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Buspirone
Systematic (IUPAC) name
8-[4-(4-pyrimidin-2-ylpiperazin-1-yl)butyl]- 8-azaspiro[4.5]decane-7,9-dione
Identifiers
CAS number	36505-84-7
ATC code	N05BE01
PubChem	2477
DrugBank	APRD00222
Chemical data
Formula	C21H31N5O2
Mol. mass	385.50314 g/mol
Pharmacokinetic data
Bioavailability	low and variable (approx. 5%), due to high first pass metabolism
Protein binding	95% bound to plasma proteins
Metabolism	mainly hepatic, active metabolite 1-Pyrimidylpiperazin (1-PP)
Half life	2-3hr
Excretion	urine (29-63%) and feces (18-38%) in the form of metabolites
Therapeutic considerations
Pregnancy cat.	B(US)
Legal status	Rx-only, not a controlled substance
Routes	oral

Buspirone (brand-names Ansial, Ansiced, Anxiron, Axoren, Bespar, BuSpar, Buspimen, Buspinol, Buspisal, Narol, Spitomin, Sorbon) is an anxiolytic agent and a serotonin receptor agonist belonging to the azaspirodecanedione class of compounds. Its structure is unrelated to those of the benzodiazepines, but it has an efficacy comparable to diazepam in treating generalized anxiety disorder.^[1][2]

It shows no potential for addiction compared to other drugs commonly prescribed for anxiety, especially benzodiazepine medications. The development of tolerance has not been noticed. Cross-tolerance to benzodiazepines, barbiturates and alcohol does not exist. Furthermore, it is non-sedating.

It is thought to act by interfering with the function of the neurotransmitter serotonin in the brain, particularly by serving as a 5-HT1A presynaptic receptor partial agonist. Additionally, it acts as a mixed agonist/antagonist on postsynaptic dopamine receptors. GABA-mediated effects are lacking. Buspirone may also have indirect effects on other neurotransmitters in the brain.

The action of a single dose is much longer than the short halflife of 2-3 hours indicates. The bioavailability of buspirone is very low and variable due to extensive first pass metabolism. The drug is quickly resorbed. Taking the drug together with food may increase the bioavailability. The drug is highly (95%) plasma-bound. The active metabolite 1-PP is also a 5-HT1A partial agonist with anxiolytic properties, but weaker so than the mother-drug.

It is also useful as an augmenting agent, for the treatment of depression, when added to SSRIs.

The main disadvantage is that 1 to 3 weeks elapse before the anxiolytic activity becomes evident. Often patients have to be initially cotreated with a benzodiazepine for immediate anxiolysis. Generally, buspirone works less well than benzodiazepines. Therefore, benzodiazepines are often the first approach in immediately treating panic attacks and social phobias. It is also particularly difficult to treat patients pretreated with benzodiazepines knowing the immediate effects of these tranquilizers.

Bristol-Myers Squibb gained FDA approval for Buspirone in 1986. The drug went generic in 2001.

• Generalized anxiety disorder of mild to moderate intensity (it is not considered effective against other types of anxiety disorders such as obsessive-compulsive disorder, with or without agoraphobia and social phobia)
• Augmention of SSRI-treatment against depression

• Myasthenia gravis
• Acute closed angle glaucoma
• Severely compromised liver- and renal-function
• Concomitant treatment with a MAO-Inhibitor (severe hypertensive crises have been seen)
• Preexisting heart conditions (e.g. myocardial infarction)

Rarely, side-effects have a dangerous nature or intensity. Some tend to disappear with continued therapy, or are less frequent if the initial dose is low and increased gradually (vertigo, agitation, insomnia).

• Most frequent: vertigo, headaches, nervousness, agitation, light-headedness, nausea;
• Often (>1%) : drowsiness, insomnia, concentration disorders, confusion, depression, agitation, intestinal disorders, paresthesia, coordination disorders, tremors, disturbed vision, tinnitus, fatigue, weakness, Angina pectoris, sore throat, tachycardias, palpitations, dry mouth, pain in muscles and joints;
• Seldom: allergic reactions, subdermal bleeding, extrapyramidal symptoms, hallucinations, psychosis, ataxia, epileptic seizures, syncope, tunnel vision, urine retention, alopecia, pruritus, hot flashes.

There are no dyscognitive side-effects like those seen in benzodiazepines.

Other side-effects have been seen, but are not more frequent than those encountered with placebo. An unusual side effect reported by patients has been an enhanced sense of smell.

Buspirone has no known potential for abuse, psychological and physical dependence.

The only documented case of abuse involving buspirone is in jails where inmates crush the pill up and snort it.^{[citation needed]}

• Haloperidol : increased plasma-levels of haloperidol
• Rifampicin : decreased plasma-levels of buspirone
• MAO-Inhibitors : severe hypertensive crises are possible.
• Alcohol : The sedative properties of alcohol are increased slightly.
• Grapefruit, Grapefruit juice, Grapefruit extract : drastically increased plasma-levels of Buspirone ^[3]