Objective To characterize the hemodynamic effects of dexmedetomidine, with or without MK-467, following intramuscular (IM) administration in cats. Study design Randomized, crossover, experimental study. Animals Six healthy adult male castrated purpose-bred cats. Methods Cats were anesthetized with isoflurane in oxygen and instrumented. Cats were administered dexmedetomidine (25 μg kg−1), with (DM) or without (D) MK-467 (600 μg kg−1), IM in the epaxial muscles. Cardiovascular variables, respiratory variables, temperature, and arterial and mixed-venous pH, blood gases and electrolytes were measured prior to drug administration and at various time points for 6 hours thereafter, during anesthesia with isoflurane. Additional variables were calculated from the measurements, using standard equations. Results were analyzed with a two-way repeated-measures analysis of variance, followed by Dunnett's and paired t tests where appropriate. Results Dexmedetomidine resulted in a significant decrease in cardiac index (CI) and significant increases in mean arterial pressure (MAP) and systemic vascular resistance index (SVRI). The addition of MK-467 failed to prevent most of the early cardiovascular effects of dexmedetomidine, but the duration of systemic vasoconstriction was shorter and CI did not decrease. The lowest and highest post-treatment values in each treatment were 0.1 ± 0.03 and 0.13 ± 0.03 L minute−1 BW−0.67 (D) versus 0.14 ± 0.01 and 0.19 ± 0.03 L minute−1 BW−0.67 (DM) for CI, 87 ± 13 and 181 ± 21 mmHg (D) versus 70 ± 11 and 153 ± 18 mmHg (DM) for MAP and 58,948 ± 17,754 and 119,432 ± 40,423 dynes second cm−5 BW−0.67 (D) versus 25,870 ± 3782 and 76,498 ± 17,258 dynes second cm−5 BW−0.67 (DM) for SVRI, respectively. Conclusion and clinical relevance IM coadministration of MK-467 and dexmedetomidine in isoflurane-anesthetized cats shortened dexmedetomidine-induced cardiovascular effects. This drug combination may be useful in cats in which longer-lasting hypertension and hemodynamic depression is of concern.
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