Fenbendazole is a common anthelmintic (dewormer) for dogs and other animals. As a veterinarian, I prescribed this drug for pets all the time. So how did this dog dewormer become known as a treatment option for cancer patients? The story is fascinating.
In August 2016, Joe Tippens was undergoing treatment for small-cell lung cancer. This is an aggressive cancer and difficult to treat. In spite of intensive treatments, the cancer continued to spread all over his body and he was given 3 months to live. As a last ditch effort, they enrolled him in a clinical trial studying a new anti-cancer drug (Keytruda) in January 2017.
Joe had a veterinarian friend who called him and told him about a study in mice that had been done by a scientist with Merck pharmaceutical company. The mice were in a cancer research study, but they had parasites, so this scientist gave the mice fenbendazole. Surprisingly, the tumors in the mice disappeared along with the parasites. This was obviously an unexpected finding and was reported in the research paper. This same scientist was later diagnosed with stage 4 brain cancer and started taking fenbendazole and her cancer went into remission!
Joe’s veterinary friend (shout out to veterinarians who often know more than medical doctors!), said why don’t you give this a try, what have you got to lose? Without telling his doctors, Joe started taking fenbendazole (222mg) along with curcumin, vitamin E and CBD oil while he was part of the clinical trial. He was in bad shape at 115 pounds with metastases all over his body. After 3 months of this regimen, a PET scan showed no evidence of disease anywhere. Joe was the only one of 1100 participants in the clinical trial who survived and he is still alive today! His story became a global sensation.
Since that time, fenbendazole has been studied in cell cultures and animal models, demonstrating anti-tumor effects against multiple cancer types including pancreatic, ovarian, lung, melanoma, lymphoma and more. They have found many mechanisms of action for fenbendazole against cancer, but it is not approved for use in humans. There is still a lot of controversy around this drug, which I will touch on in this post.
WHAT IS FENBENDAZOLE (FBZ)?
Fenbendazole belongs to a class of drugs called benzimidazoles, which are anti-parasitic agents. Human versions of this drug include Mebendazole, Flubendazole and Albendazole. All of these drugs were developed in the 1970s and used mainly to treat worms in humans and animals.
The main way FBZ works is by inhibiting microtubule function. Microtubules are hollow tubes made up of proteins. They play a crucial role in many functions of cells including cell division, cell structure, intracellular transport of cellular components and organelles and even division of chromosomes during mitosis.
FBZ is a microtubule destabilizing agent, which causes microtubule depolymerization. In plain English, this means it binds to one of the proteins that makes up the microtubule, called beta-tubulin and breaks the microtubule down into its smaller components. This shrinks the microtubule down and disrupts its functions.
The reason I am telling you all this is because this is the exact same thing that some very common chemotherapy agents do. These chemo drugs are called vinca alkaloids and include vincristine and vinblastine among others. The difference between FBZ and these chemo drugs is that FBZ binds to a different area of the receptor than they do and is way less toxic.
Paclitaxel and Docetaxel, two commonly used chemo agents for treating uterine cancer, are microtubule stabilizing agents. Whether you destabilize or stabilize microtubules, you disrupt the microtubule dynamics in rapidly dividing cells. This stops their ability to divide and leads to cell cycle arrest and eventually apoptosis (cell death). This is how these drugs kill cancer cells.
HOW DOES FENBENDAZOLE TREAT CANCER?
Besides disrupting microtubules, FBZ has other mechanisms of action against cancer cells, which I will outline below.
- By down regulating glucose uptake in cancer cells and reducing lactic acid in the tumor microenvironment, FBZ starves cancer cells of energy. It is also effective against drug-resistant cancer cells which thrive in an acidic tumor microenvironment
- According to Dr. Thomas Seyfried, a well-known metabolic disease and cancer researcher, cancer and parasitic worms depend on fermentation metabolism, thus drugs that block this tend to kill both
- FBZ depletes glycogen stores in cancer cells. Cancer cells need a constant supply of nutrients and energy. If you deplete the stored glycogen in the cells, you starve the cancer
- It induces oxidative stress in cancer cells, leading to cell death
- Enhances apoptosis
- Inhibits cancer cell viability by inhibiting the PI3K/mTOR signaling pathways
- Inhibits cancer cell migration and invasion related to epithelial to mesenchymal transition, where cancer cells take on stem-cell properties
- May impair tumor angiogenesis via decreases in Wnt-β catenin and VEGFR levels
- Decreases signaling proteins necessary for cell proliferation and survival
- Reduces tumor colony formation and inhibits stem-ness of cancer cells
- FBZ works synergistically with other chemotherapy drugs (paclitaxel, docetaxel and others) to be more effective at killing cancer cells
- FBZ boosts production and increases activation of p53. P53 is a very important tumor-suppressor gene that is often turned off or mutated in uterine cancer patients. Without this gene cancer cells can continue to proliferate unchecked. By reactivating this gene you stop cancer proliferation
- Inhibits GLUT1 transporter. The GLUT 1 transporter is highly expressed in 50% of patients with adenocarcinoma (most uterine cancers are endometrial adenocarcinoma). Glucose is delivered across the cell membrane through this transporter. Without glucose, cancer cells can’t survive, it is their primary energy source
- Not only does it stop the glucose from being delivered, it inhibits glucose metabolism by cancer cells
- Has been shown to have cytostatic (suppression) and cytotoxic (killing) effects on tumor cells in culture with 24 hours incubation and higher concentrations
- Minimal toxicity to normal cells, but highly toxic to cancer cells
IS FENBENDAZOLE SAFE?
Fenbendazole differs by one atom from mebendazole, the FDA approved human benzimidazole. Mebendazole, albendazole and flubendazole (human drugs) are being studied for their anti-cancer effects in human trials, but not fenbendazole, even though they are all very similar as you can see below.
All four of these drugs are metabolized in the liver to a common active compound called oxfendazole. Oxfendazole is well-tolerated in humans. Pharmaceutical companies it seems, are trying to develop oxfendazole into an anti-cancer drug. In one study with 70 healthy human subjects, oxfendazole was found to be safe even after repeated daily doses of 15 mg/kg dosing. So why is fenbendazole not being studied in human trials and being suppressed as an anti-cancer drug? Once again, it likely comes down to money.
Pharmaceutical companies will not make money on FBZ so it has not been approved for human use. It is very cheap and you can buy it over the counter from any pet supply store. Mebendazole, on the other hand, is very expensive. I once bought a bottle of 30 capsules for over $80 dollars. Remember, they are not concerned with curing cancer or even promoting effective alternative treatments if it will not benefit them monetarily.
Not only do they not want us to know about FBZ, but it seems they want to scare people away from using it. There are two case reports of liver toxicity in patients who self-administered FBZ and they pop up almost immediately with a Google search on FBZ and cancer.
Let me tell you about these two case reports
- In one, a 67 year old woman, with a history of colorectal cancer, started taking FBZ for a suspected pre-cancerous skin lesion. She was also on hormone replacement therapy, taking cephalexin (an antibiotic) and drank 2 glasses of wine per day. She self-administered FBZ at 3 grams per day, 3 days a week for one year when she developed severe liver toxicity. Within 3 months of stopping the FBZ, the liver injury resolved. This was a massive dose of FBZ and for a very long period of time, but it’s interesting that she didn’t develop toxicity until she started taking the antibiotic.
- In another case report, an 80 year old woman with stage 4 non-small cell lung cancer on Pembrolizumab (Keytruda), started taking FBZ 1 gram per day 3 days a week for one month. She developed liver toxicity, which completely resolved when she stopped the FBZ. In this case we have a very elderly woman with stage 4 cancer, taking the highest recommended dose of FBZ for a month and who knows what other medications she may have been on.
So is FBZ safe? Yes, if you take safe doses and use caution. In this paper (you have to scroll way down to find it), they make the following statement: Based on limited human data it appears that doses up to 500 mg per person did not result in adverse effects. Moreover, single doses up to 2000 mg (2 grams) per person were reported to cause no adverse effects. Read More
POSSIBLE SIDE EFFECTS OF FENBENDAZOLE
Side effects from FBZ are rare, but they do occur as with any drug. FBZ is still much safer than chemotherapy drugs.
FBZ is metabolized in the liver and excreted in the feces and the urine. If you have liver disease or genetic abnormalities with the CYP450 and other CYP enzymes in your liver, use caution when using FBZ. Liver toxicity may occur, which is reversible.
FBZ has been reported to cause bone marrow suppression with high doses in a dog, mice, birds and reptiles. This is a very rare side effect in animals and was associated with high doses of FBZ. In my research, this has never been reported with the use of FBZ in humans, but it has been reported with the use of mebendazole.
Gastrointestinal upset including nausea, diarrhea, vomiting or cramping may occur.
Please note, all of these same side effects are reported for mebendazole as well.
HOW IS FENBENDAZOLE USED
Fenbendazole, also known as Panacur and Safeguard in the veterinary world, comes in capsules and powdered forms.
It is not well absorbed in the intestinal tract and bioavailability is low due to its poor water solubility. For this reason it is best if taken with a fatty meal.
There are three dosing regimens:
LOW-DOSE 222 mg daily
INTERMEDIATE DOSE 444 mg daily
HIGH DOSE 1000 mg (1 gram) 4 days on, 3 days off
Joe Tippens took 222 mg of FBZ 3 days per week. This is the 10 pound dog dose of Panacur. One packet is 222 mg of fenbendazole in 1 gram of powder. I also took this dose 3 days a week with no problems. I mixed the powder with full-fat yogurt and a little stevia and never noticed it.
FBZ may be even more powerful against cancer when combined with ivermectin. See my post on ivermectin here.
It is always best to work with a naturopathic doctor to help you navigate repurposed drug use and monitor your labs and make sure you are tolerating these medications. Do not take high doses of this drug without supervision by a doctor.
SCIENTIFIC REFERENCES
The benzimidazoles are effective against cancer, whether it is FBZ, mebendazole, flubendazole or others. Here are some references.
- Oral fenbendazole for cancer therapy in humans and animals Read More
- The antitumor potentials of benzimidazole anthelmintics as repurposing drugs Read More
- A novel treatment to enhance survival for end stage triple negative breast cancer using repurposed veterinary anthelmintics combined with gut‑supporting/immune enhancing molecules Read More
- Unexpected antitumorigenic effect of fenbendazole when combined with supplementary vitamins Read More
- Fenbendazole acts as a moderate microtubule destabilizing agent and causes cancer cell death by modulating multiple cellular pathways Read More
- Case Reports: Fenbendazole enhancing the anti-tumor effect: A case series Read More
- Mebendazole as a candidate for drug repurposing in oncology: An extensive review of current literature Read More
- Oxfendazole induces apoptosis in ovarian cancer cells by activating JNK/MAPK pathway and inducing reactive oxygen species generation Read More
- The anthelmintic agent oxfendazole inhibits cell growth in non‑small cell lung cancer by suppressing c‑Src activation Read More
- The anthelmintic flubendazole inhibits microtubule function through a mechanism distinct from vinca alkaloids and displays preclinical activity in leukemia and myeloma Read More
- Emerging insights on functions of the anthelmintic flubendazole as a repurposed anticancer agent Read More
SOME CONTROVERSY AROUND BENZIMIDAZOLES FOR CANCER
These anti-parasitic drugs are being studied and shown to be effective against cancer through many different mechanisms. Whether it is FBZ, mebendazole or others. These drugs have a long track record of being safe and well-tolerated. Of course, each of us is different. Where one person might respond to these drugs, another one may not, so make sure to keep that in mind.
There is also some conflicting data and anecdotal reports showing progression of tumors when patients are taking very high doses of benzimidazoles, including mebendazole. Here is one example. Read More
When I read this study, I realized just how flawed it was for many reasons. There was no evidence that any of these patients had confirmed hyper-progression of their cancer due to the treatment with mebendazole, even though they said there was. When you really dig into the results, this is not conclusive.
In fact, the authors stated that the continued tumor progression, without standard of care treatments, was at a higher or similar speed as during the treatment with mebendazole. It’s important to note that hyper-progression of cancer can occur with chemotherapy and other cancer drugs in up to 25% of patients. One thing they did find is that patients were able to tolerate doses up to 4 grams of mebendazole per day without any major side effects. Remember FBZ differs by one atom from mebendazole. I believe FBZ is just as safe for use as the mebendazole was in this clinical trial.
In conclusion, make sure to do your own research and talk to your naturopathic doctor to see if FBZ might be right for you. I would caution against using megadoses in an effort to shrink tumors. One other point is that, FBZ combined with ivermectin and other vitamins and supplements may be more effective.
“For I know the plans I have for you”, declares the Lord, “plans to prosper you and not to harm you, plans to give you hope and a future.” – Jeremiah 29:11