{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,27]],"date-time":"2026-08-27T13:39:37Z","timestamp":1787837977848,"version":"build-2784847793"},"reference-count":28,"publisher":"Wiley","issue":"4","license":[{"start":{"date-parts":[[2014,1,31]],"date-time":"2014-01-31T00:00:00Z","timestamp":1391126400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Vet Pharm &amp; Therapeutics"],"published-print":{"date-parts":[[2014,8]]},"abstract":"<jats:p>The objective of the current study was to describe the pharmacokinetics of morphine and its metabolites following intravenous administration to the horse. A total of eight horses (two per dose group) received a single intravenous dose of 0.05, 0.1, 0.2, or 0.5\u00a0mg\/kg morphine. Blood samples were collected up to 72\u00a0h postdrug administration, analyzed using<jats:styled-content style=\"fixed-case\">LC<\/jats:styled-content>\u2010<jats:styled-content style=\"fixed-case\">MS<\/jats:styled-content>\/<jats:styled-content style=\"fixed-case\">MS<\/jats:styled-content>and pharmacokinetic parameters determined. Behavior, step counts, and gastrointestinal activity were also assessed. The beta and gamma half\u2010life for morphine ranged from 0.675 to 2.09 and 6.70 to 18.1\u00a0h, respectively, following administration of the four different IV doses. The volume of distribution at steady\u2010state and systemic clearance ranged from 6.95 to 15.8\u00a0L\/kg and 28.3 to 35.7\u00a0mL\u00b7min\/kg, respectively. The only metabolites identified in blood samples were the primary metabolites identified in other species, 3\u2010morphine\u2010glucuronide and 6\u2010morphine\u2010glucuronide. Muscle fasciculations were observed at 0.2 and 0.5\u00a0mg\/kg and ataxia noted at 0.5\u00a0mg\/kg. Gastrointestinal activity was decreased in all dose groups (for up to 8\u00a0h in 7\/8 horses and 24\u00a0h in one horse). This study extends previous studies and is the first report describing the metabolites of morphine in the horse. Plasma concentrations of morphine\u20103\u2010glucuronide, a metabolite with demonstrated neuro\u2010excitatory activity in mice, far exceeded that of morphine\u20106\u2010glucuronide. Further study is warranted to assess whether the high levels of the morphine\u20103\u2010glucuronide contribute to the dose\u2010dependent excitation observed at high morphine doses.<\/jats:p>","DOI":"10.1111\/jvp.12098","type":"journal-article","created":{"date-parts":[[2014,1,31]],"date-time":"2014-01-31T11:45:31Z","timestamp":1391168731000},"page":"374-381","source":"Crossref","is-referenced-by-count":38,"title":["Preliminary pharmacokinetics of morphine and its major metabolites following intravenous administration of four doses to horses"],"prefix":"10.1111","volume":"37","author":[{"given":"H. K.","family":"Knych","sequence":"first","affiliation":[{"name":"K.L. Maddy Equine Analytical Chemistry Laboratory School of Veterinary Medicine University of California Davis CA USA"},{"name":"Department of Veterinary Molecular Biosciences School of Veterinary Medicine University of California Davis CA USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"E. P.","family":"Steffey","sequence":"additional","affiliation":[{"name":"K.L. Maddy Equine Analytical Chemistry Laboratory School of Veterinary Medicine University of California Davis CA USA"},{"name":"Department of Veterinary Surgery and Radiology School of Veterinary Medicine University of California Davis CA USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"D. S.","family":"McKemie","sequence":"additional","affiliation":[{"name":"K.L. Maddy Equine Analytical Chemistry Laboratory School of Veterinary Medicine University of California Davis CA USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2014,1,31]]},"reference":[{"key":"e_1_2_6_2_1","doi-asserted-by":"publisher","DOI":"10.1016\/S0885-3924(02)00531-6"},{"key":"e_1_2_6_3_1","doi-asserted-by":"publisher","DOI":"10.1016\/0024-3205(94)00552-4"},{"key":"e_1_2_6_4_1","doi-asserted-by":"publisher","DOI":"10.2460\/ajvr.67.6.992"},{"key":"e_1_2_6_5_1","doi-asserted-by":"publisher","DOI":"10.1007\/BF01065191"},{"key":"e_1_2_6_6_1","first-page":"377","article-title":"The pharmacology of narcotic analgesics in the horse IV. 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