Pharmacokinetics of haloperidol: an update

Higher activity of polymorphic NAD(P)H:quinone oxidoreductase in liver cytosols from blacks compared to whites

In human liver, the two-electron reduction of quinone compounds, such as menadione is catalyzed by cytosolic carbonyl reductase (CBR) and NAD(P)H:quinone oxidoreductase (NQO1) activities. We assessed the relative contributions of CBR and NQO1 activities to the total menadione reducing capacity in liver cytosols from black (n=31) and white donors (n=63). Maximal menadione reductase activities did not differ between black (13.0+/-5.0 nmol/min mg), and white donors (11.4+/-6.6 nmol/min mg; p=0.208). In addition, both groups presented similar levels of CBR activities (CBR(blacks)=10.9+/-4.1 nmol/min mg) versus CBR(whites)=10.5+/-5.8 nmol/min mg; p=0.708). In contrast, blacks showed higher NQO1 activities (two-fold) than whites (NQO1(blacks)=2.1+/-3.0 nmol/min mg versus NQO1(whites)=0.9+/-1.6 nmol/min mg, p<0.01). To further explore this disparity, we tested whether NQO1 activity was associated with the common NQO1(*)2 genetic polymorphism by using paired DNA samples for genotyping. Cytosolic NQO1 activities differed significantly by NQO1 genotype status in whites (NQO1(whites[NQO1*1/*1])=1.3+/-1.7 nmol/min mg versus NQO1(whites[NQO1*1/*2+NQO1*2/*2])=0.5+/-0.7 nmol/min mg, p<0.01), but not in blacks (NQO1(blacks[NQO1*1/*1])=2.6+/-3.4 nmol/min mg versus NQO1(blacks[NQO1*1/*2])=1.1+/-1.2 nmol/min mg, p=0.134). Our findings pinpoint the presence of significant interethnic differences in polymorphic hepatic NQO1 activity.

Receptor occupancy-based analysis of the contributions of various receptors to antipsychotics-induced weight gain and diabetes mellitus

OBJECTIVE

Among various adverse reactions of atypical antipsychotics, weight gain and impaired glucose tolerance are clinically significant. The aim of this study is to analyze quantitatively the contributions of various receptors to these antipsychotics-induced adverse reactions based on the receptor occupancy theory.

METHODS

Two indices of antipsychotics-induced weight gain (the values estimated by a meta-analysis and the observed values in clinical trials) and the morbidity rate of type 2 diabetes mellitus during treatment with antipsychotics were taken from the literature. We calculated the estimated mean receptor occupancies of alpha1 adrenergic, alpha2 adrenergic, dopamine D2, histamine H1, muscarinic acetylcholine (mACh), serotonin 5-HT1A, 5-HT2A and 5-HT2C receptors by antipsychotics by using the pharmacokinetic parameters and receptor dissociation constants, and analyzed the correlation between the occupancies and the extent of adverse reactions as assessed using the aforementioned indices.

RESULTS

There were statistically significant correlations between the estimated occupancies of H1 and mACh receptors and antipsychotics-induced weight gain estimated by meta-analysis (r(s) = 0.81 and r(s) = 0.83, respectively, p < 0.01). There were also statistically significant correlations between these receptor occupancies and observed weight gain in clinical trials (r(s) = 0.66 in each case, p < 0.01). The morbidity rate of type 2 diabetes mellitus was highly correlated with H1, mACh, and 5-HT2C receptor occupancies (r(s) = 0.90 in each case, p < 0.05). However, H1 receptor occupancy was also highly correlated with mACh receptor occupancy among antipsychotics, so that only one of them may be critically associated with the adverse reactions. Considering that these adverse reactions have not been reported for drugs with mACh receptor antagonistic action, other than antipsychotics, the H1 receptor may contribute predominantly to the antipsychotics-induced weight gain and diabetes mellitus.

DISCUSSION/CONCLUSION

Model analysis based on receptor occupancy indicates that H1 receptor blockade is the primary cause of antipsychotics-induced weight gain and diabetes mellitus.

Rapid determination of haloperidol and its metabolites in human plasma by HPLC using monolithic silica column and solid-phase extraction

A rapid, sensitive and reproducible HPLC method was developed and validated for the analysis of haloperidol and its three main metabolites in human plasma. The analysis was carried out on a monolithic silica column (Chromolith Performance RP-18e, 100 x 4.6 mm). The mobile phase consisted of sodium phosphate (0.1 m, pH 3.5)-acetonitrile (80:20, v/v) at a flow rate of 2.0 mL/min. UV detection at 230 nm was used, with the detection limits of these compounds ranging from 2 to 5 ng. The separation factors of all studied compounds were in the range 2.30-16.32, while the resolution factors were from 1.00 to 5.37.

Interactions between Antiepileptic and Antipsychotic Drugs

Antiepileptic and antipsychotic drugs are often prescribed together. Interactions between the drugs may affect both efficacy and toxicity. This is a review of human clinical data on the interactions between the antiepileptic drugs carbamazepine, valproic acid (sodium valproate), vigabatrin, lamotrigine, gabapentin, topiramate, tiagabine, oxcarbazepine, levetiracetam, pregabalin, felbamate, zonisamide, phenobarbital and phenytoin with the antipsychotic drugs risperidone, olanzapine, quetiapine, clozapine, amisulpride, sulpiride, ziprasidone, aripiprazole, haloperidol and chlorpromazine; the limited information on interactions between antiepileptic drugs and zuclopenthixol, periciazine, fluphenazine, flupenthixol and pimozide is also presented. Many of the interactions depend on the induction or inhibition of the cytochrome P450 isoenzymes, but other important mechanisms involve the uridine diphosphate glucuronosyltransferase isoenzymes and protein binding. There is some evidence for the following effects. Carbamazepine decreases the plasma concentrations of both risperidone and its active metabolite. It also decreases concentrations of olanzapine, clozapine, ziprasidone, haloperidol, zuclopenthixol, flupenthixol and probably chlorpromazine and fluphenazine. Quetiapine increases the ratio of carbamazepine epoxide to carbamazepine and this may lead to toxicity. The data on valproic acid are conflicting; it may either increase or decrease clozapine concentrations, and it appears to decrease aripiprazole concentrations. Chlorpromazine possibly increases valproic acid concentrations. Lamotrigine possibly increases clozapine concentrations. Phenobarbital decreases clozapine, haloperidol and chlorpromazine concentrations. Phenytoin decreases quetiapine, clozapine, haloperidol and possibly chlorpromazine concentrations. There are major gaps in the data. In many cases there are no published clinical data on interactions that would be predicted on theoretical grounds.

An overview of psychotropic drug-drug interactions

The psychotropic drug-drug interactions most likely to be relevant to psychiatrists' practices are examined. The metabolism and the enzymatic and P-glycoprotein inhibition/induction profiles of all antidepressants, antipsychotics, and mood stabilizers are described; all clinically meaningful drug-drug interactions between agents in these psychotropic classes, as well as with frequently encountered nonpsychotropic agents, are detailed; and information on the pharmacokinetic/pharmacodynamic results, mechanisms, and clinical consequences of these interactions is presented. Although the range of drug-drug interactions involving psychotropic agents is large, it is a finite and manageable subset of the much larger domain of all possible drug-drug interactions. Sophisticated computer programs will ultimately provide the best means of avoiding drug-drug interactions. Until these programs are developed, the best defense against drug-drug interactions is awareness and focused attention to this issue.

Block of delayed-rectifier potassium channels by reduced haloperidol and related compounds in mouse cortical neurons

Haloperidol is known as an antagonist of dopamine D2 receptors. However, it also blocks a variety of ion channels at concentrations above the therapeutic range. Reduced haloperidol (R-haloperidol), one of the main metabolites of haloperidol, has been reported to accumulate in certain tissues, particularly in brain cortex, and it may produce the pharmacological effects associated with haloperidol treatment. In this study, we assessed the effect of R-haloperidol and other related compounds on native delayed-rectifier potassium channels (K(DR)) in mouse cortical neurons by using the whole-cell patch-clamp technique. Although R-haloperidol has much lower affinity to D2 receptors than haloperidol, the IC50 of R-haloperidol to block K(DR) currents was 4.4 microM, similar to its parent compound. The binding site of R-haloperidol is on the cytoplasmic side of the channel because its quaternary derivative preferentially inhibited the currents from intracellular side. 4-Chlorophenyl-4-hydroxypiperidine (4C4HP) is the active fragment of haloperidol because other compounds containing this moiety, including L-741,626 (3-[4-(4-chlorophenyl)-4-hydroxypiperidin-L-yl]-methyl-1H-indole) and loperamide, also blocked K(DR) channels. The potency of the 4C4HP fragment positively correlated with the hydrophobicity index (clogP) of the compounds tested. We conclude that R-haloperidol is a K(DR) channel blocker, although it does not interfere with the normal channel function at a clinically relevant concentration.

Drug bioactivation, covalent binding to target proteins and toxicity relevance

A number of therapeutic drugs with different structures and mechanisms of action have been reported to undergo metabolic activation by Phase I or Phase II drug-metabolizing enzymes. The bioactivation gives rise to reactive metabolites/intermediates, which readily confer covalent binding to various target proteins by nucleophilic substitution and/or Schiff's base mechanism. These drugs include analgesics (e.g., acetaminophen), antibacterial agents (e.g., sulfonamides and macrolide antibiotics), anticancer drugs (e.g., irinotecan), antiepileptic drugs (e.g., carbamazepine), anti-HIV agents (e.g., ritonavir), antipsychotics (e.g., clozapine), cardiovascular drugs (e.g., procainamide and hydralazine), immunosupressants (e.g., cyclosporine A), inhalational anesthetics (e.g., halothane), nonsteroidal anti-inflammatory drugs (NSAIDSs) (e.g., diclofenac), and steroids and their receptor modulators (e.g., estrogens and tamoxifen). Some herbal and dietary constituents are also bioactivated to reactive metabolites capable of binding covalently and inactivating cytochrome P450s (CYPs). A number of important target proteins of drugs have been identified by mass spectrometric techniques and proteomic approaches. The covalent binding and formation of drug-protein adducts are generally considered to be related to drug toxicity, and selective protein covalent binding by drug metabolites may lead to selective organ toxicity. However, the mechanisms involved in the protein adduct-induced toxicity are largely undefined, although it has been suggested that drug-protein adducts may cause toxicity either through impairing physiological functions of the modified proteins or through immune-mediated mechanisms. In addition, mechanism-based inhibition of CYPs may result in toxic drug-drug interactions. The clinical consequences of drug bioactivation and covalent binding to proteins are unpredictable, depending on many factors that are associated with the administered drugs and patients. Further studies using proteomic and genomic approaches with high throughput capacity are needed to identify the protein targets of reactive drug metabolites, and to elucidate the structure-activity relationships of drug's covalent binding to proteins and their clinical outcomes.

Carbonyl reduction of naltrexone and dolasetron by oxidoreductases isolated from human liver cytosol

The opioid receptor antagonist naltrexone and the antiemetic 5-HT(3) receptor antagonist dolasetron are ketonic drugs that are efficiently reduced to their corresponding alcohols in-vivo. These experiments aimed at characterizing the role in these reactions of individual oxidoreductases present in human liver cytosol. Aldo-keto reductases (AKRs) and carbonyl reductase (CR, EC 1.1.1.184) purified from human liver cytosol were incubated with varying substrate concentrations and 6beta-naltrexol or reduced dolasetron were analysed by HPLC. AKR1C1, AKR1C2, and AKR1C4 were able to reduce both substrates. On the basis of k(cat)/K(m) values, AKR1C4 was nearly 1000-fold more efficient in reducing naltrexone than was AKR1C1, while AKR1C2 was of intermediate efficiency. Substrate inhibition was observed on incubating AKR1C2 or AKR1C4 with naltrexone. In contrast, dolasetron was also a substrate of CR. AKR1C1 and AKR1C4 were the most efficient enzymes in producing reduced dolasetron. We concluded that the efficient reduction of naltrexone by AKR1C4 probably causes the high 6beta-naltrexol/naltrexone ratio in man. The rapid disappearance from human plasma of dolasetron given intravenously and its virtual absence after oral dosage are explained by its liability to reduction by several enzymes, including CR which shows widespread expression in human tissues.

Measurement of xenobiotic carbonyl reduction in human liver fractions

Carbonyl reducing enzymes are involved in the metabolism of endogenous as well as xenobiotic molecules. Enzymes that catalyze the reversible oxidoreduction of aldehyde and ketone moieties include alcohol dehydrogenases, aldo-keto reductases, quinone reductases, and short-chain dehydrogenases/reductases. These enzymes differ with respect to subcellular location, cofactor dependence, and susceptibility to chemical inhibitors. Thus, it is possible to assess the relative contributions of these enzyme systems in the hepatic metabolism of a particular xenobiotic through simple in vitro experiments with commercially available reagents. The approaches described in this unit assume the availability of analytical procedures for measuring the parent compound and metabolites, such as HPLC with radiochemical, UV, or MS detection. Thus, the purpose of this unit is to outline methods for the study of the enzymatic carbonyl reduction of a drug development candidate or other xenobiotic molecule of interest.

Pharmacokinetic-Pharmacodynamic Analysis of Antipsychotics-induced Extrapyramidal Symptoms based on Receptor Occupancy Theory Incorporating Endogenous Dopamine Release

We aimed to analyze the risks of extrapyramidal symptoms (EPS) induced by typical and atypical antipsychotic drugs using a common pharmacokinetic-pharmacodynamic (PK-PD) model based on the receptor occupancy. We collected the data for EPS induced by atypical antipsychotics, risperidone, olanzapine and quetiapine, and a typical antipsychotic, haloperidol from literature and analyzed the following five indices of EPS, the ratio of patients obliged to take anticholinergic medication, the occurrence rates of plural extrapyramidal symptoms (more than one of tremor, dystonia, hypokinesia, akathisia, extrapyramidal syndrome, etc.), parkinsonism, akathisia, and extrapyramidal syndrome. We tested two models, i.e., a model incorporating endogenous dopamine release owing to 5-HT2A receptor inhibition and a model not considering the endogenous dopamine release, and used them to examine the relationship between the D2 receptor occupancy of endogenous dopamine and the extent of drug-induced EPS. The model incorporating endogenous dopamine release better described the relationship between the mean D2 receptor occupancy of endogenous dopamine and the extent of EPS than the other model, as assessed by the final sum of squares of residuals (final SS) and Akaike's Information Criteria (AIC). Furthermore, the former model could appropriately predict the risks of EPS induced by two other atypical antipsychotics, clozapine and ziprasidone, which were not incorporated into the model development. The developed model incorporating endogenous dopamine release owing to 5-HT2A receptor inhibition may be useful for the prediction of antipsychotics-induced EPS.

Haloperidol half-life after chronic dosing

In normal subjects after a single oral dose, haloperidol half-life has been reported to range 14.5-36.7 hours (or up to 1.5 days). After chronic administration, half-lives of up to 21 days have been reported. The objective of this study was to evaluate specific factors that might account for differences in haloperidol half-life in patients taking haloperidol chronically, including gender, age, weight, race, CYP2D6 and CYP3A5 genotypes, comedication, and smoking.Thirty-one patients were administered haloperidol for 4 weeks followed by a 1-week washout before administration of clozapine. Haloperidol plasma levels were measured weekly for at least 2 months after discontinuation. The geometric mean for haloperidol half-life and detectable levels duration were 3.9 and 13.8 days, respectively. Within 31 subjects, 58% (18/31) had half-lives <3 days (1.2-2.3 days) and 42% (13/31) had half-lives > or =3 days. Two of 3 patients with half-lives longer than 30 days (720 hours) and levels detectable >2 months had received haloperidol decanoate. Five patients who received haloperidol decanoate in the prior year were excluded from a comparison between patients with long haloperidol half-lives (> or =3 days, n = 10) and patients with short half-lives (<3 days, n = 16). The only significant difference between the two groups was that African-Americans (n = 4) were all found to have a long haloperidol half-life (P = 0.014). CYP3A5 genotype did not appear to influence haloperidol half-life but the two CYP2D6 poor metabolizer had half-lives > or =3 days. This study suggests that haloperidol half-life following repeated drug administration is substantially more prolonged than what has been observed after acute haloperidol administration.

Treatment of the metabolic disturbances caused by antipsychotic drugs: focus on potential drug interactions

The risk of excessive bodyweight gain, glucose dysregulation and hyperlipidaemia is differentially increased by conventional and atypical antipsychotic drugs. Switching or combining agents may be sufficient in some cases, but in many instances additional drug treatment will be required. This includes oral antidiabetics, insulin and agents to treat hyperlipidaemia, hypertension and platelet dysfunction, among others. Numerous pharmacokinetic and pharmacodynamic interactions with the antipsychotics are possible, although few have been tested in formal studies. After reviewing the literature, the authors provide preliminary guidelines to assist clinicians in drug selection for this complex and fragile clinical population.

Human Carbonyl Reduction Pathways and a Strategy for Their Study In Vitro

Carbonyl reduction plays a significant role in physiological processes throughout the body. Although much is known about endogenous carbonyl metabolism, much less is known about the roles of carbonyl-reducing enzymes in xenobiotic metabolism. Multiple pathways exist in humans for metabolizing carbonyl moieties of xenobiotics to their corresponding alcohols, readying these molecules for subsequent conjugation and/or excretion. When exploring carbonyl reduction clearance pathways for a drug development candidate, it is possible to assess the relative contributions of these enzymes due to their differences in subcellular locations, cofactor dependence, and inhibitor profiles. In addition, the contributions of these enzymes may be explored by varying incubation conditions, such as pH. Presently, individual isoforms of carbonyl-reducing enzymes are not widely available, either in recombinant or purified form. However, it is possible to study carbonyl reduction clearance pathways from simple experiments with commercially available reagents. This article provides an overview of carbonyl-reducing enzymes, including some kinetic data for substrates and inhibitors. In addition, an experimental strategy for the study of these enzymes in vitro is presented.

Glucuronidation of haloperidol by rat liver microsomes: involvement of family 2 UDP-glucuronosyltransferases

The purposes of this study were to develop a HPLC method to assay for haloperidol glucuronide (HALG); to apply this assay method to the in vitro determination of haloperidol (HAL) UDP-glucuronosyltransferase (UGT) enzyme kinetics in rat liver microsomes (RLM); and to identify the UGT isoforms catalyzing glucuronidation of HAL in rats. Incubation of Brij-activated RLM with HAL and UDP-glucuronic acid (UDPGA) in TRIS pH 7.4 buffer resulted in the formation of a single peak in the HPLC chromatogram at 270 nm. The identity of this peak was confirmed to be that of HALG by 1) beta-glucuronidase hydrolysis; 2) incubation without UDPGA; 3) UV spectral analysis; and 4) LC/MS/MS to yield the expected mass of 552.1. Enzyme kinetic studies using single enzyme Michaelis-Menton model showed an apparent Vmax = 271.9 +/- 10.1 pmoles min(-1) mg protein(-1) and Km = 61 +/- 7.2 microM. Glucuronidation activity in homozygous Gunn (j/j) rats was approximately 80% as compared to Sprague-Dawley RLM. HALG formation was approximately doubled in PB-induced RLM. There was no increase in glucuronidation activities in 3MC-induced RLM. The Gunn rat and the PB-induced RLM data suggest predominant but not exclusive involvement of the UGT2B family in the formation of HALG. Because the UGTs exhibit overlapping substrate specificities and most substrates are glucuronidated by more than one isoform, inhibition studies with UGT2B1 substrate probe testosterone and the UGT2B12 substrate probe borneol were conducted. UGT2B1 and UGT2B12 exhibited 40% and 90% inhibition of HAL glucuronidation, respectively. Thus, UGT2B12 and UGT 2B1 isoforms are responsible for catalyzing HAL glucuronidation in rats. Our HPLC assay provides a specific and sensitive technique for the measurement of in vitro HAL-UGT activity.

Update on Psychotropic Medication Use in Renal Disease

Renal failure is a common medical condition, and many patients have comorbid psychiatric disorders. In this review, which is intended as a resource for consultation psychiatrists, the authors discuss pharmacokinetic considerations and provide information about the use of individual psychotropic medications in patients with renal disease. Most psychotropic medications are fat soluble, easily pass the blood-brain barrier, are not dialyzable, are metabolized primarily by the liver, and are excreted mainly in bile. Consequently, the majority of these drugs can be safely used with the end-stage renal disease population.

Delayed onset of oculogyric crisis and torticollis with intramuscular haloperidol

OBJECTIVE

To report a case of delayed-onset dystonic reactions, oculogyric crisis (OGC), and torticollis after treatment with intramuscular haloperidol lactate injection.

CASE SUMMARY

A 22-year-old Mexican American woman received intramuscular haloperidol lactate 7.5 mg followed 4 hours later by 10 mg. Twenty-six hours after the first injection, the patient reported that she was unable to lower her gaze and that her neck was stiff. She was immediately given intramuscular benztropine 2 mg; there was a nearly complete remission of symptoms within 15 minutes of treatment. An objective causality assessment revealed a probable relationship between the OGC/torticollis and haloperidol therapy.

DISCUSSION

Dystonic reactions have been reported in 10-60% of patients treated with neuroleptic medication, most commonly when patients just start or increase the dose of the drug. The highest frequency of dystonic reactions has occurred in patients receiving high-potency neuroleptics. It has also been suggested that haloperidol-induced dystonic reactions are a result of the toxic metabolites of that agent.

CONCLUSIONS

OGC and torticollis reactions may occur 12-24 hours after treatment with a high-potency neuroleptic, even in the absence of symptoms of extrapyramidal side effects (EPSEs). The delayed dystonic reaction may begin suddenly (no early EPSE symptomatology).

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.

Pharmacological management of aggression and violence

The pharmacological management of violence and aggression is a common and substantial clinical dilemma in the emergency psychiatric situation. A literature search was conducted through PubMed and using the Cochrane Library. This was followed by a manual search of selected literature. Randomised controlled trials were sought that specifically addressed the acute situation, rather than the ongoing management of chronic conditions. There was a paucity of well-controlled data and insufficient evidence to support the use of many agents in emergency situations. Many studies had considerable limitations making comparison difficult. Efficacy data for a range of treatment options exists, including the use of classical and atypical anti-psychotic agents, benzodiazepines and combination therapies. Clinical risk, tolerability and environmental factors need to form part of a careful and considered judgement in the choice of treatment. Safety, tolerability and the potential for a positive experience are major considerations, thus paving the way for long term compliance.

Interindividual variation of serum haloperidol concentrations in Japanese patients--clinical considerations on steady-state serum level-dose ratios

OBJECTIVE

Marked interpatient variability in haloperidol (HAL) level-dose (L/D) ratios makes it difficult to use the administered dose for predicting serum concentrations.

OBJECTIVE

To investigate the effect of dose, age, total body weight and co-medication on steady-state HAL L/D ratios.

METHOD

Retrospective analysis of dose and HAL blood level data from 168 patients.

RESULTS

The HAL L/D ratio decreased curvilinearly with increasing daily dose of HAL. The patients treated with concomitant antiparkinsonian drugs showed a mean HAL L/D ratio that was 24.9% higher than those without antiparkinsonian drugs. The patients treated with concomitant antiepileptic drugs showed a mean HAL L/D ratio that was 27.2% lower than those without antiepileptic drugs. The mean HAL L/D ratio of patients treated with concomitant CYP2D6 substrates was not significantly different from those without CYP2D6 substrates.

CONCLUSION

There is a wide interindividual variability in blood levels of HAL in patients given the same dose. Routine monitoring of HAL serum level is useful, especially in patients who require associated antiepileptic and/or antiparkinsonian medication.

Assessment of the contributions of CYP3A4 and CYP3A5 in the metabolism of the antipsychotic agent haloperidol to its potentially neurotoxic pyridinium metabolite and effect of antidepressants on the bioactivation pathway

As a plausible explanation for the large interindividual variability in the pharmacokinetics of the neuroleptic agent haloperidol, the contributions of CYP3A isozymes (CYP3A4 and the polymorphic CYP3A5) predominantly involved in haloperidol bioactivation to the neurotoxic pyridinium species 4-(4-Chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-pyridinium (HPP(+)) were assessed in human liver microsomes and heterologously expressed enzymes. Based on recent reports on drug-drug interactions between haloperidol and antidepressants including selective serotonin reuptake inhibitors, the inhibitory effects of antidepressants on the CYP3A4/5-mediated haloperidol bioactivation were also evaluated. HPP(+) formation followed Michaelis-Menten kinetics in microsomes, recombinant CYP3A4, and CYP3A5 with K(m) values of 24.4 +/- 8.9 microM, 18.3 +/- 4.9 microM, and 200.2 +/- 47.6 microM, respectively, and V(max) values of 157.6 +/- 13.2 pmol/min/mg of protein, 10.4 +/- 0.6 pmol/min/pmol P450, and 5.16 +/- 0.6 pmol/min/pmol P450, respectively. The similarity in K(m) values between human liver microsomal and recombinant CYP3A4 incubations suggests that polymorphic CYP3A5 may not be an important genetic contributor to the interindividual variability in CYP3A-mediated haloperidol clearance pathways. Besides HPP(+), a novel 4-fluorophenyl-ring-hydroxylated metabolite of haloperidol in microsomes/CYP3A enzymes was also detected. Its formation was consistent with previous reports on the detection of O-sulfate and -glucuronide conjugates of a fluorophenyl ring-hydroxylated metabolite of haloperidol in human urine. Finally, all antidepressants except buspirone inhibited the CYP3A4/5-catalyzed oxidation of haloperidol to HPP(+) in a concentration-dependent manner. Based on the estimated IC(50) values for inhibition of HPP(+) formation in microsomes, the antidepressants were ranked in the following order: fluoxetine, nefazodone, norfluoxetine, trazodone, and fluvoxamine. These inhibition results suggest that clinically observed drug-drug interactions between haloperidol and antidepressants may arise via the attenuation of CYP3A4/5-mediated 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-4-piperidinol biotransformation pathways.

Pharmacogenetics for the individualization of psychiatric treatment

Drug treatment of psychiatric disorders is troubled by severe adverse effects, low compliance and lack of efficacy in about 30% of patients. Pharmacogenetic research in psychiatry aims to elucidate the reasons for treatment failure and adverse reactions. Genetic variations in cytochrome P450 (CYP) enzymes have the potential to directly influence the efficacy and tolerability of commonly used antipsychotic and antidepressant drugs. The activity of psychiatric drugs can also be influenced by genetic alterations affecting the drug target molecule. These include the dopaminergic and serotonergic receptors, neurotransmitter transporters and other receptors and enzymes involved in psychiatric disorders. Association studies investigating the relation between genetic polymorphisms in metabolic enzymes and neurotransmitter receptors on psychiatric treatment outcome provide a step towards the individualization of psychiatric treatment through enabling the selection of the most beneficial drug according to the individual's genetic background.

Antiepileptic-antipsychotic drug interactions: a critical review of the evidence

The potential for drug-drug interactions in psychiatry and patients with epilepsy is very high. Moreover, antiepileptic drugs are widely used outside epilepsy as psychotropic agents and their spectrum of activity on behavior is of considerable interest to psychopharmacology. In both neurologic and psychiatric practice, pharmacotherapy combinations are commonly used to treat comorbid psychiatric and neurologic disorders, to reduce or control the adverse effects of a medication or to increase its efficacy. This paper focuses on the metabolic pharmacokinetic interactions between two classes of psychotropic drugs: antiepileptic and antipsychotic drugs. The degree of documentation varies for many interactions from clinical case-report experiences to well established research outcomes. The evidence and the clinical significance of these interactions are reviewed. In general, it is better to use as few drugs as possible, as multicolored politherapies increase the possible adverse effects of drug interactions and reduce patient compliance.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Pharmacotherapy of behavioral and psychological symptoms of dementia: time for a different paradigm?

Behavioral and psychological symptoms of dementia can occur in 60-80% of patients with Alzheimer's disease or other dementing illnesses, and are important in that they are a source of significant caregiver stress and often precipitate nursing home placement. These symptoms, namely, aggression, delusions, hallucinations, apathy, anxiety, and depression, are clinically managed with a variety of psychotropic drugs such as antipsychotics, antidepressants, antiepileptic drugs, and benzodiazepines. Various advances in the neuropathophysiology and pharmacotherapy must be considered in the optimal design of regimens for patients with these symptoms.

Effects of fluvoxamine treatment on the in vivo binding of [F-18]FESP in drug naive depressed patients: a PET study

This study investigates the effect of chronic treatment with Fluvoxamine, a potent and specific serotonin reuptake sites inhibitor (SSRI), on 5HT(2) serotonin and D(2) dopamine receptors in the brain of drug naive unipolar depressed patients. Drug effect was evaluated in different cortical areas and in the basal ganglia by positron emission tomography (PET) and fluoro-ethyl-spiperone ([(18)F]FESP), an high affinity 5HT(2) serotonin and D(2) dopamine receptors antagonist. Patients underwent a PET study at recruitment and after clinical response to Fluvoxamine treatment. Nine of the 15 patients recruited completed the study. Fluvoxamine treatment significantly improved clinical symptoms and modified [(18)F]FESP binding in the frontal and occipital cortex of all of the nine patients who completed the study; in these regions a mean 31% increase in the in vivo [(18)F]FESP binding was found (P < 0.01). On the contrary, no significant changes in the in vivo [(18)F]FESP binding were found in the basal ganglia where [(18)F]FESP binds mainly to D(2) dopamine receptors. Chronic treatment with Fluvoxamine significantly increases the in vivo binding of [(18)F]FESP in the frontal and occipital cortex of drug naive unipolar depressed patients. The increase of the in vivo binding of [(18)F]FESP may reflect a modification in 5HT(2) binding capacity secondary to changes in cortical serotonin activity.