StacksVerified U.S. regulatory reference

21 CFR §520.2520b

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
  1. (a)Specifications. Each bolus contains either 7.3, 10.9, 14.6, or 18.2 g of trichlorfon.
  2. (b)Sponsor. See No. 054771 in § 510.600(c) of this chapter.
  3. (c)Conditions of use in horses—(1) Amount. 18.2 milligrams per pound of body weight, except for strongyles use 36.4 milligrams per pound of body weight.
    1. (2)Indications for use. For horses for removal of bots (Gastrophilus nasalis, Gastrophilus intestinalis), large strongyles (Strongylus vulgaris), small strongyles, large roundworms (ascarids, Parascaris equorum), and pinworms (Oxyuris equi).
    2. (3)Limitations. Do not use in horses intended for human consumption. Federal law restricts this drug to use by or on the order of a licensed veterinarian.