Chapter: Modern Pharmacology with Clinical Applications: Sedative-hypnotic and Anxiolytic Drugs

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Azapirones

Buspirone (BuSpar) is the first example of a class of anxiolytic agents that can relieve some symptoms of anxiety in doses that do not cause sedation.

AZAPIRONES

Buspirone (BuSpar) is the first example of a class of anxiolytic agents that can relieve some symptoms of anxiety in doses that do not cause sedation. Buspirone is structurally unrelated to existing psychotropic drugs.

Mechanism of Action

Although buspirone has been shown to interact with a number of neurotransmitter systems in the brain, it ap-pears that its clinically relevant effects are mediated through interactions at the serotonin (5-hydroxytrypta-mine, 5-HT) 5-HT1A receptor, where it acts as a partial agonist.

Pharmacokinetics

Buspirone is well absorbed from the gastrointestinal tract, and peak blood levels are achieved in 1 to 1.5 hours; the drug is more than 95% bound to plasma pro-teins. Buspirone is extensively metabolized, with less than 1% of the parent drug excreted into the urine un-changed. At least one of the metabolic products of bus-pirone is biologically active. The parent drug has an elimination half-life of 4 to 6 hours.

Pharmacological Actions

Buspirone is as effective as the benzodiazepines in the treatment of general anxiety. However, the full anxiolytic effect of buspirone takes several weeks to develop, whereas the anxiolytic effect of the benzodiazepines is maximal after a few days of therapy. In therapeutic doses, buspirone has little or no sedative effect and lacks the muscle relaxant and anticonvulsant properties of the benzodiazepines. In addition, buspirone does not potentiate the central nervous system depression caused by sedative–hypnotic drugs or by alcohol, and it does not prevent the symptoms associated with benzo-diazepine withdrawal.

Clinical Uses

Buspirone is effective in general anxiety and in anxiety with depression.

Adverse Effects

Like the benzodiazepines, buspirone appears to be safe even when given in very high doses. The most common side effects are dizziness, light-headedness, and head-ache. Abuse, dependence, and withdrawal have not been reported, and buspirone administration does not pro-duce any cross-tolerance to the benzodiazepines. Bus-pirone has been reported to increase blood pressure in patients taking monoamine oxidase inhibitors, and it may increase plasma levels of haloperidol if coadminis-tered with that agent.

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