Tricyclic antidepressant drugs are thought to modulate pain by inhibiting the uptake of norepinephrine and serotonin in the CNS. Sandford et al. (1992) have suggested that the tricyclic antidepressants exert an analgesic effect by making more serotonin available in the CNS, thereby potentiating the inhibitory action of the dorsal horn of the spinal cord. Unfortunately, these medications are often sedating and produce a variety of anticholinergic side effects.
The partial effectiveness of tricyclic antidepressants (TCA) in some SCI patients with dysesthetic pain suggests that this drug is simply affecting the pain by treating the depression. Sandford et al. (1992) noted that pain and depression maybe chemically linked. Depression can lower pain thresholds or pain tolerances thereby increasing the patient’s experience of pain. However, Max et al. (1987) were able to show that TCA had analgesic properties despite low doses or short treatment cycles with analgesic activity occurring independent of mood changes.
Davidoff et al. (1987b) reported trazodone’s lack of effectiveness in relieving pain in 19 SCI patients with chronic dysesthetic pain, using a double-blind placebo controlled trial. Trazodone reportedly selectively inhibits serotonin and norepinephrine uptake in a ratio of 25:1, and is thought to produce greater analgesia and less anticholinergic side-effects compared to non-selective agents such as amitriptyline.