California Code, Food and Agricultural Code (Formerly Agricultural Code) - FAC § 14401

A medically important antimicrobial drug shall not be administered to livestock unless it is ordered by a licensed veterinarian through a prescription or veterinary feed directive that complies with federal and state law, including, but not limited to, Part 514 (commencing with Section 514.1), Part 530 (commencing with Section 530.1), and Part 558 (commencing with Section 558.3) of Subchapter E of Chapter I of Title 21 of the Code of Federal Regulations and Section 4826.6 of the Business and Professions Code.  A prescription for labeled use of a medically important antimicrobial drug shall be issued pursuant to a veterinarian-client-patient relationship that meets the requirements of Section 4826.6 of the Business and Professions Code.  Veterinary feed directives and prescriptions for extralabel use of a medically important antimicrobial drug shall be issued pursuant to a veterinarian-client-patient relationship that meets the requirements of Section 530.3 of Title 21 of the Code of Federal Regulations.