quetiapine, Seroquel, Seroquel XR (cont.)

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The initial dose for schizophrenia is 25 mg twice daily (50 mg/day) of immediate release tablets. The dose can be increased by 25-50 mg two or three times daily. The target dose is 300-400 mg/day in two or three doses. Patients respond to 150-750 mg/day, and doses greater than 800 mg/day have not been evaluated. The starting dose is 300 mg once daily and the target dose is 400-800 mg once daily when using extended release tablets.

The dose range for treating major depression is 150-300 mg/day of extended release tablets. The starting does is 50 mg in the evening for 2 days increasing to 150 mg in the evening.

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 and result in lower blood pressure.

Quetiapine can add to 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), erythromycin, clarithromycin (Biaxin), nefazodone (Serzone), verapamil (Calan, Isoptin, Verelan), diltiazem (Cardizem, Tiazac, Dilacor) may cause elevated and toxic levels of quetiapine.

Medically Reviewed by a Doctor on 4/1/2013

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