RESEARCH PAPER Epidural administration of tiletamine/zolazepam in horses Claudio C Natalini  DVM, MS, PhD, Diplomate CBCAV, Simone DL Alvesy DVM, MS, Alonso GP Guedesy DVM, MS, Alexandre S Polydoroy DVM, MS, Juliana T Brondaniy DVM & Simone Boppy DVM  Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Skip Bertman Drive, Baton Rouge, LA 70803, USA yUnivesidade Federal de Santa Maria, Santa Maria, RS 97105-900, Brazil Correspondence: Claudio C Natalini DVM, MS, PhD, Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Skip Bertman Drive, Baton Rouge, LA 70803, USA. E-mail: cnatalini@vetmed.lsu.edu Abstract Objectives To evaluate the analgesic, physiologic, and behavioral e¡ects of the epidural administration of tiletamine/zolazepam in horses. Study design Prospective, double-blind, randomized experimental study. Animals Five adult, healthyhorses aged10^16 years and weighing (mean  SD) 400  98 kg. Methods The horses were sedated with 1.0 mg kg 1 intravenous (IV) xylazine, and an epidural catheter was placed into the ¢rst intercoccygeal interver- tebral space. After a 48-hour resting period, epidural tiletamine/zolazepam, 0.5 mg kg 1 (treatment I) or 1.0 mg kg 1 (treatment II), diluted up to 5 mL in ster- ile water, was administered with a 1-week interval between the treatments. Heart rate, respiratory rate, arterial blood pressure, and sedation were evaluated. In order to evaluate the respiratory e¡ects, blood from the carotid artery was withdrawn at time 0 (baseline), and then after 60 and 240 minutes. Analgesia was evaluated by applying a noxious stimulus with blunt- tipped forceps on the perineal region, and graded as complete, moderate, or absent. Data were collected beforetiletamine/zolazepamadministrationandat15- minute intervals for 120 minutes, and 4 hours after tiletamine/zolazepam administration. Data were ana- lyzed with ANOVA and Bonferroni's test with p < 0.05. Results The results showed no signi¢cant di¡erence between treatments in cardiovascular and respira- tory measurements. Sedation was observed with both doses, and it was signi¢cantly di¡erent from baseline at 60, 75, and 90 minutes in treatment II. Moderate analgesia and locomotor ataxia were observed with both the treatments. Conclusions and clinical relevance The results sug- gest that caudal epidural 0.5 and1.0 mg kg 1 tileta- mine/zolazepam increases the threshold to pressure stimulation in the perineal region in horses. The use of epidural tiletamine/zolazepam could be indicated for short-term moderate epidural analgesia. There are no studies examining spinal toxicity of Telazol, and further studies are necessary before recom- mending clinical use of this technique. Keywords ataxia, epidural analgesia, sedation, tileta- mine/zolazepam. Introduction In human and animal anesthesia, the epidural administration of drugs is used to provide surgical anesthesia and/or post-operative analgesia. Several local anesthetic drugs are used to produce epidural anesthesia such as lidocaine, bupivacaine, ropiva- caine, and mepivacaine (Skarda & Muir 1983, 1999, 2001; Skarda 1996). Epidural analgesia is obtained with opioid agonists, alpha-2 adrenergic agonists, and ketamine (Valverde et al. 1990; Skarda 1996; Go¨ mez de Segura et al.1998). In horses, caudal epidural anesthesia is used to desensitizetheanus,rectum,perineum,vulva,vagina, urethra, and bladder. The goal is to produce surgical regional anesthesia without loosing the motor func- tion of the hind limbs (Skarda1996). A combination of a local anesthetic drug with an alpha-2 adrenergic Veterinary Anaesthesia and Analgesia, 2004, 31, 79^85 79