Influence of Fentanyl, Ketamine, and Lidocaine on Tear Production in Healthy Conscious Dogs

Tear production is an important factor in maintaining proper function of the cornea and conjunctiva. The purpose of this study was to determine the effects of bolus followed by infusion of fentanyl, lidocaine, and ketamine on tear production as measured by the Schirmer I Tear Test (STT-I) in dogs. A prospective, randomized, “double-blind” study was performed. A total of 55 healthy conscious client-owned dogs were included in the study. Dogs were randomly allocated to one of four groups and given intravenous fentanyl 0.005 mg kg-1 followed by 0.005 mg kg-1 hour−1 (FEN-group), ketamine 0.6 mg kg−1 followed by 0.6 mg kg−1 hour−1 (KET-group), lidocaine 1 mg kg-1 followed by 1 mg kg−1 hour−1 (LID-group), or saline 0.3 mL kg−1 followed by 2 mL kg−1 hour−1 (SAL-group). The STT-I was performed prior to (baseline) and again 30 minutes (T30) after initiation of drug administration. Data were expressed as the median (minimum – maximum) and analyzed by Wilcoxon and Steel-Dwass tests (P < .05). The STT-I values increased little but were statistically significant in the KET-group from 18 (14-23) to 19 (14-25) (P = .039) and in the LID-group from 21 (14-25) to 20 (17-29) (P = .027). At 30 minutes, STT-I values were significantly higher in LID-group 20 (17-29) than in FEN-group 18 (12-22) (P = .006). Fentanyl, ketamine, and lidocaine administered at the studied doses as a bolus and then followed by an infusion within 30 minutes in healthy conscious dogs demonstrated a clinically insignificant effect on tear production as measured by STT-I.