Gary McCleane, (Pain Clinic, Craigavon Area Hospital, Ireland.
Topical application of doxepin hydrochloride, capsaicin and a combination of both produces analgesia in chronic human neuropathic pain: a randomized, double-blind, placebo-controlled study.
Br. J.Clin. Pharmacol 49(6), June 2000, 574-579.
Tricyclic antidepressants (TCAS) have an analgesic effect in neuropathic pain and this effect is independent of their antidepressant action. Capsaicin causes release of substance P from C fibre afferent neurones and repeated application reversibly depletes stores of substance P and reduces pain transmission. An analgesic effect of topically applied TCA doxepin in chronic human neuropathic pain has recently been reported.
In this study, 200 consenting adult patients were included. Patients applied placebo, doxepin, capsaicin or doxepin/capsaicin cream daily for 4 weeks. They recorded on a daily basis overall pain, shooting, burning, paraesthesia and numbness using a 0-10 visual analogue scale during the week prior to cream application (baseline level) and for the 4 week study period. Side-effects and desire to continue treatment were also recorded.
Conclusions of the study were topical application of 3.3%, doxepin, 0.025% capsaicin produce analgesia of similar magnitude. The combination produces more rapid analgesia.