Pharmacokinetics of Tramadol and O-Desmethyltramadol Enantiomers Following Administration of Extended-Release Tablets to Elderly and Young Subjects.

BACKGROUND: Tramadol is frequently used in geriatric patients; however, pharmacokinetic (PK) publications on tramadol and O-desmethyltramadol (ODM) in elderly patients are rare. OBJECTIVE: Our objective was to characterize the PK of tramadol and ODM, including absorption processes and covariates for tramadol, in elderly and young subjects after single-dose administration of 200-mg extended-release tablets. METHODS: We conducted a PK study in 15 elderly (aged ≥75 years) subjects with mild renal insufficiency and 20 young (18-40 years) subjects; blood and urine samples were collected for 48 h post-dose. Non-compartmental analysis (NCA) of each tramadol and ODM enantiomer included area under the concentration-time curve (AUC), terminal elimination rate (k el), total body clearance, volume of distribution (V area/ F), and renal clearance (Clr0-48). A one-compartment population model of total tramadol concentration was parameterized with clearance (CL/F), volume of distribution (V/F), and mixed order absorption (first-order and zero-order absorption rate constants with lag times). RESULTS: NCA demonstrated comparable maximum plasma concentration (C max) and AUC between age groups for tramadol enantiomers, but significant differences in V area/ F (mean 34% higher) and k el (mean 28% lower) in the elderly. PK of ODM were significantly different in the elderly for AUC0-inf (mean 35% higher), Clr0-48 (mean 29% lower), and k el (mean 33% lower). The population analysis identified age as a covariate of V/F (young 305 L; elderly 426 L), with a 50% longer mean elimination half-life in the elderly. No differences in absorption processes were observed. CONCLUSIONS: Tramadol exposure was similar between the age groups; exposure to ODM was higher in elderly subjects.