Riluzole Serum Concentration in Pediatric Patients Treated for Obsessive-Compulsive Disorder.

PURPOSE/BACKGROUND: The goals of this study were to determine whether pediatric serum concentration of riluzole is similar to that observed in adults and to determine whether riluzole serum concentration is associated with adverse effects or efficacy in children and adolescents with treatment-refractory obsessive-compulsive disorder. METHODS/PROCEDURES: Data were drawn from previously published studies: 1 open-label trial and 1 randomized controlled trial with an open-label extension phase. Serum was drawn at 24, 36, and 52 weeks in 37 patients who were taking approximately 100 mg riluzole daily (mean dose at 24 weeks, 99 ± 28 mg). FINDINGS/RESULTS: Across all samples, serum riluzole concentration ranged from 7 to 963 ng/mL. At week 24 (n = 37), the median concentration was 76 ng/mL (interquartile range, 53-172 ng/mL). Within-patient concentration was relatively stable. One subject who had the highest serum concentration levels during the study developed pancreatitis after exiting the study. The patient had recently added fluvoxamine to the riluzole regimen. Controlling for concomitant fluvoxamine (in 6 participants) and time of draw, serum riluzole concentration was not associated with obsessive-compulsive disorder symptom severity, nor was it associated with adverse effect profile. IMPLICATIONS/CONCLUSIONS: The dose of riluzole used in these pediatric subjects seems to have achieved serum concentration levels similar to those observed in adults. However, as previously reported in adults, the serum concentration had no discernable relationship to efficacy or adverse effects.

Riluzole prodrugs for melanoma and ALS: design, synthesis, and in vitro metabolic profiling.

Riluzole (1) is an approved therapeutic for the treatment of ALS and has also demonstrated anti-melanoma activity in metabotropic glutamate GRM1 positive cell lines, a mouse xenograft assay and human clinical trials. Highly variable drug exposure following oral administration among patients, likely due to variable first pass effects from heterogeneous CYP1A2 expression, hinders its clinical use. In an effort to mitigate effects of this clearance pathway and uniformly administer riluzole at efficacious exposure levels, several classes of prodrugs of riluzole were designed, synthesized, and evaluated in multiple in vitro stability assays to predict in vivo drug levels. The optimal prodrug would possess the following profile: stability while transiting the digestive system, stability towards first pass metabolism, and metabolic lability in the plasma releasing riluzole. (S)-O-Benzyl serine derivative 9 was identified as the most promising therapeutically acceptable prodrug.

Quantitative estimation of riluzole in human plasma by LC-ESI-MS/MS and its application to a bioequivalence study.

A novel simple, sensitive, selective, and rapid high-performance liquid chromatography coupled with tandem mass spectrometry method was developed and validated for quantification of riluzole in human plasma. The chromatography was performed by using a Zorbax-SB-C18 (4.6 x 75 mm, 3.5 microm) column , isocratic mobile phase 0.1% formic acid/acetonitrile (10:90 v/v), and an isotope-labeled internal standard (IS), [(13)C,(15)N(2)]riluzole. The extraction of drug and internal standard was performed by liquid-liquid extraction and analyzed by MS in the multiple reaction monitoring (MRM) mode using the respective [M+H](+) ions, m/z 235.0/165.9 for riluzole and m/z 238.1/169.0 for the IS. The calibration curve was linear over the concentration range 0.5-500.0 ng/ml for riluzole in human plasma. The limit of quantification (LOQ) was demonstrated at 0.5 ng/ml. The within-batch and between-batch precision were 0.6-2.3% and 1.4-5.7%, and accuracy was 97.1-101.1% and 98.8-101.2% for riluzole respectively. Drug and IS were eluted within 3.0 min. The validated method was successfully applied in a bioequivalence study of riluzole in human plasma.

Riluzole Oral Suspension: Bioavailability Following Percutaneous Gastrostomy Tube-modeled Administration Versus Direct Oral Administration.

PURPOSE: During amyotrophic lateral sclerosis progression, up to 85% of patients develop dysphagia. Riluzole oral suspension 50 mg/10 mL is bioequivalent to riluzole 50-mg film-coated tablets administered orally under fasting conditions. Here, we compare the bioavailability of a single 50-mg dose of riluzole oral suspension via intragastric tube, a proxy for percutaneous endoscopic gastrostomy administration, with that of oral administration in healthy volunteers under fasting conditions. Secondary objectives included the plasma pharmacokinetic and safety profiles of each administration route. METHODS: This was a single-center, single-dose, open-label, randomized, 2-period, 2-sequence, crossover bioequivalence/bioavailability study. Healthy volunteers were randomized to riluzole oral suspension 50 mg/10 mL either via nasogastric tube or orally, with a 5-day washout before crossover. FINDINGS: A total of 32 subjects were randomized (safety population); 30 were eligible for pharmacokinetic analysis. The ratios (nasogastric tube/oral) of the geometric least squares means and the geometric 90% CIs of AUC0-t, AUC0-inf, and Cmax were calculated to be 90.60% (85.66%-95.82%), 90.43% (85.47%-95.67%), and 96.99% (89.40%-105.23%), respectively, indicating bioequivalence. No significant differences in Cmax, Tmax, Kel, and t1/2el between treatments were found. Overall, riluzole oral suspension was well tolerated. No deaths or other serious adverse events were reported. IMPLICATIONS: In this study, riluzole oral suspension was bioequivalent when administered intragastrically and orally in healthy subjects under fasting conditions. Both administration methods were well tolerated. These results show that intragastric administration of riluzole oral suspension may provide an important formulation option in people with amyotrophic lateral sclerosis who have a percutaneous endoscopic gastrostomy tube.

Pharmacokinetics of Riluzole in Beagle Dogs.

BACKGROUND: Riluzole is a benzothiazole anticonvulsant used in the treatment of patients with amyotrophic lateral sclerosis and it is being investigated for clinical use in patients with spinal cord injury. The present study evaluated the pharmacokinetics of riluzole in beagle dogs after oral dose administration. METHODS: The oral doses (1.5, 5, 15 and 50 mg/kg) of riluzole were administered to beagle dogs and blood samples were collected from 0 h to 24 h post drug administration. Riluzole was quantified by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). RESULTS: The method was sensitive, precise, accurate and selective to riluzole quantification in plasma of beagle dogs. The pharmacokinetics following oral administration was linear from 1.5 to 15 mg/kg and the t1/2 was 2.16, 1.5, 1.8 and 3.0 h after oral administration of 1.5, 5.0, 15 and 50 mg/kg riluzole. CONCLUSION: The riluzole pharmacokinetics was linear up to 15 mg/kg and had a significantlyshorter t1/2 in beagle dogs than in humans.

UPLC-MS/MS assay of riluzole in human plasma and cerebrospinal fluid (CSF): Application in samples from spinal cord injured patients.

In the present study, a sensitive and robust LC-MS/MS method has been developed and validated for the quantification of riluzole in human plasma and cerebrospinal fluid (CSF) in clinical samples from patients with spinal cord injury (SCI). Riluzole and its labeled internal standard (IS) were isolated from plasma and CSF by liquid-liquid extraction using ethyl acetate. Riluzole (m/z 235→166) and IS (m/z 238→169) were detected by electrospray ionization (ESI) using multiple reaction monitoring (MRM) in a positive mode. The assay was linear in the concentration range of 0.5 (LLOQ, signal/noise ratio>10)-800ng/ml in plasma, and 1.0 (LLOQ)-800ng/ml in CSF samples. The intra- and inter-day accuracy in plasma were 94.2-110.0% and 97.8-102.0%, respectively, and those in CSF were 87.6-105.1% and 91.9-98.8%, respectively. The intra- and inter-day precision were 2.2-7.2% and 4.0-9.1%, respectively, in plasma, and 1.4-14.1% and 2.6-11.5%, respectively in CSF. Matrix effect was negligible from both matrices with signal percentages of 97.6-100.6% in plasma and 99.4-106.4% in CSF. The recoveries were >75% in plasma, >84% in CSF with low protein (53.9mg/dl), and >68% in CSF with high protein (348.2mg/dl). This method was successfully applied to quantify riluzole concentrations in plasma and CSF from patients with SCI.

Population pharmacokinetics of riluzole in patients with amyotrophic lateral sclerosis.

OBJECTIVES: To characterize the population pharmacokinetic of riluzole in patients with amyotrophic lateral sclerosis (ALS). METHODS: One hundred patients with ALS who were participating in a multicenter phase III dose-ranging trial of riluzole were sampled on 179 visits. The sampling strategy (two samples per visit) was varied across patients to define the population kinetic profile (full screen). Riluzole plasma levels were determined by HPLC, and the data were analyzed by nonlinear mixed-effect modeling (NONMEM program) with use of a one-compartment structural model. The model incorporated interoccasion (visit-to visit) variability. RESULTS: In the basic one-compartment pharmacokinetic model, interindividual variability in plasma clearance (51.4%) was higher than intraindividual (visit-to-visit) variability (28.0%), indicating uniform pharmacokinetic behavior during long-term therapy. Riluzole clearance was independent of dosage (25 to 100 mg twice daily), treatment duration (up to 10 months), age, and renal function; gender and smoking were the most important patient covariates, with hepatic function having lesser influence. Typical value of clearance was 51.4 L/hr for a nonsmoking male patient. It was 32% lower in women than in men and 36% lower in nonsmokers than in smokers. Gender- and smoking-related variations in riluzole exposure at the recommended dosage (50 mg twice daily) were within the range of exposures achieved (with no untoward effect) in this dose-ranging study. CONCLUSION: The pharmacokinetics of riluzole has been characterized in patients during long-term therapy. Riluzole clearance is independent of dose and treatment duration. Within-patient variability is low. Gender and smoking status are the main covariates to explain interpatient variability.

Inter- and intraindividual variability of riluzole serum concentrations in patients with ALS.

All patients with amyotrophic lateral sclerosis (ALS) are treated with the same dose of riluzole: 50 mg twice daily. Reasonably large interindividual differences in clearance of the drug have been reported. The relatively small group of patients with high blood concentrations of riluzole has probably primarily influenced the efficacy and the incidence of side-effects in the previously conducted clinical trials with riluzole. Individual dosing of the drug may, in the case of large interindividual differences in serum concentrations of the drug, be necessary in the future. Exact data concerning the plasma and serum concentrations of riluzole in patients with ALS, after standardized intake of the drug, diet and blood sampling are unknown so far. In this study, inter- and intraindividual variability of serum and plasma levels of riluzole in 21 patients with "probable" or "definite" ALS were determined. The interindividual variability of peak serum levels (coefficient of variation=74%) was significantly larger than intraindividual variability (p<0.001). Serum levels were not correlated with age or smoking status. The determination of a correlation between riluzole serum concentrations and survival of patients with ALS will be the aim of further studies.

Liquid chromatographic assay for riluzole in mouse plasma and central nervous system tissues.

An isocratic, reversed-phase high-performance liquid chromatographic procedure (HPLC) was developed for determination of the neuroprotective agent riluzole in mice plasma, brain and spinal cord. The procedure is based on isolation of the compound and the internal standard from plasma and central nervous system tissues using a Bakerbond spe C8 cartridge, with satisfactory recovery and specificity. Separation was on a C18 column, coupled with an UV detector at 263 nm. The assay was linear over a wide range, with a lower limit of quantification of 100 ng ml(-1) or g(-1) using 0.1 ml of plasma and about 100mg of brain tissue. The precision and accuracy were within the acceptable limits for an HPLC assay. The method is currently used to support pharmacological studies of the activity of riluzole when given in combination with other potential neuroprotective agents in an animal model of familiar amyotrophic lateral sclerosis (SOD1-G93A transgenic mice).

An association study of riluzole serum concentration and survival and disease progression in patients with ALS.

Patients with amyotrophic lateral sclerosis (ALS) who are treated with the antiglutamatergic drug riluzole receive a fixed-dose regimen of 50 mg b.i.d. The drug has been shown to increase tracheostomy-free survival by 3-6 months. The pharmacokinetics of riluzole show a high interindividual variability. Riluzole serum concentrations are associated with side effects and ALS symptoms, but the effect of the actual blood level of riluzole on disease progression and survival is unknown. We measured trough and peak serum concentrations of riluzole in 160 patients with ALS, and estimated the area under the curve for one dosage interval (AUCi) using a Bayesian method. We then determined the association between riluzole AUCi and survival over a 5-year period, and between riluzole AUCi and disease progression, defined by the rates of decline of arm strength and vital lung capacity. No significant association was found between riluzole AUCi and survival or disease progression.

Riluzole metabolism and CYP1A1/2 polymorphisms in patients with ALS.

Riluzole is the only FDA approved drug for the treatment of amyotrophic lateral sclerosis. Riluzole is assumed to be mainly metabolized by the liver cytochrome CYP1A2 and by the extra-hepatic cytochrome CYP1A1. CYP1A2 and CYP1A1 genetic polymorphisms are known, but their relationship to riluzole metabolism in ALS patients has not been investigated. The aim of this study was to determine whether the polymorphisms of the CYP1A2 and the CYP1A1 genes in ALS patients are associated with riluzole metabolic profiles. Thirty-two patients with a diagnosis of probable or definite ALS and who were on riluzole, participated in the study. Trough and peak plasma riluzole levels were measured using analytical chromatography-mass spectrometry methods. Association of the genotypes of the SNPs spanning the CYP1A1 and CYP1A2 genes (including one SNP in the intergenic region) with mean riluzole peak and trough levels was studied using ANOVA and Tukey's HSD. The mean peak riluzole level was 202+/-111 ng/ml and mean trough level 54.3+/-37.5 ng/ml. Our data do not support any association of the four CYP1A1 and CYP1A2 polymorphisms with the riluzole metabolic profile. In conclusion, genetic variations in CYP1A1 and CYP1A2 genes do not seem to influence riluzole levels. Further work is needed to better understand the genetic regulation of CYP1A enzymes and their role in riluzole metabolism.

Minocycline and riluzole brain disposition: interactions with p-glycoprotein at the blood-brain barrier.

Amyotrophic lateral sclerosis is a neurodegenerative fatal disease. The only drug recognized to increase the survival time is riluzole(RLZ). In animal models, minocycline (MNC) delayed the onset of the disease and increased the survival time (in combination with RLZ). The objective of our work was to study the interactions between RLZ, MNC and the efflux pump p-glycoprotein (p-gp) at the blood-brain barrier. We investigated these two drugs as: (i) p-gp substrates by comparing their brain uptake in CF1 mdr1a (-/-) and mdr1a (+/+) mice, (ii) p-gp modulators by studying their effect on the cerebral uptake of digoxin. mdr1a (-/-) mice showed higher brain uptake of MNC and RLZ than mdr1a (+/+) (in a 1.6- and 1.4-fold, respectively); and in mdr1a (+/+) mice pre-treated with repeated doses of MNC, brain uptake of digoxin was increased. When both drugs were administrated to mdr1a (+/+) mice, MNC increased the brain uptake of RLZ in a 2.1-fold. In conclusion, MNC and RLZ are both p-gp substrates. MNC is also a p-gp inhibitor and increases the brain diffusion of RLZ. In vitro experiments with the GPNT cell line confirmed these results. These interactions should be taken into account in the design of future clinical trials.

A validated HPLC assay to monitor riluzole plasma or serum concentrations in patients with amyotrophic lateral sclerosis.

A specific, accurate and precise high-performance liquid chromatographic assay was developed for the determination of riluzole, a drug used to treat patients with amyotrophic lateral sclerosis. Samples were treated by extraction with dichloromethane followed by reversed-phase chromatography with ultraviolet detection at 260 nm. Preset validation criteria were met from 20 to 2000 ng/mL with a linear response curve. Extraction recovery of riluzole was 65-76%. The accuracy of the method was 102-103%. Intra- and inter-day coefficients of variation were in the ranges 2.8-4.9% and 1.8-9.7%. A detection limit of 5 ng/mL was found. Determination of concentrations in serum and plasma resulted in similar results below 500 ng/mL. At higher values a matrix effect cannot be excluded. This presented method can be used to monitor plasma or serum levels in ALS patients treated with riluzole.

Riluzole suppresses motor cortex facilitation in correlation to its plasma level. A study using transcranial magnetic stimulation.

The aim of our study was to measure the effects of the glutamate antagonist riluzole on different parameters of motor excitability, using transcranial magnetic stimulation (TMS) during 7 days of riluzole administration, and to correlate these effects with riluzole plasma levels. Nine healthy volunteers received a dose of 100 mg riluzole from day 1 to 7 of the study period. Electrophysiological examinations were performed on day 1 before and 2 h, 5 h and 8 h after riluzole administration, on day 2, day 3 and day 5 before riluzole administration, and on day 8. Plasma samples were taken simultaneously. The excitability of the motor cortex, supraspinal and spinal motor pathways was tested by studying intracortical facilitation and inhibition, the cortical silent period and motor threshold after TMS, as well as the peripheral silent period and F-wave amplitudes after electrical peripheral nerve stimulation. We found a significant reduction of intracortical facilitation, which correlated significantly with riluzole plasma levels. To a lesser extent, intracortical inhibition was enhanced on day 1, motor threshold was increased on day 8 and F-wave amplitudes were reduced. These changes did not correlate with riluzole plasma levels. We conclude that the main effect of riluzole in vivo is a reduction of intracortical facilitation, which is closely related to the drug's level in the plasma. The most probable mechanism involves an effect on glutamatergic synaptic transmission.

Riluzole serum concentrations in patients with ALS: associations with side effects and symptoms.

Riluzole exerts a dose-dependent effect on survival of patients with ALS and, although serum levels show a high interindividual variability, is usually prescribed in a fixed dose. In this study, riluzole serum levels and area under the curve per kilogram of body weight (AUC/kg) of 169 patients with ALS showed a high interindividual variability. Patients with high serum levels and AUC/kg more often had diarrhea but less often had fasciculations and muscle stiffness. It may therefore be advantageous to raise the riluzole dose in patients with low riluzole serum concentrations without the risk of serious side effects.