Risk factors for valproic acid induced hyperammonemia and its association with cognitive functions.

OBJECTIVE: Valproic acid (VPA)-induced hyperammonemia (VIH), is an increase in blood ammonia levels without any alteration of hepatic enzymes, which can occur during VPA treatment. We aimed to determine the prevalence rate and the risk factors for VIH and its association with cognitive functions. METHOD: A prospective, cross-sectional study was conducted. Patients aged between 18 and 64 who were on VPA treatment and who diagnosed with mood disorders or epilepsy were enrolled in this study (n = 107). For cognitive assessment, Serial 7's and Subjective Memory Complaints Questionnaire (SMCQ) were used. Blood samples were collected for blood VPA and ammonia levels along with other laboratory tests. RESULTS: 55,3% of the sample were considered as VIH. Blood ammonia level significantly correlates with VPA blood levels, total daily dose of VPA and total number of medications concurrently used, but no significant correlation was found between blood ammonia level and cognitive test scores. Gender, body weight, blood VPA levels and the total number of medications concurrently used significantly predicted blood ammonia levels (F(4,81) = 2670, p = 0,038, R2 = 0,116). CONCLUSION: VIH is relatively high in our sample. There is a dose-dependent association between VPA and blood ammonia level. No association was found between cognitive functions and hyperammonemia however with some limitations. Future, prospective cohort studies are needed.

Accuracy of Valproic Acid Concentration Correction Based on Serum Albumin.

BACKGROUND: Patient-specific factors can alter the pharmacokinetic disposition of valproic acid. Specifically, the free fraction of valproic acid can increase substantially in patients with hypoalbuminemia or as serum drug concentrations rise due to saturable protein binding. Direct measurement of free serum drug concentrations allows for accurate assessment of drug levels, but the assay may not be readily available in all institutions. The effect of hypoalbuminemia on free fraction has been quantified and serves as the basis of an equation used to "correct" measured total valproic acid concentrations. The aim of this study was to evaluate the accuracy of the equation. METHODS: This retrospective study included adult patients with measurable free and total valproic acid concentrations between July 2014 and June 2017. The primary aim was to assess the relationship between measured and predicted free valproic acid concentrations. Free levels were categorized as subtherapeutic, therapeutic, or supratherapeutic based on the reference range of 7-23 mg/L. Concordance was defined as measured and predicted concentrations falling within the same category. RESULTS: The analysis included 174 patients with a median age of 58 years and a median albumin of 3 g/dL. The majority of patients were hospitalized (88.5%). Concordance occurred in 56.9% of samples. A Spearman's correlation coefficient of 0.60 (p < 0.001) was found between the measured and predicted free valproic acid concentrations. Concordance of concentrations was 42% for ICU patients, 63% for floor patients, and 65% for outpatients. Of those with discordant concentrations, 97% of the predicted concentrations underestimated the measured concentrations. CONCLUSIONS: There is discordance between predicted and measured free serum valproic acid concentrations when using the proposed equation. Because of the potential impact of underestimation and variability of free valproic acid concentrations, a measured free level is the ideal option for therapeutic drug monitoring of valproic acid.

Therapeutic regimen of L-arginine for MELAS: 9-year, prospective, multicenter, clinical research.

OBJECTIVE: To examine the efficacy and safety of the therapeutic regimen using oral and intravenous L-arginine for pediatric and adult patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). METHODS: In the presence and absence of an ictus of stroke-like episodes within 6 h prior to efficacy assessment, we correspondingly conducted the systematic administration of oral and intravenous L-arginine to 15 and 10 patients with MELAS in two, 2-year, prospective, multicenter clinical trials at 10 medical institutions in Japan. Subsequently, patients were followed up for 7 years. The primary endpoint in the clinical trial of oral L-arginine was the MELAS scale, while that for intravenous L-arginine was the improvement rates of headache and nausea/vomiting at 2 h after completion of the initial intravenous administration. The relationships between the ictuses of stroke-like episodes and plasma arginine concentrations were examined. RESULTS: Oral L-arginine extended the interictal phase (p = 0.0625) and decreased the incidence and severity of ictuses. Intravenous L-arginine improved the rates of four major symptoms-headache, nausea/vomiting, impaired consciousness, and visual disturbance. The maximal plasma arginine concentration was 167 µmol/L when an ictus developed. Neither death nor bedriddenness occurred during the 2-year clinical trials, and the latter did not develop during the 7-year follow-up despite the progressively neurodegenerative and eventually life-threatening nature of MELAS. No treatment-related adverse events occurred, and the formulations of L-arginine were well tolerated. CONCLUSIONS: The systematic administration of oral and intravenous L-arginine may be therapeutically beneficial and clinically useful for patients with MELAS.

Fingerprints of CNS drug effects: a plasma neuroendocrine reflection of D2 receptor activation using multi-biomarker pharmacokinetic/pharmacodynamic modelling.

BACKGROUND AND PURPOSE: Because biological systems behave as networks, multi-biomarker approaches increasingly replace single biomarker approaches in drug development. To improve the mechanistic insights into CNS drug effects, a plasma neuroendocrine fingerprint was identified using multi-biomarker pharmacokinetic/pharmacodynamic (PK/PD) modelling. Short- and long-term D2 receptor activation was evaluated using quinpirole as a paradigm compound. EXPERIMENTAL APPROACH: Rats received 0, 0.17 or 0.86 mg·kg-1 of the D2 agonist quinpirole i.v. Quinpirole concentrations in plasma and brain extracellular fluid (brainECF ), as well as plasma concentrations of 13 hormones and neuropeptides, were measured. Experiments were performed at day 1 and repeated after 7-day s.c. drug administration. PK/PD modelling was applied to identify the in vivo concentration-effect relations and neuroendocrine dynamics. KEY RESULTS: The quinpirole pharmacokinetics were adequately described by a two-compartment model with an unbound brainECF -to-plasma concentration ratio of 5. The release of adenocorticotropic hormone (ACTH), growth hormone, prolactin and thyroid-stimulating hormone (TSH) from the pituitary was influenced. Except for ACTH, D2 receptor expression levels on the pituitary hormone-releasing cells predicted the concentration-effect relationship differences. Baseline levels (ACTH, prolactin, TSH), hormone release (ACTH) and potency (TSH) changed with treatment duration. CONCLUSIONS AND IMPLICATIONS: The integrated multi-biomarker PK/PD approach revealed a fingerprint reflecting D2 receptor activation. This forms the conceptual basis for in vivo evaluation of on- and off-target CNS drug effects. The effect of treatment duration is highly relevant given the long-term use of D2 agonists in clinical practice. Further development towards quantitative systems pharmacology models will eventually facilitate mechanistic drug development.

Reduced clearance of venlafaxine in a combined treatment with quetiapine.

Venlafaxine and the atypical antipsychotic quetiapine are often administered concomitantly. Both drugs share several metabolic hepatic pathways. However, pharmacokinetic interactions between venlafaxine and quetiapine have not been studied yet. A therapeutic drug monitoring database containing serum concentrations of venlafaxine (VEN) and its active metabolite O-desmethylvenlafaxine (ODVEN) was analyzed. Two groups of patients were compared: venlafaxine monotherapy V0 (n = 153) and co-medication with quetiapine, VQUE (n = 71). Serum concentrations of VEN, ODVEN, and active moiety, AM (VEN + ODVEN), metabolite to parent compound ratio (ODVEN/VEN) and dose adjusted serum concentrations were compared using non-parametrical tests without information on CYP2D6 genotype. The two groups did not differ in terms of the daily dosage of venlafaxine, age, or sex. Median serum concentrations in the quetiapine group showed significantly, 15.8% and 29.3% higher values for AM and ODVEN (p = 0.002, Cohen's d = 0,41; p = 0.003, d = 0,44), respectively. Dose adjusted serum concentrations of active moiety and ODVEN revealed comparable differences (p = 0.038, d = 0,32; p = 0.015, d = 0,28) with significantly higher values in the co-medicated group. Significantly higher values for ODVEN and AM suggest a reduced clearance of ODVEN and active moiety when quetiapine is co-administered. This may be a consequence of a reduced metabolism of venlafaxine to the inactive metabolite N-desmethylvenlafaxine via CYP3A4, the main metabolizing enzyme for quetiapine, and a shift towards a higher proportion of the active metabolite ODVEN. Therapeutic drug monitoring is recommended in the case of co-medication to ensure clinical efficacy and patient safety. Although the increase of AM is moderate, we consider it relevant for clinicians given the prevalence of concomitant medication of quetiapine and venlafaxine.

Distribution of Eight QT-Prolonging Drugs and Their Main Metabolites Between Postmortem Cardiac Tissue and Blood Reveals Potential Pitfalls in Toxicological Interpretation.

Femoral blood concentrations are usually used in postmortem toxicology to assess possible toxic effects of drugs. This includes QT-prolongation and other cardiac dysrhythmia, which could have been the cause of death. However, blood concentration is only a surrogate for the active site concentration, and therefore cardiac tissue concentration may provide a more accurate toxicological interpretation. Thus, cardiac tissue and femoral and cardiac blood concentrations were examined for eight frequently used QT-prolonging drugs (QTD) and their metabolites in a mentally ill population. In total, 180 cases were included from the Danish autopsy-based forensic study SURVIVE. The concentrations were analyzed using ultra-performance liquid chromatography coupled with tandem mass spectrometry utilizing stable isotopically labeled internal standards. The results showed that the cardiac tissue concentrations were significantly higher compared to femoral and cardiac blood concentrations, with two exceptions. The median cardiac tissue-to-femoral blood concentration ratio (Kb) ranged from 2.2 (venlafaxine) to 15 (nortriptyline). The inter-individual fold difference between the minimum and maximum Kb ranged from 2.6-fold (Z-hydroxynortriptyline) to 61 (venlafaxine). For 12 compounds, postmortem redistribution appeared to be minimal, whereas four compounds displayed some degree of postmortem redistribution. Citalopram and quetiapine were selected for in-depth analysis of the relation between the toxicological interpretation and femoral blood/cardiac tissue concentrations. Within this dataset, citalopram displayed a wide overlap in cardiac tissue concentrations (~50%) between non-toxic and toxic citalopram cases, as estimated from femoral blood concentrations. In contrast, quetiapine displayed no overlap in cardiac tissue concentrations between non-toxic and toxic quetiapine cases based on femoral blood concentrations. The implication of the citalopram finding is that possible intoxications can be overlooked when only considering femoral blood concentrations. Based on the present findings, non-toxic cardiac tissue 10th-90th percentile concentration ranges were estimated for citalopram (0.93-4.4 mg/kg) and quetiapine (0.0073-0.60 mg/kg).

Prediction of brain:blood unbound concentration ratios in CNS drug discovery employing in silico and in vitro model systems.

Recent years have seen a paradigm shift away from optimizing the brain:blood concentration ratio toward the more relevant brain:blood unbound concentration ratio (Kp,uu,br) in CNS drug discovery. Here, we review the recent developments in the in silico and in vitro model systems to predict the Kp,uu,br of discovery compounds with special emphasis on the in-vitro-in-vivo correlation. We also discuss clinical 'translation' of rodent Kp,uu,br and highlight the future directions for improvement in brain penetration prediction. Important in this regard are in silico Kp,uu,br models built on larger datasets of high quality, calibration and deeper understanding of experimental in vitro transporter systems, and better understanding of blood-brain barrier transporters and their in vivo relevance aside from P-gp and BCRP.

High brain distribution of a new central nervous system drug candidate despite its P-glycoprotein-mediated efflux at the mouse blood-brain barrier.

Efficacy of drugs aimed at treating central nervous system (CNS) disorders rely partly on their ability to cross the cerebral endothelium, also called the blood-brain barrier (BBB), which constitutes the main interface modulating exchanges of compounds between the brain and blood. In this work, we used both, conventional pharmacokinetics (PK) approach and in situ brain perfusion technique to study the blood and brain PK of PKRinh, an inhibitor of the double-stranded RNA-dependent protein kinase (PKR) activation, in mice. PKRinh showed a supra dose-proportional blood exposure that was not observed in the brain, and a brain to blood AUC ratio of unbound drug smaller than 1 at all tested doses. These data suggested the implication of an active efflux at the BBB. Using in situ brain perfusion technique, we showed that PKRinh has a very high brain uptake clearance which saturates with increasing concentrations. Fitting the data to a Michaelis-Menten equation revealed that PKRinh transport through the BBB is composed of a passive unsaturable flux and an active saturable protein-mediated efflux with a km of ≅ 3 µM. We were able to show that the ATP-binding cassette (ABC) transporter P-gp (Abcb1), but not Bcrp (Abcg2), was involved in the brain to blood efflux of PKRinh. At the circulating PKRinh concentrations of this study, the P-gp was not saturated, in accordance with the linear brain PKRinh PK. Finally, PKRinh had high brain uptake clearance (14 µl/g/s) despite it is a good P-gp substrate (P-gp Efflux ratio ≅ 3.6), and reached similar values than the cerebral blood flow reference, diazepam, in P-gp saturation conditions. With its very unique brain transport properties, PKRinh improves our knowledge about P-gp-mediated efflux across the BBB for the development of new CNS directed drugs.

Simulating therapeutic drug monitoring results for dose individualisation to maintain investigator blinding in a randomised controlled trial.

BACKGROUND: Therapeutic drug monitoring (TDM) is essential practice when dosing drugs with a narrow therapeutic index in order to achieve a plasma drug concentration within a narrow target range above the efficacy concentration but below the toxicity concentration. However, TDM with dose individualisation is challenging during a double-blind clinical trial with laboratory staff and investigators blinded to treatment arm allocation. METHODS: Drug concentrations were simulated for participants in the placebo arm by an unblinded independent statistician, utilising the measured values from the treatment arm participants. Simulated and actual concentrations were re-blinded and passed on to a dose-adjusting investigator, who made dose adjustment recommendations but was not directly responsible for clinical care of participants. RESULTS: A total of 257 sham lithium plasma concentrations were simulated utilising 242 true lithium plasma concentrations in real time as the trial progressed. The simulated values had a median (interquartile range) of 0.59 (0.46, 0.72) compared to 0.53 (0.39, 0.72) in the treatment arm. Blinding of the laboratory staff and dose-adjusting investigator was maintained successfully. CONCLUSIONS: We succeeded in simulating sham lithium plasma concentrations while maintaining blinding. Our simulated values have a smaller range than the observed data, which can be explained by the challenges with respect to drug adherence and dose timing that were experienced. TRIAL REGISTRATION: Pan African Clinical Trials Registry, PACTR201310000635418 . Registered on 30 August 2013.

Determination of drugs in plasma samples by disposable pipette extraction with C18-BSA phase and liquid chromatography-tandem mass spectrometry.

This work describes restricted access material (RAM) constituted of porous octadecylsilane particles with the outer surface covered with bovine serum albumin (C18-BSA) as a stationary phase to extract drugs from plasma samples by disposable pipette extraction (DPX) for further analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The C18-BSA phase simultaneously excluded macromolecules by chemical diffusion barrier (BSA network) and enrichment of the interior phase (C18) with drug traces by sorption. The hydrophilic barrier of the C18-BSA allows small molecules (drugs) to permeate through the hydrophobic part (C18), while at the same time it excludes the macromolecules by chemical diffusion barrier (BSA network). Optimization of the DPX variables (sorption equilibration time, exclusion of endogenous compounds, and elution step) improved the sensitivity and selectivity of the method, which presented a linear range from the lower limit of quantification (0.5-20.0ngmL-1) to the upper limit of quantification (32.5-10,500ngmL-1), inter- and intra-assay precision with coefficients of variation (CV) lower than 15%, and relative standard error (RSE) of the accuracy ranging from -12% to 11%. The developed method was successfully used to determine five antipsychotics (olanzapine, quetiapine, clozapine, haloperidol, and chlorpromazine) in combination with seven antidepressants (mirtazapine, paroxetine, citalopram, sertraline, imipramine, clomipramine, and fluoxetine), two anticonvulsants (carbamazepine and lamotrigine), and two anxiolytics (diazepam and clonazepam) in plasma samples from schizophrenic patients for therapeutic drug monitoring.

Clinically Relevant Levels of 4-Aminopyridine Strengthen Physiological Responses in Intact Motor Circuits in Rats, Especially After Pyramidal Tract Injury.

BACKGROUND: 4-Aminopyridine (4-AP) is a Food and Drug Administration-approved drug to improve motor function in people with multiple sclerosis. Preliminary results suggest the drug may act on intact neural circuits and not just on demyelinated ones. OBJECTIVE: To determine if 4-AP at clinically relevant levels alters the excitability of intact motor circuits. METHODS: In anesthetized rats, electrodes were placed over motor cortex and the dorsal cervical spinal cord for electrical stimulation, and electromyogram electrodes were inserted into biceps muscle to measure responses. The motor responses to brain and spinal cord stimulation were measured before and for 5 hours after 4-AP administration both in uninjured rats and rats with a cut lesion of the pyramidal tract. Blood was collected at the same time as electrophysiology to determine drug plasma concentration with a goal of 20 to 100 ng/mL. RESULTS: We first determined that a bolus infusion of 0.32 mg/kg 4-AP was optimal: it produced on average 61.5 ± 1.8 ng/mL over the 5 hours after infusion. This dose of 4-AP increased responses to spinal cord stimulation by 1.3-fold in uninjured rats and 3-fold in rats with pyramidal tract lesion. Responses to cortical stimulation also increased by 2-fold in uninjured rats and up to 4-fold in the injured. CONCLUSION: Clinically relevant levels of 4-AP strongly augment physiological responses in intact circuits, an effect that was more robust after partial injury, demonstrating its broad potential in treating central nervous system injuries.

Clozapine N-Oxide Administration Produces Behavioral Effects in Long-Evans Rats: Implications for Designing DREADD Experiments.

Clozapine N-oxide (CNO) is a ligand for a powerful chemogenetic system that can selectively inhibit or activate neurons; the so-called Designer Receptors Exclusively Activated by Designer Drugs (DREADD) system. This system consists of synthetic G-protein-coupled receptors, which are not believed to be activated by any endogenous ligand, but are activated by the otherwise inert CNO. However, it has previously been shown that the administration of CNO in humans and rats leads to detectable levels of the bioactive compounds clozapine and N-desmethylclozapine (N-Des). As a follow-up, experiments were conducted to investigate the effects of CNO in male Long-Evans rats. It was found that 1 mg/kg CNO reduced the acoustic startle reflex but had no effect on prepulse inhibition (PPI; a measure of sensorimotor gating). CNO (2 and 5 mg/kg) had no effect on the disruption to PPI induced by the NMDA antagonist phencyclidine or the muscarinic antagonist scopolamine. In locomotor studies, CNO alone (at 1, 2, and 5 mg/kg) had no effect on spontaneous locomotion, but 5 mg/kg CNO pretreatment significantly attenuated d-amphetamine-induced hyperlocomotion. In line with the behavioral results, fast-scan cyclic voltammetry found that 5 mg/kg CNO significantly attenuated the d-amphetamine-induced increase in evoked dopamine. However, the effects seen after CNO administration cannot be definitively ascribed to CNO because biologically relevant levels of clozapine and N-Des were found in plasma after CNO injection. Our results show that CNO has multiple dose-dependent effects in vivo and is converted to clozapine and N-Des emphasizing the need for a CNO-only DREADD-free control group when designing DREADD-based experiments.

Do blood plasma levels of oxytocin moderate the effect of nasally administered oxytocin on social orienting in high-functioning male adults with autism spectrum disorder?

OBJECTIVE: The study investigated whether baseline plasma oxytocin (OXT) concentrations might moderate the effects of nasally administered OXT on social orienting. METHODS: Thirty-one males with Autism spectrum disorder (ASD) and thirty healthy males participated in a double-blind placebo-controlled crossover trial. After administration of the compound, participants were viewing pictures from the International Affective Picture System that represented a systematic variation of pleasant, unpleasant and neutral scenes with and without humans. The outcome measures were a cardiac evoked response (ECR) and a cortical evoked long latency parietal positivity (LPP). RESULTS: Males with ASD had significantly higher plasma baseline levels than the controls. In the absence of general treatment effects, higher baseline concentrations were found to be associated with larger treatment effects, particularly in the group of males with ASD. Higher post-treatment plasma OXT concentrations were found to be associated with smaller treatment effects and larger orienting responses in the placebo situation in the group of controls. CONCLUSIONS: We interpret our findings as suggesting that it is the central availability of OXT determining how much of the nasally administered OXT will become centrally absorbed and how much of it will become released into the bloodstream.

Effects of low dose ibogaine on subjective mood state and psychological performance.

ETHNOPHARMACOLOGICAL RELEVANCE: Root bark from Tabernanthe iboga has been used traditionally in West Africa as a psychoactive substance in religious rituals. In smaller doses it is reported anecdotally to have stimulant properties. AIM OF THE STUDY: To evaluate the influence of a single 20mg ibogaine dose on psychological variables reflecting subjective mood state and a range of cognitive functions. MATERIALS AND METHODS: 21 healthy male volunteers received single 20mg doses of ibogaine after 6 days pretreatment with double-blind paroxetine or placebo. We compared responses to a battery of psychometric tests and subjective mood ratings performed before and 2h after ibogaine dosing, and assessed relationships between changes in test scores and concentrations of active moiety (the sum of molar noribogaine and ibogaine concentrations). Psychological tests were chosen based on responsiveness to opioid and serotonergic ligands. RESULTS: Ibogaine had minimal influence on psychological tests and mood ratings. The ability to selectively ignore distracting spatial information showed some evidence of modulation; however because this effect was limited to the less challenging condition calls into question the reliability of this result. CONCLUSION: We were unable to identify stimulant effects after single 20mg doses of ibogaine. Future research is needed to confirm whether active moiety concentrations impact selective attention abilities while leaving other cognitive functions and mood state unaffected.

A randomized, controlled, double-blind, crossover trial of zonisamide in myoclonus-dystonia.

OBJECTIVE: To evaluate the efficacy and safety of zonisamide in patients with myoclonus-dystonia. METHODS: We conducted a randomized, double-blind, placebo-controlled crossover trial of zonisamide (300 mg/d) in 24 patients with myoclonus-dystonia. Each treatment period consisted of a 6-week titration phase followed by a 3-week fixed-dose phase. The periods were separated by a 5-week washout period. The co-primary outcomes were action myoclonus severity (section 4 of the Unified Myoclonus Rating Scale [UMRS 4]) and myoclonus-related functional disability (UMRS 5). Secondary outcomes included dystonia severity, assessed with the movement and disability subscales of the Burke-Fahn-Marsden-Dystonia Rating Scale (BFM), the Clinical Global Impression-Improvement scale (CGI), and safety measures. Wilcoxon signed-rank tests for paired data were used to analyze treatment effects. RESULTS: Twenty-three patients (11 men, 12 women) were analyzed in the intention-to-treat analysis. Zonisamide significantly improved both action myoclonus (median improvement [95% confidence limits] -5 [-9.25 to -1.44], p = 0.003) and myoclonus-related functional disability (median improvement [95% confidence limits] -2 [-2.58 to -2.46], p = 0.007) compared to placebo. Zonisamide also significantly improved dystonia (BFM movement) compared to placebo (median improvement [95% confidence limits] -3 [-8.46 to 0.03], p = 0.009). No difference was found between zonisamide and placebo with respect to the CGI (median improvement [95% confidence limits] -1 [-1.31 to 0.09], p = 0.1). Zonisamide was well-tolerated. CONCLUSIONS: Zonisamide is well-tolerated and effective on the motor symptoms of myoclonus-dystonia. CLASSIFICATION OF EVIDENCE: This study provides Class I evidence that zonisamide improves myoclonus and related disability in patients with myoclonus-dystonia.

Search for fungi-specific metabolites of four model drugs in postmortem blood as potential indicators of postmortem fungal metabolism.

Fungi colonizing cadavers are capable of drug metabolism and may thus change the metabolite pattern or concentration of drugs in forensic postmortem samples. The purpose of this study was to check for the presence of such changes by searching fungi-specific metabolites of four model drugs (amitriptyline, metoprolol, mirtazapine, and zolpidem) in decomposed postmortem blood samples from 33 cases involving these drugs. After isolation and identification of fungal strains present in the samples, each isolate was incubated in Sabouraud medium at 25°C for up to 120h with each model drug. One part of the supernatants was directly analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), another after liquid-liquid extraction with chlorobutane and concentration. From 21 out of 33 decomposed postmortem blood samples (64%) a total of 30 different strains could be isolated, one from the class of Ascomycete and the rest belonging to 15 species from 8 different genera (number of species): Aspergillus (2), Botrytis (1), Candida (8), Fusarium (1), Mucor (1), Penicillium (1), and Rodothorula (1). In the in vitro studies, these microorganisms were found capable of N-demethylation and N-oxidation of amitriptyline and mirtazapine, O-demethylation followed by side chain oxidation of metoprolol as well as hydroxylation of all four-model drugs. In two of the postmortem blood samples, from which the fungi Aspergillus jensenii, Candida parapsilosis. and Mucor circinelloides had been isolated, a fungi-specific hydroxy zolpidem metabolite was detected. The presence of this metabolite in postmortem samples likely indicates postmortem fungal biodegradation.

Brain-blood ratio: implications in brain drug delivery.

INTRODUCTION: The brain-blood ratio is an important model correlating the brain-targeting ability of neurotherapeutics with the CNS pharmacokinetics, which need to be presented before the scientific community for exploration of its scientific worth. The purpose of this article is to bring this key concept and its precise discussion to the attention of the researchers. AREAS COVERED: Three major points are discussed herein: First, the significance of brain-blood ratio with respect to investigational neurotherapeutics, and carrier systems and correlation of its research findings with the brain targeting efficiency. Second, the various factors influencing the brain-blood ratio. Third, the various strategies for enhancing the brain-blood ratio. In addition, the benchmark criteria for CNS-likeness of drug molecules and the correlation of brain-blood ratio with brain targeting ability of neurotherapeutics have been tabulated. EXPERT OPINION: The brain-blood ratio (also referred to as the brain-plasma ratio) represents one of the tools available today for estimation of CNS pharmacokinetics. It is preferred over other complicated techniques (in situ brain perfusion and microdialysis) due to its ease of use and practicality. We are optimistic that the brain-blood ratio offers an excellent way of evaluating brain-targeting efficiency of neurotherapeutics effectively. In our opinion, it is a very fundamental aspect of brain bioavailability and needs to be presented in a precise way.

Pupil function as an indicator of being under the influence of central nervous system-acting substances from a traffic-medicine perspective - Part II.

In order to evaluate driving abilities of each traffic participant, standardised and objective measurement methods are needed. The applicability and value of infrared pupillography as an objective measurement method to indicate possible influence of central nervous acting substances has been demonstrated in former publications. Healthy test subjects (n = 41), as well as persons who were under the influence of drugs and/or medication (n = 105), were exposed to different light stimuli using infrared technology in order to demonstrate the relevance of specific parameters of the pupillary light reflex (PLR) in the field of traffic medicine. Based on former reported results, the statistical examination was extended to further parameters of the PLR, which again confirmed the high value of infrared pupillography as a reliable indicator of previous consumption of drugs and/or medication.

Simulation of PET scan timings for receptor occupancy studies of CNS drugs: a simple fixed-time design performed as well as scattered time point designs.

PURPOSE: This study aimed to determine the effect of PET scan timings on the reliability of occupancy parameter estimates and to identify the scan timing design that gives the most reliable occupancy parameter estimates. METHODS: We compared the performance of designs with various sets of sampling time points using the stochastic simulation and estimation method in Perl-speaks-NONMEM. Biases, relative standard errors, relative estimation errors, and root mean square errors were used to compare the performance of designs. RESULTS: Unlike the results of a previous report, we found that rather complicated designs where each subject or group of subjects are allocated to different scan timings were not superior to the simple, conventional fixed-time designs regardless of whether effect compartment or receptor binding models were used. CONCLUSIONS: We conclude that the conventional fixed-time designs that have been used so far may give robust PD parameter estimates for occupancy data obtained from human PET studies of CNS drugs.

Circadian rhythms of hemostatic factors in tetraplegia: a double-blind, randomized, placebo-controlled cross-over study of melatonin.

STUDY DESIGN: This is a double-blind, randomized, placebo-controlled cross-over study of melatonin in complete tetraplegia. OBJECTIVES: Tetraplegic patients have an increased risk of venous thrombosis despite prophylaxis, blunted variations in melatonin and altered circadian variation of several hemostatic markers. To examine whether melatonin could modify the regulation of hemostasis, we measured plasma melatonin and several markers of hemostasis in tetraplegic subjects with or without melatonin supplement. SETTING: The study was conducted in the Section for Spinal Cord Injury, Sunnaas Hospital, Nesoddtangen, Norway. METHODS: Six subjects with long-standing complete tetraplegia were included in this cross-over study with 2 mg of melatonin or placebo given 4 days before sampling. We also included six able-bodied men without any intervention. Plasma samples were then collected frequently during a 24-h awake/sleep cycle. The plasma concentrations of melatonin and the various markers were analyzed using linear mixed models. RESULTS: The 24-h profiles of prothrombin fragment 1+2 and von Willebrand factor, but not D-dimer, activated FVII, tissue factor pathway inhibitor and plasminogen activator inhibitor type 1, differed (P<0.05) between tetraplegic patients and able-bodied subjects. The absolute plasma concentration of activated FVII was higher (P<0.05) among the able-bodied compared with the tetraplegic groups. Supplementation of melatonin had no impact on these findings. CONCLUSIONS: We found differences in circadian variation of several hemostatic markers between able-bodied and tetraplegics. These differences were apparently unrelated to fluctuations in the melatonin concentrations, suggesting little or no role of melatonin in the regulation of hemostasis in tetraplegia. SPONSORSHIP: Financial support was provided from the Throne Holst Foundation.