68Ga-Labeled bismacrocyclic methylene phosphonate as potential bone seeking PET radiopharmaceutical.

Phosphonates-based agents are well-known bone-seeking radiopharmaceuticals with application in detection and therapy. With higher sensitivity and resolution offered by Positron Emission Tomography (PET), tracers based on this technique are gaining huge attention. 68Ga-based generator and radiotracers render independence from the on-site cyclotron. We report the development of 68Ga-labeled DOTA-based bismacrocyclic phosphonate derivative, for bone PET imaging. The synthesis and characterization of 68Ga- DO3P-AME-DO3P was carried out in > 95% purity. The radiotracer displayed high stability and low binding affinity (<3%) to blood serum. High in vitro binding affinity were observed for synthetic hydroxyapatite, SAOS-2, osteoclast and osteoblast cells. In vivo pharmacokinetics revealed fast washout with biphasic release pattern. The deposition of radiotracer in osseous tissues was high (Bone/Muscle ratio:18), as studied from the biodistribution studies. In vivo PET/CT and biodistribution analyses revealed the ability of 68Ga-DO3P-AME-DO3P to target and accumulate in bone, thus displaying its potential as a PET bone imaging agent.

A novel variant of the 13C-methacetin liver function breath test that eliminates the confounding effect of individual differences in systemic CO2 kinetics.

The principle of dynamic liver function breath tests is founded on the administration of a 13C-labeled drug and subsequent monitoring of 13CO2 in the breath, quantified as time series delta over natural baseline 13CO2 (DOB) liberated from the drug during hepatic CYP-dependent detoxification. One confounding factor limiting the diagnostic value of such tests is that only a fraction of the liberated 13CO2 is immediately exhaled, while another fraction is taken up by body compartments from which it returns with delay to the plasma. The aims of this study were to establish a novel variant of the methacetin-based breath test LiMAx that allows to estimate and to eliminate the confounding effect of systemic 13CO2 distribution on the DOB curve and thus enables a more reliable assessment of the hepatic detoxification capacity compared with the conventional LiMAx test. We designed a new test variant (named "2DOB") consisting of two consecutive phases. Phase 1 is initiated by the intravenous administration of 13C-bicarbonate. Phase 2 starts about 30 min later with the intravenous administration of the 13C-labelled test drug. Using compartment modelling, the resulting 2-phasic DOB curve yields the rate constants for the irreversible elimination and the reversible exchange of plasma 13CO2 with body compartments (phase 1) and for the detoxification and exchange of the drug with body compartments (phase 2). We carried out the 2DOB test with the test drug 13C-methacetin in 16 subjects with chronic liver pathologies and 22 normal subjects, who also underwent the conventional LiMAx test. Individual differences in the systemic CO2 kinetics can lead to deviations up to a factor of 2 in the maximum of DOB curves (coefficient of variation CV ≈ 0.2) which, in particular, may hamper the discrimination between subjects with normal or mildly impaired detoxification capacities. The novel test revealed that a significant portion of the drug is not immediately metabolized, but transiently taken up into a storage compartment. Intriguingly, not only the hepatic detoxification rate but also the storage capacity of the drug, turned out to be indicative for a normal liver function. We thus used both parameters to define a scoring function which yielded an excellent disease classification (AUC = 0.95) and a high correlation with the MELD score (RSpearman = 0.92). The novel test variant 2DOB promises a significant improvement in the assessment of impaired hepatic detoxification capacity. The suitability of the test for the reliable characterization of the natural history of chronic liver diseases (fatty liver-fibrosis-cirrhosis) has to be assessed in further studies.

The food contaminant acetamide is not an in vivo clastogen, aneugen, or mutagen in rodent hematopoietic tissue.

Acetamide (CAS 60-35-5) is classified by IARC as a Group 2B, possible human carcinogen, based on the induction of hepatocellular carcinomas in rats following chronic exposure to high doses. Recently, acetamide was found to be present in a variety of human foods, warranting further investigation. The regulatory body JECFA has previously noted conflicting reports on acetamide's ability to induce micronuclei (MN) in mice in vivo. To better understand the potential in vivo genotoxicity of acetamide, we performed acute MN studies in rats and mice, and a subchronic study in rats, the target species for liver cancer. In the acute exposure, animals were gavaged with water vehicle control, 250, 1000, or 2000 mg/kg acetamide, or the positive control (1 mg/kg mitomycin C). In the subchronic assay, bone marrow of rats gavaged at 1000 mg/kg/day (limit dose) for 28 days was evaluated. Both acute and subchronic exposures showed no change in the ratio of polychromatic to total erythrocytes (P/E) at any dose, nor was there any increase in the incidence of micronucleated polychromatic erythrocytes (MN-PCE). Potential mutagenicity of acetamide was evaluated in male rats gavaged with vehicle control or 1500 mg/kg/day acetamide using the in vivoPig-a gene mutation assay. There was no increase in mutant red blood cells or reticulocytes in acetamide-treated animals. In both acute and sub-chronic studies, elevated blood plasma acetamide in treated animals provided evidence of systemic exposure. We conclude based on this study that acetamide is not clastogenic, aneugenic, or mutagenic in vivo in rodent hematopoietic tissue warranting a formal regulatory re-evaluation.

Species differences in metabolism of a new antiepileptic drug candidate, DSP-0565 [2-(2'-fluoro[1,1'-biphenyl]-2-yl)acetamide].

The metabolism and pharmacokinetics of DSP-0565 [2-(2'-fluoro[1,1'-biphenyl]-2-yl)acetamide], an antiepileptic drug candidate, was investigated in rats, dogs, and humans. In human hepatocytes, [14 C]DSP-0565 was primarily metabolized via amide bond hydrolysis to (2'-fluoro[1,1'-biphenyl]-2-yl)acetic acid (M8), while in rat and dog hepatocytes, it was primarily metabolized via both hydrolysis to M8 and hydroxylation at the benzene ring or the benzyl site to oxidized metabolites. After single oral administration of [14 C]DSP-0565 to rats and dogs, the major radioactivity fraction was recovered in the urine (71-72% of dose) with a much smaller fraction recovered in feces (23-25% of dose). As primary metabolites in their excreta, M8, oxidized metabolites, and glucuronide of DSP-0565 were detected. The contribution of metabolic pathways was estimated from metabolite profiles in their excreta: the major metabolic pathway was oxidation (57-62%) and the next highest was the hydrolysis pathway (23-33%). These results suggest that there are marked species differences in the metabolic pathways of DSP-0565 between humans and animals. Finally, DSP-0565 human oral clearance (CL/F) was predicted using in vitro-in vivo extrapolation (IVIVE) with/without animal scaling factors (SF, in vivo intrinsic clearance/in vitro intrinsic clearance). The SF improved the underestimation of IVIVE (fold error = 0.22), but the prediction was overestimated (fold error = 2.4-3.3). In contrast, the use of SF for hydrolysis pathway was the most accurate for the prediction (fold error = 1.0-1.4). Our findings suggest that understanding of species differences in metabolic pathways between humans and animals is important for predicting human metabolic clearance when using animal SF.

Reliable and Easy-To-Use Liquid Chromatography-Tandem Mass Spectrometry Assay for Quantification of Olorofim (F901318), a Novel Antifungal Drug, in Human Plasma and Serum.

A fast and easy-to-use liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination and quantification of a novel antifungal drug, olorofim (F901318), a member of the novel class of orotomides, in human plasma and serum was developed and validated. Sample preparation was based on protein precipitation with acetonitrile and subsequent centrifugation. An isotope-labeled analogue of F901318 was employed as an internal standard. Chromatographic separation was achieved using a 50-mm by 2.1-mm, 1.9-µm, polar Hypersil Gold C18 column and isocratic mobile phase consisting of 0.1% formic acid-acetonitrile (60%-40%, vol/vol) at a flow rate of 330 µl/min. The analyte was detected using a triple-stage quadrupole mass spectrometer operated in selected reaction monitoring (SRM) mode with positive heated electrospray ionization (HESI+) within a single runtime of 2.00 min. The present LC-MS/MS method was validated according to the international guidelines of the International Conference on Harmonisation (ICH) and the U.S. Food and Drug Administration (FDA). Linearity of F901318 concentration ranges was verified by the Mandel test. The calibration curve was tested linear across the range and fitted using least-squares regression with a weighting factor of the reciprocal concentration. The limit of detection was 0.0011 mg/liter, and the lower limit of quantitation was 0.0033 mg/liter. Intraday and interday precisions ranged from 1.17% to 3.23% for F901318, and intraday and interday accuracies (percent bias) ranged from 0.75% to 5.01%. In conclusion, a method was established for the rapid quantitation of F901318 concentrations in serum and plasma samples in patient trials, and it optimizes therapeutic drug monitoring in applying an easy-to-use single method.

The metabolism and drug-drug interaction potential of the selective prostacyclin receptor agonist selexipag.

1. The metabolism of selexipag has been studied in vivo in man and the main excreted metabolites were identified. Also, metabolites circulating in human plasma have been structurally identified and quantified. 2. The main metabolic pathway of selexipag in man is the formation of the active metabolite ACT-333679. Other metabolic pathways include oxidation and dealkylation reactions. All primary metabolites undergo subsequent hydrolysis of the sulphonamide moiety to their corresponding acids. ACT-333679 undergoes conjugation with glucuronic acid and aromatic hydroxylation to P10, the main metabolite detected in human faeces. 3. The formation of the active metabolite ACT-333679 is catalysed by carboxylesterases, while the oxidation and dealkylation reactions are metabolized by CYP2C8 and CYP3A4. CYP2C8 is the only P450 isoform catalysing the aromatic hydroxylation to P10. CYP2C8 together with CYP3A4 are also involved in the formation of several minor ACT-333679 metabolites. UGT1A3 and UGT2B7 catalyse the glucuronidation of ACT-333679. 4. The potential of selexipag to inhibit or induce cytochrome P450 enzymes or drug transport proteins was studied in vitro. Selexipag is an inhibitor of CYP2C8 and CYP2C9 and induces CYP3A4 and CYP2C9 in vitro. Also, selexipag inhibits the transporters OATP1B1, OATP1B3, OAT1, OAT3, and BCRP. However, due to its low dose and relatively low unbound exposure, selexipag has a low potential for causing drug-drug interactions.

Positron emission tomography measurement of brain MAO-B inhibition in patients with Alzheimer's disease and elderly controls after oral administration of sembragiline.

PURPOSE: In Alzheimer's disease (AD), increased metabolism of monoamines by monoamine oxidase type B (MAO-B) leads to the production of toxic reactive oxygen species (ROS), which are thought to contribute to disease pathogenesis. Inhibition of the MAO-B enzyme may restore brain levels of monoaminergic neurotransmitters, reduce the formation of toxic ROS and reduce neuroinflammation (reactive astrocytosis), potentially leading to neuroprotection. Sembragiline (also referred as RO4602522, RG1577 and EVT 302 in previous communications) is a potent, selective and reversible inhibitor of MAO-B developed as a potential treatment for AD. METHODS: This study assessed the relationship between plasma concentration of sembragiline and brain MAO-B inhibition in patients with AD and in healthy elderly control (EC) subjects. Positron emission tomography (PET) scans using [11C]-L-deprenyl-D2 radiotracer were performed in ten patients with AD and six EC subjects, who received sembragiline each day for 6-15 days. RESULTS: At steady state, the relationship between sembragiline plasma concentration and MAO-B inhibition resulted in an Emax of ∼80-90 % across brain regions of interest and in an EC50 of 1-2 ng/mL. Data in patients with AD and EC subjects showed that near-maximal inhibition of brain MAO-B was achieved with 1 mg sembragiline daily, regardless of the population, whereas lower doses resulted in lower and variable brain MAO-B inhibition. CONCLUSIONS: This PET study confirmed that daily treatment of at least 1 mg sembragiline resulted in near-maximal inhibition of brain MAO-B enzyme in patients with AD.

Therapeutic Drug Monitoring of Lacosamide in Norway: Focus on Pharmacokinetic Variability, Efficacy and Tolerability.

Lacosamide (LCM) is a new antiepileptic drug (AED). Experience from therapeutic drug monitoring (TDM) in clinical practice is limited. The purpose of this study is to evaluate the pharmacokinetic variability of LCM in relation to efficacy and tolerability in patients with refractory epilepsy in a real-life setting. Variables included age, gender, daily doses and serum concentrations of LCM and other AEDs from the TDM-database at the National Center for Epilepsy in Norway. Clinical data regarding efficacy and tolerability were collected from medical records. The Norwegian Prescription Database (NorPD) was used to include population-based numbers of users. TDM-data from 344 patients were included. The median dose, serum concentration, and concentration/dose (C/D)-ratio of LCM was 350 (range 25-700) mg/day, 19.7 (range 8.1-56.2) µmol/L, and 0.06 (0.02-0.82) µmol/L/mg, respectively. Serum concentrations were reduced by 28% by concomitant use of enzyme inducers and increased by 30% in patients aged >65 years. Efficacy and tolerability were assessed in 227 patients: 29% had >50% seizure reduction (eight seizure free), 30% had no effect, and 44% reported adverse effects. In Norway, there were on average 500 patients per year using LCM in this period based on NorPD. The study demonstrated pharmacokinetic variability and use of TDM of LCM in Norway. Data were collected from multiple sources for improved pharmacovigilance. Serum concentrations were influenced by enzyme inducers and ageing, indicating the usefulness of TDM. Effect and tolerability were favorable within a suggested reference range of 10-40 µmol/L given drug-fasting conditions.

Effect of gemfibrozil and rifampicin on the pharmacokinetics of selexipag and its active metabolite in healthy subjects.

AIMS: Based on in vitro data, there is evidence to suggest that cytochrome P450 (CYP) 2C8 is involved in the metabolism of selexipag and its active metabolite, ACT-333679. The present study evaluated the possible pharmacokinetic interactions of selexipag with gemfibrozil, a strong CYP2C8 inhibitor, and rifampicin, an inducer of CYP2C8. METHODS: The study consisted of two independent parts, each conducted according to an open-label, randomized, crossover design. The pharmacokinetics and safety of selexipag and ACT-333679 were studied following single-dose administration either alone or in the presence of multiple-dose gemfibrozil (part I) or rifampicin (part II) in healthy male subjects. RESULTS: Gemfibrozil had comparatively small effects on selexipag (less than 2-fold difference in any pharmacokinetic variable) but, with respect to ACT-333679, increased the maximum plasma concentration (Cmax ) 3.6-fold [90% confidence interval (CI) 3.1, 4.3] and the area under the plasma concentration-time curve from zero to infinity (AUC0-∞ ) 11.1-fold (90% CI 9.2, 13.4). The marked increased exposure to ACT-333679, which mediates the majority of the pharmacological activity of selexipag, was accompanied by significantly more adverse events such as headache, nausea and vomiting. Coadministration of rifampicin increased the Cmax of selexipag 1.8-fold (90% CI 1.4, 2.2) and its AUC0-∞ 1.3-fold (90% CI 1.1, 1.4); its effects on ACT-333679 were to increase its Cmax 1.3-fold (90% CI 1.1, 1.6), shorten its half-life by 63% and reduce its AUC0-∞ by half (90% CI 0.45, 0.59). CONCLUSION: Concomitant administration of selexipag and strong inhibitors of CYP2C8 must be avoided, whereas when coadministered with inducers of CYP2C8, dose adjustments of selexipag should be envisaged.

Evaluation of a Novel Immunoassay for Lacosamide Therapeutic Drug Monitoring: Comparison With a Liquid Chromatography-Mass Spectrometry Assay.

BACKGROUND: Monitoring serum levels of lacosamide, other than to establish individualized reference ranges may be helpful in several settings, including patients with liver and/or kidney failure or settings that may result in altered pharmacokinetic characteristics and to assess patients' compliance with therapy. In this study, the EurekaOne liquid chromatography-mass spectrometry (LC-MS/MS) method (in use method) and the ARK immunoassay method (new method) for lacosamide monitoring were compared. METHODS: Lacosamide concentrations were determined in 39 patient samples using (1) antiepileptic drug LC-MS/MS kit by EurekaOne on a Thermo Fisher Scientific TSQuantum Access Max system and (2) the lacosamide immunoassay by ARK Diagnostic Inc. (research use only kit), on a Abbott Architect System. RESULTS: Measured total imprecision of the new method is 6.29% at 6.59 µmol/L, 8.82% at 30.20 µmol/L, and 6.45% at 64.51 µmol/L. Passing-Bablok regression analysis showed a nonsignificant intercept of -0.03015 [95% confidence interval (CI), -1.2243 to 0.8593] and a slope of 1.05 (95% CI, 0.9973-1.1166), showing that the method does not deviate from linearity and absence of proportional systematic error. Bland-Altman analysis showed a systematic bias of -3.296% (95% CI, -5.81 to -0.78) with 95% of the LC-MS/MS-ARK mean % of differences ranging from -18.5 to 11.9. Despite this bias, data of the combined imprecision of the 2 methods show that the new method is still acceptable within the maximum allowable error of 15%. CONCLUSIONS: The performance of the new ARK method on the Architect system is acceptable and may be used routinely to measure serum lacosamide concentration in the clinic although the nature of the bias has to be carefully addressed.

Absolute oral bioavailability of selexipag, a novel oral prostacyclin IP receptor agonist.

PURPOSE: The aim of this single-center, open-label study was to assess the absolute bioavailability of an oral (tablet) versus intravenous (i.v.) formulation of selexipag in healthy subjects. METHODS: A pilot phase in three healthy male subjects, which preceded the main study, consisted of a single 20-minute i.v. infusion of 50 µg selexipag. Its objectives were to ensure the safety of the i.v. formulation and to select the i.v. dose for the main study. The main study had a randomized, two-way crossover design in 16 healthy male subjects. Subjects received a single oral dose of 400 µg selexipag and a single 80-minute i.v. infusion of 200 µg selexipag. RESULTS: Three subjects in the pilot and 15 in the main phase completed the study as planned, whereas one subject of the main study withdrew the consent. A geometric mean total body clearance (95% confidence interval (CI)) of 17.9 L/h (15.0-21.5) and a volume of distribution of 11.7 L (10.6-13.0) were determined. The absolute oral bioavailability of selexipag (90% CI) was 49.4% (42.6-57.2). Selexipag was well-tolerated; no adverse event (AE) occurred during the pilot phase, and the main observed AEs were headache, nausea, and vomiting. CONCLUSION: A single i.v. administration of selexipag in healthy subjects was safe and well-tolerated. The bioavailability of selexipag after oral administration is approximately 50%.

A pharmacokinetic drug-drug interaction study between selexipag and midazolam, a CYP3A4 substrate, in healthy male subjects.

PURPOSE: In vitro data showed that selexipag and its active metabolite (ACT-333679) have an inductive effect on CYP3A4, CYP2B6, and CYP2C9 at concentrations approximately 100-fold higher than the maximum plasma concentration (C max) measured under steady-state conditions. In order to confirm in vivo the lack of induction at the enterocyte level, we assessed the effect of selexipag on midazolam, a substrate of hepatic and intestinal CYP3A4. METHODS: This study was conducted according to an open-label, randomized, two-way crossover design. A total of 20 subjects received a single oral dose of 7.5 mg midazolam alone (treatment A) or on top of steady-state selexipag (treatment B). Selexipag was administered twice daily using an up-titration scheme consisting of three steps: 400, 600, 1000, and 1600 µg with increments every fourth day. A 24-h pharmacokinetic profile was performed following midazolam administration, and bioequivalence criteria were investigated on an exploratory basis. RESULTS: The C max of midazolam and 1-hydroxymidazolam was decreased by approximately 20 and 14%, respectively, following treatment B compared to A. The time to reach C max for midazolam and 1-hydroxymidazolam was similar between treatments. The terminal half-life was reduced in treatment B compared to A for both midazolam (16%) and 1-hydroxymidazolam (20%). Exposure (area under the curve) to midazolam and 1-hydroxymidazolam was similar between treatments, and the 90% confidence intervals of geometric mean ratios were within the bioequivalence interval. Treatment with midazolam, selexipag, and the combination was safe and well tolerated. CONCLUSION: Exposure to midazolam and 1-hydroxymidazolam was not affected by treatment with selexipag.

An HPLC-UV method for determining plasma dimethylacetamide concentrations in patients receiving intravenous busulfan.

Dimethylacetamide (DMA) is a solvent used in the preparation of intravenous busulfan, an alkylating agent used in blood or marrow transplantation. DMA may contribute to hepatic toxicity, so it is important to monitor its clearance. The aim of this study was to develop an HPLC-UV assay for measurement of DMA in human plasma. After precipitation of plasma proteins with acetonitrile followed by dilution (1:4) with water, the extract was injected onto the HPLC and detected at 195 nm. Separation was performed using a Cogent-HPS 5 µm C18 column (250 × 4.6 mm) preceded by a Brownlee 7 µm RP18 , pre-column (1.5 cm × 3.2 mm). The mobile phase was 25 mm sodium phosphate buffer (pH 3), containing 2.5% (v/v) acetonitrile and 0.0005% (v/v) sodium-octyl-sulfonate. Using a flow rate of 1 mL/min, the retention times of DMA and the internal standard (IS), 2-chloroacetamide, were 9.5 and 3.5 min, respectively. Peak area ratio (DMA:IS) was a linear function of concentration from 1 to 1000 µg/mL. There was excellent intraday precision (<5% for 5-700 µg/mL DMA), accuracy (<3% deviation from the true concentration) and recovery (74-98%). The limits of detection and quantification were 1 and 5 µg/mL, respectively. In eight children who received intravenous busulfan, DMA concentrations ranged from 110 to 438 µg/mL.

Bioequivalence and Pharmacokinetic Profiles of Agomelatine 25-mg Tablets in Healthy Chinese Subjects: A Four-Way Replicate Crossover Study Demonstrating High Intra- and Inter-Individual Variations.

The present study was designed to assess the bioequivalence of two agomelatine formulations (25-mg tablets) in healthy Chinese male subjects. This single-dose, open-label, randomized, four-way replicate study with a 1-week washout period was conducted in 60 healthy Chinese male volunteers under fasting conditions. Blood samples were collected over a 12-h period after a single dose of the 25-mg agomelatine test (T) formulation or a reference (R) formulation, and the drug concentrations were assayed by liquid chromatography tandem mass spectrometry (LC-MS/MS). Pharmacokinetic parameters were calculated using a non-compartmental model. Bioequivalence between the formulations was assessed. Tolerability and safety were monitored by physical examination, electrocardiogram (12-lead ECG), clinical laboratory tests, and adverse events (AEs). A total of 56 out of 60 subjects completed the study. No AEs were observed. The values of maximum plasma concentration (Cmax), maximum concentration (Tmax), area under curve (AUC)0-t and t1/2 were 12.032 ng/mL, 0.658 h, 12.637 ng·h/mL, and 0.813 h, respectively, for the test formulation, and 10.891 ng/mL, 0.709 h, 11.572 ng·h/mL, and 0.96 h, respectively, for the reference formulation. The intra-individual variability of Cmax and AUC0-t were 78.3 and 61.8%, respectively. The inter-individual coefficients of variance (CVs) of Cmax and AUC0-t were approximately 100%. The 90% confidence intervals for the ratio of means for the log-transformed Cmax (97.7-124.9%), AUC0-t (98.2-118%), and AUC0-∞ (97.8-117.2%) were within the guideline range of bioequivalence (80-125%). The test and reference formulations of agomelatine met the regulatory criteria for bioequivalence of the Chinese Food and Drug Administration. Significant intra-individual and inter-individual variations were found.

Comparison of lacosamide concentrations in cerebrospinal fluid and serum in patients with epilepsy.

OBJECTIVE: This study was carried out to estimate the exposure of the central nervous system (CNS) to the antiepileptic drug (AED) lacosamide, under steady state conditions, in patients with epilepsy who take oral lacosamide alongside up to three other AEDs. METHODS: Twenty-seven serum and cerebral spinal fluid (CSF) samples were collected from 21 patients receiving lacosamide for the treatment of epilepsy (50-600 mg/day over two or three doses). This included 23 time-matched pairs of serum and CSF samples from 19 patients. The concentration of lacosamide in each sample was determined using high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). Linear regression was used to characterize the relationship between the CSF-to-serum ratio of lacosamide concentration and the time since dosing, the daily lacosamide dose, or the daily dose normalized by volume of distribution (Vd , approximated to total body water), and between the drug concentrations in each compartment (CSF vs. serum). RESULTS: Concentrations of lacosamide in CSF (mean ± standard deviation [SD] 7.37 ± 3.73 µg/ml, range 1.24-14.95, n = 27) and serum (mean ± SD 8.16 ± 3.82 µg/ml, range 2.29-15.45, n = 27) samples showed a good correlation over the dose range investigated. The mean CSF-to-serum ratio of lacosamide concentrations was 0.897 ± 0.193 (range 0.492-1.254, n = 23 time-matched pairs) and was independent of lacosamide dose. SIGNIFICANCE: Drug concentrations in the CSF are often used to indicate those in the brain interstitial fluid. In patients with epilepsy who follow a stable oral AED dosing regimen, lacosamide concentration in CSF is approximately 85% of that found in serum, suggesting that serum may be a valuable indicator of lacosamide concentration in the CNS.

Acute or chronic use of lacosamide does not alter its distribution between serum and cerebrospinal fluid.

OBJECTIVE: The site of action for antiepileptic drugs (AEDs) is within the brain; however, cerebrospinal fluid (CSF) concentration is highly variable. Lacosamide (LCM) is approved by the U.S. Food and Drug Administration (FDA) for treatment of partial-onset seizures in adults, and has linear pharmacokinetics in serum. Penetration across the blood-brain barrier (BBB) is unknown. This study aims to provide additional insights into the pharmacokinetics of LCM. METHODS: Thirty adults undergoing craniotomy for treatment of intractable epilepsy or brain tumor were recruited and were either taking LCM long term (group 1, n = 15), or were LCM naive, receiving LCM as prophylaxis for surgery (group 2, n = 15). All patients received one intravenous (IV) dose (15 min infusion) immediately prior to craniotomy. CSF and arterial blood were collected simultaneously following craniotomy. LCM concentrations were measured in serum and CSF. RESULTS: LCM concentration differences between groups 1 and 2 for both CSF and serum were statistically significant (p ≤ 0.0005), but there was no statistically significant difference in CSF/serum ratios (group 1 = 0.726 ± 0.231; group 2 = 0.556 ±0.241; p = 0.0585). LCM concentration in serum correlated positively with CSF concentration in group 1 (Pearson r = 0.8527, p < 0.0001). The time interval between the end of dose delivery and sample collection correlated positively with the CSF/serum ratio for the drug-naive group (Pearson r = 0.6525; p = 0.0084). Treatment with other AEDs did not affect LCM distribution between serum and CSF. SIGNIFICANCE: Although chronic dosing resulted in higher LCM concentrations in serum and CSF compared to drug-naive patients, the CSF/serum ratio was not affected by LCM pretreatment. These data suggest that LCM serum concentration may reliably predict CSF concentration.

Effect of lopinavir/ritonavir on the pharmacokinetics of selexipag an oral prostacyclin receptor agonist and its active metabolite in healthy subjects.

AIMS: This study investigated the effect of a fixed dose combination of lopinavir/ritonavir on the pharmacokinetics (PK) of selexipag and its active metabolite ACT-333679. METHODS: This was an open label, randomized, single centre, two way, crossover study. Twenty healthy male subjects were treated with a single dose of 400 µg selexipag alone and in combination with multiple doses of lopinavir/ritonavir (400/100 mg) twice daily. RESULTS: The results showed that lopinavir/ritonavir approximately doubled the exposure to selexipag. The area under the plasma concentration-time curve from time zero to infinity (AUC(0,∞) and the maximum plasma concentration (Cmax) of selexipag were 2.2- and 2.1-fold higher, respectively, than under selexipag alone, with a 90% confidence interval (CI) of the geometric mean ratio (GMR) of 1.9, 2.7 and 1.7, 2.6, respectively. For ACT-333679, the clinically more relevant component of selexipag, systemic exposure was increased by 8% (GMR of AUC(0,∞) 1.1, 90% CI 0.9, 1.3), when lopinavir/ritonavir was co-administered with selexipag. The most frequently reported adverse event (AE) was headache. A single dose of selexipag, administered either alone or together with multiple doses of lopinavir/ritonavir, was safe and well tolerated. CONCLUSIONS: Lopinavir/ritonavir does not affect the PK parameters of selexipag and ACT-333679 to a clinically relevant extent. Therefore, adaptation of the selexipag dose is not required when co-administered with inhibitors of the organic anion-transporting polypeptide (OATP) 1B1/ 1B3, P-glycoprotein (P-gp) and/or CYP3A4.

High-throughput method for the quantification of lacosamide in serum using ultrafast SPE-MS/MS.

BACKGROUND: Lacosamide is an anticonvulsant drug approved for adjunctive therapy of partial-onset seizures in adults. Monitoring serum lacosamide concentrations may be useful in assessing compliance and optimizing therapy. The clinical need for faster turn-around-times and increased testing volumes has led to the desire to develop faster methods of analysis for higher throughput of samples. METHODS: Fifty microliters of calibration standards, quality controls, and patient samples were precipitated with methanol containing deuterated internal standard. The supernatant was then diluted with aqueous mobile phase and injected on an ultrafast solid-phase extraction-mass spectrometry with a cycle time of <10 seconds per sample. RESULTS: The analytic linear range for the assay was 0.5-50.0 mcg/mL with a limit of detection of 0.05 mcg/mL. The assay showed interassay and intraassay precision coefficient of variations <7%, with no significant carryover after a sample twice the upper limit of quantitation, and no interference from the top 24 prescribed drugs, other anticonvulsants, or common drugs of abuse. Analytical accuracy was determined by comparing 26 results (19 patients, 7 standards and quality control) with a reference laboratory using liquid chromatography-mass spectrometry in addition to 11 proficiency samples from the LGC Standards Proficiency Testing survey. The results were compared using a standard linear regression with the equation of the line being y = 1.093x - 0.166, with an r(2) = 0.99, and a y intercept 95% confidence interval that included zero. CONCLUSIONS: Herein, the authors present a method for the quantification of lacosamide in serum with ultrafast solid-phase extraction-mass spectrometry that uses 50 µL of sample, is linear from 0.5 to 50 mcg/mL, has interassay and intraassay coefficient of variations of <7%, and has much faster sample cycle times with similar analytic results compared with traditional liquid chromatography-mass spectrometry.

A fully validated method for the determination of lacosamide in human plasma using gas chromatography with mass spectrometry: application for therapeutic drug monitoring.

A simple gas chromatographic method with mass spectrometry detection was developed and validated for the determination of lacosamide in human plasma. Lacosamide and the internal standard, levetiracetam-d6, were extracted from 200 µL plasma, by a solid-phase extraction through HF Bond Elut C18 columns, and derivatized using N-methyl-N-tert-butyldimethylsilyltrifluoroacetamide with 1% tert-butyldimethylsilylchloride in acetonitrile. The limit of quantification was found to be 0.20 µg/mL and the assay was linear up to 20.0 µg/mL with correlation coefficient ≥0.994. The intra- and interday precision values were <4.1% in terms of relative standard deviation (%) and the values of intra- and interday accuracy were found to be within -7.2 and 5.3% in terms of relative error (%). Absolute recovery of the method for lacosamide was determined at three concentration levels and ranged from 92.5 to 97.6%. The developed method uses small volumes of plasma and proved to be simple, rapid, and sensitive for the determination of lacosamide in plasma. This method can be used in routine every day analysis of plasma samples obtained from patients who follow respective antiepileptic treatment and for the investigation of clinical and forensic cases where lacosamide is involved.

Clinical population pharmacokinetics and toxicodynamics of linezolid.

Thrombocytopenia is a common side effect of linezolid, an oxazolidinone antibiotic often used to treat multidrug-resistant Gram-positive bacterial infections. Various risk factors have been suggested, including linezolid dose and duration of therapy, baseline platelet counts, and renal dysfunction; still, the mechanisms behind this potentially treatment-limiting toxicity are largely unknown. A clinical study was conducted to investigate the relationship between linezolid pharmacokinetics and toxicodynamics and inform strategies to prevent and manage linezolid-associated toxicity. Forty-one patients received 42 separate treatment courses of linezolid (600 mg every 12 h). A new mechanism-based, population pharmacokinetic/toxicodynamic model was developed to describe the time course of plasma linezolid concentrations and platelets. A linezolid concentration of 8.06 mg/liter (101% between-patient variability) inhibited the synthesis of platelet precursor cells by 50%. Simulations predicted treatment durations of 5 and 7 days to carry a substantially lower risk than 10- to 28-day therapy for platelet nadirs of <100 ×10(9)/liter. The risk for toxicity did not differ noticeably between 14 and 28 days of therapy and was significantly higher for patients with lower baseline platelet counts. Due to the increased risk of toxicity after longer durations of linezolid therapy and large between-patient variability, close monitoring of patients for development of toxicity is important. Dose individualization based on plasma linezolid concentration profiles and platelet counts should be considered to minimize linezolid-associated thrombocytopenia. Overall, oxazolidinone therapy over 5 to 7 days even at relatively high doses was predicted to be as safe as 10-day therapy of 600 mg linezolid every 12 h.