BUSPIRONE HYDROCHLORIDE
Clinical safety rating: safe
Animal studies have demonstrated safety
Partial agonist at serotonin 5-HT1A receptors, primarily in the raphe nuclei and hippocampus; also exhibits antagonist properties at presynaptic 5-HT1A autoreceptors and postsynaptic 5-HT1A receptors, resulting in decreased serotonergic activity. Additionally, it has moderate affinity for dopamine D2 receptors (antagonist) and alpha2-adrenergic receptors.
| Metabolism | Primarily hepatic via CYP3A4; metabolites include 1-(2-pyrimidinyl)piperazine (1-PP) which has alpha2-adrenergic antagonist activity; also undergoes oxidative metabolism via CYP3A4 and aldehyde oxidase. |
| Excretion | Renal: 29-63% (as metabolites; <1% unchanged); Fecal: 18-38%; Hepatic metabolism primarily via CYP3A4; total clearance 1.5-3.5 L/h/kg. |
| Half-life | 2-3 hours terminal half-life; clinical context: requires multiple daily dosing (3 times daily) due to short half-life; no active metabolites prolonging effect. |
| Protein binding | Approximately 86% bound to plasma proteins (primarily albumin and alpha-1-acid glycoprotein). |
| Volume of Distribution | 5.3 L/kg (mean); extensive distribution beyond plasma volume, indicating significant tissue binding. |
| Bioavailability | Oral: 4% (range 1-13%) due to extensive first-pass metabolism; bioavailability increased by food (delay but no AUC change). |
| Onset of Action | Oral: 2-4 weeks for clinically significant anxiolytic effect; immediate relief not expected; no immediate onset for acute anxiety. |
| Duration of Action | Oral: 6-8 hours after single dose; steady-state achieved in 2-3 weeks; minimal withdrawal symptoms due to sustained use. |
Initial dose: 7.5 mg orally twice daily; may increase by 2.5-5 mg every 2-3 days to a target dose of 15-30 mg/day in divided doses (2-3 times daily). Maximum dose: 60 mg/day divided twice daily.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment recommended for mild to moderate renal impairment. For severe renal impairment (CrCl < 30 mL/min), reduce dose by 25-50% and titrate cautiously. |
| Liver impairment | Child-Pugh A: reduce dose by 25-50%; Child-Pugh B: reduce dose by 50-75%; Child-Pugh C: contraindicated or use with extreme caution at reduced doses. |
| Pediatric use | Not FDA-approved for pediatric use. Limited data: 2.5-5 mg twice daily with gradual titration; maximum 30 mg/day. |
| Geriatric use | Initial dose: 2.5-5 mg twice daily; increase slowly by 2.5-5 mg every 3-4 days. Maximum dose: 30 mg/day in divided doses. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
MAOIs may increase blood pressure Use cautiously with other CNS depressants Not effective for benzodiazepine withdrawal.
| Breastfeeding | Buspirone is excreted into human breast milk in small amounts; estimated infant dose is approximately 0.5-1% of maternal weight-adjusted dose. M/P ratio not established. Caution advised; monitor infant for drowsiness, poor feeding, and hypotonia. |
| Teratogenic Risk | FDA Pregnancy Category B: No evidence of teratogenicity in animal studies, but adequate human studies are lacking. First trimester: Limited data suggest no major malformations, but cannot rule out risk. Second and third trimesters: No known fetal harm, but potential for neonatal serotonin discontinuation syndrome if used near term. |
■ FDA Black Box Warning
None
| Common Effects | Dizziness |
| Serious Effects |
["Hypersensitivity to buspirone or any component","Concurrent use of monoamine oxidase inhibitors (MAOIs) due to risk of hypertensive crisis","Concurrent use of selegiline or other MAO-B inhibitors","Severe hepatic impairment"]
| Precautions | ["Serotonin syndrome: risk when co-administered with other serotonergic drugs (e.g., SSRIs, SNRIs, MAOIs, triptans)","CNS depression: may impair cognitive or motor function; caution with alcohol or other CNS depressants","Dizziness and drowsiness: common during first few weeks of therapy","Discontinuation syndrome: not typically associated with significant withdrawal symptoms, but gradual tapering recommended after prolonged use","Use in hepatic impairment: dose reduction recommended in cirrhosis","Use in renal impairment: caution in severe renal impairment"] |
| Food/Dietary |
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| Fetal Monitoring | Monitor for maternal adverse effects (dizziness, drowsiness, lightheadedness). No specific fetal monitoring required; standard prenatal care. Consider neonatal withdrawal syndrome (irritability, feeding problems) if used late in pregnancy. |
| Fertility Effects | No well-controlled studies; animal studies show no impaired fertility. Clinically, no significant impact on fertility reported, but limited data. May affect libido in some patients. |
| Avoid grapefruit and grapefruit juice; may increase buspirone levels. No other significant food interactions. May be taken with or without food. |
| Clinical Pearls | Onset of therapeutic effect may be delayed 2-4 weeks; not effective for PRN use. No cross-tolerance with benzodiazepines; do not use as substitute for benzodiazepine withdrawal. Avoid concurrent use with MAOIs due to risk of serotonin syndrome. Dose adjustments needed in hepatic impairment; no dose adjustment in renal impairment. Can cause dizziness and drowsiness; caution with driving. |
| Patient Advice | Take consistently with or without food, but avoid grapefruit juice as it may increase levels. · May take 2-4 weeks to feel full effect; do not expect immediate relief. · Do not stop abruptly; taper under doctor's guidance to avoid withdrawal symptoms. · Avoid alcohol and other CNS depressants. · Inform doctor of all medications, especially MAOIs, SSRIs, and other serotonergic drugs. · Report any unusual symptoms like serotonin syndrome (agitation, hallucinations, rapid heart rate, fever, muscle stiffness, loss of coordination). |