Interaction of olanzapine with fluvoxamine

The Impact of Smoking, Sex, Infection, and Comedication Administration on Oral Olanzapine: A Population Pharmacokinetic Model in Chinese Psychiatric Patients

BACKGROUND AND OBJECTIVE: Prior olanzapine population pharmacokinetic (PPK) models have focused on the effects of sex and smoking on olanzapine clearance. This PPK model in Chinese adult psychiatric patients also investigated the influence of comedications and co-occurrence of infections on olanzapine clearance, and explored how to personalize oral olanzapine dosage in the clinical setting.

METHODS

A total of 1546 serum concentrations from 354 patients were collected in this study. A one-compartment model with first-order absorption was employed to develop the PPK model using a nonlinear mixed-effects modeling approach. Covariates included demographic parameters, co-occurrence of infection and concomitant medications (including dangguilonghui tablets, a Chinese herbal medicine for constipation). Bootstrap validation (1000 runs) and external validation of 50 patients were employed to evaluate the final model. Simulations were performed to explore the personalization of olanzapine dosing after stratification by sex, smoking, and comedication with valproate.

RESULTS

Typical estimates for the absorption rate constant (K_a), apparent clearance (CL/F), and apparent distribution volume (V/F) were 0.30 h^-1, 12.88 L/h, and 754.41 L, respectively. Olanzapine clearance was increased by the following variables: 1.23-fold by male sex, 1.23-fold by smoking, 1.23-fold by comedication with valproate, 1.16-fold by sertraline, and 2.01-fold by dangguilonghui tablets. Olanzapine clearance was decreased by the following variables: 0.75-fold by co-occurrence of infection, 0.70-fold by fluvoxamine, and 0.78-fold by perphenazine. The model evaluation indicated that the final model's performance was good, stable, and precise.

CONCLUSION

This study contributes to the personalization of oral olanzapine dosing, but further studies should be performed to verify the effects of infection and comedications, including valproate and dangguilonghui.

Clinically relevant interactions between newer antidepressants and second-generation antipsychotics

INTRODUCTION

Combinations of newer antidepressants and second-generation antipsychotics (SGAs) are frequently used by clinicians. Pharmacokinetic drug interaction (PK DI) and poorly understood pharmacodynamic (PD) drug interaction (PD DI) can occur between them.

AREAS COVERED

This paper comprehensively reviews PD DI and PK DI studies.

EXPERT OPINION

More PK DI studies are needed to better establish dose correction factors after adding fluoxetine and paroxetine to aripiprazole, iloperidone and risperidone. Further PK DI studies and case reports are also needed to better establish the need for dose correction factors after adding i) fluoxetine to clozapine, lurasidone, quetiapine and olanzapine; ii) paroxetine to olanzapine; iii) fluvoxamine to asenapine, aripiprazole, iloperidone, lurasidone, olanzapine, quetiapine and risperidone; iv) high sertraline doses to aripiprazole, clozapine, iloperidone and risperidone: v) bupropion and duloxetine to aripiprazole, clozapine, iloperidone and risperidone; and vi) asenapine to paroxetine and venlafaxine. Possible beneficial PD DI effects occur after adding SGAs to newer antidepressants for treatment-resistant major depressive and obsessive-compulsive disorders. The lack of studies combining newer antidepressants and SGAs in psychotic depression is worrisome. PD DIs between newer antidepressants and SGAs may be more likely for mirtazapine and bupropion. Adding selective serotonin reuptake inhibitors and SGAs may increase QTc interval and may very rarely contribute to torsades de pointes.

Olanzapine: a 5-year perspective

Olanzapine is a novel antipsychotic, approved for the acute and maintenance treatment of schizophrenia and bipolar I disorder. Despite the publicity regarding reported adverse events with the novel antipsychotics, such as weight gain and Type II diabetes mellitus, olanzapine remains a useful and important medicine. It is a selective monoaminergic antagonist with high-affinity binding to a number of receptors thought to be implicated in some psychotic and mood symptoms. The complex pharmacology of olanzapine has lead to studies exploring its use in treating substance abuse, aggression/violence, borderline personality disorder, schizotypal personality disorder, obsessive-compulsive disorder and as a neuroprotective agent in schizophrenia. As the pharmacology of olanzapine and other novel antipsychotics becomes better understood, future effective treatment strategies are likely to match an individual's genetic makeup and receptor profiles to the most compatible agent.

Considering CYP1A2 phenotype and genotype for optimizing the dose of olanzapine in the management of schizophrenia

INTRODUCTION

Schizophrenia, a mental disorder, is a debilitating condition which typically strikes young people in their early 20's. Antipsychotic medications are widely prescribed for the treatment of schizophrenia however a balancing act is necessary to provide the correct dose to each patient. It is suggested that a large number of patients discontinue antipsychotic pharmacotherapy because the treatments provided do not always reduce the positive symptoms of the disease, while many have adverse effects on the patients. This implies that neither the incorrect drug nor the optimal dosage for that patient is achieved.

AREAS COVERED

The current review investigates variability in response to olanzapine with a specific focus on the common intrinsic and extrinsic factors that influence both olanzapine and CYP1A2 activity. Furthermore, the authors discuss the utilization of phenotyping and genotyping of CYP1A2 and their potential utility in clinical practice for olanzapine dosing regimens. The authors also consider the potential of pharmacometrics compared to pharmacogenomics as a tool to personalize medicine.

EXPERT OPINION

Careful consideration must be given to the impact of a genetic variant on the disposition of a drug prior to implementing genetic 'tests' to determine response. CYP1A2 phenotypic assessment can yield important information regarding the disposition of olanzapine; however, it relies on the accuracy of the metric and the minimal impact of other metabolic pathways. The application of pharmacometrics provides an effective method to establish covariates that significantly influence olanzapine disposition which can incorporate phenotype and/or genotype.

Clinically relevant drug interactions in anxiety disorders

OBJECTIVE

Certain drugs used in the treatment of patients with anxiety disorders can interact with other psychotropic drugs and with pharmacological treatments for physical illnesses. There is a need for an updated comparative review of clinically relevant drug interactions in this area.

DESIGN

Relevant literature on drug interactions with medications used in the treatment of anxiety disorders was identified through a search in MEDLINE and EMBASE.

RESULTS

Drug interactions involving medications used to treat anxiety disorders may be pharmacokinetic, such as enzyme inhibition or induction in the cytochrome P450 system and transporter-mediated drug interactions, or pharmacodynamic, such as additive effects in causing drowsiness or additive effects at neurotransmitter receptors. Certain selective serotonin reuptake inhibitors (fluoxetine, fluvoxamine, and paroxetine) are particularly liable to be potentially involved in untoward pharmacokinetic interactions.

CONCLUSIONS

The potential for drug interactions with medications used in anxiety disorders should be the cause of clinical concern, particularly in elderly individuals. However, the liability for harmful drug interactions may be anticipated, and the risk reduced. Although not all interactions are clinically relevant, careful monitoring of clinical response and possible interactions is essential.

Clinically relevant pharmacokinetic drug interactions with second-generation antidepressants: an update

BACKGROUND

The second-generation antidepressants include selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), and other compounds with different mechanisms of action. All second-generation antidepressants are metabolized in the liver by the cytochrome P450 (CYP) enzyme system. Concomitant intake of inhibitors or inducers of the CYP isozymes involved in the biotransformation of specific antidepressants may alter plasma concentrations of these agents, although this effect is unlikely to be associated with clinically relevant interactions. Rather, concern about drug interactions with second-generation antidepressants is based on their in vitro potential to inhibit > or = 1 CYP isozyme.

OBJECTIVE

The goal of this article was to review the current literature on clinically relevant pharmacokinetic drug interactions with second-generation antidepressants.

METHODS

A search of MEDLINE and EMBASE was conducted for original research and review articles published in English between January 1985 and February 2008. Among the search terms were drug interactions, second-generation antidepressants, newer antidepressants, SSRIs, SNRIs, fluoxetine, paroxetine, fluvoxamine, sertraline, citalopram, escitalopram, venlafaxine, duloxetine, mirtazapine, reboxetine, bupropion, nefazodone, pharmacokinetics, drug metabolism, and cytochrome P450. Only articles published in peer-reviewed journals were included, and meeting abstracts were excluded. The reference lists of relevant articles were hand-searched for additional publications.

RESULTS

Second-generation antidepressants differ in their potential for pharmacokinetic drug interactions. Fluoxetine and paroxetine are potent inhibitors of CYP2D6, fluvoxamine markedly inhibits CYP1A2 and CYP2C19, and nefazodone is a substantial inhibitor of CYP3A4. Therefore, clinically relevant interactions may be expected when these antidepressants are coadministered with substrates of the pertinent isozymes, particularly those with a narrow therapeutic index. Duloxetine and bupropion are moderate inhibitors of CYP2D6, and sertraline may cause significant inhibition of this isoform, but only at high doses. Citalopram, escitalopram, venlafaxine, mirtazapine, and reboxetine are weak or negligible inhibitors of CYP isozymes in vitro and are less likely than other second-generation antidepressants to interact with co-administered medications.

CONCLUSIONS

Second-generation antidepressants are not equivalent in their potential for pharmacokinetic drug interactions. Although interactions may be predictable in specific circumstances, use of an antidepressant with a more favorable drug-interaction profile may be justified.

Metabolic drug interactions with newer antipsychotics: a comparative review

Newer antipsychotics introduced in clinical practice in recent years include clozapine, risperidone, olanzapine, quetiapine, sertindole, ziprasidone, aripiprazole and amisulpride. These agents are subject to drug-drug interactions with other psychotropic agents or with medications used in the treatment of concomitant physical illnesses. Most pharmacokinetic interactions with newer antipsychotics occur at the metabolic level and usually involve changes in the activity of the major drug-metabolizing enzymes involved in their biotransformation, i.e. the cytochrome P450 (CYP) monooxygenases and/or uridine diphosphate-glucuronosyltransferases (UGT). Clozapine is metabolized primarily by CYP1A2, with additional contribution by other CYP isoforms. Risperidone is metabolized primarily by CYP2D6 and, to a lesser extent, CYP3A4. Olanzapine undergoes both direct conjugation and CYP1A2-mediated oxidation. Quetiapine is metabolized by CYP3A4, while sertindole and aripiprazole are metabolized by CYP2D6 and CYP3A4. Ziprasidone pathways include aldehyde oxidase-mediated reduction and CYP3A4-mediated oxidation. Amisulpride is primarily excreted in the urine and undergoes relatively little metabolism. While novel antipsychotics are unlikely to interfere with the elimination of other drugs, co-administration of inhibitors or inducers of the major enzymes responsible for their metabolism may modify their plasma concentrations, leading to potentially significant effects. Most documented metabolic interactions involve antidepressant and anti-epileptic drugs. Of a particular clinical significance is the interaction between fluvoxamine, a potent CYP1A2 inhibitor, and clozapine. Differences in the interaction potential among the novel antipsychotics currently available may be predicted based on their metabolic pathways. The clinical relevance of these interactions should be interpreted in relation to the relative width of their therapeutic index. Avoidance of unnecessary polypharmacy, knowledge of the interaction profiles of individual agents, and careful individualization of dosage based on close evaluation of clinical response and, possibly, plasma drug concentrations are essential to prevent and minimize potentially adverse drug interactions in patients receiving newer antipsychotics.

Hypersalivation induced by olanzapine with fluvoxamine

Hypersalivation has been reported as a side effect of atypical antipsychotics such as clozapine and olanzapine. As it is very common for antipsychotics to cause dry mouth due to anticholinergic effects, hypersalivation seems to be paradoxical. We present the case of a 34-year-old Japanese man with delusional disorder, somatic type (DSM-IV). He had chronic neck pain as well as somatic hallucination with hypochondriacal delusion for 4 years. Since combination therapy with atypical antipsychotics and selective serotonin reuptake inhibitors (SSRIs) has been introduced in the treatment of refractory psychiatric disorders such as schizophrenia, olanzapine (10 mg/day) was added to fluvoxamine treatment (200 mg/day) in this case. Subsequently, hypersalivation was induced without any extrapyramidal symptoms. It is suggested that hypersalivation was an adverse effect of olanzapine. Possible interaction olanzapine with fluvoxamine might increase the risk of the adverse effect. When combination therapy of atypical antipsychotics and SSRI is introduced, it should be used cautiously with careful observation. Underlying pharmacological and clinical problems will be discussed.

Low-dose fluvoxamine as an adjunct to reduce olanzapine therapeutic dose requirements: a prospective dose-adjusted drug interaction strategy

Despite the advances in antipsychotic pharmacotherapy over the past decade, many atypical antipsychotic agents are not readily accessible by patients with major psychosis or in developing countries where the acquisition costs may be prohibitive. Olanzapine is an efficacious and widely prescribed atypical antipsychotic agent. In theory, olanzapine therapeutic dose requirement may be reduced during concurrent treatment with inhibitors of drug metabolism. In vitro studies suggest that smoking-inducible cytochrome P450 (CYP) 1A2 contributes to formation of the metabolite 4'-N-desmethylolanzapine. The present prospective study tested the hypothesis that olanzapine steady-state doses can be significantly decreased by coadministration of a low subclinical dose of fluvoxamine, a potent inhibitor of cytochrome P450 1A2. The study design followed a targeted "at-risk" population approach with a focus on smokers who were likely to exhibit increased cytochrome P450 1A2 expression. Patients with stable psychotic illness (N = 10 men, all smokers) and receiving chronic olanzapine treatment were evaluated for steady-state plasma concentrations of olanzapine and 4'-N-desmethylolanzapine. Subsequently, olanzapine dose was reduced from 17.5 +/- 4.2 mg/d (mean +/- SD) to 13.0 +/- 3.3 mg/d, and a nontherapeutic dose of fluvoxamine (25 mg/d, PO) was added to regimen. Patients were reevaluated at 2, 4, and 6 weeks during olanzapine-fluvoxamine cotreatment. There was no significant change in olanzapine plasma concentration, antipsychotic response, or metabolic indices (eg, serum glucose and lipids) after dose reduction in the presence of fluvoxamine (P > 0.05). 4'-N-desmethylolanzapine/olanzapine metabolic ratio decreased from 0.45 +/- 0.20 at baseline to 0.25 +/- 0.11 at week 6, suggesting inhibition of the cytochrome P450 1A2-mediated olanzapine 4'-N-demethylation by fluvoxamine (P < 0.05). In conclusion, this prospective pilot study suggests that a 26% reduction in olanzapine therapeutic dose requirement may be achieved by coadministration of a nontherapeutic oral dose of fluvoxamine.

Metabolic drug interactions with new psychotropic agents

New psychotropic drugs introduced in clinical practice in recent years include new antidepressants, such as selective serotonin reuptake inhibitors (SSRI) and 'third generation' antidepressants, and atypical antipsychotics, i.e. clozapine, risperidone, olanzapine, quetiapine, ziprasidone and amisulpride. These agents are extensively metabolized in the liver by cytochrome P450 (CYP) enzymes and are therefore susceptible to metabolically based drug interactions with other psychotropic medications or with compounds used for the treatment of concomitant somatic illnesses. New antidepressants differ in their potential for metabolic drug interactions. Fluoxetine and paroxetine are potent inhibitors of CYP2D6, fluvoxamine markedly inhibits CYP1A2 and CYP2C19, while nefazodone is a potent inhibitor of CYP3A4. These antidepressants may be involved in clinically significant interactions when coadministered with substrates of these isoforms, especially those with a narrow therapeutic index. Other new antidepressants including sertraline, citalopram, venlafaxine, mirtazapine and reboxetine are weak in vitro inhibitors of the different CYP isoforms and appear to have less propensity for important metabolic interactions. The new atypical antipsychotics do not affect significantly the activity of CYP isoenzymes and are not expected to impair the elimination of other medications. Conversely, coadministration of inhibitors or inducers of the CYP isoenzymes involved in metabolism of the various antipsychotic compounds may alter their plasma concentrations, possibly leading to clinically significant effects. The potential for metabolically based drug interactions of any new psychotropic agent may be anticipated on the basis of knowledge about the CYP enzymes responsible for its metabolism and about its effect on the activity of these enzymes. This information is essential for rational prescribing and may guide selection of an appropriate compound which is less likely to interact with already taken medication(s).

Olanzapine augmentation of paroxetine-refractory obsessive-compulsive disorder

The aim of the present study was to investigate the effect of adjunctive olanzapine in patients with obsessive-compulsive disorder (OCD) refractory to paroxetine. Twenty-one patients unresponsive to treatment with paroxetine, administered for at least 12 weeks at the dose of 60 mg/day, participated to a 12-week open-label, add-on trial with olanzapine (10 mg/day). The psychopathological state was evaluated by the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) and by Clinical Global Impression (CGI). Three patients did not complete the 12-week adjunctive treatment with olanzapine. In the 18 completers, the mean Y-BOCS score decreased significantly from 27.1+/-4.0 at baseline to 20.1+/-3.9 at final evaluation (P<.001). Seven patients (38.9%) were rated as responders at final evaluation. Steady-state plasma concentrations of paroxetine were not modified during olanzapine coadministration. The drug combination was generally well tolerated and initial sedation and weight gain were the most frequent unwanted effects. Our findings confirm the results of previous studies and indicate that the addition of olanzapine to ongoing treatment with serotonin reuptake inhibitors (SRI) may be beneficial in some patients unresponsive to SRI monotherapy.

Role of the smoking-induced cytochrome P450 (CYP)1A2 and polymorphic CYP2D6 in steady-state concentration of olanzapine

This study investigated whether the smokinginducible cytochrome P450 (CYP) 1A2 and the polymorphic CYP2D6 play significant roles in the metabolism of olanzapine and its clinical effects at steady-state treatment. Caffeine and debrisoquine were used as measures of CYP1A2 and CYP2D6, respectively. After drug therapy for 15 days, the effect of olanzapine on the activities of CYP1A2 and CYP2D6 was also examined. Seventeen psychiatric patients (9 men and 8 women) were orally administered olanzapine, at a mean +/- standard deviation (SD) dosage of 10 mg/d for all smokers (n = 8) and 7.5 +/- 2.5 mg/d (range, 5-10 mg) for nonsmokers (n = 9;p <0.01). The plasma concentration-to-dose (C:D) ratio was closely correlated to the CYP1A2 activity ( s = -0.89;p <0.0001). The mean urinary caffeine indexes of nonsmokers and smokers were 17 +/- 8 and 101 +/- 44, respectively, indicating that smoking had induced a sixfold higher CYP1A2 activity (p <0.0001). Likewise, the olanzapine plasma C:D ratio (ng.mL.mg) was about fivefold lower in smokers (7.9 +/- 2.6) than in nonsmokers (1.56 +/- 1.1;p <0.0001). On day 15 of the antipsychotic therapy, the percentage decrease in Brief Psychiatric Rating Scale (BPRS) total score relative to the predosing score (in the drug-free period) was higher for nonsmokers than for smokers (30.4 +/- 10% vs. 12.5 +/- 14%;p <0.01). Six nonsmokers and three smokers experienced side effects with olanzapine. After 15 days of drug treatment, olanzapine had caused significant (p <0.0001) and substantial CYP1A2 inhibition (by 50%) in comparison with predosing values, and such inhibition can contribute to adverse drug interactions. In conclusion, smoking-induced increased CYP1A2 activity significantly diminished plasma olanzapine concentrations and the antipsychotic effect of the drug. The performance of a simple caffeine test may assist in individualization of the olanzapine dosage.

Fluvoxamine augmentation of olanzapine in chronic schizophrenia: pharmacokinetic interactions and clinical effects

Olanzapine is a substrate of the cytochrome P450 enzyme (CYP) 1A2. In this study, pharmacokinetic interactions and clinical effects of adding the CYP1A2 inhibitor fluvoxamine to steady-state olanzapine was examined in patients suffering from schizophrenia. Eight patients had been treated for at least 3 months with 10 to 20 mg/day olanzapine. Fluvoxamine (100 mg/day) was added (week 0) to the olanzapine treatment and continued for 8 weeks. Concentrations of olanzapine and its metabolite N-desmethylolanzapine and of fluvoxamine were analyzed at weeks 0, 1, 4, and 8. Addition of fluvoxamine resulted in a 12% to 112% ( < 0.01) increase of olanzapine from 31 +/- SD 15 ng/mL (week 0) to 56 +/- 31 ng/mL (week 8) in all patients. N-desmethylolanzapine concentrations were not significantly changed ( > 0.05). Fluvoxamine concentrations were 48 +/- 26 ng/mL on week 1 and 83 +/- 47 ng/mL on week 8. It is concluded that fluvoxamine affects olanzapine degradation and thus increases olanzapine concentrations. Although the combination was well tolerated in this sample and the negative symptom response appeared to be favorable in at least five patients, the combination therapy of olanzapine and fluvoxamine should be used cautiously and should be controlled by therapeutic drug monitoring to avoid olanzapine-induced side effects or intoxications.

Cytochrome P450 polymorphisms and response to antipsychotic therapy

Antipsychotic drugs are used for the treatment of schizophrenia and other related psychotic disorders. The antipsychotics currently available include older or classical compounds and newer or atypical agents. Most antipsychotic drugs are highly lipophilic compounds and undergo extensive metabolism by cytochrome P450 (CYP) enzymes in order to be excreted. There is a wide interindividual variability in the biotransformation of antipsychotic drugs, resulting in pronounced differences in steady-state plasma concentrations and, possibly, in therapeutic and toxic effects, during treatment with fixed doses. Many classical and some newer antipsychotics are metabolized to a significant extent by the polymorphic CYP2D6, which shows large interindividual variation in activity. Other CYPs, especially CYP1A2 and CYP3A4, also contribute to the interindividual variability in the kinetics of antipsychotics and occurrence of drug interactions. No relationship between CYP2D6 genotype or activity and therapeutic effects of classical antipsychotic drugs has been found in the few studies performed. On the other hand, some investigations suggest that poor metabolizers (PMs) of CYP2D6 would be more prone to over-sedation and, possibly, Parkinsonism during treatment with classical antipsychotics, while other studies, mostly retrospective, have been negative or inconclusive. For the newer antipsychotics, such data are lacking. To date, CYP2D6 phenotyping and genotyping appear, therefore, to be clinically useful for dose predicting only in special cases and for a limited number of antipsychotics, while their usefulness in predicting clinical effects must be further explored.