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Fenbendazole

Also known as: Fenbendazole, C15H13N3O2S

Overview

Fenbendazole is a synthetic benzimidazole anthelmintic primarily used in veterinary medicine to treat parasitic worm infections. It is not naturally derived but chemically synthesized. Traditionally, it's used for gastrointestinal parasites in animals. Recently, it has been explored off-label for anticancer and immunomodulatory effects. Fenbendazole disrupts microtubule formation in parasites, leading to their death. It also shows microtubule depolymerizing activity in mammalian cancer cells. Research is well-established in veterinary parasitology but emerging and experimental in oncology and immunology. Evidence is mostly preclinical and small-scale studies; no large-scale RCTs or meta-analyses in humans for cancer or other novel uses. It is not approved for human use by regulatory bodies such as the FDA.

Benefits

Fenbendazole is effective against various gastrointestinal parasites in animals. However, one controlled veterinary study showed lower efficacy compared to metronidazole. Preclinical studies suggest anticancer potential, exhibiting cytotoxic effects on cancer cells, including 5-fluorouracil-resistant cancer cell lines, by inducing cell cycle arrest (G2/M phase), microtubule destabilization, oxidative stress, and activation of apoptosis pathways. Animal studies also suggest immunomodulatory effects, including effects on bone marrow and B cell activation, potentially reducing autoantibody production in models of spinal cord injury. Fenbendazole or related benzimidazole treatment improved locomotor function in animal models of spinal cord injury.

How it works

Fenbendazole binds to tubulin, inhibiting microtubule polymerization, which disrupts cytoskeletal functions essential for parasite survival and cancer cell division. It targets microtubules in parasites and mammalian cells. In animal models, it modulates immune cell activation and antibody production. Molecularly, it targets tubulin proteins and activates the MEK3/6-p38MAPK signaling pathway in cancer cells, leading to apoptosis. Oral administration is common in veterinary use; bioavailability in humans is not well characterized.

Side effects

Fenbendazole is generally well-tolerated in animals at therapeutic doses, but human safety data are limited. Common side effects are not well-documented in humans; in animals, minimal adverse effects are reported at standard doses. Uncommon and rare side effects are largely unknown in humans. Animal studies report no significant reproductive toxicity. Drug interactions are not well-documented in humans; caution is advised due to microtubule effects. Contraindications are not established in humans; veterinary contraindications include hypersensitivity. Due to the lack of human studies, the safety profile in humans is not well understood, and caution is advised.

Dosage

Veterinary doses are typically 50 mg/kg orally once daily for 5 days for parasitic infections. The anticancer dosing in humans is not established. The maximum safe dose is also not established in humans; veterinary doses are generally well-tolerated. For parasites, daily dosing for consecutive days is standard. Experimental cancer studies use varied dosing schedules. Oral administration is the standard. Absorption factors are not well-studied in humans. There are no established required cofactors. Human dosage recommendations cannot be provided due to a lack of clinical trials.

FAQs

Is fenbendazole safe for human use?

Currently, fenbendazole is approved for veterinary use only. Human safety and efficacy are not established, and it is not FDA-approved for human use.

Can fenbendazole treat cancer in humans?

Preclinical studies show potential anticancer effects, but no high-quality clinical trials confirm efficacy or safety in humans. Its use in cancer therapy remains investigational.

How does fenbendazole compare to other antiparasitics?

It is effective but may be less efficacious than metronidazole against Giardia in dogs, according to veterinary studies.

Are there known side effects?

Side effects are minimal in animals at recommended doses. Human side effects are largely unknown due to a lack of clinical trials.

Is fenbendazole approved for human use?

No, it is not FDA-approved for human use. It is only approved for veterinary applications as an antiparasitic medication.

Research Sources

  • https://pmc.ncbi.nlm.nih.gov/articles/PMC9437363/ – This preclinical study investigated fenbendazole's effects on cancer cell lines resistant to 5-fluorouracil. The findings suggest that fenbendazole inhibited the growth of these resistant cancer cells, indicating its potential as an alternative therapeutic agent. However, the study is limited by its preclinical nature, as it lacks human data.
  • https://ar.iiarjournals.org/content/44/9/3725 – This study reviews and presents in vitro and in vivo data showing that fenbendazole disrupts microtubules, induces apoptosis, and inhibits cancer cell proliferation. The research spans various cancer models, highlighting fenbendazole's potential as an anticancer agent. However, it is limited by the absence of human clinical trials to validate these findings.
  • https://pmc.ncbi.nlm.nih.gov/articles/PMC9413524/ – This animal study examined the effects of fenbendazole on mice and rats with spinal cord injuries. The results indicated that fenbendazole improved locomotor function and modulated the immune response in these animals. The study's limitation lies in its animal model, which may have limited translation to human outcomes.
  • https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2021.626424/full – This randomized controlled trial in dogs with Giardia infection compared the efficacy of fenbendazole to metronidazole. The study found that fenbendazole was less effective than metronidazole in clearing Giardia cysts. While the study is of high quality within the veterinary context, its findings are specific to veterinary medicine and may not directly apply to human health.
  • https://ar.iiarjournals.org/content/anticanres/44/9/3725.full.pdf – This resource provides a comprehensive review and presents in vitro and in vivo studies, demonstrating that fenbendazole disrupts microtubules, induces apoptosis, and inhibits cancer cell proliferation. The research spans various cancer models, highlighting fenbendazole's potential as an anticancer agent. However, it is limited by the absence of human clinical trials to validate these findings.