21 CFR § 520.1900 - Primidone.

---
identifier: "/us/cfr/t21/s520.1900"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "21 CFR § 520.1900 - Primidone."
title_number: 21
title_name: "Food and Drugs"
section_number: "520.1900"
section_name: "Primidone."
chapter_name: "FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES"
subchapter_number: "E"
subchapter_name: "ANIMAL DRUGS, FEEDS, AND RELATED PRODUCTS"
part_number: "520"
part_name: "ORAL DOSAGE FORM NEW ANIMAL DRUGS"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "21 U.S.C. 360b."
regulatory_source: "40 FR 13838, Mar. 27, 1975, unless otherwise noted."
cfr_part: "520"
---


# 520.1900 Primidone.

(a) *Specifications.* Each tablet contains 50 or 250 milligrams of primidone.

(b) *Sponsors.* See sponsor numbers in § 510.600(c) of this chapter.

(1) No. 069043 for use of 250 milligram tablets.

(2) No. 054771 for use of 50 and 250 milligram tablets.

(c) *Conditions of use in dogs*—(1) *Amount.* Twenty-five milligrams of primidone per pound of body weight (55 milligrams per kilogram of body weight) daily.

(2) *Indications for use.* For the control of convulsions associated with idiopathic epilepsy, epileptiform convulsions, viral encephalitis, distemper, and hardpad disease that occurs as a clinically recognizable lesion in certain entities in dogs.

(3) *Limitations.* Federal law restricts this drug to use by or on the order of a licensed veterinarian.

[42 FR 61594, Dec. 6, 1977, as amended at 43 FR 55386, Nov. 28, 1978; 46 FR 8467, Jan. 27, 1981; 46 FR 57477, Nov. 24, 1981; 53 FR 40727, Oct. 18, 1988; 56 FR 37473, Aug. 7, 1991; 62 FR 35076, June 30, 1997; 78 FR 21060, Apr. 9, 2013; 79 FR 28827, May 20, 2014; 83 FR 48946, Sept. 28, 2018]