{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,6]],"date-time":"2026-06-06T16:03:06Z","timestamp":1780761786810,"version":"3.54.1"},"reference-count":31,"publisher":"American Veterinary Medical Association (AVMA)","issue":"2","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["ajvr"],"published-print":{"date-parts":[[2003,2,1]]},"abstract":"<jats:title>Abstract<\/jats:title>\n\t\t\t\t<jats:p>\n\t\t\t\t\t<jats:bold>Objective<\/jats:bold>\u2014To quantitate dose- and time-related\nmagnitudes of interactive effects of morphine (MOR)\nand isoflurane (ISO) in horses and to characterize\npharmacokinetics of MOR in plasma and the ventilatory\nresponse to MOR during administration of ISO.<\/jats:p>\n\t\t\t\t<jats:p>\n\t\t\t\t\t<jats:bold>Animals<\/jats:bold>\u20146 adult horses.<\/jats:p>\n\t\t\t\t<jats:p>\n\t\t\t\t\t<jats:bold>Procedure<\/jats:bold>\u2014Horses were anesthetized 3 times to\ndetermine the minimum alveolar concentration (MAC)\nof ISO in O<jats:sub>2<\/jats:sub> and then to characterize the change in\nanesthetic requirement as defined by the alteration in\nISO MAC following IV administration of saline (0.9%\nNaCl) solution and 2 doses of MOR (low dose, 0.25\nmg\/kg; high dose, 2.0 mg\/kg). Arterial blood samples\nwere obtained before and after MOR and analyzed.<\/jats:p>\n\t\t\t\t<jats:p>\n\t\t\t\t\t<jats:bold>Results<\/jats:bold>\u2014Mean \u00b1 SD baseline ISO MAC was 1.43 \u00b1\n0.06%. The ISO MAC did not change with time after\nadministration of saline solution. Effects of MOR on\nISO MAC varied. Maximal change in MAC ranged\nfrom \u201320.2 to +28.3% and \u201318.9 to +56.2% after low\nand high doses of MOR, respectively. Typical half-life\nof MOR in plasma was 40 to 60 minutes and related\nto dose. Mean PaCO<jats:sub>2<\/jats:sub> increased from 70 mm Hg\nbefore MOR to 88 to 102 mm Hg for 30 to 240 minutes\nafter the high dose of MOR. Recovery from\nanesthesia after administration of the high dose of\nMOR was considered undesirable and dangerous.<\/jats:p>\n\t\t\t\t<jats:p>\n\t\t\t\t\t<jats:bold>Conclusions and Clinical Relevance<\/jats:bold>\u2014Our results\ndo not support routine clinical use of MOR administered\nIV at dosages of 0.25 or 2.0 mg\/kg as an adjuvant\nto anesthesia in horses administered ISO. 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