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Many drugs have been associated with QTc prolongation and, in some cases, this is augmented by concomitant administration with metabolic inhibitors. The effects of 6 antipsychotics on the QTc interval at and around the time of estimated peak plasma/serum concentrations in the absence and presence of metabolic inhibition were characterized in a prospective, randomized study in which patients with psychotic disorders reached steady-state on either haloperidol 15 mg/d (n = 27), thioridazine 300 mg/d (n = 30), ziprasidone 160 mg/d (n = 31), quetiapine 750 mg/d (n = 27), olanzapine 20 mg/d (n = 24), or risperidone 6-8 mg/d increased to 16 mg/d (n = 25/20). Electrocardiograms (ECGs) were done at estimated Cmax at steady-state on both antipsychotic monotherapy and after concomitant administration of appropriate cytochrome P-450 (CYP450) inhibitor(s). Mean QTc intervals did not exceed 500 milliseconds in any patient taking any of the antipsychotics studied, in the absence or presence of metabolic inhibition. The mean QTc interval change was greatest in the thioridazine group, both in the presence and absence of metabolic inhibition. The presence of metabolic inhibition did not significantly augment QTc prolongation associated with any agent. Each of the antipsychotics studied was associated with measurable QTc prolongation at steady-state peak plasma concentrations, which was not augmented by metabolic inhibition. The theoretical risk of cardiotoxicity associated with QTc prolongation should be balanced against the substantial clinical benefits associated with atypical antipsychotics and the likelihood of other toxicities.

The effects of haloperidol, risperidone, and thioridazine on the pharmacokinetics and side-effect profile of quetiapine were investigated in 36 patients with schizophrenia, schizoaffective disorder, or bipolar disorder in a single-center, two-period, multiple-dose, open-label, randomized trial. Over a one-to two-week period, quetiapine doses were escalated to 300 mg twice daily (bid). Patients were then treated for at least 7 days at the target quetiapine dose and subsequently entered into the combination therapy period, receiving haloperidol (7.5 mg, bid), risperidone (3 mg, bid), or thioridazine (200 mg, bid) for 8.5 days (after 3 days of dose escalation). Key assessments included the pharmacokinetics of quetiapine at steady state (area under the curve within a dosing interval [AUCtSS], maximum [CmaxSS], and minimum [CminSS] observed plasma concentrations, and oral clearance [Cl/f]), as well as the UKU Side Effect Rating Scale scores and safety evaluations. Neither risperidone nor haloperidol had significant effects on quetiapine pharmacokinetics. However, thioridazine produced statistically significant changes, decreasing the least squares means values of the AUCtSS, CmaxSS, and CminSS by 40%, 47%, and 31%, respectively, and increasing Cl/f by 68%. Increases in the following adverse events were noted during coadministration: somnolence (risperidone), insomnia and dry mouth (all three coadministered therapies), and dizziness (thioridazine). UKU side effect items that became worse in >or= 25% of patients during each coadministration period included sedation and increased sleep duration. Results of laboratory tests, electrocardiograms, and vital sign measurements revealed few clinically important changes. Clinical stability can be maintained with good tolerability during the transition from quetiapine monotherapy to periods of coadministration with haloperidol, risperidone, or thioridazine. Coadministration of either haloperidol or risperidone did not have any important effects on the steady-state pharmacokinetics of quetiapine. Thioridazine significantly increased the oral clearance of quetiapine. Increased doses of quetiapine may be necessary to control psychotic symptoms when thioridazine is coadministered with quetiapine.

A 10-week study was conducted in four phases comparing the short-term efficacy of thioridazine tablets and thioridazine suspension for decreasing severe behavioral symptoms of psychotic retarded children. Behavioral observations were conducted in the classroom before and after medication, both during structured activity and during free play. Thioridazine was dispensed in phases I and III in tablet form and in phases II and IV in suspension, in the same amount of milligrams per subject throughout all four phases. Across all four phases the difference between the effects of thioridazine tablet and suspension was nonsignificant. On short-term observation both forms of thioridazine proved to be effective in reducing aggression, disruptive tantrumming, self-abuse, stereotype self-stimulation, and pica eating. The cumulative average symptom reduction was 27.4% within 35 minutes following medication intake.