Evaluation of the safety of fenbendazole in cats
Open accessAbstract
OBJECTIVE: To evaluate the safety of fenbendazole in domestic cats. ANIMALS: 28 six- to seven-month old domestic short-hair cats. PROCEDURE: Cats were randomly assigned to 1 of 3 treatment groups or a control group (n = 7/group). Cats in the treatment groups were given fenbendazole at a dosage of 50, 150, or 250 mg/kg, PO, every 24 hours for 9 days; control cats were given a placebo. A fecal examination, coagulation tests, serum biochemical analyses, CBC, and urinalyses were performed before and 5, 9, and 21 days after initiation of treatment; cats were closely monitored for adverse reactions. After the last dose of fenbendazole was given, 4 control cats and 4 cats given fenbendazole at the highest dosage were euthanatized, and necropsies were performed. RESULTS: None of the cats developed any adverse reactions. For cats in the control and all treated groups, laboratory test results were within reference limits, and there were no significant differences in results of laboratory tests among groups. No gross or histologic lesions were identified in the control or treated cats that were euthanatized. CONCLUSIONS AND CLINICAL RELEVANCE: Fenbendazole administered to healthy cats at a dosage 5 times the dosage and 3 times the duration approved for use in dogs and wild felids did not cause any acute or subacute adverse reactions or pathologic changes. Results suggest that cats may be safely treated with fenbendazole.
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Claims the paper makes
0 of 11 cited sources checked · 0 supported · 0 flagged
- Findingown data
Results of all tests from all groups were considered normal for domestic cats.
“Results of all tests from all groups were considered normal for domestic cats.”
Quote in the paperSubstantial claim - Findingown data
Results of coagulation tests, serum biochemical analyses, and CBC were not significantly different among groups.
“Results of coagulation tests, serum biochemical analyses, and CBC were not significantly different among groups.”
Quote in the paperSubstantial claim - Findingown data
Results of urinalyses were not significantly different among or within groups.
“Results of urinalyses were not significantly different among or within groups.”
Quote in the paperSubstantial claim - Findingown data
The only gross lesions detected in the 4 control cats and 4 cats treated with fenbendazole at the highest dosage were congestion of the mesenteric blood vessels, a small right external parathyroid gland, and a small left lobe of the thyroid gland in 1 control cat.
“The only gross lesions detected in the 4 control cats and 4 cats treated with fenben-dazole at the highest dosage were congestion of the mesenteric blood vessels, a small right external parathyroid gland, and a small left lobe of the thyroid gland in 1 control cat.”
Quote in the paperSubstantial claim - Findingown data
There were no significant differences in results of laboratory tests among groups.
“there were no significant differences in results of laboratory tests among groups.”
Quote in the paperSubstantial claim
- Findingown data
For cats in the control and all treated groups, laboratory test results were within reference limits.
“For cats in the control and all treated groups, laboratory test results were within reference limits”
Quote in the paperSubstantial claim - Findingown data
No gross or histologic lesions were identified in the control or treated cats that were euthanatized.
“No gross or histologic lesions were identified in the control or treated cats that were euthanatized.”
Quote in the paperSubstantial claim - Findingown data
Pulse and respiratory rates were not significantly different within or between groups during the study.
“Pulse and respiratory rates were not significantly different within or between groups during the study.”
Quote in the paperSubstantial claim - Findingown data
No clinically significant histologic lesions were detected in any of these cats.
“No clinically significant histologic lesions were detected in any of these cats.”
Quote in the paperSubstantial claim - Findingown data
None of the cats developed any adverse reactions.
“None of the cats developed any adverse reactions.”
- Also stated in: § Results · plain
“No other adverse reactions were observed during the 9-day treatment period or the 12 days after the end of treatment.”
Quote in the paperSubstantial claim - Also stated in: § Results · plain
- Interpretationown data
Results suggest that cats may be safely treated with fenbendazole.
“Results suggest that cats may be safely treated with fenbendazole.”
Quote in the paperSubstantial claim - Interpretationown data
Fenbendazole administered to healthy cats at a dosage 5 times the dosage and 3 times the duration approved for use in dogs and wild felids did not cause any acute or subacute adverse reactions or pathologic changes.
“Fenbendazole administered to healthy cats at a dosage 5 times the dosage and 3 times the duration approved for use in dogs and wild felids did not cause any acute or subacute adverse reactions or pathologic changes.”
Quote in the paperSubstantial claim - Interpretationown data
Fenbendazole is safe when administered to healthy, adult, nonpregnant cats at a dosage of 250 mg/kg every 24 hours for 9 days, which is 5 times the approved dosage and 3 times the approved duration of treatment for dogs and wild felids.
“The authors conclude that fenbendazole is safe when administered to healthy, adult, nonpregnant cats at a dosage of 250 mg/kg every 24 hours for 9 days, which is 5 times the approved dosage and 3 times the approved duration of treatment for dogs and wild felids.”
Quote in the paperSubstantial claim
- May combine two claims. 6
- Classified as probably not a substantial claim. 16
May combine two claims.
Findingown dataGeneral health, behavior, and hydration status of all cats were normal throughout the study.
“General health, behavior, and hydration status of all cats were normal throughout the study.”
Quote in the paperSubstantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
Study design and conductreasoningFenbendazole was administered to treated cats in gelatin capsules to ensure that they ingested the entire dose.
“fenbenzdazole was administered to treated cats in gelatin capsules to ensure that they ingested the entire dose.”
Quote in the paperNot a substantial claimClassified as probably not a substantial claim.
Study design and conductown dataCats were randomly assigned to 1 of 3 treatment groups or a control group.
“Cats were randomly assigned to 1 of 3 treatment groups or to a control group.”
Quote in the paperSubstantial claimProbably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.
Study design and conductreasoningGroups were balanced on the basis of sex and body weight, so that each group consisted of 4 male and 3 female cats.
“Groups were balanced on the basis of sex and body weight, so that each group consisted of 4 male and 3 female cats.”
Quote in the paperNot a substantial claimClassified as probably not a substantial claim.
Study design and conductnone givenAll cats were observed for signs of toxicosis 2, 4, 8, and 24 hours after treatment.
“All cats were observed for signs of toxicosis 2, 4, 8, and 24 hours after treatment.”
Quote in the paperSubstantial claimProbably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.
Study design and conductreasoningCats were dosed individually and monitored to make sure the dose was not regurgitated.
“Cats were dosed individually and monitored to make sure the dose was not regurgitated.”
Quote in the paperNot a substantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
PremisecitationFenbendazole has a wide margin of safety in monogastric and ruminant animals, with 10 to 400 times the label dosage being tolerated.
“Fenbendazole has been shown to have a wide margin of safety in monogastric and ruminant animals, 6 with 10 to 400 times the label dosage being tolerated.”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [6] source
Probably not a substantial claim: may not pass S3 (load-bearing).
Study design and conductnone givenThe study was conducted according to Good Laboratory Practice Regulations (21 CFR Part 58).
“The study was conducted according to Good Laboratory Practice Regulations (21 CFR Part 58).”
Quote in the paperNot a substantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
Study design and conductcitationThe protocol was designed to meet the FDA Center for Veterinary Medicine's requirements for a target animal safety study.
“The protocol was designed to meet the FDA Center for Veterinary Medicine' s requirements for a target animal safety study.7”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [7] Target animal safety guidelines for new animal drugs. Office of New Animal Drug Evaluation, Center for Veterinary Medicine, Food and Drug Administration, June 1989.
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
May combine two claims.
Study design and conductown dataDuring the treatment period, 3 cats regurgitated capsules (2 control cats and 1 cat given fenbendazole at the highest dosage) during the first 2 days of treatment; capsules were promptly re-administered.
“During the treatment period, 3 cats regurgitated capsules (2 control cats and 1 cat given fenbendazole at the highest dosage) during the first 2 days of treatment; capsules were promptly re-administered.”
Quote in the paperNot a substantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
PremisecitationPrevious studies have found that fenbendazole is effective in the treatment of numerous helminth parasites in cats.
“Previous studies have found that fenbendazole is effective in the treatment of numerous helminth parasites in cats.”
Quote in the paperNot a substantial claim0 of 3 sources checked- cites [2] Vig MM, 1986, Compend Contin Educ Pract Vet
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
- cites [3] Hamilton JM, 1984, Vet Rec source
- cites [4] Roudebush P, 1982, J Am Vet Med Assoc
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
Probably not a substantial claim: may not pass S3 (load-bearing).
PremisecitationFenbendazole has not been approved for use in domestic cats.
“it has not been approved for use in domestic cats.”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [1] 1997, Kan: Veterinary Medicine Publishing Group
Not checked in the free run.
Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.
PremisecitationIn the United States, fenbendazole has been approved for use in cattle, pigs, horses, dogs, and several zoo animals including lions, panthers, and tigers.
“In the United States, it has been approved for use in cattle, pigs, horses, dogs, and several zoo animals, including lions, panthers, and tigers 1”
- Also stated in: § Discussion · plain
“Fenbendazole is currently approved for use in dogs, wild felids, pigs, horses, cattle, and wild ungulates in the United States.”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [1] 1997, Kan: Veterinary Medicine Publishing Group
Not checked in the free run.
- Also stated in: § Discussion · plain
Classified as probably not a substantial claim.
PremisecitationThe basic experiment design requires a control group and treatment groups encompassing dosages ranging from the recommended dosage up to 5 times the recommended dose, administered for 3 times the recommended duration.
“The basic experiment design requires a control group and treatment groups encompassing dosages ranging from the recommended dosage up to 5 times the recommended dose, administered for 3 times the recommended duration.”
Quote in the paperSubstantial claim0 of 1 sources checked- cites [7] Target animal safety guidelines for new animal drugs. Office of New Animal Drug Evaluation, Center for Veterinary Medicine, Food and Drug Administration, June 1989.
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
Probably not a substantial claim: may not pass S3 (load-bearing).
PremisecitationBenzimidazoles that have low solubility, such as fenbendazole, appear least likely to produce toxic effects, in part, because of this low solubility.
“McKellar and Scott 10 state that benzimidazoles that have low solubility, such as fenbendazole, appear least likely to produce toxic effects, in part, because of this low solubility.”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [10] McKellar QA, 1990, J Vet Pharmacol Therap source
May combine two claims.
Interpretationown dataIn this study, fenbendazole was administered to 14 cats at dosages exceeding the dosage found in a previous study to be effective in cats with common gastrointestinal parasites and to 7 cats at the reported dose for 3 times the reported duration; these dosages did not cause any clinical, subclinical, gross, or histologic changes.
“In this study, fenbendazole was administered to 14 cats at dosages exceeding the dosage found in a previous study 5 to be effective in cats with common gastrointestinal parasites and to 7 cats at the reported dose 5 for 3 times the reported duration.These dosages did not cause any clinical, subclinical (as determined by serum biochemical analyses and CBC), gross, or histologic changes.”
Quote in the paperSubstantial claim0 of 1 sources checked- cites [5] Roberson EL, 1980, Am J Vet Res source
Classified as probably not a substantial claim.
Study design and conductnone givenWe decided prior to initiation of the study that if none of the cats in any group developed any clinical or laboratory abnormalities, then only 4 control cats and 4 cats given fenbendazole at the highest dosage would be euthanatized.
“We decided prior to initiation of the study that if none of the cats in any group developed any clinical or laboratory abnormalities, then only 4 control cats and 4 cats given fenbendazole at the highest dosage would be euthanatized.”
Quote in the paperSubstantial claimClassified as probably not a substantial claim.
Study design and conductreasoningAdditional cats were to be euthanatized only if gross or histologic abnormalities were detected in these cats.
“Additional cats were to be euthanatized only if gross or histologic abnormalities were detected in these cats.”
Quote in the paperSubstantial claimClassified as probably not a substantial claim.
PremisecitationTarget animal safety studies conducted under FDA-CVM guidelines are intended to determine whether a drug will be safe for use in the species for which it is intended.
“Target animal safety studies conducted under FDA-CVM guidelines are intended to determine whether a drug will be safe for use in the species for which it is intended.”
Quote in the paperSubstantial claim0 of 1 sources checked- cites [7] Target animal safety guidelines for new animal drugs. Office of New Animal Drug Evaluation, Center for Veterinary Medicine, Food and Drug Administration, June 1989.
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
The paper relies on this without support.
Direct assessments of the safety of fenbendazole in domestic cats have not previously been published.
“direct assessments of the safety of fenbendazole in domestic cats have not previously been published, to our knowledge.”
The paper relies on this without support.
A recommended dosage of fenbendazole for use in domestic cats has not been determined.
“Because a recommended dosage of fenbendazole for use in the domestic cat has not been determined”
The paper relies on this without support.
None of the adverse effects reported for other benzimidazoles have been reported with the use of fenbendazole.
“However, none of these adverse effects have been reported with the use of fenbendazole.”
Self-check
Percentages, sums and reported differences re-computed from the paper’s own numbers.
Each contradiction between two passages listed here was confirmed by an independent check.
Abstract denies an adverse reaction described in the results
MinorThe abstract says no cats developed adverse reactions. The results describe a treated cat regurgitating food and refer to the absence of any *other* adverse reactions.
“None of the cats developed any adverse reactions.”
“One cat given fenbendazole at the highest dosage regurgitated food once 18 days after initiation of treatment.No other adverse reactions were observed during the 9-day treatment period or the 12 days after the end of treatment.”
Abstract denies gross lesions reported in a control cat
MinorThe abstract says no gross lesions were identified in euthanatized cats, but the results list three gross findings in one euthanatized control cat.
“No gross or histologic lesions were identified in the control or treated cats that were euthanatized.”
“The only gross lesions detected in the 4 control cats and 4 cats treated with fenben-dazole at the highest dosage were congestion of the mesenteric blood vessels, a small right external parathyroid gland, and a small left lobe of the thyroid gland in 1 control cat.”
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Development of bone marrow toxicosis after albendazole administration in a dog and cat
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Flagged first, then by citations
Research works printed but not linked: 4
- 1997, Kan: Veterinary Medicine Publishing Group, 1120
- Vig MM, 1986, Compend Contin Educ Pract Vet, 8, 214
- Roudebush P, 1982, J Am Vet Med Assoc, 180, 545
- Roberson EL, 1980, Am J Vet Res, 41, 1499
Cited by
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Metronidazole for the treatment of feline giardiasis
Scorza, A. V., & Lappin, M. R. (2004) · Journal of Feline Medicine and Surgery · doi:10.1016/j.jfms.2003.11.007 · Cited by 53 · see citing works
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Exceptional Repositioning of Dog Dewormer: Fenbendazole Fever
Sultana, T., Jan, U., Lee, H., Lee, H., & Lee, J. I. (2022) · Current Issues in Molecular Biology · doi:10.3390/cimb44100338 · Cited by 14 · see citing works
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Techniques for Monitoring Drug Efficacy
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Ein Update zur felinen und caninen Giardiose
Kanski, S., Weber, K., & Busch, K. (2023) · Tierärztliche Praxis Ausgabe K Kleintiere / Heimtiere · doi:10.1055/a-2191-1723 · Cited by 3 · see citing works
Concordance between Results from Animal Toxicology Studies and Adverse Reactions in Animals
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Inhibitory Effect on Hexokinase II by Benzimidazoles and the Insight into Interactions
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- Authors
- Schwartz, R. D., Donoghue, A. R., Baggs, R. B., Clark, T., & Partington, C.
- Affiliations
- University of Rochester Medicine (US)
- Venue
- American Journal of Veterinary Research
- Published
- 2000-03-01
- Volume
- 61
- Issue
- 3
- Pages
- 330-332
- ISSN
- 0002-9645 (ISSN-L)
- OpenAlex
- W2012274362
- Semantic Scholar
- a92c81532c15db2d94f6396646bfb0c6e52d92d2
- Cited by
- 26
- References
- 9
- Citations by year
- 2026: 2 · 2025: 1 · 2023: 4 · 2022: 4 · 2021: 5 · 2018: 2 · 2015: 1 · 2012: 1
- FWCI
- 0.00
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- American Journal of Veterinary Research (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Veterinary › Small Animals › Veterinary Pharmacology and Anesthesia
- Health Sciences › Veterinary › Small Animals › Helminth infection and control
- Health Sciences › Veterinary › Small Animals › Veterinary Medicine and Surgery
- Keywords
- fenbendazole, cats, drug safety, anthelmintic toxicity, adverse drug reactions, dose escalation, fecal analysis, coagulation tests, serum biochemistry, autopsy findings, Felidae
- MeSH terms
- Animals, Anthelmintics, Blood Chemical Analysis, Body Temperature, Cats, Feces, Female, Fenbendazole, Male, Mesenteric Arteries, Parasite Egg Count, Parathyroid Glands, Partial Thromboplastin Time, Prothrombin Time, Random Allocation, Safety, Thrombin Time, Thyroid Gland, Urinalysis
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