Population pharmacokinetic modelling of aripiprazole and its active metabolite,dehydroaripiprazole, in psychiatric patients

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Almost all reported studies have investigated the pharmacokinetics of aripiprazole in healthy volunteers.
• The pharmacokinetics of dehydroaripiprazole have not been identified in a combined model with aripiprazole.

WHAT THIS STUDY ADDS

• The data on aripiprazole and dehydroaripiprazole in psychiatric patients were modelled jointly using a population approach.
• The apparent clearance of aripiprazole in cytochrome P450 (CYP) 2D6 intermediate metabolizers (IM) was approximately 60% of that in CYP2D6 extensive metabolizers (EM) having two functional alleles, but the exposure to dehydroaripiprazole in CYP2D6 IM was similar to that in EM.

AIMS

The aims of this study were to develop a combined population pharmacokinetic model for both aripiprazole and its active metabolite, dehydroaripiprazole, in psychiatric patients and to identify to what extent the genetic polymorphisms of cytochrome P450 (CYP) enzymes contribute to the variability in pharmacokinetics (PK).

METHODS

A population pharmacokinetic analysis was performed using NONMEM software based on 141 plasma concentrations at steady state from 80 patients receiving multiple oral doses of aripiprazole (10–30 mg day¹).

RESULTS

A one-compartment model with first-order kinetics for aripiprazole and dehydroaripiprazole each was developed to describe simultaneously the concentration data. The absorption rate constant was fixed to 1.06 h¹. The typical value of apparent distribution volume of aripiprazole was estimated to be 192 l. Covariate analysis showed that CYP2D6 genetic polymorphisms significantly influenced the apparent clearance of aripiprazole (CL/F), reducing the interindividual variability on CL/F from 37.8% CV (coefficient of variation) to 30.5%. The CL/F in the CYP2D6 IMs was approximately 60% of that in CYP2D6 EMs having two functional alleles. Based on the CYP2D6 genotype, the metabolic ratios were calculated at 0.20–0.34. However, the plasma concentration : dose ratios of dehydroaripiprazole were not different across the CYP2D6 genotype.

CONCLUSIONS

This population pharmacokinetic model provided an adequate fit to the data for both aripiprazole and dehydroaripiprazole in psychiatric patients. The usefulness of CYP genotyping as an aid to select the starting dose should be further investigated.     

Risperidone in combination with mood stabilizers for acute mania: a multicentre, open study

The primary aims of this study were (i) a replication of the effectiveness and tolerability of risperidone in the treatment of patients with acute mania in a very large cohort in a naturalistic treatment setting and (ii) to extend the data on the effect and tolerability of risperidone in the treatment of patients with acute mania to an Asian population. A total of 909 patients fulfilling DSM-IV criteria of bipolar disorder (current manic and hypomanic episode) entered this large, open, multicentre study. The Young Mania Rating Scale (YMRS), Clinical Global Impression (CGI) and Simpson-Angus Rating Scale (SARS) were measured at baseline and weeks 1, 3 and 6, for the assessment of effectiveness and extrapyramidal symptoms. This study showed a statistically significant reduction of scores on the YMRS and CGI-severity (mean change=-23.5+/-11.8, P<0.0001; mean change=-2.7+/-1.5, P<0.0001, respectively) from baseline to endpoint (week 6). The number of patients with a 50% reduction or more in the YMRS and CGI-severity scores was 693 (77.8%) and 630 (70.7%) at endpoint, respectively. There were no statistically significant increments of scores on SARS. Risperidone was generally well tolerated. The present larger open study indicates that risperidone add-on therapy is effective and tolerable in treatment of bipolar disorder, replicating results in various controlled and uncontrolled studies from Western countries.     

Postural relief of food impaction in a patient with stenosed esophagus--a case report

A patient with past history of esophageal stenosis complained of sudden dysphagia in the erect position which was relieved transiently in the supine position. Initial esophagoscopy failed to detect any mass in the lumen. Esophagogram revealed shifting foreign body from lower stenotic site to upper dilated area with postural change from the erect to the supine position. A French bean was detected and removed during the second esophagoscopy.     

EEG abnormalities during treatment with typical and atypical antipsychotics.

OBJECTIVE: Clozapine produces EEG abnormalities and dose-dependent risk of epileptic seizures. Much less is known about EEG effects of newer antipsychotics. The present study therefore examined the risk of EEG abnormalities associated with various antipsychotic drugs. METHOD: EEG recordings from 323 hospitalized psychiatric patients (293 treated with antipsychotics, 30 who did not receive any antipsychotic treatment) were graded blind to diagnosis and treatment for type and severity of EEG abnormalities. Drug type, dose, and clinical factors were evaluated for association with EEG abnormalities by multivariate logistic regression. RESULTS: EEG abnormalities occurred in 56 subjects (19.1%) treated and four (13.3%) not treated with antipsychotics. EEG abnormality risk among antipsychotic agents varied greatly (clozapine=47.1%, olanzapine=38.5%, risperidone=28.0%, typical neuroleptics=14.5%, quetiapine=0.0%). Significant risk factors in order of influence were hypertension, use of an atypical antipsychotic, bipolar diagnosis, and older age; benzodiazepine cotreatment lowered risk. Unassociated with risk were sex, treatment response, length of hospital stay, drug potency, daily dose (in mg or mg/kg), drug exposure time, or cotreatments. CONCLUSIONS: EEG abnormality risk varied widely among specific antipsychotics. Risk was particularly high with clozapine and olanzapine, moderate with risperidone and typical neuroleptics, and low with quetiapine. Comorbid hypertension, bipolarity, and older age-but not dose or clinical response-were associated with risk.