Elevated clozapine levels after fluvoxamine initiation

Selective Serotonin Reuptake Inhibitors and Clozapine: Clinically Relevant Interactions and Considerations

The monoamine hypothesis of depression attributes the symptoms of major depressive disorders to imbalances of serotonin, noradrenaline, and dopamine in the limbic areas of the brain. The preferential targeting of serotonin receptor (SERT) by selective serotonin reuptake inhibitors (SSRIs) has offered an opportunity to reduce the range of these side effects and improve patient adherence to pharmacotherapy. Clozapine remains an effective drug against treatment-resistant schizophrenia, defined as failing treatment with at least two different antipsychotic medications. Patients with schizophrenia who display a constellation of negative symptoms respond poorly to antipsychotic monotherapy. Negative symptoms include the diminution of motivation, interest, or expression. Conversely to the depressive symptomology of interest presently, supplementation of antipsychotics with SSRIs in schizophrenic patients with negative symptoms lead to synergistic improvements in the function of these patients. Fluvoxamine is one of the most potent inhibitors of CYP1A2 and can lead to an increase in clozapine levels. Similar increases in serum clozapine were detected in two patients taking sertraline. However, studies have been contradictory as well, showing no such increases, which are worrying. Clinicians should be aware that clozapine levels should be monitored with any coadministration with SSRIs.

Use of anticonvulsants as prophylaxis for seizures in patients on clozapine

OBJECTIVE

The aim of this study is to conduct a critical review of the literature regarding the use of anticonvulsants in the prophylaxis of clozapine-induced seizures, to examine the relationship of the latter with clozapine daily dose, serum concentration and other factors than dosage that effect clozapine blood concentration, and to make recommendations for the management of clozapine-induced seizures.

METHOD

A systematic review of English-language MEDLINE articles was undertaken.

CONCLUSIONS

Clozapine-induced seizures may occur at any dose; the risk increases with dose and goes up to 4% at ≥ 600 mg/day. Some authors have advocated that patients on that dose regimen have anticonvulsant added as a primary prophylactic measure. The author discusses the pitfalls of this recommendation and highlights that seizures are better predicted from serum concentration (1300 ng/ml) rather than dose alone, and that serum concentration is strongly influenced by sex, age, smoking habit, drug-drug interactions and variations in the 1A2, 2D6 and 3A4 genotypes. Anticonvulsants are not recommended as a primary prophylaxis for clozapine-induced seizures. When deemed necessary as secondary prophylaxis, the clinician's choice should consider drug-drug interactions that may increase/decrease clozapine serum concentration and lead to more side effects, including neutropenia/agranulocytosis and seizures, or compromise therapeutic response. Recommendations for primary and secondary prophylaxis of clozapine related-seizures are provided.

The Differential Effects of Steady-State Fluvoxamine on the Pharmacokinetics of Olanzapine and Clozapine in Healthy Volunteers

The combination of atypical antipsychotics and selective serotonin reuptake inhibitors is an effective strategy in the treatment of certain psychiatric disorders. However, pharmacokinetic interactions between the two classes of drugs remain to be explored. The present study was designed to determine whether there were different effects of steady-state fluvoxamine on the pharmacokinetics of a single dose of olanzapine and clozapine in healthy male volunteers. One single dose of 10 mg olanzapine (n = 12) or clozapine (n = 9) was administered orally. Following a drug washout of at least 4 weeks, all subjects received fluvoxamine (100 mg/day) for 9 days, and one single dose of 10 mg olanzapine or clozapine was added on day 4. Plasma concentrations of olanzapine, clozapine, and N-desmethylclozapine were assayed at serial time points after the antipsychotics were given alone and when added to fluvoxamine. No bioequivalence was found in olanzapine alone and cotreatment with fluvoxamine for the mean peak plasma concentration (C(max)), the area under the concentration-time curve from time 0 to last sampling time point (AUC(0-t)), and from time 0 to infinity (AUC(0- infinity )). Under the cotreatment, C(max) of olanzapine was significantly elevated by 49%, with a 32% reduced time (t(max)) to C(max), whereas the C(max) and t(max) of clozapine were unaltered. The cotreatment increased the AUC(0-t) and AUC(0- infinity ) of olanzapine by 68% and 76%, respectively, greater than those of clozapine (40% and 41%). The presence of fluvoxamine also prolonged the elimination half-life (t(1/2)) of olanzapine by 40% and, to a much greater extent, clozapine by 370% but reduced the total body clearance (CL/F) of clozapine (78%) more significantly than it did for olanzapine (42%). The apparent volume of distribution (V(d)) was suppressed by 31% in olanzapine combined with fluvoxamine but was unaltered in the clozapine regimen. A significant reduction in the N-desmethylclozapine to clozapine ratio was present in the clozapine with fluvoxamine regimen. The effects of fluvoxamine on different aspects of pharmacokinetics of the two antipsychotics may have implications for clinical therapeutics.

Clozapine toxicity: A discussion of pharmacokinetic factors

This report seeks to analyze and discuss different pharmacokinetic factors that might be responsible for a case of clozapine toxicity on a conventional clozapine dose. A 41-year-old Caucasian male with schizoaffective disorder was cross-titrated to 400mg/day of clozapine to manage inadequate response on 6mg/day of risperidone. A week later the patient became gradually confused and disoriented and eventually lost consciousness. The combined clozapine and norclozapine levels were elevated at 2500ng/mL. Patient's symptoms resolved after clozapine was reduced to 75mg/day with a reduction in clozapine and norclozapine levels to 420ng/mL. Toxic clozapine levels may result from abnormal drug absorption, distribution, metabolism or elimination. Changes in absorption and/or distribution are unlikely to explain the toxic levels as clozapine has relatively high oral bioavailability at steady state and a large volume of distribution. In terms of metabolism, clozapine is primarily metabolized by CYP1A2, which biotransforms clozapine to norclozapine. However, it is unlikely that CYP1A2 was responsible, as any reduction in CYP1A2 activity would have likely altered clozapine and norclozapine ratio, which was not observed in this patient. Involvement of other CYP enzymes in the development of clozapine toxicity was ruled out through genotyping. Since liver and renal function tests were also within normal limit, it is difficult to pinpoint a single pharmacokinetic factor responsible for unusually high clozapine and norclozapine levels in this patient. However, a combination of various pharmacokinetic factors may provide an explanation for clozapine toxicity in this patient.

CONCLUSION

Some patients can develop unusually high levels of clozapine and/or its metabolites on routine clozapine dosages resulting in clinically serious adverse effects as observed in our patient.

Plasma clozapine levels and clinical response in treatment-refractory Chinese schizophrenic patients

PURPOSE

To evaluate clinical efficacy of clozapine in relation with its plasma level in a group of Chinese patients with treatment-resistant schizophrenia. In addition, the relationship between plasma level and side effects were examined.

METHOD

Fifty-one patients with treatment-resistant schizophrenia were put on a fixed dose of clozapine at 300 mg/day for 6 weeks. Non-responders to week 6 received 500 mg/day in subsequent 6 weeks. Responders to week 6 continued to receive 300 mg/day. Clozapine plasma levels were checked at weeks 6 and 12.

FINDINGS

No association was found between clozapine plasma level, response and side effects. Sodium valproate was found to elevate clozapine plasma level while lowering norclozapine/clozapine ratio.

CONCLUSION

Clozapine plasma level was not found to be associated with response and side effect in Chinese treatment-resistant schizophrenic patients. Various explanations were postulated for the lack of relationship observed between clozapine plasma level and response in this population.

Augmentation strategies in clozapine-resistant schizophrenia

The introduction of antipsychotics in the 1950s revolutionised the treatment of schizophrenia, but it soon became apparent that a substantial number of patients demonstrated a suboptimal response to these antipsychotics. Clozapine proved to be beneficial in patients whose symptoms were treatment resistant, but it too had limitations, with as many as 40-70% of those treated with clozapine demonstrating inadequate response to this drug as well. The availability of other 'atypical' antipsychotics offers options, but clozapine appears to remain the most effective option in treatment-resistant schizophrenia. This, of course, raises the question of what to do when clozapine is only partially effective. To address the issue of treatment in patients who have demonstrated a suboptimal response to clozapine, efforts have focused on a variety of augmentation strategies, including numerous medications and electroconvulsive therapy. The current body of evidence consists largely of data from smaller open trials and case series/reports, although data from a limited number of controlled studies are now available. Not surprisingly, the evidence drawn from the former is more supportive of augmentation strategies, although the controlled trials are not without positive findings. The available information is certainly not so overwhelming as to endorse any single augmentation approach. Indeed, it argues for more controlled data and cautions us regarding the cost-benefit ratio in adopting this strategy. Over and above the added adverse effects of another treatment, there is evidence to indicate that actual clinical worsening can occur. Without compelling evidence, clinicians must resort to guiding principles. The potential benefits of augmentation cannot be ruled out, but it should be approached with caution and in a systematic fashion. Factors compromising clozapine response should first be ruled out, and any augmentation trials should be guided by existing evidence and a treatment plan that incorporates a clear understanding of target symptoms. A means of evaluating outcome effectively needs to be in place, and the trial should be circumscribed to prevent needless polypharmacy. A priori, an endpoint needs to be established and the trial discontinued unless results firmly support added benefits.

[Obsessive-compulsive symptoms treatment in: schizophrenia]

Obsessive-compulsive symptoms (OCSs) frequently occur in schizophrenia and seem to worsen prognosis. Many case studies suggest that OCSs appear or worsen with an atypical antipsychotic agent treatment (that is, with risperidone, olanzapine, and clozapine). Therefore, family or personal history of OCS should be investigated before initiating such treatment, and OCS onset should be monitored during treatment. Clozapine is involved in most such cases. When OCSs appear with clozapine, dosage can be reduced and a serotonin reuptake inhibitor treatment added. Current studies suggest that patients with schizophrenia and OCSs should benefit from treatment with an antipsychotic and an antiobsessive medication. Two controlled trials deal with OCS treatment in schizophrenia: the first, with clomipramine; and the second, with fluvoxamine. Both have proven their efficacy, but these trials include a small number of patients with heterogeneous characteristics.

Fluvoxamine as an adjunctive agent in schizophrenia

Schizophrenia is a common mental disorder that has an early onset and rates high as a cause of medical disability. Antipsychotic agents are the mainstay of treatment but response is often inadequate. Negative symptoms (disturbances in volition, social interaction and affective functions) are particularly difficult to treat and form a major obstacle to rehabilitation. A promising approach to improve response of negative symptoms has been to add a selective serotonin reuptake inhibitor (SSRI) antidepressant to antipsychotic treatment. This review examines evidence pertaining to the efficacy, tolerability, and safety of the SSRI fluvoxamine, combined with antipsychotic agents, in the treatment of negative symptoms in schizophrenia. Important methodological issues, such as differentiating primary and secondary negative symptoms, are discussed. The balance of available evidence indicates that fluvoxamine can improve primary negative symptoms in chronic schizophrenia patients treated with typical antipsychotics and suggests that it may also do so in some patients treated with clozapine. This combination is generally safe and well tolerated although, as antipsychotic drug concentrations may be elevated, attention to dose and drug monitoring should be considered appropriately. Combination with clozapine may require particular caution because of potential toxicity if serum clozapine levels rise steeply. The fluvoxamine doses effective in augmentation are lower than those usually used to treat depression. Evidence regarding the use of fluvoxamine augmentation to treat phenomena, such as obsessions and aggression, which may be associated with schizophrenia, is also examined. An important goal of future studies will be to define which patient groups can benefit from combined treatment.

Drug metabolism and atypical antipsychotics

The introduction of the atypical antipsychotics clozapine, risperidone, olanzapine, quetiapine and sertindole for the treatment of schizophrenia has coincided with an increased awareness of the potential of drug-drug interactions, particularly involving the cytochrome P450 (CYP) enzymes. The current literature describing the pharmacokinetics of the metabolism of these agents, including their potential to influence the metabolism of other medications, is reviewed. Clozapine appears to be metabolized primarily by CYP1A2 and CYP3A4, with additional contributions by CYP2C19 and CYP2D6. In addition, clozapine may inhibit the activity of CYP2C9 and CYP2C19, and induce CYP1A, CYP2B and CYP3A. Risperidone is metabolized by CYP2D6, and possibly CYP3A4. In vitro data indicate that olanzapine is metabolized by CYP1A2 and CYP2D6. Quetiapine is metabolised by CYP3A4 and sertindole by CYP2D6. There is, however, a general paucity of in vivo data regarding the metabolism of the atypical antipsychotics, indicating a need for further research in this area.

Pharmacokinetic-pharmacodynamic relationship of the selective serotonin reuptake inhibitors

The recently introduced antidepressants, the selective serotonin reuptake inhibitors (SSRIs) [citalopram, fluoxetine, fluvoxamine, paroxetine and sertraline], are known for their clinical efficacy, good tolerability and relative safety. They differ from each other in chemical structure, metabolism and pharmacokinetic properties. Therapeutic drug monitoring of these compounds is not widely used, as the plasma concentration ranges within which clinical response with minimal adverse effects appears to be optimal are not clearly defined. Almost all recent assays developed for the quantitative determination of SSRIs and their metabolites in blood are based either on the separation of SSRIs by high performance liquid chromatography (HPLC) or gas chromatography (GC). Citalopram and fluoxetine have been introduced as racemic compounds. There are some differences in the pharmacological profile, metabolism and pharmacokinetics between the enantiomers of the parent compounds and their demethylated metabolites. Stereoselective chromatographic methods for their analysis in blood are now available. With regard to the SSRIs presently available, no clearcut plasma concentration-clinical effectiveness relationship in patients with depression has been shown, nor any threshold which defines toxic concentrations. This may be explained by their low toxicity and use at dosages where serious adverse effects do not appear. SSRIs vary widely in their qualitative and quantitative interaction with cytochrome P450 (CYP) isozymes in the liver. CYP2D6 is inhibited by SSRIs, in order of decreasing potency paroxetine, norfluoxetine, fluoxetine, sertraline, citalopram and fluvoxamine. This may have clinical consequences with some but not all SSRIs, when they are taken with tricyclic antidepressants. Except for citalopram and paroxetine, little is known about the enzymes which control the biotransformation of the SSRIs. There have been many reports on marked pharmacokinetic interactions between fluoxetine and tricyclic antidepressants. Fluoxetine has a stronger effect on their hydroxylation than on their demethylation. Interactions observed between fluoxetine and alprazolam, midazolam and carbamazepine seem to occur on the level of CYP3A. Fluvoxamine strongly inhibits the N-demethylation of some tricyclic antidepressants of the tertiary amine type and of clozapine. This may lead to adverse effects but augmentation with fluvoxamine can also improve response in very rapid metabolisers, as it increases the bioavailability of the comedication. Fluvoxamine inhibits with decreasing potency, CYP1A2, CYP2C19, CYP2D6 and CYP1A1, but it is also an inhibitor of CYP3A. Fluoxetine and fluvoxamine have shown to increase methadone plasma concentrations in dependent patients. Some authors warn about a combination of monoamine oxidase (MAO) inhibitors with SSRIs, as this could lead to a serotonergic syndrome. Studies with healthy volunteers suggest, however, that a combination of moclobemide and SSRIs, such as fluvoxamine, should not present serious risks in promoting a serotonin syndrome. A combination of moclobemide and fluvoxamine has successfully been used in refractory depression, but more studies are needed, including plasma-concentration monitoring, before this combined treatment can be recommended. Paroxetine is a substrate of CYP2D6, but other enzyme(s) could also be involved. Its pharmacokinetics are linear in poor metabolisers of sparteine, and non-linear in extensive metabolisers. Due to its potent CYP2D6 inhibiting properties, comedication with this SSRI can lead to an increase of tricyclic antidepressants in plasma, as shown with amitriptyline and trimipramine. CYP3A has been claimed to be involved in the biotransformation of sertraline to norsertraline. Clinical investigations (with desipramine) confirmed in vitro findings that CYP2D6 inhibition by sertraline is only moderate. (ABSTRACT TRUNCATED)