Pharmacokinetics of tramadol and o-desmethyltramadol in goats after intravenous and oral administration

The aim of this trial was to implement a method to obtain a tool for analyses of tramadol and the main metabolite, o-desmethyltramadol (M1), in goat's plasma, and to evaluate the pharmacokinetics of these substances following intravenous (i.v.) and oral (p.o.) administration in female goats. The pharmacokinetics of tramadol and M1 were examined following i.v. or p.o. tramadol administration to six female goats (2 mg/kg). Average retention time was 5.13 min for tramadol and 2.42 min for M1. The calculated parameters for half-life, volume of distribution and total body clearance were 0.94 ± 0.34 h, 2.48 ± 0.58 L/kg and 2.18 ± 0.23 L/kg/h following 2 mg/kg tramadol HCl administered intravenously. The systemic availability was 36.9 ± 9.1% and half-life 2.67 ± 0.54 h following tramadol 2 mg/kg p.o. M1 had a half-life of 2.89 ± 0.43 h following i.v. administration of tramadol. Following p.o., M1 was not detectable.