CFR > Title 21 - Food and Drugs > CHAPTER I—FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES > SUBCHAPTER E—ANIMAL DRUGS, FEEDS, AND RELATED PRODUCTS (parts 500 to 590) > PART 524—OPHTHALMIC AND TOPICAL DOSAGE FORM NEW ANIMAL DRUGS > 524.920—Fenthion.

524.920—Fenthion.

(a) Chemical name. O,O-Dimethyl O-[4-(methylthio)-m- tolyl] phosphorothioate.
(b) Specifications. (1) The drug is in a liquid form containing 3 percent of fenthion.
(2) Sponsor. See No. 000859 in § 510.600(c) of this chapter.
(3) Special considerations. Do not use on animals simultaneously or within a few days before or after treatment with or exposure to cholinesterase-inhibiting drugs, pesticides, or chemicals.
(4) Related tolerances. See 40 CFR 180.214.
(5) Conditions of use. (i) The drug is used as a pour-on formulation for the control of grubs and lice in beef and nonlactating cattle.
(ii) It is used at the rate of one-half fluid ounce per 100 pounds of body weight placed on the backline of the animal. Only one application per season should be made for grub control and this will also provide initial control of lice. A second application for lice control may be made if animals become reinfested, but no sooner than 35 days after the first treatment. Proper timing of treatment is important for grub control; cattle should be treated as soon as possible after heel-fly activity ceases. Cattle should not be slaughtered within 35 days following a single treatment. If a second application is made for lice control, cattle should not be slaughtered within 45 days of the second treatment. The drug must not be used within 28 days of freshening of dairy cattle. If freshening should occur within 28 days after treatment, do not use milk as human food for the balance of the 28-day interval. Do not treat lactating dairy cattle; calves less than 3 months old; or sick, convalescent, or stressed livestock. Do not treat cattle for 10 days before or after shipping, weaning, or dehorning or after exposure to contagious infectious diseases.
(c) Specifications. (1) The drug is in a liquid form containing 20 percent fenthion.
(2) Sponsor. See No. 000859 in § 510.600(c) of this chapter.
(3) Special considerations. Do not use on animals simultaneously or within a few days before or after treatment with or exposure to cholinesterase-inhibiting drugs, pesticides, or chemicals.
(4) Related tolerances. See 40 CFR 180.214.
(5) Conditions of use. (i) The drug is used for control of cattle grubs and as an aid in controlling lice on beef cattle and on dairy cattle not of breeding age.
(ii) It is applied as a single application placed on the backline of animals as follows:
Weight of animal Dosage (milliliters)
150 to 300 lb 4
301 to 600 lb 8
601 to 900 lb 12
901 to 1,200 lb 16
Over 1,200 lb 20

Code of Federal Regulations

For most effective results, cattle should be treated as soon as possible after heel-fly activity ceases. Host-parasite reactions such as bloat, salivation, staggering and paralysis may sometimes occur when cattle are treated while the common cattle grub (Hypoderma lineatum) is in the gullet, or while the northern cattle grub (H. bovis) is in the area of the spinal cord. Cattle should be treated before these stages of grub development. Consult your veterinarian, extension livestock specialist, or extension entomologist regarding the timing of treatment. If it is impossible to determine the area from which the cattle came and/or exact stage of the grubs, it is recommended that the cattle receive only a maintenance ration of low-energy feed during the treatment period. This lessens the likelihood of severe bloat which may occur in cattle on full feed when the common grub is killed while in the gullet. A second application is required for animals heavily infested with lice or for those which become reinfested. A second application should be made no sooner than 35 days after the first treatment.
(iii) Do not treat dairy cattle of breeding age; calves less than 3 months old; sick, convalescent, or severely stressed livestock.
(iv) Do not treat cattle for 10 days before or after shipping, weaning, dehorning, or after exposure to contagious or infectious diseases.
(v) Do not slaughter within 45 days of treatment.
(d) Specifications. (1) The drug is a solution containing either 5.6 or 13.8 percent fenthion. Each concentration is available in 2 volumes which are contained in single-dose applicators.
(2) Sponsor. See No. 000859 in § 510.600(c) of this chapter.
(3) Special considerations. Fenthion is a cholinesterase inhibitor. Do not use this product on dogs simultaneously with or within 14 days before or after treatment with or exposure to cholinesterase-inhibiting drugs, pesticides, or chemicals. Do not use with flea or tick collars.
(4) Conditions of use— (i) Amount. Four to 8 milligrams per kilogram of body weight.
(ii) Indications for use. For flea control on dogs only.
(iii) Limitations. Apply the contents of the proper size, single-dose tube directly to one spot on the dog's skin. Frequency of repeat treatments depends upon rate of flea reinfestations. Do not use more often than once every 2 weeks. Treatment at 2-week intervals is not to exceed 6 months. Do not use on puppies under 10 weeks of age. Do not use on sick, stressed, or convalescing dogs. Safe use in breeding males has not been established. Federal law restricts this drug to use by or on the order of a licensed veterinarian.

Code of Federal Regulations

[40 FR 13873, Mar. 27, 1975, as amended at 41 FR 16656, Apr. 21, 1976; 42 FR 58741, Nov. 11, 1977; 45 FR 62425, Sept. 19, 1980; 50 FR 19169, May 7, 1985]