Buspirone

Absorption

Buspirone is rapidly absorbed following oral administration. Bioavailability is low and variable (approximately 5%) due to extensive first pass metabolism. While absorption of buspirone is decreased with concomitant food intake, the first-pass metabolism of the drug is also decreased, resulting in an increased bioavailability as well as increased Cmax and AUC. Following oral administration of single oral doses of 20 mg, the Cmax ranged from 1 to 6 ng/mL and the Tmax ranged from 40 to 90 minutes.

Toxicity

The oral LD50 of buspirone is 196 mg/kg in rat, 655 mg/kg in mouse, 586 mg/kg in dog, and 356 mg/kg in monkey. The intraperitoneal LD50 is 136 mg/kg in rat and 146 mg/kg in mouse.
In clinical pharmacology trials, administration of buspirone at the dose of 375 mg/day resulted in symptoms of nausea, vomiting, dizziness, drowsiness, miosis, and gastric distress. Few cases of overdosage that have been reported usually resulted in complete recovery. In case of overdose, the use of general symptomatic and supportive treatment is recommended along with immediate gastric lavage and monitoring of respiration, pulse, and blood pressure.

The Uses of Buspirone

Buspirone is an extremely specific drug that could possibly represent a new chemical class of anxiolytics—azaspirones. As an anxiolytic, its activity is equal to that of benzodiazepines; however, it is devoid of anticonvulsant and muscle relaxant properties, which are characteristic of benzodiazepines.

The Uses of Buspirone

Tranquilizer (minor).

The Uses of Buspirone

5-Chloro Buspirone is an impurity of Buspirone Hydrochloride (B689850), a non-benzodiazepine anxiolytic and a 5-hydroxytryptamine (5-HT1) receptor agonist.

What are the applications of Application

Buspirone is 5-hydroxytryptamine (5-HT1) receptor agonist

Background

Buspirone is a novel anxiolytic agent with a unique structure and a pharmacological profile. Belonging to the azaspirodecanedione drug class, buspirone is a serotonin 5-HT1A receptor agonist that is not chemically or pharmacologically related to benzodiazepines, barbiturates, and other sedative/anxiolytic drugs. Unlike many drugs used to treat anxiety, buspirone does not exhibit anticonvulsant, sedative, hypnotic, and muscle-relaxant properties. Due to these characteristics, buspirone been termed 'anxioselective'. First synthesized in 1968 then patented in 1975, it is commonly marketed under the brand name Buspar?. Buspirone was first approved in 1986 by the FDA and has been used to treat anxiety disorders, such as generalized anxiety disorder (GAD), and relieve symptoms of anxiety. It has also been used as a second-line therapy for unipolar depression when the use of selective serotonin reuptake inhibitors (SSRIs) is deemed clinically inadequate or inappropriate. The potential use of buspirone in combination with melatonin in depression and cognitive impairment via promoting neurogenesis has also been investigated.

Indications

Indicated for the management of anxiety disorders or the short-term relief of the symptoms of anxiety.

Definition

ChEBI: An azaspiro compound that is 8-azaspiro[4.5]decane-7,9-dione substituted at the nitrogen atom by a 4-(piperazin-1-yl)butyl group which in turn is substituted by a pyrimidin-2-yl group at the N4 position.

brand name

Buspar (Bristol-Myers Squibb).

Biological Functions

Buspirone (BuSpar) is the first example of a class of anxiolytic agents that can relieve some symptoms of anxiety in doses that do not cause sedation. Buspirone is structurally unrelated to existing psychotropic drugs.

General Description

The initial compound in this series, buspirone (BuSpar), hasanxiolytic and antidepressant activities and is a partial5-HT_1A agonist. Its anxiolytic activity is reportedly causedby its ability to diminish 5-HT release (via 5-HT_1A agonism).High short-term synaptic levels of 5-HT are characteristic ofanxiety. Also, because it is a partial agonist, it can stimulatepostsynaptic receptors when 5-HT levels are low in thesynapse, as is the case in depression. Several other spironesare in development as anxiolytics and antidepressants.

Mechanism of action

Although buspirone has been shown to interact with a number of neurotransmitter systems in the brain, it appears that its clinically relevant effects are mediated through interactions at the serotonin (5-hydroxytryptamine, 5-HT) 5-HT_1A receptor, where it acts as a partial agonist.

Pharmacokinetics

The clinical effect of buspirone in alleviating the symptoms of generalized anxiety disorders typically takes 2 to 4 weeks to achieve. The delayed onset of action of buspirone suggests that the therapeutic effectiveness in generalized anxiety may involved more than its molecular mechanism of action at the 5-HT1A receptors, or buspirone may induce adaptations of 5-HT1A receptors. Buspirone was not shown to alter the psychomotor or cognitive function in healthy volunteers, and the risk of developing sedation is relatively low compared to other anxiolytics, such as benzodiazepines. Unlike benzodiazepines and barbiturates used in anxiety disorders, buspirone is not associated with a risk for developing physical dependence or withdrawal, or any significant interaction with central nervous system depressants such as ethanol. This is due to the lack of effects on GABA receptors. Buspirone also does not exhibit any anticonvulsant or muscle-relaxing properties, but may interfere with arousal reactions due to its inhibitory action on the aactivity of noradrenergic locus coerulus neurons.
Despite its clinical effectiveness in generalized anxiety, buspirone demonstrated limited clinical effectiveness on panic disorders, severe anxiety, phobias, and obsessive compulsive disorders. The clinical effectiveness of the long-term use of buspirone, for more than 3 to 4 weeks, has not demonstrated in controlled trials but there were no observable significant adverse events in patients receiving buspirone for a year in a study of long-term use.

Pharmacology

Buspirone is as effective as the benzodiazepines in the treatment of general anxiety. However, the full anxiolytic effect of buspirone takes several weeks to develop, whereas the anxiolytic effect of the benzodiazepines is maximal after a few days of therapy. In therapeutic doses, buspirone has little or no sedative effect and lacks the muscle relaxant and anticonvulsant properties of the benzodiazepines. In addition, buspirone does not potentiate the central nervous system depression caused by sedative–hypnotic drugs or by alcohol, and it does not prevent the symptoms associated with benzodiazepine withdrawal.

Clinical Use

Buspirone is effective in general anxiety and in anxiety with depression.

Side Effects

Like the benzodiazepines, buspirone appears to be safe even when given in very high doses. The most common side effects are dizziness, light-headedness, and headache. Abuse, dependence, and withdrawal have not been reported, and buspirone administration does not produce any cross-tolerance to the benzodiazepines. Buspirone has been reported to increase blood pressure in patients taking monoamine oxidase inhibitors, and it may increase plasma levels of haloperidol if coadministered with that agent.

Synthesis

Buspirone, 8-[4-[4-(2-pyrimidyl)-1-piperazinyl]butyl]-8-azaspiro [4,5] decan-7,9-dione (5.2.6), is synthesized by the reaction of 1-(2-pyrimidyl)-4- (4-aminobutyl)piperazine (5.2.4) with 8-oxaspiro[4,5]decan-7,9-dione (5.2.5). In turn, 1- (2-pyrimidyl)-4-(4-aminobutyl)piperazine (5.2.4) is synthesized by the reaction of 1-(2-pyrimidyl)piperazine with 4-chlorobutyronitrile, giving 4-(2-pyrimidyl)-1-(3- cyanopropyl)piperazine (5.2.3), which is hydrogenated with Raney nickel into buspirone (5.2.4) [51¨C55].

Metabolism

Buspirone is well absorbed from the gastrointestinal tract, and peak blood levels are achieved in 1 to 1.5 hours; the drug is more than 95% bound to plasma proteins. Buspirone is extensively metabolized, with less than 1% of the parent drug excreted into the urine unchanged. At least one of the metabolic products of buspirone is biologically active. The parent drug has an elimination half-life of 4 to 6 hours.

Metabolism

Buspirone is extensively metabolized upon administration, where it primarily undergoes hepatic oxidation mediated by the CYP3A4 enzyme. Hydroxylated derivatives are produced, including a pharmacologically active metabolite 1-pyrimidinylpiperazine (1-PP). In animal studies, 1-PP possessed about one quarter of the pharmacological activity of buspirone.