The influence of cigarette smoking on haloperidol pharmacokinetics

Pharmacokinetic drug interactions with oral haloperidol in adults: dose correction factors from a combined weighted analysis

INTRODUCTION

Pharmacokinetic (PK) drug-drug interactions (DDIs) of oral haloperidol, a first-generation antipsychotic, are systematically reviewed.

AREAS COVERED

After exclusions, the search for DDIs with oral haloperidol provided 47 articles as victim and 7 as perpetrator. Changes in mean haloperidol concentration-to-dose (C/D) ratios after weighting each study's size were used to calculate the effects of other drugs (inhibitors/inducers) on haloperidol. These changes of haloperidol C/D ratio were used to estimate dose-correction factors (<1 for inhibitors and >1 for inducers).

EXPERT OPINION

A box summarizes our recommendations for clinicians regarding our current knowledge of haloperidol PK DDIs, which will need to be updated as new information becomes available. Moderate to strong inducers (carbamazepine, phenobarbital, phenytoin, or rifampin) should be avoided since they required dose-correction factors of 2-5. Smoking appeared to be a weak inducer (dose-correction factor 1.2). Fluvoxamine, promethazine, and combinations of CYP3A4 and CYP2D6 inhibitors should be avoided. There are no long-term studies on fluoxetine to provide a dose correction factor. Limited information suggests that valproate may be an inhibitor (dose-correction factor 0.6). In most patients, haloperidol may not have clinically relevant effects as a perpetrator, but in vitro and clinical studies suggest it is a weak CYP2D6 inhibitor.

Pharmacogenetics and schizophrenia

The wide interindividual variability in clinical response and tolerability of antipsychotic medications has led investigators to postulate that these variabilities may be under genetic control. Although not always consistent, there are promising indications from emergent pharmacogenetic studies that efficacy of antipsychotic medications for the various symptom domains of psychopathology in schizophrenia may be genetically regulated. This is an encouraging approach. Moreover, there are also suggestive findings that the side-effect profiles of second-generation antipsychotic medications and their propensity to cause weight gain and glucose and lipid abnormalities as well as tardive dyskinesia may be related to pharmacogenetic factors in this patient population. Ultimately, such approaches could drive choices of antipsychotic medication based on the likelihood of clinical response and development of side effects in light of a particular patient's genetic profile. In the future, this targeted approach (personalized medicine) may become informative for clinicians choosing an antipsychotic medication for an individual patient with schizophrenia.

Cognitive performance and cigarette smoking in first-episode psychosis

The purpose of this study is to describe possible differences in cognitive functioning between smoking and non-smoking patients with first-episode psychosis and to determine whether there is a better cognitive profile associated with smoking. We assessed 61 first-episode psychosis patients with a neuropsychological battery that included computerized measurements of attention, working memory, and executive functioning. Patients were grouped into two categories: non-smokers (0 cigarettes/day; n = 30) and smokers (>/=20 cigarettes/day; n = 31). No significant differences were detected in sociodemographic and clinical data between the two groups. For attention tasks, smokers exhibited shorter reaction times in the sustained attention test than non-smokers (P = 0.039) and needed less time to complete the Stroop interference test (P = 0.013). In the working memory task, smokers exhibited shorter reaction times (P = 0.029) and presented a significantly lower percentage of omission (P = 0.002) and commission errors (P = 0.020) than non-smokers. For executive functioning, no differences were detected between groups in performance on the Wisconsin Card Sorting Test. Results indicate that first-episode psychosis patients who are nicotine users have better cognitive functioning in the areas of attention and working memory than patients who are not nicotine users. This study supports the cognitive approach to the self-medication hypothesis, to explain the high rates of cigarette smoking among psychosis patients. These results may be relevant for developing new strategies involving nicotinic receptors for cognitive enhancement in psychosis.

Pharmacogenetics and schizophrenia

Emergent pharmacogenetic studies indicate that the efficacy of antipsychotic medications in schizophrenia may be predicted through genetic analysis. There also is evidence that the side-effect profiles of second-generation antipsychotic medications and their propensity to cause weight gain, glucose and lipid abnormalities, and tardive dyskinesia may be predicted by pharmacogenetic analysis in this patient population. In the future, this targeted approach with the choice of antipsychotic medication based on the likelihood of clinical response and development of side effects in light of a particular patient's genetic status may gain hold as new treatments are developed with even fewer side effects.

Challenging the smoking culture within a mental health service supportively

Smoking is an entrenched part of the culture of mental health care services. This paper discusses the smoking culture in mental health care settings and demonstrates a supportive model to engage staff to actively address their tobacco use and to influence a change in smoking-related workplace policy, practice, and culture. With management endorsement, two 9-week staff smoking cessation support groups were implemented and subsidized nicotine replacement therapy was provided to staff within the Alma Street Mental Health Service, Fremantle Hospital, Western Australia. Eighteen staff members from nursing, social work, administration staff, and patient care assistants participated in the group programme. At the conclusion of the programme, 61% (n = 11) of participants had quit as a result of the groups. Furthermore, a 3-month follow-up evaluation revealed that 39% (n = 7) of the group had abstained from smoking because of the programme. More importantly, the groups engaged staff to discuss workplace smoking issues and produced five recommendations to review policy and practice to further influence a change in the smoking culture of the mental health care service. The groups also provided the opportunity to develop a model of intervention to address smoking in a mental health setting and to raise the public health role of mental health nurses.

Combined effects of itraconazole and CYP2D6*10 genetic polymorphism on the pharmacokinetics and pharmacodynamics of haloperidol in healthy subjects

This study was to evaluate the combined effects of the CYP3A4 inhibitor itraconazole and the CYP2D6*10 genotype on the pharmacokinetics and pharmacodynamics of haloperidol, a substrate of both CYP2D6 and CYP3A4, in healthy subjects. Nineteen healthy volunteers whose CYP2D6 genotypes were predetermined were enrolled (9 for CYP2D6*1/*1 and 10 for CYP2D6*10/*10). Four subjects (1 for CYP2D6*1/*1 and 3 for CYP2D6*10/*10) did not complete the study because of adverse events. The pharmacokinetics of haloperidol and its pharmacodynamic effects measured for QTc prolongation and neurologic side effects were evaluated after a single dose of 5 mg haloperidol following a pretreatment of placebo or itraconazole at 200 mg/d for 10 days in a randomized crossover manner. Itraconazole pretreatment increased the mean area under the time-concentration curves (AUCs) of haloperidol by 55% compared to placebo pretreatment (21.7 +/- 11.3 vs 33.5 +/- 29.3 ng h/mL). The subjects with CYP2D6*10/*10 genotype showed 81% higher AUC compared to that of subjects with CYP2D6*1/*1 genotype (27.6 +/- 22.2 vs 50.2 +/- 47.1 ng h/mL). In the presence of itraconazole, subjects with CYP2D6*10/*10 showed 3-fold higher AUC of haloperidol compared to that of placebo pretreated subjects with CYP2D6*1/*1 genotype (21.7 +/- 11.3 vs 66.7 +/- 62.1 ng h/mL; P < 0.05). The CYP2D6*10 genotype and itraconazole pretreatment decreased the oral clearance of haloperidol by 24% and 25%, respectively, but without a statistical significance. In the subjects with both CYP2D6*10 genotype and itraconazole pretreatment, however, the oral clearance was significantly decreased to 42% of subjects with wild genotype in the placebo pretreatment (4.7 +/- 3.6 vs 2.0 +/- 1.9 L/h/kg; P < 0.05). Barnes Akathisia Rating Scale (BARS) of subjects with CYP2D6*10/*10 in the presence of itraconazole pretreatment was significantly higher than that of subjects with CYP2D6*1/*1 genotype in the period of placebo pretreatment. Except for this, all other pharmacodynamic estimations did not reach to statistical significance although each CYP2D6*10 genotype and itraconazole pretreatment caused higher value of UKU side effect and BARS scores. The moderate effect of CYP2D6*10 genotype on the pharmacokinetics and pharmacodynamics of haloperidol seems to be augmented by the presence of itraconazole pretreatment.

Genetic association analysis of functional polymorphisms in the cytochrome P450 1A2 (CYP1A2) gene with tardive dyskinesia in Japanese patients with schizophrenia

OBJECTIVE

Recent studies have revealed positive associations between tardive dyskinesia (TD) and genetic polymorphisms of several cytochrome P450 (CYP) subfamilies that are involved in pharmacokinetic process of antipsychotic drugs. In the present study, we analyzed the relationship between TD and two polymorphisms of the CYP1A2 gene, 734C/A and -2964G/A, in a sample of Japanese patients with schizophrenia.

METHODS

We studied 199 Japanese patients with schizophrenia. We used the Abnormal Involuntary Movement Scale to evaluate TD. Two polymorphisms of the CYP1A2 gene, 734C/A and -2964 G/A were genotyped by means of polymerase chain reaction and restriction fragment length polymorphism analysis.

RESULTS

Neither the 734C/A nor the -2964G/A polymorphism was associated with TD [734C/A genotype: chi2=0.02, degrees of freedom (df)=2, P=1.00; allele: chi2=0.02, df=1, P=0.89; -2964G/A genotype: chi2=0.21, df=2, P=0.90; allele: chi2=0.15, df=1, P=0.70]. In addition, CYP1A2 haplotype was associated with TD (chi2=0.24, df=3, P=0.97). Furthermore, in both the subgroup of smokers and the subgroup of patients receiving high-dosage antipsychotics (chlorpromazine equivalent >1000 mg), neither the 734C/A nor the -2964G/A polymorphism was associated with TD.

CONCLUSIONS

We did not find significant associations between the 734C/A and -2964G/A polymorphisms of CYP1A2 gene and TD in Japanese patients with schizophrenia. Our results suggest that these CYP1A2 gene polymorphisms may not contribute to TD susceptibility.

Prolonged nicotine administration results in biphasic, brain-specific changes in kynurenate levels in the rat

The content of the endogenous NMDA and alpha7 nicotinic acetylcholine receptor antagonist kynurenate (KYNA) is increased in the cerebral cortex and cerebrospinal fluid of patients with schizophrenia. In view of the very high incidence of smoking in schizophrenic individuals, a study was designed to examine the effect of acute and prolonged nicotine administration on brain KYNA levels in experimental animals. Adult male rats received subcutaneous nicotine injections twice daily for up to 10 days, and animals were routinely killed 1 h after the last injection. Neither acute treatment nor a 2-day regimen with 1 mg/kg nicotine (= 0.35 mg/kg pure base) caused changes in cerebral KYNA levels. Four- or 6 day-treatment with this dose resulted in 20-40% decreases in cerebral KYNA content. Animals treated with 1 or 10 mg/kg nicotine for 10 days showed dose-dependent, significant increases in KYNA in hippocampus, striatum, and cortex, but not in the serum. Discontinuation of nicotine treatment for 7 days restored brain KYNA to control levels. Separate animals, implanted with osmotic minipumps delivering 2 mg/kg of nicotine/day for 10 days also showed significant elevations in brain KYNA. Hippocampal microdialysis, performed in animals receiving nicotine (1 mg/kg) for 10 days, revealed a significant increase in basal extracellular KYNA levels compared to controls, whereas acute treatment with this dose produced no such change. Measurements of KYNA's bioprecursor kynurenine in brain or blood did not reveal any nicotine-induced changes. These results indicate that nicotine has a brain-specific, biphasic effect on the transamination of kynurenine to KYNA. Such nicotine-induced fluctuations in brain KYNA may cause functional changes in processes that regulate glutamatergic and cholinergic neurotransmission in the normal and diseased brain.

Effects of smoking and cytochrome P450 2D6*10 allele on the plasma haloperidol concentration/dose ratio

OBJECTIVE

This study was carried out to evaluate the influence of CYP2D6 polymorphism and smoking on the plasma clearance of haloperidol (HAL) levels, accounting for the antipsychotic dose, body weight, and coadministration of other drugs.

METHODS

Subjects were 110 Japanese patients (66 male, 44 female) diagnosed with schizophrenia, dementia, or mood disorder and treated orally with HAL. Venous blood was obtained from each patient to determine the HAL concentration/dose (C/D) ratio (plasma concentration of HAL divided by the daily dose of HAL per body weight) and for CYP2D6 genotyping.

RESULTS

There was no significant difference in the HAL C/D ratio between nonsmokers and smokers. In patients with a non-2D6*10 homozygous genotype, smokers had a significantly lower HAL C/D ratio than nonsmokers, whereas smokers with a 2D6*10 homozygous genotype had a significantly higher HAL C/D ratio than those with a non-2D6*10 homozygous genotype.

CONCLUSION

Our results suggest that the effect of smoking on the HAL C/D ratio depends on the CYP2D6*10 genotype.

The association between schizophrenia and cigarette smoking: a review of the literature and implications for mental health nursing practice

Despite a fall in smoking activity among the general population, individuals with schizophrenia continue to smoke at alarming rates and suffer poor health as a consequence. It would appear that limited and conflicting knowledge, outdated perceptions, and ineffective interventions have hindered efforts to promote healthy behaviours among this group. This paper reviews the literature on the association between nicotine dependence and schizophrenia and explores explanations for the phenomenon. Complex psychopathological, biochemical, and neuropharmacological interactions between smoking and schizophrenia are revealed. The interface of schizophrenia and smoking behaviour, particularly among those hospitalized in mental health facilities, and rationales for the management of this manifestation are examined. In addition, inferences regarding the role of mental health nurses in the care of this population are reached, and implications for nursing practice are discussed.

Abnormal movements and tardive dyskinesia in smokers and nonsmokers with schizophrenia genotyped for cytochrome P450 2D6

STUDY OBJECTIVE

To investigate the relationships between cytochrome P450 (CYP) 2D6 genotype, antipsychotic drug exposure, abnormal movements and tardive dyskinesia, and cigarette smoking.

DESIGN

Prospective, longitudinal study.

SETTING

University mental health research center.

PATIENTS

Thirty-seven patients with schizophrenia.

INTERVENTION

Patients were genotyped for CYP2D6*1, *3, and *4 alleles, and data were collected on their psychiatric symptoms, cigarette smoking status, and antipsychotic drug exposure. Abnormal movements were measured using the Abnormal Involuntary Movement Scale (AIMS). Presence of tardive dyskinesia was also evaluated.

MEASUREMENTS AND MAIN RESULTS

A linear regression model used the AIMS scores as the dependent variable, and genotype, sex, smoking status, and antipsychotic drug exposure as independent variables. Antipsychotic drug exposure, genotype, and cigarette smoking interaction was significant (p<0.0212) for patients with the CYP2D6*1/*3, *4 genotype. Seventy-eight percent of smokers with the CYP2D6*1/*3, *4 genotype had tardive dyskinesia compared with 20-33% of patients in other groups.

CONCLUSION

Patients with a CYP2D6*3 or *4 allele may shunt antipsychotic metabolism through other pathways that are induced by cigarette smoke. This induction may result in formation of neurotoxic metabolites, leading to increased AIMS scores and a higher frequency of tardive dyskinesia compared with patients without these alleles.

Lack of impact of CYP1A2 genetic polymorphism (C/A polymorphism at position 734 in intron 1 and G/A polymorphism at position -2964 in the 5'-flanking region of CYP1A2) on the plasma concentration of haloperidol in smoking male Japanese with schizophrenia

The impact of genetic polymorphism of CYP1A2 that are related to the induction of the isozyme on the plasma levels of haloperidol (HAL) in 40 male smokers with schizophrenia was investigated. A point mutation from C to A in intron 1 at position 734 and a point mutation from G to A at position -2964 in the 5'-flanking region of CYP1A2 were identified by polymerase chain-reaction-restricted fragment length polymorphism method. Regarding C/A polymorphism in intron 1 at position 734, no significant difference was found in the plasma concentrations of HAL corrected for dose and weight among the subjects with A/A (n = 21), A/C (n = 14) and C/C (n = 5) genotypes (one-way analysis of variance: 63.1 +/- 18.5, 47.8 +/- 12.5 and 50.8 +/- 15.1 ng/ml/mg/kg, respectively, F(2,37) = 2.556, P = .09). Regarding G/A polymorphism at position -2964 in the 5'-flanking region, no significant difference was found in the plasma concentrations of HAL corrected for dose and weight between subjects with G/G (n = 24) and G/A (n = 15) (two-tailed t test: G/G and G/A = 51.2 +/- 16.6 and 59.0 +/- 17.6 ng/ml/mg/kg, respectively, df = 28, P = .22). The present study suggests that the genotyping of CYP1A2 cannot predict the steady state plasma levels of HAL in male smoking schizophrenics.

Smoking in patients receiving psychotropic medications: a pharmacokinetic perspective

Many psychiatric patients smoke, and are believed to be heavier smokers than those without psychiatric disorders. Cigarette smoking is one of the environmental factors that contributes to interindividual variations in response to an administered drug. Polycyclic aromatic hydrocarbons (PAHs) present in cigarette smoke induce hepatic aryl hydrocarbon hydroxylases, thereby increasing metabolic clearance of drugs that are substrates for these enzymes. PAHs have been shown to induce 3 hepatic cytochrome P450 (CYP) isozymes, primarily CYP1A1, 1A2 and 2E1. Drug therapy can also be affected pharmacodynamically by nicotine. The most common effect of smoking on drug disposition in humans is an increase in biotransformation rate, consistent with induction of drug-metabolising enzymes. Induction of hepatic enzymes has been shown to increase the metabolism and to decrease the plasma concentrations of imipramine, clomipramine, fluvoxamine and trazodone. The effect of smoking on the plasma concentrations of amitriptyline and nortriptyline is variable. Amfebutamone (bupropion) does not appear to be affected by cigarette smoking. Smoking is associated with increased clearance of tiotixene, fluphenazine, haloperidol and olanzapine. Plasma concentrations of chlorpromazine and clozapine are reduced by cigarette smoking. Clinically, reduced drowsiness in smokers receiving chlorpromazine, and benzodiazepines, compared with nonsmokers has been reported. Increased clearance of the benzodiazepines alprazolam, lorazepam, oxazepam, diazepam and demethyl-diazepam is found in cigarette smokers, whereas chlordiazepoxide does not appear to be affected by smoking. Carbamazepine appears to be minimally affected by cigarette smoke, perhaps because hepatic enzymes are already stimulated by its own autoinductive properties. Cigarette smoking can affect the pharmacokinetic and pharmacodynamic properties of many psychotropic drugs. Clinicians should consider smoking as an important factor in the disposition of these drugs.

Lack of association between a functional polymorphism of the cytochrome P450 1A2 (CYP1A2) gene and tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a common side effect of long-term medication with typical neuroleptics. TD presents itself by abnormal involuntary movements and may lead to a potentially disabling and chronic clinical course. A vast majority of patients suffering from schizophrenia are smokers. Smoking has been reported to induce the activity of the CYP1A2 enzyme, which is an established metabolic pathway within the disposition of antipsychotics. Recently, a C-->A genetic polymorphism in the first intron of the CYP1A2 gene was reported to influence CYP1A2 activity in smokers. Subsequently, a pharmacogenetic study in 85 U.S. patients with schizophrenia (44 smokers, 41 individuals with unknown smoking status) showed the C/C genotype to be associated with higher TD severity (measured by the Abnormal Involuntary Movement Scale, AIMS) than the A/C or A/A genotype. This finding prompted us to investigate whether this effect was also present in a larger German sample of 119 patients with schizophrenia (82 smokers, 37 individuals with unknown smoking status). However, we could not replicate the reported association. The median AIMS scores did not differ between individuals with the A/A, A/C, or C/C genotypes. In an additional analysis, we compared the genotypic and allelic distribution among individuals grouped according to the criteria established by Schooler and Kane [1982: Arch Gen Psychiatry 39:486-487] (persistent TD vs. absent TD). We did not observe a differential genotypic or allelic distribution between the two diagnostic groups. Thus, our results do not support the hypothesis that the C-->A polymorphism in the CYP1A2 gene is involved in the etiology of TD in the German population.

Factors affecting serum haloperidol level assessed by longitudinal therapeutic monitoring

1. Since the development of a kit for the assay of haloperidol by enzyme immunoassay, therapeutic monitoring of haloperidol has been utilised in Japan for several years. By retrospectively analysing the accumulated data, this study was carried out to investigate the factors affecting haloperidol level. Especially, the effects of enzyme-inducing comedications were analysed in relation to serum gamma-glutamyltransferase (GGT) level, which has been measured simultaneously with haloperidol. Serum haloperidol level measurements were obtained from medical records of inpatients on multiple medications (n = 102). For each subject, average haloperidol level was computed during the same prescription and doses. The effects of age, sex, smoking status, and the coadministration of carbamazepine and barbiturates (including phenobarbital, amobarbital and pentobarbital) were analysed using correlation, between-group comparison and multiple regression analysis. Separately, the effect of comedications on haloperidol and GGT levels were analysed individually in a small number of patients (n = 5) who had received those comedications intermittently. Significant lowering of serum haloperidol level by the coadministration of carbamazepine and/or barbiturates was observed. The coadministration was also correlated with the elevated GGT level in between-group comparison. In the separate analysis, the change in haloperidol level was correlated with the change in GGT level in some individuals but not in others. None of the other clinical factors investigated in the study showed significant effect on haloperidol level. This study suggests that the lowering of haloperidol level and the elevation of GGT level may often occur coincidentally by the coadministration of enzyme-inducing drugs. However, whether there is a causal relationship between these phenomena and whether elevated serum GGT level could serve as a clinically useful marker need to be clarified by further basic pharmacological research.

A functional polymorphism of the cytochrome P450 1A2 (CYP1A2) gene: association with tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a common and potentially irreversible side effect associated with long-term treatment with typical antipsychotics. Approximately, 80% or more of patients with schizophrenia are smokers. Smoking is a potent inducer of the CYP1A2 enzyme, and is known to cause a significant decrease in plasma concentrations of some antipsychotics. Therefore, person-to-person differences in the extent of CYP1A2 induction by smoking may contribute to risk for the development of TD. Recently, a (C-->A) genetic polymorphism in the first intron of the CYP1A2 gene was found to be associated with variation in CYP1A2 inducibility in healthy volunteer smokers. The aim of this study was to test the clinical importance of the (C-->A) polymorphism in CYP1A2 in relation to TD severity. A total of 85 patients with schizophrenia were assessed for TD severity using the Abnormal Involuntary Movement Scale (AIMS), and were subsequently genotyped for the (C-->A) polymorphism in CYP1A2. The mean AIMS score in patients with the (C/C) genotype (associated with reduced CYP1A2 inducibility) was 2.7- and 3.4-fold greater than in those with the (A/C) or (A/A) genotype, respectively (F[2,82] = 7.4, P = 0.0007). Further, a subanalysis in the 44 known smokers in our sample, revealed a more pronounced effect. The means AIMS score in smokers was 5.4- and 4. 7-fold greater in (C/C) homozygotes when compared to heterozygotes and (A/A) homozygotes, respectively (F[2,41] = 3.7, P = 0.008). These data suggest that the (C-->A) genetic polymorphism in the CYP1A2 gene may serve as a genetic risk factor for the development of TD in patients with schizophrenia. Further studies in independent samples are warranted to evaluate the applicability of our findings to the general patient population receiving antipsychotic medications.

Effect of a genetic polymorphism of CYP1A2 inducibility on the steady state plasma concentrations of haloperidol and reduced haloperidol in Japanese patients with schizophrenia

The effect of a genetic polymorphism of inducibility of cytochrome P450 (CYP) 1A2 on the steady state plasma concentrations (Css) of haloperidol and reduced haloperidol was studied to clarify if these Css are dependent on the CYP1A2 activity. The subjects were 101 Japanese schizophrenic inpatients receiving oral haloperidol 12 mg/d. The Css of haloperidol and reduced haloperidol were measured in duplicate by high performance liquid chromatographic method, and were corrected to the mean body weight. A point mutation from guanine (wild-type) to adenine (mutated-type) at position -2964 in the 5'-flanking region of CYP1A2 gene was identified by polymerase chain reaction (PCR)-fragment length polymorphism method. Based on the present results, i.e., significant effects of CYP2D6 genotypes on the Css of haloperidol and reduced haloperidol, analyses were separately performed in two groups, i.e., patients with 0 mutated allele of the CYP2D6 (41 cases) and those with 1 or 2 mutated alleles (60 cases). Subjects in each CYP2D6 genotype group consisted of 4 subgroups according to smoking habit and the presence of the mutated allele of the CYP1A2. Neither the Css of haloperidol nor that of reduced haloperidol significantly differed among the 4 subgroups in either CYP2D6 genotype group. The present study thus suggests that the CYP1A2 activity does not play an important role in controlling the Css of haloperidol or reduced haloperidol.

Effects of smoking, CYP2D6 genotype, and concomitant drug intake on the steady state plasma concentrations of haloperidol and reduced haloperidol in schizophrenic inpatients

The effects of smoking, CYP2D6 genotype, and concomitant use of enzyme inducers or inhibitors on the steady state plasma concentrations of haloperidol (HAL) and reduced haloperidol (RHAL) were evaluated in 92 schizophrenic inpatients. All but three of these patients received concomitant medication, in many cases with drugs potentially interacting with HAL. Of the 92 patients, 63 were treated orally with HAL in a daily dose of 0.4 to 50 mg; 29 patients were treated intramuscularly with a daily equivalent dose of HAL decanoate (expressed as HAL) of 1.8 to 17.9 mg. A wide interindividual variation in HAL dose and in steady state plasma concentrations of HAL and RHAL was observed. In the patients treated orally, the daily oral dose was about 4 times higher and the dose-normalized HAL (but not RHAL) plasma concentrations were significantly lower in smokers (n = 40) than in nonsmokers (n = 23) (p < 0.01). The dose-normalized RHAL (but not HAL) plasma concentrations and the RHAL/HAL ratio were significantly higher in poor metabolizers (PMs) than in extensive metabolizers (EMs). There was a trend toward an effect of potentially interacting drugs (inducers or inhibitors) on dose, dose-normalized HAL and RHAL plasma concentrations, and the RHAL/HAL ratio. In the patients treated intramuscularly, the dose-normalized HAL (but not RHAL) plasma concentrations were significantly lower in smokers than in nonsmokers, but no differences in doses were observed. This naturalistic study of modest sample size in a polymedicated population shows an effect of smoking and CYP2D6 genotype (and to a lesser extent, of interacting drugs) on the kinetics of HAL.

Metabolism, pharmacogenetics, and metabolic drug-drug interactions of antipsychotic drugs

1. Antipsychotic drugs are extensively metabolised by cytochrome P450 (CYP) enzymes. 2. Dispositions of a number of antipsychotic drugs have been shown to cosegregate with polymorphism of CYP2D6. 3. Metabolic drug-drug interactions have frequently been observed when antipsychotics are coadministered with other drugs. 4. Many antipsychotic drugs are converted to active metabolites which can contribute to the therapeutic or side effects of the parent drug. 5. Information concerning the individual CYP isoenzymes involved in the metabolism of antipsychotic drugs is important for the safe clinical use of this group of drugs.

Lower plasma levels of haloperidol in smoking than in nonsmoking schizophrenic patients

The impact of smoking on plasma haloperidol (HAL) concentrations was investigated in 66 Japanese male schizophrenic inpatients treated orally with HAL. The subjects consisted of 22 nonsmokers and 44 smokers each smoking ten cigarettes per day. Plasma concentrations of HAL were determined by an enzyme immunoassay method. There were significant positive correlations between the plasma HAL concentration and the daily dose of HAL per kg body weight (Y = 58.1X-0.01 (r = 0.86)). Smokers had significantly lower HAL concentrations per daily dose of HAL/kg body weight than nonsmokers (smokers vs. nonsmokers = 54.3+/-16.6 vs. 70.6+/-23.2 ng/mL/mg/kg). In doses less than 0.2 mg/kg of HAL, smokers showed significantly lower HAL concentrations per daily dose of HAL/kg body weight than nonsmokers (smokers vs. nonsmokers = 55.1+/-14.4 vs. 79.5+/-27.1 ng/mL/mg/kg), whereas no significant difference in HAL concentrations per daily dose of HAL/kg body weight was observed between smokers and nonsmokers when treated with more than 0.2 mg/kg (smokers vs. nonsmokers = 52.9+/-20.7 vs. 60.0+/-11.1 ng/mL/mg/kg). Our results indicate that smoking may induce the enzyme(s) metabolizing HAL, which results in lower plasma HAL concentrations in smokers than in nonsmokers, particularly at low doses of HAL.

Effects of itraconazole on the steady-state plasma concentrations of haloperidol and its reduced metabolite in schizophrenic patients: in vivo evidence of the involvement of CYP3A4 for haloperidol metabolism

The effects of itraconazole, a potent inhibitor of cytochrome P450 (CYP) 3A4, on the steady-state plasma concentrations of haloperidol and reduced haloperidol were examined in schizophrenic patients. Thirteen schizophrenic patients treated with haloperidol 12 or 24 mg/day received 200 mg/day of itraconazole for 7 days. Plasma concentrations of haloperidol and reduced haloperidol were measured by high-performance liquid chromatography together with clinical assessment by the Brief Psychiatric Rating Scale (BPRS) and the Udvalg for Kliniske Undersogelser side effect rating scale just before and during itraconazole treatment and 1 week after its discontinuation. Plasma concentrations of haloperidol and reduced haloperidol during the itraconazole treatment (16.9 +/- 11.2 and 6.1 +/- 6.6 ng/mL, respectively) were significantly (p < 0.01) higher than those observed before itraconazole treatment (13.0 +/- 7.9 and 4.9 +/- 5.1 ng/mL) or 1 week after its discontinuation (13.5 +/- 8.2 and 4.9 +/- 5.0 ng/mL). No change was found in clinical symptoms assessed by BPRS, whereas neurologic side effects were significantly (p < 0.05) increased during itraconazole coadministration. The elevated plasma concentrations of haloperidol and reduced haloperidol during itraconazole coadministration were likely due to the inhibitory effects of itraconazole on the metabolism of haloperidol and reduced haloperidol. Thus, this study may provide in vivo evidence of involvement of CYP3A4 in the metabolism of haloperidol and possibly in that of reduced haloperidol. Deterioration of neurologic side effects during itraconazole treatment may result from the increased plasma concentrations of haloperidol and reduced haloperidol during itraconazole treatment.