Rivaroxaban population pharmacokinetic and pharmacodynamic modeling in Iranian patients.

WHAT IS KNOWN AND OBJECTIVE: Although predictable pharmacokinetic and pharmacodynamic of rivaroxaban allow fixed dosing regimens without routine coagulation monitoring, there is still the necessity to monitor and predict the effects of rivaroxaban in specific conditions and different populations. The current study was designed and conducted to analyze the rivaroxaban population pharmacokinetics in Iranian patients and establish a pharmacokinetic/pharmacodynamic model to predict the relationship between rivaroxaban concentration and its anticoagulant activity. METHODS: A sequential nonlinear mixed effect pharmacokinetic/pharmacodynamic modeling method was used to establish the relation between rivaroxaban concentration and anti-factor Xa activity, prothrombin time, and activated partial thromboplastin time (aPTT) as pharmacodynamic biomarkers in a population of sixty-nine Iranian patients under treatment with oral rivaroxaban. Rivaroxaban plasma concentration was quantified by a validated high-performance liquid chromatography-tandem mass spectrometry. RESULTS AND DISCUSSION: The typical population values (inter-individual variability%) of the oral volume of distribution and clearance for a one-compartment model were 61.2 L (21%) and 3.68 L·h-1 (61%), respectively. Creatinine clearance and Child-Turcotte-Pugh score were found to affect the clearance. A direct link linear structural model best fitted the data for both prothrombin time and aPTT. The baseline estimates of aPTT and prothrombin time in the population were 35.0 (15%) and 12.6 (2%) seconds, respectively. The slope of the relationship between apTT, prothrombin time, and rivaroxaban concentration was 0.033 (28%) and 0.018 (54%) s·ml·ng-1 , respectively. The selected model for anti-factor Xa activity consisted of a direct link inhibitory Emax model with Hill coefficient. The maximum level of inhibition (Emax ) was 4 IU·ml-1 . The concentration of rivaroxaban producing 50% of the maximum inhibitory effect (EC50 ) was 180 (24%) ng·ml-1 , and Hill coefficient (γ) was 1.44 (108%). No covariates showed a statistically significant effect on PT and activated partial thromboplastin time prolonging properties and anti-factor Xa activity. WHAT IS NEW AND CONCLUSION: Our results confirmed that pharmacokinetic/pharmacodynamic models similar to those of the other studies describe the relationship between the rivaroxaban concentration and its anticoagulant effect in Iranian patients. However, considerable differences were observed in the parameters of the pharmacodynamics-pharmacokinetic models with the results of other reports that can explain the unpredictable effects of rivaroxaban in some patients.

Oral delivery of indinavir using mPEG-PCL nanoparticles: preparation, optimization, cellular uptake, transport and pharmacokinetic evaluation.

Introduction: Indinavir (IDV) is a potent HIV protease inhibitor used in the treatment of human immunodeficiency virus (HIV). IDV is a weak base with limited aqueous solubility in its unprotonated form; therefore, solubility of IDV in the gastrointestinal tract fluids is the rate-limiting step of its absorption and onset of action. However, in many cases, drugs are not absorbed well in the gastrointestinal tract; polymer nanoparticles were recognized as an effective carrier system for drug encapsulation and are now studied as a vehicle for oral delivery of insoluble compounds. Preparation of methoxy poly (ethylene glycol)-poly (e-caprolactone) (mPEG-PCL) nanoparticles is among the strategies to overcome low bioavailability of drugs with poor aqueous solubility. Materials and method: The structure of the copolymers was characterized using 1H NMR, FTIR, DSC and GPC techniques. IDV loaded mPEG- PCL nanoparticles prepared by emulsification solvent evaporation method were optimized using D-optimal experimental design and were characterized by various techniques such as DLS, DSC, XRD, AFM and SEM. Using Caco-2 cells as a cellular model, we studied the cellular uptake and transport. Results: In vivo pharmacokinetic studies were performed in rats. The plasma AUC (0-t), t1/2 and Cmax of IDV-mPEG-PCL NPs were increased by 5.30, 5.57 and 1.37 fold compared to the IDV solution, respectively. Conclusion: The results of this study are promising for the use of biodegradable polymeric nanoparticles to improve oral drug delivery.

Magnetic brain targeting of naproxen-loaded polymeric micelles: pharmacokinetics and biodistribution study.

The blood brain barrier is a major obstacle to the entry of the majority of CNS-active agents. In the present research, the potential of magnetic polymeric micelles (MPMs) for brain-targeting of naproxen was evaluated. The MPMs were made of methoxy poly(ethyleneglycol)-poly (caprolactone) copolymer and super paramagnetic iron oxide nanoparticles (SPIONs). To investigate the impact of particle size on the in vivo biofate of nanoparticles, MPMs with two different sizes were prepared. The prepared magnetic polymeric micelles had diameters of 137 ±â€¯3.5 nm (MPM137) and 242 ±â€¯6.2 nm (MPM242) and their surface charges were about -6.5 and - 4.5 mV, respectively. Pharmacokinetic and biodistribution of nanoparticles were characterized in rats using an external magnet of 0.4 Tesla field strength located on the skull of anesthetized animals. Significant differences in volumes of central as well as peripheral compartments were observed between both MPM formulations and free naproxen solution. After 8 h of administration, the brain concentration of naproxen was shown to be higher in the case of MPM137 in comparison with MPM242 and free drug. The findings revealed that the polymeric magnetic micelles with diameters smaller than 150 nm could be initially considered as a promising carrier to improve therapeutic agent accumulation in the brain for the treatment of CNS diseases.

Neuropharmacokinetic evaluation of lactoferrin-treated indinavir-loaded nanoemulsions: remarkable brain delivery enhancement.

OBJECTIVE: Indinavir (IDV), an antiretroviral protease inhibitor used in treatment of HIV infection, has limited entry into brain due to efflux by the P-glycoprotein presented in blood-brain barrier. The aim of present study was to develop lactoferrin-treated nanoemulsion containing indinavir (Lf-IDV-NEs) for delivery to brain. METHODS: Indinavir-loaded nanoemulsions (IDV-NEs) were prepared by high-speed homogenization method, and then lactoferrin was coupled to IDV-NEs by water soluble EDC method. RESULTS: The hydrodynamic diameters, polydispersity index, and zeta potential of IDV-NEs were 112 ± 3.5 nm, 0.20 ± 0.02, and -33.2 ± 2.6 mV, respectively. From in vivo studies in animal model of rats, the AUC0-4 h of brain concentration-time profile of IDV-NEs and Lf-IDV-NEs were 1.6 and 4.1 times higher than free drug, respectively. The brain uptake clearance of IDV-NEs and Lf-IDV-NEs were, interestingly, 393- and 420-times higher than the free drug. CONCLUSIONS: It can be concluded that applying both lactoferrin-treated and non-treated nanoemulsions clearly leads to significant brain penetration enhancement of indinavir, an effect which is more pronounced in the case of Lf-IDV-NEs with the higher drug residence time in brain.

Silencing the tobacco gene for RNA-dependent RNA polymerase 1 and infection by potato virus Y cause remodeling of cellular organelles.

RNA-dependent RNA polymerase 1 (RDR1) has been shown to be involved in DNA methylation, RNA silencing and regulating expression of other genes. RDR1 gene expression is stimulated by infection with potato virus Y° (PVY). Transgenic Nicotiana tabacum plants silenced for RDR1 gene expression showed morphological changes in mesophyll cells, associated with remodeling of the nuclei, chloroplasts and mitochondria. RDR1 silencing led to decreased nuclear size, increased heterochromatin content and aggregation, decreased numbers of chloroplasts, plus changes in shape, internal structures and integrity of chloroplasts and mitochondria. RDR1-silenced transgenic plants showed increased PVY accumulation and ultrastructural remodeling was intensified in both chloroplasts and mitochondria of PVY-infected, RDR1-silenced plants. By contrast, heterochromatin condensation was reduced by PVY infection, and in non-transgenic plants the nuclei were translucent and lacked morphology after PVY infection. Thus, RDR1 regulates gene expression leading to remodeling of chromosomes, and PVY infection counteracts these effects on chromosomal remodeling.

Naproxen conjugated mPEG-PCL micelles for dual triggered drug delivery.

A conjugate of the NSAIDs drug, naproxen, with diblock methoxy poly(ethylene glycol)-poly(ε-caprolactone) (mPEG-PCL) copolymer was synthesized by the reaction of copolymer with naproxen in the presence of dicyclohexylcarbodiimide and dimethylaminopyridine. The naproxen conjugated copolymers were characterized with different techniques including (1)HNMR, FTIR, and DSC. The naproxen conjugated mPEG-PCL copolymers were self-assembled into micelles in aqueous solution. The TEM analysis revealed that the micelles had the average size of about 80 nm. The release behavior of conjugated copolymer was investigated in two different media with the pH values of 7.4 and 5.2. In vitro release study showed that the drug release rate was dependant on pH as it was higher at lower pH compared to neutral pH. Another feature of the conjugated micelles was a more sustained release profile compared to the conjugated copolymer. The kinetic of the drug release from naproxen conjugated micelles under different values of pH was also investigated by different kinetic models such as first-order, Makoid-Banakar, Weibull, Logistic, and Gompertz.

Population Pharmacokinetic Analysis of the Oral Absorption Process and Explaining Intra-Subject Variability in Plasma Exposures of Imatinib in Healthy Volunteers.

BACKGROUND AND OBJECTIVE: Imatinib mesylate is presently the first-line treatment for chronic myeloid leukemia (CML). The aim of this study was to investigate the absorption and distribution kinetics of imatinib in healthy Iranian volunteers using nonlinear mixed effects modeling (NLMEM) to assess the overall, intra- and inter-subject variabilities in pharmacokinetic parameters after oral administration. METHODS: This analysis was based on data from 24 healthy subjects who participated in a bioequivalence study after administering a single dose of 200 mg of each formulation. Imatinib concentrations were quantified using a validated liquid chromatography method. To simultaneously describe the imatinib pharmacokinetic profiles obtained with both formulations, a population pharmacokinetic model was applied to data using SAEM algorithm implemented in MONOLIX, whilst simulations were used by numerical solving of ordinary differential equations to calculate secondary parameters in individuals for bioequivalence studies. RESULTS: According to goodness-of-fit criteria, a two-compartment open model with sequential zero- then first-order absorption and first-order elimination was used as the structural pharmacokinetic model. Inter-individual variability (IIV) was considered for all parameters. Typical population estimates (% IIV) were fraction of the drug absorbed with a zero-order kinetic (Fr) of 0.153 (47.9 %) in period (Tk0) of 0.714 h (47.4 %), first-order absorption rate constant (k a) of 0.94 h(-1)(31.2 %), oral clearance of 19 L/h (27.9 %), central volume of distribution (V c/F) of 139 L (21.5 %), apparent peripheral volume of distribution (V p/F) of 130 L (29.7 %) and the apparent inter-compartment clearance (Q/F) of 29.6 L/h (41.8 %). Body mass index (BMI) was the only covariate found to significantly affect V p /F. The coefficient of variation for intra-individual plasma exposure (AUC0-∞) was 27.8 %. CONCLUSIONS: Analyses using NLMEM for imatinib exhibited absorption complexities such as two input rates and medium to high intra-individual variability in drug exposure.

Predictive performance of Vancomycin population pharmacokinetic models in Iranian patients underwent hematopoietic stem cell transplantation.

OBJECTIVE: Many hematopoietic stem cell transplantation (HSCT) patients receive vancomycin empirically during febrile neutropenia. There are several models for estimation of vancomycin pharmacokinetic parameters and calculation of initial dosing regimen accordingly. However, the performance of these methods in HSCT patients remained to be evaluated. The aim of the study was to determine which of the vancomycin population pharmacokinetic methods best fit Iranian HSCT patients. METHODS: In order to evaluate predicted performance of seven vancomycin population pharmacokinetic models, the pharmacokinetic parameters of patients were estimated using each model's equations. Then the predicted steady-state trough vancomycin concentration was calculated based on each model's parameters and using a formula based on Sawchuk-Zaske method. The predicted steady-state trough vancomycin concentration and the real measured concentrations were compared to see which method was the most precise and least biased using mean squared error (MSE) and mean prediction error (ME) respectively. FINDINGS: Forty-six patients (65% men) were included in the study. Calculated metrics showed a range of 38% under-prediction bias with Rodvold to 34% over-prediction bias with Matzke and Burton models. Birt and revised Burton methods showed no significant bias (ME [95% confidence interval (CI)]: -0.067 [-0.235-0.101] and 0.066 [-0.105-0.238]). Birt and revised Burton were not different significantly considering MSE (95% CI) of 0.385 (0.227-0.544) and 0.401 (0.255-0.546), respectively. Comparisons of precision with naive predictors revealed a delta MSE (95% CI) of -0.128 (-1.379-1.890) for Birt and 0.026 (-0.596-0.940) for revised Burton models. CONCLUSION: Although the Birt and Burton revised methods performed well, none of the studied models showed acceptable performance to be implemented as a routine method for initial dose calculation in HSCT patients. A vancomycin pharmacokinetic model specific for this high-risk subpopulation of Iranian patients should be designed and validated.

Rotylenchus castilloi n. sp. (Nematoda: Hoplolaimidae), a new species with long stylet from northern Iran.

Rotylenchus castilloi n. sp., a new bisexual species is described and illustrated based on morphological, morphometric and molecular data. The new species is characterised by having a hemispherical, continuous lip region with an irregular corncob-like appearance under SEM, very long stylet (62-68 µm), vulva located at 49.7-62.2% of body length from anterior end, with a protruding double epiptygma, a rounded to convex-conoid (rarely bi-lobed) tail with 8-12 annuli and specific sequences of D2-D3 segments of 28S and ITS1-rRNA genes. Differences between the new species and four other species of the genus (R. mesorobustus, R. cazorlaensis, R. magnus and R. jaeni) are discussed. Morphologically, the new species can be separated from these species mostly by its body length, lip region characters, stylet length and location of phasmid. Phylogenetic analyses using 721 bp partial sequences of D2-D3 expansion segments of the 28S and 590 bp ITS1-rRNA genes revealed the new species forming a clade with two isolates of R. eximius and two isolates of R. unisexus, two morphologically unrelated species.

High-performance liquid chromatographic determination of propofol in human plasma: comparison of different heteroscedastic calibration curve models.

PURPOSE: The aim of this study was to select the best calibration model for determination of propofol plasma concentration by high-performance liquid chromatography method. METHODS: Determination of propofol in plasma after deproteinization with acetonitrile containing thymol (as internal standard) was carried out on a C18 column with a mixture of acetonitrile and trifluoroacetic acid 0.1% (60:40) as mobile phase which delivered at the flow rate of 1.2 mL/minute . Fluorescence detection was done at the excitation and emission wavelengths of 276 and 310 nm, respectively. After fitting different equations to the calibration data using weighted regression, the adequacy of models were assessed by lack-of-fit test, significance of all model parameters, adjusted coefficient of determination (R(2) adjusted) and by measuring the predictive performance with median relative prediction error and median absolute relative prediction error of the validation data set. RESULTS: The best model was a linear equation without intercept with median relative prediction error and median absolute relative prediction error of 4.0 and 9.4%, respectively in the range of 10-5000 ng/mL. The method showed good accuracy and precision. CONCLUSION: The presented statistical framework could be used to choose the best model for heteroscedastic calibration data for analytes like propofol with wide range of expected concentration.

Influence of flocculating agents and structural vehicles on the physical stability and rheological behavior of nitrofurantoin suspension.

BACKGROUND: Nitrofurantoin is a nitrofuran antibiotic that has been used for treatment of urinary tract against positive and negative bacteria. OBJECTIVES: The aim of this study was to evaluate the effect of structural vehicles and flocculating agents on physical stability and rheological behavior of nitrofurantoin suspension. MATERIALS AND METHODS: To formulate the suspensions, the effect of glycerin and polysorbate 80 as wetting agents was evaluated and their particle sizes were determined using the sieve method. Then to achieve controlled flocculation, sodium citrate and aluminum chloride were added. After choosing the suitable wetting and flocculating agents, structural vehicles such as sodium carboxyl methyl cellulose and Veegum were evaluated individually and in combination. In addition, the effect of sorbitol on density of continuous phase and some physical stability parameters such as sedimentation volume, degree of flocculation and ease of redispersion of the suspensions were evaluated. After incorporation of structural vehicles, the rheological properties of formulations were also determined to find their flow behavior. RESULTS: According to the results, glycerin (0.2%) and sodium citrate (0.3%) had the best effect on the suspension stability as wetting and flocculating agents, respectively. Rheological properties of formulations showed pseudoplastic behavior with some degree of thixotropy. CONCLUSIONS: In conclusion, the suspension containing Veegum 1%, sodium carboxy methyl cellulose 1%, glycerine 0.2%, sodium citrate 0.3% and sorbitol 20 % was chosen as the most physically stable formulation.

Population pharmacokinetics of imatinib in Iranian patients with chronic-phase chronic myeloid leukemia.

PURPOSE: We evaluated the population pharmacokinetics (PPK) and exposure-response relationship of imatinib mesylate in Iranian patients with chronic myeloid leukemia (CML).This study was designed to assess steady state (SS) imatinib trough concentrations (Cmin) and pharmacokinetics parameters of imatinib in patients with CML in chronic phase after at least 12-month treatment. METHODS: Plasma concentrations from a randomized controlled trial consist of 61 patients who received oral imatinib at doses ranged between 300 and 800 mg in various dosing interval, which were quantified using a validated reversed-phase high-performance liquid chromatographic method with UV detection method on different occasions at SS and evaluated using PPK model. RESULTS: A one-compartment model with zero-order absorption and a lag time was sufficient in describing the concentration-time profile. Inter-individual variability (IIV) was modeled for all parameters. Oral clearance (CL/F) and the volume of distribution (V/F) were estimated to 10.8 L/h with 30 % IIV and 265 L with 53 % IIV, respectively. Inter-occasion variability (IOV) was included in CL/F (17 %) and V/F (22 %).The proportional residual error of the model was 8 %. CONCLUSIONS: Simulation analysis from individual parameters shows exposure to imatinib is highly variable among patients. Imatinib trough plasma levels <1,257 ng/mL were associated with lower rates of major molecular response. Because of the wide IIV compared with IOV with imatinib in our study, trough levels may play a role in investigating instances of suboptimal response.

Antinociceptive effect of some biuret derivatives on formalin test in mice.

PURPOSE: The current study was designed to investigate the antinociceptive effects of several biuret derivatives with N, N`-diphenyl, N-phenyl-N`-alkylphenyl, N,N`-bis alkylphenyl, 2-methylquinoline-4-yl, benzo[d]thiazol-2-ylthio and (1-phenyl-1H-tetrazol-5-yl)thio substituents on the formalin-evoked pain in mice. METHODS: Antinociceptive activity of the nine biurets derivatives were assessed at different doses in mice using formalin test and the results were compared with those of indomethacin(20 mg/kg) and vehicle of the compounds. Area under the pain score curve against time (AUEC) up to 60 minutes was used as the measure of pain behavior. RESULTS: A rather good analgesic effect was seen for most of the tested biuret derivatives. Significant reduction in median AUEC0-5 minutes was observed at the doses of 50 and 25 mg/kg for biurets with either benzyl and 2-methylquinoline-4-yl (C8) or phenylethyl and benzo[d]thiazol-2-ylthio(C9) moieties, respectively(p-value<0.0044). Antinociceptive activities of compound C7 (with bis phenylropyl substituent), C8 and C9 during the late phase of formaldehyde-induced pain were comparable to that of indomethacin. CONCLUSION: Unlike indomethacin, the tested biuret compounds are able to induce antinociception in both phases of formalin test and could be considered comparable to indomethacin at the selected doses.

Percutaneous absorption of salicylic Acid after administration of trolamine salicylate cream in rats with transcutol(®) and eucalyptus oil pre-treated skin.

PURPOSE: This study was conducted to assess the effect of skin pre-treatment with Transcutol(®) and eucalyptus oil on systemic absorption of topical trolamine salicylate in rat. METHODS: Pharmacokinetic parameters of salicylic acid following administration of trolamine salicylate on rat skin pre-treated with either Transcutol(®) or eucalyptus oil were determined using both non-compartmental and non-linear mixed effect modeling approaches and compared with those of control group. RESULTS: Median (% of interquartile range/median) of salicylic acid AUC0-8hr (ng/mL/hr) values in Transcutol(®) or eucalyptus oil treated rats were 2522(139%) and 58976(141%), respectively as compared to the 3023(327%) of the control group. Skin pre-treatment with eucalyptus oil could significantly decrease extravascular volume of distribution (V/F) and elimination rate constant (k) of salicylic acid. CONCLUSION: Unlike Transcutol(®), eucalyptus oil lead to enhanced transdermal absorption of trolamine salicylate through rat skin.

Rheological behavior and stability of ciprofloxacin suspension: Impact of structural vehicles and flocculating agent.

Ciprofloxacin is a fluoroquinolone and is used against a broad spectrum of gram-negative and gram-positive bacteria. The aim of the study is to investigate the effect of structural vehicles and other formulating factors on physical stability and rheological behavior of ciprofloxacin suspension. To formulate the suspensions, the effect of glycerin and polysorbate 80 as wetting agents was evaluated. Then to achieve controlled flocculation, different concentrations of sodium chloride and calcium chloride were added. After choosing suitable wetting and flocculating agents, structural vehicles such as sodium carboxyl methyl cellulose (NaCMC), hydroxypropylmethylcellulose (HPMC) and Veegum were evaluated. Physical stability parameters such as sedimentation volume, the degree of flocculation and the ease of redispersion of the suspensions and growth of crystals were evaluated. After incorporation of structural vehicles, the rheological properties of formulations containing were also studied to find out their rheological behavior. According to the results, suspension containing glycerin (0.2% w/v) and sodium chloride (0.05% w/v) as wetting agent and flocculating agent, respectively, were the most stable formulations regarding their F and N. Microscopic observations showed the growth of crystals in ciprofloxacin suspension in formulation without excipients and the minimum amount of crystal growth was seen in suspension containing NaCMC (0.25% w/v), Veegum (0.1% w/v) and NaCl (0.05% w/v). Rheological studies showed that almost all of the formulations had psuedoplastic behavior with different degree of thixotropy. The formulation containing NaCMC (0.25% w/v), Veegum (0.1% w/v) and NaCl (0.05% w/v) was the most stable formulation. It may be concluded that by altering the amount ratios of formulation factors, the best rheological behavior and the most proper thixotropy may be achieved.

In silico and in vitro comparative activity of novel experimental derivatives against Leishmania major and Leishmania infantum promastigotes.

This in silico and in vitro comparative study was designed to evaluate the effectiveness of some biurets (K1 to K8) and glucantime against Leishmania major and Leishmania infantum promastigotes. Overall, eight experimental ligands and glucantime were docked using AutoDock 4.3 program into the active sites of Leishmania major and Leishmania infantum pteridine reductase 1, which were modeled using homology modeling programs. The colorimetric MTT assay was used to find L. major and L. infantum promastigotes viability at different concentrations of biuret derivatives in a concentration and time-dependent manner and the obtained results were expressed as 50% and 90% of inhibitory concentration (IC50 and IC90). In silico method showed that out of eight experimental ligands, four compounds were more active on pteridine reductase 1. K3 was the most active against L. major promastigotes with an IC50 of 6.8 µM and an IC90 of 40.2 µM, whereas for L. infantum promastigotes was K8 with IC50 of 7.8 µM. The phenylethyl derivative (K7) showed less toxicity (IC50s>60 µM) in both Leishmania strains. Glucantime displayed less growth inhibition in concentration of about 20 µM. In silico and especially docking results in a recent study were in accordance with the in vitro activity of these compounds in presented study and compound K3, K2 and K8 showed reasonable levels of selectivity for the Leishmania pteridine reductase 1.

Vancomycin Pharmacokinetic Parameters in Patients Undergoing Hematopoietic Stem Cell Transplantation (HSCT).

BACKGROUND: Vancomycin is used abundantly in patients undergoing HSCT, especially during neutropenic fever. Despite its widespread use little is known about vancomycin pharmacokinetics in HSCT patients. We conducted this study to investigate vancomycin pharmacokinetic parameters in our HSCT patients and to evaluate current dosing regimen based on trough vancomycin concentrations measurement. METHODS: Vancomycin serum concentration at steady-state was determined prospectively in 46 adult HSCT patients who received vancomycin as empirical treatment of neutropenic fever. Individual steady-steady pharmacokinetic parameters were also determined in 20 patients who had two vancomycin levels from an administered dose, assuming one-compartment model. Acute kidney injury was also evaluated in our patients during vancomycin therapy. RESULTS: Mean (±SD) apparent volume of distribution (L/kg) and clearance (mL/min) were 0.6 (± 0.33) and 109.7 (± 57.5) respectively. With mean (±SD) total daily dose of vancomycin 31.9 (±10.5) mg/kg/day that was administered, more than 90% of measured vancomycin trough concentrations were outside the range of 15-20 mg/L and 54.3% of patients had trough concentrations below 10 mg/L. Of 46 patients, 21 patients (45.7%) developed acute kidney injury (AKI) during vancomycin therapy; among them 19 patients were receiving nephrotoxic drug(s) concomitantly. CONCLUSION: Current vancomycin dosage regimen could not lead to recommended therapeutic serum concentrations in our patients. Large variation in vancomycin pharmacokinetic parameters observed among patients of this study along with difference of vancomycin pharmacokinetics in our study and other similar studies further explain the need for therapeutic drug monitoring and individualization of vancomycin dosing.

Development and Validation of a High-Performance Liquid Chromatography Method With UV Detection for Determination of 1-(2-phenylethyl)-5- (quinaldin-4-yl) Biuret in Rat Plasma.

BACKGROUND: Recently, biuret derivatives have been reported as showing moderate to good cytotoxic effect against certain cancer cell lines. In this study, a high-performance liquid chromatography method was developed for determination of 1-(2-phenylethyl)-5-(quinaldin-4-yl) biuret (PEQB) in rat plasma to use in future studies on this compound and related derivatives. OBJECTIVES: In this study, we describe a simple and sensitive high-performance liquid chromatography method with UV detection for determination of 1-(2-phenylethyl)-6-(quinaldin-4-yl) biuret (PEQB) in rat plasma. MATERIALS AND METHODS: Separations were performed on a Nucleosil-100 CN HPLC column (125 × 4.0 mm) (5 µm), using a mixture of acetonitrile: methanol: potassium dihydrogen phosphate buffer (0.05 M, pH 3.5) (10:10:80) as mobile phase delivered at a flow rate of 1 mL/minute. Detection of PEQB and internal standard (1-([[3-(1,3-benzothiazol-2-ylsulfanyl)propyl]carbamoyl]amino)-N-phenylformamide) was performed at 235 nm and ambient temperature. Plasma samples (200 µL) were prepared by addition of 40 µL internal standard (100 µg/mL), and 400 µL acetonitrile. After vortex mixing and centrifugation at 10000 g, 50 µL of the clear supernatant was directly injected onto the chromatography column. Calibration curves were constructed by fitting the peak area ratio of the biuret to internal standard against concentration of biuret to a power model using generalized least squares nonlinear regression method. RESULTS: Under the above chromatography condition, biuret compound (PEQB) and the internal standard were detected at 4.5 and 13.5 minutes, respectively. Limit of quantitation of the PEQB was 0.1 µg/mL. Accuracy of the method over the concentration range of 0.1-100 µg/mL was between 88-109%. Inter- and intraday precisions were 4-19% and 6-8%, respectively. A good relationship in the form of a power model was found for two separate concentration ranges of 0.1-1 and 2.5-100 µg/mL (R (2)> 0.99). CONCLUSIONS: The presented simple HPLC method is sufficiently accurate, precise and sensitive for the quantitation of 1-(2-phenylethyl)-5-(quinaldin-4-yl) biuret in rat plasma.

Development and validation of limited sampling strategies for estimation of cyclosporine area under the concentration-time curve in hematopoietic stem cell transplant patients.

The aim of this study was to develop and validate limited sampling strategies for accurately predicting 12-hour area under the concentration-time curve (AUC(0-12 h)) to provide a practical method for more precise therapeutic drug monitoring of cyclosporine A in stem cell transplant patients. Steady-state cyclosporine blood concentrations were measured within a dosing interval (12 hours post administration) in 35 allogeneic bone marrow transplant patients receiving 238 mg (±117 mg) twice-daily dose of cyclosporine. Limited sampling strategies were developed by multiple linear regression analysis of relationship between cyclosporine A full AUC(0-12 h) values and different combinations of preselected blood concentrations. Validation of the estimating equations was done by a bootstrap-like cross-validation method. Cross-validation results showed that cyclosporine AUC(0-12 h) could be estimated using either 2 or 3 samples within the first 4 hours after drug administration with good accuracy and precision (absolute prediction error of less than 6.2%). The number of estimated area under the drug concentration-time curves within 15% of observed values was greater than 26 (74%) for models used predose concentration with either c(2h) and c(4h) or both. Most of the previously reported single-sample models showed a systematic error in predicting AUC(0-12 h). Although a statistically significant difference in precision of prediction was seen between 3-sample model using c(0), c(2h), and c(4h) and 2-sample models (c(0), c(2h) or c(0), and c(4h)), such a difference (2%) could not be of clinical importance. Other 2-sample estimating equations (models using c(2h) with either c(6h) or c(10h)) with the same degree of precision appear to be less feasible clinically. Cyclosporine AUC(0-12 h) in bone marrow transplant patients could be estimated using 2 or 3 samples within the first 4 hours after drug administration with good accuracy and precision.

Optimization of the simultaneous determination of imatinib and its major metabolite, CGP74588, in human plasma by a rapid HPLC method using D-optimal experimental design.

A simple, rapid and specific HPLC method has been developed and validated for the simultaneous determination of imatinib, a tyrosine kinase inhibitor, and its major metabolite, CGP74588, in human plasma. The optimization of the HPLC procedure involved several variables, of which the influences of each was studied. After a series of preliminary-screening experiments, the composition of the mobile phase and the pH of the added buffer solution were set as the investigated variables, while the resolution between imatinib and CGP74588 peaks, the retention time and the imatinib peak width were chosen as the dependent variables. Applying D-optimal design, the optimal chromatographic conditions for the separation were defined. The method proved to show good agreement between the experimental data and predictive values throughout the studied parameter range. The optimum assay conditions were achieved with a Chromolith™ Performance RP-8e 100 mm × 4.6 mm column and a mixture of methanol/acetonitrile/triethylamine/diammonium hydrogen phosphate (pH 6.25, 0.048 mol L(-1)) (20:20:0.1:59.9, v/v/v/v) as the mobile phase at a flow rate of 2 mL min(-1) and detection wavelength of 261 nm. The run time was less than 5 min, which is much shorter than the previously optimized methods. The optimized method was validated according to FDA guidelines to confirm specificity, linearity, accuracy and precision.