Simple and validated HPLC–UV analysis of levetiracetam in deproteinized plasma of patients with epilepsy

A Cross-Sectional Study Comparing Oxidative Stress in Patients with Epilepsy Treated with Old and New Generation Antiseizure Medications

Background and Objectives: Oxidative stress resulting from a disturbance of the endogenous redox system is suspected in numerous diseases of the central nervous system, including epilepsy. In addition, antiseizure medications (ASMs), especially those of the old generation, may further increase oxidative stress. To evaluate the effects of ASM generation on oxidative stress, we conducted a cross-sectional study in patients with epilepsy treated with old, new, and polytherapy. Materials and Methods: The antioxidant activity of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase, as well as the concentrations of malondialdehyde, protein carbonyl, nitrate, nitrite, and glutathione in reduced and oxidized forms, were measured in 49 patients with epilepsy and 14 healthy controls. In addition, the plasma concentrations of ASMs and metabolites of carbamazepine and valproic acid were measured in the patients. Results: Patients with epilepsy showed increased activities of superoxide dismutase and catalase (p < 0.001), concentrations of glutathione disulfide and markers of nitric oxide metabolism (p < 0.001), and decreased activities of glutathione peroxidase, glutathione reductase, glutathione, and nitrite concentrations (p ≤ 0.005) compared to healthy controls. A comparison of ASM generations revealed increased levels of superoxide dismutase and catalase (p ≤ 0.007) and decreased levels of glutathione peroxidase and glutathione reductase (p ≤ 0.01) in patients treated with old ASMs compared to those treated with new generation ASMs. In addition, an increase in protein carbonyl and nitric oxide metabolites (p ≤ 0.002) was observed in patients treated with old generation ASMs compared to those treated with new generation ASMs. Most oxidative stress parameters in patients receiving polytherapy with ASMs were intermediate between the results of patients treated with the old and new generations of ASMs. Conclusions: An increase in oxidative stress markers and modulation of antioxidant enzyme activities was observed in patients with epilepsy compared to controls. The results of our study showed significantly higher oxidative stress in patients treated with old ASMs compared to those treated with new generation ASMs.

Titania-based fabric phase sorptive extraction approach for the determination of antiepileptic drugs, levetiracetam and lamotrigine in urine samples using high-performance liquid chromatography-photo diode array detection

A new fabric phase sorptive extraction (FPSE) based separation and enrichment method was developed for sensitive determination of two antiepileptic drug molecules, Levetiracetam (LEV) and Lamotrigine (LTG). The analysis of these drug molecules was performed with high-performance liquid chromatography equipped with photodiode array detector (HPLC-PDA) after FPSE. HPLC analysis was carried out by using phenyl hexyl column, under isocratic conditions with the mobile phase composed of pH 3.0 buffer-acetonitrile (77:23 v: v). All parameters affecting the separation and enrichment process were studied and optimized step by step. The linear working range of the developed method was calculated in the range of 10.0-1000.0 ng mL-1 for both the drug molecules (LEV and LTG). The limits of detection of the method (LODs) were calculated as 2.72 and 3.64 ng mL-1, respectively. The relative standard deviation (%RSD) values of the developed method as an indicator of precision were varied between 4.0 and 7.3. The accuracy of the optimized FPSE method was determined by the recovery tests utilizing spiked samples and results were assessed in the range from 94.6 to 106.3%. This is the first application of sol-gel Titania polycaprolactone-polydimethylsiloxane-polycaprolactone (Ti-PCAP-PDMS-PCAP) based FPSE membrane in the determination of antiepileptic drug molecules.

Quantification of levetiracetam in plasma and urine and its application to a pharmacokinetic study of traumatic brain injury patients

Background: Levetiracetam is an antiepileptic drug used to prevent or treat seizure in patients with severe traumatic brain injury. This study aimed to develop and validate methodology suitable for measuring levetiracetam concentrations in human plasma and urine. Methods: Plasma or urine (10 μl) samples were spiked with [²H₆]-levetiracetam and processed using an acetonitrile precipitation. ESI-LC-MS/MS was employed for analyte detection. Results: The levetiracetam calibration was linear from 0.1 to 50 mg/l in a combined matrix of plasma and urine. Intra- and inter-assay imprecision and accuracy in plasma were <7.7 and 109%, and in urine were <7.9 and 108%, respectively. Conclusion: The validated method was applied to a pharmacokinetic study of levetiracetam in critically ill patients with severe traumatic brain injury.

Development and Validation of a Simple HPLC-UV Assay Method for Determination of Levetiracetam Concentrations in Human Plasma

Levetiracetam (LEV) is a broad spectrum antiseizure medication that is used in various seizure types. There is evidence that therapeutic drug monitoring (TDM) of LEV is of value in selected patient populations, therefore determination of LEV plasma concentrations is essential. Herein we developed and validated a simple, reproducible, and practical method for the quantification of LEV concentrations in human plasma samples using high performance liquid chromatography (HPLC). Plasma samples (0.3 mL) deproteinization was done using acetonitrile. HPLC chromatographic separation of plasma samples was accomplished by reversed phase C18 column. The mobile phase constituted water and acetonitrile (90:10, v/v) ran at flow rate of 1 mL/min. Signal acquisition was conducted at a wavelength of 192 nm. Calibration curves showed excellent linearity (Correlation coefficient r2 > 0.99) over a concentration range of 3–80 μg/mL. Both inter and intraday assay accuracy and precision were less than 8% (except for the lowest limit of quantification was within 20%). Elution time was 15 min. The developed method excluded the use of buffers and utilized small volumes of plasma samples with simple mobile phase composition. Therefore, our method could be practically applied to routine TDM.

Application of response surface methodology (RSM) in statistical optimization and pharmaceutical characterization of a patient compliance effervescent tablet formulation of an antiepileptic drug levetiracetam

Background

The main objective of the present study was to develop and optimize an effervescent tablet of levetiracetam, an antiepileptic drug, using central composite design with response surface methodology (RSM).The present investigation helps to overcome the problem associated with levetiracetam tablets and liquid dosage forms with children and elderly people like bad taste and swallowing difficulties. It also facilitates as an alternative manufacturing process for advanced patented technology like 3D printing process employed in SPRITAM® tablet.

Levetiracetam effervescent tablets were prepared by dry granulation (roll compaction) method using water-soluble excipients and optimized by central composite rotatable design (CCRD) using two variables (citric acid and effersoda) at two levels (high and low). Overall, fourteen formulation trials were generated through statistical software Minitab 17.3.0 placing 6 center points, 4 cube points, and 4 axial points. All formulations were subjected to compression using single punch machine.

Results

Quality attributes of compressed tablets were evaluated using various compendial and non-compendial tests. RSM was used to observe the responses like effervescent time, hardness, and friability of the prepared tablet batches for different levels of all the variables. Polynomial equations were developed, and model plots (contour plot and 3-dimensional model surface plots) were generated to study the impact of acid-base couple on the responses. Finally, the optimized formulation was selected on the basis of desired effervescent time, hardness, friability, percent drug release, and drug content. From the studied RSM design, it was observed that small changes in the independent variables (citric acid and effersoda) correlate with shifts in the dependent variables, i.e., the desired responses. The study reveals that all the independent variables (citric acid and effersoda) and dependent variables (effervescent time, hardness, and friability) have a good correlation as indicated by good linear regression coefficient of 0.9808, 0.9939, and 0.9892 for effervescent time, hardness, and friability respectively.

Conclusion

Levetiracetam effervescent tablets are satisfactorily prepared by dry granulation (roll compaction) approach. All desired critical quality attributes were found to be satisfactory. The applicability of RSM with desirability function in optimizing the levetiracetam formulation has made it possible to identify the impact of various independent variables and explore their effect on required responses.

Determination of levetiracetam in human plasma by online heart-cutting liquid chromatography: Application to therapeutic drug monitoring

Levetiracetam is an antiepileptic drug for the treatment of psychiatric patients. In this study, a selective, straightforward, and rapid online heart-cutting liquid chromatography method was developed for the therapeutic drug monitoring of levetiracetam. This method allows for the determination of levetiracetam in human plasma without complex sample preparation. The mobile phases consisted of 30 mM aq. orthophosphoric acid solution/methanol (70:30) at a flow rate of 1 mL/min for the first system and 10 mM aq. orthophosphoric acid solution/methanol (55:45) at a flow rate of 1 mL/min for the second system. The first separation was carried out on a GL Sciences Intersil ODS-3 column (4.6 mm × 150 mm, 3 µm) and the second separation was carried out on a Restek Ultra PFPP column (4.6 mm × 150 mm, 5 µm). The detection was carried out at 205 nm for both systems. The method was validated for selectivity and linearity, which were in the 6-60 µg/mL range. Intra- and interassay accuracies were <112.6%, and the intra- and interassay precisions were <6.4% for all quality control samples. The lower limit of quantitation was 6 µg/mL. The developed method was successfully applied for therapeutic drug monitoring of plasma samples from patients.

Population Pharmacokinetics and Dosing Recommendations of Levetiracetam in Adult and Elderly Patients With Epilepsy

The objective was to develop and externally validate a population pharmacokinetic model of levetiracetam in adult and elderly patients with epilepsy, and to perform dosing simulations to propose individualized dosing regimens more likely to achieve therapeutic concentrations. This prospective study included 367 plasma samples from 107 patients receiving oral levetiracetam. Samples were analyzed by HPLC-UV. Pharmacokinetic data, as well as patient demographic, clinical characteristics, other drug therapy, and the use of innovator or generic products of levetiracetam, were collected. Population modeling was performed with NONMEM and included internal and external validations of the final model. Simulations were used to propose optimized dosing regimens. The pharmacokinetics of levetiracetam was described by a one-compartment model with first-order absorption and linear elimination. Body surface area had a significant effect on the apparent volume of distribution, as did creatinine clearance (CrCL) over the drug clearance (p < 0.01). The final model performed adequately during external validation testing. The final model showed a better predictive performance. Dosing simulations support 1000 mg 12-hourly dosing of levetiracetam for patients with CrCL ~60-75 mL/min with higher dose needed for higher values (1500 mg 12-hourly for CrCL ~93-111 mL/min). Dosing regimens should be personalized to the patient's CrCL to maximize the likelihood of therapeutic concentrations.

Levetiracetam

A comprehensive profile of levetiracetam is presented in this chapter which includes its description, formula, elemental analysis, appearance, uses and applications. Different earlier studies included for example methods of synthesis are described with its typical structural schemes. The profile also listed the drug's physical characteristics indicating its solubility, X-ray powder diffraction pattern, thermal methods of analysis as well as its spectroscopic characteristics. Different methods of analysis which includes compendial method of analysis, as well as reported method of analysis which include spectrophotometry, spectrofluorometry, electrochemical method, chromatographic method, and immunoassay method of analysis. The study was include drug stability, clinical pharmacology, e.g., mechanism of action, pharmacokinetic study. Around 70 references are recorded as a proof of this chapter.

Development and full validation of an innovative HPLC-diode array detection technique to simultaneously quantify lacosamide, levetiracetam and zonisamide in human plasma

AIM

To implement pharmacokinetic drug monitoring and individualize the posology of new antiepileptic drugs, the first HPLC-diode array detection method was developed and validated to simultaneously quantify lacosamide, levetiracetam and zonisamide in human plasma.

MATERIALS & METHODS

Preceded by a reproducible liquid-liquid extraction, chromatographic separation was achieved by using a C18 column of 5 cm length and a mobile phase of water/acetonitrile. Full validation was performed according to international guidelines.

RESULTS

The method was linear within 0.5-30, 2.5-40.0 and 0.5-50.0 μg ml-1 for lacosamide, levetiracetam and zonisamide, respectively (r2 ≥ 0.998), accurate (-12.411-8.303%), precise (≤8.875%).

CONCLUSION

This innovative HPLC-diode array detection method was successfully employed in clinical practice and is expected to empower epileptic patients with a personalized pharmacotherapy service. [Formula: see text].

Population pharmacokinetics of levetiracetam in neonates with seizures

WHAT IS KNOWN AND OBJECTIVE

This study developed a population pharmacokinetic (PK) model of levetiracetam (LEV) for treating neonatal seizures (NS) and determined the influence of clinically relevant covariates to explain the interindividual variability and residual error.

METHODS

Twenty newborns admitted to the Neonatal Intensive Care Unit at the Hospital Central "Dr. Ignacio Morones Prieto" were included. LEV doses were administered by intermittent infusion. Blood samples were drawn 3 times post-infusion. Levetiracetam was quantified by a chromatographic technique. NONMEM software was used to determine the population PK model of LEV in neonates and the influence of clinical covariates on drug disposition.

RESULTS AND DISCUSSION

The LEV PK in neonates is described by a one-compartment open model with first-order elimination. The influence of creatinine clearance (CRCL) and body weight (BW) on clearance (CL[L/h] = 0.47*CRCL), as well as the volume of the distribution (Vd[L] = 0.65*BW) of LEV, were confirmed, considering interindividual variabilities of 36% and 22%, respectively, and a residual error of 13%.

WHAT IS NEW AND CONCLUSION

Based on the PK of LEV in neonates and the influence of the final PK model, a priori dosing guidelines are proposed considering CRCL, BW and LEV plasma concentrations between 6 and 20 mg/L for NS treatment.

Sensitive inexpensive spectrophotometric and spectrofluorimetric analysis of ezogabine, levetiracetam and topiramate in tablet formulations using Hantzsch condensation reaction

Two highly sensitive, simple and selective spectrophotometric and spectrofluorimetric assays have been investigated for the analysis of ezogabine, levetiracetam and topiramate in their pure and in pharmaceutical dosage forms. The suggested methods depend on the condensation of the primary amino-groups in the three drugs with acetylacetone and formaldehyde according to Hantzsch reaction yielding highly fluorescent yellow colored dihydropyridine derivatives. The reaction products of ezogabine, levetiracetam and topiramate were measured spectrophotometrically at 418, 390 and 380nm or spectrofluorimetrically at λ_em/ex of 495/425nm, 490/415nm and 488/410nm, respectively. Various experimental conditions have been carefully studied to maximize the reaction yield. At the optimum reaction conditions, the calibration curves were rectilinear over the concentration ranges of 8-25, 60-180 and 80-200μg/mL spectrophotometrically and 0.02-0.2, 0.2-1.2 and 0.2-1.5μg/mL spectrofluorimetrically for ezogabine, levetiracetam and topiramate, respectively with good correlation coefficients. The suggested methods were applied successfully for the analysis of ezogabine, levetiracetam and topiramate in their commercial tablets with high percentage recoveries and negligible interference from various excipients in pharmaceutical dosage forms. The results were statistically analyzed and showed the absence of any significant difference between both developed and published methods. The procedures were validated and evaluated by the ICH guidelines revealing good reproducibility and accuracy. Therefore, the two proposed methods may be considered of high interest for practical and reliable analysis of ezogabine, levetiracetam and topiramate in pharmaceutical dosage forms.

Chromatographic Characterization and Method Development for Determination of Levetiracetam in Saliva: Application to Correlation with Plasma Levels

Levetiracetam (LVT) is a widely used antiepileptic drug (AED). A less invasive sampling method for therapeutic drug monitoring (TDM) would be very useful particularly for children. Saliva has been shown as an adequate sample for TDM of some AEDs. Due to the high hydrophilicity of LVT its separation on common stationary phases is quite a challenge so that previous methods for determination of LVT in saliva employed either gradient high performance liquid chromatographic (HPLC) system or mass spectrometer as a detector. In this study the retention behavior of LVT on some common stationary phases was examined, with C8 being the most retentive. A simple isocratic HPLC method that is based on simple protein precipitation was developed and validated for the determination of LVT in saliva. The method was applied to a sample group of epileptic children for the purpose of assessing potential correlation with plasma LVT levels and to investigate patient's compliance. The results confirmed a reasonable correlation between plasma and salivary levels of LVT (R = 0.9) which supports the use of saliva for TDM of LVT. The study also revealed a significant percentage of epileptic patients having LVT levels below the estimated therapeutic range.

A simple and cost-effective HPLC-UV method for the detection of levetiracetam in plasma/serum of patients with epilepsy

A simple, fast and cost-effective method was developed and validated for the determination of levetiracetam (LEV) in plasma/serum of patients using high performance liquid chromatography (HPLC) with ultraviolet detection. The stability of LEV plasma/serum samples over time and in different blood collection tubes was evaluated. Serum/plasma samples were deproteinized by methanol spiked with the internal standard, gabapentin. HPLC was carried out on a Venusil XBP C₁₈ , 250 × 4.6 mm, 5 μm column, at a flow rate of 1.0 mL/min and with mobile phase consisting of 50 mm potassium dihydrogen phosphate-acetonitrile at a pH of 5.5. The UV detector was set at 205 nm and 10 μL was injected. Total runtime was 15 min. Calibration curves were linear (correlation coefficient = 0.999) over a concentration range of 1-60 μg/mL. Relative standard deviation values for both the inter-day and intra-day precision and accuracy were <5% for the concentration range. The influence of different collection tubes and the effect of time on the stability of LEV was investigated. These factors may cause inaccuracies owing to drug-protein binding and interference in the matrix. This method is simple, fast, cost-effective, reliable and accurate with minimal sample preparation for daily routine use in therapeutic drug monitoring.

Sensitive inexpensive HPLC determination of four antiepileptic drugs in human plasma: application to PK studies

Aim: Recently, polytherapy regimen has been introduced for the treatment of epileptic patients for better seizure control with lesser side effects and better control of multiple seizure types. Methodology: A simple, sensitive and highly specific reversed-phase HPLC method was developed for simultaneous determination of four antiepileptic drugs (AEDs), levetiracetam, lamotrigine, oxcarbazepine and carbamazepine, in real human plasma without interference from endogenous components of plasma. Conclusion: The method was proved to be linear in the range of 0.5–50 µg/ml for all drugs. It was successfully applied for clinical PK study of the AEDs in healthy volunteers following single administration. Also, this method was applied for simultaneous determination of the studied drugs in volunteers’ plasma receiving synergistic binary combinations from the four AEDs when used as add-on therapy. The good precision and selectivity of the developed method allow it to be used for routine therapeutic drug monitoring of such drugs as a useful tool in epilepsy management.

Determination of Levetiracetam in Human Plasma by Dispersive Liquid-Liquid Microextraction Followed by Gas Chromatography-Mass Spectrometry

Levetiracetam (LEV) is an antiepileptic drug that is clinically effective in generalized and partial epilepsy syndromes. The use of this drug has been increasing in clinical practice and intra- or -interindividual variability has been exhibited for special population. For this reason, bioanalytical methods are required for drug monitoring in biological matrices. So this work presents a dispersive liquid-liquid microextraction method followed by gas chromatography-mass spectrometry (DLLME-GC-MS) for LEV quantification in human plasma. However, due to the matrix complexity a previous purification step is required. Unlike other pretreatment techniques presented in the literature, for the first time, a procedure employing ultrafiltration tubes Amicon® (10 kDa porous size) without organic solvent consumption was developed. GC-MS analyses were carried out using a linear temperature program, capillary fused silica column, and helium as the carrier gas. DLLME optimized parameters were type and volume of extraction and dispersing solvents, salt addition, and vortex agitation time. Under chosen parameters (extraction solvent: chloroform, 130 μL; dispersing solvent: isopropyl alcohol, 400 μL; no salt addition and no vortex agitation time), the method was completely validated and all parameters were in agreement with the literature recommendations. LEV was quantified in patient's plasma sample using less than 550 μL of organic solvent.

Intrapatient variation in antiepileptic drug plasma concentration after generic substitution vs stable brand-name drug regimens

Generic substitution of antiepileptic drugs (AEDs) is still a matter of controversy and concern among clinicians and patients. We aimed to assess intrasubject variation in plasma concentrations of lamotrigine (LTG), levetiracetam (LEV) and topiramate (TPM) after generic substitution compared with a stable brand-name drug regimen in a population of patients with epilepsy. A retrospective analysis was performed on prospectively collected and stored data from our therapeutic drug monitoring (TDM) database for the years 2009-2014. The main outcome variable was the proportion of patients who, after switching from branded to generic formulations, showed a greater than ±20% change in AED plasma concentrations compared to the proportion of control patients showing a change in AED plasma concentrations of the same extent while receiving stable branded formulations over repeated TDM tests. Fifty patients on LTG, 27 on LEV and 16 on TPM showing at least one TDM test while receiving generic products fulfilled the inclusion/exclusion criteria for the analysis and were compared with 200 control patients for LTG, 120 for LEV and 80 for TPM. The proportion of patients showing an intrasubject change greater than ±20% in AED plasma concentrations was similar in the brand name vs generic group compared with the control one for LTG (22% vs 33%) and LEV (44% vs 38%), while it was higher in the control group for TPM (41% vs 6%, p<0.01). These are the first data in the literature about the within-patient variation in steady-state plasma concentrations of a series of stable treatments with brand-name AEDs in a real clinical setting. In conclusion, a significant interday variability in intrapatient LTG, LEV and TPM plasma concentrations can be observed even in patients stabilized with the same brand name product over time. This suggests that any change in plasma AED concentration and possible related clinical effects after generic substitution may be not necessarily related to the switch. Our results should be confirmed by large, prospective, blinded, randomized controlled studies in people with epilepsy.

Stir bar-sorptive extraction, solid phase extraction and liquid-liquid extraction for levetiracetam determination in human plasma: comparing recovery rates

<p>Levetiracetam (LEV), an antiepileptic drug (AED) with favorable pharmacokinetic profile, is increasingly being used in clinical practice, although information on its metabolism and disposition are still being generated. Therefore a simple, robust and fast liquid-liquid extraction (LLE) followed by high-performance liquid chromatography method is described that could be used for both pharmacokinetic and therapeutic drug monitoring (TDM) purposes. Moreover, recovery rates of LEV in plasma were compared among LLE, stir bar-sorptive extraction (SBSE), and solid-phase extraction (SPE). Solvent extraction with dichloromethane yielded a plasma residue free from usual interferences such as commonly co-prescribed AEDs, and recoveries around 90% (LLE), 60% (SPE) and 10% (SBSE). Separation was obtained using reverse phase Select B column with ultraviolet detection (235 nm). Mobile phase consisted of methanol:sodium acetate buffer 0.125 M pH 4.4 (20:80, v/v). The method was linear over a range of 2.8-220.0 µg mL^-1. The intra- and inter-assay precision and accuracy were studied at three concentrations; relative standard deviation was less than 10%. The limit of quantification was 2.8 µg mL^-1. This robust method was successfully applied to analyze plasma samples from patients with epilepsy and therefore might be used for pharmacokinetic and TDM purposes.</p>

Rapid and simultaneous quantification of levetiracetam and its carboxylic metabolite in human plasma by liquid chromatography tandem mass spectrometry

A simple liquid chromatography tandem mass spectrometry method was developed and validated according to the guidelines of the US Food and Drug Administration and the European Medicines Agency for a simultaneous quantification of levetiracetam (LEV) and its metabolite, UCB L057 in the plasma of patients. A 0.050 mL plasma sample was prepared by a simple and direct protein precipitation with 0.450 mL acetonitrile (ACN) containing 1 µg/mL of internal standard (IS, diphenhydramine), then vortex mixed and centrifuged. A 0.100 mL of the clear supernatant was diluted with 0.400 mL water and well mixed. A 0.010 mL of the resultant solution was injected into an Agilent Zorbax SB-C18 (2.1 mm×100 mm, 3.5 µm) column with an isocratic elution at 0.5 mL/min using a mixture of 0.1% formic acid in water and ACN (40:60 v/v). Detection was performed using an AB Sciex API 3000 triple quadrupole mass spectrometer, equipped with a Turbo Ion Spray source, operating in a positive mode: LEV at transition 171.1>154.1, UCB L057 at 172.5>126.1, and IS at 256.3>167.3; with an assay run time of 2 minutes. The lower limit of quantification (LLOQ) for both LEV and UCB L057 was validated at 0.5 µg/mL, while their lower limit of detection (LOD) was 0.25 µg/mL. The calibration curves were linear between 0.5 and 100 µg/mL for both analytes. The inaccuracy and imprecision of both intra-assay and inter-assay were less than 10%. Matrix effects were consistent between sources of plasma and the recoveries of all compounds were between 100% and 110%. Stability was established under various storage and processing conditions. The carryovers from both LEV and UCB L057 were less than 6% of the LLOQ and 0.13% of the IS. This assay method has been successfully applied to a population pharmacokinetic study of LEV in patients with epilepsy.

Development of new method for simultaneous analysis of piracetam and levetiracetam in pharmaceuticals and biological fluids: application in stability studies

RP-HPLC ultraviolet detection simultaneous quantification of piracetam and levetiracetam has been developed and validated. The chromatography was obtained on a Nucleosil C18 column of 25 cm×0.46 cm, 10 μm, dimension. The mobile phase was a (70:30 v/v) mixture of 0.1 g/L of triethylamine and acetonitrile. Smooth flow of mobile phase at 1 mL/min was set and 205 nm wavelength was selected. Results were evaluated through statistical parameters which qualify the method reproducibility and selectivity for the quantification of piracetam, levetiracetam, and their impurities hence proving stability-indicating properties. The proposed method is significantly important, permitting the separation of the main constituent piracetam from levetiracetam. Linear behavior was observed between 20 ng/mL and 10,000 ng/mL for both drugs. The proposed method was checked in bulk drugs, dosage formulations, physiological condition, and clinical investigations and excellent outcome was witnessed.

Population pharmacokinetics modeling of levetiracetam in Chinese children with epilepsy

AIM

To establish a population pharmacokinetics (PPK) model of levetiracetam in Chinese children with epilepsy.

METHODS

A total of 418 samples from 361 epileptic children in Peking University First Hospital were analyzed. These patients were divided into two groups: the PPK model group (n=311) and the PPK validation group (n=50). Levetiracetam concentrations were determined by HPLC. The PPK model of levetiracetam was established using NONMEM, according to a one-compartment model with first-order absorption and elimination. To validate the model, the mean prediction error (MPE), mean squared prediction error (MSPE), root mean-squared prediction error (RMSPE), weight residues (WRES), and the 95% confidence intervals (95% CI) were calculated.

RESULTS

A regression equation of the basic model of levetiracetam was obtained, with clearance (CL/F)=0.988 L/h, volume of distribution (V/F)=12.3 L, and K(a)=1.95 h(-1). The final model was as follows: K(a)=1.56 h(-1), V/F=12.1 (L), CL/F=1.04×(WEIG/25)(0.583) (L/h). For the basic model, the MPE, MSPE, RMSPE, WRES, and the 95%CI were 9.834 (-0.587-197.720), 50.919 (0.012-1286.429), 1.680 (0.021-34.184), and 0.0621 (-1.100-1.980). For the final model, the MPE, MSPE, RMSPE, WRES, and the 95% CI were 0.199 (-0.369-0.563), 0.002082 (0.00001-0.01054), 0.0293 (0.001-0.110), and 0.153 (-0.030-1.950).

CONCLUSION

A one-compartment model with first-order absorption adequately described the levetiracetam concentrations. Body weight was identified as a significant covariate for levetiracetam clearance in this study. This model will be valuable to facilitate individualized dosage regimens.

Transglycosylation specificity of Acremonium sp. α-rhamnosyl-β-glucosidase and its application to the synthesis of the new fluorogenic substrate 4-methylumbelliferyl-rutinoside

Transglycosylation potential of the fungal diglycosidase α-rhamnosyl-β-glucosidase was explored. The biocatalyst was shown to have broad acceptor specificity toward aliphatic and aromatic alcohols. This feature allowed the synthesis of the diglycoconjugated fluorogenic substrate 4-methylumbelliferyl-rutinoside. The synthesis was performed in one step from the corresponding aglycone, 4-methylumbelliferone, and hesperidin as rutinose donor. 4-Methylumbelliferyl-rutinoside was produced in an agitated reactor using the immobilized biocatalyst with a 16% yield regarding the sugar acceptor. The compound was purified by solvent extraction and silica gel chromatography. MALDI-TOF/TOF data recorded for the [M+Na](+) ions correlated with the theoretical monoisotopic mass (calcd [M+Na](+): 507.44 m/z; obs. [M+Na](+): 507.465 m/z). 4-Methylumbelliferyl-rutinoside differs from 4-methylumbelliferyl-glucoside in the rhamnosyl substitution at the C-6 of glucose, and this property brings about the possibility to explore in nature the occurrence of endo-β-glucosidases by zymographic analysis.

Modern methods for analysis of antiepileptic drugs in the biological fluids for pharmacokinetics, bioequivalence and therapeutic drug monitoring

Epilepsy is a chronic disease occurring in approximately 1.0% of the world's population. About 30% of the epileptic patients treated with availably antiepileptic drugs (AEDs) continue to have seizures and are considered therapy-resistant or refractory patients. The ultimate goal for the use of AEDs is complete cessation of seizures without side effects. Because of a narrow therapeutic index of AEDs, a complete understanding of its clinical pharmacokinetics is essential for understanding of the pharmacodynamics of these drugs. These drug concentrations in biological fluids serve as surrogate markers and can be used to guide or target drug dosing. Because early studies demonstrated clinical and/or electroencephalographic correlations with serum concentrations of several AEDs, It has been almost 50 years since clinicians started using plasma concentrations of AEDs to optimize pharmacotherapy in patients with epilepsy. Therefore, validated analytical method for concentrations of AEDs in biological fluids is a necessity in order to explore pharmacokinetics, bioequivalence and TDM in various clinical situations. There are hundreds of published articles on the analysis of specific AEDs by a wide variety of analytical methods in biological samples have appears over the past decade. This review intends to provide an updated, concise overview on the modern method development for monitoring AEDs for pharmacokinetic studies, bioequivalence and therapeutic drug monitoring.