Design of a potent, soluble glucokinase activator with excellent in vivo efficacy

The optimisation of a series of glucokinase activators is described, including attempts to uncouple the relationship between potency and plasma protein binding, and to better understand the key pharmacokinetic properties of the series. The use of unbound clearance as an optimisation parameter facilitated the identification of GKA50, a compound which combines excellent potency and pharmacokinetics with good free drug levels and solubility, and exhibits in vivo efficacy at 1mg/kg po in an acute rat OGTT model.     

A pharmacokinetic model of filgrastim and pegfilgrastim application in normal mice and those with cyclophosphamide-induced granulocytopaenia

Objectives:  Recombinant human granulocyte colony-stimulating factor (rhG-CSF) is widely used as treatment for granulocytopaenia during cytotoxic chemotherapy; however, optimal scheduling of this pharmaceutical is unknown. Biomathematical models can help to pre-select optimal application schedules but precise pharmacokinetic properties of the pharmaceuticals are required at first. In this study, we have aimed to construct a pharmacokinetic model of G-CSF derivatives filgrastim and pegfilgrastim in mice.
Methods:  Healthy CD-1 mice and those with cyclophosphamide-induced granulocytopaenia were studied after administration of filgrastim and pegfilgrastim in different dosing and timing schedules. Close meshed time series of granulocytes and G-CSF plasma concentrations were determined. An ordinary differential equations model of pharmacokinetics was constructed on the basis of known mechanisms of drug distribution and degradation.
Results:  Predictions of the model fit well with all experimental data for both filgrastim and pegfilgrastim. We obtained a unique parameter setting for all experimental scenarios. Differences in pharmacokinetics between filgrastim and pegfilgrastim can be explained by different estimates of model parameters rather than by different model mechanisms. Parameter estimates with respect to distribution and clearance of the drug derivatives are in agreement with qualitative experimental results.
Conclusion:  Dynamics of filgrastim and pegfilgrastim plasma levels can be explained by the same pharmacokinetic model but different model parameters. Beause of a strong clearance mechanism mediated by granulocytes, granulocytotic and granulocytopaenic conditions must be studied simultaneously to construct a reliable model. The pharmacokinetic model will be extended to a murine model of granulopoiesis under chemotherapy and G-CSF application.     

A mechanistic framework for a priori pharmacokinetic predictions of orally inhaled drugs

The fate of orally inhaled drugs is determined by pulmonary pharmacokinetic processes such as particle deposition, pulmonary drug dissolution, and mucociliary clearance. Even though each single process has been systematically investigated, a quantitative understanding on the interaction of processes remains limited and therefore identifying optimal drug and formulation characteristics for orally inhaled drugs is still challenging. To investigate this complex interplay, the pulmonary processes can be integrated into mathematical models. However, existing modeling attempts considerably simplify these processes or are not systematically evaluated against (clinical) data. In this work, we developed a mathematical framework based on physiologically-structured population equations to integrate all relevant pulmonary processes mechanistically. A tailored numerical resolution strategy was chosen and the mechanistic model was evaluated systematically against data from different clinical studies. Without adapting the mechanistic model or estimating kinetic parameters based on individual study data, the developed model was able to predict simultaneously (i) lung retention profiles of inhaled insoluble particles, (ii) particle size-dependent pharmacokinetics of inhaled monodisperse particles, (iii) pharmacokinetic differences between inhaled fluticasone propionate and budesonide, as well as (iv) pharmacokinetic differences between healthy volunteers and asthmatic patients. Finally, to identify the most impactful optimization criteria for orally inhaled drugs, the developed mechanistic model was applied to investigate the impact of input parameters on both the pulmonary and systemic exposure. Interestingly, the solubility of the inhaled drug did not have any relevant impact on the local and systemic pharmacokinetics. Instead, the pulmonary dissolution rate, the particle size, the tissue affinity, and the systemic clearance were the most impactful potential optimization parameters. In the future, the developed prediction framework should be considered a powerful tool for identifying optimal drug and formulation characteristics.     

Permeability of Gemcitabine and PBPK Modeling to Assess Oral Administration

Gemcitabine is a nucleoside analog effective against several solid tumors. Standard treatment consists of an intravenous infusion over 30 min. This is an invasive, uncomfortable and often painful method, involving recurring visits to the hospital and costs associated with medical staff and equipment. Gemcitabine’s activity is significantly limited by numerous factors, including metabolic inactivation, rapid systemic clearance of gemcitabine and transporter deficiency-associated resistance. As such, there have been research efforts to improve gemcitabine-based therapy efficacy, as well as strategies to enhance its oral bioavailability. In this work, gemcitabine in vitro and clinical data were analyzed and in silico tools were used to study the pharmacokinetics of gemcitabine after oral administration following different regimens. Several physiologically based pharmacokinetic (PBPK) models were developed using simulation software GastroPlus™, predicting the PK parameters and plasma concentration–time profiles. The integrative biomedical data analyses presented here are promising, with some regimens of oral administration reaching higher AUC in comparison to the traditional IV infusion, supporting this route of administration as a viable alternative to IV infusions. This study further contributes to personalized health care based on potential new formulations for oral administration of gemcitabine, as well nanotechnology-based drug delivery systems.     

Pharmacokinetic interactions of flunixin meglumine and enrofloxacin in ICR mice.

We examined the pharmacokinetic interactions of enrofloxacin and flunixin in male ICR mice that were subcutaneously (SC) administered with both or either one of the drugs. The experiments were performed on the following three groups: flunixin alone (2 mg/kg, SC), combination of flunixin (2 mg/kg, SC) and enrofloxacin (10 mg/kg, SC), and enrofloxacin alone (10 mg/kg, SC). Blood samples were collected at 5, 15 and 30 min, and 1, 2, 3, 4, 5 and 6 h after the drug administration, and the pharmacokinetic parameters of flunixin and enrofloxacin were evaluated from the plasma drug concentrations. Significant changes were detected in the pharmacokinetics of flunixin following its coadministration with enrofloxacin. Coadministration of flunixin and enrofloxacin resulted in a 41% increase of the area under the curve (AUC) and a 53% extension of the terminal half-life of flunixin; moreover, flunixin attained the maximum plasma drug concentration 2.75 times faster than when administered alone. The terminal rate constant and the maximum plasma drug concentration showed significant decreases of 34% and 33%, respectively, following the coadministration of enrofloxacin and flunixin as compared to those following the administration of flunixin alone. In contrast, no significant difference in the pharmacokinetics of enrofloxacin was detected following its coadministration with flunixin, as compared to those following the administration of enrofloxacin alone. Following the administration of enrofloxacin alone or its coadministration with flunixin, the plasma level of ciprofloxacin, the metabolite of enrofloxacin, was very low or undetectable. In conclusion, the pharmacokinetics of flunixin in ICR mice are altered by the coadministration of flunixin and enrofloxacin.     

Sulfate conjugation in drug metabolism: role of inorganic sulfate

Conjugation with sulfate is a major pathway for the biotransformation of phenolic drugs in humans and many animal species. It is a process of limited capacity; the extent of sulfate conjugate formation and the metabolic clearance of drugs subject to conjugation with sulfate depend therefore on the dose, the dosage form, the route of administration, and the rate and duration of administration as well as on the pharmacokinetic parameters of competing processes. The effect of these variables is exemplified by the pharmacokinetics of salicylamide and acetaminophen in humans and rats. In our experience so far, the proximate cause of the nonlinear pharmacokinetics of sulfate conjugation of phenolic drugs is the limited availability and consequent depletion of inorganic sulfate. When this is prevented by direct or indirect (via sulfate donors such as N-acetylcysteine) repletion, the saturability of phenol sulfotransferase (EC 2.8.2.1) activity can become evident. The major mechanism of inorganic sulfate homeostasis is nonlinear renal clearance, which is due largely to saturable renal tubular reabsorption. Systemic depletion of inorganic sulfate secondary to utilization of this anion for the sulfation of drugs affects the availability of sulfate in the central nervous system and may, therefore, modify the disposition of certain neurotransmitters and other endogenous substances that are subject to sulfate conjugation.     

不同给药途径的治疗性纳米抗体研究进展

骆驼科及鲨鱼科动物血清中天然存在的纳米抗体具有不同于传统单克隆抗体的独特结构和分子量,这为抗体药物开发提供了全新的思路。纳米抗体较小的分子量和优异的稳定性使其在给药方面具有更大的灵活性,可以在一定程度上克服传统单克隆抗体在给药途径方面存在的局限性。同时,较小的分子量使纳米抗体具有双重药代动力学特征,既有优异的组织渗透性,又表现出快速的血液清除。重点介绍纳米抗体的药物代谢动力学特征和进一步改善药代动力学的方法,综述不同给药途径的纳米抗体药物研究进展,对其治疗特定疾病的可行性、安全性以及治疗效果进行分析,以期为纳米抗体药物研发中给药途径的选择提供参考。     

Bayesian Population Physiologically-Based Pharmacokinetic (PBPK) Approach for a Physiologically Realistic Characterization of Interindividual Variability in Clinically Relevant Populations

Interindividual variability in anatomical and physiological properties results in significant differences in drug pharmacokinetics. The consideration of such pharmacokinetic variability supports optimal drug efficacy and safety for each single individual, e.g. by identification of individual-specific dosings. One clear objective in clinical drug development is therefore a thorough characterization of the physiological sources of interindividual variability. In this work, we present a Bayesian population physiologically-based pharmacokinetic (PBPK) approach for the mechanistically and physiologically realistic identification of interindividual variability. The consideration of a generic and highly detailed mechanistic PBPK model structure enables the integration of large amounts of prior physiological knowledge, which is then updated with new experimental data in a Bayesian framework. A covariate model integrates known relationships of physiological parameters to age, gender and body height. We further provide a framework for estimation of the a posteriori parameter dependency structure at the population level. The approach is demonstrated considering a cohort of healthy individuals and theophylline as an application example. The variability and co-variability of physiological parameters are specified within the population; respectively. Significant correlations are identified between population parameters and are applied for individual- and population-specific visual predictive checks of the pharmacokinetic behavior, which leads to improved results compared to present population approaches. In the future, the integration of a generic PBPK model into an hierarchical approach allows for extrapolations to other populations or drugs, while the Bayesian paradigm allows for an iterative application of the approach and thereby a continuous updating of physiological knowledge with new data. This will facilitate decision making e.g. from preclinical to clinical development or extrapolation of PK behavior from healthy to clinically significant populations.     

Complex patterns of viral load decay under antiretroviral therapy: influence of pharmacokinetics and intracellular delay

We present a model of HIV dynamics under antiretroviral therapy that combines drug pharmacokinetics and intracellular delay. A two compartment pharmacokinetic model is employed to determine the time evolution of the intracellular concentrations of the active forms of drugs, and thereby drug efficacy. The viral replication period is divided into pre- and post-drug action parts, allowing for the introduction of an intracellular delay in drug action. The standard model of viral dynamics is modified to account for the drug dependence of intracellular delay and continuously varying drug efficacy. Model calculations reveal that viral load decay in HIV infected patients under monotherapy can exhibit remarkably complex patterns depending on the relative magnitudes of the pharmacokinetic, intracellular, and intrinsic viral dynamic time-scales. The commonly assumed exponential decay is only a special case. However, uncertainties in measurement and the low sampling frequencies employed in present clinical studies preclude the identification of these patterns from existing clinical viral load data.     

Pharmacological and pharmacokinetic properties of lanthipeptides undergoing clinical studies

The intrinsic qualities of lanthipeptides for their use as therapeutic drugs present several challenges because of their properties, which include stability, solubility and bioavailability, which, under physiological conditions, are very low. Researches have encouraged clinical evaluation of a few compounds, such as mutacin 1140, microbisporicin, actagardine and duramycin, with pharmacokinetic profiles showing rapid distribution and elimination rates, good bioavailability and fecal excretion, as well as high protein binding. Local and parenteral administration are currently suitable to minimize environmental influences on lanthipeptides and ensure efficient activity. Nevertheless, valuable improvements on pharmacodynamic and pharmacokinetic properties may also permit systemic applications via enteral routes. Understanding how rational modifications influence the desired pharmacological and pharmacokinetic properties of these biomolecules would help to answer some specific questions about their susceptibility to environmental changes, mechanism of action and how to engineer other peptides of the same group to improve their clinical relevance.     

Effect of cyclosporine, a P-glycoprotein inhibitor, on the pharmacokinetics of cefepime in rat blood and brain: a microdialysis study.

In clinical application, cefepime and cyclosporine are regularly combined in the treatment of organ transplant patients, so the interaction of these two drugs can be hypothesized. Therefore, the pharmacokinetics of cefepime alone and in combination with cyclosporine in rat using microdialysis coupled with HPLC-UV on-line system was evaluated in the study. Cefepime at three doses (20, 50, and 100 mg/kg) showed linear kinetics. After addition of cyclosporine, the mean residence time was increased from 34.9 min to 48.6 min (p<0.05, n=6), and the area under the concentration versus time curve (AUC) increased from 4775 min microg/ml to 6960 min microg/ml (p<0.01, n=6). While in the brain, AUC increased from 64.3 min microg/ml to 110.2 min microg/ml. In summary, cyclosporine (20 mg/kg) could significantly alter the simultaneously administered cefepime (50 mg/kg) unbound drug pharmacokinetic parameters in both blood and brain.     

Lung specific stealth liposomes as antitubercular drug carriers in guinea pigs

The problem of patient non-compliance in the management of tuberculosis (TB) can be overcome by reducing the dosing frequency of antitubercular drugs (ATD) employing drug carriers. This study reports on the intravenous (iv) administration of lung specific stealth liposomes encapsulating ATD (rifampicin and isoniazid in combination) to guinea pigs and the detailed pharmacokinetic/chemotherapeutic studies. Following a single iv administration of liposomal drugs, the latter were found to exhibit sustained therapeutic levels in plasma for 96-168 hr with half-lives of 24-70 hr, mean residence time (MRT) of 35-81 hr and organ drug levels up to day 7. The relative bioavailability (as compared to oral free drugs) was increased by 5.4-8.9 folds, whereas the absolute bioavailability (as compared to iv free drugs) was increased by 2.9-4.2 folds. Weekly therapy with liposomal ATD for 6 weeks produced equivalent clearance of Mycobacterium tuberculosis from organs as did daily therapy with oral free drugs. Hence, intravenous liposomal ATD offer the therapeutic advantage of reducing the dosing frequency and improving the patient compliance in the management of TB.     

Pharmacokinetic basis for using tobramycin and sisomicin in treating pyelonephritis of the transplanted kidney

The pharmacokinetics of tobramycin and sisomicin in patients after kidney transplantations was studied. A significant variability of the pharmacokinetic parameters of tobramycin and sisomicin under conditions of the changing function of the kidney transplant was shown. This required individual control of the drug serum levels in such patients. Linear correlation between the exponent (beta) and the clearance of endogenous creatinine was observed. On the basis of this correlation a nomogram providing a decrease in the percentage of the errors in determining the dosage intervals was plotted.     

Pharmacokinetic requirements for successful site-directed targeting of drugs

Targeted drugs can be defined as those in which features of the molecule, additional to those required for receptor interaction, substantially improve the concentration ratio of active substance at the site of action compared to the site where side-effects occur.These requirements for successful targeting of systemically administered drugs can be determined by pharmacokinetic modeling. The requirements depend on the mechanism of targeting and on whether targeting is to be achieved for continuous therapy or for acute treatment. For continuous therapy (lasting several days) the success of targeting using a prodrug which is locally activated and has linear pharmacokinetics is proportional to the clearance of active drug from the body and inversely proportional the rate constant for leaving the site of action and to the volume of the tissue. The relationship can be mapped graphically and typical values for these parameters are considered so that situations where targeting can be successful can be identified. The prodrug must also have properties which result in sufficient concentration of drug being formed at the site of action. These properties can also be described by simple proportionality relationships and the conditions for success illustrated graphically.Kinetic considerations are also important for targeting. For continuous therapy it is desirable that steady drug concentrations should be reached rapidly. This is best achieved by using molecules which rapidly exchange between body compartments and have low tissue binding. For acute therapy the rules for targeting can be quite different and an example is given where binding can be responsible for a form of targeting.The results emphasise the need for careful consideration of the properties of targeted system taking into account transport, binding and clearance of both prodrug and drug. Specific details of the disease are also critical both in terms of local tissue properties and the desired time course of drug action.     

A comprehensive approach for drug safety assessment

A comprehensive, multidisciplinary approach is proposed here for the development of a drug with an acceptable safety profile. Key parameters to be considered for drug safety evaluation based on this comprehensive approach include the following: (1) Pharmacology: Possible toxicity due to drug-target interactions, including interactions with unintended molecular targets, or with molecular targets in unintended organs. (2) Chemistry: Chemical scaffolding and side-chains with safety concerns. (3) Toxicology: Toxicity in animals in vivo, and in relevant animal and human cells in culture. (4) Drug metabolism and pharmacokinetics: Safety concerns due to toxification or detoxification, organ distribution, clearance and pharmacokinetic drug-drug interactions. (5) Risk factors: Physiological, environmental and genetic factors that may enhance a patient's susceptibility. It is proposed that this integrated, multidisciplinary approach to safety evaluation may enhance the accuracy of the prediction of drug safety and thereby the efficiency of drug development.     

Chronopharmacokinetics and Chronotoxicity of Lithium in Mice Eating Normal and Low-Sodium Diets

The temporal aspects of the pharmacokinetics and toxicity of lithium were studied in mice eating normal and low-sodium diets. ICR male mice, housed under a lightrdark (LD; 12:12) cycle, were injected with variable doses of lithium chloride i.p. A circadian rhythm was found in lithium clearance after a single administration in mice eating the normal diet showed the maximum value in the early dark phase and the minimum in the early light phase. The repeated administration of lithium did not affect the rhythm of the pharmacokinetics of the drug under the LD cycle. Although the low-sodium diet significantly decreased the lithium clearance, it did not influence the rhythm of the clearance. Higher toxicity was demonstrated in mice injected with the drug at the time of day with lower lithium clearance in the single-dose study but not in the repeated-doses study, regardless of the diet conditions. The low-sodium diet increased the acute and chronic toxicity of lithium. The results indicate that there is a circadian rhythm of acute toxicity and clearance of lithium after a single dose or repeated administration of the drug in mice eating normal and low-sodium diets and that the low-sodium diet increases lithium toxicity by reducing the clearance of the drug without influencing the rhythm characteristics.     

Chronopharmacokinetics and Chronotoxicity of Lithium in Mice Eating Normal and Low-Sodium Diets

The temporal aspects of the pharmacokinetics and toxicity of lithium were studied in mice eating normal and low-sodium diets. ICR male mice, housed under a lightrdark (LD; 12:12) cycle, were injected with variable doses of lithium chloride i.p. A circadian rhythm was found in lithium clearance after a single administration in mice eating the normal diet showed the maximum value in the early dark phase and the minimum in the early light phase. The repeated administration of lithium did not affect the rhythm of the pharmacokinetics of the drug under the LD cycle. Although the low-sodium diet significantly decreased the lithium clearance, it did not influence the rhythm of the clearance. Higher toxicity was demonstrated in mice injected with the drug at the time of day with lower lithium clearance in the single-dose study but not in the repeated-doses study, regardless of the diet conditions. The low-sodium diet increased the acute and chronic toxicity of lithium. The results indicate that there is a circadian rhythm of acute toxicity and clearance of lithium after a single dose or repeated administration of the drug in mice eating normal and low-sodium diets and that the low-sodium diet increases lithium toxicity by reducing the clearance of the drug without influencing the rhythm characteristics.     

Effects of Gender and Phase of the Menstrual Cycle on the Kinetics of Ranitidine in Healthy Volunteers

The present study was undertaken to determine if differences exist in the pharmacokinetic parameters of oral ranitidine caused by gender and stage of the menstrual cycle. The study was performed in two steps, in the first a pharmacokinetic study was performed on 10 men (average age 35.5 yrs) and 10 women (average age 34.7 yrs) during the follicular phase, and in the second the pharmacokinetic study was performed only on the same women in their luteal phase. Subjects received a tablet dose of 300 mg ranitidine, and blood samples were drawn at several times after its ingestion. Plasma ranitidine concentration was determined by high performance liquid chromatography. Comparison of the pharmacokinetic parameters of women and men revealed statistically significant differences both in distribution volume (Vd) with values of 2.0 and 6.3 l/kg, Area Under Curve (AUC) with values of 7312.15 and 11471.94 ng/ml/h, and clearance (CLt) with values of 0.65 and 0.59 l/kg/h, respectively. Several pharmacokinetic parameters in women were different in the follicular compared to the luteal phase; for example, Vd was 2.0 and 5.6 l/kg, AUC was 7312.15 and 5195.83 ng/ml/h, and CLt was 0.65 and 0.97 l/kg/h, in the respective phases. Moreover, the maximum concentration (Cmax) was 1086 ng/ml in the follicular vs. 864 ng/ml in the luteal phase. The first study detected differences between men and women in several pharmacokinetic parameters, mainly those indicative of drug availability, for example, Vd, AUC, and CLt. Comparison of data obtained in the follicular phase with those obtained in the luteal phase revealed differences in most pharmacokinetic parameters, which is seemingly indicative of the characteristic physiological changes associated with the luteal phase that largely affect the kinetics and availability of drugs such as ranitidine. Although it has been postulated that hormonal fluctuation within the menstrual cycle phase is the primary cause of documented gender differences in the pharmacokinetics and pharmacodynamics of drugs, further study of related factors is required to fully understand how gender and menstrual cycle rhythms affect the pharmacokinetic process in their entirety.     

Administration-time differences in the pharmacokinetics of gentamicin intravenously delivered to human beings

Administration-time differences of gentamicin pharmacokinetics were studied by crossover design after a single intravenous administration of gentamicin (80 mg) to 10 human subjects at 09:00 (morning time) and 22:00 (nighttime). The profiles of serum gentamicin concentration showed a significant statistical difference between 09:00 and 22:00, suggesting circadian variations of pharmacokinetic behaviors. A significant circadian rhythm of pharmacokinetic parameters as a function of time of day was noted in human subjects, showing lower total body clearance Clt and higher serum area under the curve (AUC) when given at nighttime. The half-life t1/2 was shorter in the morning (2.82 h +/- 0.43 h) when compared to the nighttime (2.97 h +/- 0.36 h), but the difference was not statistically significant. The AUC was significantly greater in the morning (23.4 +/- 3.84 micrograms-h/mL) than that in the nighttime (26.3 +/- 5.79 micrograms-h/mL) (p < .05), most likely because the Clt was significantly higher when gentamicin was given in the morning (3.51 +/- 0.57 L/h) versus in the nighttime (3.18 +/- 0.65 L/h). Although the volume of distribution Vd decreased when given at nighttime, it was independent of the dosing time. From this study, there was an administration-time difference of gentamicin pharmacokinetics in human beings. The optimized dosing regimen of gentamicin can be decided by considering circadian rhythm and rest-activity routine so that minimized toxicity and effective therapy are established for patients. The current findings also can be applied to other drugs with circadian rhythms of pharmacokinetics and narrow therapeutic windows in clinical chronotherapeutics.