Oxfendazole (Synanthic, Benzelmin): adverse event reports that FDA received

Signs that the reports list

A sign is a coded term from the report. The words in brackets are a plain gloss of the term. The percentage is the share of the 301 reports that list the sign. One report can list more than one sign.

The sign that is in the largest number of the reports comes first.

1. Death50.8%153 reports
2. Lack of efficacy - NOS[the product did not have the expected effect]21.9%66 reports
3. Lack of efficacy (bacteria) - NOS[the product did not have the expected effect: target not specified]6.6%20 reports
4. Death by euthanasia[the animal was euthanized]6.3%19 reports
5. Culture/titer data abnormal4%12 reports
6. Necropsy performed4%12 reports
7. Lack of efficacy (bacteria NOS)[the product did not have the expected effect: bacteria NOS]3.7%11 reports
8. NT - Abnormal necropsy finding NOS[NOS: not otherwise specified]3.7%11 reports
9. Respiratory signs3.7%11 reports
10. Caps, Abnormal[a product quality report, not a sign in an animal]3.3%10 reports
11. Ineffective, strongyles[legacy FDA term: the product did not have the expected effect (strongyles)]3.3%10 reports
12. Lack of efficacy (endoparasite) - NOS[the product did not have the expected effect: target not specified]3.3%10 reports
13. Lack of efficacy (virus) - NOS[the product did not have the expected effect: target not specified]3.3%10 reports
14. Respiratory tract disorder NOS[NOS: not otherwise specified]3.3%10 reports

The list shows 30 of 252 coded signs. A report is not proof that a drug caused a sign. Download all signs (CSV)

Reports by species

• Cattle73.1%220
• Dog6.3%19
• Sheep2%6
• Goat1.3%4
• Horse1.3%4
• Human exposure1.3%4

The share is of all 301 reports that name oxfendazole. The other reports give a different species or no species.

Reports for each month, Jul 2021 to Jun 2026

The month is the month in which FDA received the report. Each chart has its own scale. FDA says that a report can take 3 to 6 months to reach the public data. The newest months can get more reports in a later update.

Reports by year

• Dog
• Cat
• Horse
• Other or not given

2026 has the reports that FDA received through Feb 2026. Download the years (CSV)

What the reports record

Each bar is on a scale of 0 to 100%.

Next in the A to Z list

• opAFP-GHc2 rDNA construct
• Orbifloxacin
• Orbifloxacin + Posaconazole
• Ormetoprim + Sulfadimethoxine
• Oxibendazole
• Oxytetracycline
• Oxytetracycline + Oxytetracycline Dihydrate
• Oxytetracycline + Polymyxin B Sulfate

All drugs by active ingredient. Brand names A to Z

FDA pages for this drug

• How to Report Animal Drug and Device Side Effects and Product ProblemsThe FDA page that tells an owner or a veterinarian how to send a report.
• Green Book record of NADA 140-854The FDA record of the application for Synanthic Bovine Dewormer Suspension 22.5%, Synanthic Bovine Dewormer Suspension 9.06%.
• Green Book record of NADA 140-892The FDA record of the application for Synanthic Bovine Dewormer Paste, 18.5%.
• Green Book record of NADA 110-776The FDA record of the application for Benzelmin Powder For Suspension.
• Green Book record of NADA 110-777The FDA record of the application for Benzelmin Top Dress..
• Green Book record of NADA 132-105The FDA record of the application for Benzelmin Equine Anthelmic Paste, Synanthic Oral Paste.
• Green Book record of NADA 133-841The FDA record of the application for Benzelmin Equine Anthelmintic Suspension, Synanthic Suspension.
• Animal Drugs @ FDAThe search page of the Green Book, the FDA list of approved animal drugs.

The site checked these addresses on 2 Oct 2026. The links open in a new tab.

Cite this page

Pet Drug Reports. Oxfendazole: adverse event reports that FDA received. https://petdrugreports.com/drug/oxfendazole/ Source: FDA Center for Veterinary Medicine, openFDA Animal and Veterinary adverse event reports, export of 30 Oct 2026. Reports received through 26 Jun 2026.

Where the data come from

Questions about these reports

Which brand are these reports about?

The openFDA records give the value "MSK" for the brand name and for the manufacturer name of each drug. FDA says that MSK means "masked". So the site cannot count a report for a brand. The Green Book section of this page lists the brand names with this active ingredient.

Do the reports show that the drug caused the signs?

No. FDA states this about the data.

When looking at the results, be aware that there is no certainty that the reported drug or device caused the adverse event.

The adverse event may have been related to an underlying disease, other drugs used at the same time or other non-drug related sources.

FDA Center for Veterinary Medicine. Source: Adverse Event Reports for Animal Drugs and Devices

How many reports did FDA receive in the latest 12 months?

FDA received 14 reports in the 12 months to June 2026. It received 13 reports in the 12 months before. FDA says that a report can take 3 to 6 months to reach the public data. The newest months can get more reports in a later update.

What kinds of report are in the count?

Of the 301 reports received from October 1987 to February 2026, 42.9% are about a safety issue only. 43.9% are about a lack of expected effectiveness, alone or with a safety issue. 13.3% are about a defect of the product or its package.