Randomized, double-blind, placebo-controlled trial to examine the safety, pharmacokinetics and effects of Epimedium prenylflavonoids, on bone specific alkaline phosphatase and the osteoclast adaptor protein TRAF6 in post-menopausal women.

BACKGROUND: Fragility fractures due to menopausal osteoporosis are a major cause of morbidity and mortality. Osteoporotic medications have substantial side effects that limit long term use. HYPOTHESES: Ingestion of a purified extract of Epimedium spp. (EP) is safe, can increase serum levels of prenylflavonoid metabolites, exert positive changes in bone specific alkaline phosphatase (BSAP), suppress of tumor necrosis factor receptor associated factor 6 (TRAF6) protein in osteoclast-precursor monocytes in peripheral blood and therefore have the potential to reduce post-menopausal bone loss. STUDY DESIGN & METHODS: Healthy postmenopausal women were randomized in a double-blind fashion to consume either EP prenylflavonoid extract (740 mg daily) or placebo daily for 6 weeks. The main outcome measures were safety and pharmacokinetics of EP flavonoids. Fasting blood was collected at 3- and 6-weeks, and two weeks after stopping medication for safety evaluations and measurement of BSAP. Peripheral blood monocytes were harvested for measurement of TRAF6 levels. Serum levels of the EP metabolites icariin, icariside I & II, icaritin and desmethylicaritin were measured using tandem mass spectrometry, and non-compartmental pharmacokinetic analyses performed using WinNonlin software. RESULTS: Between October 2018 and Jun 2020, 58 postmenopausal women, aged 57.9 ± 8.9 years, were randomized and completed the study. Consumption of EP prenylflavonoids was not associated with any significant adverse symptoms, with no changes in hepatic, hematological, and renal parameters observed. The main metabolites detected in sera after ingestion of EP prenylflavonoid capsules were desmethylicaritin, icaritin and icariside II. Icariin and icariside I were below detection levels. Ingestion of EP prenylflavonoids induced a median Cmax and AUC0→∞ for desmethylicaritin of 60.9 nM, and 157.9 nM ×day, respectively; and were associated with higher levels of BSAP (p < 0.05) and a trend (p = 0.068) towards lower levels of TRAF6 in peripheral blood monocytes eight weeks after commencing prenylflavonoid ingestion. Prenylflavonoid metabolites were not detected in the sera of placebo participants. CONCLUSIONS: Despite the widespread consumption of EP extracts, the safety, mechanisms of action of their bioactive compounds, and therapeutic indications in humans are unknown. Daily consumption of EP prenylflavonoids for six weeks was safe. The predominant metabolite in sera was desmethylicaritin. Rise in prenylflavonoid metabolites was associated with higher levels of the bone anabolic marker BSAP, suggesting potential therapeutic value for post-menopausal osteoporosis.

Computer modelling of heat strain responses of exercising personnel in tropical climate.

Physiologically based thermoregulatory models are useful for deriving predictions of heat strain for pragmatic applications such as planning of continuous exercise/work-rest protocols. The SCENARIO model is an example of a thermoregulatory model that predicts heat strain including body core temperature (Tc) from individual characteristics, physical activity, clothing properties and environmental conditions. This paper presents work to optimize and enhance the SCENARIO model for prediction of Tc during high intensity load carriage tasks under predominantly tropical climate conditions. Data for model optimization (in-sample analysis) and model external validation were derived from four and two load carriage studies respectively. A total of four parameters characterizing metabolic heat production, sweat evaporation and ice ingestion for hydration were identified for model optimization based on physiological reasoning. The accuracy of Tc estimates was evaluated based on bias, root mean square deviation (RMSD), RMSD based on mean values (RMSD-Mean), and standard deviation fall-in percentage (SDP). Under in-sample analysis, the optimized model achieved bias, RMSD, RMSD-Mean and SDP of 0.01°C, 0.39°C, 0.14°C and 99%, respectively. When externally validated against two sets of unseen data, the model achieved comparable bias, RMSD, RMSD-Mean and SDP values of 0.06°C, 0.32°C, 0.13°C, 92% and 0.08°C, 0.39°C, 0.19°C, 92%, respectively. Overall, the results indicate the robustness of the optimized SCENARIO model for predicting the Tc responses during prolonged, high-intensity physical tasks under hot and humid environments. Future work to further validate the model against data beyond the range of the present study's experimental data and enhancing it for more accurate simulations of other heat strain markers including heart rate is recommended.

Pharmacokinetics of Prenylflavonoids following Oral Ingestion of Standardized Epimedium Extract in Humans.

Leaves of the Epimedium plant are traditionally consumed for bone health and other indications. The aim of this study was to establish the safety and pharmacokinetics of the metabolites of prenylflavonoids (icariin, icariside I, icariside II, icaritin, and desmethylicaritin) following single doses of a defined Epimedium prenylflavonoid extract in humans. A single oral dose of 370, 740, or 1110 mg of a standardized Epimedium prenylflavonoid extract was administered to 30 healthy male subjects in a randomized, placebo-controlled trial. Serum samples were collected over a 48-h period and analyzed by liquid chromatography-tandem mass spectrometry and non-compartmental pharmacokinetic modelling. Epimedium prenylflavonoid extracts were well tolerated and no adverse effects were observed. The principle metabolites detected in the serum were icariside II and desmethylicaritin. Icariside II had a T max of between 4.1 - 4.3 h, reaching a maximum AUC0→∞ of 23.0 (17.5, 29.9) h×ng/mL (median [IQR: interquartile range]) with the highest dose of the Epimedium prenylflavonoid. On the other hand, desmethylicaritin had a delayed T max of 24.1 - 24.4 h and reached a maximum AUC0→∞ of 126.1 (62.4, 202.9) h×ng/mL. The median maximum plasma concentration and AUC0→∞ of desmethyliciaritin showed an increase with higher doses of the Epimedium prenylflavonoid (p < 0.05). Icariin, icariside I, and icaritin levels were below detection limits. Levels of Epimedium prenylflavonoid metabolites observed in this study were consistent with levels demonstrated to have anti-osteoporotic effects in cellular and animal studies. Coupled with the favorable safety profile of the extract observed, further studies are required to explore the utility of Epimedium prenylflavonoid extracts to prevent osteoporosis in postmenopausal women.

Adjunctive use of celecoxib with anti-tuberculosis drugs: evaluation in a whole-blood bactericidal activity model.

COX-2 inhibition may be of benefit in the treatment of tuberculosis (TB) through a number of pathways including efflux pump inhibition (increasing intracellular TB drug levels) and diverse effects on inflammation and the immune response. We investigated celecoxib (a COX-2 inhibitor) alone and with standard anti-tuberculosis drugs in the whole-blood bactericidal activity (WBA) model. Healthy volunteers took a single dose of celecoxib (400 mg), followed (after 1 week) by a single dose of either rifampicin (10 mg/kg) or pyrazinamide (25 mg/kg), followed (after 2 or 7 days respectively) by the same anti-tuberculosis drug with celecoxib. WBA was measured at intervals until 8 hours post-dose (by inoculating blood samples with Mycobacterium tuberculosis and estimating the change in bacterial colony forming units after 72 hours incubation). Celecoxib had no activity alone in the WBA assay (cumulative WBA over 8 hours post-dose: 0.03 ± 0.01ΔlogCFU, p = 1.00 versus zero). Celecoxib did not increase cumulative WBA of standard TB drugs (mean cumulative WBA -0.10 ± 0.13ΔlogCFU versus -0.10 ± 0.12ΔlogCFU for TB drugs alone versus TB drugs and celecoxib; mean difference -0.01, 95% CI -0.02 to 0.00; p = 0.16). The lack of benefit of celecoxib suggests that efflux pump inhibition or eicosanoid pathway-related responses are of limited importance in mycobacterial killing in the WBA assay.

Activity of faropenem with and without rifampicin against Mycobacterium tuberculosis: evaluation in a whole-blood bactericidal activity trial.

Background: Faropenem has in vitro activity against Mycobacterium tuberculosis (Mtb) and shows synergy with rifampicin. We tested this in a whole-blood bactericidal activity (WBA) trial. Methods: We randomized healthy volunteers to receive a single oral dose of faropenem (600 mg) with amoxicillin/clavulanic acid (500/125 mg) ( n = 8), rifampicin (10 mg/kg) ( n = 14) or the combination rifampicin + faropenem + amoxicillin/clavulanic acid ( n = 14). Blood was drawn at intervals to 8 h post-dose. Drug levels were measured using LC-tandem MS. WBA was measured by inoculating blood samples with Mtb and estimating the change in bacterial cfu after 72 h. Trial registration: ClinicalTrials.gov (NCT02393586). Results: There was no activity in the faropenem + amoxicillin/clavulanic acid group (cumulative WBA 0.02 Δlog cfu; P = 0.99 versus zero change). There was a suggestion of a trend favouring the rifampicin + faropenem + amoxicillin/clavulanic acid group at 8 h (cumulative WBA -0.19 ±âŸ0.03 and -0.26 ±âŸ0.03 Δlog cfu in the rifampicin and rifampicin + faropenem + amoxicillin/clavulanic acid groups, respectively; P = 0.180), which was significant in the first hour post-dose ( P = 0.032). Faropenem C max and AUC were 5.4 mg/L and 16.2 mg·h/L, respectively, and MIC for Mtb H37Rv was 5-10 mg/L. Conclusions: Faropenem is not active when used alone, possibly due to inadequate plasma levels relative to MIC. However, there was a suggestion of modest synergy with rifampicin that may merit further testing in clinical trials.

Nonlinear mixed effects modelling for the analysis of longitudinal body core temperature data in healthy volunteers.

Many longitudinal studies have collected serial body core temperature (T c) data to understand thermal work strain of workers under various environmental and operational heat stress environments. This provides the opportunity for the development of mathematical models to analyse and forecast temporal T c changes across populations of subjects. Such models can reduce the need for invasive methods that continuously measure T c. This current work sought to develop a nonlinear mixed effects modelling framework to delineate the dynamic changes of T c and its association with a set of covariates of interest (e.g. heart rate, chest skin temperature), and the structure of the variability of T c in various longitudinal studies. Data to train and evaluate the model were derived from two laboratory investigations involving male soldiers who participated in either a 12 (N = 18) or 15 km (N = 16) foot march with varied clothing, load and heat acclimatisation status. Model qualification was conducted using nonparametric bootstrap and cross validation procedures. For cross validation, the trajectory of a new subject's T c was simulated via Bayesian maximum a posteriori estimation when using only the baseline T c or using the baseline T c as well as measured T c at the end of every work (march) phase. The final model described T c versus time profiles using a parametric function with its main parameters modelled as a sigmoid hyperbolic function of the load and/or chest skin temperature. Overall, T c predictions corresponded well with the measured data (root mean square deviation: 0.16 °C), and compared favourably with those provided by two recently published Kalman filter models.

Phenotyping of UGT1A1 Activity Using Raltegravir Predicts Pharmacokinetics and Toxicity of Irinotecan in FOLFIRI.

BACKGROUND: Irinotecan toxicity correlates with UGT1A1 activity. We explored whether phenotyping UGT1A1 using a probe approach works better than current genotyping methods. METHODS: Twenty-four Asian cancer patients received irinotecan as part of the FOLFIRI regimen. Subjects took raltegravir 400 mg orally and intravenous midazolam 1 mg. Pharmacokinetic analyses were performed using WinNonLin and NONMEM. Genomic DNA was isolated and screened for the known genetic variants in UGT1A1 and CYP3A4/5. RESULTS: SN-38G/SN-38 AUC ratio correlated well with Raltegravir glucuronide/ Raltegravir AUC ratio (r = 0.784 p<0.01). Midazolam clearance correlated well with irinotecan clearance (r = 0.563 p<0.01). SN-38 AUC correlated well with Log10Nadir Absolute Neutrophil Count (ANC) (r = -0.397 p<0.05). Significant correlation was found between nadir ANC and formation rate constant of raltegravir glucuronide (r = 0.598, P<0.005), but not UGT1A1 genotype. CONCLUSION: Raltegravir glucuronide formation is a good predictor of nadir ANC, and can predict neutropenia in East Asian patients. Prospective studies with dose adjustments should be done to develop raltegravir as a probe to optimize irinotecan therapy. TRIAL REGISTRATION: Clinicaltrials.gov NCT00808184.

Population pharmacokinetics of rifampicin and 25-deacetyl-rifampicin in healthy Asian adults.

OBJECTIVES: Rifampicin is a first-line anti-TB drug. The objectives of this analysis were to evaluate the population pharmacokinetics of rifampicin and its partly active metabolite, 25-deacetyl-rifampicin, with and without isoniazid, and to identify covariates that may explain variability in their disposition under steady-state conditions. METHODS: Thirty-four healthy Asian subjects were randomized to receive rifampicin (600 mg) or rifampicin (600 mg)/isoniazid (300 mg) daily for 14 days. After a 14 day washout, subjects were switched over to rifampicin (600 mg)/isoniazid (300 mg) or rifampicin (600 mg) daily. Plasma concentration-time data were analysed using NONMEM to estimate population pharmacokinetic parameters and evaluate relationships between parameters and demographic factors, and metabolic enzyme, transporter and transcriptional regulator genotypes. Allometric scaling of clearance and volume of distribution terms based on body weight was applied. RESULTS: A one-compartment model in which absorption was described by a transit absorption model best described the rifampicin data. 25-Deacetyl-rifampicin pharmacokinetic data were best described by a two-compartment model linked to the rifampicin model. None of the investigated covariates significantly influenced the disposition of rifampicin and 25-deacetyl-rifampicin. The apparent clearance of rifampicin and 25-deacetyl-rifampicin was estimated at 10.3 [relative standard error (RSE) 5.6%] and 95.8 (RSE 10%) L/h, respectively, for 70 kg adults. CONCLUSIONS: The pharmacokinetics of rifampicin and its main metabolite were characterized. Prospective studies with a larger number of participants, including patients, are needed to validate the results of this study.

Population pharmacokinetic analysis of isoniazid, acetylisoniazid, and isonicotinic acid in healthy volunteers.

In this study, we aimed to quantify the effects of the N-acetyltransferase 2 (NAT2) phenotype on isoniazid (INH) metabolism in vivo and identify other sources of pharmacokinetic variability following single-dose administration in healthy Asian adults. The concentrations of INH and its metabolites acetylisoniazid (AcINH) and isonicotinic acid (INA) in plasma were evaluated in 33 healthy Asians who were also given efavirenz and rifampin. The pharmacokinetics of INH, AcINH, and INA were analyzed using nonlinear mixed-effects modeling (NONMEM) to estimate the population pharmacokinetic parameters and evaluate the relationships between the parameters and the elimination status (fast, intermediate, and slow acetylators), demographic status, and measures of renal and hepatic function. A two-compartment model with first-order absorption best described the INH pharmacokinetics. AcINH and INA data were best described by a two- and a one-compartment model, respectively, linked to the INH model. In the final model for INH, the derived metabolic phenotypes for NAT2 were identified as a significant covariate in the INH clearance, reducing its interindividual variability from 86% to 14%. The INH clearance in fast eliminators was 1.9- and 7.7-fold higher than in intermediate and slow eliminators, respectively (65 versus 35 and 8 liters/h). Creatinine clearance was confirmed as a significant covariate for AcINH clearance. Simulations suggested that the current dosing guidelines (200 mg for 30 to 45 kg and 300 mg for >45 kg) may be suboptimal (3 mg/liter ≤ Cmax ≤ 6 mg/liter) irrespective of the acetylator class. The analysis established a model that adequately characterizes INH, AcINH, and INA pharmacokinetics in healthy Asians. Our results refine the NAT2 phenotype-based predictions of the pharmacokinetics for INH.

Vitamin E Isoform γ-Tocotrienol Downregulates House Dust Mite-Induced Asthma.

Inflammation and oxidative damage contribute to the pathogenesis of asthma. Although corticosteroid is the first-line treatment for asthma, a subset of patients is steroid resistant, and chronic steroid use causes side effects. Because vitamin E isoform γ-tocotrienol possesses both antioxidative and anti-inflammatory properties, we sought to determine protective effects of γ-tocotrienol in a house dust mite (HDM) experimental asthma model. BALB/c mice were sensitized and challenged with HDM. Bronchoalveolar lavage (BAL) fluid was assessed for total and differential cell counts, oxidative damage biomarkers, and cytokine levels. Lungs were examined for cell infiltration and mucus hypersecretion, as well as the expression of antioxidants and proinflammatory biomarkers. Sera were assayed for IgE and γ-tocotrienol levels. Airway hyperresponsiveness in response to methacholine was measured. γ-Tocotrienol displayed better free radical-neutralizing activity in vitro and inhibition of BAL fluid total, eosinophil, and neutrophil counts in HDM mouse asthma in vivo, as compared with other vitamin E isoforms, including α-tocopherol. Besides, γ-tocotrienol abated HDM-induced elevation of BAL fluid cytokine and chemokine levels, total reactive oxygen species and oxidative damage biomarker levels, and of serum IgE levels, but it promoted lung-endogenous antioxidant activities. Mechanistically, γ-tocotrienol was found to block nuclear NF-κB level and enhance nuclear Nrf2 levels in lung lysates to greater extents than did α-tocopherol and prednisolone. More importantly, γ-tocotrienol markedly suppressed methacholine-induced airway hyperresponsiveness in experimental asthma. To our knowledge, we have shown for the first time the protective actions of vitamin E isoform γ-tocotrienol in allergic asthma.

CYP3A5*3 and bilirubin predict midazolam population pharmacokinetics in Asian cancer patients.

We aim to evaluate the influence of covariates, including cytochrome P450 3A (CYP3A) genetic polymorphisms, on the pharmacokinetics of midazolam (MDZ) in Asian cancer patients, using a population pharmacokinetic approach. Pharmacokinetic data were obtained from 24 adult cancer patients who received an intravenous bolus dose of 1 mg MDZ as a CYP3A phenotyping probe, 1-day before starting FOLFIRI chemotherapy. Concentrations of MDZ and its major metabolites, 1'-hydroxymidazolam (1OHM) and 1'-hydroxymidazolam glucuronide (HMG) were measured using liquid chromatography/mass spectrometry. The population pharmacokinetic study was conducted using NONMEM. Demographics, clinical characteristics, and genetic polymorphisms were screened as covariates. A two-compartment model for MDZ and two sequential compartments representing 1OHM and HMG best described the data. The CYP3A5*3 and total bilirubin level significantly influenced MDZ clearance. The population typical MDZ clearance for CYP3A5*3 expressers was 22% lower than non-expressers. Baseline bodyweight was a statistically significant covariate for clearance and distribution volume of 1OHM. Creatinine clearance was positively correlated with HMG clearance. Our data indicate that CYP3A5*3, total bilirubin, bodyweight, and creatinine clearance are important predictors of MDZ and metabolite pharmacokinetics. Further studies in more patients are needed to explore the links between the identified covariates and the disposition of MDZ and its metabolites.

Calibration and validation of a physiologically based model for soman intoxication in the rat, marmoset, guinea pig and pig.

A physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) model has been developed for low, medium and high levels of soman intoxication in the rat, marmoset, guinea pig and pig. The primary objective of this model was to describe the pharmacokinetics of soman after intravenous, intramuscular and subcutaneous administration in the rat, marmoset, guinea pig, and pig as well as its subsequent pharmacodynamic effects on blood acetylcholinesterase (AChE) levels, relating dosimetry to physiological response. The reactions modelled in each physiologically realistic compartment are: (1) partitioning of C(±)P(±) soman from the blood into the tissue; (2) inhibition of AChE and carboxylesterase (CaE) by soman; (3) elimination of soman by enzymatic hydrolysis; (4) de novo synthesis and degradation of AChE and CaE; and (5) aging of AChE-soman and CaE-soman complexes. The model was first calibrated for the rat, then extrapolated for validation in the marmoset, guinea pig and pig. Adequate fits to experimental data on the time course of soman pharmacokinetics and AChE inhibition were achieved in the mammalian models. In conclusion, the present model adequately predicts the dose-response relationship resulting from soman intoxication and can potentially be applied to predict soman pharmacokinetics and pharmacodynamics in other species, including human.

Population pharmacokinetics of modafinil and its acid and sulfone metabolites in Chinese males.

BACKGROUND: Modafinil is a psychostimulant used to treat excessive sleepiness. The aim of this study was to develop a population pharmacokinetic model of modafinil and its major metabolites in Chinese male adults and to identify covariates that predict variability in disposition. METHODS: Eighty healthy volunteer subjects were randomized to 4 oral dose groups: 3 doses of 50 mg of modafinil, 3 doses of 100 mg of modafinil, 2 doses of 200 mg of modafinil plus 1 dose of placebo, or 3 doses of placebo (each dose given 8 hourly). Blood samples were collected up to 58 hours post-first dose for plasma concentrations of modafinil and its metabolites. Pharmacokinetic data analyses were performed using noncompartmental and compartmental approaches. The population pharmacokinetic study was conducted using the nonlinear mixed-effects model software, NONMEM, and validated using the bootstrap, crossvalidation and visual predictive check approaches. RESULTS: Data were best described by a 5-compartment model: 2 compartments for modafinil (first-order absorption from gut compartment) and 1 each for modafinil acid and modafinil sulfone. A covariate analysis identified body weight as influencing volumes of the central and peripheral compartments for modafinil. All the parameters were estimated with good precision (relative standard error < 39%). The visual predictive check found that the final pharmacokinetic model adequately predicted observed concentrations of all 3 molecular species. The authors developed dosing schedules to achieve minimum trough plasma modafinil concentrations of 3 mcg/mL. CONCLUSIONS: A robust population pharmacokinetic model for modafinil and its metabolites was developed for the first time. Based on this model, individualized dosing based on weight is now possible.

Pharmacokinetic modeling of plasma and intracellular concentrations of raltegravir in healthy volunteers.

Raltegravir is a potent inhibitor of HIV integrase. Persistently high intracellular concentrations of raltegravir may explain sustained efficacy despite high pharmacokinetic variability. We performed a pharmacokinetic study of healthy volunteers. Paired blood samples for plasma and peripheral blood mononuclear cells (PBMCs) were collected predose and 4, 8, 12, 24, and 48 h after a single 400-mg dose of raltegravir. Samples of plasma only were collected more frequently. Raltegravir concentrations were determined using liquid chromatography-mass spectrometry. The lower limits of quantitation for plasma and PBMC lysate raltegravir were 2 nmol/liter and 0.225 nmol/liter, respectively. Noncompartmental analyses were performed using WinNonLin. Population pharmacokinetic analysis was performed using NONMEM. Six male subjects were included in the study; their median weight was 67.4 kg, and their median age was 33.5 years. The geometric mean (GM) (95% confidence interval shown in parentheses) maximum concentration of drug (C(max)), area under the concentration-time curve from 0 to 12 h (AUC(0-12)), and area under the concentration-time curve from 0 h to infinity (AUC(0-∞)) for raltegravir in plasma were 2,246 (1,175 to 4,294) nM, 10,776 (5,770 to 20,126) nM · h, and 13,119 (7,235 to 23,788) nM · h, respectively. The apparent plasma raltegravir half-life was 7.8 (5.5 to 11.3) h. GM intracellular raltegravir C(max), AUC(0-12), and AUC(0-∞) were 383 (114 to 1,281) nM, 2,073 (683 to 6,290) nM · h, and 2,435 (808 to 7,337) nM · h (95% confidence interval shown in parentheses). The apparent intracellular raltegravir half-life was 4.5 (3.3 to 6.0) h. Intracellular/plasma ratios were stable for each patient without significant time-related trends over 48 h. Population pharmacokinetic modeling yielded an intracellular-to-plasma partitioning ratio of 11.2% with a relative standard error of 35%. The results suggest that there is no intracellular accumulation or persistence of raltegravir in PBMCs.

Interrelations between plasma caffeine concentrations and neurobehavioural effects in healthy volunteers: model analysis using NONMEM.

The objective was to develop a population pharmacokinetic-pharmacodynamic model of caffeine's psychomotor effects in healthy, non-habitual users of caffeine. Twenty Chinese males each received a single dose of 250 mg of caffeine orally. Plasma concentrations of caffeine were determined at various times within 24 h after dosing. The subjects' psychomotor performance was evaluated before and at various times after dosing by a test battery consisting of oculomotor assessment (saccadic velocity) as well as the computerised Swedish Performance Evaluation System. Nonlinear mixed-effects modelling to analyse the pharmacokinetic-pharmacodynamic relationships was performed using NONMEM. Model robustness was assessed by a nonparametric bootstrap. The results showed that caffeine caused significant improvements in psychomotor functioning. The time course of these effects was best described by pharmacokinetic/pharmacodynamic models involving an effect compartment. The transfer half-lives between plasma and effect site for different domains of psychomotor functioning were in the range 24.8-49.5 min. Evaluation of the final models showed close agreement between pairs of bootstrapped and final model parameter estimates (all differences<10%). These results provided the first suggestive evidence that caffeine effects on psychomotor performance occur after some time delay relative to changes in plasma caffeine concentration. The models for the neurobehavioural tests provided similar transfer half-lives between plasma and effect site.

Sensitivity analysis on a physiologically-based pharmacokinetic and pharmacodynamic model for diisopropylfluorophosphate-induced toxicity in mice and rats.

A physiologically-based pharmacokinetic and pharmacodynamic (PBPK/PD) model was recently developed to study the effect of diisopropylfluorophosphate (DFP) on acetylcholinesterase (AChE) activity in mouse and rat. That model takes into account relatively complex interactions involving many parameters, some of which may be uncertain and/or highly variable, especially those characterizing AChE activity after DFP intoxication. The primary objective of this study was to identify parameters that contribute most to the variability of AChE dynamics for model optimization against data. For this purpose, the influence of the variability of the rate constants for synthesis (K(syn)) and degradation (K(deg)) of AChE, and regeneration (K(reg)) and aging (K(age)) of inhibited AChE on the variability of AChE activity in mice and rat venous blood and brain was first calculated by a global sensitivity analysis. Next, the mouse PBPK/PD model was calibrated by optimizing the values of K(syn), K(deg), K(reg) and K(age). Thereafter, scale-up of the DFP-induced AChE activity was performed from mouse to rat. Validation of the rat model was performed by comparing the time course of venous blood and brain AChE activities from a Monte Carlo analysis to those obtained in vivo. Sensitivity analysis on the verified models showed that K(reg) and K(syn) were the most influential factors of AChE activity at shorter and longer durations, respectively, after DFP challenge. Scale-up of the AChE dynamics from mouse to rat was also successful, as evidenced by significant overlapping between the predicted 95(th) percentile confidence intervals and the experimental data.

Fuzzy least squares for identification of individual pharmacokinetic parameters.

In this paper, we examined the added value of fuzzy nonlinear regression to identify individual pharmacokinetic parameters in the case of noisy fuzzy data and/or small sample sizes. We first described three approaches that use least squares of errors as a fitting criterion for parameter estimation by fuzzy regression. Next, we compared the estimation and prediction capability of fuzzy least squares (FLS) and ordinary least squares (OLS) regressions via a simulation experiment, so as to determine the conditions of data size and variability under which one approach could be deemed superior over the other. We considered two empirical pharmacokinetic models. Our results showed that OLS regression outperformed FLS regression when the sample size was larger and/or there existed more outliers in the data. Overall, FLS regression was more powerful as the dataset size decreased. When the data were smaller in size and contained more variability, FLS regression's performance remained better than that of the OLS regression. Although the accuracy of the three FLS regression approaches was very close in almost all instances, those that estimated fuzzy parameters were superior in terms of predictive capability. These findings could aid in selecting the proper regression technique to employ in the presence of fuzzy data.

Retrospective population pharmacokinetic/pharmacodynamic analysis of pyridostigmine, a cholinesterase inhibitor, in Chinese males.

OBJECTIVES: We have characterised the population pharmacokinetics-pharmacodynamics of pyridostigmine given as pyridostigmine bromide. METHODS: Over three days 50 healthy Chinese male subjects each received seven doses of 30 mg pyridostigmine bromide orally (3 x 10 mg every 8 h). Plasma concentrations of pyridostigmine and red blood cell acetylcholinesterase (AChE) activity were determined at various times within the eight hours after the first and the seventh doses. The resulting pharmacokinetic data were fitted to a single compartment open model with first-order absorption and elimination. The pharmacodynamics were modelled using an inhibitory E(max) model. The potential influence of demographic and biological covariates on the model parameters was investigated. Nonlinear mixed effects modelling was performed using NONMEM. KEY FINDINGS: The apparent clearance and volume of distribution as well as absorption rate constant of plasma pyridostigmine were estimated to be 136 l/h, 130 l and 0.68 1/h, respectively. The maximum red blood cell AChE activity decrease (E(max)) and plasma pyridostigmine concentration producing 50% of this reduction (EC50) were estimated to be 9.32 AChE units per gram haemoglobin and 51.9 ng/ml, respectively. None of the tested covariates were found to be correlated with any of the model parameters. Dosing simulations suggested that 30 mg repeated every six hours might be needed to achieve steady-state trough percentage inhibition above the recommended 10% in healthy Chinese males. CONCLUSIONS: The pharmacokinetics and the effects of pyridostigmine on red blood cell AChE activity were described using a mixed effects model. For Chinese males, the dosing interval may have been shorter than that recommended for the Caucasian population. Additional studies are needed to confirm these findings.

Physiologically based pharmacokinetic modeling of drug disposition in rat and human: a fuzzy arithmetic approach.

PURPOSE: Probabilistic methods are insufficient for dealing with the vagueness inherent in human judgment of minimal data available during early drug development. We sought to use fuzzy set theory as a basis for quantifying and propagating vague judgment in a physiologically based pharmacokinetic (PBPK) model for diazepam disposition. MATERIALS AND METHODS: First, using diazepam distribution data in rat tissues and fuzzy regression, we estimated fuzzy rat tissue-to-plasma partition coefficients (Kp's). We scaled the coefficients prior to human PBPK modeling. Next, we constructed the fuzzy set of hepatic intrinsic clearance (CLint) by integrating CLint values measured in vitro from human hepatocytes. Finally, we used these parameters, and other physiological and biochemical information, to predict human diazepam disposition. We compared the simulated plasma kinetics with published concentration-time profiles. RESULTS: We successfully identified rat Kp's by fuzzy regression. The predicted rat tissue concentration-time contours enveloped the animal tissue distribution data. For the human PBPK model, the mean in vivo plasma concentrations were contained in the simulated concentration-time envelopes. CONCLUSIONS: We present a novel computational approach for handling information paucity in PBPK models using fuzzy arithmetic. Our methodology can model the vagueness associated with human perception and interpretation of minimal drug discovery data.

Comparison of statistical data models for identifying differentially expressed genes using a generalized likelihood ratio test.

Currently, statistical techniques for analysis of microarray-generated data sets have deficiencies due to limited understanding of errors inherent in the data. A generalized likelihood ratio (GLR) test based on an error model has been recently proposed to identify differentially expressed genes from microarray experiments. However, the use of different error structures under the GLR test has not been evaluated, nor has this method been compared to commonly used statistical tests such as the parametric t-test. The concomitant effects of varying data signal-to-noise ratio and replication number on the performance of statistical tests also remain largely unexplored. In this study, we compared the effects of different underlying statistical error structures on the GLR test's power in identifying differentially expressed genes in microarray data. We evaluated such variants of the GLR test as well as the one sample t-test based on simulated data by means of receiver operating characteristic (ROC) curves. Further, we used bootstrapping of ROC curves to assess statistical significance of differences between the areas under the curves. Our results showed that i) the GLR tests outperformed the t-test for detecting differential gene expression, ii) the identity of the underlying error structure was important in determining the GLR tests' performance, and iii) signal-to-noise ratio was a more important contributor than sample replication in identifying statistically significant differential gene expression.