Buspirone

Buspirone
Brand Name: BuSpar

Drug Monograph

Contents

• Pharmacology
• Indications
• Contraindications
• Warnings
• Precautions
• Adverse Effects
• Overdose
• Dosage
• Supplied
• Research

Pharmacology

Anxiolytic

Buspirone is a psychotropic drug with anxiolytic properties which belongs chemically to the class of compounds known as the azaspirodecanediones.

Buspirone shares some of the properties of the benzodiazepines and the neuroleptics, as well as demonstrating other pharmacological action. It attenuates punishment suppressed behavior in animals and exerts a taming effect, but is devoid of anticonvulsant and muscle relaxant properties and does not bind to the benzodiazepine/GABA receptor complex. Buspirone affects a variety of dopamine mediated biochemical and behavioral events, but is free of cataleptic activity. Buspirone has an affinity for brain D(2)-dopamine receptors, where it acts as an antagonist and agonist, and for the 5-HT(1A) receptors, where it acts as an agonist. Buspirone does not block the neuronal reuptake of monoamines and, on chronic administration, it does not lead to changes in receptor density in the models investigated. However, the mechanism of action of buspirone remains to be fully elucidated.

Buspirone is rapidly absorbed in man and undergoes extensive first pass metabolism. Following oral administration, low peak plasma levels of unchanged drug, of 1 to 6 ng/mL were observed 40 to 90 minutes after a single 20 mg dose. In a number of studies performed in healthy volunteers, the mean half-life of buspirone ranged from 2 to 3 hours up to approximately 11 hours with considerable variation in individual values. Multiple dose studies suggest that steady state plasma levels were usually achieved within a few days. Buspirone is metabolized primarily by oxidation, producing several hydroxylated derivatives and a pharmacologically active metabolite, 1-pyrimidinylpiperazine (1-PP). Peak plasma levels of 1-PP have been found to be higher than those of its parent drug and its half-life to be approximately double that of unchanged buspirone. In a single dose study using (14)C labeled buspirone, 29 to 63% of the dose was excreted in the urine within 24 hours, primarily as metabolites, while fecal excretion accounted for 18 to 38% of the dose. In man, approximately 95% of buspirone is plasma protein bound, but other highly bound drugs, e.g. phenytoin, propranolol and warfarin, are not displaced by buspirone from plasma protein in vitro. However, in vitro binding studies show that buspirone does displace digoxin.

The effect of food upon the bioavailability of buspirone was studied in 8 subjects. The area under the plasma concentration curve (AUC) and peak plasma concentration (C(max)) of unchanged buspirone increased by 84% and 116% respectively when the drug was administered with food, but the total amount of buspirone immunoreactive material did not change. The significance of this finding is not known, but it could indicate that food may decrease the presystemic clearance of buspirone.

Buspirone had no effect on hepatic microsomal enzyme activity when administered to rats for 5 days. In man, the effect of buspirone on drug metabolism or concomitant drug disposition has not been studied. The pharmacokinetics of buspirone in patients with hepatic or renal dysfunction, and in the elderly, has also not been clearly established.

Indications

Short-term symptomatic relief of excessive anxiety in patients with generalized anxiety disorder (psychoneurotic disorder).

Eight 3-way short-term, controlled clinical trials involving buspirone, diazepam and placebo are considered central to the evaluation of buspirone as an anxiolytic agent. In 4 of the 8 clinical trials, buspirone demonstrated a significant difference from placebo. In the other 4 trials, there was no significant difference between buspirone and placebo, but a significantly greater improvement was observed in 2 of these trials with diazepam than with placebo. The adverse effect profiles of buspirone and diazepam in these clinical trials were, however, different.

Contraindications

In patients hypersensitive to buspirone HCl.

Buspirone is contraindicated in patients with severe hepatic or severe renal impairment.

Warnings

The occurrence of elevated blood pressure in patients receiving both buspirone and a MAO inhibitor has been reported. Therefore, it is recommended that buspirone should not be used concomitantly with a MAO inhibitor.

Since buspirone can bind to central dopaminergic receptors, the possibility of acute and chronic changes in dopamine mediated neurological function (e.g. dystonia, pseudo-parkinsonism, akathisia and tardive dyskinesia) should be considered (see Precautions).

Since the effects of buspirone have not been evaluated in patients with a history of convulsive disorders and since it lacks anticonvulsant activity in animals, buspirone is not recommended for patients with seizure disorders.

Use of Buspirone in Patients Previously Treated with a Benzodiazepine: Patients who have previously taken benzodiazepines may be less likely to respond to buspirone than those who have not. In 2 clinical studies to date, substitution of buspirone did not ameliorate or prevent withdrawal symptoms in either abrupt or gradual withdrawal from various benzodiazepines following long-term use. Therefore, if it is considered desirable to switch a patient who has been receiving benzodiazepine therapy to buspirone, the benzodiazepine should first be withdrawn gradually. A drug-free interval is desirable between withdrawal of the benzodiazepine and initiation of buspirone, in order to increase the likelihood of distinguishing between benzodiazepine withdrawal effects and unrelieved anxiety due to possible failure of buspirone in this category of patients.

Benzodiazepine rebound or withdrawal symptoms may occur over varying time periods depending in part on the type of drug and its effective half-life of elimination. These symptoms may appear as any combination of irritability, anxiety, agitation, insomnia, tremor, abdominal cramps, muscle cramps, vomiting, sweating, flu-like symptoms without fever and, occasionally, seizures, and should be treated symptomatically.

Pregnancy and Lactation:

The safety of buspirone during pregnancy and lactation has not been established and, therefore, it should not be used in women of childbearing potential or nursing mothers, unless, in the opinion of the physician, the potential benefits to the patient outweigh the possible hazards to the fetus. Buspirone and its metabolites are excreted in milk in rats. The extent of excretion in human milk has not yet been determined.

Precautions

Effects on Cognitive and Motor Performance:

In controlled studies in healthy volunteers, single doses of buspirone up to 20 mg had little effect on most tests of cognitive and psychomotor function, although performance on a vigilance task was impaired in a dose-related manner. The effect of higher single doses of buspirone on psychomotor performance has not been investigated.

Ten mg of buspirone given 3 times daily for 7 days to healthy volunteers produced considerable subjective sedation but no significant effect on psychomotor performance (no vigilance tasks were used in this study). It also caused transient dizziness, especially on standing and walking.

Occupational Hazards:

Until further experience is obtained with buspirone, patients should be warned not to operate an automobile or undertake activities requiring mental alertness, judgment and physical coordination, until they are reasonably certain that buspirone does not affect them adversely.

Significant Interactions:

In laboratory studies in healthy volunteers, buspirone in doses up to 20 mg did not potentiate the psychomotor impairment produced by relatively modest doses of alcohol. However, decreased contentedness or dysphoria was observed with a combination of alcohol and a 20 mg single dose of buspirone. Since no data are available on concomitant use of higher doses of buspirone and alcohol, it is prudent to advise patients to avoid alcohol during buspirone therapy.

Food increased the bioavailability of unchanged buspirone in healthy subjects, possibly due to a reduced first-pass effect.

Concomitant use of MAO inhibitors and buspirone has been reported to cause an increase in blood pressure. Therefore, concomitant use of these medications is not recommended.

In a study in normal volunteers, no interaction of buspirone with amitriptyline was seen. A similar study with buspirone and diazepam showed an increase in the levels of nordiazepam.

In another study in normal volunteers, concomitant administration of buspirone and haloperidol resulted in increased serum haloperidol concentrations. The clinical significance of this finding is not clear.

There is 1 report suggesting that the concomitant use of trazodone and buspirone may have caused 3- to 6-fold elevations in ALT (SGPT) in a few patients. In a similar study, attempting to replicate this finding, no interactive effect on hepatic transaminases was identified.

Because the effects of concomitant administration of buspirone with most other psychotropic drugs have not been studied, the concomitant use of buspirone with other CNS active drugs should be approached with caution.

In vitro, buspirone does not displace tightly bound drugs like phenytoin, propranolol and warfarin from serum proteins. However, there has been 1 report of prolonged prothrombin time when buspirone was added to the regimen of a patient treated with warfarin. The patient was also chronically receiving phenytoin, phenobarbital, digoxin and Synthroid. In vitro, buspirone may displace less firmly bound drugs like digoxin. The clinical significance of this property is unknown.

There have been no reports to date of interference of buspirone with commonly employed clinical laboratory tests.

Drug Abuse and Dependence:

Although preliminary animal and human investigations suggest that buspirone may be significantly devoid of potential for producing physical or psychological dependence, only extensive clinical experience with the drug will provide conclusive evidence. Meanwhile, physicians should carefully evaluate patients for a history of drug abuse and follow such patients closely, observing them for signs of buspirone misuse and abuse.

Patients with Impaired Hepatic or Renal Function:

Since it is metabolized by the liver and excreted by the kidneys, buspirone should be used with caution in patients with a history of hepatic or renal impairment. It is contraindicated in patients with severe hepatic or renal impairment.

Children:

The safety and effectiveness of buspirone in individuals below the age of 18 years have not been established.

Geriatrics:

Buspirone has not been systematically evaluated in older patients. Although it would appear from limited pharmacokinetic and clinical studies that buspirone does not behave differently in the elderly, there is little known about the effects of buspirone in this age group at doses above 30 mg/day. Therefore, it is recommended that buspirone should be used in the elderly at doses not exceeding 30 mg/day for a duration not exceeding 4 weeks.

Neuroendocrine Effects:

Single doses of 30 mg or higher of buspirone resulted in significantly elevated plasma prolactin and growth hormone concentrations in normal volunteers. No effect was seen at lower doses. In another study, no such increases were observed after buspirone was administered in divided doses (10 mg t.i.d.) for 28 days.

Possible Concerns Related to Buspirone’s Binding to Dopamine Receptors:

Because buspirone can bind to central dopamine receptors, a question has been raised about its potential to cause acute and chronic changes in dopamine mediated neurological function (e.g., dystonia, pseudoparkinsonism, akathisia, and tardive dyskinesia). Clinical experience in controlled trials has failed to identify any significant neuroleptic-like activity; however, a syndrome of restlessness, appearing shortly after initiation of treatment, has been reported in some small fraction of buspirone treated patients. The syndrome may be explained in several ways. For example, buspirone may increase central noradrenergic activity; alternatively, the effect may be attributable to dopaminergic effects (i.e., represent akathisia). Obviously, the question cannot be totally resolved at this point in time. Generally, long-term sequelae of any drug’s use can be identified only after several years of marketing.

Adverse Effects

The most common adverse reactions encountered with buspirone are dizziness, headache, drowsiness and nausea. During premarketing clinical trials, approximately 10% of the patients discontinued treatment due to an adverse event.

Adverse reactions reported include the following:

CNS: Dizziness, headache, drowsiness, lightheadedness, insomnia, fatigue, nervousness, decreased concentration, excitement, depression, confusion, nightmares/vivid dreams, anger/hostility. Infrequently (<1%) depersonalization, noise intolerance, euphoria/feeling high, dissociative reaction, fear, loss of interest, dysphoria, hallucinations, seizures, suicidal thoughts. Rarely, slurred speech, claustrophobia, cold intolerance, stupor, psychosis.

Neurologic: Paresthesia, weakness, incoordination, tremor, numbness. Infrequently, muscle cramps and spasms, rigid/stiff muscles, involuntary movements, akathisia, slowed reaction time. Rarely, tingling of limbs, stiff neck, rigidity of jaw, ataxia.

Autonomic: Dry mouth, sweating/clamminess, blurred vision, constipation. Infrequently, urinary frequency, retention and burning, flushing.

Cardiovascular: Tachycardia, chest pain, palpitations. Infrequently, syncope, hypotension, hypertension. Rarely, congestive heart failure, cerebrovascular accident, myocardial infarction, cardiomyopathy, bradycardia, EKG change.

Gastrointestinal: Nausea, gastrointestinal distress, diarrhea, vomiting. Infrequently, flatulence, increased appetite, anorexia, hypersalivation, rectal bleeding, irritable colon. Rarely, burning tongue.

Respiratory: Nasal congestion. Infrequently, shortness of breath, chest congestion, difficulty breathing, hyperventilation. Rarely, epistaxis.

Endocrine: Infrequently, decreased and increased libido, weight gain, weight loss, menstrual irregularity/breakthrough bleeding. Rarely, delayed ejaculation, impotence, galactorrhea, amenorrhea, thyroid abnormality.

Allergic or Toxic: Skin rash, sore throat. Infrequently, edema/facial edema, pruritus, chills/fever. Rarely, photophobia, erythema, flu-like symptoms.

Clinical Laboratory: Infrequently, increases in liver enzymes. Rarely, eosinophilia, leukopenia, thrombocytopenia.

Miscellaneous: Tinnitus, muscle aches/pains. Infrequently, redness/itching of eyes, altered taste/smell, roaring sensation in head, malaise, easy bruising, dry skin, arthralgia, blisters, hair loss. Rarely, acne, thinning of nails, sore eyes, inner ear abnormality, pressure on eyes, nocturia, enuresis, hiccups, voice loss, alcohol abuse.

Post Introduction Clinical Experience: Post-marketing experience in the US has shown an adverse experience profile similar to that given above. Additional reports have included rare occurrences of allergic reaction, cogwheel rigidity, dystonic reaction, ecchymosis, emotional lability and tunnel vision. Because of the uncontrolled nature of these spontaneous reports, a causal relationship to buspirone treatment has not been determined.

Overdose

Symptoms: In clinical pharmacology trials, buspirone up to 400 mg/day was administered to healthy male volunteers. As this dose was approached, the following symptoms were observed in descending order of frequency: drowsiness, ataxia, nausea and vomiting, dizziness, clammy feeling, difficulty thinking, feeling high, rushing sensation, gastric distress, headache, itching, miosis, hypotension, tremor, incoordination, insomnia and hallucinations. In a dose ranging study in acute psychotic patients, up to 2400 mg/day was administered. Dizziness, nausea and vomiting were the most common adverse effects. One patient developed extrapyramidal symptoms at 600 mg/day.

Treatment: There is no specific antidote for buspirone. Management should, therefore, be symptomatic and supportive. Any patient suspected of having taken an overdose should be admitted to a hospital as soon as possible, and the stomach emptied by gastric lavage. Respiration, pulse and blood pressure should be monitored, as in all cases of drug overdosage. As with the management of intentional overdosage with any drug, the ingestion of multiple agents should be suspected. In 6 anuric patients, hemodialysis either had no effect on the pharmacokinetics of buspirone or decreased its clearance.

Dosage

Dosage should be individually adjusted, according to tolerance and response.

The recommended initial dose is 5 mg 2 to 3 times daily. This may be titrated according to the needs of the patient and the daily dose increased by 5 mg increments every 2 to 3 days up to a maximum of 45 mg daily in divided doses. The usual therapeutic dose is 20 to 30 mg daily in 2 or 3 divided doses.

Geriatrics: Limited pharmacokinetic and clinical data have shown no difference in the effects of buspirone between elderly patients and healthy adult volunteers. However, until more information has accumulated in the elderly, it is recommended that the maximum daily dose should not exceed 30 mg for a duration not exceeding 4 weeks.

Note: If buspirone is administered to patients with compromised hepatic or renal function, careful monitoring will be required together with appropriate dosage adjustment.

Supplied

Each white, biconvex, rectangular pillow shaped tablet with BUSPAR raised on one side and BL logo, bisect score and 10 on the other side contains: Buspirone HCl 10 mg. Bottles of 100.

Research

The research information is available separately on Internet Mental Health.

Note: This information is from a Canadian monograph. There can be differences in indications, dosage forms and warnings for this drug in other countries.

Internet Mental Health (www.mentalhealth.com) copyright 1995-1996 by Phillip W. Long, M.D.

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