Effect of epidural and intravenous use of the neurokinin-1 (NK-1) receptor antagonist maropitant on the sevoflurane minimum alveolar concentration (MAC) in dogs

Objective: To determine the effect of maropitant, an NK-1 receptor antagonist on the minimum alveolar concentration (MAC) of sevoflurane after intravenous and epidural administration to dogs.

Study design: Prospective experimental study.

Animals: Seven, adult, spayed-female dogs (24.8 ± 1.9 kg).

Methods: Each dog was anesthetized twice with sevoflurane in oxygen, with at least 10 days separating the anesthetic events. The minimum alveolar concentration (MAC) of sevoflurane was determined using the tail-clamp technique. During the first anesthetic event, the MAC of sevoflurane was determined initially and again after intravenous administration of maropitant (5 mg kg(-1)) and an infusion (150 μg kg(-1) hour(-1)). During the second anesthetic event, an epidural catheter was advanced to the 4th lumbar vertebra and MAC was determined after administration of saline and maropitant (1 mg kg(-1)) epidurally. All MAC determinations were done in duplicate. The MAC values were adjusted to sea level and compared using student's t-test.

Results: The baseline MAC for sevoflurane was 2.08 ± 0.25%. Intravenous maropitant decreased (p < 0.05) MAC by 16% (1.74 ± 0.17%). In contrast, epidural administration of either saline or maropitant did not change (p > 0.05) the MAC (2.17 ± 0.34% and 1.92 ± 0.12%, respectively).

Conclusion and clinical relevance: Maropitant decreased the MAC of sevoflurane when administered intravenously to dogs but not after epidural administration.