A population pharmacokinetic model that describes multiple peaks due to enterohepatic recirculation of ezetimibe

Pharmacokinetic Interactions and Tolerability of Rosuvastatin and Ezetimibe: A Randomized, Phase 1, Crossover Study in Healthy Chinese Participants

BACKGROUND AND OBJECTIVE

The combination of rosuvastatin and ezetimibe has promising clinical benefits with a significant safety and tolerability profile. However, there is a lack of clinical data supporting the drug-drug interaction (DDI) in Chinese population. Thus, the aim of this study is to assess the potential pharmacokinetic DDI between rosuvastatin and ezetimibe in a Chinese population.

METHODS

In this randomized, open-label, phase 1 study, 12 healthy volunteers were randomized to three treatment groups: 10 mg rosuvastatin plus 10 mg ezetimibe, 10 mg rosuvastatin alone, and 10 mg ezetimibe alone under fasting conditions. The plasma concentrations of rosuvastatin and ezetimibe were determined, and the pharmacokinetic parameters were calculated. Primary endpoints were peak plasma concentration (C_max), area under the curve from zero to last measurement (AUC_0-t), and area under the curve from zero to infinity (AUC_0-∞) that were log-transformed, and co-administration was compared with monotherapy to evaluate the DDI.

RESULTS

The geometric mean ratios (GMRs) of rosuvastatin with 90% confidence intervals (CIs) were 0.94 (0.80-1.12) for C_max, 0.96 (0.85-1.08) for AUC_0-t, and 0.96 (0.86-1.07) for AUC_0-∞ when administered in combination with ezetimibe versus administered alone. The GMRs of unconjugated ezetimibe and total ezetimibe with 90% CIs were 1.15 (1.00-1.32) and 0.93 (0.80-1.07) for C_max, 0.96 (0.84-1.10) and 0.95 (0.83-1.08) for AUC_0-t, and 1.06 (0.96-1.18) and 0.94 (0.80-1.11) for AUC_0-∞, respectively, when administered in combination with rosuvastatin versus administered alone.

CONCLUSION

Co-administration of rosuvastatin and ezetimibe showed no clinically significant pharmacokinetic interactions in a healthy Chinese population.

A Population Pharmacokinetic-Pharmacodynamic Model of Navtemadlin, its Major Active Metabolite (M1) and Serum Macrophage Inhibitory Cykokine-1 (MIC-1)

Navtemadlin is a potent, selective, orally available inhibitor of murine double minute 2 that restores p53 activity to induce apoptosis in TP53 wild-type malignancies. Using richly sampled pharmacokinetic (PK) and pharmacodynamic (PD) data from healthy volunteers, a population PK/PD model was developed. A population PK (PPK) model described the PK characteristics of navtemadlin and its major metabolite acyl glucuronide (M1) and quantified enterohepatic recirculation (EHR). Post hoc individual PK parameters from this model were coupled with PD data for serum macrophage inhibitory cytokine-1 (MIC-1, GDF15), a cytokine biomarker of p53 activation, to construct a population PK/PD model that described plasma concentration-driven MIC-1 excursions and enabled simulation of the extent and duration of navtemadlin PD effects. The median apparent clearance (CL/F) and apparent central volume (V2/F) of navtemadlin were 36.4 L/hr and 159 L. The typical maximum stimulatory effect (S_max) was close to the median maximum MIC-1 ratio to baseline of 7.29 in observed data. Simulation revealed a dose-dependent increase of MIC-1 with steady state attained in approximately 7 days, in a 7-day-on/21-day-off dose regimen. Elevated MIC-1 concentrations persist through 17-19 days, leaving about 9-11 PD-free days in a 28-day cycle.

Antilipidemic ezetimibe induces regression of endometriotic explants in a rat model of endometriosis with its anti-inflammatory and anti-angiogenic effects

To assess the potential therapeutic role of antilipidemic ezetimibe on endometriosis in an experimental rat model. A standard experimental endometriosis model was created with 18 Whistar-Albino rats, and after 1 month, the sizes of the endometriotic explants were measured. The rats were randomized as study and control groups. A total of 1 mg/kg/day ezetimibe and 1 ml/kg/day saline were administered orally to the study and control groups respectively for 28 days. At the end of 28 days, the explants were measured again, excised, and sent for histopathologic assessment for expression of tumor necrosis factor-alpha (TNF-α) and vascular endothelial growth factor (VEGF) and number of mast cells. At the end of the study period, the size of the endometriotic explants decreased significantly in the study group; but not in the control group (from 145.3 ± 120.5 to 89.8 ± 60.1 vs 174.72 ± 88.3 to 87.65 ± 27.1 cm3 respectively); however, the amount of post- and pretreatment differences in explant sizes was similar in the groups. The median TNF-α and VEGF levels were significantly lower in the ezetimibe group when compared to the control group (4 [3-4] vs 2 [1-3], p 0.029; 4 [3-4] vs 2 [2-3], p 0.002; respectively). And numbers of mast cells in all uterine layers were also lower in the ezetimibe group. Ezetimibe decreased the size of the endometriotic explants with its anti-inflammatory and anti-angiogenic properties. This agent alone or with combination of other agents may have a potential role in the treatment of endometriosis.

On the population pharmacokinetics and the enterohepatic recirculation of hyzetimibe and its main metabolite in Chinese healthy subjects

BACKGROUNDS

Hyzetimibe (HS-25), a new drug approved for hypercholesterolemia, exhibits obvious enterohepatic recirculation (EHC) after oral administration. Up to now, little is known about the kinetics of HS-25. Therefore, we performed this population pharmacokinetic (PopPK) analysis aiming to describe the PK behavior of HS-25 and its main metabolite (M1), and to identify significant covariates contributing to the variability.

METHODS

The plasma concentration data used for modeling were obtained from an open-label, single-dose, randomized, two-period crossover bioequivalence study. PopPK modeling was performed with NONMEM 7.4.1 using nonlinear mixed effect modeling approach. Goodness of fit plots, bootstrap and visual predictive check were used for model internal validation. Data from another study was used for external validation.

RESULTS

Data from 16 male and 8 female subjects were used in the PopPK analysis. HS-25 and M1 concentrations in the modeling cohort were well described by a one-compartment model incorporating first-pass metabolism and a gallbladder compartment, accounting for the EHC process. The release kinetic of gall was mimicked by a first-order constant plus a switch on/off effect. Body weight was identified as a significant covariate effecting on the clearance and apparent distribution volume of HS-25, as well as k_mg , the transfer rate from metabolite compartment to gallbladder compartment. Internal and external validation demonstrated an acceptable predictive ability of the final model.

CONCLUSIONS

We present the first PopPK model describing HS-25 and M1 concentrations simultaneously, with the EHC process considered. The modeling and simulation results could provide reference for the clinical use of HS-25.

Approved drugs ezetimibe and disulfiram enhance mitochondrial Ca2+ uptake and suppress cardiac arrhythmogenesis

BACKGROUND AND PURPOSE

Treatment of cardiac arrhythmia remains challenging due to severe side effects of common anti-arrhythmic drugs. We previously demonstrated that mitochondrial Ca²⁺ uptake in cardiomyocytes represents a promising new candidate structure for safer drug therapy. However, druggable agonists of mitochondrial Ca²⁺ uptake suitable for preclinical and clinical studies are still missing.

EXPERIMENTAL APPROACH

Herewe screened 727 compounds with a history of use in human clinical trials in a three-step screening approach. As a primary screening platform we used a permeabilized HeLa cell-based mitochondrial Ca²⁺ uptake assay. Hits were validated in cultured HL-1 cardiomyocytes and finally tested for anti-arrhythmic efficacy in three translational models: a Ca²⁺ overload zebrafish model and cardiomyocytes of both a mouse model for catecholaminergic polymorphic ventricular tachycardia (CPVT) and induced pluripotent stem cell derived cardiomyocytes from a CPVT patient.

KEY RESULTS

We identifiedtwo candidate compounds, the clinically approved drugs ezetimibe and disulfiram, which stimulate SR-mitochondria Ca²⁺ transfer at nanomolar concentrations. This is significantly lower compared to the previously described mitochondrial Ca²⁺ uptake enhancers (MiCUps) efsevin, a gating modifier of the voltage-dependent anion channel 2, and kaempferol, an agonist of the mitochondrial Ca²⁺ uniporter. Both substances restored rhythmic cardiac contractions in a zebrafish cardiac arrhythmia model and significantly suppressed arrhythmogenesis in freshly isolated ventricular cardiomyocytes from a CPVT mouse model as well as induced pluripotent stem cell derived cardiomyocytes from a CPVT patient.

CONCLUSION AND IMPLICATIONS

Taken together we identified ezetimibe and disulfiram as novel MiCUps and efficient suppressors of arrhythmogenesis and as such as, promising candidates for future preclinical and clinical studies.

Fixed Dose Single Tablet Formulation with Differential Release of Amlodipine Besylate and Simvastatin and Its Pharmacokinetic Profile: QbD and Risk Assessment Approach

Purpose

A differential release fixed dose matrix tablet of amlodipine besylate (AML-B) and simvastatin (SIM) was formulated to enhance patient compliance.

Material and Method

In the first phase, release controlling parameters of AML-B and SIM granules were identified and in the second phase a fixed dose AML-B and SIM tablet formulation was prepared and optimized for a differential release of the drugs using a quality by design (QbD) and risk assessment approach. A validated HPLC method was employed for simultaneous determination of AML-B and SIM for FDC formulation. A pharmacokinetics of the above drugs was studied in healthy dogs in the third phase.

Results

In QbD-based optimized formulation, Eudragit^® RSPO-dicalcium phosphate (DCP) blend controlled the release of AML-B over 8 h, though this diffusion-controlled release assumed first order kinetics. DCP and Eudragit^® RS 100 also retarded release of SIM causing SIM release over 8 h after AML-B release from the optimized FDC tablet formulation. The HPLC retention times of AML-B and SIM were 2.10 and 15.52 min, respectively. Linearity for AML-B was 5.0–50 ng/mL and 0.01–2.0 µg/mL for SIM with percent recoveries of 92.85–101.53% and 94.51–117.75% for AML-B and SIM. AUC_0-∞ of AML-B was increased 3 fold, while AUC_0-∞ of SIM was decreased 2 fold. The t_max values for AML-B and SIM were 12 and 6 h, respectively. AML-B was absorbed without any lag time (t_lag) while t_lag was 6.33 ± 0.81 h for SIM, thus met the study objective.

Conclusion

The pharmacokinetic study showed an immediate absorption of AML-B while that of SIM was withheld for 6 h, close to the desired delay time of 8 h.

Population Pharmacokinetic Modelling and Simulation to Determine the Optimal Dose of Nanoparticulated Sorafenib to the Reference Sorafenib

Sorafenib, an oral multikinase inhibitor, exhibits a highly variable absorption profile due to enterohepatic reabsorption and poor solubility. SYO-1644 improved the solubility of sorafenib by nanoparticulation technology leading to enhanced bioavailability. To evaluate the pharmacokinetically equivalent dose of SYO-1644 to the reference Nexavar^® 200 mg, a randomized, open-label, replicated two-period study was conducted in healthy volunteers. A total of 32 subjects orally received a single dose of the following assigned treatment under a fasted state in the first period and repeated once more in the second period with a two-week washout: SYO-1644 100, 150 and 200 mg and Nexavar^® 200 mg. Pharmacokinetic (PK) samples were collected up to 168 h post-dose. The PK profile was evaluated by both non-compartmental analysis and population PK method. With the final model, 2 × 2 crossover trial scenarios with Nexavar^® 200 mg and each dose of SYO-1644 ranging from 100 to 150 mg were repeated 500 times by Monte Carlo simulation, and the proportion of bioequivalence achievement was assessed. Transit absorption compartments, followed by a one-compartment model with first-order elimination and enterohepatic reabsorption components were selected as the final model. The simulation results demonstrated that the SYO-1644 dose between 120 and 125 mg could yielded the highest proportion of bioequivalence.

Impact of gastrointestinal tract variability on oral drug absorption and pharmacokinetics: An UNGAP review

The absorption of oral drugs is frequently plagued by significant variability with potentially serious therapeutic consequences. The source of variability can be traced back to interindividual variability in physiology, differences in special populations (age- and disease-dependent), drug and formulation properties, or food-drug interactions. Clinical evidence for the impact of some of these factors on drug pharmacokinetic variability is mounting: e.g. gastric pH and emptying time, small intestinal fluid properties, differences in pediatrics and the elderly, and surgical changes in gastrointestinal anatomy. However, the link of colonic factors variability (transit time, fluid composition, microbiome), sex differences (male vs. female) and gut-related diseases (chronic constipation, anorexia and cachexia) to drug absorption variability has not been firmly established yet. At the same time, a way to decrease oral drug pharmacokinetic variability is provided by the pharmaceutical industry: clinical evidence suggests that formulation approaches employed during drug development can decrease the variability in oral exposure. This review outlines the main drivers of oral drug exposure variability and potential approaches to overcome them, while highlighting existing knowledge gaps and guiding future studies in this area.

Delay differential equations for the description of Irbesartan pharmacokinetics: A population approach to model absorption complexities leading to dual peaks

Irbesartan is a poorly soluble BCS class II compound with weak acidic properties. After oral administration, dual peaks are noted in its concentration (C) - time (t) profile, a phenomenon that may be attributed to enterohepatic recirculation, gastric emptying and/or other absorption complexities related to its pH- and buffer capacity-dependent dissolution behavior. A population pharmacokinetic model, encompassing delay differential equations, was found the most appropriate approach to describe dual peaks in irbesartan's C-t profiles. Parameters estimated were: the absorption rate constant in the central compartment (ka = 0.304 h^-1), the constant time delay between the administration and the absorption (T=1.68 h), the apparent volume of distribution of the central (V1/F = 13.8 L) and peripheral (V2/F = 85.8 L) compartment, the apparent clearance from the central compartment (CL/F = 13.5 L/h), and the inter-compartmental clearance (Q/F = 17.7 L/h). Using simulations, it was made evident that changing the time delay results in significant changes of peak plasma concentrations but not of its blood pressure-lowering effect. In conclusion, delay differential equations may be useful to model dual peaks arising from absorption complexities, while changes of the time delay that reflect physiological processes that take place before absorption may have significant implications in proving bioequivalence.

Development of a joint population pharmacokinetic model of ezetimibe and its conjugated metabolite

Ezetimibe (EZE) is an extensively used antihyperlipidemic drug with an important cholesterol lowering activity. It undergoes extensive first-pass metabolism to form its active glucuronide metabolite (EZEG). Both drugs exhibit complex pharmacokinetic profiles attributed mainly to repetitive enterohepatic kinetics. The aim of the present study was the investigation of EZE and EZEG pharmacokinetics (PK), through the development of a joint population pharmacokinetic model able to characterize their kinetic processes and enterohepatic recirculation simultaneously. Concentration-time data derived from a bioequivalence study in 28 healthy subjects were used for the analysis. Population PK modeling was performed on the obtained data using nonlinear mixed effect modeling approach, where different methodologies were applied for the description of the complex metabolism and recirculation processes of the two compounds. EZE and EZEG concentrations were best described by a population PK model incorporating first-pass metabolism and an enterohepatic recirculation loop, accounting for the recycling process of the two moieties. This is the first joint population pharmacokinetic model describing the kinetics of both EZE and EZEG.

On the population pharmacokinetics and the enterohepatic recirculation of total ezetimibe

Ezetimibe is a potent cholesterol absorption inhibitor, with an erratic pharmacokinetic (PK) profile, attributed to an extensive enterohepatic recirculation (EHC). The aim of this study was to develop a population PK model able to adequately characterize the complex distribution processes of total ezetimibe. The analysis was performed on the individual concentration-time data obtained from 28 healthy subjects who participated in a bioequivalence study comparing two oral ezetimibe formulations. The population PK analysis was performed using nonlinear mixed effect modeling, where different EHC models were developed and evaluated for their performance. Total ezetimibe pharmacokinetics was best described by a four-compartment model featuring EHC through the inclusion of an additional gallbladder compartment, which was assumed to release drug at specific time-intervals consistent with food intake. The final PK model was able to adequately estimate the population pharmacokinetic parameters and to allow for a formal characterization of the pharmacokinetic profile and the secondary peaks due to enterohepatic recirculation.

Pharmacokinetic interactions and tolerability of rosuvastatin and ezetimibe: an open-label, randomized, multiple-dose, crossover study in healthy male volunteers

Purpose

Rosuvastatin is a synthetic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor that effectively reduces low-density lipoprotein cholesterol levels. However, statin monotherapy does not always achieve acceptable low-density lipoprotein cholesterol levels in patients with severe hypercholesterolemia. Ezetimibe, a selective cholesterol-absorption inhibitor, is approved for use as a monotherapy or combination therapy with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors for patients with hypercholesterolemia. The aim of this study was to examine the pharmacokinetics (PKs) of drug interactions between rosuvastatin and ezetimibe, and the tolerability of combined administration in healthy Korean male volunteers.

Subjects and methods

Healthy subjects (n=24) were randomly allocated to 3 treatment groups: rosuvastatin (20 mg) alone, ezetimibe (10 mg) alone, and rosuvastatin (20 mg) plus ezetimibe (10 mg). The drugs were taken once every 24 hours over a period of 10 days. Blood samples were collected to analyze steady-state PKs.

Results

All adverse events observed during the study were mild, and the frequency was no higher for combined administration than for mono administration. For rosuvastatin, the steady-state mean ratios (90% CI) of the combined over the single dose were 1.076 (1.019–1.136) for AUC_τ,ss and 1.099 (1.003–1.204) for concentration at steady-state, respectively. In the case of free and total ezetimibe, the steady-state ratios of AUC_τ,ss and concentration at steady-state were 1.131 (1.051–1.218) and 1.182 (1.038–1.346), and 1.055 (0.969–1.148) and 0.996 (0.873–1.135), respectively.

Conclusion

Combined administration of rosuvastatin and ezetimibe was well tolerated. No clinically significant PK interactions between rosuvastatin and ezetimibe were observed when the 2 drugs were administered concomitantly.

Ezetimibe

Each month, subscribers to The Formulary Monograph Service receive five to six well-documented monographs on drugs that are newly released or are in late Phase III trials. The monographs are targeted to your Pharmacy and Therapeutics Committee. Subscribers also receive monthly one-page summary monographs on the agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation (DUE) is also provided each month. The monographs are published in printed form and on diskettes that allow customization. Subscribers to the The Formulary Monograph Service also receive access to a pharmacy bulletin board, The Formulary Information Exchange (The F.I.X.). All topics pertinent to clinical and hospital pharmacy are discussed on The F.I.X.

Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800–322–4349. The March 2003 monograph topics are adalimumab, eletriptan, cyclosporine ophthalmic emulsion, montelukast for allergic rhinitis, and icodextrin peritoneal dialysis solution. The DUE is on adalimumab.

Glucuronidation: driving factors and their impact on glucuronide disposition

Glucuronidation is a well-recognized phase II metabolic pathway for a variety of chemicals including drugs and endogenous substances. Although it is usually the secondary metabolic pathway for a compound preceded by phase I hydroxylation, glucuronidation alone could serve as the dominant metabolic pathway for many compounds, including some with high aqueous solubility. Glucuronidation involves the metabolism of parent compound by UDP-glucuronosyltransferases (UGTs) into hydrophilic and negatively charged glucuronides that cannot exit the cell without the aid of efflux transporters. Therefore, elimination of parent compound via glucuronidation in a metabolic active cell is controlled by two driving forces: the formation of glucuronides by UGT enzymes and the (polarized) excretion of these glucuronides by efflux transporters located on the cell surfaces in various drug disposition organs. Contrary to the common assumption that the glucuronides reaching the systemic circulation were destined for urinary excretion, recent evidences suggest that hepatocytes are capable of highly efficient biliary clearance of the gut-generated glucuronides. Furthermore, the biliary- and enteric-eliminated glucuronides participate into recycling schemes involving intestinal microbes, which often prolong their local and systemic exposure, albeit at low systemic concentrations. Taken together, these recent research advances indicate that although UGT determines the rate and extent of glucuronide generation, the efflux and uptake transporters determine the distribution of these glucuronides into blood and then to various organs for elimination. Recycling schemes impact the apparent plasma half-life of parent compounds and their glucuronides that reach intestinal lumen, in addition to prolonging their gut and colon exposure.

The Interpretation of Cholesterol Balance Derived Synthesis Data and Surrogate Noncholesterol Plasma Markers for Cholesterol Synthesis under Lipid Lowering Therapies

The cholesterol balance procedure allows the calculation of cholesterol synthesis based on the assumption that loss of endogenous cholesterol via fecal excretion and bile acid synthesis is compensated by de novo synthesis. Under ezetimibe therapy hepatic cholesterol is diminished which can be compensated by hepatic de novo synthesis and hepatic extraction of plasma cholesterol. The plasma lathosterol concentration corrected for total cholesterol concentration (R_Lath) as a marker of de novo cholesterol synthesis is increased during ezetimibe treatment but unchanged under treatment with ezetimibe and simvastatin. Cholesterol balance derived synthesis data increase during both therapies. We hypothesize the following. (1) The cholesterol balance data must be applied to the hepatobiliary cholesterol pool. (2) The calculated cholesterol synthesis value is the sum of hepatic de novo synthesis and the net plasma-liver cholesterol exchange rate. (3) The reduced rate of biliary cholesterol absorption is the major trigger for the regulation of hepatic cholesterol metabolism under ezetimibe treatment. Supportive experimental and literature data are presented that describe changes of cholesterol fluxes under ezetimibe, statin, and combined treatments in omnivores and vegans, link plasma R_Lath to liver function, and define hepatic de novo synthesis as target for regulation of synthesis. An ezetimibe dependent direct hepatic drug effect cannot be excluded.

Role of enterohepatic recirculation in drug disposition: cooperation and complications

Enterohepatic recirculation (EHC) concerns many physiological processes and notably affects pharmacokinetic parameters such as plasma half-life and AUC as well as estimates of bioavailability of drugs. Also, EHC plays a detrimental role as the compounds/drugs are allowed to recycle. An in-depth comprehension of this phenomenon and its consequences on the pharmacological effects of affected drugs is important and decisive in the design and development of new candidate drugs. EHC of a compound/drug occurs by biliary excretion and intestinal reabsorption, sometimes with hepatic conjugation and intestinal deconjugation. EHC leads to prolonged elimination half-life of the drugs, altered pharmacokinetics and pharmacodynamics. Study of the EHC of any drug is complicated due to unavailability of the apposite model, sophisticated procedures and ethical concerns. Different in vitro and in vivo methods for studies in experimental animals and humans have been devised, each having its own merits and demerits. Involvement of the different transporters in biliary excretion, intra- and inter-species, pathological and biochemical variabilities obscure the study of the phenomenon. Modeling of drugs undergoing EHC has always been intricate and exigent models have been exploited to interpret the pharmacokinetic profiles of drugs witnessing multiple peaks due to EHC. Here, we critically appraise the mechanisms of bile formation, factors affecting biliary drug elimination, methods to estimate biliary excretion of drugs, EHC, multiple peak phenomenon and its modeling.

Solitary Inhibition of the Breast Cancer Resistance Protein Efflux Transporter Results in a Clinically Significant Drug-Drug Interaction with Rosuvastatin by Causing up to a 2-Fold Increase in Statin Exposure

The intestinal efflux transporter breast cancer resistance protein (BCRP) restricts the absorption of rosuvastatin. Of the transporters important to rosuvastatin disposition, fostamatinib inhibited BCRP (IC50 = 50 nM) and organic anion-transporting polypeptide 1B1 (OATP1B1; IC50 > 10 μM), but not organic anion transporter 3, in vitro, predicting a drug-drug interaction (DDI) in vivo through inhibition of BCRP only. Consequently, a clinical interaction study between fostamatinib and rosuvastatin was performed (and reported elsewhere). This confirmed the critical role BCRP plays in statin absorption, as inhibition by fostamatinib resulted in a significant 1.96-fold and 1.88-fold increase in rosuvastatin area under the plasma concentration-time curve (AUC) and Cmax, respectively. An in vitro BCRP inhibition assay, using polarized Caco-2 cells and rosuvastatin as probe substrate, was subsequently validated with literature inhibitors and used to determine BCRP inhibitory potencies (IC50) of the perpetrator drugs eltrombopag, darunavir, lopinavir, clopidogrel, ezetimibe, fenofibrate, and fluconazole. OATP1B1 inhibition was also determined using human embryonic kidney 293-OATP1B1 cells versus estradiol 17β-glucuronide. Calculated parameters of maximum enterocyte concentration [Igut max], maximum unbound hepatic inlet concentration, transporter fraction excreted value, and determined IC50 value were incorporated into mechanistic static equations to compute theoretical increases in rosuvastatin AUC due to inhibition of BCRP and/or OATP1B1. Calculated theoretical increases in exposure correctly predicted the clinically observed changes in rosuvastatin exposure and suggested intestinal BCRP inhibition (not OATP1B1) to be the mechanism underlying the DDIs with these drugs. In conclusion, solitary inhibition of the intestinal BCRP transporter can result in clinically significant DDIs with rosuvastatin, causing up to a maximum 2-fold increase in exposure, which may warrant statin dose adjustment in clinical practice.

Comparative study on solid self-nanoemulsifying drug delivery and solid dispersion system for enhanced solubility and bioavailability of ezetimibe

Background

The objective of this study was to compare the physicochemical characteristics, solubility, dissolution, and oral bioavailability of an ezetimibe-loaded solid self-nanoemulsifying drug delivery system (SNEDDS), surface modified solid dispersion (SMSD), and solvent evaporated solid dispersion (SESD) to identify the best drug delivery system with the highest oral bioavailability.

Methods

For the liquid SNEDDS formulation, Capryol 90, Cremophor EL, and Tween 80 were selected as the oil, surfactant, and cosurfactant, respectively. The nanoemulsion-forming region was sketched using a pseudoternary phase diagram on the basis of reduced emulsion size. The optimized liquid SNEDDS was converted to solid SNEDDS by spray drying with silicon dioxide. Furthermore, SMSDs were prepared using the spray drying technique with various amounts of hydroxypropylcellulose and Tween 80, optimized on the basis of their drug solubility. The SESD formulation was prepared with the same composition of optimized SMSD. The aqueous solubility, dissolution, physicochemical properties, and pharmacokinetics of all of the formulations were investigated and compared with the drug powder.

Results

The drug existed in the crystalline form in SMSD, but was changed into an amorphous form in SNEDDS and SESD, giving particle sizes of approximately 24, 6, and 11 µm, respectively. All of these formulations significantly improved the aqueous solubility and dissolution in the order of solid SNEDDS ≥ SESD > SMSD, and showed a total higher plasma concentration than did the drug powder. Moreover, SESD gave a higher area under the drug concentration time curve from zero to infinity than did SNEDDS and SMSD, even if they were not significantly different, suggesting more improved oral bioavailability.

Conclusion

Among the various formulations tested in this study, the SESD system would be strongly recommended as a drug delivery system for the oral administration of ezetimibe with poor water solubility.

Population Pharmacokinetic Modeling of the Enterohepatic Recirculation of Fimasartan in Rats, Dogs, and Humans

Enterohepatic recirculation (EHC) can greatly enhance plasma drug exposures and therapeutic effects. This study aimed to develop a population pharmacokinetic model that can simultaneously characterize the extent and time-course of EHC in three species using fimasartan, a novel angiotensin II receptor blocker, as a model drug. All fimasartan plasma concentration profiles in 32 rats (intravenous doses, 0.3-3 mg/kg; oral doses, 1-10 mg/kg), 34 dogs (intravenous doses, 0.3-1 mg/kg; oral doses, 1-10 mg/kg), and 42 healthy volunteers (single or multiple oral doses, 20-480 mg) were determined via liquid chromatography-tandem mass spectrometry (LC-MS/MS) and simultaneously modeled in S-ADAPT. The proposed model quantitatively characterized EHC in three species after oral and intravenous dosing. The median (range) fraction of drug undergoing recirculation was 76.3% (64.9-88.7%) in rats, 33.3% (24.0-45.9%) in dogs, and 65.6% (56.5-72.0%) in humans. In the presence compared with the absence of EHC, the area under the curve in plasma was predicted to be 4.22-fold (2.85-8.85) as high in rats, 1.50-fold (1.32-1.85) in dogs, and 2.91-fold (2.30-3.57) in humans. The modeled oral bioavailability in rats (median (range), 38.7% (20.0-59.8%)) and dogs (median, 7.13% to 15.4%, depending on the formulation) matched the non-compartmental estimates well. In humans, the predicted oral bioavailability was 25.1% (15.1-43.9%) under fasting and 18.2% (12.2-31.0%) under fed conditions. The allometrically scaled area under the curve predicted from rats was 420 ng·h/mL for 60 mg fimasartan compared with 424 ± 63 ng·h/mL observed in humans. The developed population pharmacokinetic model can be utilized to characterize the impact of EHC on plasma drug exposure in animals and humans.

Nanostructured reverse hexagonal liquid crystals sustain plasma concentrations for a poorly water-soluble drug after oral administration

Reverse hexagonal (H2) liquid crystals formed from selachyl alcohol were demonstrated to sustain the absorption of the poorly water-soluble drug cinnarizine (CZ) after oral administration to rats. When CZ was administered as a bolus lipid solution in selachyl alcohol, the T max was observed to be 23.5 ± 5.9 h, significantly longer than the control suspension (1 h). Administration of selachyl alcohol as dispersed nanoparticles (hexosomes) also resulted in a sustained plasma profile, with drug concentrations maintained from 20 to 40 ng/mL over the first 24 h after administration. Sustained absorption of CZ from the selachyl alcohol hexosomes led to a significant enhancement (p < 0.05) in oral bioavailability (F% = 17%) compared to the control CZ suspension (9%). Analysis of selachyl alcohol hexosomes using small-angle x-ray scattering indicated that neither the presence of CZ (7 mg/g) nor simulated intestinal fluid altered the H2 nanostructure. Selachyl alcohol is not susceptible to digestion. Prolonged absorption from the selachyl alcohol-based H2 systems was attributed to the non-digestible nature of the lipid, similar to non-digestible phytantriol cubic (V2) systems previously reported. Furthermore, the likely presence of non-sink conditions in the gastric compartment provides a drug reservoir requiring gastric emptying to stimulate drug release from the formulation. This study highlights the potential use of non-digestible liquid crystalline systems generally and nanostructured liquid crystalline particles in particular as novel sustained oral drug delivery systems.

Pharmacokinetic non-interaction analysis in a fixed-dose formulation in combination of atorvastatin and ezetimibe

Recent clinical research has shown that atorvastatin (ATO) in combination with cholesterol absorption inhibitor ezetimibe (EZE) significantly reduces LDL-C level in patients with hypercholesterolemia, showing a superior lipid-lowering efficacy compared to statin alone. With no information currently available on the interaction between the two drugs, a pharmacokinetic study was conducted to investigate the influence of EZE on ATO and conversely when the two drugs were coadministered. The purpose of this study was to investigate the presence of differences in the pharmacokinetic profiles of capsules containing ATO 80 mg, EZE 10 mg or the combination of both 80/10 mg administered to healthy Mexican volunteers. This was a randomized, three-period, six-sequences crossover study. 36 eligible subjects aged between 20 to 50 years were included. Blood samples were collected up to 96 h after dosing, and pharmacokinetic parameters were obtained by non-compartmental analysis. Adverse events were evaluated based on subject interviews and physical examinations. Area under the concentration-time curve (AUC) and maximum plasma drug concentration (C_max) were measured for each drug alone or together and tested for bioequivalence-based hypothesis. The estimation computed (90% confidence intervals) for AUC and C_max, were 96.04% (85.88–107.42%) and 97.04% (82.36–114.35%), respectively for ATO–EZE combination versus ATO alone, while 84.42% (77.19–92.32%) and 95.60% (82.43–110.88%), respectively, for ATO–EZE combination versus EZE alone were estimated. These results suggest that ATO and EZE have no relevant pharmacokinetic drug–drug interaction.

Empirical and semi-mechanistic modelling of double-peaked pharmacokinetic profile phenomenon due to gastric emptying

Models have been developed to explain double-peaked plasma concentration-time profiles using mechanisms such as variable absorption and enterohepatic recirculation. Interruption of gastric emptying has also been shown to produce double-peaks, and this work proposes models for analysis of such data. In the presence of levodopa, gastric emptying is interrupted at times associated with double-peaks in pharmacokinetic profiles. Data from a simultaneous scintigraphy and paracetamol absorption study with levodopa was obtained, and models with compartments for stomach, intestine, central and peripheral tissue were developed to describe levodopa and paracetamol pharmacokinetics, including the double-peak phenomenon. The empirical model uses two gastric emptying parameter rates which are applied over separate time periods to describe the varying gastric emptying rate. The semi-mechanistic model uses a feedback mechanism acting via an effect compartment to link the plasma concentration of levodopa to the rate of gastric emptying, allowing levodopa pharmacokinetics to vary the rate of gastric emptying and give rise to a multiple-peaked plasma pharmacokinetic profile. The models were applied to plasma levodopa and paracetamol pharmacokinetic data with and without simultaneous analysis of scintigraphy data, in both cases giving a good fit and in the absence of scintigraphy data adequately predicting the stomach profile. For the semi-mechanistic model, the first-order constant governing gastric emptying was shown to switch between fast and slow values at a critical levodopa effect compartment concentration. New models have thus been proposed for analysis of plasma concentration profiles that exhibit double-peak phenomenon and applied successfully to levodopa data.

A reappraisal of the risks and benefits of treating to target with cholesterol lowering drugs

Atherosclerotic cardiovascular disease (CVD) is the number one cause of death globally, and lipid modification, particularly lowering of low density lipoprotein cholesterol (LDLc), is one of the cornerstones of prevention and treatment. However, even after lowering of LDLc to conventional goals, a sizeable number of patients continue to suffer cardiovascular events. More aggressive lowering of LDLc and optimization of other lipid parameters like triglycerides (TG) and high density lipoprotein cholesterol (HDLc) have been proposed as two potential strategies to address this residual risk. These strategies entail use of maximal doses of highly potent HMG CoA reductase inhibitors (statins) and combination therapy with other lipid modifying agents. Though statins in general are fairly well tolerated, adverse events like myopathy are dose related. There are further risks with combination therapy. In this article, we review the adverse effects of lipid modifying agents used alone and in combination and weigh these effects against the evidence demonstrating their efficacy in reducing cardiovascular events, cardiovascular mortality, and all cause mortality. For patients with established CVD, statins are the only group of drugs that have shown consistent reductions in hard outcomes. Though more aggressive lipid lowering with high dose potent statins can reduce rates of non fatal events and need for interventions, the incremental mortality benefits remain unclear, and their use is associated with a higher rate of drug related adverse effects. Myopathy and renal events have been a significant concern with the use of high potency statin drugs, in particular simvastatin and rosuvastatin. For patients who have not reached target LDL levels or have residual lipid abnormalities on maximal doses of statins, the addition of other agents has not been shown to improve clinical outcomes and carries an increased risk of adverse events. The clinical benefits of drugs to raise HDLc remain unproven. In patients without known cardiovascular disease, there is conflicting evidence as to the benefits of aggressive pursuit of numerical lipid targets, particularly with respect to all cause mortality. Certainly, in statin intolerant patients, alternative agents with a low side effect profile are desirable. Bile acid sequestrants are an effective and safe choice for decreasing LDLc, and omega-3 fatty acids are safe agents to decrease TG. There remains an obvious need to design and carry out large scale studies to help determine which agents, when combined with statins, have the greatest benefit on cardiovascular disease with the least added risk. These studies should be designed to assess the impact on clinical outcomes rather than surrogate endpoints, and require a comprehensive assessment and reporting of safety outcomes.

New insights into the molecular mechanism of intestinal fatty acid absorption

BACKGROUND

Dietary fat is one of the most important energy sources of all the nutrients. Fatty acids, stored as triacylglycerols (also called triglycerides) in the body, are an important reservoir of stored energy and derived primarily from animal fats and vegetable oils.

DESIGN

Although the molecular mechanisms for the transport of water-insoluble amphipathic fatty acids across cell membranes have been debated for many years, it is now believed that the dominant means for intestinal fatty acid uptake is via membrane-associated fatty acid-binding proteins, that is, fatty acid transporters on the apical membrane of enterocytes.

RESULTS

These findings indicate that intestinal fatty acid absorption is a multistep process that is regulated by multiple genes at the enterocyte level, and intestinal fatty acid absorption efficiency could be determined by factors influencing intraluminal fatty acid molecules across the brush border membrane of enterocytes. To facilitate research on intestinal, hepatic and plasma triacylglycerol metabolism, it is imperative to establish standard protocols for precisely and accurately measuring the efficiency of intestinal fatty acid absorption in humans and animal models. In this review, we will discuss the chemical structure and nomenclature of fatty acids and summarize recent progress in investigating the molecular mechanisms underlying the intestinal absorption of fatty acids, with a particular emphasis on the physical chemistry of intestinal lipids and the molecular physiology of intestinal fatty acid transporters.

CONCLUSIONS

A better understanding of the molecular mechanism of intestinal fatty acid absorption should lead to novel approaches to the treatment and the prevention of fatty acid-related metabolic diseases that are prevalent worldwide.

Interaction of Single-Dose Ezetimibe and Steady-State Cyclosporine in Renal Transplant Patients

This open-label, single-period study evaluated the single-dose pharmacokinetics of ezetimibe (EZE) 10 mg in the setting of steady-state cyclosporine (CyA) dosing in renal transplant patients. A single 10-mg dose of EZE was coadministered with the morning dose of CyA (75-150 mg twice a day). Total EZE (sum of unconjugated, parent EZE and EZE-glucuronide; EZE-total) AUC(0-last) and Cmax were compared to values derived from a prespecified database of healthy volunteers. Geometric mean ratios (90% CIs) for (EZE + CyA)/EZE alone for EZE-total AUC((0-last)) and Cmax were 3.41 (2.55, 4.56) and 3.91 (3.13, 4.89), respectively. Compared to healthy controls, EZE-total AUC((0-last)) was 3.4-fold higher in transplant patients receiving CyA; similar exposure levels were seen in a prior multiple-dose study in which EZE 50 mg was administered to healthy volunteers without dose-related toxicity. Because the long-term safety implications of both higher EZE exposures and undetermined effect on CyA are not yet understood, the clinical significance of this interaction is unknown.

Ezetimibe

Ezetimibe is a drug substance which can be used for lowering low-density lipoprotein cholesterol. Its crystal form and polymorphism have been determined using X-ray diffraction and thermal methods. Quantitative and qualitative analysis of Ezetimibe as well as study of its impurities and degradations were summarized in this chapter.

Effects of UDP-glucuronosyltransferase polymorphisms on the pharmacokinetics of ezetimibe in healthy subjects

PURPOSE

Ezetimibe is the first lipid-lowering drug that inhibits the intestinal uptake of dietary and biliary cholesterol without affecting the absorption of fat-soluble nutrients. Ezetimibe is readily absorbed, and undergoes rapid and almost complete glucuronidation by UGT, particularly UGT1A1, in enterocytes during its first pass. Genetic polymorphisms of UGT1A1 may decrease ezetimibe glucuronidation. Therefore, we tested the effects of the UGT1A1*6 and *28 alleles on the pharmacokinetics of ezetimibe.

METHODS

Three hundred and ninety healthy Korean subjects (347 male and 43 female) were recruited and genotyped for UGT1A1 (*6 and *28 variants). Forty-three subjects among them participated in a pharmacokinetic study of ezetimibe. These 43 subjects were divided into three groups (UGT1A1*1/*1, UGT1A1*1/*X, and UGT1A1*X/*X; where *X = *6 or *28) according to the number of UGT1A1 variant alleles. All received a single 10-mg oral dose of ezetimibe. The concentrations of unchanged ezetimibe and ezetimibe-glucuronide in plasma were determined by LC-MS/MS.

RESULTS

The frequencies of the UGT1A1 genotypes were 47.69%, 23.85%, 19.49%, 3.33%, 3.33%, and 2.31% for the *1/*1, *1/*6, *1/*28, *6/*6, *6/*28, and *28/*28 genotypes respectively. Besides the C(max) of unchanged ezetimibe, no significant difference was found in any other pharmacokinetic parameter of unchanged ezetimibe or ezetimibe-glucuronide in the three groups. C(max) and AUC(0-48) in subjects with UGT1A1*28/*28 in the UGT1A1*X/*X group were significantly different from those in the wild-type.

CONCLUSIONS

The UGT1A1*6 allele was not found to significantly affect the pharmacokinetics of ezetimibe, but the UGT1A1*28 allele might.

Ezetimibe inhibits expression of acid sphingomyelinase in liver and intestine

Ezetimibe inhibits cholesterol absorption in the intestine. Sphingomyelin has strong interactions with cholesterol. We investigated the effects of ezetimibe on Sphingomyelinase (SMase) expression in intestine and liver. After feeding rats with ezetimibe (5 mg/kg per day) for 14 days, acid SMase activities in the liver and in the proximal part of small intestine were reduced by 34 and 25%, respectively. Alkaline SMase (alk-SMase) was increased in the proximal part of the small intestine. Administration of lower doses of ezetimibe reduced acid SMase only in the liver by 14% (P < 0.05). In cell culture studies, ezetimibe decreased acid SMase activity in Hep G2 and Caco-2 cells dose-dependently. The reductions were more rapid for Hep G2 cells than for Caco-2 cells. Western blot showed that acid SMase protein was decreased in both Hep G2 and Caco-2 cells by 100 microM ezetimibe. The SM content was increased in Hep G2 cells but not Caco-2 cells, and total cholesterol content was increased in both cell lines 24 h after stimulation with 100 microM ezetimibe. Mevastatin, the inhibitor of cholesterol synthesis, induced a mild increase in acid SMase activity in Hep G2 cells but not Caco-2 cells. Following the reduction of acid SMase, ezetimibe at high dose slightly increased alk-SMase activity. In conclusion, the study demonstrates an inhibitory effect of ezetimibe on acid SMase activity and expression in both liver and intestine.