Detailed Drug Information:

DRUG CLASS AND MECHANISM: Quetiapine is an oral drug that is used for treating psychoses, for example, schizophrenia. 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.

PREPARATIONS: Quetiapine is available as 25 mg (peach), 100 mg (yellow) and 200 mg (white) tablets.

STORAGE:Tablets should be stored at room temperature, 15-30°C (59-86°F).

PRESCRIBED FOR: Quetiapine is used to treat severe mental disorders like schizophrenia, which are characterized by distorted thoughts, perceptions, and emotions,.

DOSING: Quetiapine usually is taken twice or three times per day. The dose usually is increased slowly over several days to weeks to achieve the desired effect. Quetiapine can be taken with or without food.

DRUG INTERACTIONS: Phenytoin (Dilantin) markedly decreases the amount of quetiapine that is absorbed from the intestine and thereby reduces its effectiveness. Thus, patients taking phenytoin require higher doses of quetiapine.

Quetiapine can cause orthostatic hypotension, a drop in blood pressure that occurs upon rising that may cause dizziness or light-headedness. Diazepam (Valium) or related benzodiazepines and alcohol can promote the orthostatic hypotension caused by quetiapine, and they should not be taken together with quetiapine.

Quetiapine can add to the sedating effects of other drugs that cause sedation. Such drugs include narcotic pain relievers (e.g. Percocet), 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, e.g., 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 can be used in pregnancy if the physician feels that it is necessary.

NURSING MOTHERS: Quetiapine is excreted in the milk of animals during lactation. It is not known if it is excreted in human milk, but it is recommended that women taking quetiapine not breast feed.

SIDE EFFECTS: Quetiapine can cause orthostatic hypotension especially during the first 3-5 day period of treatment, when it is restarted after temporary discontinuation, and after an increase in the dose. The risk of orthostatic hypotension is about 1 in 100 (one of every hundred patients who takes quetiapine). Quetiapine frequently causes tiredness (1 in 5 patients), especially during the first 3-5 days of treatment. Because of this tiredness, care should be exercised in any activity requiring mental alertness, such as operating a motor vehicle (including automobiles) or hazardous machinery. Less common side effects include seizures (1 in 125 patients) and hypothyroidism (1 in 250 patients).

As with other antipsychotics, long-term use of quetiapine may lead to a potentially irreversible condition called tardive dyskinesia which consists of involuntary movements of the jaw, lips, and tongue.

A potentially fatal complex referred to as neuroleptic malignant syndrome (NMS) has been reported with antipsychotic drugs, and two possible cases of NMS have been reported with quetiapine. Patients who develop NMS may have high fevers, muscle rigidity, altered mental status, irregular pulse or blood pressure, rapid heart rate, excessive sweating, and heart arrhythmias.

In animals, quetiapine has been associated with the development of cataracts, and cataracts have been reported in patients using quetiapine for prolonged periods. Although it is not clear if quetiapine is responsible for the cataracts seen in humans, eye examinations by slit-lamp (to identify cataracts before they impair vision) are recommended at the beginning of treatment and every six months during treatment. If cataracts form, treatment should be discontinued.

Quetiapine may increase blood concentrations of cholesterol and triglycerides by 11% and 17%, respectively.

Although there is no clear link between quetiapine and diabetes, patients should be tested during treatment for elevated blood-sugars. Additionally, persons with risk factors for diabetes, including obesity or a family history of diabetes, should have their fasting levels of blood sugar tested before starting treatment and periodically throughout treatment to detect the onset of diabetes. Any patient developing symptoms that suggest diabetes during treatment should be tested for diabetes.

Pharmacy Author: Emmanuel Saltiel, Pharm. D.

Medical Editor: Jay M. Marks, M.D.