Quetiapine is classified as an atypical antipsychotic. It is used to treat psychotic disorders such as schizophrenia.
Quetiapine is thought to modify the actions of several chemicals in the brain. It is chemically related to another atypical antipsychotic agent, clozapine, but differs both chemically and pharmacologically from the earlier phenothiazine antipsychotics.
It is available 25-mg, 100-mg, and 200-mg tablets.
Initially, a dosage of 25 mg should be taken twice a day. Each dose should be increased by 25-50 mg increments every three to four days until a target dose of 300-400 mg per day, administered in two or three divided doses, is achieved. It is not known whether doses higher than 800 mg per day are safe.
Quetiapine may cause liver damage. As a result, patients should notify their health care provider if they experience flu-like symptoms, notice yellowing of their skin or eyes, or experience abdominal pain. Liver function should be assessed periodically. The drug should be used cautiously in people with a history of liver disease or alcoholic cirrhosis.
Quetiapine may alter the function of the thyroid gland. Those taking supplements for low thyroid function may require dosage adjustments in their thyroid medication.
Quetiapine may increase cholesterol levels and contribute to the formation of cataracts. Because of this possibility, cholesterol levels should be checked periodically and yearly eye exams should be performed.
Quetiapine should be used carefully in those with a history of seizure disorders because it may increase the tendency to have seizures.
Quetiapine may cause extreme drowsiness and should be used carefully by people who need to be mentally alert.
Relatively common side effects that accompany quetiapine include drowsiness, dizziness, rash, dry mouth, insomnia, fatigue, muscular weakness, anorexia, blurred vision, some loss of muscular control, and amenorrhea (lack of menstruation) in women.
Dystonia (difficulty walking or moving) may occur with quetiapine use. This condition may subside in 24 to 48 hours even when the person continues taking the drug and usually disappears when quetiapine is discontinued.
Quetiapine use may lead to the development of symptoms that resemble Parkinson's disease. These symptoms may include a tight or mask-like expression on the face, drooling, tremors, pill-rolling motions in the hands, cogwheel rigidity (abnormal rigidity in muscles characterized by jerky movements when the muscle is passively stretched), and a shuffling gait. Taking anti-Parkinson drugs benztropine mesylate or trihexyphenidyl hydrochloride along with the quetiapine usually controls these symptoms.
Quetiapine has the potential to produce a serious side effect called tardive dyskinesia. This syndrome consists of involuntary, uncoordinated movements that may appear late in therapy and may not disappear even after the drug is stopped. Tardive dyskinesia involves involuntary movements of the tongue, jaw, mouth or face or other groups of skeletal muscles. The incidence of tardive dyskinesia increases with increasing age and with increasing dosage of quetiapine. Women are at greater risk than men for developing tardive dyskinesia. There is no known effective treatment for tardive dyskinesia, although gradual (but rarely complete) improvement may occur over a long period.
An occasionally reported side effect of quetiapine is neuroleptic malignant syndrome. This is a complicated and potentially fatal condition characterized by muscle rigidity, high fever, alterations in mental status, and cardiac symptoms such as irregular pulse or blood pressure, sweating, tachycardia (fast heartbeat), and arrhythmias (irregular heartbeat). People who think they may be experiencing any side effects from this or any other medication should talk to their physician promptly.
Quetiapine may be less effective when it is taken with drugs like carbamazepine (Tegretol), phenytoin (Dilantin), rifampin (Rifadin), barbiturates, thioridazine (Mellaril), or corticosteroids such as prednisolone, methlylprednisolone, prednisone, and dexamethasone because these drugs increase the breakdown of quetiapine in the liver causing lower-than-normal levels of the drug.
Antifungal drugs such as fluconazole (Diflucan) or ketoconazole (Nizerol), antibiotics such as erythromycin or clarithromycin (Biaxin), and cimetidine (Tagamet), because these drugs may decrease the breakdown of quetiapine in the liver causing higher-than-normal levels of the drug.
Any drug that causes drowsiness may lead to decreased mental alertness and impaired motor skills when taken with Quetiapine. Some examples include alcohol, antidepressants such as imipramine (Tofranil) or paroxetine (Paxil), antipsychotics such as thioridazine (Mellaril), and some antihistamines.
AstraZeneca Staff. Seroquel Package Insert. Wilmington, DE: AstraZeneca Pharmaceuticals LP, 2001.
Ellsworth, Allan J., and others, eds. Mosby's Medical Drug Reference. St. Louis, MO: Mosby, Inc, 1999.
Facts and Comparisons Staff. Drug Facts and Comparisons. 6th Edition. St. Louis, MO: Facts and Comparisons,2002.
Kelly Karpa, RPh, Ph.D.