Products
Quetiapine is commercially available in the form of film-coated tablets and sustained-release tablets (Seroquel / XR, generic, auto-generic). It has been approved in many countries since 1999. Generics of film-coated tablets entered the market in 2012, and generics of sustained-release tablets were first registered in 2013.
Structure and properties
Quetiapine (C21H25N3O2S, Mr = 383.5 g/mol) is present in drugs as quetiapine fumarate, a white crystalline powder that is somewhat soluble in water. It is a piperazine derivative and, like clotiapine (entumin), belongs to the dibenzothiazepines. The active metabolite norquetiapine is involved in the effects.
Effects
Quetiapine (ATC N05AH04) has antipsychotic, antidepressant, and depressant properties. The effects are primarily attributed to antagonism at serotonin and dopamine receptors, with a higher affinity for serotonin receptors. Quetiapine also binds to the norepinephrine transporter (NET). Antagonism at histamine H1 receptors may cause drowsiness and antagonism at alpha1-adrenoceptors may cause low blood pressure. Quetiapine is classified as an atypical neuroleptic because it causes fewer extrapyramidal side effects than the classic agents. It has a half-life of seven to 12 hours.
Indications
For the treatment of schizophrenia, for manic or depressive episodes in bipolar disorder (including relapse prevention), and for the treatment of unipolar depression. Quetiapine is also commonly prescribed off-label in a low dosage (e.g., – – 25 mg) for sleep disorders, but is not approved by regulatory agencies for this purpose!
Dosage
According to the professional information. Dosing is gradual and intake is independent of meals. Due to interaction with CYP3A4, quetiapine should not be taken concomitantly with grapefruit juice. The drug must be discontinued gradually to avoid discontinuation symptoms.
Abuse
Quetiapine is abused as an intoxicant because of its psychotropic and depressant properties.
Contraindications
- Hypersensitivity
- Breastfeeding
- Combination with strong CYP3A4 inhibitors.
Full precautions can be found in the drug label.
Interactions
Quetiapine is metabolized primarily by CYP3A4. Concomitant administration of potent CYP3A4 inhibitors may result in sometimes massive increases in concentrations. Quetiapine should not be taken with grapefruit juice because grapefruit juice is a known inhibitor of CYP3A4. Other interactions have been described with central depressant drugs, alcohol, lithium, and enzyme inducers, among others.
Adverse effects
The most common potential adverse effects include weight gain, headache, discontinuation symptoms after cessation of therapy, drowsiness, dizziness, hypotension, dry mouth, and vomiting. Quetiapine may rarely prolong the QT interval.
