The anticataplectic and REM suppression effect of milnacipran, an SNRI, on human and canine narcolepsy

Abstract

Cataplexy is a sudden drop of antigravity-muscle tone triggered most often by positive emotional factors, which is one of the major symptoms of narcolepsy. Cataplexy has been treated pharmacologically, most often with tricyclic antidepressants. Even though tricyclic antidepressants are effective in reducing sleep paralysis and hypnagogic hallucinations, they even enhance daytime sleepiness, dizziness, and orthostatic hypotension. We assessed the anticataplectic effect of milnacipran, an SNRI, on human and canine narcolepsy. We also assessed the effect of milnacipran on REM sleep suppression in nocturnal sleep. Ten human patients with narcolepsy–cataplexy who changed medication from clomipramine to milnacipran due to side effects were enrolled. The change in the frequency of cataplexy and side effects before and after drug replacement was investigated. To assess milnacipran’s depressant effect on REM sleep, we performed nocturnal polysomnography examinations twice on each eight healthy adult subjects who were administered with milnacipran or placebo. In the study on canine narcolepsy, four genetically narcoleptic Doberman pinschers were enrolled. The food-elicited cataplexy test was used to assess the anticataplectic effect of milnacipran. Milnacipran significantly reduced cataplexy from 9.3 to 5.5 episodes per month in human patients without much side effects. The percentage of REM sleep significantly decreased (p = 0.042) in the subjects with milnacipran (17.5 ± 1.7%) compared to subjects with placebo (21.5 ± 2.3%). Milnacipran also significantly reduced cataplexy dose-dependently in the study on canine narcolepsy. Milnacipran reduced cataplexy in human patients and REM sleep in healthy human subjects. Our study contributes further to previously reported role of adrenergic uptake inhibition in cataplexy. This compound had less side effect than those of tricyclic antidepressant, clomipramine.