Mianserin



Mianserin (Bolvidon, Depnon, Norval, Tolvon) is a psychoactive drug of the tetracyclic antidepressant (TeCA) chemical class which is classified as a noradrenergic and specific serotonergic antidepressant (NaSSA) and has antidepressant, anxiolytic, hypnotic, antiemetic, orexigenic, and antihistamine effects. It was previously available internationally, however in most markets it has been phased out in favor of its analogue and successor mirtazapine (Remeron).

An interesting finding is that upon administration, mianserin has been shown to increase the life span of the nematode Caenorhabditis elegans by as much as 30% via dietary restriction caused by modulation of serotonin receptors in the species, but if the animals are kept in a high-food environment, mianserin increases obesity and actually decreases the lifespan.

Pharmacology
Mianserin is an antagonist at the H1, 5-HT1D, 5-HT2A, 5-HT2C, 5-HT3, 5-HT6, 5-HT7, α1-adrenergic, and α2-adrenergic receptors, and also acts as a norepinephrine reuptake inhibitor (NRI) via blockade of the norepinephrine transporter (NET). As a high affinity H1 receptor antagonist, mianserin has strong antihistamine effects; however, it has negligible affinity for the muscarinic acetylcholine receptors, and therefore lacks any anticholinergic properties.

In addition, mianserin also appears to be a potent antagonist of the neuronal octopamine receptor. What implications this may have on mood are currently unknown, however octopamine has been implicated in the regulation of sleep, appetite and insulin production and therefore may theoretically contribute to the overall side effect profile of mianserin.

Blockade of the H1 and α1-adrenergic receptors has sedative and anxiolytic effects, while antagonism of the 5-HT2A and α1-adrenergic receptors inhibits activation of intracellular phospholipase C (PLC), which seems to be common target for several different classes of antidepressants. By antagonizing the somatodendritic and presynaptic α2-adrenergic receptors which function predominantly as inhibitory autoreceptors and heteroreceptors, mianserin disinhibits the release of norepinephrine, dopamine, serotonin, and acetylcholine in various areas of the brain and body.

Side effects
Common side effects of mianserin may include dizziness, blurred vision, sedation, drowsiness or somnolence, increased appetite or hyperphagia and subsequent weight gain, dry mouth or xerostomia, and constipation, among others. Potentially serious adverse reactions may include allergic reaction, fainting or syncope, seizures or convulsions, and white blood cell reduction or agranulocytosis.

Discontinuation
Abrupt or rapid discontinuation of mianserin may provoke a withdrawal, the effects of which may include depression, anxiety, panic attacks, decreased appetite or anorexia, insomnia, diarrhea, nausea and vomiting, and flu-like symptoms, such as allergies or pruritus, among others.

Enantioselectivity
(S)-(+)-Mianserin is approximately 200-300 times more active than its antipode (R)-(–)-mianserin.