Zimelidine inhibits the central neuronal reuptake of
serotonin and has undergone clinical evaluation as an
antidepressant. Twenty patients with
chronic pain of non-malignant origin (mean duration 15.8 years) were entered into a double blind cross-over study of the
analgesic efficacy of
zimelidine and placebo. The duration of each treatment phase was 6 weeks and there was a comprehensive assessment of each patient prior to the commencement and at the completion of the study, during a brief period of hospitalisation.
Zimelidine was superior (P less than 0.05) to placebo with respect to
pain relief based on a global assessment (by the clinical investigators) performed at the completion of each treatment phase. However, there was no significant difference in
analgesic efficacy between the
zimelidine and placebo treatment phases based on the following criteria: (a) changes in the minimum effective blood concentration of
pethidine necessary to provide
pain relief in each patient, measured during a
pethidine infusion of 1.67 mg/min for 60 min; (b) changes in
pain scores estimated by patients using the visual analogue
pain scale (VAPS); (c) changes in patients' estimates of
pain intensity associated with various daily activities. Significant
pain relief was apparent within 2-3 days in those patients who had a beneficial effect, which contrasts with the documented 3-4 weeks for maximal
antidepressant effects. The results of this study suggest that
serotonin reuptake blockers do not provide consistent
pain relief in patients with
chronic pain, but may contribute an
analgesic effect in the treatment of some patients.