Intraindividual differences in pain relief and functional improvement in osteoarthritis with diclofenac or tramadol

To investigate how individual patients with painful osteoarthritis (OA) respond to the non-steroidal anti-inflammatory drug (NSAID) diclofenac and the centrally acting analgesic tramadol when individual on-demand dose titration is allowed. In addition, we studied whether the differences in the mode of action of the different analgesics were important for functional outcome in OA patients.

This was performed as a double-blind, crossover, randomised study in 60 patients with OA of the hip (19 patients) or knee (41 patients) without clinical joint inflammation. Patients received either tramadol (50 to 100mg up to three times daily, on demand) for 4 weeks, followed by diclofenac (25 to 50mg up to three times daily, on demand) for 4 weeks, or vice versa. The multidimensional 'Western Ontario and McMaster Universities Osteoarthritis Index' (WOMAC) questionnaire (pain, stiffness and functional impairment) was used to assess the effect of the drugs on pain and functional capability.

54 patients completed both study periods. The mean (+/- SD) daily dose of tramadol consumed was 164.8mg (+/- 54.1mg) and that of diclofenac was 86.9mg (+/- 21.4mg). Both treatments modestly improved median pain intensity, paralleled by an improvement in functional parameters, and there were no statistically significant differences between the groups. However, individual treatment effects varied greatly, and within individual patients there were considerable variations in analgesic effectiveness between the two treatments. Consistently, pain relief correlated linearly with functional improvement. More patients reported adverse events with tramadol than with diclofenac (20 vs 3%, p = 0.0056), but there was no difference in adverse event-related withdrawals (p = 0.69).

OA patients' response to analgesic treatment was highly individual and the response to one drug was not predictive of that to another drug. A significant proportion of patients were not treated satisfactorily with diclofenac or tramadol alone. The results obtained from a descriptive analysis of group effects (means, medians) were inappropriate for drawing conclusions on individual treatment benefits. Improvement of functional capability apparently was a consequence of pain relief. Effective pain relief should therefore be the main therapeutic goal in patients with OA where inflammation is less prominent.