The use of clozapine plasma levels in optimising therapy

A Case Report of a Patient with Soaring Clozapine Levels after Developing a Urinary Tract Infection

Clozapine is an antipsychotic medicine used to treat mental illnesses that is resistant to therapy. It can induce dose-dependent adverse effects such as increased susceptibility to infections and hematological irregularities. In this case report, we present a 37-year-old woman with schizoaffective disorder who experienced clozapine side effects following a moderate urinary tract infection (UTI). Her serum clozapine levels and side effects were increased throughout her UTI but resolved once the UTI was managed conservatively. We reviewed clozapine's pharmacokinetic properties to understand why serum levels rose during infection. While we could not definitely explain the mechanism of elevation, we emphasize the importance of monitoring serum clozapine levels and keeping watchful for adverse effects, as well as heightened scrutiny, evaluation for recent infections, and regular monitoring of patients.

Effect of Cigarette Smoking on Clozapine Dose and on Plasma Clozapine and N-Desmethylclozapine (Norclozapine) Concentrations in Clinical Practice

BACKGROUND

Cigarette smoking enhances plasma clozapine clearance and thus affects the clozapine dose requirement.

METHODS

We compared clozapine daily dose and plasma clozapine and N-desmethylclozapine (norclozapine) concentrations in male and female smokers and nonsmokers in samples submitted for clozapine therapeutic drug monitoring (1996-2017).

RESULTS

There were 105,316/60,792 and 34,290/31,309 samples with dose information from male and female smokers/nonsmokers, respectively. There was information on the number of cigarettes smoked daily for 12,842 samples (8409 patients) and 3948 samples (2753 patients) from men and women, respectively. Of these, 574 and 253 samples were from men and women, respectively, who reported smoking 1-9 cigarettes daily.In both sexes, the median clozapine doses in the nonsmokers were 75%-80% of those in the smokers, but the median plasma clozapine and norclozapine concentrations were 136% higher. The effect of smoking on the dose and on median plasma clozapine and norclozapine concentrations seemed maximal after 2-3, perhaps fewer, cigarettes daily in males. In females, the effect of smoking seemed to be near maximal after some 4-5 cigarettes per day.

IMPLICATIONS

The optimum target range for predose plasma clozapine may be different in smokers (0.35-0.45 mg L-1) as opposed to nonsmokers (0.50-0.60 mg L-1). That changes in clozapine clearance are likely near maximal with cigarette smoking as low as 2-3 d-1 in males, perhaps slightly more in females, emphasizes that covert or passive smoking may be an important factor in seemingly random changes in plasma clozapine concentration at constant dose.

Maintenance doses for clozapine

The British National Formulary (BNF) entry for clozapine clearly distinguishes the treatment dose (200–450 mg daily, maximum 900 mg) from the maintenance dose (150–300 mg daily). We looked at 44 patients maintained on clozapine locally and found that 36 (82%) received doses above the BNF guidelines. This has considerable cost implications. While it is always good practice to maintain patients on the lowest possible dose of antipsychotic, the BNF guidelines are not based on objective outcome data, and should be treated cautiously.

Clozapine dose for schizophrenia

BACKGROUND

Schizophrenia and related disorders such as schizophreniform and schizoaffective disorder are serious mental illnesses characterised by profound disruptions in thinking and speech, emotional processes, behaviour and sense of self. Clozapine is useful in the treatment of schizophrenia and related disorders, particularly when other antipsychotic medications have failed. It improves positive symptoms (such as delusions and hallucinations) and negative symptoms (such as withdrawal and poverty of speech). However, it is unclear what dose of clozapine is most effective with the least side effects.

OBJECTIVES

To compare the efficacy and tolerability of clozapine at different doses and to identify the optimal dose of clozapine in the treatment of schizophrenia, schizophreniform and schizoaffective disorders.

SEARCH METHODS

We searched the Cochrane Schizophrenia Group's Study-Based Register of Trials (August 2011 and 8 December 2016).

SELECTION CRITERIA

All relevant randomised controlled trials (RCTs), irrespective of blinding status or language, that compared the effects of clozapine at different doses in people with schizophrenia and related disorders, diagnosed by any criteria.

DATA COLLECTION AND ANALYSIS

We independently inspected citations from the searches, identified relevant abstracts, obtained full articles of relevant abstracts, and classified trials as included or excluded. We included trials that met our inclusion criteria and reported useable data. For dichotomous data, we calculated the relative risk (RR) and the 95% confidence interval (CI) on an intention-to-treat basis based on a random-effects model. For continuous data, we calculated mean differences (MD) again based on a random-effects model. We assessed risk of bias for included studies and created 'Summary of findings' tables using GRADE.

MAIN RESULTS

We identified five studies that could be included. Each compared the effects of clozapine at very low dose (up to 149 mg/day), low dose (150 mg/day to 300 mg/day) and standard dose (301 mg/day to 600 mg/day). Four of the five included studies were based on a small number of participants. We rated all the evidence reported for the main outcomes of interest as low or very low quality. No data were available for the main outcomes of global state, service use or quality of life. Very low dose compared to low doseWe found no evidence of effect on mental state between low and very low doses of clozapine in terms of average Brief Psychiatric Rating Scale-Anchored (BPRS-A) endpoint score (1 RCT, n = 31, MD 3.55, 95% CI -4.50 to 11.60, very low quality evidence). One study found no difference between groups in body mass index (BMI) in the short term (1 RCT, n = 59, MD -0.10, 95% CI -0.95 to 0.75, low-quality evidence). Very low dose compared to standard doseWe found no evidence of effect on mental state between very low doses and standard doses of clozapine in terms of average BPRS-A endpoint score (1 RCT, n = 31, MD 6.67, 95% CI -2.09 to 15.43, very low quality evidence). One study found no difference between groups in BMI in the short term (1 RCT, n = 58, MD 0.10, 95% CI -0.76 to 0.96, low-quality evidence) Low dose compared to standard doseWe found no evidence of effect on mental state between low doses and standard doses of clozapine in terms of both clinician-assessed clinical improvement (2 RCTs, n = 141, RR 0.76, 95% CI 0.36 to 1.61, medium-quality evidence) and clinically important response as more than 30% change in BPRS score (1 RCT, n = 176, RR 0.93, 95% CI 0.78 to 1.10, medium-quality evidence). One study found no difference between groups in BMI in the short term (1 RCT, n = 57, MD 0.20, 95% CI -0.84 to 1.24, low-quality evidence).We found some evidence of effect for other adverse effect outcomes; however, the data were again limited. Very low dose compared to low doseThere was limited evidence that serum triglycerides were lower at low-dose clozapine compared to very low dose in the short term (1 RCT, n = 59, MD 1.00, 95% CI 0.51 to 1.49). Low dose compared to standard doseWeight gain was lower at very low dose compared to standard dose (1 RCT, n = 27, MD -2.70, 95% CI -5.38 to -0.02). Glucose level one hour after meal was also lower at very lose dose (1 RCT, n = 58, MD -1.60, 95% CI -2.90 to -0.30). Total cholesterol levels were higher at very low compared to standard dose (1 RCT, n = 58, n = 58, MD 1.00, 95% CI 0.20 to 1.80). Low dose compared to standard doseThere was evidence of fewer adverse effects, measured as lower TESS scores, in the low-dose group in the short term (2 RCTs, n = 266, MD -3.99, 95% CI -5.75 to -2.24); and in one study there was evidence that the incidence of lethargy (RR 0.77, 95% CI 0.60 to 0.97), hypersalivation (RR 0.70, 95% CI 0.57 to 0.84), dizziness (RR 0.56, 95% CI 0.39 to 0.81) and tachycardia (RR 0.57, 95% CI 0.45 to 0.71) was less at low dose compared to standard dose.

AUTHORS' CONCLUSIONS

We found no evidence of effect on mental state between standard, low and very low dose regimes, but we did not identify any trials on high or very high doses of clozapine. BMI measurements were similar between groups in the short term, although weight gain was less at very low dose compared to standard dose in one study. There was limited evidence that the incidence of some adverse effects was greater at standard dose compared to lower dose regimes. We found very little useful data and the evidence available is generally of low or very low quality. More studies are needed to validate our findings and report on outcomes such as relapse, remission, social functioning, service utilisation, cost-effectiveness, satisfaction with care, and quality of life. There is a particular lack of medium- or long-term outcome data, and on dose regimes above the standard rate.

Optimising plasma levels of clozapine during metabolic interactions: a review and case report with adjunct rifampicin treatment

BACKGROUND

Clozapine is the only licensed medication for treatment-resistant schizophrenia. The metabolism of clozapine is affected by multiple pharmacokinetic interactions, so the co-administration of adjunct medications can have a significant clinical effect. The anti- tuberculosis medication rifampicin is a potent inducer of the cytochrome P450 system and therefore can cause a reduction in the plasma concentration of clozapine. There is limited clinical evidence regarding co-administration of these medications; in particular there is a lack of data regarding the effect on plasma clozapine levels, which is the key factor determining clinical efficacy. This is clinically relevant given evidence of an increased risk of tuberculosis in patients with schizophrenia.

CASE PRESENTATION

We present a case of a 28 year old British man with a diagnosis of schizoaffective disorder who presented with persistent psychotic symptoms. He developed a systemic inflammatory condition, diagnosed as tuberculosis, and was commenced on a six month course of treatment that included rifampicin. This case presents comprehensive data to illustrate the effect on clozapine plasma levels of a complete course of tuberculosis therapy.

CONCLUSION

This case report provides guidance to clinicians in managing drug interactions between clozapine and rifampicin to enable safe and effective treatment. The co-administration of these medications is likely to increase as the existing underuse of clozapine is recognised whilst the incidence of tuberculosis increases.

Pharmacokinetic interactions involving clozapine

BACKGROUND

Metabolism of clozapine is complex and not fully understood. Pharmacokinetic interactions with other drugs have been described but, in some cases, their mechanism is unknown.

METHOD

Published trials and case reports relevant to the human metabolism of clozapine and to suspected pharmacokinetic interactions were reviewed.

RESULTS

Metabolism of clozapine appears to be largely controlled by the function of the hepatic cytochrome p450IA2 (CYPIA2). Compounds which induce CYPIA2 activity (carbamazepine, tobacco smoke) may reduce plasma clozapine levels. Inhibitors of CYPIA2 (caffeine, erythromycin) have the opposite effect. Drugs which inhibit the hepatic cytochrome p4502D6 (CYP2D6) have also been reported to elevate plasma clozapine levels. The mechanism of this interaction is unclear.

CONCLUSIONS

The co-administration of clozapine and compounds reported to alter its metabolism should be avoided where possible. A host of other interactions can be predicted and so caution should be exercised when co-administering drugs which affect the function of CYPIA2 and CYP2D6. The pharmacokinetics of clozapine require further investigation so that its safe use can be assured.