@article{natalini_2006,  title={Plasma and cerebrospinal fluid alfentanil, butorphanol, and morphine concentrations following caudal epidural administration in horses},  volume={36},  ISSN={0103-8478},  url={https://doi.org/10.1590/S0103-84782006000500014},  DOI={10.1590/S0103-84782006000500014},  number={5},  journal={Ciência Rural},  publisher={Universidade Federal de Santa Maria},  author={Natalini, Cláudio Corrêa},  year={2006},  month={Sep},  pages={1436–1443} }