21 C.F.R. § 1305.07
A supplier of thiafentanil, carfentanil, etorphine hydrochloride, or diprenorphine, if he or she determines that the purchaser is a veterinarian engaged in zoo and exotic animal practice, wildlife management programs, or research, and is authorized by the Administrator to handle these substances, may fill the order in accordance with the procedures set forth in § 1305.17 except that:
[70 FR 16911, Apr. 1, 2005, as amended at 81 FR 58839, Aug. 26, 2016]