Buspirone was first made in 1968 and approved for medical use in the United States in 1986. It is available as a generic medication. In 2017, it was the 80th most commonly prescribed medication in the United States, with more than ten million prescriptions.
SSRI and SNRI antidepressants such as paroxetine and venlafaxine may cause jaw pain/jaw spasm reversible syndrome (although it is not common), and buspirone appears to be successful in treating bruxism on SSRI/SNRI-induced jaw clenching.
Buspirone has been shown in vitro to be metabolized by the enzymeCYP3A4. This finding is consistent with the in vivo interactions observed between buspirone and these inhibitors or inducers of cytochrome P450 3A4 (CYP3A4), among others:
A major metabolite of buspirone, 1-(2-pyrimidinyl)piperazine (1-PP), occurs at higher circulating levels than buspirone itself, and is known to act as a potent α2-adrenergic receptor antagonist. It may be responsible for the increased noradrenergic and dopaminergic activity observed with buspirone in animals. In addition, 1-PP may play an important role in the antidepressant effects of buspirone. Buspirone also has very weak and probably clinically unimportant affinity for the α1-adrenergic receptor. However, buspirone has been reported to have shown "significant and selective intrinsic efficacy" at the α1-adrenergic receptor expressed in a "tissue- and species-dependent manner".
Buspirone has a low oralbioavailability of 3.9% relative to intravenous injection due to extensive first-pass metabolism. The time to peak plasma levels following ingestion is 0.9 to 1.5 hours. It is reported to have an elimination half-life of 2.8 hours, although a review of 14 studies found that the mean terminal half-life ranged between 2 and 11 hours, and one study even reported a terminal half-life of 33 hours. Buspirone is metabolized primarily by CYP3A4, and prominent drug interactions with inhibitors and inducers of this enzyme have been observed. Major metabolites of buspirone include 5-hydroxybuspirone, 6-hydroxybuspirone, 8-hydroxybuspirone, and 1-PP. 6-Hydroxybuspirone has been identified as the predominant hepatic metabolite of buspirone, with plasma levels that are 40-fold greater than those of buspirone after oral administration of buspirone to humans. The metabolite is a high-affinity partial agonist of the 5-HT1A receptor (Ki = 25 nM) similarly to buspirone, and has demonstrated occupancy of the 5-HT1A receptor in vivo. As such, it is likely to play an important role in the therapeutic effects of buspirone. 1-PP has also been found to circulate at higher levels than those of buspirone itself and may similarly play a significant role in the clinical effects of buspirone.
Alkylation of 1-(2-pyrimidyl)piperazine (1) with 3-chloro-1-cyanopropane (2, 4-chlorobutyronitrile) gives 3, which is reduced either by hydrogenation over Raney nickel catalyst, or with LAH. The resulting 1° amine (4) from the previous step is then reacted with 3,3-tetramethyleneglutaric anhydride (5, 8-Oxaspiro[4.5]decane-7,9-dione) in order to yield buspirone (6).
Buspirone was primarily sold under the brand name Buspar. Buspar is currently listed as discontinued by the US Federal Drug Administration. In 2010, in response to a citizen petition, the US FDA determined that Buspar was not withdrawn for sale because of reasons of safety or effectiveness.
Due to interrupted production at a Mylan Pharmaceuticals plant in Morgantown West Virginia, the United States experienced a shortage of buspirone in 2019.
Some tentative research supports other uses such as the treatment of depression and behavioral problems following brain damage.
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