Primidone

Med ReportRequired

Medication Facts

Performance enhancing: No
Total hours to clear: Not recorded
Frequently used: N/A
ESC ID: PRIMID-0745
Trade names: Mysoline
Drug type: Anticonvulsant
Plasma half-life · hours: Not Published
Equine dosing: Consult Veterinarian
Cmax · peak plasma concentration: Not Published
Tmax · time to peak plasma concentration: Not Published
ESC concentration guidance: May not exceed (LDL) Lowest Detectable Level of .05 ng/mL or 50 picograms per mL
Primary withdrawal · hours: 24
Washout withdrawal · hours: 0
ESC control type: C1 - Strictly Controlled - Restricted - Performance
Medication report required: MED REPORT REQUIRED

Uses & side effects

Product-specific side effects await source review.

Drug interactions

Contraindications

Veterinary guidance

Dosing and pharmacokinetic data are sourced from publicly available resources, and accuracy is not guaranteed. The dosing samples provided are for illustrative purposes only and should not be used for actual administration; they assume a single medication is delivered at the correct individual dose. Loading doses, or combinations with other substances to increase efficacy or mask concentration levels, are strictly prohibited. Veterinarians must prescribe all medications and determine appropriate withdrawal times based on the horse's health, administration route, drug strength, and timing. The health of the horse must always take priority over performance.

Medication combinations

Combining certain substances or use of can trigger dangerous interactions or contraindications, posing severe health risks or creating unintended performance-enhancing effects. If a medical treatment causes these interactions or alters performance, the horse must be withdrawn from competition until its system clears, or face an adverse drug test.

Sanctioning-body comparison

Plasma only. Compare published competition guidance for this medication. ESC guidance remains in Medication Facts above. A dosing guideline, withdrawal recommendation and laboratory detection threshold are different measures.

Sources reviewed September 23, 2026. “Not verified” means a gap in this comparison, not zero tolerance or permission. Doses describe the cited rules; your veterinarian must determine treatment and withdrawal.

Published guidance by organization
Organization	Published dose & route	Plasma concentration	Withdrawal / timing	Control / penalty class
AQHA Show HorsesShow rules · 2026 handbook Conditions & sources An unverified entry is not permission to use this medication. Consult the linked current rules. Reviewed 2026-09-23 2026 AQHA Handbook · VIO400–406 Current AQHA rulebook	Not verified for this medication.	Not verified for this medication.	Not verified for this medication.	Medication-specific control not yet verified.
APHA Paint Show HorsesShow rules · 2026 Rule Book Conditions & sources An unverified entry is not permission to use this medication. Consult the linked current rules. Reviewed 2026-09-23 2026 APHA Rule Book · SC-085, pp. 75–80 Current APHA rulebook	Not verified for this medication.	Not verified for this medication.	Not verified for this medication.	Medication-specific control not yet verified.
ARCI Model RulesRacing model · Rules 15 / UCG 20.0 / CTMS 4.2.1 Conditions & sources An unverified entry is not permission to use this medication. Consult the linked current rules. ARCI model comparison only; no state-specific rule is substituted. Schedule timing is tied to its stated regimen and is not a clearance guarantee. UCG 20.0 PDF p. 48 Reviewed 2026-09-23 ARCI UCG 20.0 · April 2026 ARCI CTMS 4.2.1 · December 2020 ARCI Model Rules 15 · August 2026	Not verified for this medication.	Not verified for this medication.	Not verified for this medication.	Drug Class 3 · Penalty Class B. No dosing permission is implied by classification.
USEFNational Therapeutic Substance Provisions · 2026 + July amendment Conditions & sources An unverified entry is not permission to use this medication. Consult the linked current rules. Reviewed 2026-09-23 2026 USEF Drugs & Medications Guidelines · August 10 update USEF July 27, 2026 update	Not verified for this medication.	Not verified for this medication.	Not verified for this medication.	Medication-specific control not yet verified.