Determination of the effective dosage of tiletamine-zolazepam-ketamine-xylazine, with or without methadone, in dogs.

Objective: To determine the effective dosage of the combination tiletamine-zolazepam-ketamine-xylazine (TKX), with or without methadone, in dogs.

Study Design: Prospective, randomized, experimental study.

Animals: A total of 29 dogs.

Methods: Dogs were randomly administered TKX (group TKX, n = 13) or combined with 0.3 mg kg of methadone (group TKXM, n = 16) intramuscularly. The TKX solution contained tiletamine (50 mg mL), zolazepam (50 mg mL), ketamine (80 mg mL) and xylazine (20 mg mL). The effective dosages for immobility in 50% and 95% of the population (ED and ED) were estimated using the up-and-down method. Approximately 20 minutes after drug administration, a skin incision was performed and the response was judged as positive or negative if the dogs moved or did not move, respectively. The TKX volume for the subsequent dog in the same group was increased or decreased by 0.005 mL kg if the response of the previous dog was positive or negative, respectively. Heart and respiratory rates, and sedation/anesthesia scores (range 0-21) were recorded before and 15 minutes after drug administration.

Results: Estimated ED and ED (95% confidence intervals) were: TKX, 0.025 (0.020-0.029) and 0.026 (0.010-0.042) mL kg; TKXM, 0.022 (0.018-0.025) and 0.033 (0.017-0.049) mL kg. Median (interquartile range) scores for sedation/anesthesia were 17 (16-18) and 17 (15-20), and times until lateral recumbency were 5 (4-6) and 6 (4-10) minutes in TKX and TKXM, respectively (p > 0.05). In both groups heart and respiratory rates decreased, but values remained acceptable for anesthetized dogs.

Conclusions And Clinical Relevance: The results provide a guide for volumes of TKX and TKXM in dogs requiring restraint for minimally invasive procedures. Inclusion of methadone in the TKX combination did not influence ED.