Victus Drug Interactions

Alcohol: Quetiapine potentiates the cognitive and motor effects of alcohol. Avoid alcohol during quetiapine therapy.
Anticholinergic Agents: Potential pharmacologic interaction (possible disruption of body temperature regulation). Use quetiapine with caution in patients concurrently receiving drugs with anticholinergic activity.
Grapefruit Juice: Concomitant use is not recommended. Drinking grapefruit juice during treatment with quetiapine may be expected to increase exposure to the drug owing to inactivation of intestinal CYP3A4.
Hepatic CYP3A4 Inducers (e.g., phenytoin, carbamazepine, barbiturates, rifampicin, glucocorticoids, St. John's Wort, etc.): Quetiapine dose should be increased up to 5-fold of the original dose when used in combination with a chronic treatment (e.g., greater than 7 to 14 days) of a potent CYP3A4 inducer. The dose should be titrated based on the clinical response and tolerability of the patient. When the CYP3A4 inducer is discontinued, the dose of quetiapine should be reduced to the original level within 7 to 14 days. Caution should be exercised if phenytoin is withdrawn and replaced with a non-inducer (e.g., valproate).
Hepatic CYP3A4 Inhibitors (e.g., ketoconazole, itraconazole, fluconazole, erythromycin, HIV-protease inhibitors): Quetiapine dose should be reduced to one sixth of the original dose when given concomitantly with a potent CYP3A4 inhibitor. When the CYP3A4 inhibitor is discontinued, the dose of quetiapine should be returned to its original dose.
Antihypertensive Agents: Quetiapine may add to the blood pressure lowering effects of these agents.
Drugs known to cause electrolyte imbalance or increase QT interval: Caution should be used when quetiapine is used concomitantly with these drugs.
Lorazepam: The mean oral clearance of lorazepam was reduced by 20% in the presence of quetiapine.
Thioridazine: Increased oral clearance of quetiapine by 65%.
Levodopa and dopamine agonists: Quetiapine may antagonize the effects of these drugs.
Divalproex: Coadministration of quetiapine and divalproex increased the mean maximum plasma concentration of quetiapine at steady state by 17% without affecting the extent of absorption or mean oral clearance.
The mean maximum concentration and extent of absorption of total and free valproic acid at steady state were decreased by 10 to 20% when divalproex was administered with quetiapine. The mean oral clearance of total valproic acid was increased by 11% in the presence of quetiapine. The changes were not significant.
Cimetidine: Use of multiple daily doses of cimetidine (400 mg three times a day for 4 days) resulted in a 20% decrease in the mean oral clearance of quetiapine. Dosage adjustment for quetiapine is not required.
Lithium: Concomitant use of quetiapine with lithium had no effect on any of the steady-state pharmacokinetic parameters of lithium.
Fluoxetine, Imipramine, Haloperidol, or Risperidone: Concomitant use of these drugs with quetiapine did not alter the steady-state pharmacokinetics of quetiapine.
Antipyrine: Administration of quetiapine to subjects with selected psychotic disorders had no clinically relevant effect on the clearance of antipyrine or urinary recovery of antipyrine metabolites. Objects with selected psychotic disorders had no clinically relevant effect on the clearance of antipyrine or urinary recovery of antipyrine metabolites.
Laboratory Test Alterations: There have been reports of false positive urine drug screens for methadone or tricyclic antidepressants in patients taking quetiapine. Caution should be exercised in the interpretation of positive urine drug screen results for these drugs, and confirmation by alternative analytical technique (e.g., chromatographic methods) should be considered.