Effect of Medetomidine, Dexmedetomidine, and Their Reversal with Atipamezole on the Nociceptive Withdrawal Reflex in Beagles

• Published in: Animals
• Main Authors: Joëlle Siegenthaler, Tekla Pleyers, Mathieu Raillard, Claudia Spadavecchia, Olivier Louis Levionnois
• Format: Article
• Language: English
• Published: MDPI AG 2020-07-01
• Subjects: antinociception; atipamezole; dexmedetomidine; dog; nociceptive withdrawal reflex; sedation
• Online Access: https://www.mdpi.com/2076-2615/10/7/1240

The objectives were: (1) to compare the antinociceptive activity of dexmedetomidine and medetomidine, and (2) to investigate its modulation by atipamezole. This prospective, randomized, blinded experimental trial was carried out on eight beagles. During the first session, dogs received either medetomidine (MED) (0.02 mg kg⁻¹ intravenously (IV)] or dexmedetomidine (DEX) [0.01 mg kg⁻¹ IV), followed by either atipamezole (ATI) (0.1 mg kg⁻¹) or an equivalent volume of saline (SAL) administered intramuscularly 45 min later. The opposite treatments were administered in a second session 10–14 days later. The nociceptive withdrawal reflex (NWR) threshold was determined using a continuous tracking approach. Sedation was scored (0 to 21) every 10 min. Both drugs (MED and DEX) increased the NWR thresholds significantly up to 5.0 (3.7–5.9) and 4.4 (3.9–4.8) times the baseline (<i>p</i> = 0.547), at seven (3–11) and six (4–9) minutes (<i>p</i> = 0.938), respectively. Sedation scores were not different between MED and DEX during the first 45 min (15 (12–17), <i>p</i> = 0.67). Atipamezole antagonized sedation within 25 (15–25) minutes (<i>p</i> = 0.008) and antinociception within five (3–6) minutes (<i>p</i> = 0.008). Following atipamezole, additional analgesics may be needed to maintain pain relief.