculus we all have to make. And in this case, you’re saying the risks are way too high.
[00:16:36] >> Dr. Brooke Britton: Absolutely.
[00:16:38] >> Molly Jacobson: Thank you so much, Dr. Britton.
[00:16:39] >> Dr. Brooke Britton: My pleasure. Thank you.
[00:16:42] >> Molly Jacobson: And thank you, listener. You know, we all hope for a simple fix for our dog’s cancer, and we also hope that there’s something new because, frankly, the current strategies never guarantee that our dog’s cancer will be cured. In almost every case, there’s a lot of caveats and warnings and well we hopes and maybes and percentages that don’t add up to "this will help your dog beat cancer." And that’s an unfortunate fact about cancer.
So all of us, every one of us, including me for sure, we’re looking for the new thing that’s gonna solve the problem of cancer. Unfortunately, ivermectin is not that fix. There are promising results, that is true. Ivermectin does kill, it looks like, kill cancer cells in a Petri dish, but that’s not the same as doing it in a live body.
And right now it looks like the doses that kill cancer cells in a Petri dish are so high they would harm your dog. There are a lot of things that kill cancer cells in Petri dishes, but that does not equal a treatment that works in a warm, living, squirmy, lovely, running, chomping, happy dog body. So, at least for now, skip the ivermectin and ask your vet about treatments and medications that are proven to help with dog cancer.
You can learn about those different options out there, both the conventional treatments that you’ve heard of, but also herbal supplements, dietary changes, and many more, and all of our information on our website at dogcancer.com is science and evidence-based and vetted by veterinarians to see if it can help your dog and your dog’s specific cancer case.
I’d also like to thank Debbie for calling in. If you have a question for us like Debbie did, give us a call on our Listener Line, (808) 868-3200, and leave a message. We just might use your question for a future episode.
I’m Molly Jacobson. And from all of us here at Dog Podcast Network, I’d like to wish you and your dog a very warm, Aloha.
[00:18:55] >> Announcer: Thank you for listening to Dog Cancer Answers. If you’d like to connect, please visit our website at DogCancer.com or call our Listener Line at (808) 868-3200. And here’s a friendly reminder that you probably already know: this podcast is provided for informational and educational purposes only. It’s not meant to take the place of the advice you receive from your dog’s veterinarian.
Only veterinarians who examine your dog can give you veterinary advice or diagnose your dog’s medical condition. Your reliance on the information you hear on this podcast is solely at your own risk. If your dog has a specific health problem, contact your veterinarian. Also, please keep in mind that veterinary information can change rapidly, therefore, some information may be out of date.
Dog Cancer Answers is a presentation of Maui Media in association with Dog Podcast Network.