Simultaneous determination of albendazole sulfoxide enantiomers and albendazole sulfone in plasma

Development and validation of stability indicating UPLC methods for related substances and assay analyses of ricobendazole hydrochloride

Ricobendazole hydrochloride is an active ingredient of a veterinary antiparasitic drug. The aim of this study was to investigate the degradation of ricobendazole hydrochloride under stress and stability testing conditions, for which we developed and validated the first stability indicating, specific, precise, accurate, and robust assay and related substances UPLC methods. The Acquity UPLC BEH C18 column was used for the related substances and assay analyses of ricobendazole hydrochloride, and the analyses were performed at 25 °C sample and 30 °C column temperatures with a 2 µL injection volume. In both methods, a mixture of water and methanol (60:40, v/v) was used as the diluent, mobile phase A was a phosphate buffer (50 mM potassium dihydrogen phosphate solution, pH 3.2 ± 0.05, adjusted with 10% o-phosphoric acid), and mobile phase B was a mixture of mobile phase A and acetonitrile (50:50, v/v). For the analysis of related substances, a gradient elution system was used at a flow rate of 0.4 mL/min for 35 min with a detection wavelength of 220 nm, while for the assay analysis; a gradient elution system was used at a flow rate of 0.3 mL/min for 15 min with a detection wavelength of 290 nm. The calibration curves showed excellent linearity with high R-squared (R2) values for each compound, ricobendazole (0.9998, 0.249 - 3.740 µg/mL), ricobendazole amine (0.9998, 0.255 - 3.819 µg/mL), albendazole (0.9998, 0.255 - 7.646 µg/mL), and albendazole sulfone (1.0000, 0.251 - 15.090 µg/mL) indicating a strong correlation between the concentrations of the compounds and their respective peak areas in the UPLC analysis. The method showed excellent accuracy with relative standard deviation values of less than 2.5%. The stress and photostability studies showed that ricobendazole hydrochloride was insensitive to daylight and UV radiation and showed significant degradation at elevated temperature (85 °C, 9 days) and under all hydrolysis and oxidation conditions. The major impurity was ricobendazole amine under thermal and hydrolysis conditions, while albendazole sulfone was the major oxidative impurity.

Update on the diagnosis and management of neurocysticercosis

ABSTRACT Background: Neurocysticercosis (NCC) is a serious public health problem in several developing countries, including those in Latin America, Asia, and Africa. NCC is considered to be the main cause of late-onset epilepsy in endemic areas. Objective: This review summarizes recent advances in diagnosis and therapy of NCC. Methods: Relevant articles and books were reviewed and used as a source of information for this review. Results: The diagnosis of NCC is based upon neuroimaging studies (MRI and computed tomography) and laboratory analysis of the cerebrospinal fluid (CSF). Praziquantel and albendazole are considered parasiticidal drugs against NCC, but there is an intense debate over the value and safety of these drugs. Conclusion: Given the relative scarcity of clinical trials, more comparative interventional studies, especially randomized controlled trials in long-term clinical evolution, are required in order to clarify the controversy over the validity of parasitic therapy in patients with NCC.

Assessment of the Performance of Solid Phase Extraction Based on Pipette Tip Employing a Hybrid Molecularly Imprinted Polymer as an Adsorbent for Enantioselective Determination of Albendazole Sulfoxide

Herein, an organic–inorganic hybrid molecularly imprinted polymer (MIP) was successfully synthesized with albendazole sulfoxide (ABZSO) as a template and 3-(trimethoxysilyl)propyl methacrylate, a bifunctional group compound, as a single cross-linking agent. In this study, a simple method using HPLC–DAD was developed for the determination of ABZSO enantiomers in human urine using pipette tip-based molecularly imprinted polymer solid phase extraction (PT–MIP–SPE). Enantioseparation with satisfactory retention times (5.17 and 7.09 min), acceptable theoretical plates (N = 4,535 and 5,091) and strong resolution (Rs = 5.45) was performed with an Agilent® Eclipse Plus C18 (100 mm × 4.6 mm, 3.5 μm) coupled with a Chiralpak® IA column (100 mm × 4.6 mm, 3 μm), a mixture with ethanol:water (50:50, v/v) as the mobile phase, temperature at 40°C, flow rate at 0.9 mL min−1 and λ = 230 nm. Thereafter, certain parameters affecting the PT–MIP–SPE were investigated in detail and the better conditions were: 300 μL of water as washing solvent, 500 μL of ethanol:acetic acid (9:1, v/v) as eluting solvent, 20 mg of MIP, 500 μL of human urine at pH 9 and no addition of NaCl. Recoveries/relative standard deviation (RSD%) for (R)-(+)-ABZSO and (S)-(−)-ABZSO were 78.2 ± 0.2% and 69.7 ± 1.7%, respectively.

Liquid chromatography--tandem mass spectrometry method for simultaneous determination of albendazole and albendazole sulfoxide in human plasma for bioequivalence studies

An improved high performance liquid chromatography--tandem mass spectrometry (LC–MS/MS) method has been developed for sensitive and rapid determination of albendazole (ABZ) and its active metabolite, albendazole sulfoxide (ABZSO), in the positive ionization mode. The method utilized solid phase extraction (SPE) for sample preparation of the analytes and their deuterated internal standards (ISs) from 100 µL human plasma. The chromatography was carried out on Hypurity C₁₈ column using acetonitrile-2.0 mM ammonium acetate, pH 5.0 (80:20, v/v) as the mobile phase. The assay exhibited a linear response over the concentration range of 0.200–50.0 ng/mL for ABZ and 3.00–600 ng/mL for ABZSO. The recoveries of the analytes and ISs ranged from 86.03%–89.66% and 89.85%–98.94%, respectively. Matrix effect, expressed as IS-normalized matrix factors, ranged from 0.985 to 1.042 for the both analytes. The method was successfully applied for two separate studies in healthy subjects using single dose of 400 mg conventional tablets and 400 mg chewable ABZ tablets, respectively.

Comparative plasma disposition kinetics of albendazole and its new benzimidazol prodrug in dog

The comparative pharmacokinetic behavior of albendazole (ABZ) and its new benzimidazol prodrug [1-tert-butyloxycarbonyl-5-propylthio-1-H-benzimidazol-2ylcarbamate of methyl] (ABZBoc), following their oral administration (10mg/kg) to healthy dogs was explored. Blood samples were obtained serially over a 24h period after treatment, then the plasma was analyzed by high-performance liquid chromatography (HPLC) to search the albendazole metabolites (ABZSO and ABZSO2). However, the albendazole parent drug was not detectable at any time after both treatments (ABZ and ABZBoc). By albendazole metabolites (ABZSO and ABZSO2) were the analytes recovered in the plasma after oral administration of ABZ and ABZBoc. Furthermore, some amounts of ABZBoc were also available in the plasma samples treated with this new produg. The plasma profile of each analyte followed a similar pattern after both treatments, the active metabolite (ABZSO) was the major analyte recovered in plasma (between 1 and 24h post-treatment). The pharmacokinetic parameters of both groups were calculated (Cmax, Tmax, t1/2, AUC0-›∞), and analyzed using the Student's t-test, P<0.05. Thus,the pharmacokinetic analysis indicated four statistically significant changes in the pharmacokinetic parameters defined above of the albendazole metabolites (ABZSO, ABZSO2) between the group treated with albendazole (group A) and that treated with ABZBoc prodrug (group B). Hence, the levels of the various pharmacokinetics parameters were low in the group treated with prodrug, as well they did not reach equivalent concentrations to that of albendazole. These differences between albendazole and its new prodrug may be explained by the fact that ABZBoc prodrug was not effectively reduced in the intestine of dogs.

Determination of albendazole and metabolites in silkworm Bombyx mori hemolymph by ultrafast liquid chromatography tandem triple quadrupole mass spectrometry

Albendazole is a broad-spectrum parasiticide with high effectiveness and low host toxicity. No method is currently available for measuring albendazole and its metabolites in silkworm hemolymph. This study describes a rapid, selective, sensitive, synchronous and reliable detection method for albendazole and its metabolites in silkworm hemolymph using ultrafast liquid chromatography tandem triple quadrupole mass spectrometry (UFLC-MS/MS). The method is liquid-liquid extraction followed by UFLC separation and quantification in an MS/MS system with positive electrospray ionization in multiple reaction monitoring mode. Precursor-to-product ion transitions were monitored at 266.100 to 234.100 for albendazole (ABZ), 282.200 to 208.100 for albendazole sulfoxide (ABZSO), 298.200 to 159.100 for albendazole sulfone (ABZSO₂) and 240.200 to 133.100 for albendazole amino sulfone (ABZSO₂-NH₂). Calibration curves had good linearities with R² of 0.9905–0.9972. Limits of quantitation (LOQs) were 1.32 ng/mL for ABZ, 16.67 ng/mL for ABZSO, 0.76 ng/mL for ABZSO₂ and 5.94 ng/mL for ABZSO₂-NH₂. Recoveries were 93.12%–103.83% for ABZ, 66.51%–108.51% for ABZSO, 96.85%–105.6% for ABZSO₂ and 96.46%–106.14% for ABZSO₂-NH₂, (RSDs <8%). Accuracy, precision and stability tests showed acceptable variation in quality control (QC) samples. This analytical method successfully determined albendazole and its metabolites in silkworm hemolymph in a pharmacokinetic study. The results of single-dose treatment suggested that the concentrations of ABZ, ABZSO and ABZSO₂ increased and then fell, while ABZSO₂-NH₂ level was low without obvious change. Different trends were observed for multi-dose treatment, with concentrations of ABZSO and ABZSO₂ rising over time.

Therapy for neurocysticercosis

Therapy for neurocysticercosis has advanced during the last 20 years with the advent of albendazole (Zentel) and praziquantel (Cysticide). Albendazole is the current medication of choice for the treatment of neurocysticercosis and is recommended for symptomatic patients with multiple viable cysts in the brain parenchyma. Albendazole may also be useful in extraparenchymal cysticercosis, especially in the subarachnoid racemose form, when complete surgical resection of the cysts is usually impracticable. Currently, there is an intense debate over the value and safety of anticysticercal therapy. Causes for failure of anticysticercal therapy include high inter-individual variability in plasma concentration of albendazole sulfoxide and the complex interactions of several drugs with the albendazole metabolite. Furthermore, albendazole sulfoxide is an enantiomeric mixture of (+)- and (-)-albendazole sulfoxide with accumulation of the (+)-enantiomer in the cerebrospinal fluid. However, the question over which enantiomer is effective against cysticerci remains to be clarified.

Medical management of neurocysticercosis

INTRODUCTION

Neurocysticercosis (NCC) is considered to be the most common cause of acquired epilepsy worldwide. Formerly restricted to palliative measures, therapy for NCC has advanced with the advent of two drugs that are considered to be effective: praziquantel (PZQ) and albendazole (ALB).

AREAS COVERED

All available articles regarding research related to the treatment of NCC were searched. Relevant articles were then reviewed and used as sources of information for this review.

EXPERT OPINION

Anticysticercal therapy has been marked by intense controversy. Recent descriptions of spontaneous resolution of parenchymal cysticercosis with benign evolution, risks of complications and reports of no long-term benefits have reinforced the debate over the usefulness and safety of anticysticercal therapy. High interindividual variability and complex pharmacological interactions will require the close monitoring of plasma concentrations of ALB and PZQ metabolites in future trials. Given the relative scarcity of clinical trials, more comparative interventional studies - especially randomized controlled trials in long-term clinical evolution - are required to clarify the controversy over the validity of parasitic therapy in patients with NCC.

Albendazole-praziquantel interaction in healthy volunteers: kinetic disposition, metabolism and enantioselectivity

AIM

This study investigated the kinetic disposition, metabolism and enantioselectivity of albendazole (ABZ) and praziquantel (PZQ) administered alone and in combination to healthy volunteers.

METHODS

A randomized crossover study was carried out in three phases (n= 9), in which some volunteers started in phase 1 (400 mg ABZ), others in phase 2 (1500 mg PZQ), and the remaining volunteers in phase 3 (400 mg ABZ + 1500 mg PZQ). Serial blood samples were collected from 0-48 h after drug administration. Pharmacokinetic parameters were calculated using a monocompartmental model with lag time and were analyzed using the Wilcoxon test; P ≤ 0.05.

RESULTS

The administration of PZQ increased the plasma concentrations of (+)-ASOX (albendazole sulphoxide) by 264% (AUC 0.99 vs. 2.59 µg ml(-1) h), (-)-ASOX by 358% (0.14 vs. 0.50 µg ml(-1) h) and albendazole sulfone (ASON) by 187% (0.17 vs. 0.32 µg ml(-1) h). The administration of ABZ did not change the kinetic disposition of (+)-(S)-PZQ (-)-(R)-4-OHPZQ or (+)-(S)-4-OHPZQ, but increased the plasma concentration of (-)-(R)-PZQ by 64.77% (AUC 0.52 vs. 0.86 µg ml(-1) h).

CONCLUSIONS

The pharmacokinetic interaction between ABZ and PZQ in healthy volunteers was demonstrated by the observation of increased plasma concentrations of ASON, both ASOX enantiomers and (-)-(R)-PZQ. Clinically, the combination of ABZ and PZQ may improve the therapeutic efficacy as a consequence of higher concentration of both active drugs. On the other hand, the magnitude of this elevation may represent an increased risk of side effects, requiring, certainly, reduction of the dosage. However, further studies are necessary to evaluate the efficacy and safety of this combination.

Development and optimization of a rapid HPLC method for analysis of ricobendazole and albendazole sulfone in sheep plasma

A simple, rapid and reliable high performance liquid chromatographic (HPLC) method has been developed and validated for simultaneous determination of ricobendazole (RBZ) and its main metabolite albendazole sulfone (ABZSO(2)) in sheep plasma using an isocratic system with UV detection. The method involved solid phase extraction followed by separation on a reversed phase C-18 column. Internal standard was selected by quantitative structure retention relationships (QSRRs) analysis. A method to optimize the composition of ternary components mobile phase with the assistance of multiple linear regression is described. Retention times were within 10 min. The calibration curves were linear over a concentration range of 10-1000 ng/ml for both RBZ and ABZSO(2) (r > 0.999). Intra-day relative standard deviation at low, medium and high concentration levels were <5.5% for RBZ and <4.6% for ABZSO(2); average accuracies were 98.3, 101.0 and 100.5% for RBZ and 101.0, 102.4 and 100.8% for ABZSO(2). The inter-day variations at the same concentrations were <5.9% for RBZ and <6.4% for ABZSO(2). The extraction recoveries at these concentrations for RBZ, ABZSO(2) and the internal standard were all over 96%. The limit of detection and limit of quantitation were 2.4 and 7.1 ng/ml, respectively for RBZ, and 10ng/ml for both analytes.

Analytical and semipreparative resolution of enatiomers of albendazole sulfoxide by HPLC on amylose tris (3,5-dimethylphenylcarbamate) chiral stationary phases

Broad spectrum anthelmintic agent-albendazole sulfoxide (ABZSO) have been separated and semiprepared on amylose tris (3,5-dimethylphenylcarbamate) chiral stationary phases by HPLC using mobile phases contained with n-hexane and different alcohols. For analytical separation the influence of the nature and content of alcoholic modifiers on separation were systemically studied. Then, the analytical methods were scaled up to semipreparative loading to obtain small quantities (about 1 g) of both ABZSO enantiomers. Especially, different loading amounts were investigated for their effect on various parameters of semipreparative HPLC. In addition, optical rotation and circular dichroism (CD) of both ABZSO enantiomers collected were determined and single enantiomers were found stable in configuration for 1 year.

Enantioselective renal excretion of albendazole metabolites in patients with neurocysticercosis

The present study investigates the urinary excretion of the enantiomers of (+)- and (-)-albendazole sulfoxide (ASOX) and albendazole sulfone (ASON) in 12 patients with neurocysticercosis treated with albendazole for 8 days (7.5 mg/kg/12 h). Serial blood samples (0-12 h) and urine (three periods of 8 h) were collected after administration of the last dose of albendazole. Plasma and urine (+)-ASOX, (-)-ASOX, and ASON metabolites were determined by HPLC using a chiral phase column (Chiralpak AD) with fluorescence detection. The pharmacokinetic parameters (P < 0.05) for (+)-ASOX, (-)-ASOX, and ASON metabolites are reported as means (95% CI); amount excreted (Ae) = 3.19 (1.53-4.85) vs. 0.72 (0.41-1.04) vs. 0.08 (0.03-0.13) mg; plasma concentration-time area under the curve, AUC(0-24) = 3.56 (0.93-6.18) vs. 0.60 (0.12-1.08) vs. 0.38 (0.20-0.55) microg x h/ml, and renal clearance Cl(R) = 1.20 (0.66-1.73) vs. 2.72 (0.39-5.05) vs. 0.25 (0.13-0.37) l/h. Sulfone formation capacity, expressed as the Ae ratio ASON/ASOX + ASON, was 2.21 (1.43-2.99). These data point to enantioselectivity in the renal excretion of ASOX as a complementary mechanism to the metabolism responsible for the plasma accumulation of (+)-ASOX. The results also suggest that the metabolite ASON is partially eliminated as a reaction product of the subsequent metabolism.

Quantitative determination of albendazole metabolites in sheep spermatozoa and seminal plasma by liquid chromatographic analysis with fluorescence detection

A new analytical method for the simultaneous quantitative determination of albendazole metabolites in sheep spermatozoa and seminal plasma at levels down to 46.5 ng/mL for albendazole sulphoxide (ABZ-SO), 7.5 ng/mL for albendazole sulphone (ABZ-SO2) and 12 ng/mL for albendazole 2-aminosulphone (ABZ-SO2NH2) has been developed. Analytes were extracted from alkalinized samples with ethyl acetate. Separation was carried out on a C18 column in the presence of tetra-n-butylammonium (TBA) hydrogen sulphate and octanesulphonate sodium (OCT), as ion-pair agents. Fluorometric detection was performed with excitation and emission wavelengths set at 290 and 320 nm, respectively. Accuracy data showed overall recoveries (+/-S.E.M.) of 83.1+/-1.2% for ABZ-SO, 98.8+/-0.6% for ABZ-SO2 and 85.3+/-0.7% for ABZ-SO2NH2, in spermatozoa. Respective values in seminal plasma were 88.0+/-0.9%, 97.7+/-0.5% and 93.2+/-1.7%. Precision data suggested coefficient of variation (CV%) values lower than 5.9% for spermatozoa and 3.8% for seminal plasma. The method was successfully applied for the determination of the three albendazole metabolites in semen samples collected from rams that had been orally administered albendazole.

Simultaneous determination of albendazole and its major active metabolite in human plasma using a sensitive and specific liquid chromatographic–tandem mass spectrometric method

A method for the simultaneous determination of albendazole (ABZ) and its major active metabolite albendazole sulfoxide (ABZ-SO) was developed and validated. The analytes were extracted from plasma samples by liquid-liquid extraction and analyzed using liquid chromatography-tandem mass spectrometry with an electrospray ionization interface. Estazolam was used as the internal standard. The assay was linear in the concentration range 0.4-200 ng/ml for ABZ and 4.0-2000 ng/ml for ABZ-SO. The intra- and inter-run precision (R.S.D.), calculated from quality control (QC) samples was less than 7.1 and 9.4% for ABZ and ABZ-SO, respectively. The accuracy as determined from QC samples was within +/- 3% for the analytes. Recoveries of ABZ and ABZ-SO were greater than 77 and 53%, respectively, over the calibration curve range. The method developed was successfully applied to pharmacokinetic studies of ABZ and ABZ-SO after an oral dose of 400 mg albendazole to healthy volunteers.

Reversed-phase liquid chromatographic method with fluorescence detection for the simultaneous determination of albendazole sulphoxide, albendazole sulphone and albendazole 2-aminosulphone in sheep plasma

A rapid and sensitive HPLC method for the simultaneous quantification of albendazole sulphoxide (ABZ-SO), albendazole sulphone (ABZ-SO2) and albendazole 2-aminosulphone (ABZ-SO2NH2) in sheep blood plasma has been developed. Plasma samples were extracted with ethyl acetate under alkaline conditions. Separation was achieved on a C18 reversed-phase analytical column, in the presence of positively- (tetra-n-butylammonium hydrogen sulphate) and negatively-charged (octanesulphonate sodium) pairing ions, while detection was performed fluorometrically. Excitation and emission wavelengths were 290 and 320 nm, respectively. Limits of quantification were defined at 39 ng/ml for ABZ-SO, 4.95 ng/ml for ABZ-SO2 and 4 ng/ml for ABZ-SO2NH2. Accuracy data, in terms of recovery efficiency showed overall values (+/- S.E.M.) of 85.6 +/- 1.0% for ABZ-SO, 100.0 +/- 1.0% for ABZ-SO2 and 89.1 +/- 0.6% for ABZ-SO2NH2. The method was successfully applied to quantitatively determine the three albendazole metabolites in plasma samples collected from sheep that had been orally administered albendazole.

Albendazole sulphoxide concentrations in plasma of endemic normals from a lymphatic filariasis endemic region using liquid chromatography

A simple and sensitive reversed-phase isocratic HPLC method for the determination of albendazole and its metabolites has been developed. The mobile phase consisting of acetonitrile-water-perchloric acid (70%) (30:110:0.06 (v/v/v)) was pumped at a flow rate of 0.80 ml/min on a 5 microm, reverse phase, Discovery RPamide C16 column with UV detection at 290 nm. The calibration graphs were linear in the range of 0.05- 1 microg/ml for albendazole, albendazole sulphoxide and albendazole sulphone. The limit of quantification was 50 ng/ml for albendazole, 25 ng/ml for albendazole sulphoxide and 30 ng/ml for albendazole sulphone. The within-day and day-to-day coefficient of variation averaged 4.98 and 6.95% for albendazole, 3.83 and 6.83% for albendazole sulphoxide and 3.44 and 5.51% for albendazole sulphone, respectively. The mean extraction recoveries of albendazole, albendazole sulphoxide and albendazole sulphone were 79.25, 93.03 and 88.78%, respectively. The method was applied to determine the plasma levels of albendazole sulphoxide in endemic normals administered with albendazole during pharmacokinetic studies.

Aspects of the pharmacokinetics of albendazole sulphoxide in sheep

The plasma disposition kinetics of albendazole sulphoxide (ABZSO), ((+)ABZSO and (-)ABZSO) and its sulphone metabolite (ABZSO2) were investigated in adult sheep. Six Corriedale sheep received albendazole sulphoxide by intravenous injection at 5 mg/kg live weight. Jugular blood samples were taken serially for 72 h and the plasma was analysed by high-performance liquid chromatography (HPLC) for albendazole (ABZ), ABZ sulphoxide (ABZSO) and albendazole sulphone (ABZSO2). Albendazole was not detected in the plasma at any time after the treatment, ABZSO and ABZSO2 being the main metabolites detected between 10 min and 48 h after treatment. A biexponential plasma concentration versus time curve was observed for both ABZSO and ABZSO2 following the intravenous treatment. The plasma AUC values for ABZSO and ABZSO2 were 52.0 and 10.8 (microg x h)/ml, respectively. The ABZSO2 metabolite was measurable in plasma between 10 min and 48 h after administration of ABZSO, reaching a peak concentration of 0.38 microg/ml at 7.7 h after treatment. Using a chiral phase-based HPLC method, a biexponential plasma concentration versus time curve was observed for both ABZSO enantiomers. The total body clearance was higher for the (-) than for the (+) enantiomer, the values being 270.6 and 147.75 (ml/h)/kg, respectively. The elimination half-life of the (-) enantiomer was shorter than that of the (+) enantiomer, the values being 4.31 and 8.33 h, respectively. The enantiomeric ratio (+)ABZSO/( )ABZSO at t0 was close to unity. However, the ratio in the plasma increased with time.

Two simple methods for the estimation of albendazole and its dosage forms using chloramine-T

Two simple, rapid and reliable methods for the determination of albendazole are described. Both methods involve the use of chloramine-T as the oxidimetric reagent. In the titrimetric method, a known excess of chloramine-T is added to an acidified solution of sample, and after a specified time, the residual oxidant is determined iodometrically. Spectrophotometric procedure also involves the addition of a measured excess of chloramine-T in buffer medium of pH 2.70+/-0.1 and after the reaction is ensured to be complete, the surplus oxidant is determined by a well established colour reaction involving metol and primary arylamine that results in charge-transfer complex measurable at 520 nm. In both methods, the amount of chloramine-T corresponds to the drug content. Reaction conditions were examined and optimised. Titrimetry is based on a 1:3 stoichiometric reaction between albendazole and chloramine-T and is applicable in the range of 1-15 mg. In spectrophotometry, the absorbance was found to decrease linearly with increasing concentration of albendazole, which is corroborated by the calculated correlation coefficient value of -0.9998. The system obeys Beer's law for 2.5-25 microg x ml(-1) of albendazole. The molar absorptivity and Sandell sensitivity were calculated to be 6.24 x 10(3) l mol(-1) cm(-1) and 42.54 ng cm(-2), respectively. The limits of detection and quantification were calculated to be 1.15 and 3.83 microg x ml(-1), respectively. The proposed methods were successfully applied to the determination of albendazole in commercially available dosage forms. The reliability of the assays was established by parallel determination by the official method and recovery studies.

Use of an oxidation reaction for the quantitative determination of albendazole with Chloramine-T and acid dyes

One titrimetric and two spectrophotometric procedures have been reported for the determination of albendazole and its tablets. Using titrimetry, the drug was titrated directly with Chloramine-T under acidic conditions using a Methyl Orange indicator. The spectrophotometric procedures involve treating the sample solution with a measured excess of Chloramine-T in an acid medium, followed by an estimation of unreacted Chloramine-T by reacting with a fixed amount of either Methyl Orange or Indigo Carmine dye solution and measuring the absorbance at 510 nm or 610 nm. The stoichiometric ratio, which forms the basis for the calculations in titrimetry as well as the range of the applicability, are reported. The Beer's law range and sensitivity values for spectrophotometric procedures are included. The methods were applied to the determination of albendazole in tablets with satisfactory results.

Albendazole sulphoxide enantiomers in pregnant rats' embryo concentrations and developmental toxicity

Three single oral doses (8.5, 10, and 14 mg/kg) of a racemic formulation of albendazole sulphoxide (ABZSO) were administered to pregnant rats on day 10 of gestation. Mother plasma and embryo concentrations of ABZSO enantiomers and albendazole sulphone (ABZSO(2)) were determined 9 h after administration. The (-)-ABZSO enantiomer showed higher peak concentrations in both maternal plasma and embryo than the (+) enantiomer. An increase in embryo concentrations of ABZSO enantiomers and ABZSO(2) was only observed when dose rose to 14 mg/kg. There was an increase in resorption when the dose increased, but significant differences were only found in the higher dose group when compared with the other groups. The incidence of external and skeletal malformations (mostly of the tail, vertebrae and ribs) rose significantly in the 10 mg/kg group, producing almost 20% and 90% of malformed fetuses, respectively, and gross external and skeletal abnormalities in the thoracic region and limbs were also found.

Simultaneous liquid chromatography-tandem mass spectrometric determination of albendazole sulfoxide and albendazole sulfone in plasma

This paper describes a simple, fast, sensitive and reliable method for the simultaneous determination of albendazole sulfoxide (ASOX) and albendazole sulfone (ASON), the two most important metabolites of the drug albendazole (ABZ), in plasma samples using liquid chromatography and tandem mass spectrometry. After liquid-liquid extraction with dichloromethane, the two albendazole metabolites and the internal standard phenacetin were resolved in a CN column using the mobile phase methanol-water (4:6, v/v) acidified with 1% acetic acid. Detection by electrospray mass spectrometry was carried out in the positive ion mode. The method was linear up to 2500 and 250 ng/ml for ASOX and ASON, respectively, with mean recoveries of more than 85%. The precision and accuracy data, based on within- and between-day variations over 5 days, were lower than 15%. The quantitation limits of 0.5 and 5.0 ng/ml for ASON and ASOX are low enough for the method to be suitable for pharmacokinetic studies. Pharmacokinetic data obtained with the proposed method following oral administration of ABZ to a patient with neurocysticercosis are also reported.

Separation of albendazole sulfoxide enantiomers by chiral supercritical-fluid chromatography

The enantioseparation of albendazole sulfoxide (ABZSO) by chiral supercritical-fluid chromatography (SFC) on two columns, based on the polysaccharide derivatives Chiralpak AD and Chiralcel OD, was studied. The effect of different modifiers, methanol, ethanol, 2-propanol, and acetonitrile, was examined. The results showed that ABZSO can be separated on both columns, using an alcohol-type modifier. Using the Chiralpak AD column, the best results were obtained with 2-propanol and, in the case of the Chiralcel OD, with methanol.

A high performance liquid chromatography method for simultaneous determination of albendazole metabolites in human serum

A simple assay for albendazole (ABZ) main metabolites-albendazole sulphoxide (ABZ-SO), albendazole sulphone (ABZ-SO(2)) and albendazole amino sulphone (ABZ-SO(2)-NH(2))-in serum using high performance liquid chromatography was developed. The method involves liquid-liquid extraction of the serum by ethyl acetate, clean up with n-hexane and re-extraction with ethyl acetate, followed by separation on RP-C(8) column with a mixture of methanol: acetonitrile: acetic acid: water (40:1:10:49) as the eluting solvent. ABZ-SO and mebendazole-used as internal standard-were detected by UV (lambda=286 nm), and ABZ-SO(2) and ABZ-SO(2)-NH(2) with fluorescence spectrophotometer at (Excitation=286 nm, Emission=333 nm) and (Excitation=286 nm, Emission=315 nm), respectively. The assay was accurate and reproducible with a detection limit of 10 ng/ml for ABZ-SO, 2 ng/ml for ABZ-SO(2) and 4 ng/ml for ABZ-SO(2)-NH(2). Disregarding ABZ determination, which is not of pharmacokinetic importance as it is not found in human plasma after oral administration, the proposed method is appropriate for further pharmacokinetic and metabolism study of this drug.

HPLC assay for albendazole and metabolites in human plasma for clinical pharmacokinetic studies

A sensitive and selective HPLC chromatography method using UV detection (295 nm) was developed for the determination of albendazole, albendazole sulfoxide (ABZSO), and albendazole sulfone (ABZSO2) in human plasma. Albendazole, ABZSO, ABZSO2, and the internal standard, oxibendazole, were extracted from human plasma by loading onto a conditioned C(18) SPE cartridge, rinsing with 15% methanol, and eluting with 90% methanol. Samples were evaporated under a stream of nitrogen, reconstituted with mobile phase, 1.25% triethylamine in water-methanol-acetonitrile (72:15:13, v/v/v) (pH* 3.1), and injected onto a Waters muBondapak Phenyl 3.9 x 300 mm HPLC column. Mobile phase flow rate was 1.0 ml/min. The retention times of albendazole, ABZSO, ABZSO2, and the internal standard were approximately 24.4, 7.9, 13.4, and 11.3 min, respectively. Total run time was 30 min. The assay was linear for concentration ranges in human plasma of 20-600 ng/ml for albendazole, 20-1000 ng/ml for ABZSO, and 20-300 ng/ml for ABZSO2. The analysis of quality control samples demonstrated excellent precision. Coefficients of variation for albendazole (20, 400, 600 ng/ml) were 6.7, 8.1 and 7.0%; ABZSO (20, 400, 800 ng/ml) were 6.0, 8.5 and 5.9%; ABZSO2 (20, 150, 300 ng/ml) were 3.1, 3.9 and 2.3%, respectively. The method appears to be robust and has been applied to a pharmacokinetic study of albendazole in healthy volunteers.

Enantioselective distribution of albendazole metabolites in cerebrospinal fluid of patients with neurocysticercosis

AIMS

Albendazole (ABZ) is effective in the treatment of neurocysticercosis. ABZ undergoes extensive metabolism to (+) and (-)-albendazole sulphoxide (ASOX), which are further metabolized to albendazole sulphone (ASON). We have investigated the distribution of (+)-ASOX (-)-ASOX, and ASON in cerebrospinal fluid (CSF) of patients with neurocysticercosis.

METHODS

Twelve patients with a diagnosis of active brain parenchymal neurocysticercosis treated with albendazole for 8 days (15 mg kg(-1) day(-1)) were investigated. On day 8, serial blood samples were collected during the dose interval (0-12 h) and one CSF sample was taken from each patient by lumbar puncture at different time points up to 12 h after the last albendazole dose. Albendazole metabolites were determined in CSF and plasma samples by h.p.l.c. using a Chiralpak AD column and fluorescence detection. Population curves for CSF albendazole metabolite concentration vs time were constructed.

RESULTS

The mean plasma/CSF ratios were 2.6 (95% CI: 1.9, 3.3) for (+)-ASOX and 2.7 (95% CI: 1.8, 3.7) for (-)-ASOX, with the two-tailed P value of 0.9873 being non-significant. These data indicate that the transport of ASOX through the blood-brain barrier is not enantioselective, but rather depends on passive diffusion. The present results suggest the accumulation of the (+)-ASOX metabolite in the CSF of patients with neurocysticercosis. The CSF AUC(+)/AUC(-) ratio was 3.4 for patients receiving albendazole every 12 h. The elimination half-life of both ASOX enantiomers in CSF was 2.5 h. ASOX was the predominant metabolite in the CSF compared with ASON; the CSF AUC(ASOX)/AUC(ASON) ratio was approximately 20 and the elimination half-life of ASON in CSF was 2.6 h.

CONCLUSIONS

We have demonstrated accumulation of the (+)-ASOX metabolite in CSF, which was about three times greater than the (-) antipode. ASOX concentrations were approximately 20 times higher than those observed for the ASON metabolite.

Pharmacokinetic interaction between albendazole sulfoxide enantiomers and antiepileptic drugs in patients with neurocysticercosis

The aim of the present investigation was to determine the interaction between the antiepileptic drugs (AEDs) phenytoin, carbamazepine, and phenobarbital and the enantioselective metabolism of albendazole. Thirty-two adults with a diagnosis of the active form of intraparenchymatous neurocysticercosis and treated with albendazole at the dose of 7.5 mg/kg every 12 hours for 8 days were studied. The patients were divided into four groups based on the combined use of AEDs or not: control group (n = 9), phenytoin group (n = 9 patients treated with 3-4 mg/kg/d sodium phenytoin), carbamazepine group (n = 9 patients treated with 10-20 mg/kg/d carbamazepine), and phenobarbital group (n = 5 patients treated with 1.5-4.5 mg/kg/d phenobarbital). Serial blood collections were carried out on day 8 of albendazole treatment during the last 12-hour dose interval. Plasma concentrations of the (+)- and (-)-albendazole sulfoxide (ASOX) and albendazole sulfone (ASON) metabolites were determined by high-performance liquid chromatography using a chiral phase column and fluorescence detection. The pharmacokinetic parameters were analyzed by analysis of variance followed by the Tukey-Kramer test. The results are reported as means. The following differences (P < 0.05) were observed between the control and the phenytoin, carbamazepine, and phenobarbital groups, respectively: (+)-ASOX area under the concentration-time curve for 0 to 12 hours after treatment (AUC(0-12)) 6.1, 2.1, 3.1, 2.4 microg/h/mL; (+)-ASOX maximum plasma concentration (C(max)) 0.8, 0.3, 0.4, 0.3 microg/mL; (+)-ASOX half-life (t1/2) 8.0, 3.8, 4.1, 4.9 h; (-)-ASOX AUC(0-12) 1.8, 0.4, 0.6, 0.5 microg/h/mL; (-)-ASOX C(max) 0.2, 0.06, 0.1, 0.1 microg/mL; (-)-ASOX (t(1/2)) 4.3, 1.9, 2.2, 2.1 h; ASON AUC(0-12) 0.5, 0.2 microg/h/mL; ASON C(max) 0.8, 0.3, 0.4, 0.3 microg/mL; ASON (t(1/2)) 8.0, 3.8, 4.1 h. The results show that phenytoin, carbamazepine, and phenobarbital induce to approximately the same extent the oxidative metabolism of albendazole in a nonenantioselective manner. Notably, a significant reduction in the plasma concentration of the active ASOX metabolite was observed in patients with neurocysticercosis treated with these AEDs.

Placental transfer of albendazole sulphoxide enantiomers in sheep

Albendazole sulphoxide (ABZSO) is an anthelmintic drug used in veterinary practice. Its molecule has a chiral centre in the sulphur atom and racemic formulations are always used. The kinetics of the ABZSO enantiomers in the last third of pregnancy in ewes, and the placental transfer to the fetus, were studied after a single-dose oral administration (7.5 mg/kg) of a racemic formulation. In mothers, the area under the plasma concentration-time curve (AUC) and C(max) values of (+)-ABZSO (42.4+/-10.5 microg/mL and 1.9+/-0.4 microg/mL, respectively) were higher than those of (-)-ABZSO (15.3+/-5.1 microg/mL and 1.0+/-0.3 microg/mL). The MRT values were 17.0+/-1.6 h for (+)-ABZSO and 13.1+/-1.8 h for (-)-ABZSO. Similar kinetic parameters were obtained in the fetus for both enantiomers, but the fetal concentrations were lower compared with values for the dam. The AUC ratio between (-)-ABZSO/(+)-ABZSO in the dam was 0.36 and in the fetuses 0.64, indicating a higher impairment for the (+)-enantiomer in its placental transfer to the fetus.

Albendazole metabolism in patients with neurocysticercosis: antipyrine as a multifunctional marker drug of cytochrome P450

The present study investigates the isoform(s) of cytochrome P450 (CYP) involved in the metabolism of albendazole sulfoxide (ASOX) to albendazole sulfone (ASON) in patients with neurocysticercosis using antipyrine as a multifunctional marker drug. The study was conducted on 11 patients with neurocysticercosis treated with a multiple dose regimen of albendazole for 8 days (5 mg/kg every 8 h). On the 5th day of albendazole treatment, 500 mg antipyrine was administered po. Blood and urine samples were collected up to 72 h after antipyrine administration. Plasma concentrations of (+)-ASOX, (-)-ASOX and ASON were determined by HPLC using a chiral phase column and detection by fluorescence. The apparent clearance (CL/f) of ASON and of the (+) and (-)-ASOX enantiomers were calculated and compared to total antipyrine clearance (CL(T)) and the clearance for the production of the three major antipyrine metabolites (CLm). A correlation (P<or=0.05) was obtained only between the CL(T) of antipyrine and the CL/f of ASON (r = 0.67). The existence of a correlation suggests the involvement of CYP isoforms common to the metabolism of antipyrine and of ASOX to ASON. Since the CL(T) of antipyrine is a general measure of CYP enzymes but with a slight to moderate weight toward CYP1A2, we suggest the involvement of this enzyme in ASOX to ASON metabolism in man. The study supports the establishment of a specific marker drug of CYP1A2 in the study of the in vivo metabolism of ASOX to ASON.

Capillary electrophoresis with (R)-(--)-N-(3,5-dinitrobenzoyl)-alpha-phenylglycine as chiral selector for separation of albendazole sulfoxide enantiomers and their analysis in human plasma

The electrokinetic separation and analysis of the enantiomers of albendazole sulfoxide (ABZSO), a sulfoxide with a sulfur stereogenic center hepatically formed during therapy with the anthelmintic drug albendazole (ABZ), is reported. Using aqueous or nonaqueous alkaline background electrolytes, ABZSO enantiomers cannot be separated via single use of common neutral cyclodextrins and negatively charged carboxymethyl-beta-cyclodextrin. With the Pirkle-type (R)-(-)-N-(3,5-dinitrobenzoyl)-alpha-phenylglycine ((R)-DNBPG) chiral selector, however, ABZSO enantiomers do separate within a borate background electrolyte of pH 9.0-9.5 and can be detected by UV absorbance at 295 nm. Having untreated fused-silica capillaries and 50 mM (R)-DNBPG, enantiomeric resolution is dependent on capillary i.d., capillary length and operational temperature. Optimized separation is obtained for pH 9.25 and the lowest temperature setting. Preliminary data indicate that the same approach could be employed for analysis of the enantiomers of oxfenbendazole, a chiral anthelmintic sulfoxide employed in veterinary pharmacotherapy. Analysis of plasma extracts of patients under ABZ pharmacotherapy confirmed the known enantioselectivity in the sulfoxidation of ABZ with the (+)-ABZSO being the predominant enantiomer in blood. Commencing with 2 ml of plasma, enantiomers present at >1 microg/ml could be detected only, a limitation which is based upon the strong absorbance of the chiral selector. (R)-DNBPG and ABZSO are negatively charged at pH 9.0-9.5, which prevents the application of a partial filling technique. The mobility of (R)-DNBPG is significantly larger compared to that of ABZSO. A migrating plug-plug approach based upon a plug of (R)-DNBPG migrating across the sample plug in an electroosmosis free environment obtained via a dynamic coating produced by spermine is shown to provide chiral resolution but not increased sensitivity.

Enantioselective analysis of albendazole sulfoxide in cerebrospinal fluid by capillary electrophoresis

Albendazole (ABZ) is a benzimidazole anthelmintic drug used in the treatment of neurocysticercosis. After oral administration, ABZ is rapidly oxidized to albendazole sulfoxide (ABZSO), which has an asymmetric sulfur center, and later to albendazole sulfone (ABZSO2). ABZSO is the active metabolite responsible for the therapeutic effect of the drug. Previous studies have demonstrated pharmacokinetic differences between the two enantiomers, with the predominance of (+)-ABZSO in human biological fluids. This article describes for the first time the enantioselective analysis of ABZSO in cerebrospinal fluid (CSF) using capillary electrophoresis. The samples were prepared by liquid-liquid extraction using chloroform:isopropanol (8:2 v/v). The resolution of ABZSO enantiomers was obtained with a fused-silica capillary (60 cm x 75 microm ID) using 20 mmol/L Tris, pH 7.0, with 3.0% w/w sulfated beta-cyclodextrin as running buffer. The coefficient of variations and % relative error obtained for both within-day and between-days assays were lower than 15%. The method was linear over the concentration range of 100 to 2,500 ng/mL for each enantiomer, indicating that it is suitable for the analysis of ABZSO enantiomers in CSF from patients medicated with ABZ.

Albendazole sulphoxide enantiomeric ratios in plasma and target tissues after intravenous administration of ricobendazole to cattle

The comparative concentration profiles of the (+) and (-) albendazole sulphoxide (ABZSO) enantiomers obtained in plasma and in selected target tissues/fluids after intravenous (i.v.) administration of a racemic formulation of ricobendazole (RBZ) to cattle were characterised. Fourteen Holstein calves received RBZ (racemic solution, 150 mg/mL) by i.v. administration at 7.5 mg/kg. Jugular blood samples were collected over 48 h post-treatment (plasma kinetic trial) and two animals were sacrificed at either 4, 12, 20, 28 or 32 h post-treatment to obtain samples of abomasal/small intestine mucosal tissue, abomasal/small intestine fluids, bile, liver and lung tissue (tissue distribution study). The (-)ABZSO enantiomer was depleted significantly faster from plasma compared with the (+)ABZSO antipode. The plasma AUC for (+)ABZSO (38.3 microg. h/mL) was significantly higher (P < 0.05) compared with that obtained for (-)ABZSO (20.5 microg. h/mL). The (+)ABZSO enantiomer was the predominant antipode measured in bile, abomasal fluid and abomasal mucosa. For instance, at 12 h post-treatment the (+)/(-) concentration ratios were: 12.9 (plasma), 1.62 (abomasal mucosa), 13.0 (abomasal fluid), 2.92 (intestinal mucosa), 9.87 (intestinal fluid) and 21.5 (bile). No marked differences between the concentration profiles of both enantiomers were observed in the liver tissue. Albendazole (ABZ) was recovered from the liver, lung and gastrointestinal (GI) mucosal tissues of RBZ-treated calves up to 32 h post-treatment, probably produced by a GI microflora-mediated sulphoreduction of RBZ. An enantioselective kinetic behaviour may account both for the faster depletion of the (-) enantiomer and for the higher availabilities of the (+) antipode observed in plasma and in most of the tissues/fluids investigated. The simultaneous evaluation of the plasma kinetics and tissue concentration profiles of both enantiomeric forms reported here, may help to interpret the relationship between chiral behaviour and pharmacological action for sulphoxide derivatives of benzimidazole (BZD) methylcarbamate anthelmintics.

Enantioselective analysis of disopyramide and mono-N-dealkyldisopyramide in plasma and urine by high-performance liquid chromatography on an amylose-derived chiral stationary phase

An enantioselective high-performance liquid chromatography method was developed for the simultaneous determination of disopyramide (DP) and mono-N-dealkyldisopyramide (MND) enantiomers in plasma and urine. The drugs were extracted from plasma samples by liquid-liquid extraction with dichloromethane after protein precipitation with trichloroacetic acid; the urine samples were processed by liquid-liquid extraction with dichloromethane. The enantiomers were resolved on a Chiralpak AD column using hexane-ethanol (91:9, v/v) plus 0.1% diethylamine as the mobile phase and monitored at 270 nm. Under these conditions the enantiomeric fractions of the drug and of its metabolite were analyzed within 20 min. The extraction procedure was efficient in removing endogenous interferents and low values for the relative standard deviations were demonstrated for both within-day and between-day assays. The method described in this paper allows the determination of DP and MND enantiomers at plasma levels as low as 12.5 ng/ml and can be used in clinical pharmacokinetic studies.

Pharmacokinetic behaviour of albendazole sulphoxide enantiomers in male and female sheep

Benzimidazole anthelmintic drugs are widely used in veterinary practice. Albendazole sulphoxide (ABZSO) is a benzimidazole drug with two enantiomers, as a consequence of a chiral centre in the sulphoxide group. The kinetics of these enantiomers were studied in male and female sheep. Plasma samples were obtained from the animals between 0.5 and 72 h after oral administration of 7.5 mg/kg of a racemic formulation of ABZSO (total-ABZSO). After a liquid-liquid extraction, the samples were analysed by HPLC to determine the concentrations of total-ABZSO and of the sulphone metabolite (ABZSO2). During the chromatographic analysis, the ABZSO peak was collected and reanalysed by an HPLC technique using a Chiral AGP column to quantify the enantiomeric proportion therein. After kinetic analysis, the AUCs obtained for the (+)-ABZSO were 5.8 and 4.0 times higher than those for the (-)-ABZSO in male and female animals, respectively. The mean residence times were 23.4 and 16.1 h for (+)-ABZSO and 22.2 and 17.4 h for (-)-ABZSO for male and female animals, respectively. The only significant difference between the sexes (p < 0.05) was in the Tmax of the (-)-ABZSO. Comparing both enantiomers within each sex, significant differences were found in all the kinetic parameters. Finally, no kinetic differences were found between sex for total-ABZSO or ABZSO2.

Enantioselective kinetic disposition of albendazole sulfoxide in patients with neurocysticercosis

The enantioselectivity of the kinetic disposition of albendazole sulfoxide (ASOX) was investigated in 18 patients with neurocysticercosis treated with a multiple dose regimen of albendazole for 8 days (5 mg/kg every 8 h). Serial blood samples were collected on the eighth day of treatment during the last dose interval, with prorogation up to 12 h. Albendazole sulfone (ASON) and enantiomers of ASOX were analyzed in plasma samples by HPLC using a Chiralpak AD column and detection by fluorescence. The pharmacokinetic parameters showing statistically significant differences between the (+) ASOX and (-) ASOX enantiomers are presented as respective means (95% CI) as follows: maximum plasma concentration, Cmax = 301.6 (179.7-423.5) vs 54.9 (21.9-87.9) ng.ml-1; elimination half-life, t1/2 = 5.2 (4.1-6.3) vs 3.3 (2.8-3.8) h, area under the plasma concentration-time curve, AUCss0-8 = 1719.2 (978.6-2459.8) vs 261.4 (102.9-419.8) ng.h.ml-1 and apparent clearance, Cl/fm = 5.8 (3.8-7.8) vs 54.0 (35.2-72.7) l.h-1.kg-1. The mean value of 9.2 (7.6-10.9) for the AUC0-8(+)-ASOX/AUC0-8(-)-ASOX ratio demonstrated plasma accumulation of the (+) enantiomer. Sulfone formation capacity, expressed by the AUCss0-8 ratio ASON/ASOX + ASON, was 8.0 (7.0-8.9). The present data indicate enantioselectivity in the kinetic disposition of ASOX in patients with neurocysticercosis.

Therapeutic drug monitoring of albendazole: determination of albendazole, albendazole sulfoxide, and albendazole sulfone in human plasma using nonaqueous capillary electrophoresis

A nonaqueous capillary electrophoretic method (NACE) for the fast determination of plasma levels of albendazole (ABZ), albendazole sulfoxide (ABZSO), and albendazole sulfone (ABZSO2) is described. The assay is based upon liquid/liquid extraction of these compounds using dichloromethane at pH 10.2 (recovery between 63 and 98%), followed by a NACE separation performed within 8 min employing a 0.036 M borate buffer (apparent pH 9.9) in a mixture of methanol and N-methylformamide (1:3) and on-column absorbance detection at 280 nm. Using 0.5 mL of plasma and extract reconstitution in 200 microL N-methylformamide, drug levels between 1.0-10 microM were found to provide linear calibration graphs. Intraday and interday imprecisions evaluated from peak area ratios (n = 5) were <10% and <12%, respectively. Corresponding imprecisions of detection times (n = 5) were <1% and <6%, respectively. The limit of detection (LOD) for ABZ, ABZSO and ABZSO2 was 8 x 10(-7) M. The reliability of the method developed was verified via analysis of 45 plasma samples obtained from patients treated with ABZ. Good agreement was obtained between the levels of ABZSO and those determined by routine HPLC. ABZ was found to be undetectable in all patient samples, whereas the levels of ABZSO2 were below or close to LOD.

Determination of albendazole and its main metabolites in ovine plasma by liquid chromatography with dialysis as an integrated sample preparation technique

Albendazole is a benzimidazole derivative with a broad-spectrum activity against human and animal helminth parasites. In order to determine the main pharmacokinetic parameters in sheep after oral and intravenous administration of a new formulation of albendazole (an aqueous solution), a fully automated method was developed for the determination of this drug and its main metabolites, albendazole sulfoxide (active metabolite) and sulfone in ovine plasma. This method involves dialysis as purification step, followed by enrichment of the dialysate on a precolumn and liquid chromatography (LC). All sample handling operations were executed automatically by means of an ASTED XL system. After conditioning of the trace enrichment column (TEC) packed with octadecyl silica with pH 6.0 phosphate buffer containing sodium azide, the plasma sample, in which a protein releasing reagent (1 M HCl) containing Triton X-100 was automatically added, was loaded in the donor channel and dialysed on a cellulose acetate membrane in the static-pulsed mode. The dialysis liquid consisted of pH 2.5 phosphate buffer. By rotation of a switching valve, the analytes were eluted from the TEC in the back-flush mode by the LC mobile phase and transferred to the analytical column, packed with octyl silica. The chromatographic separation was performed at 35 degrees C and the analytes were monitored photometrically at 295 nm. Due to the differences in hydrophobic character between albendazole and its metabolites, a gradient elution was applied. The mobile phase consisted of a mixture of acetonitrile and pH 6.0 phosphate buffer. The proportion of organic modifier was increased from 10.0 to 50.1% in 12.30 min, then from 50.1 to 66.9% in 1.70 min. First, the gradient conditions and the temperature were optimised for the LC separation using the DryLab software. Then, the influence of some parameters of the dialysis process on analyte recovery was investigated. Finally, the method developed was validated. The mean recoveries for albendazole and its metabolites were about 70 and 65%, respectively. The limits of quantification for albendazole and its metabolites were 10 and 7.5 ng/ml, respectively.