Evaluation of diphenhydramine as a sedative for dogs.

Objective: To determine and compare levels of sedation achieved by IM administration of diphenhydramine, saline (0.9% NaCl) solution, and acepromazine in dogs.

Design: Prospective randomized study.

Animals: 56 dogs.

Procedure: Dogs were randomly assigned to receive diphenhydramine at 2, 4, or 8 mg/kg (0.9, 1.8, or 3.6 mg/lb, respectively) i.m.; acepromazine at 0.1 mg/kg (0.05 mg/lb) i.m.; or saline solution at 0.05 mL/kg (0.02 mL/lb) i.m. Sedation was assessed by use of a 6-category descriptive system based on observation and interaction.

Results: Dogs in the acepromazine group had significantly higher sedation scores than did dogs in the saline solution or diphenhydramine groups at 30 minutes. Dogs in the diphenhydramine groups did not have significantly different sedation scores from dogs in the saline solution group at any time point.

Conclusions And Clinical Relevance: Diphenhydramine did not cause clinically appreciable sedation in healthy dogs. Diphenhydramine is not suitable as a sole sedative prior to general anesthesia in dogs.