Several hydroxylated derivatives and a pharmacologically active metabolite, 1-pyrimidinylpiperazine (1-PP), are produced. An in vitro 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.īuspirone is metabolized primarily by oxidation, which in vitro has been shown to be mediated by cytochrome P450 3A4 (CYP3A4) (see PRECAUTIONS: Drug Interactions). However, it is not known whether these drugs cause similar effects on plasma levels of free buspirone in vivo, or whether such changes, if they do occur, cause clinically significant differences in treatment outcome. 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%. 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.Īn in vitro protein binding study indicated that approximately 86% of buspirone is bound to plasma proteins. This suggests that food may decrease the extent of presystemic clearance of buspirone (see DOSAGE AND ADMINISTRATION).Ī multiple-dose study conducted in 15 subjects suggests that buspirone has nonlinear pharmacokinetics. 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 max) of unchanged buspirone increased by 84% and 116%, respectively, but the total amount of buspirone immunoreactive material did not change. The effects of food upon the bioavailability of buspirone hydrochloride tablets have been studied in eight subjects. 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. 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. Following oral administration, plasma concentrations of unchanged buspirone are very low and variable between subjects. In a radio-labeled study, unchanged buspirone in the plasma accounted for only about 1% of the radioactivity in the plasma. Some studies do suggest that buspirone may have indirect effects on other neurotransmitter systems.īuspirone hydrochloride tablets are rapidly absorbed in man and undergoes extensive first-pass metabolism. Buspirone has no significant affinity for benzodiazepine receptors and does not affect GABA binding in vitro or in vivo when tested in preclinical models.īuspirone has moderate affinity for brain D 2-dopamine receptors. In vitro preclinical studies have shown that buspirone has a high affinity for serotonin (5-HT 1A) receptors. It also lacks the prominent sedative effect that is associated with more typical anxiolytics. Buspirone differs from typical benzodiazepine anxiolytics in that it does not exert anticonvulsant or muscle relaxant effects. The mechanism of action of buspirone is unknown. The 30 mg tablets also contain FD&C Yellow No. Buspirone hydrochloride tablets, USP contain the following inactive ingredients: anhydrous lactose, colloidal silicon dioxide, magnesium stearate, microcrystalline cellulose, and sodium starch glycolate. A single 30 mg 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). Thus, a single 15 mg 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 15 mg and 30 mg tablets are scored so they can be either bisected or trisected. 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 5 mg and 10 mg tablets are scored so they can be bisected.
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