Bioequivalence study of tramadol by intramuscular administration in healthy volunteers

Tramadol hydrochloride (CAS 36282-47-0) is a centrally acting analgesic agent binding to μ opiate receptors. The bioavailability of a new tramadol hydrochloride injection (Limadol®) was compared with a commercially available reference product by intramuscular administration in twelve healthy Chinese male volunteers by a standard two-way cross-over trial. Each volunteer received a single 100 mg injection of tramadol HCl in each phase. The bioavailability was compared using the area under the plasma concentration-time curve from time 0 to 30 h (AUC_0-30), the area under the plasma concentration-time curve from time 0 to infinity (AUC(0-∞), peak plasma concentration (C(max)), and time to reach peak plasma concentration (T(max)). No statistically significant difference was observed between the T(max), C(max) AUC_0-30 and AUC(0-∞) of the two preparations. It is concluded that test and reference formulations of tramadol hydrochloride are bioequivalent for both the extent and rate of absorption after a single intramuscular injection.