Nefazodone

Nefazodone (Serzone, Nefadar) is an antidepressant marketed by Bristol-Myers Squibb. Its sale was discontinued in 2003 in some countries due to the rare incidence of hepatotoxicity (liver damage), which could lead to the need for a liver transplant, or even death. The incidence of severe liver damage is approximately 1 in every 250,000 to 300,000 patient-years. On June 14, 2004, Bristol-Myers Squibb discontinued the sale of Serzone in the United States and Canada. Several generic formulations of nefazodone are still available.

Pharmacology
Nefazodone acts primarily as a potent antagonist at the 5-HT2A receptors (Kd 26 nM). It also has moderate affinity for the α1-adrenergic receptor (Kd 48 nM) and 5-HT1A receptor (Kd 80 nM), and very low affinity for the α2-adrenergic receptor (Kd 640 nM) and D2 receptor (Kd 910 nM). It acts as an antagonist at all of these sites. Nefazodone has low affinity for the serotonin (200 nM), norepinephrine (360 nM), and dopamine (360 nM) transporters as well, and therefore acts as a weak serotonin-norepinephrine-dopamine reuptake inhibitor (SNDRI). It has negligible affinity for the H1 receptor (24,000 nM) or muscarinic acetylcholine receptors (11,000 nM), and accordingly lacks any antihistamine or anticholinergic side effects.

Dosing
Nefazodone doses for adults typically start at 50 mg twice daily uptitrated by 100 mg/day per week to a maximum of 600 mg (300 mg twice daily), according to Food and Drug Administration (FDA) regulations. Some patients with severe depression were treated with more than 600 mg/day. Most patients were treated with 300 mg–600 mg daily.

Side effects
Common and mild side effects of nefazodone reported in clinical trials more often than placebo include dry mouth (25%), sedation/somnolence (25%), nausea (22%), dizziness (17%), blurred/abnormal vision (16%), weakness (11%), lightheadedness (10%), confusion (7%), and orthostatic hypotension (5%). Rare and serious adverse reactions may include allergic reaction, fainting, priapism (painful/prolonged erection), and jaundice.

Unlike most serotonin reuptake inhibitors, nefazodone has a low incidence of negative effects on libido or sexual function, and is actually sometimes used as an antidote to SSRI or SNRI-induced impotence and anorgasmia in men. Additionally, unlike mirtazapine, nefazodone is not especially associated with increased appetite and weight gain either.

Interactions
Nefazodone is a potent inhibitor of CYP3A4, an isozyme of the cytochrome P450 system, and may therefore interact adversely with many commonly-used medications that are metabolized by CYP3A4.

Advantages
Nefazodone's claimed advantages over other antidepressants include reduced possibility of disturbed sleep or sexual dysfunction, and ability to treat some patients who did not respond to other antidepressant drugs.

Nefazodone, though an antidepressant, may also be beneficial in the prophylaxis of migraines due to its antagonistic effects on the 5-HT2A and 5-HT2C receptors. It has a more favorable side effect profile than amitriptyline, a tricyclic antidepressant commonly used for migraine prophylaxis.

Chemistry
Nefazadone is a piperazine compound incorporating a 1,2,4-triazol-3-one ring. Rxn of the starting propionamide with phosgene leads to the corresponding imino chloride. This intermediate is condensed with hydrazine methylurethane to afford the corresponding guanidine from the displacement of chlorine by basic hydrazine nitrogen. Rxn with sodium methoxide leads first to the ionization of the amine on the side chain; this then cyclizes to a triazolone by displacing the carbamate methoxyl. Alkylation of the anion from rxn of the triazolone with a strong base with chloride affords nefazodone.