Pharmacokinetics of Tramadol and O-desmethyltramadol in Loggerhead Sea Turtles (Caretta caretta)
1Georgia Sea Turtle Center, Jekyll Island Authority, Jekyll Island, GA, USA; 2Department of Comparative Medicine, College of Veterinary Medicine, University of Tennessee, Knoxville, TN, USA; 3Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI, USA
Trauma is the most common reason for sea turtles to be presented to the Georgia Sea Turtle Center for rehabilitation. Boat strike injuries account for over 20 percent of our caseload. These injuries are likely to be extremely painful. Although pain management in reptiles has made some recent advances, data are lacking for sea turtles.1 The objective of this study was to determine the pharmacokinetics of two orally administered doses of tramadol (5 and 10 mg/kg) and its major metabolite (O-desmethyltramadol, M1) in loggerhead sea turtles (Caretta caretta). After oral administration, the half-life of tramadol administered at 5 mg/kg and 10 mg/kg was 20.35 and 22.67 hr, respectively, whereas the half-life of M1 was 10.23 and 11.26 hr, respectively. The maximum concentration (Cmax) for tramadol after oral administration at 5 mg/kg and 10 mg/kg was 373 and 719 ng/ml, respectively, whereas that of M1 was 655 and 1,376 ng/ml, respectively. We were able to determine that tramadol administered orally to loggerhead sea turtles at both dosages provided measurable plasma concentrations of tramadol and O-desmethyltramadol for several days with no adverse effects. Plasma concentrations of tramadol and O-desmethyltramadol remained ≥100 ng/ml for at least 48 hr and perhaps as long as 96 hr when tramadol was administered at 10 mg/kg. Based on therapeutic levels that are achieved in humans,2 a dosage of 10 mg/kg every 48 hr should produce similar levels, but further studies are needed to confirm this information including multi-dose and pharmacodynamic studies.
1. Baker, B.B., Sladky, K.K., Johnson S.M. 2011. Tramadol produces long-lasting analgesia with only mild respiratory depression in red-eared slider turtles (Trachemys scripta). JAVMA. 238:220–227.
2. Dayer P., Desmeules J., Collart L. 2005. Pharmacology of tramadol. Drugs. 2:18–24.