Showing papers on "Pharmacokinetics published in 2011"

Clinical pharmacokinetics of metformin

Abstract: Metformin is widely used for the treatment of type 2 diabetes mellitus. It is a biguanide developed from galegine, a guanidine derivative found in Galega officinalis (French lilac). Chemically, it is a hydrophilic base which exists at physiological pH as the cationic species (>99.9%). Consequently, its passive diffusion through cell membranes should be very limited. The mean ± SD fractional oral bioavailability (F) of metformin is 55 ± 16%. It is absorbed predominately from the small intestine. Metformin is excreted unchanged in urine. The elimination half-life (t1/2) of metformin during multiple dosages in patients with good renal function is approximately 5 hours. From published data on the pharmacokinetics of metformin, the population mean of its clearances were calculated. The population mean renal clearance (CLR) and apparent total clearance after oral administration (CL/F) of metformin were estimated to be 510 ± 130 mL/min and 1140 ± 330 mL/min, respectively, in healthy subjects and diabetic patients with good renal function. Over a range of renal function, the population mean values of CLR and CL/F of metformin are 4.3 ± 1.5 and 10.7 ± 3.5 times as great, respectively, as the clearance of creatinine (CLCR). AS the CLR and CL/F decrease approximately in proportion to CLCR, the dosage of metformin should be reduced in patients with renal impairment in proportion to the reduced CLCR. The oral absorption, hepatic uptake and renal excretion of metformin are mediated very largely by organic cation transporters (OCTs). An intron variant of OCT1 (single nucleotide polymorphism [SNP] rs622342) has been associated with a decreased effect on blood glucose in heterozygotes and a lack of effect of metformin on plasma glucose in homozygotes. An intron variant of multidrug and toxin extrusion transporter [MATE1] (G>A, SNP rs2289669) has also been associated with a small increase in antihyperglycaemic effect of metformin. Overall, the effect of structural variants of OCTs and other cation transporters on the pharmacokinetics of metformin appears small and the subsequent effects on clinical response are also limited. However, intersubject differences in the levels of expression of OCT1 and OCT3 in the liver are very large and may contribute more to the variations in the hepatic uptake and clinical effect of metformin. Lactic acidosis is the feared adverse effect of the biguanide drugs but its incidence is very low in patients treated with metformin. We suggest that the mean plasma concentrations of metformin over a dosage interval be maintained below 2.5 mg/L in order to minimize the development of this adverse effect.

Single-dose, placebo-controlled, randomized study of AMG 785, a sclerostin monoclonal antibody.

Abstract: Sclerostin, an osteocyte-secreted protein, negatively regulates osteoblasts and inhibits bone formation. In this first-in-human study, a sclerostin monoclonal antibody (AMG 785) was administered to healthy men and postmenopausal women. In this phase I, randomized, double-blind, placebo-controlled, ascending, single-dose study, 72 healthy subjects received AMG 785 or placebo (3:1) subcutaneously (0.1, 0.3, 1, 3, 5, or 10 mg/kg) or intravenously (1 or 5 mg/kg). Depending on dose, subjects were followed for up to 85 days. The effects of AMG 785 on safety and tolerability (primary objectives) and pharmacokinetics, bone turnover markers, and bone mineral density (secondary objectives) were evaluated. AMG 785 generally was well tolerated. One treatment-related serious adverse event of nonspecific hepatitis was reported and was resolved. No deaths or study discontinuations occurred. AMG 785 pharmacokinetics were nonlinear with dose. Dose-related increases in the bone-formation markers procollagen type 1 N-propeptide (P1NP), bone-specific alkaline phosphatase (BAP), and osteocalcin were observed, along with a dose-related decrease in the bone-resorption marker serum C-telopeptide (sCTx), resulting in a large anabolic window. In addition, statistically significant increases in bone mineral density of up to 5.3% at the lumbar spine and 2.8% at the total hip compared with placebo were observed on day 85. Six subjects in the higher-dose groups developed anti-AMG 785 antibodies, 2 of which were neutralizing, with no discernible effect on the pharmacokinetics or pharmacodynamics. In summary, single doses of AMG 785 generally were well tolerated, and the data support further clinical investigation of sclerostin inhibition as a potential therapeutic strategy for conditions that could benefit from increased bone formation.

Systemic administration of PRO051 in Duchenne's muscular dystrophy.

Abstract: Background Local intramuscular administration of the antisense oligonucleotide PRO051 in patients with Duchenne's muscular dystrophy with relevant mutations was previously reported to induce the skipping of exon 51 during pre–messenger RNA splicing of the dystrophin gene and to facilitate new dystrophin expression in muscle-fiber membranes. The present phase 1–2a study aimed to assess the safety, pharmacokinetics, and molecular and clinical effects of systemically administered PRO051. Methods We administered weekly abdominal subcutaneous injections of PRO051 for 5 weeks in 12 patients, with each of four possible doses (0.5, 2.0, 4.0, and 6.0 mg per kilogram of body weight) given to 3 patients. Changes in RNA splicing and protein levels in the tibialis anterior muscle were assessed at two time points. All patients subsequently entered a 12-week open-label extension phase, during which they all received PRO051 at a dose of 6.0 mg per kilogram per week. Safety, pharmacokinetics, serum creatine kinase levels,...

The Effects of Hypoalbuminaemia on Optimizing Antibacterial Dosing in Critically Ill Patients

Abstract: Low serum albumin levels are very common in critically ill patients, with reported incidences as high as 40-50%. This condition appears to be associated with alterations in the degree of protein binding of many highly protein-bound antibacterials, which lead to altered pharmacokinetics and pharmacodynamics, although this topic is infrequently considered in daily clinical practice. The effects of hypoalbuminaemia on pharmacokinetics are driven by the decrease in the extent of antibacterial bound to albumin, which increases the unbound fraction of the drug. Unlike the fraction bound to plasma proteins, the unbound fraction is the only fraction available for distribution and clearance from the plasma (central compartment). Hence, hypoalbuminaemia is likely to increase the apparent total volume of distribution (V(d)) and clearance (CL) of a drug, which would translate to lower antibacterial exposures that might compromise the attainment of pharmacodynamic targets, especially for time-dependent antibacterials. The effect of hypoalbuminaemia on unbound concentrations is also likely to have an important impact on pharmacodynamics, but there is very little information available on this area. The objectives of this review were to identify the original research papers that report variations in the highly protein-bound antibacterial pharmacokinetics (mainly V(d) and CL) in critically ill patients with hypoalbuminaemia and without renal failure, and subsequently to interpret the consequences for antibacterial dosing. All relevant articles that described the pharmacokinetics and/or pharmacodynamics of highly protein-bound antibacterials in critically ill patients with hypoalbuminaemia and conserved renal function were reviewed. We found that decreases in the protein binding of antibacterials in the presence of hypoalbuminaemia are frequently observed in critically ill patients. For example, the V(d) and CL of ceftriaxone (85-95% protein binding) in hypoalbuminaemic critically ill patients were increased 2-fold. A similar phenomenon was reported with ertapenem (85-95% protein binding), which led to failure to attain pharmacodynamic targets (40% time for which the concentration of unbound [free] antibacterial was maintained above the minimal inhibitory concentration [fT>MIC] of the bacteria throughout the dosing interval). The V(d) and CL of other highly protein-bound antibacterials such as teicoplanin, aztreonam, fusidic acid or daptomycin among others were significantly increased in critically ill patients with hypoalbuminaemia compared with healthy subjects. Increased antibacterial V(d) appeared to be the most significant pharmacokinetic effect of decreased albumin binding, together with increased CL. These pharmacokinetic changes may result in decreased achievement of pharmacodynamic targets especially for time-dependent antibacterials, resulting in sub-optimal treatment. The effects on concentration-dependent antibacterial pharmacodynamics are more controversial due to the lack of data on this topic. In conclusion, altered antibacterial-albumin binding in the presence of hypoalbuminaemia is likely to produce significant variations in the pharmacokinetics of many highly protein-bound antibacterials. Dose adjustments of these antibacterials in critically ill patients with hypoalbuminaemia should be regarded as another step for antibacterial dosing optimization. Moreover, some of the new antibacterials in development exhibit a high level of protein binding although hypoalbuminaemia is rarely considered in clinical trials in critically ill patients. Further research that defines dosing regimens that account for such altered pharmacokinetics is recommended.

Phase I randomized, double-blind pilot study of micronized resveratrol (SRT501) in patients with hepatic metastases--safety, pharmacokinetics, and pharmacodynamics.

Abstract: The phytochemical resveratrol has undergone extensive preclinical investigation for its putative cancer chemopreventive properties. Low systemic availability of the parent compound due to rapid and extensive metabolism, may confound its usefulness as a potential agent to prevent malignancies in organs remote from the site of absorption. Micronization allows increased drug absorption, thus increasing availability. Here we describe a pilot study of SRT501, micronized resveratrol, given at 5.0 g daily for 14 days, to patients with colorectal cancer and hepatic metastases scheduled to undergo hepatectomy. The purpose of the study was to assess the safety, pharmacokinetics and pharmacodynamics of the formulation. SRT501 was found to be well tolerated. Mean plasma resveratrol levels following a single dose of SRT501 administration were 1942±1422 ng/mL, exceeding those published for equivalent doses of non-micronized resveratrol by 3.6-fold. Resveratrol was detectable in hepatic tissue following SRT501 administration (up to 2287 ng/g). Cleaved caspase-3, a marker of apoptosis, was significantly increased by 39% in malignant hepatic tissue following SRT501 treatment, compared to tissue from the placebo-treated patients. SRT501 warrants further clinical exploration to assess its potential clinical utility.

Clinical pharmacokinetics and pharmacodynamics : concepts and applications

Abstract: Preface Definition of Symbols Non-Proprietary and Brand Names of Drugs in Text and Illustrations I. Basic Considerations *1. Therapeutic Relevance *2. Fundamental Concepts and Terminology II. Exposure and Response after a Single Dose *3. Kinetics Following an Intravenous Bolus Dose *4. Membranes and Distribution *5. Elimination *6. Kinetics Following an Extravascular Dose *7. Absorption *8. Response Following a Single Dose III. Therapeutic Regimens *9. Therapeutic Window *10. Constant-Rate Input *11. Multiple Dose Regimens IV. Individualization *12.Variability *13.Genetics *14. Age, Weight, and Gender *15. Disease *16. Nonlinearities *17. Drug Interactions *18. Initiating and Managing Therapy V. Supplemental Topics *19. Distribution Kinetics *20. Metabolites and Drug Response *21. New! Protein Drugs *22. New! Prediction and Refinement of Human Kinetics from In Vitro, Preclinical, and Early Clinical Data Appendices A. Assessment of AUC B. Ionization and the pH Partition Hypothesis C. Distribution of Drugs Extensively Bound to Plasma Proteins D. Plasma-to-Blood Concentration Ratio E. Well-stirred Model of Hepatic Clearance F. Absorption Kinetics G. Wagner-Nelson Method H. Mean Residence Time I. Amount of Drug in Body on Accumulation to Plateau J. Answers to Study Problems

Factors and Mechanisms for Pharmacokinetic Differences between Pediatric Population and Adults.

Abstract: Many physiologic differences between children and adults may result in age-related changes in pharmacokinetics and pharmacodynamics. Factors such as gastric pH and emptying time, intestinal transit time, immaturity of secretion and activity of bile and pancreatic fluid among other factors determine the oral bioavailability of pediatric and adult populations. Anatomical, physiological and biochemical characteristics in children also affect the bioavailability of other routes of administration. Key factors explaining differences in drug distribution between the pediatric population and adults are membrane permeability, plasma protein binding and total body water. As far as drug metabolism is concerned, important differences have been found in the pediatric population compared with adults both for phase I and phase II metabolic enzymes. Immaturity of glomerular filtration, renal tubular secretion and tubular reabsorption at birth and their maturation determine the different excretion of drugs in the pediatric population compared to adults.

Phase I Study of PARP Inhibitor ABT-888 in Combination with Topotecan in Adults with Refractory Solid Tumors and Lymphomas

Abstract: A phase I trial of ABT-888 (veliparib), a PARP inhibitor, in combination with topotecan, a topoisomerase I-targeted agent, was carried out to determine maximum tolerated dose (MTD), safety, pharmacokinetics, and pharmacodynamics of the combination in patients with refractory solid tumors and lymphomas. Varying schedules and doses of intravenous topotecan in combination with ABT-888 (10 mg) administered orally twice a day (BID) were evaluated. Plasma and urine pharmacokinetics were assessed and levels of poly(ADP-ribose) (PAR) and the DNA damage marker γH2AX were measured in tumor and peripheral blood mononuclear cells (PBMC). Twenty-four patients were enrolled. Significant myelosuppression limited the ability to coadminister ABT-888 with standard doses of topotecan, necessitating dose reductions. Preclinical studies using athymic mice carrying human tumor xenografts also informed schedule changes. The MTD was established as topotecan 0.6 mg/m²/d and ABT-888 10 mg BID on days one to five of 21-day cycles. Topotecan did not alter the pharmacokinetics of ABT-888. A more than 75% reduction in PAR levels was observed in 3 paired tumor biopsy samples; a greater than 50% reduction was observed in PBMCs from 19 of 23 patients with measurable levels. Increases in γH2AX response in circulating tumor cells (CTC) and PBMCs were observed in patients receiving ABT-888 with topotecan. We show a mechanistic interaction of a PARP inhibitor, ABT-888, with a topoisomerase I inhibitor, topotecan, in PBMCs, tumor, and CTCs. Results of this trial reveal that PARP inhibition can modulate the capacity to repair topoisomerase I-mediated DNA damage in the clinic.

Remote triggered release of doxorubicin in tumors by synergistic application of thermosensitive liposomes and gold nanorods.

Abstract: Delivery of chemotherapeutic agents after encapsulation in nanocarriers such as liposomes diminishes side-effects, as PEGylated nanocarrier pharmacokinetics decrease dosing to healthy tissues and accumulate in tumors due to the enhanced permeability and retention effect. Once in the tumor, however, dosing of the chemotherapeutic to tumor cells is limited potentially by the rate of release from the carriers and the size-constrained, poor diffusivity of nanocarriers in tumor interstitium. Here, we report the design and fabrication of a thermosensitive liposomal nanocarrier that maintains its encapsulation stability with a high concentration of doxorubicin payload, thereby minimizing “leak” and attendant toxicity. When used synergistically with PEGylated gold nanorods and near-infrared stimulation, remote triggered release of doxorubicin from thermosensitive liposomes was achieved in a mouse tumor model of human glioblastoma (U87), resulting in a significant increase in efficacy when compared to nontriggered...

Age-Related Changes in Pharmacokinetics

Abstract: Ageing is characterized by a progressive decline in the functional reserve of multiple organs and systems, which can influence drug disposition In addition, comorbidity and polypharmacy are highly prevalent in the elderly As ageing is associated with some reduction in first-pass metabolism, bioavailability of a few drugs can be increased With ageing body fat increases and total body water as well as lean body mass decrease Consequently, hydrophilic drugs have a smaller apparent volume of distribution (V) and lipophilic drugs have an increased V with a prolonged half-life Drugs with a high hepatic extraction ratio display some age-related decrease in systemic clearance (CL), but for most drugs with a low hepatic extraction ratio, CL is not reduced with advancing age In general, activities of cytochrome P450 enzymes are preserved in normal ageing and the genetic influence is much more striking than age effects Drug transporters play an important role in pharmacokinetic processes, but their function and pharmacology have not yet been fully examined for agerelated effects One third of elderly persons show no decrease in renal function (GFR > 70 mL/min/173 m2) In about two thirds of elderly subjects, the age-related decline of renal function was associated with coexisting cardiovascular diseases and other risk factors In the elderly a large interindividual variability in drug disposition is particularly prominent In conclusion, the complexity of interactions between comorbidity, polypharmacy, and age-related changes in pharmacokinetics (and pharmacodynamics) justify the old and well-known dosing aphorism " start low, go slow" for aged individuals

Comparative pharmacokinetics: principles, techniques, and applications.

Abstract: Introduction principles of drug movement in the body absorption distribution renal elimination hepatic biotransformation and biliary excretion compartmental models noncompartmental models nonlinear models physiological models dosage regimens simultaneous pharmacokinetics-pharmacodynamics modelling study design and data analysis population pharmacokinetics models and Bayesian forecasting applied to clinical pharmacokinetics dosage adjustment in renal diseases interspecies extrapolations tissue residues and withdrawal times.

Antiviral activity, safety, and pharmacokinetics/pharmacodynamics of dolutegravir as 10-day monotherapy in HIV-1-infected adults.

Abstract: Objective: To evaluate the antiviral activity, safety, pharmacokinetics, and pharmacokinetics/pharmacodynamics of dolutegravir (DTG), a next-generation HIV integrase inhibitor (INI), as short-term monotherapy. Design: A phase IIa, randomized, double-blind, dose-ranging study. Methods: In this study, INI-naive, HIV-1-infected adults currently off antiretroviral therapy were randomized to receive DTG (2, 10, or 50mg) or placebo once daily for 10 days in an eight active and two placebo randomization scheme per DTG dose. Placebo patients were pooled for the purpose of analysis. Results: Thirty-five patients (n ¼9 for DTG 2 and 10mg, n ¼10 for DTG 50mg, and n ¼7 for placebo) were enrolled. Baseline characteristics were similar across dosegroups.SignificantreductionsinplasmaHIV-1RNAfrombaselinetoday11were observed for all DTG dose groups compared with placebo (P <0.001), with a mean decrease of 1.51‐2.46log10copies/ml. In addition, a well characterized dose‐response relationship was observed for viral load decrease. Most patients (seven of 10, 70%) receiving DTG 50mg achieved plasma HIV-1 RNA less than 50copies/ml. The pharmacokinetic variability was low (coefficient of variation, range 25‐50%). Plasma HIV-1 RNA reduction was best predicted by Ct using an Emax model. The most common adverse events were diarrhea, fatigue, and headache; the majority of ad verse events were mild or moderate in severity. Conclusion: Dolutegravir demonstrated potent antiviral activity, good short-term tolerability, low pharmacokinetic variability, and a predictable pharmacokinetics/ pharmacodynamics relationship, which support once-daily dosing without a pharmacokinetic booster in integrase-naive patients in future studies. 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins AIDS 2011, 25:1737‐1745

In Vitro and In Vivo P-Glycoprotein Transport Characteristics of Rivaroxaban

Abstract: Rivaroxaban, an oral, direct factor Xa inhibitor, has a dual mode of elimination in humans, with two-thirds metabolized by the liver and one-third renally excreted unchanged P-glycoprotein (P-gp) is known to be involved in the absorption, distribution, and excretion of drugs To investigate whether rivaroxaban is a substrate of P-gp, the bidirectional flux of rivaroxaban across Caco-2, wild-type, and P-gp-overexpressing LLC-PK1 cells was investigated Furthermore, the inhibitory effect of rivaroxaban toward P-gp was determined Rivaroxaban exhibited high permeability and polarized transport across Caco-2 cells Rivaroxaban was shown to be a substrate for, but not an inhibitor of, P-gp Of a set of potential P-gp inhibitors, ketoconazole and ritonavir, but not clarithromycin or erythromycin, inhibited P-gp-mediated transport of rivaroxaban, with half-maximal inhibitory concentration values in the range of therapeutic plasma concentrations These findings are in line with observed area under the plasma concentration-time curve increases in clinical drug-drug interaction studies indicating a possible involvement of P-gp in the distribution and excretion of rivaroxaban In vivo studies in wild-type and P-gp double-knockout mice demonstrated that the impact of P-gp alone on the pharmacokinetics of rivaroxaban is minor However, in P-gp double-knockout mice, a slight increase in brain concentrations and decreased excretion into the gastrointestinal tract were observed compared with wild-type mice These studies also demonstrated that brain penetration of rivaroxaban is fairly low In addition to P-gp, a further transport protein might be involved in the secretion of rivaroxaban

Flip-flop pharmacokinetics – delivering a reversal of disposition: challenges and opportunities during drug development

Abstract: Flip-flop pharmacokinetics is a phenomenon often encountered with extravascularly administered drugs. Occurrence of flip-flop spans preclinical to human studies. The purpose of this article is to analyze both the pharmacokinetic interpretation errors and opportunities underlying the presence of flip-flop pharmacokinetics during drug development. Flip-flop occurs when the rate of absorption is slower than the rate of elimination. If it is not recognized, it can create difficulties in the acquisition and interpretation of pharmacokinetic parameters. When flip-flop is expected or discovered, a longer duration of sampling may be necessary in order to avoid overestimation of fraction of dose absorbed. Common culprits of flip-flop disposition are modified dosage formulations; however, formulation characteristics such as the drug chemical entities themselves or the incorporated excipients can also cause the phenomenon. Yet another contributing factor is the physiological makeup of the extravascular site of administration. In this article, these causes of flip-flop pharmacokinetics are discussed with incorporation of relevant examples and the implications for drug development outlined.

Identification of the Rate-Determining Process in the Hepatic Clearance of Atorvastatin in a Clinical Cassette Microdosing Study

Abstract: Clearance of atorvastatin occurs through hepatic uptake by organic anion transporting polypeptides (OATPs) and subsequent metabolism by cytochrome P450 (CYP) 3A4. To demonstrate the relative importance of OATPs and CYP3A4 in the hepatic elimination of atorvastatin in vivo, a clinical cassette microdose study was performed. A cocktail consisting of a microdose of atorvastatin along with probe substrates for OATPs (pravastatin) and CYP3A4 (midazolam) was orally administered to eight healthy volunteers. The pharmacokinetics of this cocktail was observed at baseline, after an oral dose of 600 mg rifampicin (an inhibitor of OATPs), and after an intravenous dose of 200 mg itraconazole (a CYP3A4 inhibitor). Rifampicin increased the pravastatin dose-normalized area under the plasma concentration-time curve (AUC) (4.6-fold), and itraconazole significantly increased the midazolam dose-normalized AUC (1.7-fold). The atorvastatin dose-normalized AUC increased 12-fold when coadministered with rifampicin but did not change when coadministered with itraconazole. These results indicate that hepatic uptake via OATPs makes the dominant contribution to the hepatic elimination of atorvastatin at a subtherapeutic microdose.

The Pharmacokinetics and Pharmacodynamics of Iron Preparations

Abstract: Standard approaches are not appropriate when assessing pharmacokinetics of iron supplements due to the ubiquity of endogenous iron, its compartmentalized sites of action, and the complexity of the iron metabolism. The primary site of action of iron is the erythrocyte, and, in contrast to conventional drugs, no drug-receptor interaction takes place. Notably, the process of erythropoiesis, i.e., formation of new erythrocytes, takes 3−4 weeks. Accordingly, serum iron concentration and area under the curve (AUC) are clinically irrelevant for assessing iron utilization. Iron can be administered intravenously in the form of polynuclear iron(III)-hydroxide complexes with carbohydrate ligands or orally as iron(II) (ferrous) salts or iron(III) (ferric) complexes. Several approaches have been employed to study the pharmacodynamics of iron after oral administration. Quantification of iron uptake from radiolabeled preparations by the whole body or the erythrocytes is optimal, but alternatively total iron transfer can be calculated based on known elimination rates and the intrinsic reactivity of individual preparations. Degradation kinetics, and thus the safety, of parenteral iron preparations are directly related to the molecular weight and the stability of the complex. High oral iron doses or rapid release of iron from intravenous iron preparations can saturate the iron transport system, resulting in oxidative stress with adverse clinical and subclinical consequences. Appropriate pharmacokinetics and pharmacodynamics analyses will greatly assist our understanding of the likely contribution of novel preparations to the management of anemia.

Pharmacokinetics and Metabolism of Natural Methylxanthines in Animal and Man

Abstract: Caffeine, theophylline, theobromine, and paraxanthine administered to animals and humans distribute in all body fluids and cross all biological membranes. They do not accumulate in organs or tissues and are extensively metabolized by the liver, with less than 2% of caffeine administered excreted unchanged in human urine. Dose-independent and dose-dependent pharmacokinetics of caffeine and other dimethylxanthines may be observed and explained by saturation of metabolic pathways and impaired elimination due to the immaturity of hepatic enzyme and liver diseases. While gender and menstrual cycle have little effect on their elimination, decreased clearance is seen in women using oral contraceptives and during pregnancy. Obesity, physical exercise, diseases, and particularly smoking and the interactions of drugs affect their elimination owing to either stimulation or inhibition of CYP1A2. Their metabolic pathways exhibit important quantitative and qualitative differences in animal species and man. Chronic ingestion or restriction of caffeine intake in man has a small effect on their disposition, but dietary constituents, including broccoli and herbal tea, as well as alcohol were shown to modify their plasma pharmacokinetics. Using molar ratios of metabolites in plasma and/or urine, phenotyping of various enzyme activities, such as cytochrome monooxygenases, N-acetylation, 8-hydroxylation, and xanthine oxidase, has become a valuable tool to identify polymorphisms and to understand individual variations and potential associations with health risks in epidemiological surveys.

Duloxetine: clinical pharmacokinetics and drug interactions.

Abstract: Duloxetine, a potent reuptake inhibitor of serotonin (5-HT) and norepinephrine, is effective for the treatment of major depressive disorder, diabetic neuropathic pain, stress urinary incontinence, generalized anxiety disorder and fibromyalgia. Duloxetine achieves a maximum plasma concentration (C max ) of approximately 47 ng/mL (40 mg twice-daily dosing) to 110 ng/mL (80 mg twice-daily dosing) approximately 6 hours after dosing. The elimination half-life of duloxetine is approximately 10―12 hours and the volume of distribution is approximately 1640 L. The goal of this paper is to provide a review of the literature on intrinsic and extrinsic factors that may impact the pharmacokinetics of duloxetine with a focus on concomitant medications and their clinical implications. Patient demographic characteristics found to influence the pharmacokinetics of duloxetine include sex, smoking status, age, ethnicity, cytochrome P450 (CYP) 2D6 genotype, hepatic function and renal function. Of these, only impaired hepatic function or severely impaired renal function warrant specific warnings or dose recommendations. Pharmacokinetic results from drug interaction studies show that activated charcoal decreases duloxetine exposure, and that CYP1A2 inhibition increases duloxetine exposure to a clinically significant degree. Specifically, following oral administration in the presence of fluvoxamine, the area under the plasma concentration-time curve and C max of duloxetine significantly increased by 460% (90% CI 359, 584) and 141% (90% CI 93, 200), respectively. In addition, smoking is associated with a 30% decrease in duloxetine concentration. The exposure of duloxetine with CYP2D6 inhibitors or in CYP2D6 poor metabolizers is increased to a lesser extent than that observed with CYP1A2 inhibition and does not require a dose adjustment. In addition, duloxetine increases the exposure of drugs that are metabolized by CYP2D6, but not CYP1A2. Pharmacodynamic study results indicate that duloxetine may enhance the effects of benzodiazepines, but not alcohol or warfarin. An increase in gastric pH produced by histamine H 2 -receptor antagonists or antacids did not impact the absorption of duloxetine. While duloxetine is generally well tolerated, it is important to be knowledgeable about the potential for pharmacokinetic interactions between duloxetine and drugs that inhibit CYP1A2 or drugs that are metabolized by CYP2D6 enzymes.

Review of the clinical pharmacokinetics of artesunate and its active metabolite dihydroartemisinin following intravenous, intramuscular, oral or rectal administration

Abstract: Artesunate (AS) is a clinically versatile artemisinin derivative utilized for the treatment of mild to severe malaria infection. Given the therapeutic significance of AS and the necessity of appropriate AS dosing, substantial research has been performed investigating the pharmacokinetics of AS and its active metabolite dihydroartemisinin (DHA). In this article, a comprehensive review is presented of AS clinical pharmacokinetics following administration of AS by the intravenous (IV), intramuscular (IM), oral or rectal routes. Intravenous AS is associated with high initial AS concentrations which subsequently decline rapidly, with typical AS half-life estimates of less than 15 minutes. AS clearance and volume estimates average 2 - 3 L/kg/hr and 0.1 - 0.3 L/kg, respectively. DHA concentrations peak within 25 minutes post-dose, and DHA is eliminated with a half-life of 30 - 60 minutes. DHA clearance and volume average between 0.5 - 1.5 L/kg/hr and 0.5 - 1.0 L/kg, respectively. Compared to IV administration, IM administration produces lower peaks, longer half-life values, and higher volumes of distribution for AS, as well as delayed peaks for DHA; other parameters are generally similar due to the high bioavailability, assessed by exposure to DHA, associated with IM AS administration (> 86%). Similarly high bioavailability of DHA (> 80%) is associated with oral administration. Following oral AS, peak AS concentrations (Cmax) are achieved within one hour, and AS is eliminated with a half-life of 20 - 45 minutes. DHA Cmax values are observed within two hours post-dose; DHA half-life values average 0.5 - 1.5 hours. AUC values reported for AS are often substantially lower than those reported for DHA following oral AS administration. Rectal AS administration yields pharmacokinetic results similar to those obtained from oral administration, with the exceptions of delayed AS Cmax and longer AS half-life. Drug interaction studies conducted with oral AS suggest that AS does not appreciably alter the pharmacokinetics of atovaquone/proguanil, chlorproguanil/dapsone, or sulphadoxine/pyrimethamine, and mefloquine and pyronaridine do not alter the pharmacokinetics of DHA. Finally, there is evidence suggesting that the pharmacokinetics of AS and/or DHA following AS administration may be altered by pregnancy and by acute malaria infection, but further investigation would be required to define those alterations precisely.

The Human Placental Perfusion Model: A Systematic Review and Development of a Model to Predict In Vivo Transfer of Therapeutic Drugs

Abstract: Dual perfusion of a single placental lobule is the only experimental model to study human placental transfer of substances in organized placental tissue. To date, there has not been any attempt at a systematic evaluation of this model. The aim of this study was to systematically evaluate the perfusion model in predicting placental drug transfer and to develop a pharmacokinetic model to account for nonplacental pharmacokinetic parameters in the perfusion results. In general, the fetal-to-maternal drug concentration ratios matched well between placental perfusion experiments and in vivo samples taken at the time of delivery of the infant. After modeling for differences in maternal and fetal/neonatal protein binding and blood pH, the perfusion results were able to accurately predict in vivo transfer at steady state (R² = 0.85, P < 0.0001). Placental perfusion experiments can be used to predict placental drug transfer when adjusting for extra parameters and can be useful for assessing drug therapy risks and benefits in pregnancy.

Effects of quercetin on the bioavailability of doxorubicin in rats: Role of CYP3A4 and P-gp inhibition by quercetin

Abstract: Quercetin, a flavonoid, is an inhibitor of P-glycoprotein-mediated efflux transport, and its oxidative metabolism is catalyzed by CYP enzymes. Thus, it is expected that the pharmacokinetics of both intravenous and oral doxorubicin can be changed by quercetin. The purpose of this study was to investigate the effect of oral quercetin on the bioavailability and pharmacokinetics of orally and intravenously administered doxorubicin in rats. The effects of quercetin on the P-glycoprotein (P-gp) and CYP3A4 activities were also evaluated. Quercetin inhibited CYP3A4 enzyme activity in a concentration-dependent manner with a 50% inhibition concentration (IC50) of 1.97 μM. In addition, quercetin significantly enhanced the intracellular accumulation of rhodamine-123 in MCF-7/ADR cells overexpressing P-gp. The pharmacokinetic parameters of doxorubicin were determined in rats after oral (50 mg/kg) or intravenous (10 mg/kg) administration of doxorubicin to rats in the presence and absence of quercetin (0.6, 3 or 15 mg/kg). Compared to control, quercetin significantly (p < 0.05 for 0.6 mg/kg, p < 0.01 for 3 and 15 mg/kg) increased the area under the plasma concentration-time curve (AUC0−∞, 31.2-136.0% greater) of oral doxorubicin. Quercetin also significantly increased the peak plasma concentration (Cmax) of doxorubicin, while there was no significant change in Tmax and T1/2 of doxorubicin. Consequently, the absolute bioavailability of doxorubicin was increased by quercetin compared to control, and the relative bioavailability of oral doxorubicin was increased by 1.32 to 2.36 fold. In contrast, the pharmacokinetics of intravenous doxorubicin were not affected by quercetin. These results suggest that the quercetin-induced increase in bioavailability of oral doxorubicin can be attributed to enhanced doxorubicin absorption in the gastrointestinal tract via quercetin-induced inhibition of P-gp and reduced first-pass metabolism of doxorubicin due to quercetin-induced inhibition of CYP3A in the small intestine and/or in the liver rather than reduced renal and/or hepatic elimination of doxorubicin. Therefore, it appears that the development of oral doxorubicin preparations is possible, which will be more convenient than the intravenous dosage forms. Therefore, concurrent use of quercetin provides a therapeutic benefit — it increases the bioavailability of doxorubicin administered orally.

The distribution of doxorubicin in mice following administration in niosomes

Abstract: Large multilamellar non-ionic surfactant vesicles (niosomes) with diameters of around 800-900 nm prepared from a C16 triglyceryl ether with and without cholesterol and containing doxorubicin (Adriamycin) were administered to S180 tumour-bearing NMRI mice by bolus injection. Although in-vitro drug release from cholesterol-containing niosomes is delayed, in-vivo there was little difference between the two preparations when plasma levels were compared. As previously observed, half-lives of the drug were prolonged compared with free solution profiles. Liver uptake was not significantly affected by niosome encapsulation of doxorubicin. There is minor accumulation of drug in the lung, perhaps because of aggregation of the vesicles and their physical entrapment. Tumour levels of drug were higher following administration of cholesterol-containing niosomes and this was reflected in the more effective reduction in tumour growth. Metabolism of doxorubicin is altered by niosomal administration, but more studies are required before the significance of the metabolic data can be assessed.

The Pharmacokinetics and Bioavailability of Dihydroartemisinin, Arteether, Artemether, Artesunic Acid and Artelinic Acid in Rats

Abstract: The pharmacokinetics and bioavailability of dihydroartemisinin (DQHS), artemether (AM), arteether (AE), artesunic acid (AS) and artelinic acid (AL) have been investigated in rats after single intravenous, intramuscular and intragastric doses of 10 mg kg(-1). Plasma was separated from blood samples collected at different times after dosing and analysed for parent drug. Plasma samples from rats dosed with AM, AE, AS and AL were also analysed for DQHS which is known to be an active metabolite of these compounds. Plasma levels of all parent compounds decreased biexponentially and were a reasonable fit to a two-compartment open model. The resulting pharmacokinetic parameter estimates were substantially different not only between drugs but also between routes of administration for the same drug. After intravenous injection the highest plasma level was obtained with AL, followed by DQHS, AM, AE and AS. This resulted in the lowest steady-state volume of distribution (0.39 L) for AL, increasing thereafter for DQHS (0.50 L), AM (0.67 L), AE (0.72 L) and AS (0.87 L). Clearance of AL (21-41 mL min(-1) kg(-1)) was slower than that of the other drugs for all three routes of administration (DQHS, 55-64 mL min(-1) kg(-1); AM, 91-92 mL min(-1) kg(-1); AS, 191-240 mL min(-1) kg(-1); AE, 200-323 mL min(-1) kg(-1)). In addition the terminal half-life after intravenous dosing was longest for AL (1.35 h), followed by DQHS (0.95 h), AM (0.53 h), AE (0.45 h) and AS (0.35 h). Bioavailability after intramuscular injection was highest for AS (105%), followed by AL (95%) and DQHS (85%). The low bioavailability of AM (54%) and AE (34%) is probably the result of slow, prolonged absorption of the sesame-oil formulation from the injection site. After oral administration, low bioavailability (19-35%) was observed for all five drugs. In-vivo AM, AE, AS and AL were converted to DQHS to different extents; the ranking order of percentage of total dose converted to DQHS was AS (25.3-72.7), then AE (3.4-15.9), AM (3.7-12.4) and AL (1.0-4.3). The same ranking order was obtained for all formulations and routes of administration. The drug with the highest percentage conversion to DQHS was artesunic acid. Because DQHS has significant antimalarial activity, relatively low DQHS production could still contribute significantly to the antimalarial efficacy of these drugs. This is the first time the pharmacokinetics, bioavailability and conversion to DQHS of these drugs have been directly compared after different routes of administration. The results show that of all the artemisinin drugs studied the plasma level was highest for artelinic acid; this reflects its lowest extent of conversion to DQHS and its slowest rate of elimination.

The pharmacokinetics, pharmacodynamics, and safety of orally dosed INCB018424 phosphate in healthy volunteers.

Abstract: INCB018424 phosphate, a potent inhibitor of JAK enzymes with selectivity for JAK1&2, is in development for the treatment of myelofibrosis (MF). The oral dose pharmacokinetics, pharmacodynamics, safety, and tolerability of INCB018424 were evaluated in healthy volunteers in 2 double-blind, randomized, and placebo-controlled studies. The first study evaluated single ascending doses of 5 to 200 mg INCB018424 and the effect of food, whereas the second study evaluated multiple ascending doses, including both once- and twice-daily dosing for 10 days. As a Biopharma-ceutical Classification System class I drug, INCB018424 exhibited good oral bioavailability and dose-proportional systemic exposures. INCB018424 showed low oral dose clearance and a small volume of distribution, with an approximate 3-hour plasma half-life and insignificant accumulation following repeat dosing. A high-fat meal reduced INCB018424 C(max) by 24% but had little effect on INCB018424 AUC. INCB018424 was cleared primarily by metabolism with negligible renal excretion. The pharmacodynamics of INCB018424, evaluated by the inhibition of phosphorylated STAT3 following cytokine stimulation in whole blood, showed good correlation with INCB018424 plasma concentrations. INCB018424 was generally safe and well tolerated, with 25 mg bid and 100 mg qd established as the maximum tolerated doses in healthy volunteers.

Bioavailability of dexmedetomidine after intranasal administration

Abstract: The aim of this proof-of-concept study was to characterize the pharmacokinetics and pharmacodynamics of intranasal dexmedetomidine compared with its intravenous administration in a small number of healthy volunteers. Single doses of 84 μg of dexmedetomidine were given once intravenously and once intranasally to seven healthy men. Plasma dexmedetomidine concentrations were measured for 10 h, and pharmacokinetic variables were calculated with standard noncompartmental methods. Heart rate, blood pressure, concentrations of adrenaline and noradrenaline in plasma, and central nervous system drug effects (with the Maddox wing, Bispectral Index, and three visual analog scales) were monitored to assess the pharmacological effects of dexmedetomidine. Six individuals were included in the analyses. Following intranasal administration, peak plasma concentrations of dexmedetomidine were reached in 38 (15–60) min and its absolute bioavailability was 65% (35–93%) (medians and ranges). Pharmacological effects were similar with both routes of administration, but their onset was more rapid after intravenous administration. Dexmedetomidine is rather rapidly and efficiently absorbed after intranasal administration. Compared with intravenous administration, intranasal administration may be a feasible alternative in patients requiring light sedation.