Pharmacokinetics of Tramadol Hydrochloride and its Metabolite O-Desmethyltramadol in Peafowl (Pavo cristatus)

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 because the mechanisms for analgesia have not been fully elucidated in all species. 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 bloodwork were selected for this study. Each bird was anesthetized for placement of a jugular catheter, and 7.5 mg/kg tramadol was administered orally via gavage tube. Blood samples were collected just prior to drug administration; at 30 min; and at 1, 2, 3, 4, 6, 8, 10, 12, 24, and 34 hr. Plasma levels of tramadol and M1 were measured and the pharmacokinetics for each drug was calculated. Although tramadol was quickly metabolized, plasma levels of M1 remained at or near human analgesic levels for 12–24 hr. 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.