Primidone (Mylepsin, Neurosyn): adverse event reports that FDA received
Active ingredient
The names in brackets are brand names with this active ingredient.
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.
Read this first. FDA says this about the data:
An API dataset query result cannot be used to estimate the risk associated with the product or compare one drug or device product with another. When looking at the results, be aware that there is no certainty that the reported drug or device caused the adverse event. This dataset should not be the sole source of information for clinical decision-making or other assumptions about the safety or effectiveness of a product. 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 publishes these words. Source: Adverse Event Reports for Animal Drugs and Devices, read on . The data have the reports that FDA received through .
This page is not veterinary advice. For an animal that is ill, speak to a veterinarian.
Contacting a veterinarianHow to report to FDAFrom April 1987 to May 2017, FDA received 153 adverse event reports that name a drug with primidone as its active ingredient. Of the 153 reports, 147 (96.1%) are about dogs. 2 reports are about people who were exposed to the drug (1.3%).
In January to March 2026, FDA received no reports that name this drug. The signs that appear in the largest number of the 153 reports are "Polydipsia" and "Ataxia". A report is not proof that a drug caused a sign.
Fewer than 20 reports named this drug in the 12 months before June 2026, so this page gives no change. Reports about dogs are 96.1% of the reports that name this drug, and 72.6% of all reports.
Search engines list a drug page with 500 reports or more in all years. The page also needs 30 reports or more in the 12 months to June 2026. This page is under one of these numbers. The site keeps the page and keeps it out of search engines.
Since the last update of the FDA data
The latest update of the FDA data, recorded on , changed no count of this page.
January to March 2026 is the latest closed quarter in the data. In that quarter FDA received 0 reports that name primidone: 0 dog, 0 cat, 0 horse, 0 other or not given.
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 153 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.
- Polydipsia[drinking more than usual]19%29 reports
- Ataxia[unsteady, uncoordinated movement]15%23 reports
- Depression[dull, quiet or withdrawn]13.7%21 reports
- Elevated serum alkaline phosphatase (SAP)[a liver and bone enzyme above the normal range]13.7%21 reports
- Elevated alanine aminotransferase (ALT)[a liver enzyme above the normal range]11.1%17 reports
- Apprehension10.5%16 reports
- Hyperactivity9.2%14 reports
- Confusion8.5%13 reports
- Elevated bile acids8.5%13 reports
- Pacing8.5%13 reports
- Restlessness8.5%13 reports
- Anorexia[not eating]7.8%12 reports
- Polyphagia7.8%12 reports
- Vomiting7.8%12 reports
Show the next 16 signs
- Death6.5%10 reports
- Polyuria[passing more urine than usual]6.5%10 reports
- Polypnoea[fast breathing]5.9%9 reports
- Hind limb paresis[weak hind legs]5.2%8 reports
- Ineffective, seizures[legacy FDA term: the product did not have the expected effect (seizures)]5.2%8 reports
- Lack of efficacy - NOS[the product did not have the expected effect]5.2%8 reports
- Pruritus[itching]5.2%8 reports
- Elevated liver enzymes[liver enzymes above the normal range]4.6%7 reports
- Reluctant to move4.6%7 reports
- Vocalisation[crying out or unusual noise]4.6%7 reports
- Behavioural disorder NOS[behaviour change, type not specified]3.9%6 reports
- Hypersalivation[drooling]3.9%6 reports
- Loose stool3.9%6 reports
- Pyoderma[bacterial skin infection]3.9%6 reports
- Urinary tract disorder NOS[NOS: not otherwise specified]3.9%6 reports
- Aggression3.3%5 reports
The list shows 30 of 175 coded signs. A report is not proof that a drug caused a sign. Download all signs (CSV)
Reports by species
The share is of all 153 reports that name primidone. The other reports give a different species or no species.
Reports for each month, Jul 2021 to Jun 2026
No chart: no month has 5 or more reports.
No chart: no month has 5 or more reports.
No chart: no month has 5 or more reports.
No chart: no month has 5 or more reports.
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
| Year | Dog | Cat | Horse | Other or not given | All species |
|---|---|---|---|---|---|
| 2017 | 1 | 0 | 0 | 1 | 2 |
| 2013 | 1 | 0 | 0 | 0 | 1 |
| 2012 | 1 | 0 | 0 | 0 | 1 |
| 2010 | 26 | 0 | 0 | 0 | 26 |
| 2009 | 50 | 0 | 0 | 0 | 50 |
| 2008 | 16 | 0 | 0 | 1 | 17 |
| 2007 | 5 | 0 | 0 | 0 | 5 |
| 2004 | 0 | 0 | 0 | 1 | 1 |
| 2003 | 2 | 0 | 0 | 0 | 2 |
| 2002 | 3 | 0 | 0 | 0 | 3 |
| 2001 | 2 | 0 | 0 | 0 | 2 |
| 2000 | 1 | 0 | 0 | 0 | 1 |
| 1999 | 3 | 0 | 0 | 2 | 5 |
| 1998 | 6 | 0 | 0 | 0 | 6 |
| 1997 | 2 | 0 | 0 | 0 | 2 |
| 1996 | 3 | 0 | 0 | 0 | 3 |
| 1995 | 2 | 0 | 0 | 0 | 2 |
| 1994 | 4 | 1 | 0 | 0 | 5 |
| 1993 | 5 | 0 | 0 | 0 | 5 |
| 1992 | 2 | 0 | 0 | 0 | 2 |
| 1991 | 4 | 0 | 0 | 0 | 4 |
| 1990 | 1 | 0 | 0 | 0 | 1 |
| 1989 | 6 | 0 | 0 | 0 | 6 |
| 1987 | 1 | 0 | 0 | 0 | 1 |
2017 has the reports that FDA received through May 2017. Download the years (CSV)
What the reports record
Outcome at the time of the report
- Recovered/Normal1.3%2
- Recovered with Sequela[recovered, with a lasting effect]0%0
- Ongoing0%0
- Died9.2%14
- Euthanized0.7%1
- Outcome Unknown2.6%4
An outcome in a report is not proof that the drug caused it. The person who sends the report gives the outcome. Each share is of the 153 reports that name primidone.
A report about more than one animal can have more than one outcome.
Kind of report
- Safety issue96.7%148
- Lack of expected effectiveness1.3%2
- Both safety and lack of expected effectiveness0%0
- Manufacturing or product defect2%3
- Other0%0
4 reports say if the event was serious. 100% of them have the serious flag. The person who sends the report sets the flag.
Show age, weight, breed and route
Age of the animal
- Under 1 year2%3
- 1 to 3 years25.5%39
- 4 to 7 years34.6%53
- 8 to 11 years17.6%27
- 12 years and over6.5%10
- Age not given13.7%21
Weight of the animal
- Under 5 kg (11 lb)3.3%5
- 5 to 9.9 kg (11 to 22 lb)20.3%31
- 10 to 24.9 kg (22 to 55 lb)27.5%42
- 25 to 44.9 kg (55 to 99 lb)24.8%38
- 45 kg and over (99 lb and over)6.5%10
- Weight not given17.6%27
Breed, where the report gives one breed
- Labrador Retriever9.2%14
- American Cocker Spaniel6.5%10
- Golden Retriever3.9%6
- Poodle3.3%5
- Shetland Sheepdog3.3%5
- Shih Tzu3.3%5
- Beagle2.6%4
- Boxer2.6%4
A breed with many animals has many reports.
Route in the report
- Oral96.7%148
Each bar is on a scale of 0 to 100%.
Approved animal drugs with this active ingredient (FDA Green Book)
This section is reference data. It has no report count.
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.
Brand names
- Mylepsin
- Neurosyn
What the Green Book records give
- Applications with an approval in force
- 4
- Approved species
- Dogs
- Dose forms
- Tablet
- Routes
- Oral
- Sale
- RX (prescription)
The species, dose forms and routes are the words of the Green Book records for all the applications together. One product can have fewer. The label of a product gives its approved use.
| Brand name | Active ingredients | Sponsor | Approved species | Application |
|---|---|---|---|---|
| Primidone | Primidone | Zoetis Inc. | Dogs | NADA 009-392 |
| Mylepsin Tablets | Primidone | Zoetis Inc. | Dogs | NADA 010-091 |
| Mylepsin; Primidone Medi-Pets | Primidone | Zoetis Inc. | Dogs | NADA 030-137 |
| Neurosyn Tablets | Primidone | Cronus Pharma Specialities India Private Ltd. | Dogs | NADA 117-689 |
| Primidone Tablets 250 mgapproval withdrawn | Primidone | Bolar Pharmaceutical Co., Inc. | Not in the list of major species | NADA 107-397 |
Next in the A to Z list
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 009-392The FDA record of the application for Primidone.
- Green Book record of NADA 010-091The FDA record of the application for Mylepsin Tablets.
- Green Book record of NADA 030-137The FDA record of the application for Mylepsin, Primidone Medi-Pets.
- Green Book record of NADA 117-689The FDA record of the application for Neurosyn Tablets.
- Animal Drugs @ FDAThe search page of the Green Book, the FDA list of approved animal drugs.
The site checked these addresses on . The links open in a new tab.
Cite this page
Pet Drug Reports. Primidone: adverse event reports that FDA received. https://petdrugreports.com/drug/primidone/ Source: FDA Center for Veterinary Medicine, openFDA Animal and Veterinary adverse event reports, export of . Reports received through .
Where the data come from
The counts come from the openFDA Animal and Veterinary adverse event files, export of 30 Oct 2026. The files have the reports that the FDA Center for Veterinary Medicine received through 26 Jun 2026. The files mask brand and manufacturer names. The site counts a drug by the active ingredients that each record gives, and gives no count to a brand, an application or a company. Ingredient names and the lists of approved products follow the FDA Green Book of 2 Nov 2026. The site does not use the application number that a record has.
The site does not publish report text, lot numbers or details of a reporter. FDA's record is the authority. See how the site counts reports, the data sources and the corrections page.
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 no reports in the 12 months to June 2026. It received no 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 153 reports received from April 1987 to May 2017, 96.7% are about a safety issue only. 1.3% are about a lack of expected effectiveness, alone or with a safety issue. 2% are about a defect of the product or its package.