Buspirone

Indications

• FDA-approved for the management of anxiety disorders and for the short-term relief of anxiety symptoms in adults.
• Best supported in generalized anxiety disorder, where it is a reasonable option for patients in whom benzodiazepines are undesirable.
• Off-label as an augmenting agent for major depressive disorder after inadequate SSRI response, as tested in the STAR-D program.
• Off-label for antidepressant-induced sexual dysfunction, where the 5-HT1A action may partially reverse serotonergic blunting.
• Off-label for aggression and agitation in dementia or traumatic brain injury, and for sleep-related bruxism.
• Safety and effectiveness in patients under 18 years have not been established, and pediatric trials did not demonstrate efficacy.

Mechanism of action

• Partial agonist at presynaptic and postsynaptic serotonin 5-HT1A receptors, modulating serotonergic tone rather than blocking reuptake.
• Presynaptic autoreceptor agonism initially reduces serotonin firing, and receptor desensitization over weeks yields the anxiolytic effect.
• It has no activity at the benzodiazepine site or at GABA-A receptors, which is why it produces neither sedation nor dependence.
• Moderate dopamine D2 receptor affinity explains occasional restlessness or akathisia-like symptoms in a minority of patients.
• Because it does not act on GABA, it neither treats benzodiazepine withdrawal nor provides any acute relief of panic.

Pharmacokinetics

• Rapidly absorbed but subject to very extensive first-pass metabolism, giving an oral bioavailability of only about 4 percent.
• Food slows absorption yet increases overall bioavailability, so patients should take doses consistently with or without food.
• Elimination half-life is only 2 to 3 hours, which is why divided daily dosing is required for a stable clinical effect.
• Metabolized by CYP3A4 to 1-pyrimidinylpiperazine, an active metabolite with alpha-2 adrenergic antagonist properties.
• Grapefruit juice and strong CYP3A4 inhibitors raise plasma concentrations several-fold and can cause dizziness and sedation.

Dosing

• Start 7.5 mg PO twice daily or 5 mg three times daily, then increase by 5 mg/day every 2 to 3 days as tolerated.
• The usual effective range is 20-30 mg/day in divided doses; the maximum recommended dose is 60 mg/day.
• Underdosing is the most common reason for apparent failure, since many patients are left at 15 mg/day indefinitely.
• Supplied as 5, 7.5, 10, 15, and 30 mg tablets, with the 15 and 30 mg tablets scored for flexible divided dosing.
• Reduce the dose to 2.5 mg twice daily when a strong CYP3A4 inhibitor such as itraconazole cannot be avoided.
• Not recommended in severe hepatic or severe renal impairment; no taper is needed because withdrawal does not occur.

Adverse effects

• Dizziness affects roughly 12 percent of patients and is the most common reason for early discontinuation of the drug.
• Nausea occurs in about 8 percent and headache in about 6 percent, with lightheadedness and nervousness also frequent.
• Restlessness, and occasionally akathisia-like symptoms, arise from dopamine D2 affinity and can be mistaken for worsening anxiety.
• It causes no meaningful sedation, no psychomotor impairment, and no respiratory depression, so driving is generally unaffected.
• There is no physical dependence, no withdrawal syndrome, and no established abuse liability with this agent.
• Serotonin syndrome has been reported rarely when buspirone is combined with other serotonergic drugs or an MAO inhibitor.

Monitoring

• No routine laboratory monitoring is required, which is a practical advantage over many alternative anxiolytic strategies.
• Reassess anxiety severity at 4 weeks with a standardized scale, since response is gradual and easily missed by impression alone.
• Verify the total daily dose at each visit, because failure is far more often from underdosing than from true nonresponse.
• Screen for hepatic and renal impairment before starting, as severe impairment of either organ makes the drug inappropriate.
• Ask about grapefruit juice intake and about new CYP3A4 inhibitors whenever dizziness or lightheadedness emerges.

Interactions

• Contraindicated with monoamine oxidase inhibitors and within 14 days of stopping one because of hypertensive reactions.
• Strong CYP3A4 inhibitors such as itraconazole, clarithromycin, ritonavir, and nefazodone sharply raise levels and require dose reduction.
• CYP3A4 inducers including rifampin, carbamazepine, and phenytoin lower concentrations enough to abolish the clinical effect.
• Grapefruit juice raises exposure substantially and should be avoided or kept consistent during buspirone treatment.
• Additive serotonergic risk exists with SSRIs, SNRIs, triptans, and linezolid, though clinically significant events are uncommon.

Special populations

• Human pregnancy data are limited but reassuring in the small studies available, and animal reproduction studies show no clear harm.
• Lactation data are sparse; the very low bioavailability suggests limited infant exposure, but monitoring the infant is prudent.
• Not approved under 18 years, and controlled pediatric trials in generalized anxiety disorder failed to separate from placebo.
• A reasonable anxiolytic in older adults because it avoids the falls, sedation, and cognitive impairment of benzodiazepines.
• Avoid in severe hepatic impairment and in severe renal impairment, since clearance falls and metabolite exposure rises.

Clinical pearls

• No boxed warning, no dependence, no withdrawal, and no sedation, but also no acute relief.
• Most failures are underdosing; push toward 30 mg/day divided before abandoning it.
• Useless for benzodiazepine withdrawal because it has no activity at the GABA-A receptor.