Dosage
At very low doses quetiapine acts primarily as a histamine receptor blocker (antihistamine) and α1-adrenergic blocker. When the dose is increased quetiapine activates the adrenergic system and binds strongly to serotonin receptors and autoreceptors. At high doses quetiapine starts blocking significant amounts of dopamine receptors. Use of low-dose quetiapine is not recommended except temporarily during drug titration period (less than 30 days).
Due to compensatory changes at dopamine, serotonin, adrenergic and histamine receptor sites in the central nervous system, a gradual reduction in dosage is recommended to minimise or avoid withdrawal symptoms. Withdrawal symptoms reported to occur after discontinuation of quetiapine include: insomnia, nausea, emesis, lightheadedness, diaphoresis, orthostatic hypotension, tachycardia, as well as nervousness, dizziness, headache, and anxiety. The present evidence suggests that these symptoms affect a small number of susceptible individuals treated with quetiapine.
The British National Formulary recommends a gradual withdrawal when discontinuing antipsychotic treatment to avoid acute withdrawal syndrome or rapid relapse.
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