(I wondered if this antihistamine had any mechanisms of action related to dextromethorphan (which is a morphine analog) whose primary actions for which PD patients use it are its anti NMDA actions(?)...Dimebon is also an NMDA antagonist, and in addition, affects Ca++ and mt permability pores.)

http://hdlighthouse.org/research/tri...nicaltrial.php
" Based on earlier work in Russia, it appears that this drug may regulate calcium homeostasis, prevent pathological opening of the mitochondrial permeability transition pores, and reduce the excitotoxicity of NMDA receptors.

References:

S. Bachurin, E. Bukatina, N. Lermontova, S. Tkachenko, A. Afanasiev, V. Grigoriev, I. Grigorieva, Yu. Ivanov, S. Sablin, and N. Zefirov. "Antihistamine Agent Dimebon As a Novel Neuroprotector and a Cognition Enhancer." Annals of the N.Y. Academy of Sciences 939(June 2001): 425-435.

S. Bachurin, E. P. Shevtsova, E. G. Kireeva, G. F. Oxenkrug, and S. O. Sablin. "Mitochondria as a Target for Neurotoxins and Neuroprotective Agents." Annals of the New York Academy of Sciences 993(May 2003):334-344. "

Abstract from Article related to Dimebon use in Huntington's @same web site:

"Dimebon(TM) has been shown to prevent the death of brain cells (neurons) in preclinical models of Alzheimer's disease and Huntington's disease, making it a novel potential treatment for many neurodegenerative diseases. Dimebon recently met all five efficacy endpoints in a six-month randomized, double-blinded, placebo-controlled trial of 183 patients with mild to moderate Alzheimer's disease. Patients in the trial were tested for a full spectrum of problems typically caused by Alzheimer's disease, including memory loss, behavioral disturbances, and inability to perform everyday activities such as bathing and dressing. After six months of treatment, patients on Dimebon got significantly better on all of these tests. Dimebon patients also scored significantly better on all of these tests than did placebo patients. Dimebon, which has a 20-year record of human use, also was very well tolerated in this study. Medivation and its advisors designed this study to match closely the design of pivotal registration studies previously accepted by the FDA to approve currently marketed Alzheimer's disease drugs, including duration of treatment, clinical endpoints and patient inclusion/exclusion criteria."