Pyrimethamine: adverse event reports in all combinations
Active ingredient, alone and in combinations
Brand names with this ingredient: ReBalance.
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 FDAFDA reports received through . Counts include this ingredient alone and in combinations. Why brand names have no separate count.
From July 2013 to June 2025, FDA received 55 adverse event reports that name a drug with pyrimethamine, alone or in a combination. 2 sets of active ingredients with pyrimethamine have a drug page.
Of the 55 reports, 38 (69.1%) are about horses. 2 reports are about cats (3.6%). In January to March 2026, FDA received no reports that name pyrimethamine, alone or in a combination. The signs that appear in the largest number of the 55 reports are "Lethargy" and "Leucopenia NOS". A report is not proof that a drug caused a sign.
Fewer than 20 reports named this ingredient in the 12 months before June 2026, so this page gives no change. Reports about horses are 69.1% of the reports that name this ingredient, and 1.4% of all reports.
Search engines list an ingredient 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.
Reports in the latest closed quarter
| Species | Jan to Mar 2026 | Oct to Dec 2025 | Jan to Mar 2025 |
|---|---|---|---|
| All species | 0 | 0 | 2 |
| Dog | 0 | 0 | 0 |
| Cat | 0 | 0 | 0 |
| Horse | 0 | 0 | 1 |
| Other or not given | 0 | 0 | 1 |
January to March 2026 is the latest closed quarter in the data.
Drug pages with pyrimethamine
A report names a drug by its set of active ingredients. Each set with pyrimethamine that has a drug page is in the table, in order of name. The table has 2 sets.
| Active ingredients | Reports, all years | Reports, latest 12 months |
|---|---|---|
| Pyrimethamine + Sulfadiazine | 27 | 0 |
| Pyrimethamine + Sulfadiazine Sodium | 21 | 0 |
A report can name more than one set, so the counts of the sets can add to more than the count of the page.
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.
FDA Center for Veterinary Medicine. Source: Adverse Event Reports for Animal Drugs and Devices
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 55 reports that list the sign. One report can list more than one sign and more than one drug.
The sign that is in the largest number of the reports comes first.
- Lethargy[unusually tired or inactive]12.7%7 reports
- Leucopenia NOS[low white blood cell count]12.7%7 reports
- Ataxia[unsteady, uncoordinated movement]7.3%4 reports
- Behavioural disorder NOS[behaviour change, type not specified]7.3%4 reports
- Death7.3%4 reports
- Death by euthanasia[the animal was euthanized]7.3%4 reports
- Diarrhoea[diarrhea]7.3%4 reports
- Fever7.3%4 reports
- Potency, Low7.3%4 reports
- Anorexia[not eating]5.5%3 reports
- Decreased appetite5.5%3 reports
- Lack of efficacy (protozoa) - NOS[the product did not have the expected effect: target not specified]5.5%3 reports
- Lack of efficacy - NOS[the product did not have the expected effect]5.5%3 reports
- Neutropenia[low neutrophil count]5.5%3 reports
Show the next 16 signs
- Product problem[a product quality report, not a sign in an animal]5.5%3 reports
- Suspension, Abnormal[a product quality report, not a sign in an animal]5.5%3 reports
- Convulsion[seizure]3.6%2 reports
- Decreased red blood cell count3.6%2 reports
- Elevated alanine aminotransferase (ALT)[a liver enzyme above the normal range]3.6%2 reports
- Elevated aspartate aminotransferase (AST)[a liver and muscle enzyme above the normal range]3.6%2 reports
- Eye irritation3.6%2 reports
- Neurological signs NOS[NOS: not otherwise specified]3.6%2 reports
- Non-regenerative anaemia3.6%2 reports
- Odor, Abnormal[a product quality report, not a sign in an animal]3.6%2 reports
- Pain NOS[NOS: not otherwise specified]3.6%2 reports
- Paresis3.6%2 reports
- Potency, High3.6%2 reports
- Recumbency[lying down and unable or unwilling to rise]3.6%2 reports
- Restlessness3.6%2 reports
- Unable to stand3.6%2 reports
Reports by 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 |
|---|---|---|---|---|---|
| 2025 | 0 | 0 | 2 | 2 | 4 |
| 2024 | 0 | 0 | 0 | 3 | 3 |
| 2023 | 0 | 0 | 1 | 1 | 2 |
| 2022 | 0 | 1 | 4 | 0 | 5 |
| 2021 | 0 | 0 | 2 | 3 | 5 |
| 2020 | 0 | 1 | 3 | 1 | 5 |
| 2019 | 0 | 0 | 3 | 0 | 3 |
| 2018 | 0 | 0 | 4 | 0 | 4 |
| 2017 | 0 | 0 | 4 | 1 | 5 |
| 2016 | 0 | 0 | 4 | 1 | 5 |
| 2014 | 0 | 0 | 9 | 3 | 12 |
| 2013 | 0 | 0 | 2 | 0 | 2 |
2025 has the reports that FDA received through Jun 2025. Download the years (CSV)
What the reports record
Outcome at the time of the report
- Recovered/Normal21.8%12
- Recovered with Sequela[recovered, with a lasting effect]0%0
- Ongoing5.5%3
- Died7.3%4
- Euthanized5.5%3
- Outcome Unknown40%22
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 55 reports that name pyrimethamine.
Kind of report
- Safety issue60%33
- Lack of expected effectiveness1.8%1
- Both safety and lack of expected effectiveness7.3%4
- Manufacturing or product defect30.9%17
- Other0%0
Age of the animal
- Under 1 year0%0
- 1 to 3 years5.5%3
- 4 to 7 years5.5%3
- 8 to 11 years18.2%10
- 12 years and over38.2%21
- Age not given32.7%18
Each share of kind and age is of the 55 reports that name pyrimethamine.
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
- ReBalance
What the Green Book records give
- Applications with an approval in force
- 1
- Approved species
- Horses
- Dose forms
- Liquid (Suspension)
- Routes
- Oral
- Sale
- RX (prescription)
- Earliest approval date in the records
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 |
|---|---|---|---|---|
| ReBalance | Pyrimethamine, Sulfadiazine Sodium | Pegasus Laboratories, Inc. | Horses | NADA 141-240 |
FDA pages for this ingredient
- 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 141-240The FDA record of the application for ReBalance.
- 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. Pyrimethamine, all combinations: adverse event reports that FDA received. https://petdrugreports.com/ingredient/pyrimethamine/ 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. Ingredient names follow the Green Book, with salts and forms as FDA lists them.
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 brand names with this active ingredient.
- Do the reports show that the ingredient caused the signs?
No. A report can name more than one drug, and a drug can have more than one active ingredient. 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 5 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 55 reports received from July 2013 to June 2025, 60% are about a safety issue only. 9.1% are about a lack of expected effectiveness, alone or with a safety issue. 30.9% are about a defect of the product or its package.