Pharmacokinetics of quetiapine in elderly patients with selected psychotic disorders.

OBJECTIVE: To assess the pharmacokinetics and tolerability of quetiapine in elderly patients with selected psychotic disorders. STUDY DESIGN: This was a multicentre, open-label, 27-day, rising multiple-dose trial. Descriptive statistics summarised plasma quetiapine concentrations and pharmacokinetic parameters by trial day. A two-way analysis of variance was used to evaluate all pharmacokinetic parameters, and 90% confidence intervals of the mean differences were calculated. METHODS: Antipsychotic drugs taken prior to the study period were discontinued on day 1. Quetiapine treatment began on day 3. Doses were increased stepwise, starting at 25mg three times daily and reaching 250mg three times daily by day 21. PATIENTS: Twelve patients (age 63-85 years) with schizophrenia, schizoaffective disorder or bipolar disorder. MAIN OUTCOME MEASURES AND RESULTS: Key assessments included quetiapine plasma concentrations, and neurological and safety evaluations. Under steady-state conditions, the 100 and 250mg doses of quetiapine were not significantly different in terms of dose-normalised area under the plasma concentration-time curve within an 8-hour dose administration interval, or in dose-normalised minimum plasma concentration (C(min)) at the end of a dose administration interval. The morning C(min) values for the seven discrete dose amounts evaluated also increased linearly with dose. The apparent oral clearance, volume of distribution and half-life did not change as a function of dose. There were no serious adverse events. The most common adverse events were postural hypotension (n = 6), dizziness (n = 5) and somnolence (n = 4). CONCLUSIONS: While quetiapine was well tolerated at doses up to 250mg three times daily, the potential for reduced clearance, as well as the adverse effects of postural hypotension and dizziness, indicated that quetiapine should be introduced at lower doses and titrated at a relatively slower rate in patients > or =65 years.

Pharmacokinetic profile of meropenem, administered at 500 milligrams every 8 hours, in plasma and cantharidin-induced skin blister fluid.

The pharmacokinetic disposition of meropenem, administered at 500 mg every 8 h, in plasma and cantharidin-induced blister fluid is described. Peak meropenem concentrations in blister fluid lagged behind peak meropenem concentrations in plasma, while a lower elimination rate from blister fluid was also noted. The mean penetration of meropenem into blister fluid was 67%. The pharmacokinetic profile of meropenem in blister fluid supports the utility of this dose in the management of skin and soft tissue infections.

Open-label study of the effect of combination quetiapine/lithium therapy on lithium pharmacokinetics and tolerability.

OBJECTIVE: The aim of this study was to assess the effect of oral quetiapine on the steady-state pharmacokinetics of lithium. METHODS: This was an open-label trial in patients with schizophrenia, schizoaffective disorder, or bipolar disorder who had demonstrated tolerability to combination lithium/ antipsychotic therapy. Patients received lithium for at least 1 week before screening and throughout the 18-day trial. Quetiapine was coadministered in fixed, stepwise, increasing doses of 25 to 250 mg TID on days 4 through 11, and maintained at 250 mg TID on days 12 through 14. Blood samples were drawn to monitor plasma concentrations of lithium and quetiapine. Psychiatric assessments included the Brief Psychiatric Rating Scale, the Clinical Global Impression severity of illness item, and the modified Scale for the Assessment of Negative Symptoms. Neurologic function was assessed using the Simpson-Angus Scale and the Abnormal Involuntary Movement Scale. Other assessments included clinical laboratory testing, electrocardiography, physical examinations, and monitoring for spontaneously reported adverse events. RESULTS: Nine men and 1 woman (mean [SE] age, 32.8 [1.9] years; mean [SE] body weight, 87.6 [3.3] kg) entered and completed the 18-day trial. Eight patients had bipolar disorder, 1 had paranoid schizophrenia, and 1 had schizoaffective disorder. Morning trough concentrations of lithium in serum (days 2, 6, 8, 10, 12, 14, and 17), as well as quetiapine and 2 of its metabolites in plasma (days 12, 13, and 14), did not appear to vary noticeably. Small increases were observed in the mean values of the area under the 12-hour serum lithium concentration-time curve and the maximum and minimum observed serum lithium concentrations when quetiapine was added to the lithium regimen. However, the increases were not considered clinically relevant by the investigators and were not statistically significant. A total of 91 adverse events were reported, 67 (73.6%) of which were not attributed to trial treatment. The most commonly reported adverse events during coadministration of lithium and quetiapine were somnolence (90.0% [9/10]), asthenia (70.0% [7/10]), dry mouth (30.0% [3/10]), nausea (30.0% [3/10]), vomiting (30.0% [3/10]), dizziness (30.0% [3/10]), tremor (30.0% [3/10]), and insomnia (20.0% [2/10]). There were no serious adverse events. CONCLUSIONS: Measures of lithium and quetiapine concentrations did not vary significantly during combination therapy. Coadministered lithium and quetiapine were well tolerated in the patients studied.

The safety and pharmacokinetics of quetiapine when coadministered with haloperidol, risperidone, or thioridazine.

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.

Effect of fluoxetine and imipramine on the pharmacokinetics and tolerability of the antipsychotic quetiapine.

The effects of fluoxetine and imipramine on the pharmacokinetics and nonpsychiatric side effect profile of quetiapine fumarate were investigated in 26 patients with schizophrenia, schizoaffective disorder, or bipolar disorder in a multicenter, two-period, multiple-dose, open-label, randomized trial. Over a 1- to 2-week period, patients were titrated to a 300-mg twice-daily dose of quetiapine. Patients treated for at least 7 days at the target dose entered a combination therapy period, receiving fluoxetine (60 mg daily) or imipramine (75 mg twice daily) for 8 days. Key assessments included pharmacokinetic analysis of quetiapine, the Udvalg for kliniske undersøgelser (UKU) Side Effect Rating Scale, and safety evaluations (e.g., adverse events, electrocardiograms, laboratory tests, and vital signs). Fluoxetine increased the quetiapine area under the plasma concentration time curve during a 12-hour interval (+12%), maximum plasma concentration during the dosing interval (C(ss)(max); +26%), and minimum plasma concentration at the end of the dosing interval (+8%), although it decreased oral clearance (-11%). The change in C(ss)(max) was statistically although not clinically significant. Imipramine did not affect the pharmacokinetics of quetiapine. Overall, scores on the UKU Side Effect Rating Scale improved during combination therapy with either agent, and no statistically significant deterioration was observed for any item. For safety assessments, the only clinically remarkable event was an imipramine-associated complete left bundle branch block in one patient. No unexpected side effects were reported. In conclusion, combination therapy with quetiapine and fluoxetine or imipramine had a minimal effect on quetiapine pharmacokinetics and was well tolerated.

The effect of multiple doses of cimetidine on the steady-state pharmacokinetics of quetiapine in men with selected psychotic disorders.

Quetiapine fumarate (Seroquel) is an atypical antipsychotic agent approved for the treatment of psychosis. It is extensively metabolized by the CYP450 3A4 isozyme. The principal aim of the study was to investigate the effect of multiple doses of cimetidine, a nonspecific P450 inhibitor, on the steady-state pharmacokinetics of quetiapine. Thirteen patients (seven completers) with selected psychotic disorders received escalating doses of quetiapine from 25 to 150 mg three times daily on days 3 to 8 and were then maintained at 150 mg three times daily until day 19. Cimetidine (400 mg) was initiated on the afternoon of day 15 and administered three times daily with every dose of quetiapine thereafter. Quetiapine plasma concentrations were measured before and after cimetidine coadministration, and quetiapine pharmacokinetic parameters were calculated. Of the 13 men who entered the study, seven completed it. A slight increase in quetiapine plasma levels and reduction in oral clearance were observed after cimetidine coadministration. No serious adverse events were observed during quetiapine treatment. No clinically relevant alterations in quetiapine pharmacokinetics were observed after cimetidine coadministration in patients with psychotic disorders.