impairment, muscle relaxation, physical dependence, or anticonvulsant effects. In addition, buspirone does not produce euphoria and is not a drug of abuse. Dyskinesia, akathisia, myoclonus, parkinsonism, and dystonia were reported associated with buspirone. It is unclear if there is a risk of tardive dyskinesia or other movement disorders with buspirone. Overdose Buspirone appears to be relatively benign in cases of single-drug overdose, although no definitive data on this subject appear to be available. In one clinical trial, buspirone was administered to healthy male volunteers at a dosage of 375 mg/day, and produced side effects including nausea, vomiting, dizziness, drowsiness, miosis, and gastric distress. In early clinical trials, buspirone was given at dosages even as high as 2,400 mg/day, with akathisia, tremor, and muscle rigidity observed. Deliberate overdoses with 250 mg and up to 300 mg buspirone have resulted in drowsiness in about 50% of individuals. One death has been reported in a co-ingestion of 450 mg buspirone with alprazolam, diltiazem, alcohol, cocaine. Interactions Buspirone has been shown in vitro to be metabolized by the enzyme CYP3A4. This finding is consistent with the in vivo interactions observed between buspirone and these inhibitors or inducers of cytochrome P450 3A4 (CYP3A4), among others: Itraconazole: Increased plasma level of buspirone Rifampicin: Decreased plasma levels of buspirone Nefazodone: Increased plasma levels of buspirone Haloperidol: Increased plasma levels of buspirone Carbamazepine: Decreased plasma levels of buspirone Grapefruit: Significantly increases the plasma levels of buspirone. See grapefruit–drug interactions. Fluvoxamine: Moderately increase plasma levels of buspirone. Elevated blood pressure has been reported when buspirone has been administered to patients taking monoamine oxidase inhibitors (MAOIs). Pharmacology Pharmacodynamics Buspirone acts as an agonist of the serotonin 5-HT1A receptor with high affinity. It is a partial agonist of both presynaptic 5-HT1A receptors, which are inhibitory autoreceptors, and postsynaptic 5-HT1A receptors. It is thought that the main effects of buspirone are mediated via its interaction with the presynaptic 5-HT1A receptor, thus reducing the firing of serotonin-producing neurons. Buspirone also has lower affinities for the serotonin 5-HT2A, 5-HT2B, 5-HT2C, 5-HT6, and 5-HT7 receptors. In addition to binding to serotonin receptors, buspirone is an antagonist of the dopamine D2 receptor with weak affinity. It preferentially blocks inhibitory presynaptic D2 autoreceptors, and antagonizes postsynaptic D2 receptors only at higher doses. In accordance, buspirone has been found to increase dopaminergic neurotransmission in the nigrostriatal pathway at low doses, whereas at higher doses, postsynaptic D2 receptors are