Buspirone

Drug Interactions Psychotropic Agents MAO inhibitors The use of monoamine oxidase inhibitors (MAOIs) intended to treat depression with buspirone or within 14 days of stopping treatment with buspirone is contraindicated because of an increased risk of serotonin syndrome and/or elevated blood pressure. The use of buspirone within 14 days of stopping an MAOI intended to treat depression is also contraindicated. Starting buspirone in a patient who is being treated with reversible MAOIs such as linezolid or intravenous methylene blue is also contraindicated because of an increased risk of serotonin syndrome (see WARNINGS , DOSAGE AND ADMINISTRATION AND CONCOMITANT DRUG ). Amitriptyline After addition of buspirone to the amitriptyline dose regimen, no statistically significant differences in the steady-state pharmacokinetic parameters (C max , AUC, and C min ) of amitriptyline or its metabolite nortriptyline were observed. Diazepam After addition of buspirone to the diazepam dose regimen, no statistically significant differences in the steady-state pharmacokinetic parameters (C max , AUC, and C min ) were observed for diazepam, but increases of about 15% were seen for nordiazepam, and minor adverse clinical effects (dizziness, headache, and nausea) were observed. Haloperidol In a 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. Nefazodone (See Inhibitors and Inducers of Cytochrome P450 3A4 (CYP3A4) .) Trazodone There is one report suggesting that the concomitant use of trazodone hydrochloride and buspirone may have caused 3 to 6 fold elevations on SGPT (ALT) in a few patients. In a similar study attempting to replicate this finding, no interactive effect on hepatic transaminases was identified. Triazolam/Flurazepam Coadministration of buspirone with either triazolam or flurazepam did not appear to prolong or intensify the sedative effects of either benzodiazepine. Other Psychotropics 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. Inhibitors and Inducers of Cytochrome P450 3A4 (CYP3A4) Buspirone has been shown in vitro to be metabolized by CYP3A4. This finding is consistent with the in vivo interactions observed between buspirone and the following: Diltiazem and Verapamil In a study of nine healthy volunteers, coadministration of buspirone (10 mg as a single dose) with verapamil (80 mg t.i.d.) or diltiazem (60 mg t.i.d.) increased plasma buspirone concentrations (verapamil increased AUC and C max of buspirone 3.4 fold while diltiazem increased AUC and C max 5.5 fold and 4 fold, respectively). Adverse events attributable to buspirone may be more likely during concomitant administration with either diltiazem or verapamil. Subsequent dose adjustment may be necessary and should be based on clinical assessment. Erythromycin In a study in healthy volunteers, coadministration of buspirone (10 mg as a single dose) with erythromycin (1.5 g/day for 4 days) increased plasma buspirone concentrations (5 fold increase in C max and 6 fold increase in AUC). These pharmacokinetic interactions were accompanied by an increased incidence of side effects attributable to buspirone. If the two drugs are to be used in combination, a low dose of buspirone (e.g., 2.5 mg b.i.d.) is recommended. Subsequent dose adjustment of either drug should be based on clinical assessment. Grapefruit Juice In a study in healthy volunteers, coadministration of buspirone (10 mg as a single dose) with grapefruit juice (200 mL double-strength t.i.d. for 2 days) increased plasma buspirone concentrations (4.3 fold increase in C max ; 9.2 fold increase in AUC). Patients receiving buspirone should be advised to avoid drinking such large amounts of grapefruit juice. Itraconazole In a study in healthy volunteers, coadministration of buspirone (10 mg as a single dose) with itraconazole (200 mg/day for 4 days) increased plasma buspirone concentrations (13 fold increase in C max and 19 fold increase in AUC). These pharmacokinetic interactions were accompanied by an increased incidence of side effects attributable to buspirone. If the two drugs are to be used in combination, a low dose of buspirone (e.g., 2.5 mg q.d.) is recommended. Subsequent dose adjustment of either drug should be based on clinical assessment. Nefazodone In a study of steady-state pharmacokinetics in healthy volunteers, coadministration of buspirone (2.5 or 5 mg b.i.d.) with nefazodone (250 mg b.i.d.) resulted in marked increases in plasma buspirone concentrations (increases up to 20 fold in C max and up to 50 fold in AUC) and statistically significant decreases (about 50%) in plasma concentrations of the buspirone metabolite 1-PP. With 5 mg b.i.d. doses of buspirone, slight increases in AUC were observed for nefazodone (23%) and its metabolites hydroxynefazodone (HO-NEF) (17%) and meta-chlorophenylpiperazine (9%). Slight increases in C max were observed for nefazodone (8%) and its metabolite HO-NEF (11%). Subjects receiving buspirone 5 mg b.i.d. and nefazodone 250 mg b.i.d. experienced lightheadedness, asthenia, dizziness, and somnolence, adverse events also observed with either drug alone. If the two drugs are to be used in combination, a low dose of buspirone (e.g., 2.5 mg q.d.) is recommended. Subsequent dose adjustment of either drug should be based on clinical assessment. Rifampin In a study in healthy volunteers, coadministration of buspirone (30 mg as a single dose) with rifampin (600 mg/day for 5 days) decreased the plasma concentrations (83.7% decrease in C max ; 89.6% decrease in AUC) and pharmacodynamic effects of buspirone. If the two drugs are to be used in combination, the dosage of buspirone may need adjusting to maintain anxiolytic effect. Other Inhibitors and Inducers of CYP3A4 Substances that inhibit CYP3A4, such as ketoconazole or ritonavir, may inhibit buspirone metabolism and increase plasma concentrations of buspirone while substances that induce CYP3A4, such as dexamethasone or certain anticonvulsants (phenytoin, phenobarbital, carbamazepine), may increase the rate of buspirone metabolism. If a patient has been titrated to a stable dosage on buspirone, a dose adjustment of buspirone may be necessary to avoid adverse events attributable to buspirone or diminished anxiolytic activity. Consequently, when administered with a potent inhibitor of CYP3A4, a low dose of buspirone used cautiously is recommended. When used in combination with a potent inducer of CYP3A4 the dosage of buspirone may need adjusting to maintain anxiolytic effect. Other Drugs Cimetidine Coadministration of buspirone with cimetidine was found to increase C max (40%) and T max (2 fold), but had minimal effects on the AUC of buspirone. Protein Binding In vitro , buspirone does not displace tightly bound drugs like phenytoin, propranolol, and warfarin from serum proteins. However, there has been one 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 levothyroxine sodium. In vitro , buspirone may displace less firmly bound drugs like digoxin. The clinical significance of this property is unknown. Therapeutic levels of aspirin, desipramine, diazepam, flurazepam, ibuprofen, propranolol, thioridazine, and tolbutamide had only a limited effect on the extent of binding of buspirone to plasma proteins (see CLINICAL PHARMACOLOGY ).

Buspirone hydrochloride is "indicated for the management of anxiety disorders or the short-term relief of the symptoms of anxiety," with efficacy established largely in patients meeting criteria for Generalized Anxiety Disorder (GAD). The label cautions that effectiveness "in long-term use, that is, for more than 3 to 4 weeks, has not been demonstrated in controlled trials."

DOSAGE AND ADMINISTRATION The recommended initial dose is 15 mg daily (7.5 mg b.i.d.). To achieve an optimal therapeutic response, at intervals of 2 to 3 days the dosage may be increased 5 mg per day, as needed. The maximum daily dosage should not exceed 60 mg per day. In clinical trials allowing dose titration, divided doses of 20 mg to 30 mg per day were commonly employed. The bioavailability of buspirone is increased when given with food as compared to the fasted state (see CLINICAL PHARMACOLOGY ). Consequently, patients should take buspirone in a consistent manner with regard to the timing of dosing; either always with or always without food. When buspirone is to be given with a potent inhibitor of CYP3A4, the dosage recommendations described in the PRECAUTIONS , Drug Interactions section should be followed. Switching a Patient To or From a Monoamine Oxidase Inhibitor (MAOI) Antidepressant At least 14 days should elapse between discontinuation of an MAOI intended to treat depression and initiation of therapy with buspirone hydrochloride tablets. Conversely, at least 14 days should be allowed after stopping buspirone hydrochloride tablets before starting an MAOI antidepressant CONTRAINDICATIONS and DRUG INTERACTIONS ). Use of buspirone hydrochloride tablets with (Reversible) MAOIs, Such as Linezolid or Methylene Blue Do not start buspirone hydrochloride tablets in a patient who is being treated with a reversible MAOI such as linezolid or intravenous methylene blue because there is an increased risk of serotonin syndrome. In a patient who requires more urgent treatment of a psychiatric condition, non-pharmacological interventions, including hospitalization, should be considered (see CONTRAINDICATIONS and DRUG INTERACTIONS ). In some cases, a patient already receiving therapy with buspirone hydrochloride tablets may require urgent treatment with linezolid or intravenous methylene blue. If acceptable alternatives to linezolid or intravenous methylene blue treatment are not available and the potential benefits of linezolid or intravenous methylene blue treatment are judged to outweigh the risks of serotonin syndrome in a particular patient, buspirone hydrochloride tablets should be stopped promptly, and linezolid or intravenous methylene blue can be administered. The patient should be monitored for symptoms of serotonin syndrome for 2 weeks or until 24 hours after the last dose of linezolid or intravenous methylene blue, whichever comes first. Therapy with buspirone hydrochloride tablets may be resumed 24 hours after the last dose of linezolid or intravenous methylene blue (see WARNINGS ). The risk of administering methylene blue by non-intravenous routes (such as oral tablets or by local injection) or in intravenous doses much lower than 1 mg per kg with buspirone hydrochloride tablets is unclear. The clinician should, nevertheless, be aware of the possibility of emergent symptoms of serotonin syndrome with such use (see CONTRAINDICATIONS , WARNINGS and DRUG INTERACTIONS ).

The most common adverse reactions are "dizziness, nausea, headache, nervousness, lightheadedness, and excitement." In placebo-controlled trials, dizziness occurred in about 12% of buspirone patients versus 3% on placebo. Approximately 10% of patients discontinued treatment because of adverse events, most often CNS disturbances such as dizziness and insomnia.