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Buspirone (Buspirone Hydrochloride) - Description and Clinical Pharmacology

 
 



DESCRIPTION

Buspirone hydrochloride tablets USP are an antianxiety agent that is not chemically or pharmacologically related to the benzodiazepines, barbiturates, or other sedative/anxiolytic drugs.

Buspirone hydrochloride is a white crystalline, water soluble compound. Chemically, buspirone hydrochloride is -[4-[4-(2-pyrimidinyl)-1-piperazinyl]butyl]-1,1-cyclopentanediacetamide monohydrochloride, which can be represented by the following structural formula: N

  •  

C H N O •HCl M.W. 421.96 21 31 5 2

Each tablet, for oral administration, contains 5 mg, 10 mg, 15 mg or 30 mg of buspirone hydrochloride USP (equivalent to 4.6 mg, 9.1 mg, 13.7 mg and 27.4 mg of buspirone free base, respectively). The 5 mg and 10 mg tablets are scored so they can be bisected. Thus, the 5 mg tablet can also provide a 2.5 mg dose, and the 10 mg tablet can provide a 5 mg dose. The 15 mg tablets are scored such that they may be bisected or trisected. Thus, a single tablet can provide the following doses: 15 mg (entire tablet), 10 mg (two-thirds of a tablet), 7.5 mg (one-half of a tablet), or 5 mg (one-third of a tablet). The 30 mg tablets are scored such that they may be bisected or trisected. Thus, a single tablet can provide the following doses: 30 mg (entire tablet), 20 mg (two-thirds of a tablet), 15 mg (one-half of a tablet), or 10 mg (one-third of a tablet). Buspirone hydrochloride tablets USP contain the following inactive ingredients: anhydrous lactose, colloidal silicon dioxide, magnesium stearate, microcrystalline cellulose, and sodium starch glycolate.

CLINICAL PHARMACOLOGY

The mechanism of action of buspirone is unknown. Buspirone differs from typical benzodiazepine anxiolytics in that it does not exert anticonvulsant or muscle relaxant effects. It also lacks the prominent sedative effect that is associated with more typical anxiolytics. preclinical studies have shown that buspirone has a high affinity for serotonin (5-HT) receptors. Buspirone has no significant affinity for benzodiazepine receptors and does not affect GABA binding or when tested in preclinical models. In vitro 1A in vitro in vivo

Buspirone has moderate affinity for brain D -dopamine receptors. Some studies do suggest that buspirone may have indirect effects on other neurotransmitter systems. 2

Buspirone hydrochloride tablets are rapidly absorbed in man and undergo extensive first-pass metabolism. In a radiolabeled study, unchanged buspirone in the plasma accounted for only about 1% of the radioactivity in the plasma. Following oral administration, plasma concentrations of unchanged buspirone are very low and variable between subjects. Peak plasma levels of 1 ng/mL to 6 ng/mL have been observed 40 to 90 minutes after single oral doses of 20 mg. The single-dose bioavailability of unchanged buspirone when taken as a tablet is on the average about 90% of an equivalent dose of solution, but there is large variability.

The effects of food upon the bioavailability of buspirone hydrochloride tablets have been studied in eight subjects. They were given a 20 mg dose with and without food; the area under the plasma concentration-time curve (AUC) and peak plasma concentration (C) of unchanged buspirone increased by 84% and 116%, respectively, but the total amount of buspirone immunoreactive material did not change. This suggests that food may decrease the extent of presystemic clearance of buspirone (see). max DOSAGE AND ADMINISTRATION

A multiple-dose study conducted in 15 subjects suggests that buspirone has nonlinear pharmacokinetics. Thus, dose increases and repeated dosing may lead to somewhat higher blood levels of unchanged buspirone than would be predicted from results of single-dose studies.

An protein binding study indicated that approximately 86% of buspirone is bound to plasma proteins. It was also observed that aspirin increased the plasma levels of free buspirone by 23%, while flurazepam decreased the plasma levels of free buspirone by 20%. However, it is not known whether these drugs cause similar effects on plasma levels of free buspirone, or whether such changes, if they do occur, cause clinically significant differences in treatment outcome. An study indicated that buspirone did not displace highly protein-bound drugs such as phenytoin, warfarin, and propranolol from plasma protein, and that buspirone may displace digoxin. in vitro in vivo in vitro

Buspirone is metabolized primarily by oxidation, which has been shown to be mediated by cytochrome P450 3A4 (CYP3A4) (see,). Several hydroxylated derivatives and a pharmacologically active metabolite, 1-pyrimidinylpiperazine (1-PP), are produced. In animal models predictive of anxiolytic potential, 1-PP has about one quarter of the activity of buspirone, but is present in up to 20 fold greater amounts. However, this is probably not important in humans: blood samples from humans chronically exposed to buspirone hydrochloride tablets do not exhibit high levels of 1-PP; mean values are approximately 3 ng/mL and the highest human blood level recorded among 108 chronically dosed patients was 17 ng/mL, less than 1/200th of 1-PP levels found in animals given large doses of buspirone without signs of toxicity. in vitro PRECAUTIONS Drug Interactions

In a single-dose study using C-labeled buspirone, 29% to 63% of the dose was excreted in the urine within 24 hours, primarily as metabolites; fecal excretion accounted for 18% to 38% of the dose. The average elimination half-life of unchanged buspirone after single doses of 10 to 40 mg is about 2 to 3 hours. 14

Special Populations

Age and Gender Effects

After single or multiple doses in adults, no significant differences in buspirone pharmacokinetics (AUC and C) were observed between elderly and younger subjects or between men and women. max

Hepatic Impairment

After multiple-dose administration of buspirone to patients with hepatic impairment, steady-state AUC of buspirone increased 13 fold compared with healthy subjects (see). PRECAUTIONS

Renal Impairment

After multiple-dose administration of buspirone to renally impaired (Cl = 10 to 70 mL/min/1.73 m) patients, steady-state AUC of buspirone increased 4 fold compared with healthy (Cl ≥ 80 mL/min/1.73 m) subjects (see). cr 2 cr 2 PRECAUTIONS

Race Effects

The effects of race on the pharmacokinetics of buspirone have not been studied.

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