In vivo and in vitro myocardial binding of risperidone and 9-hydroxyrisperidone

Clozapine affects the pharmacokinetics of risperidone and inhibits its metabolism and P-glycoprotein-mediated transport in vivo and in vitro: A safety attention to antipsychotic polypharmacy with clozapine and risperidone

Antipsychotic polypharmacy (APP), as one maintenance treatment strategy in patients with schizophrenia, has gained popularity in real-world clinical settings. Risperidone (RIS) and clozapine (CLZ) are the most commonly prescribed second-generation antipsychotics, and they are often used in combination as APP. In this study, the pharmacokinetics of RIS and CLZ in rats were examined after co-administration to explore the reliability and rationality of co-medication with RIS and CLZ. In addition, the effects of CLZ on RIS metabolism and transport in vitro were investigated. The results illustrated that in the 7-day continuous administration test in rats, when co-administered with CLZ, the area under curve and peak concentrations of RIS were increased by 2.2- and 3.1-fold at the first dose, respectively, increased by 3.4- and 6.2-fold at the last dose, respectively. The metabolite-to-parent ratio of RIS was approximately 22% and 33% lower than those of RIS alone group at the first and last doses, respectively. Moreover, CLZ significantly increased RIS concentrations in the brain (3.0-4.8 folds) and cerebrospinal fluid (2.1-3.5 folds) in rats, which was slightly lower than the impact of verapamil on RIS after co-medication. Experiments in vitro indicated that CLZ competitively inhibited the conversion of RIS to 9-hydroxy-RIS with the inhibition constants of 1.36 and 3.0 μM in rat and human liver microsomes, respectively. Furthermore, the efflux ratio of RIS in Caco-2 monolayers was significantly reduced by CLZ at 1 μM. Hence, CLZ may affect the exposure of RIS by inhibiting its metabolism and P-glycoprotein-mediated transport. These findings highlighted that APP with RIS and CLZ might increase the plasma concentrations of RIS and 9-hydroxy-RIS beyond the safety ranges and cause toxic side effects.

Utilizing postmortem drug concentrations in mechanistic modeling and simulation of cardiac effects: a proof of concept study with methadone

Methadone-related poisoning has been found to be the leading and increasing cause of death among intoxication cases in several countries. Aside from respiratory depression, methadone is known to cause QT-prolongation, which may lead to sudden cardiac death. Concentrations in heart tissue should be more accurate for estimating cardiotoxic effects. The aim of this study was to investigate whether the effect of methadone on the QT-interval could be simulated and whether the concentrations in heart tissues allowed for better prediction of the Bazett corrected QT-interval (QTcB). A predictive performance study was conducted using the simulation platform Cardiac Safety Simulator to mimic five literature studies using their described study conditions. Both free and total plasma and heart concentrations were investigated using two different in silico models: the O'Hara-Rudy (ORD) model and the 10 Tusscher (TNNP) model. The results showed that the QTcB of methadone was best predicted either with total plasma using the TNNP model or with free plasma using the ORD model. The ORD model was highly sensitive to the total heart concentrations, resulting in overprediction of the QTcB. The TNNP model also overpredicted the QTcB, but to a lesser degree than the ORD model. Furthermore, due to a low baseline QTcB, the ORD model underpredicted the QTcB for both the free plasma and free heart concentrations. In conclusion, it is possible to simulate the cardiac effects of methadone, yet several elements influence the approach uncertainty including but not limited to biophysically details model of cardiac electrophysiology, exposure data, and input parameters.

Effect of lipid emulsion infusion on paliperidone pharmacokinetics in the acute overdose rat model: A potential emergency treatment for paliperidone intoxication

Paliperidone prolongs cardiac repolarization in a concentration-dependent manner. Meanwhile, continuous infusion of intravenous lipid emulsion (ILE) has been established as a detoxification therapy for lipophilic drugs. However, this change in pharmacokinetics of various drugs following ILE administration remains to be clarified. Our objective is to clarify the effect of continuous infusion of ILE on the pharmacokinetics of overdosed paliperidone in rats. Paliperidone (20mg/kg) was administered orally to free-moving male Wistar rats. Continuous infusion (initial loading dose: 4ml/kg for 10min, followed by 4ml/kg/h for 12h) of ILE or acetated Ringer's solution (AR) was initiated 30min after paliperidone administration. Plasma concentration profile of paliperidone was monitored for 12h after administration. The plasma concentration and tissue/plasma concentration ratios of paliperidone were compared between ILE and AR groups. The rat group infused with ILE showed a higher area under the concentration-time curve (mean [S.D.]: 6102 [900.9] vs. 3407 [992.1]nghml^-1, p=0.02) and longer elimination half-time (t_1/2) (4.1 [0.9] vs. 2.2 [0.4]h, p=0.02) compared with the AR group. Tissue/plasma concentration ratios of paliperidone were lower in ILE rats than in AR rats (1.98 [0.70] vs. 3.82 [1.47] in the heart, p=0.04; 0.28 [0.29] vs. 1.27 [0.58] in the brain, p<0.001). In conclusion, continuous infusion of ILE would reduce tissue distribution and prolonged the t_1/2 of paliperidone in rats. These results suggest that continuous infusion of ILE has potential as an emergency treatment for acute paliperidone intoxication.

Risk of cardiovascular morbidity with risperidone or paliperidone treatment: analysis of 64 randomized, double-blind trials

A post hoc analysis of the risperidone (RIS)/paliperidone (Pali) clinical trials database comprising 64 studies was conducted. Risk of sudden death, cardiovascular (CV), and cerebrovascular events during RIS or Pali treatment was estimated. Treatment emergent CV adverse events were identified using 7 prespecified Standardised MedDRA Queries as follows: embolic/thrombotic events, cerebrovascular disorders, ischemic heart disease, cardiac arrhythmias, cardiac failure, torsades/QT prolongation, and convulsions. Risk in the RIS/Pali pooled group was significantly increased compared to placebo for the following adverse events: syncope, tachycardia, palpitations, edema peripheral, dysarthria, and transient ischemic attack. Incidence of death related to CV events was low and similar across groups. Consistent with the known pharmacologic profile and product information, this analysis of treatment emergent adverse event data from a large, randomized, controlled clinical trials database described increased risk versus placebo for several specific CV events. Apart from events described in existing product labeling, no new safety findings emerged.

Prolongation of cardiac ventricular repolarization under paliperidone: how and how much?

INTRODUCTION

Paliperidone (9-hydroxyrisperidone) is a second-generation antipsychotic. As observed with risperidone, QT interval prolongation was reported with paliperidone.

OBJECTIVE

The aim was to evaluate the effects of paliperidone on cardiac ventricular repolarization.

METHODS

(1) Patch-clamp experiments: Human ether-a-go-go-related gene (HERG)- or KCNQ1 + KCNE1-transfected cells were exposed to 0.1-100 μmol/L paliperidone (N = 39 cells, total) to assess the drug effect on HERG and KCNQ1 + KCNE1 currents. (2) Langendorff perfusion experiments: Hearts isolated from male Hartley guinea pigs (N = 9) were exposed to 0.1 μmol/L paliperidone to assess drug-induced prolongation of monophasic action potential duration measured at 90% repolarization. (3) In vivo cardiac telemetry experiments: Guinea pigs (N = 8) implanted with transmitters were injected a single intraperitoneal dose of 1 mg/kg of paliperidone, and 24-hour electrocardiogram recordings were made.

RESULTS

(1) The estimated concentration at which 50% of the maximal inhibitory effect is observed (IC(50)) for paliperidone on HERG current was 0.5276 μmol/L. In contrast, 1 μmol/L paliperidone had hardly any effect on KCNQ1 + KCNE1 current (4.0 ± 1.6% inhibition, N = 5 cells). (2) While pacing the hearts at cycle lengths of 150, 200, or 250 milliseconds, 0.1 μmol/L paliperidone prolonged monophasic action potential duration measured at 90% repolarization by, respectively, 6.1 ± 3.1, 9.8 ± 2.7, and 12.8 ± 2.7 milliseconds. (3) Paliperidone (1 mg/kg) intraperitoneal caused a maximal 15.7 ± 5.3-millisecond prolongation of QTc.

CONCLUSIONS

Paliperidone prolongs the QT interval by blocking HERG current at clinically relevant concentrations and is potentially unsafe.

Effects of CYP2D6 genotype on the pharmacokinetics, pharmacodynamics, and safety of risperidone in healthy volunteers

The objective of this study was to analyze the relationship between CYP2D6 genotype and pharmacokinetics and pharmacodynamics of risperidone. Seventy-one healthy volunteers (36 women and 35 men) received a 1-mg single oral dose of risperidone. Six major CYP2D6 polymorphisms (CYP2D6*3, *4, *5, *6, *7, and *9) and the duplication were detected. Subjects were classified into 4 phenotypic groups: 6 ultrarapid (UMs), 34 extensive (EMs), 25 intermediate (IMs), and 6 poor metabolizers (PMs). There was a clear relationship between the number of active alleles and the pharmacokinetic parameters for risperidone and 9-hydroxyrisperidone, but there were no differences for total active moiety. Area under the curve and half-life of risperidone were significantly higher in PMs and IMs compared with EMs and UMs, which showed higher area under the curve of 9-hydroxyrisperidone. Risperidone produced a small decrease in blood pressure, a mild increase in QTc and a quick increase in prolactin, without significant differences between groups. Surprisingly, the incidence of adverse reactions was lower in PMs (50%) than in other subjects (78%). In conclusion, metabolism of risperidone depends on the number of active CYP2D6 alleles. So, PM subjects show higher concentrations of risperidone and very low concentrations of 9-hydroxyrisperidone. On the contrary, EM and UM subjects show low concentrations of risperidone and high concentrations of 9-hydroxyrisperidone. However, no major pharmacodynamic differences are observed between CYP2D6 genotypes, presumably because of the similar pharmacological activity of parent drug and metabolite.

Drug-induced block of cardiac HERG potassium channels and development of torsade de pointes arrhythmias: the case of antipsychotics

The prolongation of the cardiac repolarization process, a result of the blocking of the Human Ether-a-go-go Related Gene potassium channel, is an undesired accessory property shared by many pharmacological classes of non-cardiovascular drugs. Often the delayed cardiac repolarization process can be identified by a prolongation of the QT interval of the electrocardiograph. In these conditions, premature action potentials can trigger a dangerous polymorphic ventricular tachyarrhythmia, known as torsade de pointes, which occasionally can result in lethal ventricular fibrillation. In this work, brief descriptions of the electrophysiological basis of torsade de pointes and of the several pharmacological classes of torsadogenic drugs are given. Attention is focused on antipsychotics, with a deeper overview on the experimental and clinical reports about their torsadogenic properties.

Myocardium distribution of sertindole and its metabolite dehydrosertindole in guinea-pigs

Sertindole, like other atypical antipsychotics, has been shown to increase the action potential duration and QT interval in a concentration dependent manner, in in vitro electrophysiological studies. However, this does not always translate into increased duration of the QT interval, increased risk of torsade de pointes or sudden death in clinical practice. The reasons for these apparent discrepancies are unclear and many studies have underscored the importance of the interpretation of in vitro electrophysiological data in the context of other pharmacodynamic (e.g. cardiac ion channels target, receptor affinity) and pharmacokinetic parameters (total plasma drug concentration and drug distribution). To address the possible relevance of the concentrations used in experimental studies, the myocardium distribution of sertindole and its metabolite was determined after single and repeated intraperitoneal administration to guinea-pigs. The data suggest that the plasma concentration appears to predict the concentration in the myocardium and that the myocardium concentrations of sertindole are 3.1 times higher than plasma concentrations. Using these data, the relevance of in vitro electrophysiological studies to clinical plasma concentrations has been appraised.

Atypical antipsychotics: from potassium channels to torsade de pointes and sudden death

Syncope and sudden death are features of schizophrenia that can be attributed to ischaemic heart disease, the use of antipsychotics (because of proarrhythmia or other reasons such as pharyngeal dyskinesia) or the psychiatric disease itself. Cases have been described with most antipsychotics and have led to the withdrawal, temporary suspension from the market or restricted use of antipsychotics, such as sultopride, droperidol, sertindole or thioridazine. Reviewing the available data shows that all antipsychotics tested affect the cardiac potassium channel, with the concentration that produces 50% inhibition (IC50) ranging from 1 nmol/L (haloperidol) to 6 micromol/L (olanzapine). Experimental in vitro or in vivo electrophysiological studies have shown a dose-dependent increase in the duration of the action potential with various degrees of indicators of serious arrhythmogenicity. However, this does not always translate clinically into an increased duration of the QT interval or increased risk of torsade de pointes or sudden death in clinical trials or pharmacoepidemiological studies. In turn, QT prolongation in clinical trials does not always translate to an increased risk of torsade de pointes or sudden death. The reasons for these apparent discrepancies are unclear and could be related to insufficiently powered field studies, low plasma and tissue drug concentrations with reference to in vitro data or drug effects on other receptors or ion channels that have a protective effect. Alternatively, risks that were not apparent from preclinical or clinical data could be related to the use of the drug in high-risk patients, metabolic interactions or other factors that would only be encountered in large postmarketing populations. The assessment of cardiovascular safety, both preclinical and during premarketing clinical trials, needs to be supported by appropriately powered pharmacoepidemiology studies.

Risperidone reduces K+ currents in human atrial myocytes and prolongs repolarization in human myocardium

The antipsychotic agent risperidone has been shown to cause QT prolongation. In rabbit heart preparations, we have demonstrated that risperidone markedly lengthened action potential duration and blocked the delayed rectifier current, I(Kr.) The current study was designed to investigate the risperidone effects: (i) on the main K(+) repolarizing currents on human atrial myocytes, using whole-cell patch clamp recordings; (ii) on action potentials recorded from human atrial and ventricular myocardium using conventional microelectrodes. We found that: (1) risperidone (3-30 microM) reduced significantly the sustained current, I(sus), and 30 microM decreased significantly the transient outward current I(to) but was without effect on the inward rectifier current I(K1); (2) risperidone (0.3-10 microM) lengthened significantly the final repolarization of the atrial action potential and risperidone (10 microM) markedly lengthened the final repolarization in ventricular myocardium. This study showed that risperidone exerts direct electrophysiological effects on human preparations but only at relatively high concentration.

Determination of myocardium to plasma concentration ratios of five antipsychotic drugs: comparison with their ability to induce arrhythmia and sudden death in clinical practice

Reviewing available data shows that most of antipsychotic drugs are associated with arrhythmia and sudden death. Experimental studies have shown a HERG channel blockade, a dose-dependent increase in duration of action potential or of QT interval, with various degrees of indicators of serious arrhythmogenicity. However, it seems difficult to relate these in vitro and in vivo preclinical models to clinical findings, in part, because the relationship between concentrations used and in vivo tissue concentrations during treatment in man is not known. Consequently, we established the myocardium to plasma concentration ratios for a series of antipsychotic drugs by intraperitoneal administration of different level doses to the guinea pig. Then, we compared these values to their ability to induce arrhythmia or torsade de pointes in clinical practice. The myocardium to plasma concentration ratios were 2.2 for clozapine, 2.7 for olanzapine, 3.1 for sertindole, 4.5 for risperidone, and 6.4 for haloperidol. These data suggest that when the ratio is higher than 4, arrhythmia and sudden death may be expected. On the contrary, when the ratio is less than 3, little effect may be predicted. These results underscore the importance of interpreting HERG channel data and electrophysiological data in the context of other pharmacokinetic parameters such as myocardium to plasma distribution.