Pharmacokinetics of Tramadol Hydrochloride and its Metabolite O-Desmethyltramadol in Peafowl (Pavi crustatys)
Tramadol is a centrally-acting opiate analgesic that has not been well-studied in avian species. Tramadol and its metabolites exert their effects at multiple sites, including opiate (µ, κ, and δ), adrenergic (α-2), and serotonin (5HT) receptors. This multi-receptor mode of action is advantageous for avian patients since the mechanisms for analgesia have not been fully elucidated in all species. Furthermore, in species studied, the κ-opioid receptors appear to be more important for analgesia than µ-opioid receptors.2,3 Tramadol has several advantages when compared to other analgesic agents more commonly used in birds. It is not regulated by the Drug Enforcement Agency, it is well-absorbed after oral administration in humans and dogs, and it has not been shown to have significant adverse side effects.1,4 The objective of this study was to document the pharmacokinetics of tramadol and its active metabolite O-desmethyltramadol (M1) in common peafowl (Pavo cristatus). Based on results from a pilot animal, six adult peafowl (three male, three female) judged to be clinically healthy based on physical exam and routine blood work were selected for this study. Each bird was anesthetized for placement of a jugular catheter, and tramadol was administered via gavage tube. Blood samples were collected. Plasma levels of tramadol and M1 were measured and the pharmacokinetics for each drug was calculated. Based on these data, tramadol may be a practical option as an orally-administered analgesic agent in avian patients. Further studies, including antinociceptive studies, are needed.
The authors wish to thank the animal care staff and veterinary technicians at the Saint Louis Zoo for their help in this project.
1. Malonne H, Sonet B, Streel B, Lebrun S, De Niet S, Sereno A, Vanderbist F. Pharmacokinetic evaluation of a new oral sustained release dosage form of tramadol. Br J Clin Pharmacol. 2003;57:270–278.
2. Paul-Murphy J, Hess JC, Fialkowski JP. Pharmacokinetic properties of a single intramuscular dose of buprenorphine in African grey parrots (Psittacus erithacus erithacus). J Avian Med Surg. 2004;18:224–228.
3. Sladky KK, Krugner-Higby L, Meek-Walker E, Heath TD, Paul-Murphy J. Serum concentrations and analgesic effects of liposome-encapsulated and standard butorphanol tartrate in parrots. Am J Vet Res. 2006;67:775–781.
4. Wu WN, McKown LA, Gauthier AD, Jones WJ, Raffa RB. Metabolism of the analgesic drug, tramadol hydrochloride, in rat and dog. Xenobiotica. 2001;31:423–441.