Risperidone Does Not Affect Steady-State Pharmacokinetics of Divalproex Sodium in Patients with Bipolar Disorder

Pharmacokinetic Interactions Between Antiseizure and Psychiatric Medications

Antiseizure medications and drugs for psychiatric diseases are frequently used in combination. In this context, pharmacokinetic interactions between these drugs may occur. The vast majority of these interactions are primarily observed at a metabolic level and result from changes in the activity of the cytochrome P450 (CYP). Carbamazepine, phenytoin, and barbiturates induce the oxidative biotransformation and can consequently reduce the plasma concentrations of tricyclic antidepressants, many typical and atypical antipsychotics and some benzodiazepines. Newer antiseizure medications show a lower potential for clinically relevant interactions with drugs for psychiatric disease. The pharmacokinetics of many antiseizure medications is not influenced by antipsychotics and anxiolytics, while some newer antidepressants, namely fluoxetine, fluvoxamine and viloxazine, may inhibit CYP enzymes leading to increased serum concentrations of some antiseizure medications, including phenytoin and carbamazepine. Clinically relevant pharmacokinetic interactions may be anticipated by knowledge of CYP enzymes involved in the biotransformation of individual medications and of the influence of the specific comedication on the activity of these CYP enzymes. As a general rule, these interactions can be managed by careful evaluation of clinical response and, when indicated, individualized dosage adjustments guided by measurement of drugs serum concentrations, especially if pharmacokinetic interactions may cause any change in seizure control or signs of toxicity. Further studies are required to improve predictions of pharmacokinetic interactions between antiseizure medications and drugs for psychiatric diseases providing practical helps for clinicians in the clinical setting.

Pharmacokinetic Variability of Drugs Used for Prophylactic Treatment of Migraine

In this review, we evaluate the variability in the pharmacokinetics of 11 drugs with established prophylactic effects in migraine to facilitate 'personalized medicine' with these drugs. PubMed was searched for 'single-dose' and 'steady-state' pharmacokinetic studies of these 11 drugs. The maximum plasma concentration was reported in 248 single-dose and 115 steady-state pharmacokinetic studies, and the area under the plasma concentration-time curve was reported in 299 single-dose studies and 112 steady-state pharmacokinetic studies. For each study, the coefficient of variation was calculated for maximum plasma concentration and area under the plasma concentration-time curve, and we divided the drug variability into two categories; high variability, coefficient of variation >40%, or low or moderate variability, coefficient of variation <40%. Based on the area under the plasma concentration-time curve in steady-state studies, the following drugs have high pharmacokinetic variability: propranolol in 92% (33/36), metoprolol in 85% (33/39), and amitriptyline in 60% (3/5) of studies. The following drugs have low or moderate variability: atenolol in 100% (2/2), valproate in 100% (15/15), topiramate in 88% (7/8), and naproxen and candesartan in 100% (2/2) of studies. For drugs with low or moderate pharmacokinetic variability, treatment can start without initial titration of doses, whereas titration is used to possibly enhance tolerability of topiramate and amitriptyline. The very high pharmacokinetic variability of metoprolol and propranolol can result in very high plasma concentrations in a small minority of patients, and those drugs should therefore be titrated up from a low initial dose, depending mainly on the occurrence of adverse events.

Risperidone for bipolar disorders

Atypical antipsychotic medications are a relatively new, increasingly prominent component of the treatment armamentarium for bipolar disorder -- a development that provides more options for potentially improved outcomes for patients and families affected by bipolar disorder. The US Food and Drug Administration-approved bipolar indications for risperidone include monotherapy for the short-term treatment of acute manic or mixed episodes associated with bipolar I disorder and combination therapy with lithium or valproate for the short-term treatment of acute manic or mixed episodes associated with bipolar I disorder. Risperidone is also approved in over 30 countries worldwide for bipolar mania either as monotherapy, adjunct therapy, or both monotherapy and adjunct therapy. A number of controlled and open-label treatment trials have shown risperidone's efficacy and tolerability in the manic phase of bipolar disorder. Risperidone has also been reported to be useful in the longer-term treatment of bipolar disorder. This drug profile of risperidone for bipolar disorder will address the chemistry, pharmacodynamics, pharmacokinetics and metabolism of risperidone, clinical trials in bipolar disorder, postmarketing surveillance, safety, tolerability and regulatory issues. Finally, a discussion of potential future directions, a summary of key issues and information resources are provided.

Risperidone, a risk factor for valproate-induced encephalopathy?

Valproate-induced encephalopathy (ViE) has been increasingly reported and several risk factors have been proposed. We report a case whereby a patient became encephalopathic while treated with valproate and upon initiation of risperidone. The underlying mechanism could be risperidone's interference with valproate's binding to albumin, raising free valproate levels, which would impair the urea cycle and reduce ammonia conversion, leading to a hyperammonemic encephalopathy. The present case suggests a causal link, although further studies will be necessary to establish this. Nevertheless, clinicians should be aware of this possible interaction and consider carefully before concomitant administration of valproate and risperidone, mainly in patients with other risk factors for ViE, so this complication can be avoid or promptly diagnosed and treated.

Interactions between antiepileptics and second-generation antipsychotics

INTRODUCTION

Pharmacokinetic and pharmacodynamic drug interactions (DIs) can occur between antiepileptics (AEDs) and second-generation antipsychotics (SGAPs). Some AED and SGAP pharmacodynamic mechanisms are poorly understood. AED-SGAP combinations are used for treating comorbid illnesses or increasing efficacy, particularly in bipolar disorder.

AREAS COVERED

This article provides a comprehensive review of the interactions between antiepileptics and second-generation antipsychotics. The authors cover pharmacokinetic AED-SGAP DI studies, the newest drug pharmacokinetics in addition to the limited pharmacodynamic DI studies.

EXPERT OPINION

Dosing correction factors and measuring SGAP levels can help to compensate for the inductive properties of carbamazepine, phenytoin, phenobarbital and primidone. Further studies are needed to establish the clinical relevance of combining: i) AED strong inducers with amisulpride, asenapine, iloperidone, lurasidone and paliperidone; ii) valproate with aripiprazole, asenapine, clozapine and olanzapine; iii) high doses of oxcarbazepine (≥ 1500 mg/day) or topiramate (≥ 400 mg/day) with aripiprazole, lurasidone, quetiapine, risperidone, asenapine and olanzapine. Two pharmacodynamic DIs are beneficial: i) valproate-SGAP combinations may have additive effects in bipolar disorder, ii) combining topiramate or zonisamide with SGAPs may decrease weight gain. Three pharmacodynamic DIs contributing to decreased safety are common: sedation, weight gain and swallowing disturbances. A few AED-SGAP combinations may increase risk for osteoporosis or nausea. Three potentially lethal but rare pharmacodynamic DIs include pancreatitis, agranulocytosis/leukopenia and heat stroke. The authors believe that collaboration is needed from drug agencies and pharmaceutical companies, the clinicians using these combinations, researchers with expertise in meta-analyses, grant agencies, pharmacoepidemiologists and DI pharmacologists for future progression in this field.

Valnoctamide as a valproate substitute with low teratogenic potential in mania: a double-blind, controlled, add-on clinical trial

OBJECTIVES

Valproic acid's well-known teratogenicity limits its use in women of childbearing age. Valnoctamide is an analog of valproate that does not undergo biotransformation to the corresponding free acid. In mice, valnoctamide has been shown to be distinctly less teratogenic than valproate. Valnoctamide is an anticonvulsant, and we hypothesized that valnoctamide is antimanic.

METHODS

We performed a double-blind, five-week, add-on, controlled trial of valnoctamide in mania. Patients were treated with risperidone at doses of the physician's discretion. Valnoctamide or placebo was begun at doses of 600 mg/day and increased to 1200 mg after four days. Weekly ratings by a psychiatrist blind to the study drug were conducted using the Brief Psychiatric Rating Scale (BPRS), the Young Mania Rating Scale (YMRS), and the Clinical Global Impression (CGI).

RESULTS

Fifteen valnoctamide patients and 17 placebo patients completed at least one post-baseline week and were included in data analysis. In all efficacy measures valnoctamide was more effective than placebo as an add-on to risperidone, using two-way analysis of variance (ANOVA) with time as the within-subject factor. Two-way ANOVA showed a significant effect of time (p < 0.001) and significant interaction between treatment and time (YMRS: p = 0.012; BPRS: p = 0.007; CGI: p = 0.003). Differences between valnoctamide and placebo were significant from week 3 to week 5.

CONCLUSION

Valnoctamide could be an important valproate substitute for women of childbearing age with bipolar disorder who may become pregnant.

Novel uses for risperidone: focus on depressive, anxiety and behavioral disorders

Risperidone has been shown to be a safe and effective atypical antipsychotic agent. It was initially approved for the treatment of schizophrenia, and now, in many countries, is used to treat other conditions, including bipolar disorder, dementia and behavior problems in a range of age groups. Yet, frequent off-label use by clinicians to treat other mood and anxiety disorders and behavioral disorders is common and requires an examination of the risks and benefits in such populations. A review of the literature provides varying levels of evidence supporting its use in a range of depressive and anxiety disorders, and in special populations, including children and the elderly. Most reports are based on short-term studies and include its use both as monotherapy and as an augmenting agent to other psychotropics, and in a range of doses. Further randomized controlled trials are needed to confirm the efficacy and tolerability of risperidone, both short- and long-term, in many of these conditions. The published evidence is summarized, with recommendations and suggestions for its use.

A case of pancytopenia

Sodium valproate is a commonly used anticonvulsant, particularly in the management of childhood refractory epilepsy. There is a good literature base regarding its haematological effects in this group of patients including the potential for toxic effect on the bone marrow. Valproate is increasingly being used in the treatment of psychiatric conditions, particularly bipolar affective disorder. In this article we describe a case of pancytopenia associated with a valproate level of 166 mg/l. The population of psychiatric patients is different in several ways from the population of children and young adults with epilepsy from whom the existing data comes. The psychiatric patients are older, more likely to misuse substances, more likely to take overdoses and may metabolize valproate more slowly. For these reasons it would be worthwhile investigating the relationship between valproate levels, macrocytosis, platelet counts and B12 levels in this group of patients. The results of such a study would give us a clearer understanding of what the desirable therapeutic range is for valproate in bipolar affective disorder and what, if any, monitoring should be undertaken.

Risperidone: a review of its use in the treatment of bipolar mania

Risperidone (Risperdal) is an atypical antipsychotic with high affinity for 5-hydroxytryptamine (5-HT)2A, dopamine D2 and alpha1- and alpha2-adrenergic receptors. Risperidone is now approved in the UK and the US for use in bipolar mania. Risperidone < or =6 mg/day, as monotherapy or adjunctive therapy with first-line mood stabilisers, significantly improves moderate and severe bipolar mania and improves global functioning over 3 weeks. Improvements in Young Mania Rating Scale (YMRS) scores in double-blind trials were greater with risperidone than with placebo over 3 weeks, and similar to those with haloperidol over 3 and 12 weeks. Risperidone was reasonably well tolerated. Limited data are available on the combination of risperidone and carbamazepine. Risperidone, as monotherapy or combined therapy with lithium or valproate semisodium, is an effective treatment option in bipolar mania.