Drug Interactions between fluoxetine / olanzapine and Quillivant XR

MONITOR: Coadministration with methylphenidate may increase the plasma concentrations and effects of selective serotonin reuptake inhibitors (SSRIs). Human pharmacologic studies have shown that methylphenidate may inhibit the metabolism of some antidepressants including SSRIs. There have been isolated reports of adverse reactions such as hallucinations, confusion, seizures, and serotonin syndrome during concomitant use of methylphenidate with an SSRI, which resolved following discontinuation of one or both drugs. Nevertheless, the combination has been used therapeutically to improve clinical response in the treatment of attention-deficit hyperactivity disorder and to augment the effects of SSRIs in the treatment of depression.

MANAGEMENT: Pharmacologic response to SSRIs should be monitored more closely whenever methylphenidate (racemic) or dexmethylphenidate (the more pharmacologically active d-enantiomer) is added to or withdrawn from therapy, and the dosage of one or both drugs adjusted as necessary.

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MONITOR: It is uncertain whether olanzapine causes clinically significant prolongation of the QT interval. In pooled studies of adults as well as pooled studies of adolescents, there were no significant differences between olanzapine and placebo in the proportion of patients experiencing potentially important changes in ECG parameters, including QT, QTcF (Fridericia-corrected), and PR intervals. In clinical trials, clinically meaningful QTc prolongations (QTcF >=500 msec at any time post-baseline in patients with baseline QTcF <500 msec) occurred in 0.1% to 1% of patients treated with olanzapine, with no significant differences in associated cardiac events compared to placebo. Published studies have generally reported no significant effect of olanzapine on QTc interval, although both QTc prolongation and QTc shortening have also been reported. There have been a few isolated case reports of QT prolongation in patients receiving olanzapine. However, causality is difficult to establish due to confounding factors such as concomitant use of drugs that cause QT prolongation and underlying conditions that may predispose to QT prolongation (e.g., hypokalemia, congenital long QT syndrome, preexisting conduction abnormalities).

MANAGEMENT: Some authorities recommend caution when olanzapine is used with drugs that are known to cause QT prolongation. ECG monitoring may be advisable in some cases, such as in patients with a history of cardiac arrhythmias or congenital or family history of long QT syndrome. Patients should be advised to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope.

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