Comparative bioequivalence studies of tramadol hydrochloride sustained-release 200 mg tablets

BACKGROUND Tramadol hydrochloride is available as 50 mg immediate-release (IR) and 100 mg, 200 mg, and 300 mg sustained-release (SR) tablets. The recommended dose of tramadol is 50-100 mg IR tablets every 4-6 hours. The tramadol SR 200 mg tablet is a better therapeutic option, with a reduced frequency of dosing, and improved patient compliance and quality of life. The present study evaluated the bioequivalence of a generic tramadol SR 200 mg tablet. METHODS A comparative in vitro dissolution study was performed on the test and reference products, followed by two separate single-dose bioequivalence studies under fasting and fed conditions and one multiple-dose bioequivalence study under fasting conditions. These bioequivalence studies were conducted in healthy human subjects using an open-label, randomized, two-treatment, two-period, two-sequence, crossover design. The oral administration of the test and reference products was done on day 1 for both the single-dose studies and on days 1-5 for the multiple-dose study in each study period as per the randomization code. Serial blood samples were collected at predefined time points in all the studies. Analysis of plasma concentrations of tramadol and O-desmethyltramadol (the M₁ metabolite) was done by a validated liquid chromatography-mass spectrometry analytical method. The standard acceptance criterion of bioequivalence was applied on log-transformed pharmacokinetic parameters for tramadol and its M₁ metabolite. RESULTS The ratios for geometric least-square means and 90% confidence intervals were within the acceptance range of 80%-125% for log-transformed primary pharmacokinetic parameters for tramadol and its M₁ metabolite in all the three studies. CONCLUSION The test product is bioequivalent to the reference product in terms of rate and extent of absorption, as evident from the single-dose and multiple-dose studies. Both the treatments were well tolerated.