The impact of MK-467 on sedation, heart rate and arterial blood pressure after intramuscular coadministration with dexmedetomidine in conscious cats.

OBJECTIVE: To study the effects of MK-467, a peripheral α2 -adrenoceptor antagonist, on sedation, heart rate and blood pressure after intramuscular (IM) coadministration with 25 μg kg-1 of dexmedetomidine in cats.

STUDY DESIGN: Prospective, randomized, controlled, blinded, cross-over, experimental study.

ANIMALS: A total of eight healthy, adult, neutered male cats.

METHODS: Cats were administered five IM treatments at least 2 weeks apart, consisting of dexmedetomidine 25 μg kg-1 (D25), MK-467 600 μg kg-1 (M600) and D25 combined with 300, 600 and 1200 μg kg-1 of MK-467 (D25M300, D25M600 and D25M1200, respectively). Heart rate and direct arterial blood pressure were recorded via telemetry and sedation assessed prior to treatments and at intervals for 8 hours thereafter.

RESULTS: Heart rate decreased significantly after all treatments with dexmedetomidine and remained below baseline up to 240 (D25), 20 (D25M300) and 3 minutes (D25M600 and D25M1200). Mean arterial pressure (MAP) increased with D25, remained unchanged with M600 and decreased over time with all combination treatments. The highest and lowest MAP after each treatment were 168±17 and 100±14 (D25), 157±18 and 79±11 (D25M300), 153±11 and 74±10 (D25M600), 144±12 and 69±7 (D25M1200) and 136±9 and 104±13 mmHg (M600). All treatments with dexmedetomidine produced sedation although its duration was significantly reduced by the addition of MK-467.

CONCLUSIONS AND CLINICAL RELEVANCE: Dexmedetomidine induced bradycardia and hypertension, which were attenuated by all three doses of MK-467. The duration of sedation was reduced by MK-467. MK-467 may improve the cardiovascular tolerance of IM dexmedetomidine in cats.