Plasma levels of perphenazine (Trilafon) related to development of extrapyramidal side effects

Plasma levels of second-generation antipsychotics and clinical response in acute psychosis: a review of the literature

OBJECTIVE

The objective of the study is to assess the relationships between plasma concentrations (Cps) of second-generation antipsychotics (SGAs) and clinical outcome in order to establish the clinical value of therapeutic drug monitoring.

METHOD

In April 2012, we searched PubMed and MEDLINE databases for English-language articles using the keywords risperidone, olanzapine, quetiapine, aripiprazole, ziprasidone, paliperidone, iloperidone, asenapine, lurasidone, therapeutic drug monitoring, serum level, and plasma level. One hundred and ninety-one articles were retrieved from the initial search. Articles were selected for inclusion if they involved an attempt to correlate Cps with efficacy measures, if they were prospective in nature, and if they examined patients experiencing an acute exacerbation of a psychotic illness. Ultimately 11 articles were selected.

RESULTS

Of the nine compounds involved in the search, only four were included in relevant articles, and only two of these were involved in multiple trials. No studies involving the most recently developed compounds (paliperidone, iloperidone, asenapine, and lurasidone) were identified. Studies varied widely in methodology, with only four studies adopting a fixed-dose model. Results differed considerably between studies regarding both clinical and adverse effects, with 6 of the 11 studies revealing a positive correlation between Cps and response.

CONCLUSIONS

The utility of therapeutic drug monitoring of SGAs (other than clozapine) remains an open question, although limited evidence from fixed-dose studies is encouraging. We discuss the potentially significant clinical value of antipsychotic Cps and the consequent need for further research in this area.

Genetic polymorphism of cytochrome P450 2C9 in diphenylhydantoin-induced cutaneous adverse drug reactions

BACKGROUND

Apart from allergic mechanisms, a lack or mutation of metabolic enzymes may cause adverse drug reactions. Patch testing has rarely been useful in cutaneous adverse drug reactions (CADRs) induced by diphenylhydantoin (DPH). Genetic polymorphisms leading to altered metabolic processes of cytochrome P(450) (CYP) 2C9, a main metabolic enzyme for DPH, may be the pathological mechanism for certain cases of DPH-induced CADRs.

OBJECTIVE

To examine the effects of an altered CYP2C9 variant, CYP2C9*3, on DPH-induced CADRs.

METHODS

Ten patients with DPH-induced CADRs were examined for CYP2C9 genetic polymorphisms. The results were compared with non-exposed controls and 39 neurological patients without DPH-induced CADRs despite exposure to DPH. The patients with DPH-induced CADRs were also patch tested with anti-epileptic drugs and the results were compared with 40 DPH-exposed and 58 non-exposed controls.

RESULTS

A heterozygous CYP2C9*3 variant was found in three of the 10 DPH-induced CADR patients. The crude odds ratios (OR) of the patients compared with those of exposed and non-exposed controls were 167 and 71, respectively. Only one neurological patient, who had never taken DPH, showed the variant in both exposed (P=0.007) and non-exposed (P=0.001) controls. Positive patch-test results were displayed in three of the ten DPH-induced patients, but the patients with positive patch-test reactions to DPH differed from those with the CYP2C9*3 polymorphism. No patients and controls displayed a CYP2C9*2 variant.

CONCLUSION

A CYP2C9*3 variant could play a role in the proportion of patients with DPH-induced CADRs that differ from patients with DPH-induced CADRs showing positive patch-test results.

Antipsychotic radioreceptor assay: a modification identifying selective receptor effects

Radioreceptor assays offer the advantage of a single assay that can assess uniform exposure to multiple chemical compounds. The advent of atypical antipsychotic agents has led to new awareness of the multiple receptor subtypes through which antipsychotic agents may exert their effects, and a renewed interest in comparative drug trials of antipsychotics. The objective of this study was to show the development and validation of antipsychotic radioreceptor assays using clonal cell lines stably expressing isolated human receptors. Model assays were developed using the dopamine(2) (D(2)) and D(4) receptors. D(2) and D(4) activities measured by radioreceptor assay in plasma of antipsychotic-treated subjects were highly correlated with high-performance liquid chromatography determinations of antipsychotic concentrations. Similarly, for a variety of typical and atypical antipsychotic agents, the quotients of D(4)/D(2) activity in plasma of antipsychotic-treated subjects were highly correlated with the quotients of D(4)/D(2) affinities of these agents. Valid receptor-selective antipsychotic assays can be established and may have utility for dissecting the in vivo activity of atypical antipsychotics in relation to specific outcomes in clinical trials.

Identification of the human cytochrome P450 isoforms mediating in vitro N-dealkylation of perphenazine

AIMS

To identify the human cytochrome P450 (CYP) isoforms mediating the N-dealkylation of the antipsychotic drug perphenazine in vitro and estimate the relative contributions of the CYP isoforms involved.

METHODS

cDNA-expressed CYP isoforms were used to identify the isoforms that are able to mediate the N-dealkylation of perphenazine, which is considered a major metabolic pathway for the drug. Using human liver microsomal preparations (HLM), inhibition studies were carried out to establish the relative contributions of the CYP isoforms involved in the N-dealkylation reaction.

RESULTS

CYP isoforms 1A2, 3A4, 2C8, 2C9, 2C18, 2C19 and 2D6 were able to mediate the N-dealkylation of perphenazine. Reaction velocities and their relative abundance in HLM suggested that CYP1A2, 3A4, 2C19 and 2D6 were the most important contributors to N-dealkylation. Apparent Km values of CYP1A2 and CYP2D6 were in the range 1-2 microM, and Km values of CYP2C19 and CYP3A4 were 14 microM and 7.9 microM, respectively. Ketoconazole inhibition of N-dealkylation mediated by a mixed HLM indicated that CYP3A4 accounted for about 40% of perphenazine N-dealkylation at therapeutically relevant concentrations. The contribution of the CYP isoforms 1A2, 2C19 and 2D6 amounted to 20-25% each as measured by the percentage inhibition obtained by addition of furafylline, fluvoxamine or quinidine, respectively. HLM-mediated N-dealkylation of perphenazine accounted for 57% of the total amount of substrate consumed during incubation.

CONCLUSIONS

The present in vitro study suggests that CYP isoforms 1A2, 3A4, 2C19 and 2CD6 are primarily involved in the N-dealkylation of perphenazine. The relatively modest role of CYP2D6 is at variance with in vivo studies, which indicate a greater contribution of this isoform. Alternative metabolic pathways, corresponding to 43% of the HLM-mediated metabolism of the drug, may depend more strongly on CYP2D6.

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.

Genetic polymorphism of drug metabolising enzymes in African populations: implications for the use of neuroleptics and antidepressants

Metabolism of most drugs influences their pharmacological and toxicological effects. Drugs particularly affected are those with a narrow therapeutic window and that are subjected to considerable first-pass metabolism. Much of the interindividual and interethnic differences in effects of drugs is now attributable to genetic differences in their metabolism. Genetic polymorphisms have been described for many drug-metabolising enzymes in Caucasian and Oriental populations, the most well-characterised being those for cytochrome P450 2D6, cytochrome P450 2C19, glutathione S-transferases, and N-acetyl transferase 2. African populations have been studied to a lesser extent, but it is apparent that populations within Africa are heterogeneous with respect to these polymorphisms. In addition, although some allelic variants are common to all populations throughout the world (e.g., CYP2D6*5), some allelic variants are specific for an African population (e.g., CYP2D6*17). The polymorphisms give rise to enzymes with changed or no activity towards drug substrates. Two of the most important enzymes for metabolism of neuroleptics and other psychoactive drugs are CYP2D6 and CYP2C19. This article compares the current information on polymorphisms of these two enzymes in African and other populations and discusses the implications of these polymorphisms for neuropharmacotherapy.

Dose-response relationships for the antipsychotic effects and Parkinsonian side-effects of typical neuroleptic drugs: practical and theoretical implications

1. From a review of published literature it is concluded that the minimum dose of a neuroleptic drug (NLD) required to alleviate psychosis is very similar to that producing minimal parkinsonian side effects (PSE). This conclusion is reached both from group comparisons and individual comparisons of dose/response relations (DRR) for the two effects. 2. A lower dose of NLD is usually sufficient to prevent relapse in well stabilized patients than is needed to check an active psychotic state. 3. Anticholinergic agents used to reduce side effects of typical NLD can retard the therapeutic process during neuroleptic treatment of acute psychosis. Although it is not fully established that this is a central interaction, it is consistent with the idea that minimal side effects are a necessary condition for therapeutic effectiveness with typical antipsychotic drugs. 4. In relapse-free maintenance of psychosis-prone patients, tolerance occurs to PSE. Thus few patients need experience prolonged side effects during maintenance treatment with neuroleptics. 5. The evidence reviewed is discussed with respect to a previous hypothesis of the supposedly "indirect" action of typical neuroleptic drugs in therapy for psychosis. The evidence is consistent with the idea of a close causal relation between minimal PSE of these drugs, and their therapeutic effectiveness in the acute stage of treatment.

Paroxetine potentiates the central nervous system side effects of perphenazine: contribution of cytochrome P4502D6 inhibition in vivo

BACKGROUND

Paroxetine is a frequently used antidepressant and a potent inhibitor of the CYP2D6 isozyme in vitro (inhibition constant [Ki] = 0.15 micromol/L). Most classic antipsychotic agents such as perphenazine are metabolized by the CYP2D6 isozyme and are often coadministered with antidepressant agents. This study assessed the extent of changes in CYP2D6 isozyme activity in vivo after pretreatment with paroxetine and its consequences on perphenazine kinetics and central nervous system effects.

METHODS

Eight extensive metabolizers for CYP2D6 were administered a single dose of perphenazine (0.11 mg/kg orally) or placebo following a randomized double-blind design. Perphenazine plasma concentrations and effects were assessed for a period of 8 hours. Subsequently, subjects were treated with a standard therapeutic dose of paroxetine (20 mg/day orally) for 10 days and test sessions with perphenazine and placebo were repeated.

RESULTS

Paroxetine treatment resulted in a twofold to 21-fold decrease in CYP2D6 activity (p < 0.001). After pretreatment with paroxetine, perphenazine peak plasma concentrations increased twofold to 13-fold (p < 0.01). This was associated with a significant increase in central nervous system side effects of perphenazine, including oversedation, extrapyramidal symptoms, and impairment of psychomotor performance and memory (p < 0.05).

CONCLUSION

Coadministration of perphenazine after pretreatment with a standard therapeutic dose of paroxetine increased the plasma concentration and central nervous system side effects of perphenazine, primarily as a result of inhibition of the CYP2D6 isozyme. In patients who are at steady state with paroxetine, a reduction of perphenazine dose may be required to prevent central nervous system side effects.

Motor and mental aspects of acute extrapyramidal syndromes

Acute extrapyramidal syndromes (EPS) are one of the major limitations to effective neuroleptic treatment. These disorders have both motor (objective) and mental (subjective) aspects, which must be considered in any evaluation and differential diagnosis of treatment-related side effects. The disorders of akathisia, acute dystonia and parkinsonism have unique features that are best understood in the context of a careful assessment of patient characteristics, drug factors and temporal aspects. Though acute EPS are commonly explained on the basis of dopamine D2 receptor antagonism, data from several lines of study raise important questions about this hypothesis. The roles of receptor subtype specificity, brain region selectivity and ratios of different receptor subtype antagonism are discussed. New and novel antipsychotic drugs with low rates of EPS are important clinical advancements that will increase patients' ability to participate in therapy and rehabilitation and thus improve their quality of life.

Treatment of schizophrenia: a clinical and preclinical evaluation of neuroleptic drugs

Forty years after the first clinical report on the effectiveness of chlorpromazine in psychiatric patients, neuroleptic drugs are still the most widely used drugs in the treatment of schizophrenia. Indeed, there are no other drugs which have proven to be as effective in the treatment of this severe psychiatric disorder. Yet, there are still many unresolved problems relating to neuroleptic drugs. The present review gives a comprehensive overview of our knowledge (and our lack of knowledge) with respect to the clinical and preclinical effects of neuroleptic drugs and tries to integrate this knowledge in order to identify the neuronal mechanisms underlying the therapeutic and side effects of neuroleptic drugs.

Fluoxetine and trifluoperazine in human brain: a 19F-nuclear magnetic resonance spectroscopy study

Fluorine-19 (19F) is a nonradioactive isotope that is well-suited to nuclear magnetic resonance spectroscopy (NMRS) and is a constituent of several medications used to treat psychiatric illnesses. Fluoxetine, a trifluorinated agent, generated a signal from brain that was readily measured by 19F-NMRS. Estimated brain concentrations ranged from 1.3-5.7 micrograms/ml in six subjects at a steady state dose of 40 mg/day. Enhanced sensitivity of 19F has been obtained by conforming the surface coil to the shape of the forehead. Hence, at the current state of development, 19F-NMRS can be applied to clinical questions relevant to concentrations of fluoxetine in brain. We also report observation of NMRS signals from fluorinated neuroleptics in a number of patients at steady state. These signals continue to be difficult to obtain, although a correlation between dose and estimated brain concentrations is suggested.

Disposition of the neuroleptic zuclopenthixol cosegregates with the polymorphic hydroxylation of debrisoquine in humans

The pharmacokinetics of a single oral dose of the neuroleptic drug zuclopenthixol (10 or 6 mg) was studied in 6 extensive and 6 poor metabolizers of debrisoquine. The peak plasma concentrations of zuclopenthixol did not differ between the phenotypes, whereas the plasma elimination half-life was significantly longer in poor than in extensive metabolizers (29.9 +/- 6.6 vs 17.6 +/- 6.9 h). Accordingly, the total oral plasma clearance was lower in poor than in extensive metabolizers (0.78 +/- 0.27 vs 2.12 +/- 0.65 1/h/kg). Ten of the volunteers had previously participated in a similar study in which the kinetics of perphenazine, another neuroleptic drug, were studied in poor and in extensive metabolizers of debrisoquine. There was a significant correlation between the oral clearance of perphenazine and that of zuclopenthixol among these 10 subjects. The study indicates that the disposition of zuclopenthixol, as well as that of perphenazine, is related to the genetically determined capacity to hydroxylate debrisoquine. The significance of this polymorphism for the clinical use of neuroleptics is discussed.

Neuroleptic drug-induced extrapyramidal syndromes and tardive dyskinesia

Neuroleptic (antipsychotic) drug-induced acute extrapyramidal syndromes (EPS) and the late onset tardive dyskinesia (TD) are the major side effects that limit the use of these highly efficacious agents. The appropriate strategy for controlling these side effects is based on the clinical presentations, pathophysiological mechanisms, and contributions of patient and treatment-related risk factors. New information about the mechanisms of action of neuroleptics and the long-term outcome of acute EPS and TD provide valuable insights into these syndromes. The most effective method for maximizing the benefits and minimizing the risks of neuroleptics is to use the lowest effective dose of both neuroleptic and antiEPS drugs in patients who benefit from them. The next major advancement will be to develop new compounds which effectively control psychotic symptoms and are free of the undesirable acute and tardive motor syndromes.

Perphenazine decanoate and cis(z)-flupentixol decanoate in maintenance treatment of schizophrenic outpatients. Serum levels at the minimum effective dose

Two groups of schizophrenic outpatients were treated with perphenazine decanoate (N = 20) and cis(z)-flupentixol decanoate (N = 24) respectively. Every 3 months the dose was gradually reduced until symptoms appeared that were suggestive of a prodromal phase of a psychotic episode. A slightly higher dose was then promptly reinstituted (the minimum effective dose). At each dose level, two blood samples were drawn for determination of serum concentration. The mean minimum effective dose of perphenazine decanoate was 99.3 mg/2 weeks (range 21.6-270.5), while the mean minimum effective dose of cis(z)-flupentixol decanoate was 60 mg/2 weeks (range 20-250). The corresponding mean serum level of perphenazine decanoate was 7.3 nmol/l (range 2.0-18.1) and of cis(z)-flupentixol decanoate 7.8 nmol/l (range 1.2-37.0). There was a significant correlation between the administered doses and the corresponding serum levels for both drugs (r = 0.87, P less than 0.01). A weak positive correlation was found between serum levels at the minimum effective dose and symptom intensity (BPRS total score) (r = 0.53, P less than 0.02) for perphenazine, but not cis(z)-flupentixol. No correlation was found between serum levels and side effects or length of neuroleptic treatment. It is concluded that the serum drug concentrations corresponding to the lowest effective dose are so variable that routine serum level monitoring may be of limited value in the long-term maintenance treatment of schizophrenia.

Neuroleptic side effects: acute extrapyramidal syndromes and tardive dyskinesia

The neuroleptic-induced motor system side effects of acute extrapyramidal syndromes (EPS) and tardive dyskinesia (TD) are the major limitations of these drugs. Effective strategies for managing these problems are based on the clinical presentations, pathophysiological processes, and a complex interaction of patient and treatment variables. New concepts about the causes and long-term outcome of acute EPS and TD are emerging to challenge some of the commonly held views about these syndromes. The primary method of preventing undue side effects is to use the lowest effective dose of both neuroleptic and anti-EPS drugs. The pressing need is for novel compounds which treat schizophrenia and are free of the undesirable motor system effects (a nonneuroleptic neuroleptic).

Serum levels and clinical response in long-term pharmacotherapy with zuclopenthixol decanoate

Twenty-six patients diagnosed as chronic schizophrenics were given injections of zuclopenthixol decanoate (cis(Z)-clopenthixol decanoate) 200 mg every 3 weeks for at least 6 months. Before treatment and on each day of injection the patients' mental state was assessed by Brief Psychiatric Rating Scale (BPRS), 18 items. A registration of side effects and basal laboratory data was also performed. Blood samples were drawn on each day of injection before injection and 3-7 days after injection (time of maximum concentration). Neuroleptic activity, which was considered equivalent to the concentration of zuclopenthixol, was determined in serum by radio-receptor assay (RRA). Based on amelioration scores greater than or equal to 50% on the BPRS, 15 patients were characterized as responders and 11 as non-responders. The responder group showed a statistically significant reduction in BPRS score, whereas this was not the case for the non-responders. Apart from a few patients, the serum concentrations showed a low intra-individual variation, but a relatively high inter-individual variation. The responder group had a significantly higher mean pre-injection concentration than the non-responder group, whereas no significant difference was found in day 3-7 concentrations. The fluctuation of the serum concentration expressed as the ratio between maximum (days 3-7) and minimum (pre-inj.) was found to be significantly lower for responders than for non-responders. Thus although the present study did not demonstrate a clear relationship between serum level and clinical effect, it indicates that the best antipsychotic effect is obtained with a serum concentration which fluctuates only slightly (the ratio max/min concentration not exceeding 2.1).

Therapeutic advantages of monitoring plasma concentrations of perphenazine in clinical practice

Two hundred and twenty-eight acute paranoid psychotic in-patients received continuous treatment with perphenazine for a period of at least 5 weeks, before blood samples were taken to determine perphenazine plasma levels and conclusions regarding therapeutic efficacy and motor side effects. Patients with plasma concentrations within the range of 2-6 nmol/l showed an excellent antipsychotic response, concomitantly with a low incidence of extrapyramidal side effects. However, patients with plasma levels below or above this range either demonstrated a poor therapeutic response or a high degree of side effects respectively. The results indicate that with increasing age significantly lower doses of perphenazine are required to ensure an optimal clinical response. No difference, however, was seen between sexes with regard to dose response.

Serum neuroleptic and prolactin levels in schizophrenic patients and clinical response

Following a drug-free placebo period lasting at least 1 week, 10 female and 11 male newly hospitalized schizophrenic patients received chlorpromazine (CPZ) 200 mg/day for 1 week and 400 mg/day the following week. Serum CPZ equivalent (CPZ-E) levels were measured at the end of each week of CPZ treatment with a radioreceptor assay. Chlorpromazine-E levels were significantly higher in females than males, but this finding could be accounted for by differences in body weight. Serum prolactin (PRL) levels were also higher in females than males. After differences in serum CPZ-E level were adjusted for, females still had significantly higher serum PRL levels than males. Serum PRL levels increased between the first and second treatment weeks in females but not in males. Correlations between serum CPZ-E and PRL levels were higher among males than females. Significant improvement for the patient group as a whole was observed during the 2 weeks of treatment, with a strong trend for females to improve more than males. Clinical outcome at this initial period was not predicted by either serum PRL levels or serum CPZ-E levels.

Lateral ventricular size and drug-induced Parkinsonism

Computed Tomography (CT) was used to assess lateral ventricular size in 20 psychiatric inpatients who had participated in at least 5 weeks of a fixed dose chlorpromazine (CPZ) trial. During treatment with CPZ, eight patients had required antiparkinsonian medication for treatment of rigidity. The ventricular brain ratio (VBR) of these eight patients was greater than that of either the 12 patients who did not require antiparkinsonian medication or a similarly aged control group of neurological patients, scanned for tension or migraine headaches. On the basis of these findings it is suggested that large lateral ventricular size may be associated with increased vulnerability to develop drug-induced parkinsonism.

Dose-response relationships of perphenazine in the treatment of acute psychoses

A group of 26 acute psychotic patients received continuous oral treatment with perphenazine for a period of 5 weeks. Once-weekly blood samples were drawn for measurements of perphenazine levels and, simultaneously, the therapeutic outcome was registered. Another 26 acute psychotic patients received continuous oral treatment with perphenazine for a period of up to 4 weeks. A single blood sample was drawn and the perphenazine concentration was related to the appearance of extrapyramidal side effects. The following conclusions were made: (1) a high risk of provoking extrapyramidal side effects was associated with plasma levels of perphenazine above 3 nmol/l; (2) plasma levels below 2 nmol/l were associated with a poor therapeutic outcome; (3) a 'therapeutic window' between 2 and 3 nmol/l gives maximal therapeutic effect with a low risk of provoking extrapyramidal side effects.