RESUMEN
The purpose of this study is to compare the efficacy of tramadol 37.5 mg/acetaminophen 325 mg combination tablets (tramadol/APAP) with that of nonsteroidal anti-inflammatory drugs (NSAIDs) as maintenance therapy following tramadol/APAP and NSAID combination therapy in knee osteoarthritis (OA) pain which was inadequately controlled by NSAIDs. Subjects with knee OA for over 1 year and moderate pain (numerical rating scale [NRS] ≥5) despite at least 4 weeks' NSAID therapy (meloxicam 7.5 mg or 15 mg qd or aceclofenac 100 mg bid) received tramadol/APAP add-on (combination with NSAID) for 4 weeks. Thereafter, subjects with significant pain improvement (NRS <4) were randomized to receive either tramadol/APAP or NSAID for 8 weeks. On days 29 and 57, Western Ontario and McMaster Universities (WOMAC) OA index score was measured. Secondary measures included pain intensity (NRS), pain relief score, and subjects' and investigators' overall medication assessments. Of 143 subjects enrolled, 112 completed the 4-week tramadol/APAP and NSAID combination phase and 97 (67.8%) experienced significant pain improvement. Of the 97 subjects randomized, 36 in tramadol/APAP group and 47 in NSAID group completed the 8-week comparator study. On days 29 and 57, WOMAC scores and pain intensities did not increase in both groups compared to measurements immediately after the combination therapy. At these two time points, there were no significant differences in WOMAC scores, pain intensities, and other secondary measures between the two groups. Overall adverse event rates were similar in both groups. Tramadol/APAP add-on significantly improved knee OA pain which had been inadequately controlled by NSAIDs. In those subjects who showed favorable response to tramadol/APAP and NSAID combination therapy, both tramadol/APAP and NSAIDs were effective at maintaining the pain-reduced state and there was no significant difference in efficacy between tramadol/APAP and NSAIDs.