ORIGINAL ARTICLE Intravenous administration of tramadol hydrochloride in sheep: a haematological and biochemical study Saied Habibian Dehkordi & Amin Bigham Sadegh & Ehsan Abaspour & Nasim Beigi Brojeni & Ehsan Aali & Ehsan Sadeghi Received: 11 April 2010 / Accepted: 25 August 2010 / Published online: 9 September 2010 # Springer-Verlag London Limited 2010 Abstract Tramadol is a synthetic, centrally acting opioid analgesic. This drug is a μ-opioid agonist that also inhibits the reuptake of noradrenaline and serotonin. The present study was carried out to investigate the effects of this drug on blood profile, hepatic enzymes activities and blood urea nitrogen (BUN) in sheep. For this purpose, ten healthy non- pregnant Lory ewes were used. Before the experiment, three blood samples were taken from the jugular vein as a control; ewes were then randomly divided into two groups. The test group was given tramadol IV (5 mg/kg) for five consecutive days; group 2, the sham group, was given normal saline IV (5 mg/kg) for the same time period. The results of present study showed that short-term injection of tramadol causes significant change in red blood cell count and packed cell volume value. However, level of serum activities of hepatic enzymes and BUN remained unaltered. In conclusion, these results suggest that although short-term use of tramadol may have no toxic effects on the liver and kidney, its effects on the blood profile should be kept in mind. Keywords Blood picture . Hepatic enzymes activities . BUN . Sheep . Tramadol Introduction Opioids are the most potent and effective analgesics available and have become accepted as appropriate treat- ment for acute, cancer and non-cancer chronic pain (Bannwarth 1999; Quang-Cantagrel et al. 2000; Zalys et al. 2000; Collett 2001). Tramadol, a widely used opioid in recent years, is an effective analgesic agent for the treatment of moderately to severe acute or chronic pain (Lee et al. 1993). It is a synthetic, centrally acting opioid analgesic. This drug is a μ-opioid agonist that also inhibits the reuptake of noradrenaline and serotonin (Raffa et al. 1992, 1993). The metabolism of tramadol has been studied in humans, rats, mice, Syrian hamsters, guinea pigs, rabbits and dogs. Its biotransformation in man and animals takes place via N- and O-demethylation and conjugation of O- demethylated compounds (Lintz et al. 1981). Although its use in the treatment of chronic and postoperative pain in animals has increased over the last few years, there is no information on its effects in ruminants. Therefore, the objective of this study was to investigate the biochemical and haematological effects of short-term administration of tramadol hydrochloride in sheep. Materials and methods Animals Ten healthy non-pregnant crossbred Lory ewes, body weight ranging from 42 to 48 kg with an age range between 1.5 and 2 years old, were used for this study. Sheep were housed in a quiet non-stressful environment and had free access to food and water. Prior to the experiment, three blood samples (one, every day) were S. Habibian Dehkordi (*) : E. Abaspour : N. Beigi Brojeni : E. Aali : E. Sadeghi Department of Pharmacology, Faculty of Veterinary Medicine, University of Shahrekord, 88186-115 Shahrekord, Iran e-mail: habibian@vet.sku.ac.ir A. Bigham Sadegh Department of Veterinary Surgery and Radiology, Faculty of Veterinary Medicine, University of Shahrekord, Shahrekord, Iran Comp Clin Pathol (2012) 21:289–293 DOI 10.1007/s00580-010-1094-2