Efficacy of pharmacological treatments of neuropathic pain: an update and effect related to mechanism of drug action

Tricyclic antidepressants and carbamazepine have become the mainstay in the treatment of neuropathic pain. Within the last decade, controlled trials h ave shown that numerous other drugs relieve such pain. We identified all pl acebo-controlled trials and calculated numbers needed to treat (NNT) to obt ain one patient with more than 50% pain relief in order to compare the effi cacy with the current treatments, and to search for relations between mecha nism of pain and drug action. In diabetic neuropathy, NNT was 1.4 in a stud y with optimal doses of the tricyclic antidepressant imipramine as compared to 2.4 in other studies on tricyclics. The NNT was 6.7 for selective serot onin reuptake inhibitors, 3.3 for carbamazepine, 10.0 for mexiletine, 3.7 f or gabapentin, 1.9 for dextromethorphan, 3.4 for tramadol and levodopa and 5.9 for capsaicin. In postherpetic neuralgia, the NNT was 2.3 for tricyclic s, 3.2 for gabapentin, 2.5 for oxycodone and 5.3 for capsaicin, whereas dex tromethorphan was inactive. In peripheral nerve injury, NNT was 2.5 for tri cyclics and 3.5 for capsaicin. In central pain, NNT was 2.5 for tricyclics and 3.4 for carbamazepine, whereas selective serotonin reuptake inhibitors, mexiletine and dextromethorphan were inactive. There were no clear relatio ns between mechanism of action of the drugs and the effect in distinct pain conditions or for single drug classes and different pain conditions. It is concluded that tricyclic antidepressants in optimal doses appear to be the most efficient treatment of neuropathic pain, but some of the other treatm ents may be important due to their better tolerability. Relations between d rug and pain mechanisms may be elucidated by studies focusing on specific n europathic pain phenomena such as pain paroxysms and touch-evoked pain. (C) 1999 International Association for the Study of Pain. Published by Elsevie r Science B.V.