Modelling the Double Peak Phenomenon in pharmacokinetics

Population pharmacokinetic analysis of febuxostat with high focus on absorption kinetics and food effect

Febuxostat is commonly used in clinic for the treatment of hyperuricemia. Multiple-peak phenomenon has been observed in human plasma concentration-time profiles of febuxostat, but has not been paid enough attention in previous research. This study takes a pivotal step forward by conducting a comprehensive population pharmacokinetic (PopPK) analysis of febuxostat in a healthy Chinese cohort, with a central focus on delineating its absorption profile under contrasting fasting and fed conditions, while concurrently assessing the influence of food alongside other potential covariates on febuxostat's PK profile. The plasma concentration data used for modeling was obtained from two bioequivalence (BE) studies. Subjects were administered febuxostat 20 mg or 80 mg under fasting or fed condition. Goodness-of-fit plots, visual predict check (VPC), and normalized prediction distribution error (NPDE) were used for model evaluation. Based on the established model, PK profiles in healthy Caucasian subjects were simulated with parameter adjustment for race difference on clearance and bioavailability. Data from 128 subjects were used in the PopPK analysis. Febuxostat concentration-time curves were described by a two-compartment model with two deposit absorption compartments and lag times (Tlag). Prandial states (Food) showed significant impact on absorption rate ka1 and ka2, as well as Tlag1, and body weight was identified as a significant covariate on the apparent distribution volume. The PopPK analysis of febuxostat in healthy Chinese volunteers, under both fasted and fed conditions, successfully characterized its PK profile and underscored the significant influence of food on absorption. The potential difference of absorption between Chinese population and Caucasian population indicated from the simulations needs further investigation.

Redefining Statin Dosage Post-Gastric Bypass: Insights from a Population Pharmacokinetics-Pharmacodynamics Link Approach

Roux-en-Y gastric bypass (RYGB) involves creating a small stomach pouch, bypassing part of the small intestine, and rerouting the digestive tract. These alterations can potentially change the drug exposure and response. Our primary aim was to assess the impact of RYGB on the pharmacokinetics of simvastatin lactone (SV) and its active metabolite, simvastatin hydroxy acid (SVA). Ultimately, we aimed to optimize dosing for this understudied population by employing a population pharmacokinetic-pharmacodynamic link approach. The study comprised patients who had undergone RYGB surgery and individuals without a previous history of RYGB. All participants received a single oral dose of simvastatin. Plasma concentration data were analyzed with a nonlinear mixed-effect modeling approach. A parent-metabolite model with first-order absorption, 2-compartments for SV and 1-compartment for SVA, linear elimination, and enterohepatic circulation best described the data. The model was linked to the turnover pharmacodynamic model to describe the SVA inhibition on LDL-cholesterol production. Our simulations indicated that following RYGB surgery, the exposure to SV and SVA decreased by 40%. Consequently, for low-intensity statin patients, we recommend increasing the dose from 10 to 20 mg in post-RYGB patients to maintain a comparable response to that of non-operated subjects. Moderate-intensity statin patients should require increasing doses to 40 or 60 mg or the addition of a non-statin medication to achieve similar therapeutic outcomes. In conclusion, individuals post-RYGB exhibit diminished exposure to SV and may benefit from increasing the dose or adjunctive therapy with non-statin drugs to attain equivalent responses and mitigate potential adverse events.

Comparative pharmacokinetics of a single oral dose of meloxicam in the California sea lion (Zalophus californianus) and Pacific harbor seal (Phoca vitulina richardii)

Pharmacokinetics studies have investigated meloxicam, a non-steroidal anti-inflammatory drug, dosing strategies in a wide variety of non-domestic animals; however, there is no prior study examining well-founded dosing for pinnipeds. To develop dosing protocols, pharmacokinetic information is needed, with an examination of differences between pinniped species. Apparently, healthy California sea lions (Zalophus californianus: CSL; n = 13) and Pacific harbor seals (Phoca vitulina richardii: PHS; n = 17) that had completed rehabilitation were enrolled into a population-based pharmacokinetic study. Each animal was administered a single oral dose of meloxicam at 0.1 mg/kg, and two blood samples were collected from each animal at varying intervals during a 96-h study period. Plasma concentrations of meloxicam were determined by high-pressure liquid chromatography. Data were analyzed with nonlinear mixed effects modeling (Phoenix® NLME™, Certara, St. Louis, MO 63105, USA). The results indicated that in PHS, peak plasma concentration (Cmax) was 0.33 μg/mL with an elimination half-life (Ke t½) of 31.53 h. In CSL, Cmax was 0.17 μg/mL with Ke t½ of 32.71 h. All animals enrolled completed the study without outward adverse clinical signs. The elimination half-life was longer than previously recommended dosing intervals for pinnipeds; however, we cannot speculate in the optimum clinical dose from these results.

Bioequivalence Study of Epalrestat for Healthy Chinese Subjects

Epalrestat is a reversible noncompetitive inhibitor of aldose reductase with selective inhibition of aldose reductase. It can inhibit the accumulation of sorbitol in red blood cells in patients with diabetic peripheral neuropathy and can improve patients' conscious symptoms and neurological dysfunction. This study was designed to evaluate the bioequivalence in healthy Chinese subjects of a new test formulation and reference formulation of oral epalrestat (50 mg) in the fasting state. The study was performed with 44 healthy Chinese subjects according to a randomized 2-way crossover design. The main pharmacokinetic parameters of test formulation and reference formulation as follows: 4793 and 4781 ng/mL for maximum plasma concentration, 8556 and 8431 ng h/mL for area under the plasma concentration-time curve extrapolated to infinity. The test formulation of epalrestat was bioequivalent to the reference formulation. The bioequivalence study of epalrestat in healthy Chinese subjects suggests that the test and reference formulations have similar pharmacokinetics and both formulations are well tolerated in the dose range studied in healthy Chinese subjects. All these findings provided valuable pharmacokinetic knowledge for further clinical development.

A strategy of accuracy quantification by extending the concentration monitoring coverage based on online double collision energy of ultra-high performance liquid chromatography tandem mass spectrometry: The pharmacokinetics of Toddalia asiatica as a case study

To facilitate the safety, efficacy and rationality of clinical application of traditional Chinese medicines (TCMs), pharmacokinetic research played an indispensable role. The key challenge during pharmacokinetic investigation lied at the substantial fluctuation of compound concentrations in the plasma over the course of absorption. Taking the pharmacokinetics of six compounds after administration of Toddalia asiatica (TA) as an example, an efficient strategy was established by introducing the online double collision energy (ODCE) into the quantification process applying ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). During the analytical program, double collision energy (DCE) was optimized to establish the dual calibration curve (DCC) with large concentration monitoring coverage (CMC) for meeting the wide content range of certain target compounds. Method validation test was performed in terms of linearity, precision, sensitivity, matrix effect, recovery, etc. The results displayed that the CMC of todarolactone with high exposure in plasma was extended from 1.25-2,500 ng/mL to 1.25-125,000 ng/mL. Furthermore, a rapid UHPLC-MS/MS method integrated with ODCE was successfully applied to the determination of six compounds in rat plasma, revealing an extremely high plasma concentration of todarolactone (16,662 ng/mL). This strategy could expand the range of quantification while retaining extraordinary sensitivity. Consequently, it could be a fit-for-purpose strategy to quantify compounds over a wide concentration range for in vivo process monitoring.

Pharmacokinetic and safety profile of PT109B, a novel multi-targeted compound against Alzheimer's disease

PT109B, 5-(1,2-dithiolan-3-yl)-N-((1r,4r)-4-(isoquinolin-5-ylamino) cyclohexyl) pentanamide, a novel compound structurally related to Fasudil, has been reported as a promising candidate for treating Alzheimer's disease. To investigate the pharmacokinetics and acute toxicity of PT109B in rodents, we first developed and validated a UPLC-MS/MS analytical method to detect PT109B concentration in the biological matrix. The proposed method could separate and quantify the PT109B with good precision and accuracy. The pharmacokinetic results showed that the concentrations of PT109B in rat plasma increased with the dose, but not proportionally. Meanwhile, the double-peak phenomenon disappeared when decreasing the oral administration dosage. In addition, we found that PT109B could be detected in the central nervous system, and highly distributed in the liver and kidney. At the same time, the gender difference of PT109B in rats was observed, and the exposure of PT109B in female rats was significantly higher than that in male rats after oral administration. Finally, we found that oral administration of 750 mg/kg PT109B to C57 BL/6 mice caused significant liver injury in females, which was specifically manifested as hepatomegaly, increased liver coefficient, and hepatocyte ballooning. However, no significant damage was observed in other organs, which may be related to the distribution of PT109B in the liver. In summary, we first established a UPLC-MS/MS method for the analysis of PT109B in a biological matrix and described the characteristics of pharmacokinetics, and acute toxicity of PT109B in rodents, providing a sufficient pharmacokinetic basis for further study of PT109B.

Pharmacokinetic study of high-dose oral rifampicin in critically Ill patients with multidrug-resistant Acinetobacter baumannii infection

PURPOSE

Although rifampicin (RIF) is used as a synergistic agent for multidrug-resistant Acinetobacter baumannii (MDR-AB) infection, the optimal pharmacokinetic (PK) indices of this medication have not been studied in the intensive care unit (ICU) settings. This study aimed to evaluate the PK of high dose oral RIF following fasting versus fed conditions in terms of achieving the therapeutic goals in critically ill patients with MDR-AB infections.

METHODS

29 critically ill patients were included in this study. Under fasting and non-fasting conditions, RIF was given at 1200 mg once daily through a nasogastric tube. Blood samples were obtained at seven time points: exactly before administration of the drug, and at 1, 2, 4, 8, 12, and 24 h after RIF ingestion. To quantify RIF in serum samples, high-performance liquid chromatography (HPLC) was used. The MONOLIX Software and the Monte Carlo simulations were employed to estimate the PK parameters and describe the population PK model.

RESULTS

The mean area under the curve over the last 24-h (AUC0-24) value and accuracy (mean ± standard deviation) in the fasting and fed states were 220.24 ± 119.15 and 290.55 ± 276.20 μg × h/mL, respectively. There was no significant difference among AUCs following fasting and non-fasting conditions (P > 0.05). The probability of reaching the therapeutic goals at the minimum inhibitory concentration (MIC) of 4 mg/L, was only 1.6%.

CONCLUSION

In critically ill patients with MDR-AB infections, neither fasting nor non-fasting administrations of high-dose oral RIF achieve the therapeutic aims. More research is needed in larger populations and with measuring the amount of protein-unbound RIF levels.

Population pharmacokinetics identifies rapid gastrointestinal absorption and plasma clearance of oral chlorambucil administered to cats with indolent lymphoproliferative malignancies

OBJECTIVE

To establish the pharmacokinetics of a single 2-mg oral dose of chlorambucil in cats with indolent lymphoproliferative malignancies.

ANIMALS

24 client-owned cats.

PROCEDURES

Cats were assigned to 1 of 4 groups, with each group having a total of 3 sample collection time points over 12 hours after receiving a single 2-mg oral dose of chlorambucil. Each time point combined to generate 6 full patient plasma chlorambucil concentration-time curves from the 24 cats. Chlorambucil treatment was continued every other day and a single, variably timed sample collection was obtained on day 14. Population parameter estimates were obtained by nonlinear mixed-effects modeling. Covariates investigated included age, sex, baseline serum cobalamin, study location, weight, and body condition score.

RESULTS

Chlorambucil administered orally to cats was found to have a peak plasma concentration of approximately 170 ng/mL (SE, 31.1 ng/mL), percent coefficient of variation (%CV) of 18.4% within 15 minutes, and a terminal half-life of 1.8 hours (SE, 0.21 hour; %CV, 12.4). At the 4-hour mark, a smaller secondary peak in plasma chlorambucil was found. Day 14 samples were similar to those of the initial dose. No covariates showed a significant effect in the population model.

CLINICAL RELEVANCE

In these cats, chlorambucil at a 2-mg dose administered every other day undergoes rapid gastrointestinal absorption and plasma clearance with no drug accumulation between doses. These data are critical to inform future work investigating the association of chlorambucil drug exposure with adverse events and outcome of cats with lymphoproliferative diseases.

Multi-component pharmacokinetic study of prunus mume fructus extract after oral administration in rats using UPLC-MS/MS

Prunus mume fructus (MF) is used in traditional Chinese medicine and food, as it exerts pharmacological effects, such as antibacterial, antioxidant, antitumour, thirst-relieving, and antidiarrheal effects. In the present study, a reliable and sensitive ultra-high performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for the simultaneous determination of 16 prototype components (L-(-)-malic acid, 3,4-dihydroxybenzaldehyde, protocatechuic acid, vanillic acid, caffeic acid, D-(-)-quinic acid, citric acid, ferulic acid, syringic acid, cryptochlorogenic acid, neochlorogenic acid, chlorogenic acid, amygdalin, maslinic acid, corosolic acid, and rutin) in rat plasma after oral administration of the MF extract. Plasma samples were prepared via protein precipitation using acetonitrile. The 16 components were separated on an ACQUITY UPLC BEH C18 column (2.1 × 100 mm, 1.7 μm) with a gradient mobile phase system of methanol and 0.1% (v/v) formic acid aqueous solution at a flow rate of 0.3 ml/min. All components were quantitated using Agilent Jet Stream electrospray ionisation in negative ion mode. The intra-day and inter-day accuracies ranged from-9.4 to 9.4%, and the precision of the analytes was less than 14.8%. The extraction recovery rate of the analytes ranged from 63.59 to 109.44% and the matrix effects ranged from 49.25 to 109.28%. Stability studies proved that the analytes were stable under the tested conditions, with a relative standard deviation lower than 13.7%. Hence, the developed method was successfully applied to evaluate the pharmacokinetics of 16 components in the MF extract after oral administration in rats using UPLC-MS/MS.

Phytochemical identification of Xiaoer Huanglong Granule and pharmacokinetic study in the rat using its seven major bioactive components

Xiaoer Huanglong Granule is the only Chinese Patent Medicine widely used for treating attention deficit hyperactivity disorder. However, not much is known on the bioactive components and pharmacokinetics of Xiaoer Huanglong Granule even after it was successfully introduced into clinical use. This study analyzed the components in the medication and rat plasma after oral administration with the help of UNIFI platform and Masslynx. A total of 119 and 37 components were detected in the medication and plasma, respectively, using ultra performance liquid chromatography - tandem mass spectrometer. We established a rapid and sensitive simultaneous determination of 1 triterpene saponin, 3 monoterpene glycosides, and 3 lignans in rat plasma by solid-phase extraction. The determination was accomplished within 7.50 min via gradient elution. The values of lower limit of quantification were validated at 0.08 ng/mL for tenuifolin, 0.8 ng/mL for lactiflorin, 1.828 ng/mL for albiflorin, 2 ng/mL for paeoniflorin, gomisin B, and gomisin D, 10 ng/mL for schisandrin. The results from validations of other methods were all acceptable (RSD ≤ 14.94%). This is the first report on the identification and pharmacokinetics studies of components in Xiaoer Huanglong Granule. Moreover, the pharmacokinetic behavior of lactiflorin was studied for the first time. This article is protected by copyright. All rights reserved.

Administration in fed state but not controlled release in the colon increases oral bioavailability of DF030263, a promising drug candidate for chronic lymphocytic leukemia

For treatment of chronic cancers, the oral administration route is preferred as it provides numerous advantages over other delivery routes. However, these benefits of oral chemotherapy can be limited due to unfavorable pharmacokinetics. Accordingly, pharmacokinetic development of chemotherapeutic agents is crucial to the improvement of cancer treatment. In this study, assessment and optimization of biopharmaceutical properties of a promising drug candidate for cyclin-dependent kinase 9 (CDK9) inhibitor (DF030263) was performed to promote oral delivery. Oral bioavailability of DF030263 in fasted rats was 23.8%, and a distinct double-peak phenomenon was observed. A two-site absorption windows mechanism was proposed as a possible explanation to the phenomenon. The two-site absorption window hypothesis was supported by in vitro solubility assays in biorelevant fluids with different pH levels, as well as by in silico simulation by GastroPlus™. Controlled release to the colon was conducted in rats in order to exploit the colonic absorption window but did not improve the oral bioavailability. On the other hand, oral administration at postprandial conditions in rats (performed based on the high in vitro solubility in fed state simulated fluid and reduced pH-dependency) resulted in an almost 3-fold increase in bioavailability to 63.6%. In conclusion, this study demonstrates an efficient in vitro-in vivo-in silico drug development approach for improving the oral bioavailability of DF030263, a promising candidate for the treatment of chronic lymphocytic leukemia.

The Development and Optimization of Hot-Melt Extruded Amorphous Solid Dispersions Containing Rivaroxaban in Combination with Polymers

Rivaroxaban (RXB), a novel oral anticoagulant that directly inhibits factor Xa, is a poorly soluble drug belonging to Biopharmaceutics Classification System (BCS) class II. In this study, a hot-melt extruded amorphous solid dispersion (HME-ASD) containing RXB is prepared by changing the drug:polymer ratio (Polyvinylpyrrolidione-vinyl acetate 64, 1:1–1:4) and barrel temperature (200–240 °C), fixed at 20% of Cremophor^® RH 40 and 15 rpm of the screw speed, using the hot-melt extruding technique. This study evaluates the solubility, dissolution behavior, and bioavailability for application to oral drug delivery and optimizes the formulation of rivaroxaban amorphous solid dispersion (RXB-ASD). Based on a central composite design, optimized RXB-ASD (PVP VA 64 ratio 1:4.1, barrel temperature 216.1 °C, Cremophor^® RH 40 20%, screw speed 15 rpm) showed satisfactory results for dependent variables. An in vitro drug dissolution study exhibited relatively high dissolution in four media and achieved around an 80% cumulative drug release in 120 min. Optimized RXB-ASD was stable under the accelerated condition for three months without a change in crystallinity and the dissolution rate. A pharmacokinetic study of RXB-ASD in rats showed that the absorption was markedly increased in terms of rate and amount, i.e., the systemic exposure values, compared to raw RXB powder. These results showed the application of quality by design (QbD) in the formulation development of hot-melt extruded RXB-ASD, which can be used as an oral drug delivery system by increasing the dissolution rate and bioavailability.

Preparation and evaluation of a water-in-oil nanoemulsion drug delivery system loaded with salidroside

Salidroside (SAL) is a phenolic substance with high solubility and low permeability, which make it easy to cause the efflux effect of P-glycoprotein and degradation of intestinal flora, resulting in lower bioavailability. The aim of this study was to develop and optimize a water-in-oil nanoemulsion of SAL (w/o SAL-N) to explore its suitability in oral drug delivery systems. In this work, SAL-N was successfully prepared by water titration method at K_m = 1 to construct the pseudo-ternary phase diagrams. Physical characterization including the average viscosity, pH, refractive index, particle size, PDI, TEM, DSC, the content of SAL, and stability study were performed. It was evaluated for drug release in vitro and pharmacokinetic studies in vivo. The optimized nanoemulsion formulation consisted of Labrafil M 1944CS (63%), Span-80/Tween-80/EtOH (27%) and 200 mg∙mL^-1 SAL solution (SAL-SOL) (10%). Low viscosity and suitable pH were expected for the nanoemulsion. The spherical morphology and nanoscale size of SAL-N enhanced the stability of the nanoemulsion system. In vitro drug release showed that SAL-N had a better controlled release property than SAL-SOL at earlier time points. The pharmacokinetic studies exhibited that SAL-N had significantly higher in t_1/2 (2.11-fold), AUC_{0-48 h} (1.75-fold) and MRT_{0-48 h} (2.63-fold) than SAL-SOL (P < 0.01). The w/o SAL-N prepared in this work can be effectively delivered via the oral route. It can be seen w/o nanoemulsion is a strategy for the drug with polyphenols to delay the release, enhance oral absorption and reduce metabolic rate.

What dominates the changeable pharmacokinetics of natural sesquiterpene lactones and diterpene lactones: a review focusing on absorption and metabolism

Sesquiterpene lactones (STLs) and diterpene lactones (DTLs) are two groups of common phytochemicals with similar structures. It's frequently reported that both exhibit changeable pharmacokinetics (PK) in vivo, especially the unstable absorption and extensive metabolism. However, the recognition of their PK characteristics is still scattered. In this review, representative STLs (atractylenolides, alantolactone, costunolide, artemisinin, etc.) and DTLs (ginkgolides, andrographolide, diosbulbins, triptolide, etc.) as typical cases are discussed in detail. We show how the differences of treatment regimens and subjects alter the PK of STLs and DTLs, with emphasis on the effects from absorption and metabolism. These compounds tend to be quite permeable in intestinal epithelium, but gastrointestinal pH and efflux transporters (represented by P-glycoprotein) have great impact and result in the unstable absorption. As the only characteristic functional moiety, the metabolic behavior of lactone ring is not dominant. The α, β-unsaturated lactone moiety has the strongest metabolic activity. While with the increase of low-activity saturated lactone moieties, the metabolism is led by other groups more easily. The phase I (oxidation, reduction and hydrolysis reaction) and II metabolism (conjugation reaction) are both extensive. CYP450s, mainly CYP3A4, are largely involved in biotransformation. However, only UGTs (UGT1A3, UGT1A4, UGT2B4 and UGT2B7) has been mentioned in studies about phase II metabolic enzymes. Our work offers a beneficial reference for promoting the safety evaluation and maximizing the utilization of STLs and DTLs.

First-in-patient study of hetrombopag in patients with chronic idiopathic thrombocytopenic purpura

BACKGROUND

Idiopathic thrombocytopenic purpura (ITP) especially refractory and (or) relapsed ITP, is a serious and global health burden and its clinical treatment is far from being satisfied. Hetrombopag is a novel, small-molecule thrombopoietin receptor agonist for the treatment of chronic idiopathic thrombocytopenic purpura (CITP).

OBJECTIVES

This first-in-patient study aimed to investigate the safety, pharmacokinetics, and anticipated therapeutic dose of hetrombopag in CITP patients.

METHODS

In this multicenter, first-in-patient study, CITP patients received hetrombopag in a dose escalation (2.5 mg/day, 5 mg/day, or 7.5 mg/day) cohort. All patients received hetrombopag in fasting condition once daily for 2 weeks.

RESULTS

Of 44 patients screened, 32 were enrolled and treated. Most adverse events were graded 1 to 2 (ie, mild to moderate), and the incidence and severity were similar for three study cohorts. The pharmacokinetics of hetrombopag were found to be nonlinear with greater than dose-proportional: 12.5% of patients (1/8) in the 2.5 mg/d cohort, 58.3% of patients (7/12) in the 5 mg/d cohort, 66.7% of patients (8/12) in the 7.5 mg/d cohort reached the primary study endpoint of a platelet count exceeding 50 × 109 /L on day 28.

CONCLUSION

Hetrombopag was well tolerated and preliminarily efficacious. Efficacy, safety, and pharmacokinetic data suggest that 7.5 mg hetrombopag once daily was the anticipated therapeutic dose of hetrombopag in CITP patients and has been recommended for investigation in a later confirmatory clinical study of hetrombopag.

Pharmacokinetics and Safety of Mitragynine in Beagle Dogs

Mitragynine is the most abundant psychoactive alkaloid derived from the leaves of Mitragyna speciosa (kratom), a tropical plant indigenous to regions of Southeast Asia. Mitragynine displays a moderate affinity to opioid receptors, and kratom is often self-prescribed to treat pain and/or opioid addiction. The purpose of this study was to investigate the safety and pharmacokinetic properties of mitragynine in the dog. Single dose oral (5 mg/kg) and intravenous (0.1 mg/kg) pharmacokinetic studies of mitragynine were performed in female beagle dogs. The plasma concentrations of mitragynine were measured using ultra-performance liquid chromatography coupled with a tandem mass spectrometer, and the pharmacokinetic properties were analyzed using non-compartmental analysis. Following intravenous administration, mitragynine showed a large volume of distribution (V_d, 6.3 ± 0.6 L/kg) and high clearance (Cl, 1.8 ± 0.4 L/h/kg). Following oral mitragynine dosing, first peak plasma (C_max, 278.0 ± 47.4 ng/mL) concentrations were observed within 0.5 h. A potent mu-opioid receptor agonist and active metabolite of mitragynine, 7-hydroxymitragynine, was also observed with a C_max of 31.5 ± 3.3 ng/mL and a T_max of 1.7 ± 0.6 h in orally dosed dogs while its plasma concentrations were below the lower limit of quantification (1 ng/mL) for the intravenous study. The absolute oral bioavailability of mitragynine was 69.6%. Administration of mitragynine was well tolerated, although mild sedation and anxiolytic effects were observed. These results provide the first detailed pharmacokinetic information for mitragynine in a non-rodent species (the dog) and therefore also provide significant information for allometric scaling and dose predictions when designing clinical studies.

Pharmacokinetic and bioavailability studies of α-viniferin after intravenous and oral administration to rats

Alpha-viniferin is a trimer of resveratrol and has various pharmacological activities including anti-Alzheimer's disease, anti-tuberculosis, anti-tumor, anti-inflammatory and anti-diabetic. To investigate the pharmacokinetic characteristics and absolute bioavailability of α-viniferin in rats, using naringenin as an internal standard (IS), a rapid HPLC-MS/MS method of 5 min complete run time was developed. The chromatographic separation of α-viniferin and naringenin were accomplished with Waters XBridge™ C₁₈ column (2.1 mm × 100 mm, 3.5 μm) and the mobile phase were acetonitrile and 0.1 % formic acid at a flow rate of 0.3 mL/min. Plasma samples were pretreated by ethyl acetate. The negative ion mode with electrospray ionization (ESI) source was used for detecting the sample. Oral bioavailability of α-viniferin was 4.2 %. This study will be beneficial in better understanding the pharmacological properties and the further development of α-viniferin.

Population pharmacokinetics of orally administrated bromopride: Focus on the absorption process

Bromopride is a prokinetic and antiemetic drug used to treat nausea and vomiting. Although its prescription is common in Brazil, there is a lack of studies about bromopride pharmacokinetics. Therefore, the aims of this study were to investigate the population pharmacokinetics of bromopride and to evaluate the influence of covariates on its absorption. This study is a retrospective analysis of data collected from bioequivalence studies. The data was modeled using MONOLIX 2018R2. Assuming one-compartment and linear elimination, the absorption phase was evaluated with different structural models. The model of sequential first- and zero-order with combined error and exponential inter-individual variability in all parameters best described the atypical absorption profile of bromopride. Population estimates were first-order absorption rate (ka) of 0.08 h ^- 1, fraction of dose absorbed by first-order (Fr) of 32.60%, duration of the zero-order absorption (Tk0) of 0.88 h with latency time (Tlag) of 0.47 h, volume of distribution of 230 l and clearance of 46.80 l h ^- 1. Bodyweight affects Tk0, dosage form was found to correlate with Tk0 and Tlag, while gender affects Tlag. However, simulations evaluating the clinical importance of these covariates on steady-state indicated minimal changes on bromopride exposure. The mixed absorption model was reasonable to describe the absorption process of bromopride because it had the flexibility to fit multiple-peaks profile and shows good agreement with physicochemical properties of drug.

Toxicokinetic-Toxicodynamic Modeling of the Effects of Pesticides on Growth of Rattus norvegicus

Ecological risk assessment is carried out for chemicals such as pesticides before they are released into the environment. Such risk assessment currently relies on summary statistics gathered in standardized laboratory studies. However, these statistics extract only limited information and depend on duration of exposure. Their extrapolation to realistic ecological scenarios is inherently limited. Mechanistic effect models simulate the processes underlying toxicity and so have the potential to overcome these issues. Toxicokinetic-toxicodynamic (TK-TD) models operate at the individual level, predicting the internal concentration of a chemical over time and the stress it places on an organism. TK-TD models are particularly suited to addressing the difference in exposure patterns between laboratory (constant) and field (variable) scenarios. So far, few studies have sought to predict sublethal effects of pesticide exposure to wild mammals in the field, even though such effects are of particular interest with respect to longer term exposure. We developed a TK-TD model based on the dynamic energy budget (DEB) theory, which can be parametrized and tested solely using standard regulatory studies. We demonstrate that this approach can be used effectively to predict toxic effects on the body weight of rats over time. Model predictions separate the impacts of feeding avoidance and toxic action, highlighting which was the primary driver of effects on growth. Such information is relevant to the ecological risk posed by a compound because in the environment alternative food sources may or may not be available to focal species. While this study focused on a single end point, growth, this approach could be expanded to include reproductive output. The framework developed is simple to use and could be of great utility for ecological and toxicological research as well as to risk assessors in industry and regulatory agencies.

Pharmacokinetics, excretion and metabolites analysis of DL0410, a dual‑acting cholinesterase inhibitor and histamine‑3 receptor antagonist

DL0410, a dual‑action cholinesterase inhibitor and histamine‑3 receptor antagonist with a novel structural scaffold, may be a potential candidate for the treatment of Alzheimer's disease (AD). To the best of the authors' knowledge, this is the first study to demonstrate a reliable method for the measurement of DL0410 in rat plasma, brain, bile, urine and feces samples, and identification of its primary metabolites. The pharmacokinetic properties of DL0410 were analyzed by liquid chromatography‑mass spectrometry at oral doses of 25, 50 and 100 mg/kg and intravenous dose of 5 mg/kg. The investigation of the excretion and metabolism of DL0410 was determined following liquid‑liquid extraction for biliary, urinary and fecal samples. Finally, the cytochrome (CY)P450 isoforms involved in the production of DL0410 metabolites with recombinant human cytochrome P450 enzymes were characterized. The results suggested that DL0410 was not well absorbed; however, was distributed to the entorhinal cortex and hippocampus of the brain. A total of two common metabolites of the reduction of DL0140 in the bile, urine and feces were identified and CYP2D6 was involved in this reaction. The pharmacokinetic results of DL0410 provided information for the illustration of its pharmacodynamic properties, mechanism of action and promoted its continued evaluation as a therapeutic agent for AD treatment.

Pharmacokinetics and Pharmacodynamics of Escalating Doses of SHetA2 After Vaginal Administration to Mice

SHetA2 is a novel compound with strong potential to treat cervical dysplasia, but its low aqueous solubility limits its oral bioavailability. A vaginal suppository achieved SHetA2 cervix concentrations that were severalfold above the predicted therapeutic levels. Thus, we aimed at determining the minimum dose that would achieve SHetA2 therapeutic levels while reducing cyclin D1 levels, the pharmacodynamic end point. The disposition of SHetA2 after vaginal administration of escalating SHetA2 doses and the corresponding reduction in cyclin D1 levels was compared to that after the conventional oral treatment. Vaginal administration of a 15-mg/kg dose achieved an area under the cervix concentration versus time curve (AUCcervix) that was ∼120 times larger than that after a 60 mg/kg administered orally. AUCcervix and Cmax-cervix did not increase proportionally with respect to the dose, with the 30-mg/kg dose resulting in higher AUCcervix and Cmax-cervix (1368.53 μg.mL/h and 155.38 μg/g, respectively) compared to the 15 mg/kg (334.98 μg.mL/h and 121.78 μg/g, respectively) or 60 mg/kg (1178.55 μg.mL/h and 410.38 μg/g, respectively). Likewise, the 30-mg/kg dose caused a larger reduction in cyclin D1 levels than the other doses. Thus, the 30-mg/kg dose was selected for future efficacy studies in a mouse model of cervical neoplasia.

Determination of Sophorabioside in Rat Plasma by UPLC-MS/MS and its Application to a Pharmacokinetic Study

A ultra-performance liquid chromatography tandem mass spectrometry method was initially developed and validated for quantification of sophorabioside in rat plasma using kaempferol-3-O-β-D-rutinoside as the internal standard (IS). Analyte and IS were preparation through a protein precipitation procedure with 1.0 mL of methanol to a 0.1 mL plasma sample. The processed samples were separated by C18 analytical column using methanol/water containing 0.1% formic acid with gradient elution as the mobile phase at a flow rate of 0.3 mL/min. Sophorabioside (m/z 577.15 → 269.45) and kaempferol-3-O-β-D-rutinoside (m/z 593.15 → 285.84) were detected by a triple quadrupole tandem mass spectrometer in negative electrospray ionization mode using multiple reaction monitoring. The calibration curve for sophorabioside was linear in the range of 6-1,200 ng/mL (r2 > 0.995) with a lower limit of quantification of 6 ng/mL. The inter- and intra-day precision and accuracy were well within the acceptable limits. The matrix effects were satisfactory in all of the biological matrices examined. The mean recovery of sophorabioside was always >90%. This method was successfully applied to a pharmacokinetic study of sophorabioside in rats after an oral administration of 90 mg/kg sophorabioside. The main pharmacokinetic parameters: Tmax, Cmax and t1/2 were 6.2 ± 0.8 h, 1430.83 ± 183.25 ng/mL, 7.2 ± 0.5 h, respectively.

Plasma pharmacokinetics and cerebral nuclei distribution of major constituents of Psoraleae fructus in rats after oral administration

BACKGROUND

The fruit of Psoralea corylifolia L., Psoraleae fructus (PF), is widely used in traditional Chinese medicine as a well-known herbal tonic. Previous studies have shown that PF and its major constituents may have potential values in the treatment of Parkinson and Alzheimer diseases, though their pharmacokinetics and brain distribution were largely unknown.

PURPOSE

To develop a liquid chromatographic-tandem mass spectrometry (LC-MS/MS) method for simultaneous studies of the plasma pharmacokinetics and cerebral nuclei (including cerebellum, thalamus, brainstem, hippocampus, corpus striatum and cortex) distribution in rats of eleven known PF compounds following as psoralen, isopsoralen, psoralidin, bavachin, bavachinin, isobavachin, isobavachalcone, bavachalcone, neobavaisoflavone, corylifol A, and corylin.

METHODS

Rats were orally administered via gavage at a single dose of PF extract at 1.2 g/kg. The eleven known PF compounds were extracted from rat plasma and cerebral nuclei at different time points, and then determined by the established LC-MS/MS method. Non-compartmental pharmacokinetic profiles were calculated, and the distribution in rat plasma and cerebral nuclei were compared.

RESULTS

The results showed that all the tested compounds were quickly absorbed into rat plasma and distributed almost evenly to the cerebral nuclei. The distribution concentrations at different nuclei varied at one determined time point, but the overall trends were basically similar to the plasma concentration-time results. Psoralen and isopsoralen, the two highest coumarins contained in PF, displayed far higher plasma concentrations (AUC_{0→∞, plasma}≈53,884∼65,578 ng·h/ml) and central nervous system penetration (AUC_{0→∞, brain nuclei} ≈44,659∼65,823 ng·h/g) than the prenylflavonoids (other compounds except psoralidin, AUC_{0→∞, plasma}≈69∼324 ng·h/ml; AUC_{0→∞, brain nuclei} ≈119∼3662 ng·h/g). However, the total brain-to-plasma ratios of the prenylflavonoids were higher than the coumarins, suggesting the prenylflavonoids can more readily enter the brain than the coumarins.

CONCLUSION

The established LC-MS/MS method is sensitive and specific for the simultaneous quantitation of the eleven PF compounds in rat plasma and cerebral nuclei. The results of plasma pharmacokinetics and cerebral nuclei distribution may reveal the possible substance basis for the CNS activities of PF, and highlight the application possibility of PF and its major constituents in the treatment of Parkinson and Alzheimer diseases.

Metabolite identification and pharmacokinetic profiling of PP242, an ATP-competitive inhibitor of mTOR using ultra high-performance liquid chromatography and mass spectrometry

PP242 is a second generation novel selective ATP-competitive inhibitor of mTOR that displayed promising anti-cancer activity over several cancer types by inhibiting both the complexes of mTOR (mTORC1 and mTORC2). The purpose of this study is to identify the possible metabolites and to evaluate the pharmacokinetic profile of PP242 after a single oral administration to Sprague-Dawley (SD) rats. Two metabolites, including one phase I and one phase II, were identified by in vitro and in vivo studies using rat liver microsomes (RLMs) as well as rat plasma, urine and feces, respectively, through ultra high-performance liquid chromatography-linear ion trap quadrupole-orbitrap-mass spectrometry (UHPLC-LTQ-Orbitrap-MS). The major biotransformation pathways of PP242 were hydroxylation and glucuronide conjugation. Additionally, a simple and rapid quantification method was developed and validated. The method recovery was within 79.7-84.6%, whereas the matrix effect was 78.1-96.0% in all three quality control (QC) concentrations (low, medium and high) including the LLOQ. Other parameters showed acceptable results according to the US food and drug administration (FDA) guidelines for bioanalytical method validation. Afterwards, pharmacokinetic parameters were evaluated in rat plasma by successfully applying the validated method using liquid chromatography-tandem mass spectrometry (LC-MS/MS). After a single oral administration at a dose of 5mg/kg, the maximum plasma concentration (C_max) of PP242 was 0.17±0.08μg/mL, while the elimination was moderately fast (T_1/2: 172.18±45.54min). All of the obtained information on the metabolite identification and pharmacokinetic parameter elucidation could facilitate the further development of PP242.

Effect of arteether and pyrimethamine coadministration on the pharmacokinetic and pharmacodynamic profile of ormeloxifene

The study was intended to investigate the effect of concomitant administration of antimalarial drug (pyrimethamine or arteether) on pharmacokinetic and post coitus contraceptive efficacy of ormeloxifene in female Sprague-Dawley rats. A serial sampling technique coupled with LC-MS/MS detection was utilized for quantification of ormeloxifene in plasma samples collected from female rats treated with ormeloxifene only and ormeloxifene with pyrimethamine or arteether. Coitus-proven female rats were utilized to investigate the effect of pyrimethamine or arteether coadministration on contraceptive efficacy of ormeloxifene by investigating the presence or absence of implantations and status of corpora lutea on day 10 post coitum. None of the sperm-positive rats treated with ormeloxifene with or without coadministration of pyrimethamine or arteether showed any sign of pregnancy, confirming that concomitant administration of antimalarial drugs (pyrimethamine or arteether) did not affect the pharmacodynamic profile of ormeloxifene. Although there was no sign of pharmacodynamic interaction, the volume of distribution of ormeloxifene increased significantly on cotreatment with pyrimethamine. However, coadministration of arteether did not affect any of the pharmacokinetic parameters of ormeloxifene. The compiled results of preliminary study in female rats support that pyrimethamine or arteether can be prescribed with ormeloxifene.

A Two-way Randomized Cross-over Pharmacokinetic and Pharmacodynamic Study of an Innovative Oral Solution of Midazolam (ADV6209)

PURPOSE

The objective of this study was to assess the bioavailability and the sedative effect of a single-dose administration of an innovative oral solution of midazolam containing γ-cyclodextrins (ADV6209).

METHODS

A bioavailability study with a standard two-sequences, two-periods, and crossover design was conducted. Subjects randomly received 15 mg of ADV6209 by oral route followed by 5 mg of the reference drug (midazolam hydrochloride intravenous solution (Hypnovel®, Roche) by intravenous route or vice versa. Blood samples were drawn at different time points to measure midazolam and its metabolite α-hydroxymidazolam concentrations. Non-compartmental pharmacokinetic methods were used to calculate main pharmacokinetic parameters and absolute bioavailability.

RESULTS

Caucasian healthy subjects (n = 12) were included in the study. ADV6209 had a bioavailability of 39.6%. The oral elimination half-life with ADV6209 was slightly shorter than with the reference i.v. form (2.66 h versus 2.99 h). The sedative effect was observed 27.5 ± 15.5 min after oral administration for a duration of 48.5 ± 35.4 min. Double peak phenomenon was observed in 5 patients.

CONCLUSIONS

Cyclodextrins have little impact on midazolam oral bioavailability and the pharmacokinetics parameters of midazolam formulation ADV6209 are close to those reported previously.

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.

Utility of concentration-effect modeling and simulation in a thorough QT study of losmapimod

A thorough QT study was conducted in healthy volunteers with losmapimod. Four treatment regimens were included: a therapeutic dose (7.5 mg BID for 5 days), a supratherapeutic dose (20 mg QD for 5 days), a positive control (400 mg moxifloxacin single dose on Day 5), and placebo for 5 days. Baseline and on treatment ECGs were measured on Day 1 (3 timepoints predose) and Day 5, respectively. The primary statistical analysis failed to demonstrate a lack of effect of losmapimod on the QT interval leading to a positive finding. However, simulations using the concentration-effect model established for QTcF vs. losmapimod concentration at concentrations 4× the maximum concentration of the therapeutic dose did not exceed the regulatory thresholds of concern of 5 milliseconds for the mean (4.57 milliseconds) and 10 milliseconds for the upper bound of the 90%CI (90%CI 2.88, 6.10). Modeling demonstrated that the discrepant results may have been due to a baseline shift after repeat dosing and baseline differences between the treatments. Considering the results of the concentration-effect modeling, previous losmapimod data, and the high false-positive rate associated with the ICH E14 statistical analysis, the statistical analysis was likely a false-positive.

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.

In silico, experimental, mechanistic model for extended-release felodipine disposition exhibiting complex absorption and a highly variable food interaction

The objective of this study was to develop and explore new, in silico experimental methods for deciphering complex, highly variable absorption and food interaction pharmacokinetics observed for a modified-release drug product. Toward that aim, we constructed an executable software analog of study participants to whom product was administered orally. The analog is an object- and agent-oriented, discrete event system, which consists of grid spaces and event mechanisms that map abstractly to different physiological features and processes. Analog mechanisms were made sufficiently complicated to achieve prespecified similarity criteria. An equation-based gastrointestinal transit model with nonlinear mixed effects analysis provided a standard for comparison. Subject-specific parameterizations enabled each executed analog’s plasma profile to mimic features of the corresponding six individual pairs of subject plasma profiles. All achieved prespecified, quantitative similarity criteria, and outperformed the gastrointestinal transit model estimations. We observed important subject-specific interactions within the simulation and mechanistic differences between the two models. We hypothesize that mechanisms, events, and their causes occurring during simulations had counterparts within the food interaction study: they are working, evolvable, concrete theories of dynamic interactions occurring within individual subjects. The approach presented provides new, experimental strategies for unraveling the mechanistic basis of complex pharmacological interactions and observed variability.

Human pharmacokinetic study of tutin in honey; a plant-derived neurotoxin

Over the last 150 years a number of people in New Zealand have been incapacitated, hospitalised, or died from eating honey contaminated with tutin, a plant-derived neurotoxin. A feature of the most recent poisoning incident in 2008 was the large variability in the onset time of clinical signs and symptoms of toxicity (0.5-17 h). To investigate the basis of this variability a pharmacokinetic study was undertaken in which 6 healthy males received a single oral dose of tutin-containing honey giving a tutin dose of 1.8 μg/kg body weight. The serum concentration-time curve for all volunteers exhibited two discrete peaks with the second and higher level occurring at approximately 15 h post-dose. Two subjects reported mild, transient headache at a time post-dose corresponding to maximum tutin concentrations. There were no other signs or symptoms typical of tutin intoxication such as nausea, vomiting, dizziness or seizures. Pharmacokinetic analysis using a two-site absorption model resulted in a good fit to the observed concentration data. A novel analytical method subsequently revealed the presence of glycoside conjugates of tutin in addition to unconjugated tutin in honey. These pharmacokinetic data will be important to better define a safe maximum tutin concentration in honey.

Pharmacokinetics, biodistribution and bioavailability of isoliquiritigenin after intravenous and oral administration

CONTEXT

Isoliquiritigenin (ISL) has been shown to exhibit a variety of biological activities. However, there is little research on the pharmacokinetic behavior and tissues distribution of ISL.

OBJECTIVE

Pharmacokinetics, biodistribution and bioavailability of ISL after intravenous and oral administration were determined by systematic investigation in Sprague-Dawley rats.

MATERIALS AND METHODS

ISL was dissolved in medicinal ethanol-Tween 80-0.9% sodium chloride saline in a volume ratio of 10:15:75. The ISL solution was injected in rats via a tail vein at a single dose of 10, 20 and 50 mg/kg and administered orally in rats at a single dose of 20, 50 and 100 mg/kg, respectively. Blood samples were collected at time intervals of 0.08, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 6, 8 and 12 h after intravenous injection. Tissues of interests in mice were collected immediately at each determined time point (0.5, 1, 2, 3 and 6 h) after cervical dislocation.

RESULTS

The dose-normalized AUC values were 7.3, 7.6 and 8.7 μg × h/ml (calculated based on the dose of 10 mg/kg) for intravenous doses of 10, 20 and 50 mg/kg, respectively. The elimination half-lifes (t1/2λ) were 4.9, 4.6 and 4.8 h at 10, 20 and 50 mg/kg intravenous doses, respectively. The F values were 29.86, 22.70, 33.62% for oral doses of 20, 50 and 100 mg/kg, respectively. Liver, heart and kidney were major distribution tissues of ISL in mice. The plasma protein binding of ISL in rats was 43.72%.

CONCLUSION

The work may useful for further study of the bioactive mechanism of ISL.

Synthesis and bioevaluation of novel 4-aminoquinoline-tetrazole derivatives as potent antimalarial agents

A series of novel tetrazole derivatives of 4-aminoquinoline were synthesized and screened for their antimalarial activities against both chloroquine-senstive (3D7) and chloroquine-resistant (K1) strains of Plasmodium falciparum as well as for cytotoxicity against VERO cell lines. Most of the synthesized compounds exhibited potent antimalarial activity as compared to chloroquine against K1-strain. Compounds with significant in vitro antimalarial activity were then evaluated for their in vivo efficacy in Swiss mice against Plasmodium yoelii following both intraperitoneal (ip) and oral administration, wherein compounds 20 and 23 each showed in vivo suppression of 99.99% parasitaemia on day 4.

Simultaneous determination of three alkaloids, four ginsenosides and limonin in the plasma of normal and headache rats after oral administration of Wu-Zhu-Yu decoction by a novel ultra fast liquid chromatography-tandem mass spectrometry method: application to a comparative pharmacokinetics and ethological study

A novel, sensitive and reliable ultra fast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS) method has been developed and validated for simultaneous quantitation of eight main active ingredients (evodiamine, rutaecarpine, dehydroevodiamine, limonin, ginsenoside Rb1, Rd, Re and Rg1) in rat plasma after oral administration of Wu-Zhu-Yu (WZY) decoction, which is a celebrated and widely used Traditional Chinese Medicine formula for the treatment of headache. The analytes and internal standard (IS) were separated on a SHIM-PACK XR-ODS II column, and the detection was performed on a UFLC-MS/MS system with turbo ion spray source. The lower limits of quantification were 1.5, 0.5, 1.0, 2.0, 2.0, 1.0, 0.5 and 0.2 ng ml(-1) for evodiamine, rutaecarpine, dehydroevodiamine, limonin, gensenoside Rb1, Rd, Re and Rg1, respectively. Linearity, accuracy, precision and absolute recoveries of the eight analytes were all within satisfaction. The IS-normalized matrix factor was adopted for assessing the matrix effect and accompanied with a satisfactory result. The validated method has been successfully applied to compare pharmacokinetic profiles of the eight active ingredients in rat plasma between normal and headache rats after administration. Exact pharmaceutical effect of WZY decoction on headache was demonstrated by the ethological response of headache rats induced by nitric oxide donor after administration. The results indicated that the absorption of evodiamine, rutaecarpine, gensenoside Rb1, Re and Rg1 in headache group were significantly higher than those in normal group with similar concentration-time curves while no significant differences existed in limonin and ginsenoside Rd between the two groups.

A mechanism-based approach for absorption modeling: the Gastro-Intestinal Transit Time (GITT) model

Absorption models used in the estimation of pharmacokinetic drug characteristics from plasma concentration data are generally empirical and simple, utilizing no prior information on gastro-intestinal (GI) transit patterns. Our aim was to develop and evaluate an estimation strategy based on a mechanism-based model for drug absorption, which takes into account the tablet movement through the GI transit. This work is an extension of a previous model utilizing tablet movement characteristics derived from magnetic marker monitoring (MMM) and pharmacokinetic data. The new approach, which replaces MMM data with a GI transit model, was evaluated in data sets where MMM data were available (felodipine) or not available (diclofenac). Pharmacokinetic profiles in both datasets were well described by the model according to goodness-of-fit plots. Visual predictive checks showed the model to give superior simulation properties compared with a standard empirical approach (first-order absorption rate + lag-time). This model represents a step towards an integrated mechanism-based NLME model, where the use of physiological knowledge and in vitro–in vivo correlation helps fully characterize PK and generate hypotheses for new formulations or specific populations.