Telomere-to-telomere assembled and centromere annotated genomes of the two main subspecies of the button mushroom Agaricus bisporus reveal especially polymorphic chromosome ends.

Agaricus bisporus, the most cultivated edible mushroom worldwide, is represented mainly by the subspecies var. bisporus and var. burnettii. var. bisporus has a secondarily homothallic life cycle with recombination restricted to chromosome ends, while var. burnettii is heterothallic with recombination seemingly equally distributed over the chromosomes. To better understand the relationship between genomic make-up and different lifestyles, we have de novo sequenced a burnettii homokaryon and synchronised gene annotations with updated versions of the published genomes of var. bisporus. The genomes were assembled into telomere-to-telomere chromosomes and a consistent set of gene predictions was generated. The genomes of both subspecies were largely co-linear, and especially the chromosome ends differed in gene model content between the two subspecies. A single large cluster of repeats was found on each chromosome at the same respective position in all strains, harbouring nearly 50% of all repeats and likely representing centromeres. Repeats were all heavily methylated. Finally, a mapping population of var. burnettii confirmed an even distribution of crossovers in meiosis, contrasting the recombination landscape of var. bisporus. The new findings using the exceptionally complete and well annotated genomes of this basidiomycete demonstrate the importance for unravelling genetic components underlying the different life cycles.

In Vivo Predictive Dissolution (IPD) and Biopharmaceutical Modeling and Simulation: Future Use of Modern Approaches and Methodologies in a Regulatory Context.

The overall objective of OrBiTo, a project within Innovative Medicines Initiative (IMI), is to streamline and optimize the development of orally administered drug products through the creation and efficient application of biopharmaceutics tools. This toolkit will include both experimental and computational models developed on improved understanding of the highly dynamic gastrointestinal (GI) physiology relevant to the GI absorption of drug products in both fasted and fed states. A part of the annual OrBiTo meeting in 2015 was dedicated to the presentation of the most recent progress in the development of the regulatory use of PBPK in silico modeling, in vivo predictive dissolution (IPD) tests, and their application to biowaivers. There are still several areas for improvement of in vitro dissolution testing by means of generating results relevant for the intraluminal conditions in the GI tract. The major opportunity is probably in combining IPD testing and physiologically based in silico models where the in vitro data provide input to the absorption predictions. The OrBiTo project and other current research projects include definition of test media representative for the more distal parts of the GI tract, models capturing supersaturation and precipitation phenomena, and influence of motility waves on shear and other forces of hydrodynamic origin, addressing the interindividual variability in composition and characteristics of GI fluids, food effects, definition of biorelevant buffer systems, and intestinal water volumes. In conclusion, there is currently a mismatch between the extensive industrial usage of modern in vivo predictive tools and very limited inclusion of such data in regulatory files. However, there is a great interest among all stakeholders to introduce recent progresses in prediction of in vivo GI drug absorption into regulatory context.

A survey on IVIVC/IVIVR development in the pharmaceutical industry - Past experience and current perspectives.

The present work aimed to describe the current status of IVIVC/IVIVR development in the pharmaceutical industry, focusing on the use and perception of specific approaches as well as successful and failed case studies. Two questionnaires have been distributed to 13 EFPIA partners of the Oral Biopharmaceutics Tools Initiative and to the Pharmacokinetics Working Party of the European Medicines Agency in order to capture the perspectives and experiences of industry scientists and agency members, respectively. Responses from ten companies and three European Agencies were received between May 21st 2014 and January 19th 2016. The majority of the companies acknowledged the importance of IVIVC/IVIVR throughout the drug development stages and a well-balanced rate of return on investment. However, the IVIVC/IVIVR approach seemed to be underutilized in regulatory submissions. Four of the ten companies stated to have an internal guidance related to IVIVC/IVIVR modelling, whereas three felt that an overall strategy is not necessary. Successful models mainly served to support formulation development and to provide a better mechanistic understanding. There was not yet much experience with safe-space IVIVRs as well as the use of physiologically based modelling in the field of IVIVC. At the same time, the responses from both industry and agencies indicated that there might be a need for a regulatory framework to guide the application of these novel approaches. The relevance of IVIVC/IVIVR for oral IR drug products was recognized by most of the companies. For IR formulations, relationships other than Level A correlation were more common outcomes among the provided case studies, such as multiple Level C correlation or safe-space IVIVR, which could be successfully used for requesting regulatory flexibility. Compared to the responses from industry scientists, there was a trend towards a higher appreciation of the BCS among the regulators, but a less positive attitude towards the utility of non-compendial dissolution methods for establishing a successful IVIVC/IVIVR. The lack of appropriate in vivo data and regulatory uncertainty were considered the major difficulties in IVIVC/IVIVR development. The results of this survey provide unique insights into current IVIVC/IVIVR practices in the pharmaceutical industry. Pursuing an IVIVC/IVIVR should be generally encouraged, considering its high value from both industry and regulators' perspective.

Single- and multiple-dose pharmacokinetic studies of tramadol immediate-release tablets in children and adolescents.

In these combined analyzes from 3 open-label, phase-1 studies, the pharmacokinetic profile of tramadol and its metabolite (M1) following administration of tramadol immediate-release (IR) tablets in children and adolescents, 7-16 years old (studies 1 and 2: n = 38; study 3: n = 21) with painful conditions following single oral dose of tramadol IR (25-100 mg) (studies 1 and 2) or multiple oral doses of tramadol IR tablets every 6 hours for 3 days (study 3) were compared with that of healthy adults following similar treatment. Area under the curve of tramadol and its metabolite M1 in children and adolescents was lower compared with adults (Dose-normalized [DN] AUC, h ng/mL: tramadol: 1316.87 [children]; 1418.02 [adolescents];1838.29 [adults]; M1: 342.56 [children]; 475.4 [adolescents]; 636.13 [adults]) while the Cmax remained similar (DN Cmax , ng/mL: tramadol: 203.75 [children]; 165.35 [adolescents]; 226.92 [adults]; M1: 34.93 [children]; 38.42 [adolescents]; 52.14 [adults]). The DN AUC was further lower in children and adolescents with a lower body weight (<50 kg). The weight normalized oral clearance of tramadol was higher in children and adolescents compared with adults (CL/F, mL/min/kg: 12.66 [children]; 11.75 [adolescents]; 9.06 [adults]). No new safety findings emerged. Tramadol was generally safe and well-tolerated by children and adolescents with painful conditions.

Pharmacokinetics of itraconazole and hydroxyitraconazole in healthy subjects after single and multiple doses of a novel formulation.

Originally, itraconazole for parenteral administration was licensed in a 40% hydroxypropyl-beta-cyclodextrin (HPBCD) solution for intravenous administration. A novel formulation, the NanoCrystal formulation (NCF), was prepared. NCF consists of drug particles of approximately 200 to 300 nm. The pharmacokinetics of itraconazole and its hydroxy metabolite in healthy subjects were evaluated after single and multiple doses of itraconazole as NCF. In the single-ascending-dose (SAD) study, itraconazole doses were planned to range from 50 to 500 mg, while in the multiple-ascending-dose (MAD) study, itraconazole doses of 100, 200, and 300 mg as NCF were studied, as was one dose level (200 mg) as an HBPCD solution. Samples were collected in heparinized tubes at various time points and were analyzed by high-performance liquid chromatography to allow full pharmacokinetic analysis both after the first dose and on day 7. The results of both the SAD and the MAD studies indicated that there was a dose dependency in the half-life of itraconazole from the novel formulation, increasing from 44 h (100 mg) to more than 150 h (300 mg) once steady state was achieved. Similar dose-dependent effects were observed for the hydroxy metabolite. The areas under the concentration-time curves for itraconazole and hydroxyitraconazole were also dose dependent. The pharmacokinetic profiles after 200-mg doses of itraconazole as NCF and HPBCD formulations were comparable with respect to the terminal half-life, both after a single dose and at steady state. NCF may provide an alternative to the HPBCD solution for the further optimization of antifungal treatment with itraconazole.

The metabolism and excretion of galantamine in rats, dogs, and humans.

Galantamine is a competitive acetylcholine esterase inhibitor with a beneficial therapeutic effect in patients with Alzheimer's disease. The metabolism and excretion of orally administered (3)H-labeled galantamine was investigated in rats and dogs at a dose of 2.5 mg base-Eq/kg body weight and in humans at a dose of 4 mg base-Eq. Both poor and extensive metabolizers of CYP2D6 were included in the human study. Urine, feces, and plasma samples were collected for up to 96 h (rats) or 168 h (dogs and humans) after dosing. The radioactivity of the samples and the concentrations of galantamine and its major metabolites were analyzed. In all species, galantamine and its metabolites were predominantly excreted in the urine (from 60% in male rats to 93% in humans). Excretion of radioactivity was rapid and nearly complete at 96 h after dosing in all species. Major metabolic pathways were glucuronidation, O-demethylation, N-demethylation, N-oxidation, and epimerization. All metabolic pathways observed in humans occurred in at least one animal species. In extensive metabolizers for CYP2D6, urinary metabolites resulting from O-demethylation represented 33.2% of the dose compared with 5.2% in poor metabolizers, which showed correspondingly higher urinary excretion of unchanged galantamine and its N-oxide. The glucuronide of O-desmethyl-galantamine represented up to 19% of the plasma radioactivity in extensive metabolizers but could not be detected in poor metabolizers. Nonvolatile radioactivity and unchanged galantamine plasma kinetics were similar for poor and extensive metabolizers. Genetic polymorphism in the expression of CYP2D6 is not expected to affect the pharmacodynamics of galantamine.

Role of modelling and simulation in Phase I drug development.

Although the use of pharmacokinetic/pharmacodynamic modelling and simulation (M&S) in drug development has increased during the last decade, this has most notably occurred in patient studies using the population approach. The role of M&S in Phase I, although of longer history, does not presently have the same impact on drug development. However, trends such as the increased use of biomarkers and clinical trial simulation as well as adoption of the learn/confirm concept can be expected to increase the importance of modelling in Phase I. To help identify the role of M&S, its main advantages and the obstacles to its rational use, an expert meeting was organised by COST B15 in Brussels, January 10-11, 2000. This article presents the views expressed at that meeting. Although it is clear that M&S occurs in only a minority of Phase I clinical trials, it is used for a large number of different purposes. In particular, M&S is considered valuable in the following situations: censoring because of assay limitation, characterisation of non-linearity, estimating exposure-response relationship, combined analyses, sparse sampling studies, special population studies, integrating PK/PD knowledge for decision making, simulation of Phase II trials, predicting multiple dose profile from single dose, bridging studies and formulation development. One or more of the following characteristics of M&S activities are often present and severely impede its successful integration into clinical drug development: lack of trained personnel, lack of protocol and/or analysis plan, absence of pre-specified objectives, no timelines or budget, low priority, inadequate reporting, no quality assurance of the modelling process and no evaluation of cost-benefit. The early clinical drug development phase is changing and if these implementation aspects can be appropriately addressed, M&S can fulfill an important role in reshaping the early trials by more effective extraction of information from studies, better integration of knowledge across studies and more precise predictions of trial outcome, thereby allowing more informed decision making.

Population pharmacokinetics of enterally administered cisapride in young infants with gastro-oesophageal reflux disease.

AIMS: To investigate the pharmacokinetics of enterally administered cisapride suspension in young infants being treated for gastro-oesophageal reflux disease. METHODS: Plasma cisapride concentrations in 49 subjects (weight: 825-5010 g; n=108 samples, median two per patient; concentration: 14.8-170 ng ml-1 ) were fitted to a one-compartment model with first-order absorption and elimination in the NONMEM program using a logarithmic transformation of the observed and predicted concentrations. Fitting was achieved using the first order conditional estimation (FOCE) method with interaction between the interpatient and intrapatient variabilities. The interpatient variance of clearance (CL/F ) and volume of distribution (V /F ) and their covariance were estimated using an exponential error model. Intrapatient (residual) variance was estimated using an additive model. RESULTS: The clearance of cisapride was shown to be linearly related to current body weight, slope: 0.538. The typical population values of CL/F, V /F and Ka (absorption rate constant) were 0.538 l h-1 kg-1, 21.9 l, and 2.58 h-1, respectively. The population coefficients of variation (CV%) for CL/F and V/F were 34.4% and 84.3%, respectively. The squared coefficient of correlation between random effects for CL/F and V /F was 0.45. The intrapatient variance was 0.15. V /F and Ka were not influenced significantly by any patient characteristic. CONCLUSIONS: Cisapride pharmacokinetics in infants with reflux disease were satisfactorily described by a one-compartment model. Current weight should be taken into account when calculating maintenance cisapride doses in these infants.

A combined specific target site binding and pharmacokinetic model to explore the non-linear disposition of draflazine.

The capacity-limited high-affinity target site binding of draflazine to the nucleoside transporters located on the erythrocytes is a source of nonlinearity in the pharmacokinetics of the drug. An attractive feature of draflazine is that the specific target site binding characteristics can be determined easily by simultaneously measuring plasma and whole blood concentrations of the drug. Measured drug concentrations following various infusion rates and infusion durations were used to develop a model in which the interrelated blood-plasma distribution, elimination, and specific target site binding of draflazine were incorporated simultaneously. The estimated binding (dissociation) constant Kd was 0.57 ng/ml plasma and the maximal specific erythrocyte binding capacity (BmaxRBC) was 163 ng/ml RBC. The maximal specific binding capacity to the tissues (Bmaxtissue) was estimated to be about 1 mg. The estimated volume of the central compartment (Vplasma + tissue fluids) was 12.9 L and the total intrinsic CL was 645 ml/min. After validation, the model was used to further investigate the impact of the specific high-affinity target site binding of draflazine on its disposition in plasma. The time required to reach steady-state plasma concentrations of draflazine decreased with an increasing infusion rate. Time profiles of the plasma concentrations were not always representative for the time profiles of the specific target site (RBC) occupancy of draflazine, but the t1/2,z in plasma paralleled that of the drug at target sites. The apparent Vd and the t1/2,z decreased with increasing single doses whereas the total CL remained constant. The recovery of draflazine was also dose dependent and increased with increasing doses. Finally, the total CL and apparent Vd of the first dose were greater than those of the second dose of draflazine.

Fentanyl delivery from an electrotransport system: delivery is a function of total current, not duration of current.

This open-label, parallel study of 28 men was conducted to evaluate the pharmacokinetics and safety of fentanyl delivered by the E-TRANS (fentanyl) electrotransport transdermal system (ALZA Corporation, Palo Alto, CA). The E-TRANS (fentanyl) system provided electrically assisted, transdermal, continuous delivery of fentanyl. Treatments consisted of no current (group A); a constant current of 100 microA for 26 hours plus 4 additional doses at varying currents for varying times during hour 25 (groups B, C, D); a constant current of 100 microA for 26 hours plus 4 additional doses at 1,200 microA over 2.5 minutes during hour 1 (group E); or 500 microA for 0.5 hours and 100 microA for 3.5 hours (group F). No fentanyl was detected in serum when no current had been applied. Mean serum fentanyl concentrations were similar regardless of current duration during hour 25 (treatments B, C, D). Increases in mean serum fentanyl concentrations were significantly lower during additional dosing for treatment E compared with treatments B, C, and D. Serum fentanyl concentrations sufficient for analgesia (1-3 ng/mL) were attained in treatments using the E-TRANS (fentanyl) system with basal current of 100 microA for 26 hours. There were no safety issues after treatment with E-TRANS (fentanyl) system with concurrent opioid antagonist (naltrexone) administration. The only adverse event requiring treatment was a headache (n = 1). The majority of subjects had no or barely perceptible erythema at the application site 24 hours after system removal. Application of E-TRANS (fentanyl) resulted in therapeutically significant serum fentanyl concentrations over a range of applied currents. Overall serum fentanyl concentrations were higher when the skin had been primed by constant-current fentanyl delivery.

Pharmacokinetics of lubeluzole (Prosynap) after single intravenous doses in healthy subjects.

The single-dose pharmacokinetics of lubeluzole were investigated in 2 single-blind, placebo-controlled, dose-escalation studies in healthy male subjects. In the first study, 6 subjects received an intravenous infusion of 2.5, 5, and 10 mg lubeluzole. In the second study, a 15 mg dose of lubeluzole was administered to 6 subjects, of whom 5 also received 20 mg and 2 also 25 mg lubeluzole. Following the infusion, plasma lubeluzole concentrations decayed biphasically, with a mean distribution half-life (t1/2alpha) of 30 to 65 minutes and a mean terminal half-life (t1/2beta) of 15 to 24 hours. The results of the 2 studies indicate that lubeluzole exhibits linear kinetics over the dose range tested in healthy male subjects.

Physiological red blood cell kinetic model to explain the apparent discrepancy between adenosine breakdown inhibition and nucleoside transporter occupancy of draflazine.

A physiological red blood cell (RBC) kinetic model is proposed for the adenosine (ADO) transport into erythrocytes and its subsequent intracellular deamination into inactive inosine (INO) and further breakdown into hypoxanthine (HYPO). The model and its parameters were based on previous studies investigating the kinetics of the biochemical mechanism of uptake and metabolism of ADO in human erythrocytes. Application of the model for simulations of the breakdown of ADO in a RBC suspension revealed that the predicted adenosine breakdown inhibition (ABI) of draflazine corresponded well with the ABI measured ex vivo. The model definitely explained the apparent discrepancy between the ex vivo measured ABI and the nucleoside transporter occupancy of draflazine. Intracellular deamination of ADO rather than its transport by the nucleoside transporter is the rate-limiting step in the overall catabolism of ADO. Consequently, at least 90% occupancy of the transporter by draflazine is required to inhibit adenosine breakdown ex vivo substantially. Simulations on basis of the validated model were performed to evaluate the ABI for different experimental conditions and to mimic the clinical situation. The latter may be very helpful for the design of optimal dosing schemes of draflazine. It was demonstrated that the short half-life of released ADO was prolonged substantially in a dose-related manner after a continuous infusion of draflazine. Finally, the previously found different sigmoidal Emax relationships between the measured ABI and the concentrations of draflazine in plasma and whole blood could be explained by the ADO transport and breakdown RBC kinetic model and the capacity-limited specific RBC binding characteristics of draflazine.

Effects of demographic variables on vorozole pharmacokinetics in healthy volunteers and in breast cancer patients.

PURPOSE: Vorozole (VOR) is a selective nonsteroidal inhibitor of the cytochrome P450-dependent aromatase that catalyzes the conversion of androgens to estrogens. It is currently being developed as a therapeutic agent in the endocrine treatment of postmenopausal women with breast cancer. This work was aimed to explore the effects of demographic and other variables on VOR pharmacokinetics. METHODS: VOR plasma concentration-time data were obtained in healthy volunteers and in breast cancer patients after the oral administration of 2.5 mg of VOR as a single dose or once daily. The data obtained in 6 formal pharmacokinetics (PK) studies with frequent plasma sampling were included in the data base (84 healthy male and female volunteers and 13 breast cancer patients). Also included were data from 2 clinical efficacy trials involving 286 breast cancer patients who were treated for several months (1 sample per visit, up to 14 samples/patient). The nonlinear mixed-effect modeling (NONMEM) approach was applied. The two-compartment linear PK model with first-order absorption parameterized in terms of apparent clearance (CL), apparent central and peripheral volumes of distribution (Vc and Vp, respectively), apparent distributional flow (Q), and absorption constant (ka) was used. A population model was developed using data from formal PK studies. The final estimates of fixed and random effect parameters were obtained using both formal study data and clinical-efficacy trial data. RESULTS: The typical CL value obtained after a single dose was lower in patients (4.8 l/h) as compared with healthy volunteers (8.6 l/h) and did not depend on gender. The multiple- to single-dose ratio was 0.76. CL was constant over ages of up to 50 years and then decreased slightly (0.047 l/h per year). The typical CL value did not depend on any demographic variable related to body size (total body weight, WT; body surface area; lean body mass). Q and Vc were proportional to WT (0.17 l h(-1) kg(-1) and 0.43 l/kg, respectively). Vp was also proportional to WT and was higher in women as compared with men (0.64 and 0.40 l/kg, respectively). The same was true for the apparent steady-state volume of distribution. No effect of race or the duration of therapy (0.5-28 months) was seen. The unexplained variability in CL and the residual variability in VOR plasma concentrations were 39% and 28% (coefficient of variation), respectively. CONCLUSIONS: Healthy volunteer/patient, single/multiple dosing differences, and age were identified as the fixed effects influencing the CL of VOR. WT was the main determinant of distributional PK parameters. The peripheral and steady-state volumes of distribution were gender-dependent. In view of the relatively high degree of residual interpatient variability in CL, the slight effect of age on it is unlikely to be clinically significant.

Population analysis of the non linear red blood cell partitioning and the concentration-effect relationship of draflazine following various infusion rates.

AIMS: To investigate the impact of the specific red blood cell binding on the pharmacokinetics and pharmacodynamics of the nucleoside transport inhibitor draflazine after i.v. administration at various infusion rates. It was also aimed to relate the red blood cell (RBC) occupancy of draflazine to the ex vivo measured adenosine breakdown inhibition (ABI). METHODS: Draflazine was administered to healthy volunteers as a 15-min i.v. infusion of 0.25, 0.5, 1, 1.5 and 2.5 mg immediately followed by an infusion of the same dose over 1 h. Plasma and whole blood concentrations were measured up to 120 h post dose, and were related to the ex vivo measured ABI, serving as a pharmacodynamic endpoint. The capacity-limited specific binding of draflazine to the nucleoside transporter located on the erythrocytes was evaluated by a population approach. RESULTS: The estimate of the population parameter typical value (%CV) of the binding constant Kd and the maximal specific binding capacity (Bmax) was 0.385 (3.5) ng ml-1 plasma and 158 (2.1) ng ml-1 RBC, respectively. The non-specific binding was low. The specific binding to the erythrocytes was a source of non-linearity in the pharmacokinetics of draflazine. The total plasma clearance of draflazine slightly decreased with increasing doses, whereas the total clearance in whole blood increased with increasing doses. The sigmoidal Emax equation was used to relate the plasma and whole blood concentration of draflazine to the ex vivo determined ABI. In plasma, typical values (%CV) of Emax, IC50 and Hill factor were 81.4 (1.9)%, 3.76 (9.3) ng ml-1 and 1.06 (3.4), respectively. The relationship in whole blood was much steeper with population parameter typical values (%CV) of Emax, IC50 and Hill factor of 88.2 (2.0)%, 65.7 (2.8) ng ml-1 and 4.47 (5.5), respectively. The RBC occupancy of draflazine did not coincide with the ex vivo measured ABI. The observed relationship between RBC occupancy and ABI was not directly proportional but similar for all studied infusion schemes. CONCLUSIONS: The findings of this study show that the occupancy of the nucleoside transporter by draflazine should be at least 90% in order to inhibit substantially adenosine breakdown in vivo. On the basis of these findings it is suggested that a 15 min infusion of 1 mg draflazine followed by an infusion of 1 mg h-1 could be appropriate in patients undergoing a coronary artery bypass grafting.

Influence of itraconazole on the pharmacokinetics and electrocardiographic effects of astemizole.

AIMS: The aim of this study was to investigate the influence of chronic itraconazole treatment on the pharmacokinetics and cardiovascular effects of single dose astemizole in healthy subjects was studied. METHODS: Twelve male volunteers were taking orally 200 mg twice daily itraconazole or placebo for 14 days with a washout period of 4 weeks in between. Approximately 2 h after the morning dose of itraconazole or placebo on day 11, 10 mg astemizole was orally administered. The plasma concentrations of astemizole and desmethylastemizole were measured by radioimmunoassay up to 504 h after administration; electrocardiograms with analysis of the QTc interval were recorded up to 24 h post administration. RESULTS: Itraconazole treatment did not significantly change the peak concentration of astemizole (0.74 vs 0.81 ng ml-1) but it increased the area under the curve from 0 to 24 h (5.46 to 9.95 ng ml-1 h) and from 0 to infinity (17.4 to 48.2 ng ml-1 h), and the elimination half-life (2.1 to 3.6 days). The systemic bioavailability of desmethylastemizole was also increased. The QTc interval did not increase after astemizole administration and there was no difference in the QTc intervals between the itraconazole and placebo session. CONCLUSIONS: Chronic administration of itraconazole influences the metabolism of single dose astemizole in normal volunteers without changes of cardiac repolarization during the first 24 h after astemizole administration. However, the reduction in astemizole clearance under concomitant administration of itraconazole may result in a marked increase in astemizole plasma concentrations and QTc alterations during chronic combined intake of astemizole with itraconazole.

A model with separate hepato-portal compartment ("first-pass" model): fitting to plasma concentration-time profiles in humans.

PURPOSE: To demonstrate the value of "first-pass" pharmacokinetic models (FPMs) in which the hepato-portal (HP) system is kinetically separated from the central compartment in fitting pharmacokinetic data obtained after intravenous (IV) and oral administration. METHODS: Plasma concentration-time profiles of an investigational drug obtained in six healthy subjects each received 4 mg as an intravenous (IV) bolus dose and 10 mg as an oral solution served as a real data example. The common three- and four-compartment models with the first-order absorption and lag time (3CM and 4CM, respectively) in which HP system is assumed to be part of the central compartment were used as alternative models. We tested also: (i) the sensitivity of the output of FPM to variations in its parameters assuming IV and oral administration; (ii) practical estimability of the FPM parameters by fitting it to 20 simulated noisy data sets; (iii) distinguishability of FPM, 3CM and 4CM by fitting them to the simulated data sets. RESULTS: FPM was shown to give the best fit as compared to 3CM or 4CM in 5 subjects of 6. The sensitivity of FPM was sufficient for the sake of parameter estimation. The "individual" means of parameter estimates obtained after fitting simulated data did not differ significantly from the preselected values. The variance in "individual" estimates was dependent on the sampling frequency. FPM was demonstrated to be distinguishable among relevant models. CONCLUSIONS: FPM is preferable as compared to standard compartmental models for drugs extensively taken up by the intestine and/or the liver, and may have a broad spectrum of applications.

Population analysis of the non-linear red blood cell partitioning of draflazine following various infusion durations.

OBJECTIVE: The pharmacokinetics and non-linear red blood cell partitioning of the nucleoside transport inhibitor draflazine were investigated in 19 healthy male and female subjects (age range 22-55 years) after a 15-min i.v. infusion of 1 mg, immediately followed by infusions of variable rates (0.25, 0.5 and 1 mg.h-1) and variable duration (2-24 h). METHODS: The parameters describing the capacity-limited specific binding of draflazine to the nucleoside transporters located on erythrocytes were determined by NONMEM analysis. The red blood cell nucleoside transporter occupancy of draflazine (RBC occupancy) was evaluated as a pharmacodynamic endpoint. RESULTS: The population typical value for the dissociation constant Kd (%CV) was 0.648 (12) ng.ml-1 plasma, expressing the very high affinity of draflazine for the erythrocytes. The typical value of the specific maximal binding capacity Bmax (%CV) was 155 (2) ng.ml-1 RBC. The interindividual variability (%CV) was moderate for Kd (38.9%) and low for Bmax (7.8%). As a consequence, the variability in RBC occupancy of draflazine was relatively low, allowing the justification of only one infusion scheme for all subjects. The specific binding of draflazine to the red blood cells was a source of non-linearity in draflazine pharmacokinetics. Steady-state plasma concentrations of draflazine virtually increased dose-proportionally and steady state was reached at about 18 h after the start of the continuous infusion. The t1/2 beta averaged 11.0-30.5 h and the mean CL from the plasma was 327 to 465 ml.min-1. The disposition of draflazine in whole blood was different from that in plasma. The mean t1/2 beta was 30.2 to 42.2 h and the blood CL averaged 17.4-35.6 ml.min-1. CONCLUSION: Although the pharmacokinetics of draflazine were non-linear, the data of the present study demonstrate that draflazine might be administered as a continuous infusion over a longer time period (e.g., 24 h). During a 15-min i.v. infusion of 1 mg, followed by an infusion of 1 mg.h-1, the RBC occupancy of draflazine was 96% or more. As the favored RBC occupancy should be almost complete, this dose regimen could be justified in patients.

Concentrations in plasma and safety of 7 days of intravenous itraconazole followed by 2 weeks of oral itraconazole solution in patients in intensive care units.

Pharmacokinetics and safety of a hydroxy-beta-propyl solution of itraconazole were assessed in 16 patients in an intensive care unit. On the first 2 days, four 1-h infusions of 200 mg were given at 0, 8, 24, and 32 h. From day 3 to 7, inclusive, a single 1-h infusion of 200 mg of itraconazole was given daily. The intravenous (i.v.) treatment was directly followed by repeated administrations of an oral solution of itraconazole at a dosage of either 200 mg once daily or 200 mg twice daily (b.i.d.). During i.v. treatment, steady-state concentrations of itraconazole and hydroxy-itraconazole in plasma were reached within 48 and 96 h, respectively. At the end of i.v. treatment, mean (+/- standard deviation) itraconazole and hydroxy-itraconazole trough concentrations in plasma were 0.344 +/- 0.140 and 0.605 +/- 0.205 microg/ml, respectively. After the 2-week oral follow-up of 200 mg once daily the mean trough concentration had decreased to 0.245 microg/ml, whereas after 200 mg b.i.d. it increased to 0.369 microg/ml. Diarrhea during oral treatment appeared to be dose related and may be due to the solvent hydroxypropyl-beta-cyclodextrin. More severe laboratory abnormalities were noted during the i.v. than the oral treatment phase, probably related to more severe illness in that period of intensive care, but none proved clinically important. These results suggest that plasma itraconazole levels above 0.250 microg/ml may be achieved and maintained with the 1-week i.v. schedule followed by b.i.d. oral administration, whereas the once-daily oral follow-up seems to be a suboptimal treatment.