Effects of age and sex on the disposition of retigabine.

BACKGROUND: The novel antiepileptic drug retigabine is the first selective M-current potassium channel opener for KCNQ2/3 and KCNQ3/5 channels. Retigabine undergoes phase II metabolism (N-glucuronidation, acetylation) exclusively and renal excretion. OBJECTIVE: Our objective was to evaluate the effects of age and sex on the pharmacokinetics of retigabine. METHODS: Healthy young (age range, 18-40 years) and elderly (age range, 66-81 years) white subjects (12 men and 12 women in each group) received a single 200-mg oral dose of retigabine. After dosing, blood was collected over a 72-hour period to determine plasma concentrations of retigabine and its acetylated metabolite, AWD21-360. Pharmacokinetics was compared for age group and sex by ANOVA. RESULTS: In young men, retigabine was rapidly absorbed, with the maximum concentration occurring within 2 hours, and was eliminated with an apparent clearance of 0.67 L x h(-1) x kg(-1) and a mean terminal half-life of 8.5 hours. Subjects were similarly exposed to AWD21-360. Compared with young men, young women had higher retigabine maximum concentration (56%) and exposure (20%) but similar clearance (0.68 L x h(-1) x kg(-1)); these differences were related to differences in body weight. Although maximum concentration was similar in elderly subjects, retigabine elimination was slower (30% lower apparent clearance normalized for weight), resulting in higher exposure (42%) and a longer half-life (30%). Because phase II metabolism is scarcely affected by age, these differences may be related to the known decline of renal function with age. CONCLUSIONS: Although there are no substantial sex-related differences in the disposition of retigabine, a relevant decrease in clearance resulting in higher exposure occurs in elderly patients. The results suggest that decline of renal function with age may account for some of the observed changes.

Multiple-dose, linear, dose-proportional pharmacokinetics of retigabine in healthy volunteers.

Retigabine, a first-in-class selective M-current potassium channel opener, is a novel antiepileptic compound currently in clinical development. The purpose of this randomized placebo-controlled study was to assess retigabine oral safety and pharmacokinetics in healthy male volunteers (N = 45). Subjects received one dose on day 1 and doses every 12 hours for the next 14 days. Fixed doses were given to the first four groups (200, 400, 500, and 600 mg per day). Titrated doses were given to group 5 in 100 mg increases every 4 days, achieving 700 mg per day on day 15. Serial blood samples were collected on days 1 and 15. Pharmacokinetic parameters were compared between days and among dose groups. After administration of a single dose, retigabine was rapidly absorbed, with maximum concentrations of 387 ng/ml (normalized to a 100 mg dose) occurring within 1.5 hours. Retigabine was eliminated with a mean terminal half-life of 8.0 hours and an apparent oral clearance of 0.70 L/h/kg in white subjects. In black subjects, retigabine clearance and volume of distribution were 25% and 30% lower, respectively, after normalizing by body weight, leading to higher exposure in this population. Retigabine's pharmocokinetics was linearly dose proportional. Steady-state pharmacokinetics was in agreement with single-dose pharmacokinetics, and the accumulation ratio was about 1.5. Retigabine and AWD21-360 trough evening concentrations were significantly lower (about 30% to 35%) than morning values. The titration regimen allowed for higher doses to be tolerated compared to the fixed-dose regimen. In conclusion, the pharmacokinetics of retigabine is linearly dose proportional for daily doses of 100 to 700 mg and is not modified on multiple administrations.

Evaluation of the novel antiepileptic drug, AWD 131-138, for benzodiazepine-like discriminative stimulus and reinforcing effects in squirrel monkeys.

AWD 131-138 [1-(4-chlorophenyl)-4-morpholino-imidazolin-2-one], a new low-affinity partial benzodiazepine receptor agonist with potent anticonvulsant and anxiolytic properties in rodent models, was studied in squirrel monkeys trained to discriminate intramuscular (i.m.) injections of midazolam (0.3 mg/kg) from injections of vehicle. Diazepam produced midazolam-like responding at cumulative doses of 1.0 and 3.0 mg/kg i.m. and decreased rates of responding at 3.0 mg/kg (plasma levels of about 400 ng/ml). In contrast, AWD 131-138 did not produce midazolam-like responding or alter response rates at cumulative doses up to 18.0 mg/kg i.m. (plasma levels over 2100 ng/ml). Other monkeys were trained to intravenously (i.v.) self-administer cocaine (56.0 microg/kg/injection). When AWD 131-138 (10-100 microg/kg/injection) was studied by substitution, responding declined to vehicle substitution levels within three sessions. At the dose of 100 microg/kg i.v. AWD 131-138, sufficient drug was self-administered during the first session (about 3.5 mg/kg) to produce plasma levels above 1000 ng/ml, yet responding over the next two sessions dropped to vehicle levels. The failure of AWD 131-138 to produce benzodiazepine-like discriminative effects and the absence of drug self-administration behavior when substituted for cocaine suggest that its abuse liability is low.

Simultaneous enantioselective separation of azelastine and three of its metabolites for the investigation of the enantiomeric metabolism in rats. I. Liquid chromatography-ionspray tandem mass spectrometry and electrokinetic capillary chromatography.

Enantioselective separation methods and the enantioselective determination of the anti-allergic drug azelastine and of three of its main phase I metabolites in a biological matrix underwent chromatographic and electrophoretic investigations. An enantioselective assay of a coupling of HPLC using a beta-cyclodextrin chiral stationary phase to ionspray tandem mass spectrometry is presented. Additionally, this assay is compared to another enantioselective assay using electrokinetic capillary chromatography with beta-cyclodextrin and carboxymethyl-beta-cyclodextrin in polyacrylamide-coated capillaries. For capillary electrophoresis (CE) the importance of polyacrylamide coating for the validation of this separation method is highlighted. Extracted rat plasma samples of enantioselective metabolism studies were measured by both validated assays. Differences in the pharmacokinetics and pharmacodynamics were evaluated for the main substance azelastine and its main metabolite demethylazelastine. So, a first hint about the enantioselectivity of biotransformation of azelastine in rats was seen after oral application of either enantiomer or the racemate to rats.

Sensitive quantification of roflumilast and roflumilast N-oxide in human plasma by LC-MS/MS employing parallel chromatography and electrospray ionisation.

A high throughput bioanalytical method based on semi-automated liquid extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for the sensitive quantification of roflumilast and its metabolite roflumilast N-oxide, a phosphodiesterase (PDE) inhibitor in human plasma and serum. The sample work-up procedure comprised liquid extraction using penta-deuterated analogues of both analytes as internal standards. Chromatography was performed on C18 revered phase analytical columns at a flow rate of 0.5 mL/min in the dual column mode employing a column switching technique and a linear gradient from 18% to 54% acetonitrile in 0.005 M aqueous ammonium acetate containing 0.006% formic acid. Mass spectrometry was performed on an API 4000 instrument in the positive ion SRM-mode (selected reaction monitoring) with the Turbo-V ionspray interface. The method showed linear detector responses over the entire calibration range between 0.1 ng/mL (lower limit of quantification (LLOQ)) and 50 ng/mL (upper limit of quantification (ULOQ)) for both analytes. Linear regression analysis with concentration-squared weighting (1/x(2) for roflumilast and 1/x for roflumilast N-oxide) yielded inaccuracy and precision values <15% and coefficients of correlation (r) for the calibration curves >0.99 for both analytes.

Incurred sample reproducibility: views and recommendations by the European Bioanalysis Forum.

Following intensive discussions, review, alignment of procedures and multiple surveys among their member companies, the European Bioanalysis Forum (EBF) is providing a recommendation on how to integrate incurred sample reproducibility (ISR) in the bioanalytical process. The recommendation aims to provide guidance throughout the lifecycle of a validated method, including the application of the method in study support. In its recommendation, the EBF considers both the internal discussions with EBF member companies, as well as the input provided in international meetings where ISR was discussed. The ultimate goal of the EBF recommendation is to ensure that bioanalytical methods can provide accurate and reproducible concentration data for pharmacokinetic and/or toxicokinetic evaluation, without any compromise, while safeguarding the optimal use of laboratory resources.

Pharmacokinetic interaction between retigabine and lamotrigine in healthy subjects.

PURPOSE: The antiepileptic drugs (AEDs) retigabine (RGB) and lamotrigine (LTG) undergo predominantly N-glucuronidation and renal excretion. This study was performed to evaluate potential pharmacokinetic interactions between both AEDs. METHODS: Twenty-nine healthy male subjects participated in the study. Group A ( n=14) received single oral 200-mg RGB doses on day 1 and day 7, and 25 mg o.i.d. LTG on days 3-8. Group B ( n=15) received single oral 200-mg LTG doses on day 1 and day 17, and was up-titrated to 300 mg RGB b.i.d. on days 6-20. Blood samples were collected to compare the pharmacokinetics of both AEDs and the N-acetyl metabolite of RGB (AWD21-360) after single and concomitant treatments. RESULTS: RGB was rapidly absorbed and eliminated with a mean half-life (t(1/2)) of 6.3+/-1.1 h and an apparent clearance (CL/F) of 0.69+/-1.4 l/h/kg. Under co-administration of LTG, mean RGB t(1/2) and area under the plasma concentration-time curve (AUC) were increased by 7.5% ( P=0.045) and 15% ( P=0.006), respectively, while CL/F was decreased by 13% ( P=0.06). Consistent results were obtained for AWD21-360. LTG was moderately rapidly absorbed, eliminated with a mean t(1/2) of 37+/-10.4 h and a CL/F of 0.028+/-0.007 l/h/kg. Under co-administration of RGB, mean LTG t(1/2) and AUC decreased by 15% and 18%, respectively, while CL/F increased by 22% (all parameters, P=0.001). CONCLUSIONS: RGB and LTG exhibit a modest pharmacokinetic interaction on each other. The slight decline in RGB clearance due to LTG is believed to result from competition for renal elimination rather than competition for glucuronidation. The induction of LTG clearance due to retigabine was unexpected since RGB did not show enzyme induction in various other drug-drug interaction studies. Further studies in patients are needed to assess the clinical relevance of these findings for concomitant treatment with both drugs in the upper recommended dose range.