Multivariate pharmacokinetic/pharmacodynamic (PKPD) analysis with metabolomics shows multiple effects of remoxipride in rats.

The study of central nervous system (CNS) pharmacology is limited by a lack of drug effect biomarkers. Pharmacometabolomics is a promising new tool to identify multiple molecular responses upon drug treatment. However, the pharmacodynamics is typically not evaluated in metabolomics studies, although being important properties of biomarkers. In this study we integrated pharmacometabolomics with pharmacokinetic/pharmacodynamic (PKPD) modeling to identify and quantify the multiple endogenous metabolite dose-response relations for the dopamine D2 antagonist remoxipride. Remoxipride (vehicle, 0.7 or 3.5mg/kg) was administered to rats. Endogenous metabolites were analyzed in plasma using a biogenic amine platform and PKPD models were derived for each single metabolite. These models were clustered on basis of proximity between their PKPD parameter estimates, and PKPD models were subsequently fitted for the individual clusters. Finally, the metabolites were evaluated for being significantly affected by remoxipride. In total 44 metabolites were detected in plasma, many of them showing a dose dependent decrease from baseline. We identified 6 different clusters with different time and dose dependent responses and 18 metabolites were revealed as potential biomarker. The glycine, serine and threonine pathway was associated with remoxipride pharmacology, as well as the brain uptake of the dopamine and serotonin precursors. This is the first time that pharmacometabolomics and PKPD modeling were integrated. The resulting PKPD cluster model described diverse pharmacometabolomics responses and provided a further understanding of remoxipride pharmacodynamics. Future research should focus on the simultaneous pharmacometabolomics analysis in brain and plasma to increase the interpretability of these responses.

Revealing the Neuroendocrine Response After Remoxipride Treatment Using Multi-Biomarker Discovery and Quantifying It by PK/PD Modeling.

To reveal unknown and potentially important mechanisms of drug action, multi-biomarker discovery approaches are increasingly used. Time-course relationships between drug action and multi-biomarker profiles, however, are typically missing, while such relationships will provide increased insight in the underlying body processes. The aim of this study was to investigate the effect of the dopamine D2 antagonist remoxipride on the neuroendocrine system. Different doses of remoxipride (0, 0.7, 5.2, or 14 mg/kg) were administered to rats by intravenous infusion. Serial brain extracellular fluid (brainECF) and plasma samples were collected and analyzed for remoxipride pharmacokinetics (PK). Plasma samples were analyzed for concentrations of the eight pituitary-related hormones as a function of time. A Mann-Whitney test was used to identify the responding hormones, which were further analyzed by pharmacokinetic/pharmacodynamic (PK/PD) modeling. A three-compartment PK model adequately described remoxipride PK in plasma and brainECF. Not only plasma PRL, but also adrenocorticotrophic hormone (ACTH) concentrations were increased, the latter especially at higher concentrations of remoxipride. Brain-derived neurotropic factor (BDNF), follicle stimulating hormone (FSH), growth hormone (GH), luteinizing hormone (LH), and thyroid stimulating hormones (TSH) did not respond to remoxipride at the tested doses, while oxytocin (OXT) measurements were below limit of quantification. Precursor pool models were linked to brainECF remoxipride PK by Emax drug effect models, which could accurately describe the PRL and ACTH responses. To conclude, this study shows how a multi-biomarker identification approach combined with PK/PD modeling can reveal and quantify a neuroendocrine multi-biomarker response for single drug action.

Mechanism-based PK-PD model for the prolactin biological system response following an acute dopamine inhibition challenge: quantitative extrapolation to humans.

The aim of this investigation was to develop a mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) model for the biological system prolactin response following a dopamine inhibition challenge using remoxipride as a paradigm compound. After assessment of baseline variation in prolactin concentrations, the prolactin response of remoxipride was measured following (1) single intravenous doses of 4, 8 and 16 mg/kg and (2) following double dosing of 3.8 mg/kg with different time intervals. The mechanistic PK-PD model consisted of: (i) a PK model for remoxipride concentrations in brain extracellular fluid; (ii) a pool model incorporating prolactin synthesis, storage in lactotrophs, release into- and elimination from plasma; (iii) a positive feedback component interconnecting prolactin plasma concentrations and prolactin synthesis; and (iv) a dopamine antagonism component interconnecting remoxipride brain extracellular fluid concentrations and stimulation of prolactin release. The most important findings were that the free brain concentration drives the prolactin release into plasma and that the positive feedback on prolactin synthesis in the lactotrophs, in contrast to the negative feedback in the previous models on the PK-PD correlation of remoxipride. An external validation was performed using a dataset obtained in rats following intranasal administration of 4, 8, or 16 mg/kg remoxipride. Following simulation of human remoxipride brain extracellular fluid concentrations, pharmacodynamic extrapolation from rat to humans was performed, using allometric scaling in combination with independent information on the values of biological system specific parameters as prior knowledge. The PK-PD model successfully predicted the system prolactin response in humans, indicating that positive feedback on prolactin synthesis and allometric scaling thereof could be a new feature in describing complex homeostatic mechanisms.

Systemic and direct nose-to-brain transport pharmacokinetic model for remoxipride after intravenous and intranasal administration.

Intranasal (IN) administration could be an attractive mode of delivery for drugs targeting the central nervous system, potentially providing a high bioavailability because of avoidance of a hepatic first-pass effect and rapid onset of action. However, controversy remains whether a direct transport route from the nasal cavity into the brain exists. Pharmacokinetic modeling is proposed to identify the existence of direct nose-to-brain transport in a quantitative manner. The selective dopamine-D2 receptor antagonist remoxipride was administered at different dosages, in freely moving rats, by the IN and intravenous (IV) route. Plasma and brain extracellular fluid (ECF) concentration-time profiles were obtained and simultaneously analyzed using nonlinear mixed-effects modeling. Brain ECF/plasma area under the curve ratios were 0.28 and 0.19 after IN and IV administration, respectively. A multicompartment pharmacokinetic model with two absorption compartments (nose-to-systemic and nose-to-brain) was found to best describe the observed pharmacokinetic data. Absorption was described in terms of bioavailability and rate. Total bioavailability after IN administration was 89%, of which 75% was attributed to direct nose-to brain transport. Direct nose-to-brain absorption rate was slow, explaining prolonged brain ECF exposure after IN compared with IV administration. These studies explicitly provide separation and quantitation of systemic and direct nose-to-brain transport after IN administration of remoxipride in the rat. Describing remoxipride pharmacokinetics at the target site (brain ECF) in a semiphysiology-based manner would allow for better prediction of pharmacodynamic effects.

Online solid phase extraction with liquid chromatography-tandem mass spectrometry to analyze remoxipride in small plasma-, brain homogenate-, and brain microdialysate samples.

Remoxipride is a selective dopamine D(2) receptor antagonist, and useful as a model compound in mechanism-based pharmacological investigations. To that end, studies in small animals with serial sampling over time are needed. For these small volume samples currently no suitable analytical methods are available. We propose analytical methods for the detection of low concentrations remoxipride in small sample volumes of plasma, brain homogenate, and brain microdialysate, using online solid phase extraction with liquid chromatography-tandem mass spectrometry. Method development, optimization and validation are described in terms of calibration curves, extraction yield, lower limit of quantification (LLOQ), precision, accuracy, inter-day- and intra-day variability. The 20 microl plasma samples showed an extraction yield of 76%, with a LLOQ of 0.5 ng/ml. For 0.6 ml brain homogenate samples the extraction yield was 45%, with a LLOQ of 1.8 ng/ml. The 20 microl brain microdialysate samples, without pre-treatment, had a LLOQ of 0.25 ng/ml. The precision and accuracy were well within the acceptable 15% range. Considering the small sample volumes, the high sensitivity and good reproducibility, the analytical methods are suitable for analyzing small sample volumes with low remoxipride concentrations.

Evaluation of osmotic effects on coated pellets using a mechanistic model.

The aim of this study was to develop a simple experimental methodology and to develop a mechanistic model to characterize the release mechanism from pellets developing cracks during the release process with special focus on osmotic effects. The release of remoxipride from pellets coated with an ethyl cellulose film was chosen as a case study. Dose release experiments at different bulk osmotic pressures revealed that the release process was mainly osmotically driven. The model was used to calculate the solvent permeability of the coating, 1.1 x 10(-10)m(2)h(-1)MPa(-1). The model was validated by release experiments using similar pellets having different coating thicknesses. The effective diffusion coefficient of remoxipride in the coating was also calculated and found to be 1.7 x 10(-10)m(2)h(-1). A series of experiments was performed in which the osmotic pressure of the receiving solution was changed during the experiment. From the results of these experiments, the area of the cracks in the film, formed by the hydrostatic pressure built up inside the pellets, was estimated to be 3.5 x 10(-5)m(2)/m(2) coating. It could also be deduced that the solvent permeability of the coating film was affected by swelling in the same way at different osmotic pressures.

Pharmacology of the atypical antipsychotic remoxipride, a dopamine D2 receptor antagonist.

Remoxipride is a substituted benzamide that acts as a weak but very selective antagonist of dopamine D2 receptors. It was introduced by Astra (Roxiam) at the end of the eighties and was prescribed as an atypical antipsychotic. This article reviews its putative selective effects on mesolimbic versus nigrostriatal dopaminergic systems. In animals, remoxipride has minimal cataleptic effects at doses that block dopamine agonist-induced hyperactivity. These findings are predictive of antipsychotic activity with a low likelihood of extrapyramidal symptoms. Remoxipride also appears to be effective in more recent animal models of schizophrenia, such as latent inhibition or prepulse inhibition. In clinical studies, remoxipride shows a relatively low incidence of extrapyramidal side effects and its effects on prolactin release are short-lasting and generally mild. The clinical efficacy of remoxipride is similar to that of haloperidol or chlorpromazine. Although its clinical use was severely restricted in 1993, due to reports of aplastic anemia in some patients receiving remoxipride, this drug has been found to exhibit relatively high selectivity for dopamine D2 receptors making remoxipride an interesting tool for neurochemical and behavioral studies.

Single dose pharmacodynamics of thioridazine and remoxipride in healthy younger and older volunteers.

Phenothiazines are widely used in older patients, but little experimental work has been carried out in this age group. Two groups of healthy volunteers, a younger group (Y: six males and six females, aged 20-42 years) and an older group (O: six males and eight females, aged 65-77 years) took part in a randomized double-blind three-period crossover study in which they received by mouth single doses of thioridazine (Y: 50 mg; O: 25 mg) remoxipride (Y: 100 mg; O: 50 mg) or placebo. Measures of central nervous system (CNS) and haemodynamic function were carried out before drug administration and at 1.5-h intervals up to 9 h post-dose, and blood samples were collected over a 24-h period. No significant differences in dose-corrected pharmacokinetic variables were found between the two groups. There was evidence of marked CNS depressant effects of thioridazine from both objective and subjective measures. The effects for remoxipride were similar, though generally less marked. After allowance was made for dose, there was little indication of any difference in degree of CNS depression between the two age groups. Haemodynamic measures showed orthostatic reductions in blood pressure with thioridazine which were particularly marked in the older group, who also showed lower compensatory increases in pulse rate. These results indicate potential problems with orthostatic hypotension with thioridazine in older patients. CNS depression may also be a problem, especially in patients with compromised cholinergic function.

Stereoselective determination of R-(+)- and S-(-)-remoxipride, a dopamine D2-receptor antagonist, in human plasma by chiral high-performance liquid chromatography.

A stereoselective high-performance liquid chromatographic (HPLC) method is described for the selective and sensitive quantitation in human plasma of R-(+)- and S-(-)-enantiomers of remoxipride. Remoxipride was extracted from basified plasma into hexane-methyl-tert.-butyl ether (20:80, v/v), washed with sodium hydroxide (1.0 M), then back-extracted into phosphoric acid (0.1 M). A structural analog of remoxipride was used as an internal standard. The sample extracts were chromatographed using a silica-based derivatized cellulose chiral column, Chiralcel OD-R, and a reversed-phase eluent containing 30-32% acetonitrile in 0.1 M potassium hexafluorophosphate. Ultraviolet (UV) absorbance detection was performed at 214 nm. Using 0.5-ml plasma aliquots, the method was validated in the concentration range 0.02-2.0 microg/ml and was applied in the investigation of systemic inversion of remoxipride enantiomers in man.

Disposition of remoxipride in Chinese schizophrenic patients.

The disposition of remoxipride was evaluated in 13 male chronic schizophrenic patients. A single 150 mg dose of remoxipride was administered and blood sampling performed over the following 48 hours. The mean (SD) oral clearance and half-life of remoxipride were 74.46 (25.9) ml/min and 5.46 (0.87) hours, respectively. The mean (SD) AUC for remoxipride was 25,320 (9,820) ng.h/ml. A wide interpatient variability was observed. Compared to Caucasian studies there were no significant differences in the disposition of remoxipride.

Prolactin release after remoxipride by an integrated pharmacokinetic-pharmacodynamic model with intra- and interindividual aspects.

An integrated pharmacokinetic-pharmacodynamic model is suggested for remoxipride and its effect on prolactin (PRL) release acting by preventing the inhibitory effect of dopamine D2 receptors in the anterior pituitary. The model was implemented to describe the time course of PRL plasma levels after administration of two consecutive doses of remoxipride at 5 different time intervals, 2, 8, 12, 24 and 48 hr. The model used is an indirect response model. It consists of three parts: 1) the pharmacokinetics of remoxipride; 2) a physiological substance model for PRL, incorporating the synthesis of PRL and its release into and elimination from plasma; and 3) a pharmacodynamic model describing the influence of remoxipride on the PRL release from the pool. A linear pharmacodynamic model gave the best description of the time course of PRL. The limitation in the PRL release is the amount available in the pool, which takes 24 to 48 hr to fully restore, rather than a maximal effect of remoxipride. The intra- and interindividual variability of remoxipride as well as of the PRL response was low.

Influence of the dosing interval on prolactin release after remoxipride.

1. The prolactin response following administration of the D2-dopamine receptor antagonist remoxipride was studied in eight healthy male volunteers. The purpose of the study was to investigate the duration of a refractory period of prolactin release following two doses of remoxipride. A further aim was to compare the prolactin response following remoxipride and thyrotropin release hormone (TRH) during the refractory period. The subjects received two 30 min intravenous (i.v.) infusions of remoxipride 50 mg with different time intervals between the two doses, in a randomized six period crossover design. The time intervals between the two remoxipride doses were 2, 8, 12, 24 and 48 h. On one occasion the remoxipride dose was followed by an i.v. injection of TRH after 2 h. 2. The plasma peak prolactin concentrations obtained after the first remoxipride dose correspond to a maximal release of prolactin according to earlier studies. A small second peak of prolactin was observed after 2 h. The release was gradually increased with longer time intervals between the consecutive doses. The refractory period for a second prolactin release similar to the first one after remoxipride was found to be 24 h for most of the subjects. 3. TRH resulted in a faster and higher increase in prolactin response of a shorter duration than after remoxipride administered 2 h after the first dose.

Neurochemical effects of prolonged treatment with remoxipride as assessed by intracerebral microdialysis in freely moving rats.

1. At three microdialysis sessions, dialysates were collected from the striatum of the same rats. 2. Microdialysis session 1. A single s.c. injection of remoxipride (40 mumol/kg), resulted in increased dialysate concentrations of dopamine, DOPAC and HVA. 3. Microdialysis session 2. Continuous administration of remoxipride (8.6 mumol/rat/day) for 14 days, using mini-osmotic pumps, produced maintained elevated levels of dopamine, DOPAC and HVA. 4. Microdialysis session 3. A challenge dose of remoxipride (40 mumol/kg s.c.), given to the rats after a 48-hour wash-out period following the continuous remoxipride treatment, increased the dialysate concentrations of dopamine, DOPAC and HVA to similar extent as at dialysis session 1. 5. It is concluded that after long-term treatment of remoxipride, an adaptation of the basal state of the DA system appears to take place, implying a lowering of basal DA release and DA metabolism. However, the capacity to respond with increased DA release and DA metabolism to renewed remoxipride treatment is retained, indicating little, if any, tolerance.

[Determination of remoxipride in cadaver blood using high pressure liquid chromatography]. / Bestimmung von Remoxiprid in Leichenblut mittels Hochdruckflüssigkeitschromatographie.

The suitability of high pressure liquid chromatography (HPLC) for determining remoxipride levels in cadaver blood was tested in a case of possible remoxipride intoxication. Level in our case was found to be lower than in cases of remoxipride poisoning described in the literature. The procedure developed for using HPLC to measure remoxipride levels in cadaver blood is described in detail. Using this method a distinction could be made between remoxipride and sulpiride.

[New psychopharmacologic alternatives in treatment of schizophrenia]. / Nouvelles alternatives psychopharmacologiques au traitement de la schizophrénie.

Clozapine, risperidone and remoxipride are three neuroleptics that represent an interesting alternative in the psychopharmacological treatment of schizophrenia. Pharmacodynamic and pharmacokinetic properties, efficacy, dosages as well as the indication of these three substances are studied. In certain particular situations, a complementary treatment is of important therapeutic use, the addition of benzodiazepines, lithium, carbamazepine or beta-blockers are discussed.

In vivo validation of the release rate and palatability of remoxipride-modified release suspension.

Remoxipride, a D2-dopamine receptor antagonist, is well tolerated and completely absorbed after oral administration. Because of its extremely bitter taste, an oral palatable suspension was developed by using a taste-masking microencapsulation. The bioavailability of remoxipride was investigated in two studies in healthy volunteers after administration of a 100-mg dose in suspension. The first study used a capsule as reference, and the second study a plain solution. Taste assessment was carried out in the second study. The extent of bioavailability was the same when comparing the oral suspension to a capsule and to a plain solution. However, the rate of absorption is delayed, and Tmax was 3.0 hr after the suspension, 1.0 hr after the oral solution, and 1.6 hr after the capsule. The release rate in vitro from the suspension was determined by applying the USP-paddle method. By using numerical convolution and deconvolution, the release rates in vivo and in vitro were shown to be similar when using water with 0.5% sodium lauryl sulfate as dissolution liquid. The taste-masked oral suspension is suitable for full-scale production, with good control of the encapsulation process and of the preparation of a suspension.

The pharmacokinetics of remoxipride and metabolites in patients with various degrees of renal function.

1. The pharmacokinetics of remoxipride, a new neuroleptic, were investigated in an open study with three parallel groups. Twenty-one patients with severely impaired (ClCr < 25 ml min-1), moderately impaired (ClCr 25-50 ml min-1) and normal (ClCr > 65 ml min-1) renal function were evaluated. A single oral dose of remoxipride hydrochloride 100 mg was administered, and blood and urine were collected over 48 h. Concentrations of remoxipride and metabolites were measured by h.p.l.c. 2. In patients with severely decreased renal function, the AUC and Cmax of remoxipride were increased significantly, and t1/2 was prolonged, as compared with the control patients. The renal clearance and urinary recovery of the unchanged drug were significantly diminished. 3. The unbound fraction of remoxipride in plasma was decreased in patients with renal failure, in association with a disease-related increase in alpha 1-acid glycoprotein. In spite of a 25% recovery of unchanged drug in the urine in patients with normal renal function, the AUC of unbound drug was twice as high in patients with severely impaired renal function. 4. A strong correlation between creatinine clearance and renal drug clearance was observed indicating a direct relationship between kidney function and the renal clearance of remoxipride. 5. Remoxipride was the predominant compound in plasma as well as in urine in patients with severely decreased as well as normal renal function. In patients with severely decrease renal function, remoxipride and all five pharmacologically inactive metabolites showed increased peak plasma concentrations, delayed tmax, increased AUC, prolonged half-lives and decreased renal clearance.

Disposition of remoxipride in different species. Species differences in metabolism.

The pharmacokinetics and metabolism of the new antipsychotic agent remoxipride ((S)-(-)-3-bromo-N(-)[(1-ethyl-2-pyrrolidinyl)methyl]-2, 6-dimethoxybenzamide, FLA731(-), Roxiam, CAS 80125-14-0) was studied in rodents (mice, rats, hamsters), dogs and human subjects using the unlabelled or the labelled (3H or 14C) drug. Oral administration of 20-40 mumol/kg to animals and approximately 3 mumol/kg to human volunteers showed that the absorption of remoxipride through the intestinal wall was rapid and almost complete in all species. However, the bioavailability was low in the rodents (< 10% in mice and hamsters and < 1% in rats) due to an extensive first-pass elimination in the hepato-portal system. Blood clearance estimated after the same intravenous doses was high in rodents and similar to or exceeding normal liver blood flow. In dogs and humans, clearance values were low and the bioavailability high (> 90%). In mice and rats the contribution of renal clearance to the total clearance was approximately 10%, while it was higher in dogs (approximately 15%) and humans (approximately 30%). Species differences were also observed in the degree of protein binding which was low in rodent plasma (20-30%) but fairly high in canine and human plasma (approximately 80%). In dogs and humans, remoxipride was shown to bind primarily to the plasma alpha 1-acid glycoprotein fraction. In accordance with the binding data, the volume of distribution (Vss) was higher in rodents (3-6 l/kg) than in dogs (1.6 l/kg) and man (0.7 l/kg). Studies in dogs with 14C-remoxipride showed that the compound was rapidly distributed to tissues and eliminated at rates similar to that in plasma (t1/2 3-4 h). Retention of radioactivity was only observed in melanin-rich tissues. However, studies in pigmented mice showed that the affinity of remoxipride to melanin was lower than that of the other neuroleptics haloperidol and chlorpromazine. The excretion of radioactivity following oral administration of the labelled drug mainly occurred in the urine in all species. However, species differences were observed in the identification and analysis of the various metabolites present in plasma and excreted in urine. In rodents, metabolic reactions occurred mainly at the aromatic moiety, i.e. O-demethylation and aromatic hydroxylation. The resulting phenols were excreted mainly in conjugated forms. In dogs and humans, the predominant metabolic reactions were oxidations at the alpha-carbons of the pyrrolidine moiety leading to N-demethylated and/or pyrrolidone and hydroxypyrrolidone products.(ABSTRACT TRUNCATED AT 400 WORDS)

Concentrations of remoxipride and its phenolic metabolites in rat brain and plasma. Relationship to extrapyramidal side effects and atypical antipsychotic profile.

The cataleptic effect of remoxipride was examined in the horizontal bar test after i.v.,i.p. and s.c. administration to male rats. Remoxipride induced immediate catalepsy after high i.v. doses (ED50 = 49 mumol/kg) while peak effects were seen 60-90 min after i.p. administration (ED50 = 38 mumol/kg). Following s.c. administration remoxipride failed to produce a statistically significant catalepsy in the 20-100 mumol/kg dose range (ED50 > 100 mumol/kg). In contrast, haloperidol was found to be more effective in inducing catalepsy after i.v. (ED50 = 0.4 mumol/kg) than after i.p. or s.c. administration (ED50 = 0.9 mumol/kg). The atypical antipsychotic profile of remoxipride was more pronounced when the compound was given i.v. or s.c. as compared with the i.p. route. Plasma and brain (striatum and nucleus accumbens) concentrations of remoxipride and its active phenolic metabolites FLA 797(-) and FLA 908(-) were measured by high performance liquid chromatography. The 40 mumol/kg dose of remoxipride resulted in plasma and brain concentrations of remoxipride which were 300-1000-fold higher (depending on the route of administration) than the most potent of the phenolic metabolites, e.g., FLA 797(-). The plasma and brain concentrations of remoxipride and its phenolic metabolites were related to DA D2 receptor blocking potency and to the temporal course and effectiveness to induce catalepsy. This analysis suggested that the unbound concentrations of the phenolic metabolites were too low to play a major role in the DA blocking action of remoxipride. However, FLA 797(-) may contribute marginally to the cataleptic effects following high (i.p.) doses of remoxipride.