Medications and Drugs
Pharmacy Author: Omudhome Ogbru, PharmD
Medical Editor: Jay Marks, MD
GENERIC NAME: quetiapine
BRAND NAME: Seroquel
DRUG CLASS AND MECHANISM: Quetiapine is an oral antipsychotic drug
used for treating schizophrenia and bipolar disorder. Although the mechanism of
action of quetiapine is unknown, like other anti-psychotics, it inhibits
communication between nerves of the brain. It does this by blocking receptors on
the nerves for several neurotransmitters, the chemicals that nerves use to
communicate with each other. It is thought that its beneficial effect is due to
blocking of the dopamine type 2 (D2) and serotonin type 2 (5-HT2) receptors.
PRESCRIPTION: Yes
GENERIC AVAILABLE: No
PREPARATIONS: Tablets: 25, 50, 100, 200, 300, and 400 mg
STORAGE: Tablets should be stored at room temperature, 15-30°C
(59-86°F).
PRESCRIBED FOR: Quetiapine is used alone or in combination with other
drugs to treat schizophrenia and
bipolar disorder.
DOSING:
Quetiapine usually is taken
two or three times daily. The dose usually is increased slowly over several days
or weeks to achieve the desired effect. Quetiapine can be taken with or without
food.
The initial dose for bipolar disorder is 50 mg twice daily (100 mg/d). The dose
can be increased by 100 mg/d to a daily dose of 400 mg/d. Most patients respond
to 400-800 mg/d. Doses greater than 800 mg/d have not been studied.
The initial dose for schizophrenia is 25 mg twice daily (50 mg/d). The dose
can be increased by 25-50 mg two or three times daily. The target dose is
300-400 mg/d in two or three doses. Patients respond to 150-750 mg/d, and doses
greater than 800 mg/d have not been evaluated.
DRUG INTERACTIONS: Phenytoin (Dilantin) and thioridazine (Mellaril)
markedly decrease the amount of quetiapine that is absorbed from the intestine
and thereby reduces its effectiveness. Therefore, patients taking phenytoin or
thioridazine may require higher doses of quetiapine.
Quetiapine can cause hypotension (low blood pressure) and therefore increase
the blood pressure lowering effects of antihypertensive drugs.
Quetiapine can increase the sedating effects of other drugs that sedate. Such
drugs include narcotic pain relievers [for example, oxycodone and acetaminophen
(Percocet, Roxicet, Tylox, Endocet)], barbiturates, sedatives
such as alprazolam (Xanax) and clonazepam (Klonopin),
ethanol, and blood pressure drugs that can cause orthostatic hypotension, such
as prazosin
(Minipress) and terazosin (Hytrin).
Quetiapine is eliminated from the body by an enzyme in the liver called
cytochrome P450 3A. There is a concern that drugs that strongly interfere with
the enzyme, for example, ketoconazole (Nizoral), itraconazole (Sporanox), fluconazole
(Diflucan), and erythromycin, clarithromycin (Biaxin), nefazodone (Serzone),
verapamil (Calan, Isoptin, Verelan), or diltiazem (Cardizem, Tiazac, Dilacor)
may cause elevated and toxic levels of quetiapine.
PREGNANCY: There are no
adequate studies of quetiapine in pregnant women. Studies in animals are inconsistent. Some studies suggest effects on the
fetus and others show no effects. Quetiapine should only be used in pregnancy if
the physician feels that it is absolutely necessary and that the potential
benefits justify the unknown risks.
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
- Drug Interactions - Learn about potential drug interactions you may be exposed to. Drug interactions can occur with prescription drugs, OTC medication, vitamins, herbs, and supplements.
- Posttraumatic Stress Disorder - Read about posttraumatic stress disorder (PTSD) symptoms (nightmares, flashbacks), causes (war, traumatic events), effects (depression, suicide) and treatment (medication, therapy).
- Schizophrenia - Get information on schizophrenia symptoms (delusions, hallucinations), causes (genetics), diagnosis, treatment of schizophrenics (antipsychotic medications) and types (paranoid).
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