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Purpose: Rivaroxaban is a substrate for ABCB1 transporter and is commonly used in patients undergoing hip or knee replacement surgery for thromboprophylaxis. The objective of this study was to develop a population pharmacokinetic-pharmacodynamic (PK-PD) model to investigate the influence of ABCB1 gene expression and polymorphism on rivaroxaban exposure and anticoagulation effects., Methods: Five blood samples per patient were collected during 5 days after the surgery for the determination of rivaroxaban concentration in plasma and for determination of prothrombin time and partial thromboplastin time. Non-linear mixed effects model was used for a population PK-PD analysis and for testing covariate effects., Results: A one-compartment PK model with first-order absorption adequately described the pharmacokinetic data. The typical oral clearance (CL/F) was 6.12 L/h (relative standard error, 15.8%) and was associated with ABCB1 expression. Compared to base line before the surgery, a significant ABCB1 downregulation was observed 5 days after the surgery (p < 0.001). Prothrombin time and partial thromboplastin time were both linearly associated to the logarithm of the rivaroxaban plasma concentration., Conclusions: We confirmed that variable rivaroxaban CL/F is associated with ABCB1 expression, which is in accordance with previous studies on P-glycoprotein involvement in rivaroxaban PK. Furthermore, we observed the downregulation of ABCB1 expression after the surgery. The cause remains unclear and further research is needed to explain the underlying mechanisms. more...

Vinpocetine is a poorly water soluble weakly basic drug (pK a  = 7.1) used for the treatment of several cerebrovascular and cognitive disorders. Because existing formulations exhibit poor bioavailability and scarce absorption, a dosage form with improved pharmacokinetic properties is highly desirable. Cocrystallization represents a promising approach to generate diverse novel crystal forms and to improve the aqueous solubility and in turn the oral bioavailability. In this article, a novel ionic cocrystal of vinpocetine is described, using boric acid as a coformer, and fully characterized (by means of differential scanning calorimetry, solid-state nuclear magnetic resonance, powder and single-crystal X-ray diffraction, and powder dissolution test). Pharmacokinetic performance was also tested in a human pilot study. This pharmaceutical ionic cocrystal exhibits superior solubilization kinetics and modulates important pharmacokinetic values such as maximum concentration in plasma (C max ), time to maximum concentration (t max ), and area under the plasma concentration-time curve (AUC) of the poorly soluble vinpocetine and it therefore offers an innovative approach to improve its bioavailability., (Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.) more...

Purpose: We investigated bisoprolol pharmacokinetics, including longitudinal changes and importance of patient characteristics in chronic heart failure., Methods: Forty-six patients with chronic heart failure (57 % male, NYHA class I/II/III = 2/36/8) were followed for an average of 8 ± 2 months. At baseline and follow-up, plasma bisoprolol concentrations were determined and body composition was measured using dual-energy X-ray absorptiometry. A bisoprolol pharmacokinetic model was built with non-linear mixed-effects modeling to analyze the association with various parameters of body composition., Results: Mean bisoprolol clearance (10.2 L/h) was 30 % lower than in healthy individuals and correlated with MDRD4-estimated renal function. The mean volume of distribution (230 L) was similar to healthy population and was associated with total body mass and skeletal muscle index (SMI). During follow-up, we observed minor changes in the absorption rate constant (2.83 vs. 2.27 h(-1), P = 0.030) and volume of distribution (227 vs. 250 L, P = 0.004), which are not clinically relevant., Conclusions: In patients with chronic heart failure, bisoprolol clearance was associated with estimated renal function; thus, in moderately and severely decreased renal function, patients may need to have their dose adjusted. Patients with low body weight or low SMI have greater fluctuations and higher maximal plasma concentrations of bisoprolol because of the lower volume of distribution. Longitudinal changes of bisoprolol pharmacokinetics were not associated with changes in body composition. more...

Background: Therapeutic drug monitoring of etoposide is not part of the routine clinical practice, however, measuring etoposide plasma concentration may be useful to prevent chemotherapy related adverse drug reactions. This paper describes the development and validation of a dried blood spot (DBS) assay for the determination of etoposide in blood samples of lung cancer patients., Methods: The whole blood spot was cut out of the DBS card followed by sonication assisted liquid drug extraction. Extraction solution was evaporated and re-dissolved. A high-performance-liquid-chromatography method with fluorimetric detection ( λex=230nm; λem=330nm) was used., Results: Method met the validation criteria in terms of selectivity, linearity (0.5-20.0μg/mL), accuracy (≥96.1%), precision (≤10.1%) and stability (long term 4weeks at room temperature and 40°C). Haematocrit did not influence DBS etoposide concentration. Good correlation between measured plasma and DBS concentrations was observed. The equation considering only haematocrit value was used for conversion of DBS to plasma concentration., Conclusions: DBS sampling method showed comparable results to plasma samples. Therefore, it can be concluded that the developed and validated DBS method, which is more patient-friendly and requires less sample handling, is a reliable alternative to conventional plasma methods for measuring etoposide concentration in clinical pharmacological analyses., (Copyright © 2015 Elsevier B.V. All rights reserved.) more...

Heparin is still widely used for treatment and prevention of thromboembolic diseases. Due to specific physicochemical properties, it requires frequent parenteral injections. In this study we present the development and in vitro evaluation of an advanced delivery system for prolonged subcutaneous release of heparin. The delivery system consisted of an in situ forming thermoresponsive poloxamer-based platform combined with pH-responsive polyelectrolyte heparin/chitosan nanocomplexes. Thermoresponsive hydrogels were tested for gelation temperature, gel dissolution and in vitro heparin release, whereas polyelectrolyte nanocomplexes were physico-chemically characterized, as well as tested for in vitro cytotoxicity and in vitro heparin release. Hydrogel combined of two poloxamers demonstrated the highest gelation temperature (28.6°C), while the addition of hydroxypropyl methylcellulose prolonged gel dissolution. On the other hand, nanocomplexes' dispersions, prepared at 1:1 heparin/chitosan mass ratio and in the concentration range 0.375-1.875mg/mL, demonstrated mean diameter <400nm and zeta potential >34mV. Pharmacokinetics of selected formulations (thermoresponsive hydrogel, nanocomplexes and a dual system consisting of nanocomplexes incorporated into thermoresponsive hydrogel) were studied in rats. Heparin plasma concentration-time profiles revealed a double-peak phenomenon, probably due to heparin diffusion inside the polymer matrix and gel dissolution. Pharmacokinetic parameters were determined by a non-linear mixed effects modeling approach. It was demonstrated that thermoresponsive hydrogel with heparin/chitosan nanocomplexes enabled the lowest absorption rate of heparin into systemic circulation and provided heparin concentration above the prophylaxis threshold for 5 days. In situ gelling thermoresponsive matrix combined with chitosan nanocomplexes present a promising delivery system for heparin, requiring less frequent administration during long-term treatment., (Copyright © 2015 Elsevier B.V. All rights reserved.) more...

An attractive herbal product, softgel capsules containing 10 mg of Echinacea angustifolia lipophilic extract, was given in a single oral administration to 10 human volunteers to perform a pharmacokinetic and immunological study. The plasma concentration of the major constituent was monitored, quantifying at predetermined time points the dodeca-2E,4E,8Z,10E/Z-tetraenoic isobutylamides (tetraene). The plasmatic levels of IL-2, IL-6, IL-8, IL-10 and TNF-a in samples collected before and 24 h after drug administration were analyzed by cytokine assay. The total RNA was extracted from limpho-monocyte isolated from the same blood samples and the same cytokines in terms of gene expression were evaluated. With the help of proper statistical tests the differences between the values obtained at 0 and 24 h were evaluated. Results of pharmacokinetic studies attest an approximately 3.5-fold improvement of tetraene oral bioavailability compared with previously published studies. Dodeca-2E,4E-dienoic acid isobutylamide exerts immunomodulatory effects down-regulating the gene expression and reducing the protein plasmatic levels of pro-inflammatory cytokines such as IL-6, TNF-α and IL-8, and up-regulating the expression of anti-inflammatory molecules as IL-10. Student's two-sided paired t-test and non-parametric Wilcoxon-Mann-Whitney signed rank test agree in the conclusions about the differences between the ln values at 24 h and corresponding ln values at 0 h., (Copyright © 2015 Elsevier B.V. All rights reserved.) more...

Therapeutic drug monitoring (TDM) is a multi-disciplinary clinical specialty used for optimization and individualization of drug therapy in the general and special populations. Since most antiepileptic drugs (AEDs) are characterized by pronounced intra- and inter-individual variability, it can be especially valuable as an aid for dosing adjustments in patients with epilepsy. Dried blood spots (DBS) sampling technique is recognized as a suitable alternative for conventional sampling methods as TDM interventions should be applied in the most cost-effective, rational and clinically useful manner. In the present review we summarize the latest trends and applications of DBS in TDM of epilepsy. Quantification of AEDs in DBS was employed in various clinical settings and has been already reported for phenobarbital, phenytoin, valproic acid, clonazepam, clobazam, carbamazepine, topiramate, rufinamide, lamotrigine, 10-hydroxycarbazepine and levetiracetam. The major limitation of the published studies are restricted evaluation of critical parameters such as the impact of spotted blood volume, spot homogeneity and haematocrit effect, limited clinical validation and non-established correlations between the DBS and plasma concentrations of AEDs. Standardization of critical technical aspects for appropriate sampling, sample preparation and validation of the analytical procedures for quantification of the drugs, as well as appropriate interpretation of the results are the fields which should get more attention in upcoming studies. Limited data on clinical validation and the fact that this technique has been used in practice only for a few AEDs makes the routine implementation of TDM of AEDs using DBS method a big challenge that should be faced by the pharmaceutical scientists in the future., (Copyright © 2015 Elsevier B.V. All rights reserved.) more...

Low molecular weight heparins (LMWHs) have risen in popularity over the past decades. Owing to their appropriate pharmacokinetic profile, they enable long-term clinical applications, e.g. prophylaxis of deep vein thrombosis. Although the administration of LMWHs is not as frequent as of heparin, it still requires once daily injection at least. In order to prolong LMWH release, and thus provide less frequent subcutaneous administration, we designed and thoroughly evaluated thermoresponsive poloxamer-based systems combined with LMWH/chitosan pH-responsive nanocomplexes. A LMWH/chitosan mass ratio of 1:2 was the most appropriate for preparation of small, homogenous and stable nanocomplexes. Thermoresponsive hydrogels were examined by gelation temperature and time, thermal analysis, gel dissolution, LMWH release, and cytotoxicity in vitro. Hydrogels' behaviour was significantly shifted by gel composition e.g. the addition of hydroxypropylmethylcellulose to poloxamer-based systems decreased gelation temperature and time (from 28.6°C to 25.1°C and from 50s to 44s, respectively), but prolonged gel dissolution and LMWH release (7 and 4 days, respectively). Prolongation of drug release was additionally achieved with incorporation of LMWH/chitosan nanocomplexes into the gelling systems. As formulations demonstrated no cytotoxicity in vitro, it may be concluded that these double-responsive platforms are promising candidates for prolonged subcutaneous LMWH delivery during long-term treatment., (Copyright © 2015 Elsevier B.V. All rights reserved.) more...

Background: Chemotherapy with platinum agent and etoposide for small-cell lung cancer (SCLC) is supposed to be associated with intermediate risk (10-20%) of febrile neutropenia. Primary prophylaxis with granulocyte colony-stimulating factors (G-CSFs) is not routinely recommended by the treatment guidelines. However, in clinical practice febrile neutropenia is often observed with standard etoposide/platinum regimen. The aim of this analysis was to evaluate the frequency of neutropenia and febrile neutropenia in advanced SCLC patients in the first cycle of standard chemotherapy. Furthermore, we explored the association between severe neutropenia and etoposide peak plasma levels in the same patients., Methods: The case series based analysis of 17 patients with advanced SCLC treated with standard platinum/etoposide chemotherapy, already included in the pharmacokinetics study with etoposide, was performed. Grade 3/4 neutropenia and febrile neutropenia, observed after the first cycle are reported. The neutrophil counts were determined on day one of the second cycle unless symptoms potentially related to neutropenia occurred. Adverse events were classified according to Common Toxicity Criteria 4.0. Additionally, association between severe neutropenia and etoposide peak plasma concentrations, which were measured in the scope of pharmacokinetic study, was explored., Results: Two out of 17 patients received primary GCS-F prophylaxis. In 15 patient who did not receive primary prophylaxis the rates of both grade 3/4 neutropenia and febrile neutropenia were high (8/15 (53.3%) and 2/15 (13.3%), respectively), already in the first cycle of chemotherapy. One patient died due to febrile neutropenia related pneumonia. Neutropenic events are assumed to be related to increased etoposide plasma concentrations after a standard etoposide and cisplatin dose. While the mean etoposide peak plasma concentration in the first cycle of chemotherapy was 17.6 mg/l, the highest levels of 27.07 and 27.49 mg/l were determined in two patients with febrile neutropenia., Conclusions: Our study indicates that there is a need to reduce the risk of neutropenic events in chemotherapy treated advanced SCLC, starting in the first cycle. Mandatory use of primary G-CSF prophylaxis might be considered. Alternatively, use of improved risk models for identification of patients with increased risk for neutropenia and individualization of primary prophylaxis based on not only clinical characteristics but also on etoposide plasma concentration measurement, could be a new, promising options that deserves further evaluation. more...

Heparin is widely used as an anticoagulant for the treatment and prevention of various thrombotic diseases. However, due to its high anionic charge, heterogeneity in size distribution and high polarity, its analysis is very challenging. In this paper, a novel method based on size-exclusion chromatography (SEC) for quantitative determination of intact heparin in pharmaceuticals is presented. Analyses were performed on a BioSep-SEC-S 2000 column with Larginine solution at pH 6.5 as mobile phase and UV detection at 210 nm. The proposed method was found to be selective, linear (R2>0.997) over the concentration range of 3.1 to 1222 μg mL(-1), with a limit of detection of 1.0 μg mL(-1). Intraday and inter-day precision were below 5.1% and inaccuracy expressed as bias did not exceed 6.5 %. The reported method is simple, selective, sensitive, and requires no laborious sample preparation, which makes it appropriate for routine quantitative analysis of heparin in pharmaceuticals. more...

This study aimed to develop a population pharmacokinetic model for tramadol that combines different input rates with disposition characteristics. Data used for the analysis were pooled from two phase I bioavailability studies with immediate (IR) and prolonged release (PR) formulations in healthy volunteers. Tramadol plasma concentration-time data were described by an inverse Gaussian function to model the complete input process linked to a two-compartment disposition model with first-order elimination. Although polymorphic CYP2D6 appears to be a major enzyme involved in the metabolism of tramadol, application of a mixture model to test the assumption of two and three subpopulations did not reveal any improvement of the model. The final model estimated parameters with reasonable precision and was able to estimate the interindividual variability of all parameters except for the relative bioavailability of PR vs. IR formulation. Validity of the model was further tested using the nonparametric bootstrap approach. Finally, the model was applied to assess absorption kinetics of tramadol and predict steady-state pharmacokinetics following administration of both types of formulations. For both formulations, the final model yielded a stable estimate of the absorption time profiles. Steady-state simulation supports switching of patients from IR to PR formulation., (Copyright © 2014 Elsevier B.V. All rights reserved.) more...

Therapeutic drug monitoring (TDM) of antiepileptic drugs (AEDs) has been recognized as a useful tool in management of epilepsy. We developed a simple analytical method for simultaneous determination of four second generation AEDs, including gabapentin (GBP), pregabalin (PGB), vigabatrin (VGB), and topiramate (TOP). Analytes were extracted from human plasma using universal solid phase extraction, derivatized with 4-chloro-7-nitrobenzofurazan (NBD-Cl) and analyzed by HPLC with fluorescence detection. Using mass spectrometry we confirmed that NBD-Cl reacts with sulfamate group of TOP similarly as with amine group of the other three analytes. The method is linear (r(2)>0.998) across investigated analytical ranges (0.375-30.0μg/mL for GBP, PGB, and VGB; 0.50-20.0μg/mL for TOP). Intraday and interday precision do not exceed 9.40%. The accuracy is from 95.6% to 106%. The recovery is higher than 80.6%, and the lower limit of quantification is at least 0.5μg/mL. The method is selective and robust. For TOP determination the method was compared to a previously published method and the results obtained by the two methods were in good agreement. The developed method is suitable for routine TDM., (Copyright © 2014 Elsevier B.V. All rights reserved.) more...

Purpose: The purpose of this study was to discover differences in the human fecal microbiota composition driven by long-term omnivore versus vegan/lacto-vegetarian dietary pattern. In addition, the possible association of demographic characteristics and dietary habits such as consumption of particular foods with the fecal microbiota was examined., Methods: This study was conducted on a Slovenian population comprising 31 vegetarian participants (11 lacto-vegetarians and 20 vegans) and 29 omnivore participants. Bacterial DNA was extracted from the frozen fecal samples by Maxwell 16 Tissue DNA Purification Kit (Promega). Relative quantification of selected bacterial groups was performed by real-time PCR. Differences in fecal microbiota composition were evaluated by PCR-DGGE fingerprinting of the V3 16S rRNA region. Participants' demographic characteristics, dietary habits and health status information were collected through a questionnaire., Results: Vegetarian diet was associated with higher ratio (% of group-specific DNA in relation to all bacterial DNA) of Bacteroides-Prevotella, Bacteroides thetaiotaomicron, Clostridium clostridioforme and Faecalibacterium prausnitzii, but with lower ratio (%) of Clostridium cluster XIVa. Real-time PCR also showed a higher concentration and ratio of Enterobacteriaceae (16S rDNA copies/g and %) in female participants (p < 0.05 and p < 0.01) and decrease in Bifidobacterium with age (p < 0.01). DGGE analysis of the 16S rRNA V3 region showed that relative quantity of DGGE bands from certain bacterial groups was lower (Bifidobacterium, Streptococus, Collinsella and Lachnospiraceae) or higher (Subdoligranulum) among vegetarians, indicating the association of dietary type with bacterial community composition. Sequencing of selected DGGE bands revealed the presence of common representatives of fecal microbiota: Bacteroides, Eubacterium, Faecalibacterium, Ruminococcaceae, Bifidobacterium and Lachnospiraceae. Up to 4 % of variance in microbial community analyzed by DGGE could be explained by the vegetarian type of diet., Conclusions: Long-term vegetarian diet contributed to quantity and associated bacterial community shifts in fecal microbiota composition. Consumption of foods of animal origin (eggs, red meat, white meat, milk, yoghurt, other dairy products, fish and seafood) and vegetarian type of diet explained the largest share of variance in microbial community structure. Fecal microbiota composition was also associated with participants' age, gender and body mass. more...

Two randomized, single dose, 2-period, 2-sequence crossover studies were conducted to evaluate the comparative bioavailability of two clopidogrel formulations under fasting and fed conditions. Assessment of bioequivalence was based upon measurement of plasma concentrations of the parent drug, clopidogrel, and its major (inactive) metabolite, clopidogrel carboxylic acid, using improved methanol-free extraction. Bioequivalence of Krka's formulation to the innovator's formulation was demonstrated under both fasting and fed conditions on 205 volunteers. Confidence intervals for AUC0-t, AUC0-inf and Cmax of clopidogrel and its main metabolite were well within the acceptance range of 80.00 to 125.00 %. Food substantially increased the bioavailability of clopidogrel from both formulations, while no effect of food on the extent and rate of exposure to the metabolite was observed. The effect of food was comparable between the two formulations, as indicated by the same direction and rank of food impact on the bioavailability of both formulations. more...

In this study the role of oxidative stress in schizophrenia was investigated by evaluating the relationship of oxidative stress markers with neurochemistry, psychopathology, and extrapyramidal symptoms. Antioxidant activity of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and concentrations of malondialdehyde, protein carbonyls, nitrite, nitrate, glutathione, dopamine, noradrenaline, adrenaline, and serotonin were measured in 52 outpatients with DSM-IV diagnosis of schizophrenia treated with haloperidol decanoate. Psychopathology and extrapyramidal symptoms were assessed by positive and negative syndrome scale, global assessment of functioning, abnormal involuntary movement scale, Simpson Angus scale, and Barnes akathisia rating scale. Haloperidol dose was positively correlated with plasma protein carbonyls. Longer duration of illness was associated with decreased levels of glutathione peroxidase. Increased activity of superoxide dismutase was associated with increased levels of catalase, glutathione peroxidase, glutathione reductase and reduced glutathione, and decreased concentration of malondialdehyde, indicating joint action of various antioxidative systems. Increased levels of nitrite and noradrenaline were associated with decreased level of malondialdehyde. Akathisia was greater in patients with decreased catalase activity, indicating involvement of impaired antioxidant defense in developing extrapyramidal symptoms. These results confirm the hypothesis that oxidative stress is involved in pathophysiology of schizophrenia and severity of extrapyramidal symptoms., (© 2013 Elsevier Ireland Ltd. All rights reserved.) more...

The objective of the study was to develop population pharmacokinetic model of topiramate (TPM) using nonlinear mixed effects modelling approach. Data were collected from 78 adult epileptic patients on mono- or co-therapy of TPM and other antiepileptic drugs, such as carbamazepine (CBZ), valproic acid, lamotrigine, levetiracetam, phenobarbital and pregabalin. Steady-state TPM concentrations were determined in blood samples by high performance liquid chromatography with fluorescence detection. A one-compartment model with first order absorption and elimination was used to fit the concentration-time TPM data. Volume of distribution of TPM was estimated at 0.575 l/kg. The influence of demographic, biochemical parameters and therapy characteristics of the patients on oral clearance (CL/F) was evaluated. Daily carbamazepine dose (DCBZ) and renal function estimated by Modification of diet in renal disease (MDRD) formula significantly (p<0.001) influenced CL/F and were included in the final model: CL/F · (l/h)=1.53(l/h) · [1+0.476 · DCBZ(mg/day)/1000(mg/day)] · EXP[0.00476 · [MDRD(ml/ min)-95.72(ml/min)]]. Increase of CL/F with DCBZ and MDRD was best described by linear and exponential models. Mean TPM CL/F during CBZ co-therapy was 2.46 l/h, which is higher for 60.8% than in patients not co-treated with CBZ. Evaluation by bootstrapping showed that the final model was stable. The predictive performance was evaluated by adequate plots and indicated satisfactory precision. This model allows individualisation of TPM dosing in routine patient care, especially useful for patients on different CBZ dosing regimen., (Copyright © 2013 Elsevier B.V. All rights reserved.) more...

In situ forming systems including thermoreversible hydrogels, which undergo sol-gel transition upon an increase in temperature have been used for various biomedical applications. Heparins are the standard of anticoagulation in the prophylaxis and treatment of deep vein thrombosis and pulmonary embolism. Both conditions require long-lasting treatment with frequent subcutaneous administrations of heparin. The objective of this study was to prepare and evaluate in situ forming gel systems designed by combination of two poloxamers (P407 and P188) and hydroxypropylmethylcellulose (HPMC) for prolonged release of heparin. Thermoreversible hydrogels were prepared with heparin solution and dispersion of heparin/chitosan nanocomplexes. Nanocomplexes formed by self-assembly of heparin with chitosan at various mass ratios were thoroughly characterized. A heparin/chitosan mass ratio of 1:1 with pH 5.20 was the most appropriate for preparation of small, homogenous and stable nanocomplexes (mean diameter 123 nm; polydispersity index 0.22 and zeta potential+35.5 mV). Thermoreversible hydrogels were evaluated by gelation temperature, viscosity over the temperature range 20-40 °C, rate of hydrogel dissolution, and heparin release in vitro. The addition of P188 to P407 gel formulations resulted in an increase in gelation temperature, decrease in viscosity at room temperature and faster gel dissolution. The opposite effects were observed with formulations containing HPMC which demonstrated 18-day-long gel dissolution and complete heparin release in 9days from gels containing heparin solution. Considerable prolongation of heparin release was achieved with incorporation of heparin/chitosan nanocomplexes into the gelling systems. It may be concluded that with poloxamer mixtures at specific concentrations, addition of HPMC and use of heparin/chitosan nanocomplexes dispersions, thermoreversible formulations for prolonged subcutaneous release of heparin are feasible., (Copyright © 2013 Elsevier B.V. All rights reserved.) more...

Vincamine is a poorly soluble potent neuroprotector and cerebral vasodilator, used for the treatment for CNS disorders. In some cases, the bioavailability of pure compounds is strongly influenced by the co-administration of other constituents, and in some cases, the so called 'phytocomplex' may act as enhancer of absorption of selected phytochemicals. In this paper, the oral bioavailability of vincamine when administered as a standardised Vinca minor L. leaf dry extract rather than pure indole alkaloid is demonstrated to be higher. The chosen alkaloid-enriched and standardised dry extract was widely characterised by means of HPLC-MS, PXRD, DSC, XPS, (13)C and (15)N solid-state NMR (SSNMR) using pure vincamine as a matter of comparison. Then, the in vitro dissolution performances of the two products and their in vivo bioavailability in rats were evaluated. The sevenfold improvement in oral bioavailability of the dry extract with respect to the pure vincamine was ascribed to interactions between the indole alkaloid and the corollary of ingredients of the dry extract, giving rise to the protonation of the alkaloid vincamine, thus enhancing its dissolution in physiological fluids. Present data demonstrate that alkaloid vincamine administered as a whole plant extract has a higher bioavailability compared to the pure chemical compound., (Copyright © 2012 Elsevier B.V. All rights reserved.) more...

There is a growing body of evidence confirming the involvement of oxidative stress and inflammation in pathogenesis of schizophrenia. Inter-individual variation in antioxidant capacity caused by different genetic profile could potentially influence patient's susceptibility to oxidative damage. In this study we evaluated the polymorphisms of manganese superoxide dismutase SOD2Val16Ala, glutathione peroxidase GPX1Pro200Leu, catalase CAT-262C>T and CATc.66+78C>T, and tumour necrosis factor-alpha TNF-308G>A by assessing their association with biomarkers of oxidative stress, neurochemistry, psychopathology of schizophrenia and extrapyramidal symptoms in Caucasian schizophrenia patients treated with haloperidol depot. TNF-308G>A was associated with the increased risk of parkinsonism. No major role of polymorphism of SOD2Val16Ala, CAT-262C>T nor GPX1Pro200Leu in psychopathology of schizophrenia or extrapyramidal symptoms was observed. SOD2Val16Ala polymorphism was associated with dopamine plasma concentration and blood concentration ratio between reduced and oxidised form of glutathione, while GPX1Pro200Leu was related with concentration of reduced glutathione. CATc.66+78C>T was associated with noradrenaline plasma concentration and PANSS negative score. PANSS positive and general scores, were associated with the increased risk of tardive dyskinesia. PANSS positive, negative, and general scores, and GAF score were all associated with the increased risk of akathisia. more...

Purpose: The objectives of this study were (1) to develop a population pharmacokinetic model of high-dose methotrexate (HD-MTX) in children with acute lymphoblastic leukaemia (ALL) and malignant lymphoma (ML) in order to investigate the influence of common polymorphisms in SLC19A1, MTHFR and ABCB1 on plasma levels of MTX and (2) to estimate MTX exposure in individual patients to study the association of genetic variability in the folate metabolic pathway with MTX toxicity., Methods: The study population comprised 64 children with ALL/ML (age 1.6-16.8 years) who had received a total of 252 MTX courses (2-4 per patient). Common putative functional polymorphisms in the SLC19A1, MTHFR, MS, MTRR, TS and ABCB1 genes were analysed by PCR-based genotyping. Nonlinear mixed effects modelling was used for the pharmacokinetic analysis., Results: The population typical value of clearance was 7.43 L/h (inter-individual variability 43.9%), central compartment volume was 16.7 L (46.6%), peripheral compartment volume was 2.6 L (63.3%) and distribution clearance was 0.0952 L/h (66.6%). MTX clearance decreased to 73.8% in patients with the MTHFR 677TT genotype. Patients homozygous for the variant MTHFR 1298A > C [odds ratio (OR) 0.14, 95% confidence interval (CI) 0.037-0.54] and SLC19A1 80A > G (OR 0.15, 95% CI 0.039-0.60) were at decreased risk for leucopenia. The TS 2R > 3R polymorphism was associated with a lower incidence of thrombocytopenia (OR 0.15, 95% CI 0.039-0.61) and mucositis (OR 0.016, 95% CI  0.0012-0.20). In contrast, the MTHFR 677TT polymorphism was associated with an increased incidence of mucositis (OR 23, 95% CI 2.1-240)., Conclusions: A population pharmacokinetic model developed in this study implies only a limited influence of genetic factors on the systemic disposition of MTX. Clearance is moderately reduced in patients with the MTHFR 677TT genotype. Genetic polymorphisms in the folate metabolic pathway and SLC19A1 were associated with HD-MTX toxicity. more...

The aim of to the present study was to evaluate the effects of verapamil (VER) on plasma pharmacokinetics of ivermectin (IVM) and doramectin (DOR) in lactating Istrian Pramenka dairy sheep and to investigate the role of P-glycoprotein (P-gp) in transport of avermectins into milk. Pharmacokinetics of IVM and DOR following subcutaneous administration of 0.2mg/kg b.w. was evaluated in four groups of sheep. They were administered either IVM or DOR alone or in combination with verapamil (VER) at a dose of 3.0mg/kg b.w., 3 times at 12h intervals. Blood plasma and milk samples were collected at defined time intervals over 30 days post-treatment to determine IVM and DOR concentration levels. Pharmacokinetic parameters in sheep injected with IVM or DOR alone corresponded to previously published values. Comparison between sheep injected with IVM only, and sheep injected with IVM in combination with VER (IVM+VER) showed significant difference in pharmacokinetic parameters in blood plasma. Area under the concentration-time curve (AUC) truncated at 2 days (AUC(2)) was 15 and 28 μg day/L for group IVM and IVM+VER, respectively. With co-administration of VER, apparent plasma clearance (Cl/F) and mean residence time (MRT) of IVM decreased from 135 to 116 L/day and from 5.8 to 3.8 days, respectively. Similar trends were observed for DOR (AUC(2) 48 vs. 68 μg day/L, Cl/F 61 vs. 46 L/day, and MRT 5.6 vs. 4.4 days for groups DOR and DOR+VER, respectively). This study confirms that co-administration of VER has a significant effect on pharmacokinetic parameters of subcutaneously administered IVM in blood plasma. The influence on DOR pharmacokinetics is much weaker. This could be either due to the difference in lipophilicity or the difference in affinity towards P-gp as a result of structural differences. No significant influence of VER on AUC ratio of IVM and DOR between milk and plasma was observed suggesting that P-gp does not govern transport of avermectins into milk., (Copyright © 2011 Elsevier B.V. All rights reserved.) more...

The objective of this prospective study was to characterize the metabolism of risperidone to (+)- and (-)-9-hydroxyrisperidone in vivo and to evaluate the influence of CYP2D6 genotype. A population pharmacokinetic modeling approach was used to estimate the interindividual variability of the pharmacokinetic parameters in 50 hospitalized patients with acute episode of schizophrenia. CYP2D6 genotype remarkably influenced the formation clearances of the risperidone metabolites, while creatinine clearance was related to the plasma clearance of 9-hydroxyrisperidone. CYP2D6 genotype was also associated with the average plasma concentration of risperidone active moiety (a sum of all three active compounds). In comparison to the patients with CYP2D6*1/*1 genotype, average steady-state plasma concentration of risperidone active moiety was 3.3- and 1.6-fold higher in poor metabolizers (both alleles nonfunctional; CYP2D6*3 or *4) and intermediate metabolizers (one nonfunctional allele and one allele for diminished enzyme activity; CYP2D6*10 or *41), respectively. Additionally, average plasma concentration of risperidone active moiety was higher in the patients with dystonia (p=0.0066) and parkinsonism (p=0.046). The results of this study imply the potential role of CYP2D6 genotyping in personalizing risperidone therapy in patients with schizophrenia to reduce the incidence of adverse extrapyramidal symptoms. more...

A simple, fast, and sensitive HPLC method was developed and validated for the evaluation of pregabalin in a pharmaceutical dosage form using fluorescamine as a derivatization agent for the first time. After a precolumn derivatization (5 min, room temperature), the reaction mixture was chromatographed on a C18 column with isocratic elution using 0.2% of triethylamine in a mixture of methanol and water (10 + 90, v/v). 3-Aminopentanoic acid was used as the internal standard. Using fluorescent detection (lamdaex 395 nm, lamdaem 476 nm), a low detection limit of 0.02 microg/mL was reached. The method was linear (r > 0.999) over the lower (0.125-25 microg/mL) and higher (1.25-250 microg/mL) concentration range. The intraday and interday precision of the QC samples was < 4.3%, and the accuracy was 94.2-102.5%. The samples were stable for 24 h at 4 degrees C. The robustness study showed that the derivatization is more robust than the chromatography method. The method was applied for the analysis of pregabalin content in 25, 75, and 300 mg capsules, and a good agreement was found with the declared amount of pregabalin (the relative error did not exceed 3.2%). Finally, the method was successfully used for dissolution studies of pregabalin capsules. more...

Monitoring valproic acid (VPA) concentrations is especially challenging due to its highly variable pharmacokinetics (PK) and complex interactions with other antiepileptic drugs. We used sparse routine therapeutic drug monitoring data (n=200) from 129 adults with epilepsy to develop a population PK model of VPA, and determine the factors that influence its clearance (CL/F). Patients were on mono VPA therapy, or were concomitantly treated with carbamazepine, phenobarbital, topiramate (TPR), lamotrigine or benzodiazepines. A one-compartment model with first-order absorption and elimination was used to fit the concentration-time VPA data. Estimates generated by NONMEM indicated that VPA CL/F was influenced by the patients' body weight (increases with the 0.556 exponent), VPA daily dose (if it is greater than 1000 mg/day, CL/F increases by 43%), and co-therapy with TPR (lowering CL/F for 23%). The interindividual variability in VPA CL/F was modeled with exponentional error model. The estimated coefficient of variation was 31.9%, while the residual variability was 23.8% for the proportional and 13.2mg/l for the additive component. The model was validated in a separate set of 24 patients, and the predictive performance was evaluated, that indicated unbias and acceptable precision. This study confirms the interaction of VPA with TPR, which is presumably dependent on VPA dose. more...

Topiramate is biochemically classified as a fructopyranose sulphamate. Discovered as early as 1979, during middle 1980's it was approved in many countries for the treatment of epilepsies and migraine prevention. More recently, in the experimental stage, possible new indications have been disclosed: treatment of obesity, bipolar disorder, also cessation of smoking, neuropathic pain, cerebral pseudotumour, bulimia, periventricular leucomalatia in preterm infants and alcohol addiction. Most epileptologists consider it to be the first choice antiepileptic drug in severe pharmacoresistant epilepsies. A substantial corpus of evidence in paediatric population has been accumulated that confirms its efficiency in the treatment of generalised tonic-clonic seizures, Lenox-Gestaut syndrome, partial, absence and combined seizures. Having a unique monosaccharide chemical structure among other anticonvulsant drugs, characterizes it with special pharmacokinetic features. This substance exhibits a low interindividual variability in plasma levels and hence it features predictable pharmacokinetics. A steady state plasma concentration of topiramate increases linearly with higher dosages. Serum protein binding is approximately 15%, and biologic half-life in healthy volunteers is considered to range from 20 to 30 hours. Mean expected distribution volume rates from 0.55-0.8 l/kg, and accordingly, the drug shows a low and saturable binding capacity toward erythrocytes. It has not been present at the market for a sufficiently long time that would enable us to speak about a significant accumulation of data on its metabolism based on post-registration 4th stage clinical trials. For this purpose, we have done a literature review in order to summarise so far reported experience on topiramate pharmacokinetics in patients and healthy adults. Deeper understanding of its pharmacokinetic profile could enable a better technological design of the produced drug and the choice of the adequate route of its administration, and accordingly a more rational treatment of severe epilepsies resistant to other drugs. more...

Pharmacokinetics of eprinomectin (EPR) were studied in blood plasma and milk in two groups of six Istrian Pramenka dairy sheep and their suckling lambs following pour-on administration of EPR to ewes at dose levels of 0.5 and 1mg/kg. Maximum concentration in plasma was 2.22 and 5.25 microg/l, and AUC was 13.6 and 33.7 microg day/l for the 0.5 and 1.0mg/kg dose, respectively. These results indicate that drug exposure with a dose of 0.5mg/kg, which is commonly used in cattle, may be subtherapeutic. The concentration time course in milk paralleled plasma concentrations. In the dose range studied, linear pharmacokinetics of EPR were demonstrated. Milk-to-plasma AUC ratio was 0.79+/-0.12 and 1.12+/-0.43; the fraction of dose recovered in milk was 0.037+/-0.011 and 0.058+/-0.027% for the low and high dose, respectively. Maximum residual levels in milk were below the maximum acceptable level of 20 microg/kg; however, EPR was detected in all samples investigated. Despite low permeability in milk, AUC in plasma of suckling lambs was between 20 and 30% of the AUC in plasma of ewes. more...