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.

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.

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.

Alfentanil kinetics in the elderly.

Alfentanil disposition after an intravenous bolus of 50 micrograms/kg was followed in 15 elderly surgical patients and was compared to that in nine young adults. A two-compartment open model described alfentanil disappearance from plasma. Apparent volumes of distribution of the central compartment (201 and 211 ml/kg; means), at steady state (460 and 543 ml/kg), and of the AUC (746 and 722 ml/kg) in young adults and in elderly subjects did not differ. Plasma clearance was lower in elderly subjects (4.4 ml/min/kg) than in young adults (6.5 ml/min/kg), whereas terminal plasma t1/2 was longer in the elderly patients (137 and 83 min). Alfentanil dosage should therefore be reduced in elderly patients when large single doses, multiple doses, or long-term infusions are required.

Pharmacokinetics of the novel antipsychotic agent risperidone and the prolactin response in healthy subjects.

The pharmacokinetics of a novel antipsychotic agent, risperidone, and the prolactin response were studied in 12 dextromethorphan-phenotyped healthy men after administration of 1 mg risperidone intravenously, intramuscularly, and orally. The formation of the equipotent major metabolite, 9-hydroxyrisperidone, exhibited CYP2D6-related polymorphism. The plasma area under the concentration-time curve from time zero to infinity ratio of 9-hydroxyrisperidone to risperidone averaged 3 (intravenous and intramuscular) and 6 (oral administration) in the extensive metabolizers and 0.2 in the poor metabolizers. Risperidone half-life was about 3 hours in extensive metabolizers and 22 hours in poor metabolizers. Risperidone absolute oral bioavailability was 66%. The pharmacokinetics of the active moiety (risperidone plus 9-hydroxyrisperidone) varied little among subjects (mean terminal half-life, 20 +/- 2 1/2 hours; absolute oral and intramuscular bioavailability, 100%). The prolactin response correlated best with the plasma active moiety, which showed little hysteresis. It is concluded that risperidone metabolic polymorphism on increased plasma prolactin is minimal and that the active moiety is clinically relevant.

The pharmacokinetic properties of topical levocabastine. A review.

The linear and predictable pharmacokinetic properties of the histamine H1-receptor antagonist levocabastine make it particularly suitable for intranasal or ocular treatment of allergic rhinoconjunctivitis. Peak plasma concentrations (Cmax) occur within 1 to 2 hours of administration of single doses of levocabastine nasal spray and eye drops (0.2mg and 0.04mg, respectively). Drug absorption is incomplete after intranasal and ocular administration, with systemic availability ranging from 60 to 80% for levocabastine nasal spray and from 30 to 60% for the eye drops. However, as the amount of levocabastine applied intranasally and ocularly is small, the levocabastine plasma concentrations achieved are extremely low, with Cmax values in the ranges 1.4 to 2.2 micrograms/L and 0.26 to 0.29 micrograms/L for intranasal and ocular administration, respectively. Pharmacokinetic-pharmacodynamic modelling has indicated that the clinical benefits of levocabastine are predominantly mediated through local antihistaminic effects, although some systemic activity may contribute to the therapeutic efficacy of levocabastine nasal spray during long term use. Levocabastine undergoes minimal hepatic metabolism, i.e. ester glucuronidation, and is predominantly cleared by the kidneys. Approximately 70% of parent drug is recovered unchanged in the urine. Plasma protein binding is approximately 55% and the potential for drug interactions involving binding site displacement is negligible. Furthermore, the pharmacokinetics of this agent do not appear to be influenced by either age or gender. Levocabastine nasal spray and eye drops may thus be considered suitable for the treatment of allergic rhinoconjunctivitis in a wide patient population.

The pharmacokinetics of risperidone in humans: a summary.

Risperidone is rapidly and completely absorbed after oral administration; less than 1% is excreted unchanged in the feces. The principal metabolite was found to be 9-hydroxyrisperidone. Hydroxylation of risperidone is subject to the same genetic polymorphism as debrisoquine and dextromethorphan. In poor metabolizers the half-life of risperidone was about 19 hours compared with about 3 hours in extensive metabolizers. However, becuase the pharmacology of 9-hydroxyrisperidone is very similar to that of risperidone, the half-life for the "active fraction" (risperidone +9-hydroxyrisperidone) was found to be approximately 20 hours in extensive and poor metabolizers. We found that risperidone exhibited linear elimination kinetics and that steady state was reached within 1 day for risperidone and within 5 days for the active fraction.

Influence of age, renal and liver impairment on the pharmacokinetics of risperidone in man.

The pharmacokinetics of the antipsychotic agent risperidone were investigated in healthy young and elderly subjects, cirrhotic patients and patients with moderate and severe renal insufficiency. In a comparative trial, a single oral 1-mg dose was administered to fasting subjects. Plasma and urine concentrations of the parent compound risperidone and the active moiety (i.e. risperidone plus 9-hydroxy-risperidone) were measured by radioimmunoassays. No or only small changes in plasma protein binding were observed in hepatic and renal disease, whereas the protein binding was not influenced by aging. The inter-individual variability in plasma concentrations of the active moiety was much less than the variability in plasma concentrations of risperidone. Three out of six subjects, behaving like poor metabolizers, were on medication (thiethylperazine, amitriptyline, metoprolol) that may inhibit risperidone metabolism by CYP2D6 (debrisoquine 4-hydroxylase). The pharmacokinetics of risperidone in elderly and cirrhotic patients were comparable to those in young subjects, whereas total oral clearance was reduced in renal disease patients. The elimination rate and clearance of 9-hydroxy-risperidone was reduced in elderly and renal disease patients because of a diminished creatinine clearance. The CL(oral) of the active moiety, which is primarily 9-hydroxy-risperidone, was reduced by about 30% in the elderly and by about 50% in renal disease patients. In addition, the t1/2 of the active moiety was prolonged (19 h in young subjects versus about 25 h in elderly and renal disease patients). Based upon the pharmacokinetics of the active moiety, a dose reduction and a cautious dose titration is advised in the elderly and in patients with renal disease. In cirrhotic patients, the single-dose pharmacokinetics were comparable to those in healthy young subjects.

New non-steroidal aromatase inhibitors: focus on R76713.

R76713 is a novel triazole derivative which selectively blocks the cytochrome P450-dependent aromatase. In human placental microsomes, in FSH-stimulated rat and human granulosa cells and in human adipose stromal cells, 50% inhibition of estradiol biosynthesis was obtained at drug concentrations of 2-10 nM. In PMSG-injected female rats, R76713 lowered plasma estradiol levels by 50 and 90% 2 h after single oral doses of 0.005 and 0.05 mg/kg respectively. After 1 mg/kg, estradiol levels were suppressed by 90% for 16 h. In male cynomolgus monkeys, R76713 dose-dependently (0.03-10 micrograms/kg) inhibited peripheral aromatization with an ED50 of 0.13 microgram/kg without altering metabolic clearance rates and conversion ratios. In vitro R76713 had no effect on other P450-dependent steroidogenic enzymes up to 1000 nM at least. In rats, LHRH-, ACTH- and sodium-deprived diet stimulated plasma testosterone, corticosterone and aldosterone levels were not modified 2 h after single oral administrations of R76713 (up to 20 mg/kg). Furthermore, R76713 did not show any in vitro or in vivo estrogenic or antiestrogenic property. R76713 also induced regression of DMBA-induced mammary tumors after daily oral administration of 1 mg/kg b.i.d. In male volunteers (n = 4), a single oral dose of 5 and 10 mg lowered median plasma estradiol levels from 70 pM to the detection limit of the assay (40 pM) 4, 8 and 24 h after intake whereas no changes were detected after placebo administration. In premenopausal women (n = 15), receiving a single oral dose of 20 mg, median plasma estradiol levels decreased from 389 pM (before) to 168, 133 and 147 pM, 4, 8 and 24 h after intake whereas they remained above 420 pM after placebo (n = 7).

Pharmacokinetics of ritanserin in patients undergoing hemodialysis.

The pharmacokinetics of ritanserin were studied in five patients with chronic renal insufficiency and who were undergoing periodic hemodialysis. Immediately after breakfast, a single 10-mg ritanserin tablet was administered to each patient on a day that they did not undergo dialysis. Plasma ritanserin levels were measured by a specific high-performance liquid chromatographic assay sensitive to 2 ng/mL plasma. After the oral 10-mg dose, the average time to reach the peak plasma concentration, Tmax, was 4.4 +/- 2.2 hours in these uremic patients, with a range of 2 to 8 hours. The average peak plasma concentration was 73.6 +/- 26.9 ng/mL (range: 54.6-120.0 ng/mL). Compared with a previous study in healthy volunteers, the uremic patients had a slower absorption profile, with a 39% reduction in peak plasma concentration and mean delay of 2.5 hours in Tmax. The mean area under the plasma concentration-time curve for ritanserin (2031 +/- 636 ng.hr/mL) was 47% lower compared with that in healthy volunteers (3867 +/- 1413 ng.hr/mL). The observed delayed and lower ritanserin absorption in these uremic patients may be caused by the chronic use of antacids such as aluminum hydroxide and calcium carbonate in all patients and/or by concurrent pathologic changes in the gastrointestinal mucosa of these patients. The regular hemodialysis sessions every 2-3 days did not affect the elimination rate of ritanserin, as the terminal half-life in these patients (39 +/- 23 hr) is similar to that in healthy volunteers (41 +/- 14 hr).

Pharmacokinetics of orally administered levocabastine in patients with renal insufficiency.

The effects of renal insufficiency and hemodialysis on the pharmacokinetics of orally administered levocabastine were studied in six nondialysis patients and in six patients undergoing regular hemodialysis. Levocabastine .5 mg, supplied as a solution, was administered orally to each patient 1 hour after breakfast. Compared with data in healthy volunteers, the oral absorption and disposition of levocabastine were impaired in patients with renal insufficiency. The time to reach peak plasma concentration was increased and the peak plasma concentration was decreased in the patients with renal insufficiency compared with healthy volunteers. Urinary excretion of the unchanged drug, which is the major elimination pathway of levocabastine, was reduced in the patients with renal insufficiency. The decreased urinary excretion most likely contributed to the prolonged half-life (from 36 hours to 95 hours) and increased area under the plasma concentration-time curve (+56%) in the patients with renal insufficiency as compared with the healthy volunteers. Although the 6-hour hemodialysis procedure starting 4 hours after dosing eliminated 10% of the oral dose, the terminal half-life and the total area under the plasma concentration-time curve did not differ significantly between the hemodialysis and the nonhemodialysis patients. In conclusion, the current study showed that the initial oral absorption of levocabastine is reduced and that levocabastine elimination is prolonged in patients with renal insufficiency.

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.

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.

Safety and pharmacokinetics of the neuroprotective drug lubeluzole in patients with ischemic stroke.

A total of 22 patients with acute ischemic stroke participated in two randomized, single-masked, placebo-controlled studies that evaluated the safety and pharmacokinetics of single escalating intravenous doses of lubeluzole. The first dose of study medication in all patients was given within 6 hours of the first sign of stroke onset. In the first study, 6 patients received a single 1-hour intravenous infusion of 5 mg of lubeluzole; 4 of these patients received an additional 10-mg dose 3 to 4 days later. Two additional patients received placebo. In the second study, 4 patients received a single 1-hour infusion of 10 mg of lubeluzole, and 2 patients received placebo. After a safety evaluation of the second study, 6 additional patients received 15 mg of lubeluzole, and 2 other patients received placebo. Lubeluzole had no clinically relevant effects on any cardiovascular variable compared with placebo. The majority of adverse experiences were mild to moderate and resolved during treatment. No unexpected electroencephalogram abnormalities were observed, and no evidence of epileptiform discharges was found in any of the patients. At the end of the infusion, plasma lubeluzole concentrations decayed biphasically, with mean distribution half-lives of 46.3 to 101.0 minutes and mean terminal half-lives of 20.8 to 27.7 hours. Comparisons of the dose-normalized value of the individual plasma concentrations at the end of the infusion and the total area under the curve from time 0 to infinity suggested that lubeluzole exhibited linear kinetics over the dose range evaluated in patients with ischemic stroke. In the small number of patients studied, lubeluzole's favorable safety profile was demonstrated by the lack of clinically relevant effects on cardiovascular variables and by neurologic examination and clinical laboratory findings.

Effect of food on the pharmacokinetics of a new hydroxypropyl-beta-cyclodextrin formulation of itraconazole.

STUDY OBJECTIVE: To compare the pharmacokinetics of a single 100-mg oral dose of itraconazole administered as 10 ml of a 10-mg/ml itraconazole solution in hydroxypropyl-beta-cyclodextrin under fasting versus postprandial conditions. DESIGN: Open-label, two-way, randomized, crossover study. SETTING: Janssen Research Foundation, Belgium. PATIENTS: Twelve healthy volunteers. INTERVENTIONS: Blood samples were obtained for pharmacokinetic analyses immediately before dosing and at regular intervals up to 96 hours after each dose. Blood and urine samples were obtained for hematologic, biochemical, and urinary safety analyses at baseline and at the end of the study. MEASUREMENTS AND MAIN RESULTS: The mean peak plasma concentrations of both itraconazole and its active metabolite hydroxy-itraconazole were significantly higher under fasting conditions than under postprandial conditions. The mean times to peak concentration for both the parent compound and its metabolite were significantly shorter under fasting than under nonfasting conditions. The mean areas under the curve (AUC0-infinity and AUC0-24 hrs) were also significantly higher under fasting than under postprandial conditions. CONCLUSIONS: Our findings suggest that the higher bioavailability of this new formulation of itraconazole may be of benefit in seriously ill patients who are not able to ingest adequate quantities of food. The fact that the solution was also well tolerated and was not associated with clinically significant changes in any laboratory value further underscores the potential utility of this dosing form.

Pharmacokinetics of intravenous and oral 1,2-O-isopropylidene-3-O-3'-(N',N'-dimethylamino-n-propyl)-D-glucofuranose hydrochloride in the dog as a function of dose and characterization of metabolites.

The pharmacokinetics of 1,2-O-isopropylidene-3-O-3'-(N',N'-dimethylamino-n-propyl)-D-glucofuranose hydrochloride (1) was studied in dogs at intravenous and oral doses of 1-50 mg/kg. There was no significant difference between the electron-capture GLC of the heptafluorobutyric derivative of I and the radiochemical assay of chloroform extracts of plasma and urine for 1- to 20-mg/kg doses. Urinary amounts of I measured by GLC were 20% lower than radioassays of chloroform extracts at the 50-mg/kg dose. The pharmacokinetics of intravenous I was described by a two-compartment body model with sequential plasma half-lives of 7.5 +/- 0.7 and 136 +/- 6 min. No apparent dose-dependent pharmacokinetics for I was observed on intravenous or oral administration. The apparent volume of distribution of the central compartment, 13.1 +/- 0.7 liters, is approximately the volume of the total body water in a 20-kg dog. The apparent overall volume of distribution of 40.0 +/- 1.5 liters exceeds the total body water, indicative of sequestration of I in tissues. Total and renal clearances were 205 +/- 5 and 155 +/- 5 ml/min, respectively. The high renal clearance of I indicated an excess of tubular secretion. Renal clearance of I was not dependent on urine flow nor urine pH. Recovery of radioactivity in the feces after I was intravenously administered was less than 1%. Plasma protein binding of I was less than 5%, and the erythrocyte-plasma water partition coefficient was approximately unity. Compounds excreted in urine were separated into chloroform-extractable (pH 12), ethyl acetate-extractable (pH 2), and unextractable fractions which were further characterized by TLC. A multiple-extraction system was developed to estimate relative amounts and intrinsic partition coefficients of these extractable compounds from radioactivity counts of scraped plates and was applied tof the assay of these compounds in the urine after intravenous administration of I. There was a readily chloroform-extractable metabolite with an apparent partition coefficient of 3.3 and Rf 0.43 on TLC in the systems used. This apparent major metabolite could account for 8% of the administered radioactivity. Minor chloroform-extractable metabolites (0.8-3.3%) had lower apparent partition coefficients (0.26) but Rf values of 0.28 and 0.44 . Ethyl acetate-extractable compounds (1.3-2.7%) had an apparent partition coefficient of 0.81 with Rf values of 0.52 and 0.68. Three unextractable compounds had Rf values of 0.20, 0.50, and 0.62 and accounted for 0.16, 2.8, and 0.9% of the administered radioactivity.

Properties, stability, assay, and preliminary pharmacokinetics of the immunomodulatory 1,2-O-isopropylidene-3-O-3'(N',N'-dimethylamino-n-propyl)-D-glucofuranose hydrochloride.

1,2-O-Isopropylidene-3-O-3'(N',N'-dimethylamino-n-propyl)-D -glucofuranose hydrochloride (I) is a new agent with claimed immunomodulatory action and antiviral activity. Thin-layer chromatographic procedures and identifying tests were developed to separate the drug, its synthetic precursors, and solvolytic products, and were applied to stability studies. It is stable in 0.1 N NaOH at 60 degrees where its acid solvolysis product, 3-O-3'-(N',N'-dimethylamino-n-propyl)-D-glucose is readily degraded. The partition coefficient of I (pK'a = 9.28) between chloroform and plasma was 6.4 +/- 0.2 SEM between pH 10.5 and 11.0. Plasma and urine (0.5 ml) adjusted to pH 11.0 were extracted with 10 ml of chloroform and the extract evaporated. The reconstituted residue in 50 microliters of benzene, with the disopropylaminoethyl analog of I as an internal standard, was derivatized with 50 microliters of heptafluorobutyric anhydride at 60 degrees for 45 min and was evaporated and reconstituted in 100 microliters of benzene to be assayed for I by GLC with electron capture detection with a sensitivity of 5 ng/0.5 ml of biological fluid. The procedure was applied to pharmacokinetics in the dog and a two-compartment body model was observed with a terminal half-life of 103-130 min. At the 40-mg dose, 60-64% was excreted renally unchanged and 20-34% as unidentified metabolites. At the 200-mg dose 82-85% was excreted unchanged and 15-17% as unidentified metabolites. The respective renal clearances of I were 135 and 163 ml/min. The respective total clearances of I were 204 and 191 ml/min. These metabolites were apparently unextracted with chloroform from biological fluids at pH 11 and the liquid scintillation counting (LSC) assay of extracted radiolabeled I appeared synonomous with the GLC assay of I in such fluids.

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.