Quantification of Antimalarial Bisthiazolium Compounds and Their Neutral Bioprecursors in Plasma by Liquid Chromatography-Electrospray Mass Spectrometry

Background: A new class of antimalarial drugs targeting membrane biogenesis during intraerythrocytic Plasmodium falciparum development has been identified. The bisthiazolium salts T3 and T4 have superior in vitro and in vivo parasite-killing properties and need to be monitored.

Methods: We used a liquid chromatography–electrospray ionization mass spectrometry method (positive mode) to quantify two bisthiazolium compounds (T3 and T4) and a related prodrug (TE4c) in human and rat plasma. Verapamil was used as internal standard. Verapamil and the TE4c compound were characterized by protonated molecules at m/z 455.7 and m/z 725.7, respectively. T3 and T4 were detected through two ions [M2+/2] at m/z 227.7 and m/z 241.8 and by their adducts with trifluoroacetic acid [M+TFA]+ at m/z 568 and m/z 596, respectively. The sample clean-up procedure involved solid-phase extraction. HPLC separation was performed on a reversed-phase column, using a water–acetonitrile gradient, with both solvents containing TFA. Stability under various conditions was also investigated.

Results: The peak-area ratios (drugs/internal standard) were linked to concentrations (6.4–1282 μg/L for T3; 6.5–1309.8 μg/L for T4; 20–2000 μg/L for TE4c) according to a quadratic equation. The accuracy ranged from 85% to 113.1%, and the imprecision from 2.2% to 15%. The mean extraction recoveries were 87%, 98%, and 80% for T3, T4, and TE4c, respectively. The lower limit of quantification was 6.4 μg/L for the two bisthiazolium compounds, whereas it was 20 μg/L for TE4c, the related lipophilic prodrug.

Conclusion: This highly specific and sensitive method is suitable for analyzing samples collected during preclinical pharmacokinetic studies in rats and to determine the percentage binding of T3 and T4 to human plasma proteins.

A Simple and Sensitive Fully Validated HPLC-UV Method for the Determination of 5-Fluorouracil and Its Metabolite 5,6-Dihydrofluorouracil in Plasma

The authors developed a simple and sensitive, fully validated HPLC-UV method for the determination of both 5-FU and its metabolite DHFU in small-volume plasma samples. The analytes were separated on a 4.6 x 250 mm ID Atlantis dC18 5-microm column with isocratic elution at room temperature. Chlorouracil was used as internal standard. The analytes were detected with an UV diode array detector. DHFU was detected at 205 nm, 5-FU at 266 nm, and chlorouracil at both wavelengths. The limits of quantification in plasma were 0.040 mug /mL for 5-FU and 0.075 microg/mL for DHFU. Linearity, accuracy, precision, recovery, dilution, freeze-thaw stability, and stability in the sample compartment were evaluated. The method appeared linear over a range from 0.04 to 15.90 microg/mL for 5-FU and from 0.075 to 3.84 microg/mL for DHFU. The method appeared very suitable for therapeutic drug monitoring and pharmacokinetic studies of 5-FU because of its simple extraction and small sample volume. Problems in earlier published methods with interfering peaks and variable retention times were overcome. The method appeared also to be suitable for detection of uracil and its metabolite dihydrouracil in plasma.

Evaluation of the immunotech cyclosporine direct radioimmunoassay for the determination of whole-blood cyclosporine in renal transplant patients

Therapeutic drug monitoring (TDM) of cyclosporine (CsA) has been an accepted as an essential tool in the management of solid organ transplant recipients. The authors evaluated a new CsA method, Immunotech cyclosporine direct radioimmunoassay (Beckman Coulter, Prague, Czech Republic), for the measurement of whole-blood CsA concentrations. The performance was compared with CEDIA Plus method as well as group mean data for HPLC and other immunoassays available from the International CsA Proficiency Testing Program (www.bioanalytics.co.uk). Regression analysis of patient samples gave a relationship of RIA = 1.0822 CEDIA(+) + 69.84 (r(2) = 0.933). External CsA-spiked proficiency-testing (PT) samples gave a regression equation of RIA = 0.9672 CEDIA(+) + 4.99 (r(2) = 0.996). The correlation with the CEDIA Plus method using patient specimens (hence, including CsA metabolites) suggested that the test RIA method possibly had slightly inferior specificity for parent CsA. The results suggest that the Immunotech cyclosporine direct RIA kit is suitable for the measurement of whole-blood CsA concentrations and maintained clinically acceptable analytic precision and accuracy, displaying CVs of less than 15% and biases of less than 10%. The PT program CsA-metabolite-free samples showed that calibration between methods was comparable with the possible exception of mFPIA/TDx.

Enantioselective analysis of the metabolites of hydroxychloroquine and application to an in vitro metabolic study

A one-step chiral method for the quantification of the enantiomers of two hydroxychloroquine (HCQ) metabolites, desethylchloroquine (DCQ) and desethylhydroxychloroquine (DHCQ) by HPLC is described, in addition to its application to the in vitro study of HCQ metabolism in rat liver microsomes. Liquid-liquid extraction was used to extract the enantiomers from microsome samples and the separation was performed on a Chiralpak AD-RH column protected with an RP-8 guard column using hexane:isopropanol (92:8, v/v) plus 0.1% diethylamine as the mobile phase, at a flow rate of 1.0 mL min(-1). The detection was carried out at 343 nm. The method proved to be linear in the range of 50-5000 ng mL(-1) for DCQ enantiomers and 125-2500ngmL(-1) for DHCQ enantiomers, with a quantification limit of 50 and 125 ng mL(-1), respectively. Precision and accuracy, demonstrated by within-day and between-day assays, were lower than 15%. The metabolic study demonstrated that metabolism is stereoselective for HCQ. The major metabolites formed in the incubation of racemic HCQ were (-)-(R)-DCQ and (-)-(R)-DHCQ with R/S ratios of 2.2 and 3.3, respectively.

Simultaneous quantitation of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide and celecoxib in plasma by high-performance liquid chromatography with UV detection

A specific, accurate, precise and reproducible high performance liquid chromatography (HPLC) method was developed and validated for the simultaneous quantitation of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide and celecoxib in human plasma. The method employed a simple liquid-liquid extraction of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide and celecoxib and internal standard (IS, DRF-4367) from human plasma (500 microL) into acetonitirile. The organic layer was separated and evaporated under a gentle stream of nitrogen at 40 degrees C. The residue was reconstituted in the mobile phase and injected onto a Kromasil KR 100-5C18 column (4.6 x 250 mm, 5 microm). The chromatographic separation was achieved by gradient elution consisting of 0.05 M formic acid (pH 3)-acetonitrile-methanol-water at a flow rate of 1.0 mL/min. The eluate was monitored using an ultraviolet (UV) detector set at 235 nm. The ratio of peak area of each analyte to IS was used for quantification of plasma samples. Nominal retention times of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide, IS and celecoxib were 15.63, 17.20, 21.66, 24.95, 26.27, 30.24 and 32.22 min, respectively. The standard curve for etoricoxib, salicylic acid, valdecoxib, ketoprofen and celecoxib was linear (r2 > 0.999) in the concentration range 0.1-50 microg/mL and for nimesulide (r2 > 0.999) in the concentration range 0.5-50 microg/mL. Absolute recovery was >83% from human plasma for all the analytes and IS. The lower limit of quantification (LLOQ) of nimesulide was 0.5 microg/mL and for etoricoxib, salicylic acid, valdecoxib, ketoprofen and celecoxib the LLOQ was 0.1 microg/mL. The inter- and intra-day precisions in the measurement of QC samples, 0.1, 0.3, 15.0 and 40.0 microg/mL (for all analytes except nimesulide), were in the range 2.29-9.37% relative standard deviation (RSD) and 0.69-10.28% RSD, respectively. For nimesulide the inter- and intra-day precisions in the measurement of quality control (QC) samples, 0.5, 1.5, 15.0 and 40.0 microg/mL, were in the range 3.21-7.37% RSD and 0.97-7.06% RSD, respectively. Accuracy in the measurement of QC samples for all analytes was in the range 91.03-106.38% of the nominal values. All analytes including IS were stable in the battery of stability studies, viz. bench top, autosampler and freeze-thaw cycles. Stability of all analytes was established for 21 days at -20 degrees C. The application of the assay in an oral pharmacokinetic study in rats co-administered with celecoxib and valdecoxib is described.

Determination of picroside II in dog plasma by HPLC and its application in a pharmacokinetics study

A sensitive and simple high-performance liquid chromatography method with UV detection was developed and validated for determining picroside II in dog plasma. Paeoniflorin was employed as internal standard and the sample pre-treatment procedure consists of deproteinization by addition of acetonitrile. Chromatographic separations were performed on a Shimadzu VP-ODS column (250 x 4.6 mm i.d., 5 microm). The mobile phase consisted of acetonitrile-0.1% acetic acid aqueous (v/v), 23:77, v/v, at a rate of 1 mL/min. Detection was carried out at a wavelength of 266 nm. Calibration standards ranged from 0.25 to 500 microg/mL in dog plasma and the mean correlation coefficient of 0.9981 was found for the linear calibration curves (n = 6). The limit of quantification (LOQ) was 0.25 microg/mL. Intra- and inter-assay RSD ranged from 0.70 to 7.5%. Accuracy (%bias) ranged from -6.3 to 6.0%. This method was applied to the pharmacokinetic study of picroside II in dogs. The study demonstrated the plasma picroside II concentration-time curves were fitted to the two-compartment open model and showed linear pharmacokinetics.

Liquid chromatography determination of residue levels on apples treated with cetylpyridinium chloride

Cetylpyridinium chloride (CPC) has been found to be effective in reducing microbial contamination in apples. A sensitive and specific HPLC method was developed to determine CPC residues in apples treated with CPC. This method involves ion exchange solid-phase extraction, and the use of stearylpyridinium chloride (SPC) as internal standard. Limit of quantitation, was 0.5 microg/ml of CPC for the apple ethanolic extracts. The observed residues in apple (2.35-4.35 microg/g of apple) were lower than those previously reported for chicken and beef. The method is specific, sensitive, reproducible and accurate.

Development and validation of a fully automated LC method for the determination of cloxacillin in human plasma using anion exchange restricted access material for sample clean-up

In the framework of a preliminary investigation on the plasma profile of cloxacillin after oral administration, a simple and rapid LC method was developed for the direct determination of this compound in human plasma. The on-line sample clean-up was carried out using a weak anion exchanger (diethylaminoethyl groups) as restricted access material (RAM). The effects of the washing liquid pH, the ionic strength and the addition of organic modifier to the washing liquid were studied in order to obtain an efficient sample clean-up and a high recovery of cloxacillin. The separation was achieved on octadecylsilica stationary phase using a mobile phase consisting in a mixture of phosphate buffer (pH 4.0; 25 mM) and acetonitrile (72:28, v/v). The UV detection was performed at 215 nm. The most appropriate regression model of the response function as well as the limit of quantitation (LOQ) were first selected during the pre-validation step. These criteria were then assessed during the formal validation step. The LOQ was 50 ng/ml. The method was also validated with respect to analyte recovery, precision, trueness, accuracy and linearity. Finally, it was successfully applied for the analysis of the first plasma samples obtained from patients having taken an oral dose of 500 mg cloxacillin.

Simultaneous determination of niacin, niacinamide and nicotinuric acid in human plasma

A sensitive, specific, accurate, and reproducible HPLC/MS-method for the simultaneous quantitative determination of niacin (NA) and its main metabolites niacinamide (NAM) and nicotinuric acid (NUR) in human plasma using chinolin-3-carboxylic acid as an internal standard was developed and validated according to international guidelines for method validation. All analytes and the internal standard were separated from acidified plasma by solid phase extraction. Afterwards the extracted samples were analyzed by HPLC/MS in the positive electrospray ionization mode (ESI) and selected ion monitoring (SIM). The total run time was 7 min between injections. The assay had a lower limit of quantification of 50.0 ng/mL for each analyte using 1 mL of plasma. The calibration curves were linear in the measured range between 50.0 and 750 ng/mL plasma. The overall precision and accuracy for all concentrations of quality controls and standards was better than 15%. No indications were found for possible instabilities of niacin, niacinamide and nicotinuric acid in plasma at -20 degrees C, in the extraction solvent or after repeated thawing/freezing cycles. In stabilities were observed in whole blood and in plasma at room temperature. The recovery of the extraction method ranged from 86 to 89% for the three analytes.

Experiences in method development for the analysis of in vitro study solutions for content

Effects of drugs on the cardiovascular system are required to be assessed as part of safety pharmacology, in particular using the in vitro Human Ether-a-go-go Related Gene Product (HERG) and Purkinje fibre studies and can be used to predict safety margins prior to administration to man. Recent International Conferences on Harmonization (ICH) regulations, draft ICHS7B guidelines, indicate that levels of drug in bath solutions used should be measured if quantitative data are to be obtained for the estimation of safety margins. To accurately measure drug concentrations in bath solutions, a validated analytical method is required. This method is required to be accurate, precise, specific, and robust, and due to the increased potency of new drugs, liquid chromatography with mass spectrometric detection (LC-MS) has become the method of choice. Recent experiences validating methods for the analysis of a wide range of drugs in bath solutions has presented a major issue regarding the solubility of some drugs in bath solutions. This has resulted in the requirement of a different approach to the analysis of, in particular, lipophilic drugs that has in turn highlighted the potential for the significant overestimation of the drug concentration in these bath solutions and therefore inaccurate calculation of safety margins.

S-oxidation of S-methyl-esonarimod by flavin-containing monooxygenases in human liver microsomes

1. Studies using human liver microsomes and recombinant human cytochrome P450 (CYP) and flavin-containing monooxygenase (FMO) were performed to identify the enzymes responsible for the metabolism of S-methyl-esonarimod (M2), an active metabolite of esonarimod (KE-298, a novel antirheumatic drug). 2. S-oxidative activities of M2 significantly correlated with those of methyl p-tolyl sulfide, a specific substrate of FMOs, as tested using 10 different human liver microsomes (r(2) = 0.539, p<0.05). Thermal treatment of microsomes reduced the S-oxidative activity in the absence of the NADPH-generating system at 45 degrees C for 5 min. However, methimazole, a known competitive substrate of FMOs, was a weak inhibitor of the S-oxidation in liver microsomes. 3. Recombinant human FMO1 and FMO5 produced M3 in greater quantities than recombinant human FMO3. The S-oxidation of M2 by recombinant human FMO5 was not appreciably inhibited in the presence of methimazole. In contrast, methimazole was effective in suppressing the catalytic activity of recombinant human FMO1 and FMO3. 4. The apparent K(m) (K(m app)) for the S-oxidation of M2 in human recombinant FMO5 (2.71 microM) was similar to that obtained using human liver microsomes (2.43 microM). 5. The present results suggest that the S-oxidation of S-methyl esonarimod reflects FMO5 activity in the human liver because the recombinant FMO5 data match well with the human liver microsomal experiments.

Degradation and configurational changes of thioridazine 2-sulfoxide

Thioridazine (THD) is a phenothiazine neuroleptic drug used for the treatment of psychiatric disorders. After oral administration THD is extensively biotransformed to thioridazine 2-sulfone (THD 2-SO(2)), thioridazine 5-sulfoxide (THD 5-SO) and thioridazine 2-sulfoxide (THD 2-SO). THD 2-SO and THD 5-SO have two chiral centres and therefore exist as two diastereoisomeric pairs. The degradation and epimerization of THD 2-SO in human plasma, buffer and methanolic solutions were studied using an enantioselective HPLC method. The samples were prepared by liquid-liquid extraction with diethyl ether and the chiral resolution of the enantiomers was carried out on a Chiralpak AD column using a mobile phase consisting of hexane:ethanol:2-propanol (90:7:3, v/v/v) containing 0.2% diethylamine. The method was validated and used to study the degradation and epimerization under different conditions of incubation. Our results showed that both enantiomers were stable at varying temperatures, pH and ionic strengths; however, solubility problems were observed, mainly at pH 8.5. The influence of light on stability was studied using methanolic solutions and degradation and epimerization of the THD 2-SO enantiomers were observed under UV light of 366 and 254nm, respectively.

Simple, sensitive and rapid LC–MS/MS method for the quantitation of cerivastatin in human plasma — application to pharmacokinetic studies

A simple and sensitive liquid chromatography-tandem mass spectrometry method was developed and validated for estimation of cerivastatin (I) in human plasma, a potent hydroxy-methylglutaryl-coenzyme A reductase inhibitor. The analyte and internal standard (atorvastatin, II) were extracted by liquid/liquid extraction with diethyl ether/dichloromethane (70/30, v/v). The chromatographic separation was performed on reverse phase Xterra ODS column with a mobile phase of water/acetonitrile (30/70, v/v) with 0.03% formic acid. The protonated analyte was quantitated in positive ionization by multiple reaction monitoring with a mass spectrometer. The mass transitions m/z 460.4 --> 356.3 and 559.2 --> 440.3 were used to measure I and II, respectively. The lower limit of quantitation was 10pg/mL with a relative standard deviation of less than 15%. Acceptable precision and accuracy were obtained for concentrations over the calibration curve ranges (0.01-10ng/mL). Sample analysis time of 2min for each sample made it possible to analyze a throughput of more than 400 human plasma samples per day. The assay can be used to analyze human plasma samples to support phase I and II clinical studies.

Prodrugs of bisthiazolium salts are orally potent antimalarials

We created neutral antimalarial prodrugs that deliver bisthiazolium compounds with antimalarial activity in the nanomolar range. These drugs primarily affect early intraerythrocytic stages through rapid, nonreversible cytotoxicity. The compounds are suitable for both parenteral and oral use and plasma promotes rapid conversion of the prodrug into the drug. We demonstrate that very low doses offer protection in a murine model of malaria. The drugs show great potential for curing high parasitemia with short-course treatments. Oral administration of the TE3 prodrug completely cures Plasmodium cynomolgi infection in rhesus monkeys. The drugs specifically accumulate inside infected erythrocytes, block phosphatidylcholine biosynthesis, and interact with hemozoin. To our knowledge, this class of compounds represents one of the most potent antimalarials tested to date. These unique properties signal a promising future for this class of antimalarial.

Undeclared exposure to St. John's Wort in hospitalized patients

AIM

The herbal medicine St. John's Wort (SJW) causes substantial decreases in the plasma concentrations of a range of co-administered drugs. Therefore, we evaluated the extent of systemic exposure to hyperforin and hypericin, two of the main constituents of SJW, in patients on admission and during hospital stay, and compared the results with known use of SJW as documented in the drug chart and detected in additional interviews.

METHODS

One hundred and fifty patients aged > or = 18 years and admitted, between August 2000 and February 2002, to an internal medicine ward of a large German university hospital were included. Hyperforin and hypericin was determined in plasma by a sensitive liquid chromotography/mass spectometry (LC/MS/MS) method. To assess undeclared use of SJW the data were compared to information obtained from drug charts and from up to three interviews that had a particular focus on intake of herbal medicines and self-medication during hospitalization.

RESULTS

Hyperforin was detected in 12 patients (plasma concentration on the first day of hospitalization = 12-100 ng ml(-1) in five patients and < 3 ng ml(-1) in seven), and hypericin in five patients (0.5-4.3 ng ml(-1)). Nine patients (6%) were taking/had taken SJW without the knowledge of the medical team and the pharmacist, who conducted the additional interviews, and 11 (7.3%) were taking/had taken SJW without the knowledge of the medical team alone. Seven of these patients were treated concurrently with drugs that can interact with SJW.

CONCLUSIONS

Unrecognized use of SJW is frequent and may have an important influence on the effectiveness and safety of drug therapy during hospital stay.

Mass spectrometric quantitation of deoxyguanosine and leukotriene A4-deoxyguanosine adducts of DNA

An assay was developed using electrospray ionization negative ion tandem mass spectrometry (MS) to identify and quantitate the major product in the reaction of leukotriene A(4) (LTA(4)) with deoxyguanosine (dGuo). A second quantitative assay was established using the same separation and detection techniques to determine the amount of dGuo isolated from enzymatically processed DNA. The amount of LTA(4)-dGuo adduct could then be analytically determined in DNA samples and normalized to the amount of dGuo that had been simultaneously derived from the DNA sample. Stable isotope-labeled internal standards used for these quantitative assays were readily synthesized from isotopically labeled [(15)N(5)(13)C(10)]deoxyguanosine triphosphate and analyzed for isotopic purity using MS. A comparison of fragment ions formed from stable isotope analogs of dGuo revealed the loss of deoxyribose and secondarily the loss of a series of stable neutral small molecules in a fashion similar to patterns described previously for the collisional fragmentation of protonated guanine determined by positive ion fast atom bombardment/MS/MS. The combined quantitative assays were used for the determination of the amount of endogenously formed LTA(4)-dGuo adducts observed in DNA when isolated human neutrophils that had been incubated with arachidonic acid were stimulated with calcium ionophore to initiate leukotriene biosynthesis.

New advances in method validation and measurement uncertainty aimed at improving the quality of chemical data

The implementation of quality systems in analytical laboratories has now, in general, been achieved. While this requirement significantly modified the way that the laboratories were run, it has also improved the quality of the results. The key idea is to use analytical procedures which produce results that fulfil the users' needs and actually help when making decisions. This paper presents the implications of quality systems on the conception and development of an analytical procedure. It introduces the concept of the lifecycle of a method as a model that can be used to organize the selection, development, validation and routine application of a method. It underlines the importance of method validation, and presents a recent approach based on the accuracy profile to illustrate how validation must be fully integrated into the basic design of the method. Thanks to the beta-expectation tolerance interval introduced by Mee (Technometrics (1984) 26(3):251-253), it is possible to unambiguously demonstrate the fitness for purpose of a new method. Remembering that it is also a requirement for accredited laboratories to express the measurement uncertainty, the authors show that uncertainty can be easily related to the trueness and precision of the data collected when building the method accuracy profile.

Determination of lansoprazole in pharmaceutical capsules by flow injection analysis using UV-detection

The direct determination of lansoprazole by using a flow injection analysis (FIA) with UV-detection and its application to the pharmaceutical capsules is described, in this study. The best carrier solvent was found to be 0.01 M NaOH and it was determined at optimum conditions such as flow rate of 1 ml min(-1) and wavelength of 292 nm. Examining the repeatability of the method that was found to be 1.72% for intra-day and 2.13% for inter-day precision using the 8.01 x 10(-6) M lansoprazole concentration has validated the method. The linear range of the method was 5.4 x 10(-6) to 5.4 x 10(-5) M. The limit of detection and quantification was found to be 5.8 x 10(-7) and 1.7 x 10(-6) M, respectively. The proposed method was applied to the pharmaceutical capsules and very good results obtained. Thus, the FIA method for the quantification of lansoprazole can be proposed as a cheap, rapid, easy, accurate, and precise method for the routine determination in pharmaceutical preparations.

Development and validation of a high-performance liquid chromatographic method for the determination of cyproterone acetate in human skin

In the framework of a preliminary study on the transdermal penetration of cyproterone acetate (CPA), a simple and rapid procedure involving an extraction step coupled to a HPLC-UV determination has been developed for the separation and quantification of CPA in the two main skin layers-epidermis and dermis-after local application. The separation of epidermis and dermis layers was carefully carried out by means of a sharp spatula after skin immersion in heated water at 65 degrees C. The two skin layers were then treated separately according to the same process: (1) sample homogenization by vibration after freezing with liquid nitrogen in a Mikro-Dismembrator; (2) CPA extraction with methanol after addition of the internal standard (betamethasone dipropionate); (3) centrifugation; (4) evaporation of a supernatant aliquot; (5) dissolution of the dry residue in methanol and addition of water; (6) centrifugation; (7) injection of a supernatant aliquot into the HPLC system. The separation was achieved on octadecylsilica stationary phase using a mobile phase consisting in a mixture of acetonitrile and water (40:60 (v/v)). The method was then validated using a new approach based on accuracy profiles over a CPA concentration range from 33 to 667 ng/ml for each skin layer. Finally, the method was successfully applied to the determination of CPA to several skin samples after topical application of different gel formulations containing CPA.

Pharmacokinetic aspects of biotechnology products

In recent years, biotechnologically derived peptide and protein-based drugs have developed into mainstream therapeutic agents. Peptide and protein drugs now constitute a substantial portion of the compounds under preclinical and clinical development in the global pharmaceutical industry. Pharmacokinetic and exposure/response evaluations for peptide and protein therapeutics are frequently complicated by their similarity to endogenous peptides and proteins as well as protein nutrients. The first challenge frequently comes from a lack of sophistication in various analytical techniques for the quantification of peptide and protein drugs in biological matrices. However, advancements in bioassays and immunoassays--along with a newer generation of mass spectrometry-based techniques--can often provide capabilities for both efficient and reliable detection. Selection of the most appropriate route of administration for biotech drugs requires comprehensive knowledge of their absorption characteristics beyond physicochemical properties, including chemical and metabolic stability at the absorption site, immunoreactivity, passage through biomembranes, and active uptake and exsorption processes. Various distribution properties dictate whether peptide and protein therapeutics can reach optimum target site exposure to exert the intended pharmacological response. This poses a potential problem, especially for large protein drugs, with their typically limited distribution space. Binding phenomena and receptor-mediated cellular uptake may further complicate this issue. Elimination processes--a critical determinant for the drug's systemic exposure--may follow a combination of numerous pathways, including renal and hepatic metabolism routes as well as generalized proteolysis and receptor-mediated endocytosis. Pharmacokinetic/pharmacodynamic (PK/PD) correlations for peptide and protein-based drugs are frequently convoluted by their close interaction with endogenous substances and physiologic regulatory feedback mechanisms. Extensive use of pharmacokinetic and exposure/response concepts in all phases of drug development has in the past been identified as a crucial factor for the success of a scientifically driven, evidence-based, and thus accelerated drug development process. Thus, PK/PD concepts are likely to continue and expand their role as a fundamental factor in the successful development of biotechnologically derived drug products in the future.

Development and validation of a chiral liquid chromatographic method, based on Chiralpak® to quantify enantiomers of (±)-DRF 2725 in rat plasma: lack of inversion of ragaglitazar (S(−)-DRF 2725) to its antipode in plasma

A selective, accurate and reproducible high-performance liquid chromatographic (HPLC) method for the separation of individual enantiomers of DRF 2725 [R(+)-DRF 2725 and S(-)-DRF 2725 or ragaglitazar] was obtained on a chiral HPLC column (Chiralpak). During method optimization, the separation of enantiomers of DRF 2725 was investigated to determine whether mobile phase composition, flow-rate and column temperature could be varied to yield the base line separation of the enantiomers. Following liquid-liquid extraction, separation of enantiomers of DRF 2725 and internal standard (I.S., desmethyl diazepam) was achieved using an amylose based chiral column (Chiralpak AD) with the mobile phase, n-hexane-propanol-ethanol-trifluoro acetic acid (TFA) in the ratio of 89.5:4:6:0.5 (v/v). Baseline separation of DRF 2725 enantiomers and I.S., free from endogenous interferences, was achieved in less than 25 min. The eluate was monitored using an UV detector set at 240 nm. Ratio of peak area of each enantiomer to I.S. was used for quantification of plasma samples. Nominal retention times of R(+)-DRF 2725, S(-)-DRF 2725 and I.S. were 15.8, 17.7 and 22.4 min, respectively. The standard curves for DRF 2725 enantiomers were linear (R(2) > 0.999) in the concentration range 0.3-50 microg/ml for each enantiomer. Absolute recovery, when compared to neat standards, was 70-85% for DRF 2725 enantiomers and 96% for I.S. from rat plasma. The lower limit of quantification (LLOQ) for each enantiomers of DRF 2725 was 0.3 microg/ml. The inter-day precisions were in the range of 1.71-4.60% and 3.77-5.91% for R(+)-DRF 2725, S(-)-DRF 2725, respectively. The intra-day precisions were in the range of 1.06-11.5% and 0.58-12.7% for R(+)-DRF 2725, S(-)-DRF 2725, respectively. Accuracy in the measurement of quality control (QC) samples was in the range 83.4-113% and 83.3-113% for R(+)-DRF 2725, S(-)-DRF 2725, respectively. Both enantiomers and I.S. were stable in the battery of stability studies viz., bench-top (up to 6 h), auto-sampler (up to 12 h) and freeze/thaw cycles (n = 3). Stability of DRF 2725 enantiomers was established for 15 days at -20 degrees C. The application of the assay to a pharmacokinetic study of ragaglitazar [S(-)-DRF 2725] in rats is described. It was unequivocally demonstrated that ragaglitazar does not undergo chiral inversion to its antipode in vivo in rat plasma.

Comparison of extraction of a β-blocker from plasma onto a molecularly imprinted polymer with liquid–liquid extraction and solid phase extraction methods

An optimised solid phase extraction (SPE) method developed for the extraction of a structural analogue of the beta-blocking drug propranolol from plasma utilising a molecularly imprinted polymer (MIP) has been compared with methods based on conventional liquid-liquid extraction (LLE), and SPE using C18-bonded and immobilised phenyl boronic acid (PBA). All four methods could be used for the extraction of the analyte with acceptable accuracy and precision. The MIP-based method, unlike the other methods required a protein precipitation step prior to extraction to eliminate the effects of co-extracted protein. The best performance was seen with the LLE method followed by SPE on the C18 phase. The MIP-based method represented no advantage over the comparator methods for this analyte. Indeed the performance of the MIP-based method was marginally worse as leaching of low level template impurities prevented detection of the target analyte at low concentrations (5 ngmL(-1)). This relatively poorer performance was evident as worse accuracy at low concentrations with a consequent higher limit of quantification than the conventional methods.

HPLC determination of ferulic acid in rat plasma after oral administration of Rhizoma Chuanxiong and its compound preparation

An HPLC method is described for determination of ferulic acid in rat plasma. The concentration of ferulic acid in rat plasma was determined after deproteinization with acetonitrile using sulfamethoxazole as internal standard. Chromatographic separations were performed on a C(18) stationary phase with a mobile phase composed of acetonitrile-water (16:84, v/v) with 1% glacial acetic acid. The UV detection wavelength was set at 320 nm. The method was successfully applied to the determination of pharmacokinetic parameters in rat plasma after oral administration of Rhizoma Chuanxiong and and its compound preparation Suanzaoren decoctions. The calibration curve was linear over the range 0.0510-4.08 micro g/mL in rat plasma. Within-day and between-day precisions were less than 4.5% RSD. Mean recovery was determined as 96.9%. The limit of quantitation was 0.0510 micro g/mL. The pharmacokinetic parameters of the two preparations were different significantly (p < 0.05), which may attribute to the effects of other ingredients present in Suanzaoren decoction.

Voltammetric analysis of drugs

A review on the voltammetric analysis of drugs is presented. The review includes a summary of the rules that must be considered for drug analysis and a survey of the use of voltammetry for drug analysis in the period from 1998 till 2002.

Lack of pharmacologic interaction between paroxetine and alprazolam at steady state in healthy volunteers

This investigation aimed to provide evidence on the lack of pharmacokinetic interaction of paroxetine (20 mg/d) and alprazolam (1 mg/d) in combined therapy. In addition, the central effects of both drugs when administered alone and in combination were assessed to rule out any relevant synergistic depressant central effect. Twenty-five healthy young adult volunteers participated in a double-blind, double-dummy, placebo-controlled, repeated dose (15 days), 4-period crossover study. Each subject received each of 4 treatment sequences (ie, paroxetine-alprazolam placebo, alprazolam-paroxetine placebo, paroxetine-alprazolam, and paroxetine placebo-alprazolam placebo) in randomized order. The ratios for area under the curve within a dosing interval and maximum plasma concentration of the paroxetine plus alprazolam sequence to single agent paroxetine were 1.07 (90% confidence interval = 0.99 to 1.16) and 1.05 (90% confidence interval = 0.97 to 1.13), respectively, with no statistically significant differences between the 2 treatments. Similarly, for alprazolam, ratios for the combined to the single treatment sequence were 0.99 (90% confidence interval = 0.93 to 1.05) and 1.00 (90% confidence interval = 0.94 to 1.07) for area under the curve within a dosing interval and maximum plasma concentration, respectively, showing no evidence for interaction. Comparative pharmacodynamics on the combination was assessed using 6 Psychomotor Performance Tests and 5 Visual Analogue Scales focused on mood variables. Alprazolam and paroxetine plus alprazolam induced similar and significant performance impairment and sedation after both single and repeated dose administration, being less evident on day 15. After dosing, paroxetine plus alprazolam showed a lower recovery pattern than alprazolam alone, especially on day 15. No treatment sequence showed cumulative effects after repeated dose administration. Psychomotor Performance Tests and Visual Analogue Scales data suggested lack of pharmacodynamic interactions. Accordingly, study results showed no evidence for pharmacologic interactions between paroxetine and alprazolam at steady state. The most commonly reported adverse event was drowsiness, with a higher incidence under both single and combined alprazolam treatments.

High performance capillary electrophoresis for determination of the enantiomers of 2-arylpropionic acid derivatives in human serum

A stereospecific capillary zone electrophoresis (CZE) method for determination of the enantiomers of some 2-arylpropionic acid derivatives (2-APA, profens) in human serum has been developed. Racemic-ibuprofen (rac-IBP), racemic-flurbiprofen (rac-FBP), racemic-ketoprofen (rac-KTP) and (+)-S-naproxen ((+)-S-NPX--an internal standard) were chosen for these studies. The 2-APA enantiomers were extracted from acidified serum samples using methylene chloride separated in a fused silica capillary. The capillary was filled with a background electrolyte, which consisted of 0.05 M heptakis 2,3,6-tri-O-methyl-beta-cyclodextrin (TMbetaCD) (chiral selector) in 0.02 M triethanolamine-phosphate buffer of pH 5.0. Separation and resolution of the enantiomer mixture were obtained in one analytical run. The calculated electrophoretic parameters of the analytes were as follows: electrophoretic mobility, micorep(-)-R = -0.75 x 10(-4) to -0.30 x 10(-4) cm2/Vs; micorep(+)-S = -0.83 -(-0.38) cm2/Vs and electroosmotic mobility, microEOF = 2.35 x 10(-4) cm2/Vs, migration times, tmigr R = 12.55 - 16.07 min; tmigr s = 13.08 - 16.9 min, resolution factors, RS = 1.88 - 3.70 and chiral selectivity, alpha = 1.16 - 1.34. The method developed for the enantiomers was validated. The calibration curves were linear in the range of 0.5-50.0 microg/ml for FBP or KTP and of 1.0-50.0 microg/ml for IBP enantiomer concentrations. Recovery of the enantiomers from serum was about 90%. At the limit of quantification (LOQ) precision and accuracy were within 15%. The validated method was successfully applied to pharmacokinetic and bioavailability studies on KTP enantiomers in humans after administration of standard and sustained release tablets of rac-KTP. Significant differences in the pharmacokinetic parameters of both formulations were observed and the studied formulations were not bioequivalent.

Simultaneous determination of dexamethasone and 6β-hydroxydexamethasone in urine using solid-phase extraction and liquid chromatography: applications to in vivo measurement of cytochrome P450 3A4 activity

It has been demonstrated that the formation of the hydrophilic metabolites of dexamethasone, 6 alpha- and 6 beta-hydroxydexamethasone, correlated with cytochrome P450 (CYP) 3A4 enzyme levels. So, the 6 beta-hydroxydexamethasone/dexamethasone urinary ratio could be a specific marker for human CYP3A4 activity. We have developed a sensitive and specific high-performance liquid chromatographic method for the simultaneous quantification of urinary free dexamethasone and 6 beta-hydroxydexamethasone using 6 alpha-methylprednisolone as internal standard. This method involved a solid phase extraction of the three compounds from urine using Oasis HLB Waters cartridges with an elution solvent of ethyl acetate (2 ml) followed by diethyl ether (1 ml). Separation of the three analytes was achieved within 24 min using a reversed-phase Nova-Pak C(18) analytical column (4 microm, 300 mm x 3.9 mm i.d.). An ultraviolet detector operated at 245 nm was used with a linear response observed from 10 to 100 ng/ml for dexamethasone and from 25 to 1000 ng/ml for 6 beta-hydroxydexamethasone. Obtained from the method validation, inter-assay precision was below 15% and accuracy ranged from 95.7 to 110%. The extraction efficiency of the assay was approximately of 99% and was constant across the calibration range. The lower limit of quantitation was 10 ng/ml for dexamethasone and 25 ng/ml for 6 beta-hydroxydexamethasone; at these levels, precision was below 16% and accuracy was 99-109%. This method was applied to in vivo measure of the CYP3A4 activity.

Quantification of the N-desmethyl metabolite of rosuvastatin in human plasma by automated SPE followed by HPLC with tandem MS detection

A selective, accurate and precise assay was developed for the quantification in human plasma of the N-desmethyl metabolite of the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor rosuvastatin. The assay-employing automated SPE followed by HPLC with positive ion electrospray tandem MS (HPLC-MS/MS)-was validated. The standard curve range for N-desmethyl rosuvastatin in human plasma was 0.5-30 ng/ml with 0.5 ng/ml being the limit of quantification. Plasma samples were mixed 1:1 with sodium acetate buffer (pH 4.0; 0.1M) soon after separation from red blood cells. N-Desmethyl rosuvastatin was stable in plasma:buffer at room temperature for 24h and at -70 degrees C for 12 months. The assay was applied successfully to the quantification of N-desmethyl rosuvastatin in human plasma following administration of rosuvastatin.

Quantification of risperidone and 9-hydroxyrisperidone in plasma and saliva from adult and pediatric patients by liquid chromatography–mass spectrometry

A robust and validated LC-MS-MS quantitative method, using column switching and mutiple reaction monitoring was developed for the analysis of risperidone (RIS) and 9-hydroxyrisperidone in human plasma and saliva. The analytical range was 1-100 ng/ml. The method used 25 microl of sample precipitated with 75 microl of acetonitrile containing internal standard (R068808). Analyses were conducted on a PE Sciex API-III + triple quadrupole mass spectrometer fitted with a Turbo IonSpray source. The method was validated for human plasma using EDTA as the anticoagulant and cross-validated to heparinized human plasma and saliva. The recoveries of risperidone and 9-hydroxyrisperidone were 90-93 and 89-93%, respectively. The validated method was applied to clinical samples to study risperidone and 9-hydroxyrisperidone concentrations in plasma and saliva. Risperidone and 9-hydroxyrisperidone appear in the saliva of patients treated with risperidone. Their detection/quantification in saliva provides evidence for recent adherence with therapy.

Determination of lipoic acid in rat plasma by LC-MS/MS with electrospray ionization: Assay development, validation and application to a pharamcokinetic study

A simple, sensitive and specific LC-MS/MS method for the determination of lipoic acid was developed and validated over the linearity range 5-1000 ng/mL (r2 > 0.99) with 200 microL rat plasma using rosigliatzone as an internal standard (IS). The assay procedure involved a simple one-step liquid-liquid extraction of lipoic acid and IS from plasma into ethyl acetate. The organic layer was separated and evaporated under a gentle stream of nitrogen at 40 degrees C. The residue was reconstituted in the mobile phase and injected onto a Hichrom RPB column (4.6 x 250 mm, 5 microm). Separation of lipoic acid and IS was achieved with a mobile phase consisting of 0.05 M formic acid:acetonitrile (40:60, v/v) at a flow rate of 1.0 mL/min. The API-3000 LC-MS/MS was operated under the multiple reaction monitoring mode (MRM) using the electrospray ionization technique. Positive and negative ion acquisition within the same chromatographic run was used in the present method. For lipoic acid a pseudo-molecular ion transition pair was acquired in negative polarity, whereas for IS the transition pair was acquired in positive polarity. Quantitation was determined for both analyte and IS in MRM scan mode. Absolute recovery of lipoic acid and IS was >70 and 97%, respectively. The lower limit of quantification (LLOQ) of lipoic acid was 5.0 ng/mL. The inter- and intra-day precision in the measurement of quality control (QC) samples 5, 15, 400 and 800 ng/mL were in the range 2.18-5.99% relative standard deviation (RSD) and 0.93-13.77% RSD, respectively. Accuracy in the measurement of QC samples was in the range 87.40-114.40% of the nominal values. Analyte and IS were stable in the battery of stability studies, viz. bench-top, auto-sampler and freeze-thaw cycles. Stability of lipoic acid was established for 1 month at -80 degrees C. The application of the assay to a pharmacokinetic study in rats confirmed the utility of the assay.

High-performance liquid chromatographic method for simultaneous determination of sophoridine and matrine in rat plasma

A high-performance liquid chromatographic (HPLC) method is described for the simultaneous determination of sophoridine and matrine in rat plasma. Sophoridine and matrine in the resulting supernatant of the plasma deproteinized with acetonitrile containing an internal standard (acetanilide) were directly determined by reversed-phase HPLC and ultraviolet detection. The result of limits of quantitation for matrine and sophoridine were 200 and 350 ng/mL in plasma, respectively, and recovery of both analytes was greater than 98%. The assay was linear from 250 to 4000 ng/mL for matrine and from 500 to 8000 ng/mL for sophoridine. Variation over the range of the standard curve was less than 15%. The method was used to determine the concentration-time profiles of matrine and sophoridine in the plasma following oral administration of Kexieling tablets, which is one of the preparations of Kudouzi at a dose equivalent to 30 and 60 mg/kg of matrine and sophoridine, respectively.

Sensitive HPLC-fluorescence method for irinotecan and four major metabolites in human plasma and saliva: application to pharmacokinetic studies

BACKGROUND

We developed gradient HPLC methods for quantification of the antimitotic drug irinotecan (CPT-11) and its four metabolites, SN-38, SN-38 G, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxycamptothecin (APC), and 7-ethyl-10-[4amino-1-piperidino]-carbonyloxycamptothecin (NPC), as the sum of the lactone and carboxylate forms, in human plasma and saliva. Camptothecin was used as internal standard.

METHODS

The sample pretreatment involved protein precipitation with methanol-acetonitrile (50:50 by volume) followed by acidification with hydrochloric acid to convert the lactone ring-opened form into its lactone form, quantitatively. HPLC separation was performed on a Xterra RP18 column. The excitation wavelength was 370 nm, and the emission wavelength was set at 470 nm for the first 24 min and then at 534 nm for the next 4 min. The stabilities of irinotecan and its four metabolites in plasma, saliva, and acidic extracts were also investigated under various conditions.

RESULTS

Assays were linear in the tested range of 0.5-1000 micro g/L. For the five analytes, limits of quantification were 0.5 micro g/L in both matrices. The interassay imprecision (as relative standard deviation) was 3.2-14% in plasma and 2.6-5.6% in saliva. Assay recoveries ranged from 92.8% to 111.2% for plasma and 100.1% to 104.1% for saliva. Mean extraction recovery from plasma or saliva was 90%.

CONCLUSION

The developed assay can be used to determine pharmacokinetic parameters for CPT-11, SN-38, SN-38 G, APC, and NPC in plasma and saliva from patients with metastatic colorectal cancer.

Determination of scutellarin in rat plasma by high-performance liquid chromatography with ultraviolet detection

A validated high-performance liquid chromatography method is described for the determination of scutellarin in rat plasma using a liquid-liquid extraction and ultraviolet (UV) absorbance detection. The separation used a Diamonsil ODS column (250 mm x 4.6mm i.d., 5 microm particle size) with an isocratic mobile phase consisting of methanol-acetonitrile-50mM dihydrogen ammonium phosphate buffer (22:15:63 (v/v/v), adjusted to pH 2.5 with 1M phosphoric acid). The ultraviolet detector operated at 335 nm. Plasma samples were extracted with ethyl acetate after acidification. The extraction recovery of scutellarin ranged from 68.1 to 80.5%. High selectivity and a low quantitation limit (0.050 microg/ml) were achieved. The linear range was 0.050-12.5 microg/ml, correlation coefficient r=0.9981. The method has a good reproducibility, R.S.D. values were below 7.9% for within-day and between-day precision. The method is simple, rapid, and applicable to preliminary pharmacokinetic studies of scutellarin in rats.

A validated assay for measuring doxorubicin in biological fluids and tissues in an isolated lung perfusion model: matrix effect and heparin interference strongly influence doxorubicin measurements

Doxorubicin is an antineoplasic agent active against sarcoma pulmonary metastasis, but its clinical use is hampered by its myelotoxicity and its cumulative cardiotoxicity, when administered systemically. This limitation may be circumvented using the isolated lung perfusion (ILP) approach, wherein a therapeutic agent is infused locoregionally after vascular isolation of the lung. The influence of the mode of infusion (anterograde (AG): through the pulmonary artery (PA); retrograde (RG): through the pulmonary vein (PV)) on doxorubicin pharmacokinetics and lung distribution was unknown. Therefore, a simple, rapid and sensitive high-performance liquid chromatography method has been developed to quantify doxorubicin in four different biological matrices (infusion effluent, serum, tissues with low or high levels of doxorubicin). The related compound daunorubicin was used as internal standard (I.S.). Following a single-step protein precipitation of 500 microl samples with 250 microl acetone and 50 microl zinc sulfate 70% aqueous solution, the obtained supernatant was evaporated to dryness at 60 degrees C for exactly 45 min under a stream of nitrogen and the solid residue was solubilized in 200 microl of purified water. A 100 microl-volume was subjected to HPLC analysis onto a Nucleosil 100-5 microm C18 AB column equipped with a guard column (Nucleosil 100-5 microm C(6)H(5) (phenyl) end-capped) using a gradient elution of acetonitrile and 1-heptanesulfonic acid 0.2% pH 4: 15/85 at 0 min-->50/50 at 20 min-->100/0 at 22 min-->15/85 at 24 min-->15/85 at 26 min, delivered at 1 ml/min. The analytes were detected by fluorescence detection with excitation and emission wavelength set at 480 and 550 nm, respectively. The calibration curves were linear over the range of 2-1000 ng/ml for effluent and plasma matrices, and 0.1 microg/g-750 microg/g for tissues matrices. The method is precise with inter-day and intra-day relative standard deviation within 0.5 and 6.7% and accurate with inter-day and intra-day deviations between -5.4 and +7.7%. The in vitro stability in all matrices and in processed samples has been studied at -80 degrees C for 1 month, and at 4 degrees C for 48 h, respectively. During initial studies, heparin used as anticoagulant was found to profoundly influence the measurements of doxorubicin in effluents collected from animals under ILP. Moreover, the strong matrix effect observed with tissues samples indicate that it is mandatory to prepare doxorubicin calibration standard samples in biological matrices which would reflect at best the composition of samples to be analyzed. This method was successfully applied in animal studies for the analysis of effluent, serum and tissue samples collected from pigs and rats undergoing ILP.

An Expedient Assay for Determination of Gemcitabine and Its Metabolite in Human Plasma Using Isocratic Ion-Pair Reversed-Phase High-Performance Liquid Chromatography

An expedient method is presented for determination in human plasma of gemcitabine and its metabolite 2',2'-difluorodeoxyuridine (dFdU) by ion-pair reversed-phase HPLC. Samples were simply prepared by protein precipitation. Separation was processed on a Thermo Hypersil column (250 x 4.6 mm, 5 microm Hypersil BDS C18) with UV detection at 272 nm. The mobile phase consisted of 17% methanol and 83% phosphate buffer (20 mM, pH 3.1) containing 10 mM sodium 1-heptanesulfonate with a flow rate of 0.8 mL/min. The lower limit of quantification (LLOQ) of gemcitabine was 0.08 microg/mL with linear response over the range 0.08-20.0 microg/mL, and LLOQ of dFdU was 0.1 microg/mL with linear response over the range 0.1-50.0 microg/mL. Assay accuracy for both compounds was within +/- 4%. The coefficient of variation (CV %) for intra- and interday precision for both compounds was <7%. The correlation coefficients (r2) were greater than 0.9996 for all standard curves. The simple method with adequate sensitivity has been successfully used in phase I and II gemcitabine pharmacokinetic and pharmacodynamic studies in an Asian population.

Stability studies of selected doping agents in urine: caffeine

The stability of caffeine in urine samples has been studied. A high-performance liquid chromatography (HPLC) method for the quantification of caffeine in urine samples was validated for that purpose. The method consists of a liquid-liquid extraction at alkaline pH with chloroform-2-propanol (9:1, v/v) with a salting out effect. 7-Ethyltheophylline was used as internal standard (ISTD). Analyses were performed with an Ultrasphere ODS C18 column using water/acetonitrile (90:10, v/v) as a mobile phase at a flow rate of 1 ml/min. Ultraviolet absorption at 280 nm was monitored. Extraction recoveries for caffeine and 7-ethyltheophylline were 81.4+/-6.0 and 87.3+/-5.7%, respectively. The calibration curves were demonstrated to be linear in the working range of 6-30 microg/ml (r2>0.990). The limit of detection and the limit of quantitation were estimated as 0.7 and 2.0 microg/ml, respectively. Precisions in the range of 1.5-9.2 and 4.1-5.8% were obtained in intra- and inter-assay studies, respectively, using control samples containing 10, 14 and 26 microg/ml of caffeine. Accuracies ranging from 2.9 to 7.4% for intra-assay experiments, and from 3.9 to 5.4% in inter-assay studies were obtained. Stability of caffeine in urine samples was evaluated after long- and short-term storage at different temperature conditions. The batches of spiked urine were submitted to sterilization by filtration. No adsorption of the analyte on filters was observed. Before starting stability studies, batches of reference materials were tested for homogeneity. For long-term stability testing, caffeine concentration in freeze-dried urine stored at 4 degrees C and in liquid urine samples stored at 4, -20, -40 and -80 degrees C was determined at several time intervals for 18 months. For short-term stability testing, caffeine concentration was evaluated in liquid urine stored at 37 degrees C for 7 days. The effect of repeated freezing (at -20 degrees C) and thawing was also studied for up to three cycles. The stability of caffeine was also evaluated in non-sterile samples stored at -20 degrees C for 18 months. No significant loss of the compound was observed at any of the investigated conditions.

Determination of mifepristone levels in wild canid serum using liquid chromatography

An HPLC method was developed to determine levels of mifepristone, in coyote (Canis latrans) serum where mifepristone will be used as an oral contragestive agent for nonlethal predator control. Serum samples were extracted using C(18) solid-phase extraction cartridges. A synthetic analog of mifepristone, RTI-3021-003, was used as the internal standard. Separation of the compounds was achieved by using a C(18) (150 x 4.6 mm) column. The mobile phase was 55% acetonitrile in water running at 1.0 ml/min with UV detection at 305 nm. The assay was linear in the range of 10 to 1000 ng/ml. Inter-day accuracies for 10, 200 and 1000 ng/ml were 95.9, 99.4 and 104.7%, respectively. Inter-day precisions measured by RSD were 19.8, 9.7 and 4.5%. Intra-day accuracies were 117, 106.9 and 99.4% for 10, 200 and 1000 ng/ml, respectively. Intra-day RSDs were 19.7, 3.7 and 9.3%, respectively. A simple, sensitive and validated HPLC analytical method was developed to quantitate mifepristone in canine serum.

Rapid and sensitive quantitation of the antiproliferative agent mitoguazone in small volumes of plasma by high-performance liquid chromatography with ultraviolet detection

Mitoguazone is an antiproliferative agent used in chemotherapy. This study describes a simple and sensitive high-performance liquid chromatographic method for the determination of mitoguazone in 100 microl of plasma. Samples were deproteinized with 100 microl of a solution of internal standard (amiloride, 10 microg/ml) in acetonitrile. An aliquot of the supernatant was injected onto the column. HPLC separation was achieved on a silica column with the mobile phase of methanol-50 mM potassium phosphate buffer (pH 3)-triethylamine (80:20:0.3, v/v), at a flow-rate of 1 ml/min. The eluent was detected at 320 nm. The retention time was about 5.5 min for amiloride and 12 min for mitoguazone. No endogenous substances were found to interfere. Calibration curves were linear from 0.25 to 50 microg/ml. The absolute recoveries of mitoguazone and amiloride were both greater than 84%. The limit of quantitation was 0.25 microg/ml. The intra- and inter-day precision (expressed as RSD) was 5.8%, or less, and the accuracy was 94.7% of the nominal concentration. The method is suitable in pharmacokinetic investigation and monitoring mitoguazone concentration.

Determination of epirubicin and its metabolite epirubicinol in saliva and plasma by HPLC

We present a high-performance liquid chromatography (HPLC) method suitable for the analysis of epirubicin and its metabolite epirubicinol in saliva and plasma. Preparation of saliva and plasma samples was performed by extraction of analytes with a chloroform:2-propanol mixture (6:1, vol/vol) and evaporation of the organic phase to dryness under vacuum at a temperature of approximately 45 degrees C. The chromatographic analysis was carried out by reversed-phase isocratic elution of the anthracyclines with a Chromsep stainless steel HPLC column (150 x 4.6 mm I.D.) filled with Nucleosil 100 S C(18) material, particle size 5 micro m. The detection was accomplished by spectrofluorimetry at excitation and emission wavelengths of 474 and 551 nm, respectively. The anthracyclines eluted within 10 min of injection, and the method appeared to be specific. The method is linear over a concentration range of 5 to 1000 micro g/L for epirubicin and 2 to 400 micro g/L for epirubicinol (r > 0.99) in both saliva and plasma. The recoveries from saliva and plasma of epirubicin, epirubicinol, and the internal standard doxorubicin were 88.9 and 69.0%, 87.6 and 77.3%, and 80 and 67.9%, respectively. The lower limit of quantification was 5 micro g/L for epirubicin and 2 micro g/L for epirubicinol. The method proved to be precise and accurate, as the within-day and between-day coefficients of variation were less than 10%. Overall results indicate that our method is suitable for the bioanalysis of epirubicin and epirubicinol in saliva as well as plasma.

A strategy for liquid chromatography/tandem mass spectrometric assays of intracellular drugs: application to the validation of the triphosphorylated anabolite of antiretrovirals in peripheral blood mononuclear cells

The pharmacokinetics of intracellular drugs have recently aroused new interest because monitoring a drug's behaviour near the site of action can enhance knowledge of its efficacy and toxicity. Liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) is particularly attractive for intracellular analytes. Very few papers deal precisely with special features encountered in intracellular drug assay or with how closely the assay matches the actual recommendations. Particular problems are encountered mainly because the analytes are located intracellularly. This mainly concerns the handling of biological media, including provision of blank samples using Ficoll gradient separation, cell counts, optimisation of cell lysis, sample extraction, plotting standard curves using either fmol/10(6) cells or fmol/ml of extract or fmol/sample, the matrix effect as a function of the number of cells, stability before and during cell separation, as well as in storage conditions using clinical samples, biological matrix replacement and interference by endogenous compounds. This paper describes a strategy for the full validation and routine use of an LC/MS/MS assay applied to the simultaneous intracellular determination of the triphosphorylated anabolites of didanosine (2',3'-dideoxyadenosine triphosphate or ddA-TP) and stavudine (2',3'-didehydro-3'-deoxythymidine triphosphate or d4T-TP), two nucleoside reverse transcriptase inhibitors of HIV, in human peripheral blood mononuclear cells (PBMCs), as a guide for further LC/MS/MS assay of intracellular drugs.

Determination of tezosentan, a parenteral endothelin receptor antagonist, in human plasma by liquid chromatography-tandem mass spectrometry

An analytical method was developed for the quantification of tezosentan in human plasma obtained in clinical studies. The method was linear in the range 1 to 512 ng/ml. After liquid-liquid extraction, the samples were analyzed by reversed-phase HPLC with tandem mass spectrometry. The limit of quantification was 1 ng/ml and the extraction recovery was at least 88.2%. Intra- and inter-assay coefficients of variation were below 10%. Stability tests revealed that tezosentan is stable under the different conditions tested.

Liquid chromatographic assay for the antiviral nucleotide analogue tenofovir in plasma using derivatization with chloroacetaldehyde

A sensitive and selective reversed-phase liquid chromatographic assay for tenofovir in human plasma has been developed and validated. Tenofovir was isolated from a 200 microl plasma sample using protein precipitation with trichloroacetic acid. The fluorescent 1,N(6)-etheno derivative is formed at 98 degrees C in the buffered extract with chloroacetaldehyde. This derivative was analysed using gradient ion-pair liquid chromatography and fluorescence detection at 254 nm for excitation and 425 nm for emission. In the evaluated concentration range (20-1000 ng/ml), the intra-day precision was 4% and the inter-day precision was 5-6%. An accuracy of between 97 and 110% was determined. The lower limit of quantification was 20 ng/ml with an inter-day precision of 11%, an intra-day precision of 12% and an accuracy of 103%. The assay is subject to interference from co-administered abacavir. The usefulness of the assay was demonstrated for samples obtained from an HIV-infected patient treated with tenofovir.

Development and validation of a high-performance liquid chromatography assay for voriconazole

An analytical method for the determination of voriconazole (UK-109,496; Pfizer) in plasma was developed and validated. The method utilizes solid-phase extraction technology and high-performance liquid chromatography. The lower limit of quantitation is 0.2 microg/ml, and the range of linearity tested was 0.2 to 10 microg/ml.

Racemization and degradation of thioridazine and thioridazine 2-sulfone in human plasma and aqueous solutions

We present two methods for the enantioselective analysis of thioridazine (THD) and thioridazine 2-sulfone (THD 2-SO(2)) in human plasma based on liquid-liquid extraction with diethyl ether and chiral resolution of the enantiomers on Chiralpak AD and Chiralcel OD-H columns, respectively. After validation, the methods were used to study the degradation and racemization of both drug and metabolite. Our results showed that both enantiomers of THD and THD 2-SO(2) were stable at varying temperatures, pH, and ionic strengths; however, solubility problems for THD and THD 2-SO(2) enantiomers were observed, mainly at pH 8.5. The influence of light on the stability of the THD and THD 2-SO(2) enantiomers was also studied. Degradation of the THD enantiomers was observed under UV light (254 and 366 nm) while THD 2-SO(2) enantiomers were stable at these wavelengths and also when exposed to visible light.

High-performance liquid chromatographic method for the determination and pharmacokinetic study of dehydrotumulosic acid in the plasma of rats having taken the traditional chinese medicinal preparation Ling-Gui-Zhu-Gan decoction

A high-performance liquid chromatographic method for the determination of dehydrotumulosic acid in plasma of rats having been administrated orally with the traditional Chinese medicinal preparation Ling-Gui-Zhu-Gan decoction was developed. Plasma samples taken from rats were acidified with hydrochloric acid and extracted with ethyl acetate. Separation of the main effective constituent dehydrotumulosic acid was accomplished on a C(18) stationary phase and a mobile phase of methanol-acetonitrile-2% glacial acetic acid (13:12:10, v/v), with a UV detector setting at 242 nm. After validation, the method was used for preliminary investigation of the pharmacokinetic profiles of dehydrotumulosic acid administrated in Ling-Gui-Zhu-Gan decoction.

The 10 basic requirements for a scientific paper reporting antioxidant, antimutagenic or anticarcinogenic potential of test substances in in vitro experiments and animal studies in vivo

There is increasing evidence that chemicals/test substances cannot only have adverse effects, but that there are many substances that can (also) have a beneficial effect on health. As this journal regularly publishes papers in this area and has every intention in continuing to do so in the near future, it has become essential that studies reported in this journal reflect an adequate level of scientific scrutiny. Therefore a set of essential characteristics of studies has been defined. These basic requirements are default properties rather than non-negotiables: deviations are possible and useful, provided they can be justified on scientific grounds. The 10 basic requirements for a scientific paper reporting antioxidant, antimutagenic or anticarcinogenic potential of test substances in in vitro experiments and animal studies in vivo concern the following areas: (1) Hypothesis-driven study design; (2) The nature of the test substance; (3) Valid and invalid test systems; (4) The selection of dose levels and gender; (5) Reversal of the effects induced by oxidants, carcinogens and mutagens; (6) Route of administration; (7) Number and validity of test variables; (8) Repeatability and reproducibility; (9) Statistics; and (10) Quality Assurance.