Analytical methods validation: bioavailability, bioequivalence and pharmacokinetic studies. Conference report

Steady-state pharmacokinetics and tolerability of indinavir-lopinavir/r combination therapy in antiretroviral-experienced patients

Six HIV-positive antiretroviral experienced patients initiating therapy with a regimen including lopinavir/ritonavir (400/100 mg twice per day) and indinavir (800 mg twice per day) underwent steady-state pharmacokinetic analysis. The AUC0-12 h of indinavir when combined with lopinavir/ritonavir was comparable with previously published data on indinavir/ritonavir 800/100 mg twice per day in HIV-infected individuals. However, lopinavir AUC0-12 h, Cmax, and C12 h were lower than previously reported in the absence of indinavir. The regimen was well tolerated, although 2 patients developed grade 3 hypertriglyceridemia. No patient discontinued the regimen because of indinavir-related urologic or retinoid-type adverse effects. Further study of the regimen with larger cohorts of patients is necessary.

Pharmacokinetics and bioequivalence of ranitidine and bismuth derived from two compound preparations

AIM: To evaluate the bioequivalence of ranitidine and bismuth derived from two compound preparations.

METHODS: The bioavailability was measured in 20 healthy male Chinese volunteers following a single oral dose (equivalent to 200 mg of ranitidine and 220 mg of bismuth) of the test or reference products in the fasting state. Then blood samples were collected for 24 h. Plasma concentrations of ranitidine and bismuth were analyzed by high-performance liquid chromatography and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. The non-compartmental method was used for pharmacokinetic analysis. Log-transformed C_max, AUC_(0-t) and AUC_(0-∞) were tested for bioequivalence using ANOVA and Schuirmann two-one sided t-test. T_max was analyzed by Wilcoxon’s test.

RESULTS: Various pharmacokinetic parameters of ranitidine derived from the two compound preparations, including C_max, AUC_(0-t), AUC_(0-∞), T_max and T_1/2, were nearly consistent with previous observations. These parameters derived from test and reference drug were as follows: C_max (0.67 ± 0.21 vs 0.68 ± 0.22 mg/L), AUC_(0-t) (3.1 ± 0.6 vs 3.0 ± 0.7 mg/L per hour), AUC_(0-∞) (3.3 ± 0.6 vs 3.2 ± 0.8 mg/L per hour), T_max (2.3 ± 0.9 vs 2.1 ± 0.9 h) and T_1/2 (2.8 ± 0.3 vs 3.1 ± 0.4 h). In addition, double-peak absorption profiles of ranitidine were found in some Chinese volunteers. For bismuth, those parameters derived from test and reference drug were as follows: C_max (11.80 ± 7.36 vs 11.40 ± 6.55 μg/L), AUC_(0-t) (46.65 ± 16.97 vs 47.03 ± 21.49 μg/L per hour), T_max (0.50 ± 0.20 vs 0.50 ± 0.20 h) and T_1/2 (10.2 ± 2.3 vs 13.0 ± 6.9 h). Ninety percent of confidence intervals for the test/reference ratio of C_max, AUC_(0-t) and AUC_(0-) derived from both ranitidine and bismuth were found within the bioequivalence acceptable range of 80%-125%. No significant difference was found in T_max derived from both ranitidine and bismuth.

CONCLUSION: The two compound preparations are bioequivalent and may be prescribed interchangeably.

Soy isoflavones reduce heat shock proteins in experimental atherosclerosis

BACKGROUND

Soy isoflavones may affect several biochemical pathways like the synthesis of nitric oxide (*NO) and heat shock proteins (HSP) that are important factors for atherosclerosis development.

THE AIM OF THE STUDY

The purpose of this study was to investigate the influence of soy isoflavones on the production of *NO and HSP60, HSP70 and HSC70 in experimental atherosclerosis.

METHODS

One group of rabbits (New Zealand) was fed an atherogenic diet containing 27 % casein (CAS) and another group was fed the same diet supplemented with soy isoflavones (5 mg/kg/day) (ISO). Blood samples were obtained monthly and after six months of feeding, the rabbits were sacrificed and the aortas were removed.

RESULTS

The ISO group showed a significant reduction of cholesterol in LDL (36.2 %) and in aorta (36 %), as well as, an increase of HDL-cholesterol (2.1 times) in relation to the CAS group. The concentration of *NO metabolites (NOx) in blood plasma and the levels of reactive antibodies to HSC70 in blood plasma and to HSC70 and HSP70 in aortic tissue were significantly decreased in the ISO group. Isoflavones promoted a reduction of content of HSP60, HSP70 and HSC70 in aortic arch analyzed by immunohistochemistry. The isoflavone supplementation promoted a reduction of cholesterol content in aorta (62.2 %) (p < 0.05).

CONCLUSIONS

Soy isoflavones reduced hypercholesterolemia, the production of HSP60, HSC70 and HSP70 and reactive antibodies to HSC70 in serum and to HSC70 and HSP70 in aorta, as well as, the cholesterol content in atherosclerotic lesions in rabbits fed a casein-based atherogenic diet.

Rapid, simple and highly sensitive LC-ESI-MS/MS method for the quantification of tamsulosin in human plasma

A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for quantification of tamsulosin (I), a highly selective alpha1-adrenoceptor antagonist used for the treatment of patients with symptomatic benign prostatic hyperplasia. The analyte and internal standard, mosapride (II) were extracted by liquid-liquid extraction with diethyl ether-dichloromethane (70:30, v/v) using a Glas-Col Multi-Pulse Vortexer. The chromatographic separation was performed on a reverse phase Waters symmetry C18 column with a mobile phase of 0.03% formic acid-acetonitrile (30:70, v/v). The protonated analyte was quantitated in positive ionization by multiple reaction monitoring with a mass spectrometer. The mass transitions m/z 409.1 solidus in circle 228.1 and m/z 422.3 solidus in circle 198.3 were used to measure I and II, respectively. The assay exhibited a linear dynamic range of 0.1-50.0 ng/mL for tamsulosin in human plasma. The lower limit of quantitation was 100 pg/mL with a relative standard deviation of less than 10%. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. A run time of 2.0 min for each sample made it possible to analyze a throughput of more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.

Phase II study of imatinib mesylate plus hydroxyurea in adults with recurrent glioblastoma multiforme

PURPOSE

We performed a phase II study to evaluate the combination of imatinib mesylate, an adenosine triphosphate mimetic, tyrosine kinase inhibitor, plus hydroxyurea, a ribonucleotide reductase inhibitor, in patients with recurrent glioblastoma multiforme (GBM).

PATIENTS AND METHODS

Patients with GBM at any recurrence received imatinib mesylate plus hydroxyurea (500 mg twice a day) orally on a continuous, daily schedule. The imatinib mesylate dose was 500 mg twice a day for patients on enzyme-inducing antiepileptic drugs (EIAEDs) and 400 mg once a day for those not on EIAEDs. Assessments were performed every 28 days. The primary end point was 6-month progression-free survival (PFS).

RESULTS

Thirty-three patients enrolled with progressive disease after prior radiotherapy and at least temozolomide-based chemotherapy. With a median follow-up of 58 weeks, 27% of patients were progression-free at 6 months, and the median PFS was 14.4 weeks. Three patients (9%) achieved radiographic response, and 14 (42%) achieved stable disease. Cox regression analysis identified concurrent EIAED use and no more than one prior progression as independent positive prognostic factors of PFS. The most common toxicities included grade 3 neutropenia (16%), thrombocytopenia (6%), and edema (6%). There were no grade 4 or 5 events. Concurrent EIAED use lowered imatinib mesylate exposure. Imatinib mesylate clearance was decreased at day 28 compared with day 1 in all patients, suggesting an effect of hydroxyurea.

CONCLUSION

Imatinib mesylate plus hydroxyurea is well tolerated and associated with durable antitumor activity in some patients with recurrent GBM.

Determination of the novel non-peptidic HIV-protease inhibitor tipranavir by HPLC–UV after solid-phase extraction

An HPLC method previously described for the assay of amprenavir (APV), ritonavir (RTV), indinavir (IDV), saquinavir (SQV), nelfinavir (NFV), lopinavir (LPV), atazanavir (ATV), nevirapine (NVP) and efavirenz (EFV) can be also conveniently applied, with minor gradient program adjustment, for the determination of the novel non-peptidic HIV protease inhibitor tipranavir (TPV) in human plasma, by off-line solid-phase extraction (SPE) followed by HPLC coupled with UV-diode array detection (DAD). After viral inactivation by heat, the plasma is diluted with phosphate buffer (pH 7), and subjected to a SPE on a C18 cartridge. Matrix components are eliminated with a solution of 0.1% H3PO4 solution neutralised to pH 7, and TPV is eluted with MeOH. The resulting eluate is evaporated and reconstituted in 100 microl MeOH/H2O 50/50. A 40 microl volume is injected onto a Nucleosil C18 AB column and TPV is analysed by UV detection at 201 nm using a gradient elution program constituted of MeCN and phosphate buffer adjusted to pH 5.12 and containing 0.02% sodium heptanesulfonate. The calibration curves are linear up to 75 microg/ml, with a lower limit of quantification of 0.125 microg/ml. The mean absolute recovery of TPV is 77.1+/-4.0%. The method is precise with mean inter-day coefficient of variations (CVs) within 2.2-3.4%, and accurate (range of inter-day deviations from 0.7 to 1.2%). The method has been validated and is currently applied to the monitoring of TPV plasma levels in HIV patients.

High sensitivity assays for docetaxel and paclitaxel in plasma using solid-phase extraction and high-performance liquid chromatography with UV detection

Background

The taxanes paclitaxel and docetaxel have traditionally been used in high doses every third week in the treatment of cancer. Lately there has been a trend towards giving weekly low doses to improve the therapeutic index. This article describes the development of high performance liquid chromatographic (HPLC) methods suitable for monitoring taxane levels in patients, focusing on patients receiving low-dose therapy.

Methods

Paclitaxel and docetaxel were extracted from human plasma by solid phase extraction, and detected by absorbance at 227 nm after separation by reversed phase high performance liquid chromatography. The methods were validated and their performance were tested using samples from patients receiving paclitaxel or docetaxel.

Results

The limits of quantitation were 1 nM for docetaxel and 1.2 nM for paclitaxel. For both compounds linearity was confirmed from the limit of quantitation up to 1000 nM in plasma. The recoveries ranged between 92% and 118% for docetaxel and between 76% and 104% for paclitaxel. Accuracy and precision were within international acceptance criteria, that is within ± 15%, except at the limit of quantitation where values within ± 20% are acceptable. Low-dose patients included in an on going clinical trial had a median docetaxel concentration of 2.8 nM at 72 hours post infusion. Patients receiving 100 mg/m² of paclitaxel had a mean paclitaxel concentration of 21 nM 48 hours after the end of infusion.

Conclusion

We have developed an HPLC method using UV detection capable of quantifying 1 nM of docetaxel in plasma samples. The method should be useful for pharmacokinetic determinations at all relevant doses of docetaxel. Using a similar methodology paclitaxel can be quantified down to a concentration of 1.2 nM in plasma with acceptable accuracy and precision. We further demonstrate that the previously reported negative influence of Cremophor EL on assay performance may be overcome by degradation of the detergent by incubation with lipase.

Quantification of granisetron in human plasma by liquid chromatography coupled to electrospray tandem mass spectrometry

A simple, sensitive and rapid high-performance liquid chromatography/electrospray ionization tandem mass spectrometry method was developed and validated for the assay of granisetron in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase C18 column and analyzed by MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 313/138 for granisetron and m/z 409/228 for the IS. The assay exhibited a linear dynamic range of 0.1-20 ng/mL for granisetron in human plasma. The lower limit of quantification was 100 pg/mL with a relative standard deviation of less than 5%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.

Quantification of tizanidine in human plasma by liquid chromatography coupled to tandem mass spectrometry

A simple, sensitive and rapid high-performance liquid chromatography/positive ion electrospray tandem mass spectrometry (MS/MS) method was developed and validated for the assay of tizanidine in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase column and analyzed by MS/MS in the selected reaction monitoring mode. The assay exhibited a linear dynamic range of 50-5000 pg/mL for tizanidine in human plasma. The lower limit of quantification was 50 pg/mL with a relative standard deviation of less than 13%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.5 min for each sample made it possible to analyze more than 300 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.

Quantification of trandolapril and its metabolite trandolaprilat in human plasma by liquid chromatography/tandem mass spectrometry using solid-phase extraction

A sensitive high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (MS/MS) method was developed and validated for the simultaneous quantification of trandolapril and its metabolite trandolaprilat in human plasma using ramipril as an internal standard. Following solid-phase extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase column and analyzed by MS/MS in the multiple reaction monitoring mode using the respective [M-H]- ions, m/z 429/168 for trandolapril, m/z 401/168 for trandolaprilat and m/z 415/166 for the internal standard. The method exhibited a linear dynamic range of 20-10,000 pg/mL for both trandolapril and trandolaprilat in human plasma. The lower limit of quantification was 20 pg/mL for both trandolapril and its metabolite. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.

Simultaneous quantification of fexofenadine and pseudoephedrine in human plasma by liquid chromatography/tandem mass spectrometry with electrospray ionization: method development, validation and application to a clinical study

To support the pharmacokinetic and bioavailability study of a once-daily fexofenadine/pseudoephedrine combination, a high-performance liquid chromatography/positive ion electrospray tandem mass spectrometry (HPLC/ESI-MS/MS) method for the simultaneous quantification of fexofenadine and pseudoephedrine was developed and validated with 500 microL human plasma using mosapride as an internal standard (IS). Following solid-phase extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase column and analyzed by MS/MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 502/466 for fexofenadine, m/z 166/148 for pseuoephedrine and m/z 422/198 for the IS. The method exhibited linear dynamic ranges of 1-500 ng/mL and 2-1000 ng/mL for fexofenadine and pseudoephedrine, respectively, in human plasma. The lower limits of quantification were 1 and 2 ng/mL with a relative standard deviation of less than 10% for fexofenadine and pseudoephedrine, respectively. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The total chromatographic run time was 2 min and more than 400 human plasma samples could be analyzed in one day by running the system overnight. The method is precise and sensitive enough for its intended purpose.

Determination of paclitaxel in human plasma following the administration of Genaxol or Genetaxyl by liquid chromatography/tandem mass spectrometry

A sensitive and specific assay for paclitaxel in plasma has been developed to overcome limitations in previously published assays, using liquid chromatography with tandem mass spectrometric detection. Plasma samples (100 microL) were subjected to liquid-liquid extraction with 1-chlorobutane/acetonitrile (4:1, v/v), with [(2)H(5)]paclitaxel employed as the internal standard. Chromatography was carried out with a Waters SymmetryShield C8 column (50 x 2.1 mm, 3.5 microm). The total run time, including equilibration, was 8 min, using a gradient of acetonitrile and 10 mM ammonium formate, pH 4.0. The assay is accurate and precise over the range of 2-2500 ng/mL and has been successfully applied to study the clinical pharmacokinetics of two formulations of paclitaxel, Genaxol and Genetaxyl, given orally and intravenously.

High-throughput quantification of perindopril in human plasma by liquid chromatography/tandem mass spectrometry: application to a bioequivalence study

A simple, sensitive and rapid high-performance liquid chromatography/positive ion electrospray tandem mass spectrometry method was developed and validated for the quantification of perindopril in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase column and analyzed by mass spectrometry in the multiple reaction monitoring mode using the respective [M+H](+) ions, m/z 369/172 for perindopril and m/z 417/234 for the internal standard. The method exhibited a linear dynamic range of 0.1-100 ng/mL for perindopril in human plasma. The lower limit of quantification was 0.1 ng/mL with a relative standard deviation of less than 6.1%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 450 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability and bioequivalence studies.

Sensitive and rapid liquid chromatography/tandem mass spectrometry assay for the quantification of amlodipine in human plasma

A simple, sensitive and rapid high-performance liquid chromatography/electrospray ionization tandem mass spectrometry method was developed and validated for the assay of amlodipine in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reverse-phase C(18) column and analyzed by MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 409/238 for amlodipine and m/z 409/228 for the IS. The assay exhibited a linear dynamic range of 50-10,000 pg/mL for amlodipine in human plasma. The lower limit of quantification was 50 pg/mL with a relative standard deviation of less than 8%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The average absolute recoveries of amlodipine and the IS from spiked plasma samples were 74.7 +/- 4.6 and 72.1 +/- 2.0%, respectively. A run time of 1.5 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies. The observed maximum plasma concentration (Cmax) of amlodipine (2.5 mg oral dose) was 1425 pg/mL, time to observed maximum plasma concentration (Tmax) was 8.1 h and elimination half-life (T(1/2)) was 50.1 h.

Use of microbore LC-MS/MS for the quantification of oxcarbazepine and its active metabolite in rat brain microdialysis samples

A microbore LC-MS/MS method is developed and validated for the quantification of the anti-epileptic drug oxcarbazepine (OXC) and its active metabolite 10,11-dihydro-10-hydroxycarbamazepine (MHD) in rat brain microdialysates, together with the internal standard for microdialysis probe calibration, 2-methyl-5H-dibenz(b,f)azepine-5-carboxamide (m-CBZ). The benefits of gradient versus isocratic separation are shown, next to the improved sensitivity resulting from the addition of 0.1% formic acid to the mobile phase. The coupling of microdialysis with ESI-MS requires sample desalting for which column switching was applied. Using weighed regression to calculate the calibration curves (1-1000 ng/mL), the assay was validated in terms of linearity, accuracy and precision, yielding a sensitive (limit of quantification is 1 ng/mL) and selective method for quantification of OXC, MHD and m-CBZ. By applying this method, we were able to determine the extracellular concentrations of OXC and MHD during at least 4h after intraperitoneal (i.p.) administration of 10 mg/kg OXC.

Effect of the St. John's wort constituent hyperforin on docetaxel metabolism by human hepatocyte cultures

BACKGROUND AND PURPOSE

St. John's wort is a commonly used herbal medication that increases cytochrome P450 3A (CYP3A) activity. Because docetaxel is inactivated by CYP3A, we studied the effects of the St. John's wort constituent hyperforin on docetaxel metabolism in a human hepatocyte model.

EXPERIMENTAL DESIGN

Hepatocytes, isolated from three donor livers, were exposed to hyperforin (0.1, 0.5, or 1.5 micromol/L) or rifampin (10 micromol/L) for 48 hours. After 48 hours, hyperforin- or rifampin-containing medium was replaced with medium containing 100 micromol/L docetaxel. After 1 hour, docetaxel metabolism was characterized by liquid chromatography-tandem mass spectrometry. Subsequent incubations characterized the specific cytochrome P450s that produced the docetaxel metabolites observed in hepatocyte incubations.

RESULTS

Rifampin induced docetaxel metabolism 6.8- to 32-fold above docetaxel metabolism in control cultures. Hyperforin induced docetaxel metabolism in all three hepatocyte preparations. Hyperforin induction was dose-dependent and, at maximum, was 2.6- to 7-fold greater than that in controls. Docetaxel metabolites identified in rifampin- and hyperforin-treated hepatocyte preparations included the previously described tert-butyl-hydroxylated metabolite and two previously unidentified metabolites involving hydroxylation on the baccatin ring. CYP3A4 produced the tert-butyl-hydroxylated metabolite and the two ring-hydroxylated metabolites. CYP2C8 produced one of the newly described ring-hydroxylated metabolites.

CONCLUSIONS

Exposure to the St. John's wort constituent hyperforin induces docetaxel metabolism in vitro. This implies that subtherapeutic docetaxel concentrations may result when docetaxel is administered to patients using St. John's wort on a chronic basis. The results also show induction of previously undescribed metabolic pathways for docetaxel, one of which may be analogous to the known 6-alpha-hydroxylation of paclitaxel by CYP2C8.

Plasma pharmacokinetics, oral bioavailability, and interspecies scaling of the DNA methyltransferase inhibitor, zebularine

PURPOSE

Zebularine is a DNA methyltransferase inhibitor proposed for clinical evaluation.

EXPERIMENTAL DESIGN

We developed a liquid chromatography/mass spectrometry assay and did i.v. and oral studies in mice, rats, and rhesus monkeys.

RESULTS

In mice, plasma zebularine concentrations declined with terminal half-lives (t(1/2)) of 40 and 91 minutes after 100 mg/kg i.v. and 1,000 mg/kg given orally, respectively. Zebularine plasma concentration versus time curves (area under the curve) after 100 mg/kg i.v. and 1,000 mg/kg given orally were 7,323 and 4,935 mug/mL min, respectively, corresponding to a total body clearance (CL(tb)) of 13.65 mL/min/kg, apparent total body clearance (CL(app)) of 203 mL/min/kg, and oral bioavailability of 6.7%. In rats, plasma zebularine concentrations declined with t(1/2) of 363, 110, and 126 minutes after 50 mg/kg i.v., 250 mg/kg given orally, and 500 mg/kg given orally, respectively. Zebularine areas under the curve after 50 mg/kg i.v., 250 mg/kg given orally, and 500 mg/kg given orally were 12,526, 1,969, and 7,612 mug/mL min, respectively, corresponding to a CL(tb) of 3.99 mL/min/kg for 50 mg/kg i.v. and CL(app) of 127 and 66 mL/min/kg for 250 and 500 mg/kg given orally, respectively. Bioavailabilities of 3.1% and 6.1% were calculated for the 250 and 500 mg/kg oral doses, respectively. In monkeys, zebularine t(1/2) was 70 and 150 minutes, CL(tb) was 3.55 and 10.85 mL/min/kg after i.v. administration, and CL(app) was 886 and 39,572 mL/min/kg after oral administration of 500 and 1,000 mg/kg, respectively. Zebularine oral bioavailability was <1% in monkeys. Interspecies scaling produced the following relationship: CL(tb) = 6.46(weight(0.9)).

CONCLUSIONS

Zebularine has limited oral bioavailability. Interspecies scaling projects a CL(tb) of 296 mL/min in humans.

Method to Detect Minimal Amounts of Calcium Dissolved in Acidic Solutions

The study describes the application of the Arsenazo III method for detection of minimal amounts of calcium 12.4-49.4 micromol/l in different acidic solutions (hydrochloric acid, oxalic acid, maleic acid, phosphoric acid, tartaric acid, citric acid, lactic acid and acetic acid) adjusted to pH 2.0, 2.3 and 3.0. A mixture of the respective calcium concentrations with distilled water served as control. The experiments were run with ten repeats in series. Assessment of intra- and interassay coefficient of variation, and lower limit of quantification revealed that depending on the acid used, the Arsenazo III method is a reliable tool to quantify minimal calcium contents in acidic solutions.

Stochastic Differential Equations in NONMEM®: Implementation, Application, and Comparison with Ordinary Differential Equations

PURPOSE

The objective of the present analysis was to explore the use of stochastic differential equations (SDEs) in population pharmacokinetic/pharmacodynamic (PK/PD) modeling.

METHODS

The intra-individual variability in nonlinear mixed-effects models based on SDEs is decomposed into two types of noise: a measurement and a system noise term. The measurement noise represents uncorrelated error due to, for example, assay error while the system noise accounts for structural misspecifications, approximations of the dynamical model, and true random physiological fluctuations. Since the system noise accounts for model misspecifications, the SDEs provide a diagnostic tool for model appropriateness. The focus of the article is on the implementation of the Extended Kalman Filter (EKF) in NONMEM for parameter estimation in SDE models.

RESULTS

Various applications of SDEs in population PK/PD modeling are illustrated through a systematic model development example using clinical PK data of the gonadotropin releasing hormone (GnRH) antagonist degarelix. The dynamic noise estimates were used to track variations in model parameters and systematically build an absorption model for subcutaneously administered degarelix.

CONCLUSIONS

The EKF-based algorithm was successfully implemented in NONMEM for parameter estimation in population PK/PD models described by systems of SDEs. The example indicated that it was possible to pinpoint structural model deficiencies, and that valuable information may be obtained by tracking unexplained variations in parameters.

Pharmacokinetic/Pharmacodynamic Modellingof GnRH Antagonist Degarelix: A Comparisonof the Non-linear Mixed-Effects Programs NONMEM and NLME

In this paper, the two non-linear mixed-effects programs NONMEM and NLME were compared for their use in population pharmacokinetic/pharmacodynamic (PK/PD) modelling. We have described the first-order conditional estimation (FOCE) method as implemented in NONMEM and the alternating algorithm in NLME proposed by Lindstrom and Bates. The two programs were tested using clinical PK/PD data of a new gonadotropin-releasing hormone (GnRH) antagonist degarelix currently being developed for prostate cancer treatment. The pharmacokinetics of intravenous administered degarelix was analysed using a three compartment model while the pharmacodynamics was analysed using a turnover model with a pool compartment. The results indicated that the two algorithms produce consistent parameter estimates. The bias and precision of the two algorithms were further investigated using a parametric bootstrap procedure which showed that NONMEM produced more accurate results than NLME together with the nlmeODE package for this specific study.

Stability, pKa and plasma protein binding of roscovitine

In the present investigation, the binding of roscovitine (100, 500 and 1500 ng/mL) to plasma proteins was studied at 25 and 37 degrees C by ultrafiltration and equilibrium dialysis methods. Drug stability in plasma was assessed during a 48 h at 4, 25 and 37 degrees C. The effect of thawing and freezing on drug stability was studied. The pKa of roscovitine was measured using capillary electrophoresis coupled with mass spectrometry. Roscovitine was quantified utilizing liquid chromatography and tandem mass spectrometry. Roscovitine is highly bound to plasma proteins (90%). Binding of roscovitine to human serum albumin was constant (about 90%) within concentration range studied while the binding to alpha1-acid glycoprotein decreased with increasing drug concentration indicating that albumin is more important in clinical settings. However, alpha1-acid glycoprotein might be important when plasma proteins change with disease. Protein binding was higher at 25 degrees C compared to 37 degrees C. The results obtained by equilibrium dialysis were in good agreement with those obtained by ultrafiltration. Roscovitine was stable at all temperatures studied during 48 h. Roscovitine has a pKa of 4.4 showing that the drug mainly acts like a weak mono-base. The results obtained in our studies are important prior to clinical trials and to perform pharmacokinetic studies.

Quantitative analysis of Δ9-tetrahydrocannabinol in preserved oral fluid by liquid chromatography–tandem mass spectrometry

A rapid and sensitive method for the analysis of delta9-tetrahydrocannabinol (THC) in preserved oral fluid was developed and fully validated. Oral fluid was collected with the Intercept, a Food and Drug Administration (FDA) approved sampling device that is used on a large scale in the U.S. for workplace drug testing. The method comprised a simple liquid-liquid extraction with hexane, followed by liquid chromatography-tandem mass spectrometry (LC-MS-MS) analysis. Chromatographic separation was achieved using a XTerra MS C18 column, eluted isocratically with 1 mM ammonium formate-methanol (10:90, v/v). Selectivity of the method was achieved by a combination of retention time, and two precursor-product ion transitions. The use of the liquid-liquid extraction was demonstrated to be highly effective and led to significant decreases in the interferences present in the matrix. Validation of the method was performed using both 100 and 500 MicroL of oral fluid. The method was linear over the range investigated (0.5-100 ng/mL and 0. 1-10 ng/mL when 100 and 500 microL, respectively, of oral fluid were used) with an excellent intra-assay and inter-assay precision (relative standard deviations, RSD <6%) for quality control samples spiked at a concentration of 2.5 and 25 ng/mL and 0.5 and 2.5 ng/mL, respectively. Limits of quantification were 0.5 and 0.1 ng/mL when using 100 and 500 microL, respectively. In contrast to existing GC-MS methods, no extensive sample clean-up and time-consuming derivatisation steps were needed. The method was subsequently applied to Intercept samples collected at the roadside and collected during a controlled study with cannabis.

Preclinical toxicity of a geldanamycin analog, 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG), in rats and dogs: potential clinical relevance

PURPOSE

17-DMAG is a hydrophilic derivative of the molecular chaperone inhibitor 17-(allylamino)-17-demethoxygeldanamycin (17-AAG; NSC-330507), which is currently being evaluated for the treatment of cancer in clinical trials. 17-DMAG offers a potential advantage over 17-AAG because its aqueous solubility eliminates the need for complicated formulations that are currently used for administration of 17-AAG. In addition, 17-DMAG undergoes only limited metabolism compared to 17-AAG. The present results are from preclinical toxicity studies evaluating 17-DMAG in rats and dogs.

METHODS

Doses of 0, 2.4, 12 and 24 mg/m2 per day were administered to rats, while dogs received doses of 0, 8 or 16 mg/m2 per day. In both species, 17-DMAG was administered i.v. (slow bolus for rats; 1-h infusion for dogs) daily for 5 days. An additional cohort of dogs received 16 mg/m2 per day orally for 5 days. Clinical observations were noted, and standard hematology and clinical chemistry parameters were monitored. Selected tissues were evaluated microscopically for drug-related lesions. Tissue and plasma 17-DMAG concentrations were measured by HPLC/MS at selected time-points on days 1 and 5.

RESULTS

Daily i.v. administration of 17-DMAG at doses of 24 mg/m2 per day in rats or 16 mg/m2 per day in dogs produced lethality on day 6, approximately 24 h following the last dose. Body weight loss was common in rats and dogs. Drug-related gastrointestinal, bone marrow and hepatic toxicities were also common in rats and dogs. Dogs also exhibited signs of renal and gallbladder toxicity. Plasma concentrations of 17-DMAG increased proportionately with dose in rats and disproportionately with dose in dogs. In rat tissues, however, only fourfold to sixfold increases in 17-DMAG concentrations were observed with a tenfold increase in dose. The highest concentrations of 17-DMAG were found in the liver of rats, with progressively lower concentrations in the spleen, lung, kidney and plasma. Regardless of the route of administration, higher drug concentrations were present in plasma (rat and dog) and tissue (rat) samples obtained on day 5 compared to those obtained on day 1. Although plasma concentrations decreased with time, 17-DMAG was still detected in dog plasma for at least 24 h after drug administration.

CONCLUSIONS

With the recent approval of 17-DMAG for clinical use, the data generated from these preclinical studies will provide guidance to clinicians as they administer this drug to their patients. The MTD of 17-DMAG was 12 mg/m2 per day in rats and 8 mg/m2 per day in dogs; therefore, the recommended starting dose for phase I trial is 1.3 mg/m2 per day for 5 days. Gastrointestinal and bone marrow toxicity were dose-limiting in rats, and gastrointestinal, renal, gallbladder and bone marrow toxicity were dose-limiting in dogs. All adverse effects were fully reversible in surviving animals after treatment was complete.

Tissue distribution and excretion of 125I-lidamycin in mice and rats

AIM: To investigate the tissue distribution, urinary and fecal excretions of ¹²⁵I-lidamycin (¹²⁵I-C-1027) in mice and its biliary excretion in rats.

METHODS: The total radioactivity assay (RA method) and the radioactivity assay after precipitation with 200 mL/L trichloroacetic acid (TCA-RA method) were used to dete-rmine the tissue distribution, and the urinary and fecal excretions of ¹²⁵I-C-1027 in mice and its biliary excretion in rats.

RESULTS: Tissue concentrations reached the peak at the fifth minute after administration of ¹²⁵I-C-1027 to mice. The highest concentration was in kidney, and the lowest in brain at all test-time points. The organs of the concentr-ations of ¹²⁵I-C-1027 from high to low were kidney, lung, liver, stomach, spleen, uterus, ovary, intestine, muscle, heart, testis, fat, and brain in mice. The accumulative excretion amounts of 0-24 h, and 0-96 h after administration of ¹²⁵I-C-1027 were 68.36 and 71.64% in urine, and 2.60 and 3.21% in feces of mice, respectively, and the accumulative excretion amount of 0-24 h was 3.57% in bile in rats.

CONCLUSION: Our results reflect the characteristics of the tissue distribution, urinary and fecal excretions of ¹²⁵I-C-1027 in mice and the biliary excretion of ¹²⁵I-C-1027 and its metabolites in rats, and indicate that ¹²⁵I-C-1027 and its metabolites are mainly distributed in kidney, and excreted in urine.

A validated liquid chromatography–mass spectrometry method for the determination of leukotrienes B4 and B5 produced by stimulated human polymorphonuclear leukocytes

A validated high-performance liquid chromatography (HPLC)-mass spectrometry method has been developed for the simultaneous assay of leukotrienes (LTs) B4 and B5, derived from omega-6 arachidonic acid and omega-3 polyunsaturated fatty acids (PUFA), respectively, produced by human polymorphonuclear leukocytes (PMNLs) stimulated with calcium ionophore A23187. The HPLC separation of PMNL ether extracts was performed on a reversed-phase column using a gradient elution program of 15 mM ammonium acetate and MeOH. Detection was performed by electrospray ionization-single quadripole mass spectrometry using single ion reaction monitoring in the negative mode at m/z 333.3 [M-H](-) and m/z 335.2 for prostaglandin B2/LTB5 and LTB4, respectively. The calibration curves for LTB4 and LTB5 were linear over the ranges 165-990 and 0.825-13.2 ng/ml, respectively. The lower limit of quantification for LTB5 was 0.66 ng/ml. The mean absolute recoveries for LTB4 and LTB5 were 81+/-4.8% and 82+/-5.9%, respectively. The method is precise with mean interday CVs for LTB4 and LTB5 within 7.1-10.7, and 3.8-9.4%, respectively, and accurate (range of interday deviations for LTB4 and LTB5 were -7.8 to 1, and -5 to 9% , respectively). The method has been validated and is being applied to the simultaneous quantification of the leukotrienes B4 and B5 in stimulated PMNLs in a clinical protocol studying the influence of a diet enriched in omega-3 PUFA on various surrogate markers of inflammation in young cystic fibrosis patients.

Suitability of a malachite green procedure to detect minimal amounts of phosphate dissolved in acidic solutions

The study describes the suitability of a colorimetric method (malachite green procedure) for detection of minimal amounts of phosphate (7.3-29.1 micromol/L) in different acidic solutions (hydrochloric acid, oxalic acid, maleic acid, perchloric acid, tartaric acid, citric acid, lactic acid and acetic acid) adjusted to pH 2.0. A mixture of the respective phosphate concentrations with distilled water served as control. The experiments were run with ten repeats in series. Assessment of intra- and interassay coefficient of variation and lower limit of quantification revealed that depending on the acid used, the applied method is a reliable and suitable tool to detect and quantify minimal phosphate contents in small samples of acidic solutions that have the potential to cause erosive dental lesions.

Bioavailability of diclofenac potassium at low doses

AIM

Diclofenac-K has been recently launched at low oral doses in different countries for over-the-counter use. However, given the considerable first-pass metabolism of diclofenac, the degree of absorption of diclofenac-K at low doses remained to be determined. The aim of this study was to determine the bioavailability of low-dose diclofenac-K.

METHODS

A randomized, three-way, cross-over study was performed in 10 subjects. Each received diclofenac-K, 22.5 mg via short-term i.v. infusion and orally at single doses of 12.5 mg and 25 mg.

RESULTS

Mean (+/- SD) times to maximal plasma concentration (t(max)) of diclofenac were 0.48 +/- 0.28 h (12.5 mg) and 0.93 +/- 0.96 h (25 mg). The absolute bioavailability of diclofenac-K after oral administration did not differ significantly in the 12.5-mg and 25-mg dose group (63.1 +/- 12.6%vs. 65.1 +/- 19.4%, respectively). The 90% confidence intervals for the AUC(infinity) and AUC(t) ratios for the two oral regimes were 82.6, 103.4% (point estimate 92.4%) and 86.2, 112.9% (point estimate 98.6%), respectively. These values were within the acceptance criteria for bioequivalence (80-125%).

CONCLUSIONS

Our data indicate that diclofenac-K is rapidly and well absorbed at low dose, and are consistent with a rapid onset of action of the drug. Abbreviations AUC, area under plasma concentration-time curve; C(max), peak plasma concentration; CI, confidence interval; COX, cyclooxygenase; D, dose; F, absolute bioavailability; t(max), time to reach C(max).

Determination of thiamine and its phosphorylated forms in human plasma, erythrocytes and urine by HPLC and fluorescence detection: a preliminary study on cancer patients

In man, neurotoxicity associated to ifosfamide treatment can be reversed by intravenous thiamine administration. Trying to explain this clinical finding, we decided to study possible changes in thiamine availability and activation in patients exposed to ifosfamide. Free thiamine and its phosphate esters levels were measured in plasma, erythrocytes and urine by an ion-pair HPLC method with pre-column derivatization, which allowed separation of the fluorescent compounds in less than 10 min. The method was validated by linearity, sensitivity and reproducibility studies, whose values met the demands for bioanalytical assays. This method was applied to assess thiamine status in cancer patients exposed to ifosfamide therapy for advanced disease.

Stereospecific high-performance liquid chromatographic analysis of naringenin in urine

A method of analysis of naringenin [(+/-)-4',5,7-trihydroxyflavanone] in biological fluids is necessary to study the kinetics of in vitro and in vivo metabolism, tissue distribution in fruits and humans. A simple high-performance liquid chromatographic method was developed for simultaneous determination of naringenin enantiomers in rat and human urine. Urine (0.1 ml) was precipitated with cold acetonitrile after addition of the internal standard, daidzein. Separation was achieved on a Chiralcel OD-RH column with UV detection at 292 nm. The calibration curves were linear ranging from 0.5 to 100 microg/ml for each enantiomer. The mean extraction efficiency was >99%. Precision of the assay was <9.4% (CV), and was within 5.4% at the limit of quantitation (0.5 microg/ml). Bias of the assay was lower than 16%, and was within 15% at the limit of quantitation. The assay was applied successfully to the urinary excretion of naringenin in rats and humans.

Validation of a liquid chromatography assay for the quantification of the Raf kinase inhibitor BAY 43-9006 in small volumes of mouse serum

BAY 43-9006 is a selective Raf-1 kinase inhibitor with antitumor activity against a variety of human cancers. A highly sensitive HPLC method for determination of BAY 43-9006 in small volumes of serum (30 microl) was developed. Sample preparation involved a liquid-liquid extraction procedure with tolnaftate as internal standard followed by linear gradient elution at a reversed phase C18 column and UV detection. The method was selective and the calibration curves were linear over the concentration range of 80-2000 ng/ml. The intra-day accuracy ranged from 99.9 to 107.6% and the inter-day accuracy from 94.6 to 115%. The lower limit of quantitation (LOQ) was 80 ng/ml with an accuracy of 105.8%. Thus, this method has been validated and can be applied for the drug monitoring or pharmacokinetic studies of BAY 43-9006 in small volumes of serum samples.

Stereospecific high-performance liquid chromatographic analysis of hesperetin in biological matrices

A method of analysis of hesperetin (+/--3,5,7-trihydroxy-4'-methoxyflavanone) in biological fluids is necessary to study the kinetics of in vitro and in vivo metabolism and tissue distribution. A simple high-performance liquid chromatographic method was developed for simultaneous determination of hesperetin enantiomers in rat serum, and rat and human urine. Serum and urine (0.1 ml) were precipitated with cold acetonitrile after addition of the internal standard, 7-methoxycoumarin. Separation was achieved on a Chiralpak AD-RH column with UV detection at 298 nm. The calibration curve was linear ranging from 0.5 to 100 microg/ml for each enantiomer. The mean extraction efficiency was >98%. Precision of the assay was <5% (CV), and was within 5% at the limit of quantitation (0.5 microg/ml). Bias of the assay was lower than 5%, and was within 5% at the limit of quantitation. The assay was applied successfully to the urinary excretion of hesperetin in rats and humans.

BIBN4096BS Antagonizes Human α-calcitonin Gene Related Peptide–induced Headache and Extracerebral Artery Dilatation*

BACKGROUND AND OBJECTIVE

Calcitonin gene-related peptide (CGRP) plays a pivotal role in migraine pathogenesis. BIBN4096BS is the first CGRP receptor antagonist available for human studies, and its efficacy in the acute treatment of migraine has been demonstrated. We investigated the ability of BIBN4096BS to inhibit human alphaCGRP (h-alphaCGRP)-induced headache and cerebral hemodynamic changes in healthy volunteers.

METHODS

Ten healthy volunteers completed this double-blind, placebo-controlled crossover study with 2.5 mg BIBN4096BS and placebo as pretreatments before a 20-minute intravenous infusion of h-alphaCGRP (1.5 microg/min). Transcranial Doppler ultrasonography was used to measure blood flow velocity in the middle cerebral artery (MCA); regional and global cerebral blood flow (CBF) was measured by xenon 133 inhalation single-photon emission computed tomography. The temporal and radial artery diameter was measured by high-frequency ultrasound. Systemic hemodynamics, end-tidal partial pressure of carbon dioxide (PETCO(2)), and headache were monitored.

RESULTS

Of the 10 volunteers, 6 had a CGRP-induced headache during the in-hospital phase after placebo pretreatment but none after BIBN4096BS (P = .031). BIBN4096BS did not affect changes in the diameter of the MCA or changes in CBF induced by h-alphaCGRP. Vasodilatation of the extracranial arteries was, however, significantly inhibited (P < .001 for temporal artery and P = .001 for radial artery).

CONCLUSIONS

These results show that BIBN4096BS effectively prevents CGRP-induced headache and extracerebral vasodilatation but does not significantly affect the induced cerebral hemodynamic changes.

Simple and rapid HPLC method for determination of amlodipine in human serum with fluorescence detection and its use in pharmacokinetic studies

A fast, sensitive and specific high performance liquid chromatographic method using fluorescence detection is described for analysis of amlodipine in human serum. Amlodipine is extracted from serum by ethyl acetate and involves precolumn derivatization with 4-chloro-7-nitrobenzofurazan (NBD-Cl) and reverse-phase chromatography on C18 column. The mobile phase was sodium phosphate buffer (pH 2.5) containing 1 ml/l triethylamine and methanol at flow rate of 2.8 ml/min. Propranolol was used as internal standard. The standard curve was linear over the range 0.25-16 ng/ml of amlodipine in human serum. The within-day and between-day precision studies showed good reproducibility with coefficients of variation less than 12% for all the analytes. The limit of quantification was 0.25 ng/ml of serum. The method has been applied to a bioequivalence study after administration of 10 mg amlodipine in 12 normal subjects.

Pharmacokinetics of C-1027 in mice as determined by TCA-RA method

AIM

To validate a radioactivity assay, the TCA-RA method, for the measurement of C-1027 in serum and to evaluate its application in determination of pharmacokinetics of C-1027 in mice.

METHODS

(125)I-C-1027 was prepared by the Iodogen method and separated by HPLC. The radioactivity assay was established and used to determine (125)I-C-1027 in mice at doses of 10, 50 and 100 microg/kg after precipitation with 20% trichloroacetic acid (TCA-RA method). Several pharmacokinetic parameters were determined after intravenous injection of (125)I-C-1027 to mice.

RESULTS

After intravenous injection of (125)I-C-1027 to mice, at doses of 10, 50 and 100 microg/kg; the apparent distribution volumes (V(d)) were 0.26, 0.31 and 0.33 L/kg; the biological half-lives (T(1/2)) were 3.10, 3.40 and 3.90 h; the areas under curve (AUC) were 18.41, 103.69 and 202.74 ng/h/mL; the elimination rate constants (K) were 1.04, 1.26 and 0.58/h; and the total body clearance (Cl) were 0.54, 0.48 and 0.49 L/kg/h, respectively.

CONCLUSION

TCA-RA is a sensitive, reliable and suitable method for the determination of (125)I-C-1027 in mouse serum.

Automated, fast, and sensitive quantification of drugs in human plasma by LC/LC-MS: quantification of 6 protease inhibitors and 3 nonnucleoside transcriptase inhibitors

An analytic assay based on automated sample preparation and liquid chromatography (LC) coupled with electrospray mass spectrometry (ESI-MS) was developed for the quantification of 6 protease inhibitors (PIs) and 3 nonnucleoside reverse transcriptase inhibitors (NNRTIs). The 6 PIs, amprenavir, indinavir, ritonavir, lopinavir, nelfinavir, and saquinavir, as well as the three NNRTIs, nevirapine, efavirenz, and delavirdine, require a succinct analysis technique for therapeutic drug monitoring in HIV/AIDS patients. After protein precipitation, samples were loaded on a C8, 10 x 4-mm extraction column, washed, and, after activation of the column-switching valve, backflushed onto the 30 x 2.1 mm C8 analytic column. [M+H] ions were detected in the selected ion mode. A nonlinear fit (y(-1) = a + b/x, all r2 > 0.999) for amprenavir, indinavir, ritonavir, lopinavir, nelfinavir, and saquinavir and a linear fit (y = ax + b, all r2 > 0.999) for nevirapine, efavirenz, and delavirdine led to best regression. Absolute recoveries were as follows: PIs > 81%; NNRTIs > 76%. Interday and intraday precision were <12.5% for the PIs and <11.7% for the NNRTIs. Interday and intraday accuracy were <12.2% for the PIs and <14.9% for the NNRTIs. Limits of quantification were 20, 40, 50, 40, 40, 20, and 100 microg/L for amprenavir, indinavir, ritonavir, lopinavir, nelfinavir, saquinavir, and the NNRTIs, respectively. The assay allows fast analysis of patient samples for therapeutic drug monitoring (TDM) and has successfully been used for TDM and pharmacokinetic drug-drug interactions studies.

Pharmacokinetics of intravenous paracetamol in children and adolescents under major surgery

BACKGROUND

The aim of this study was to describe the pharmacokinetics of paracetamol (acetaminophen) and to get primary information on its metabolism after first indicated intravenous administration of paracetamol in children and adolescents undergoing major surgery.

METHODS

About 4 weeks after the last chemotherapy, seven children and adolescents (five osteosarcoma, two Ewing tumors) received paracetamol infusion (median: 15.0 mg/kg) for analgesia. Sparse serum (37 samples; 4-7 per patient) and urine samples (27 samples; 0-15 per patient) were analyzed for paracetamol, paracetamol-glucuronide, paracetamol-sulfate, paracetamol-mercapturate and paracetamol-cysteine using capillary electrophoresis. Nonlinear mixed-effect models were used to describe the pharmacokinetics of paracetamol in plasma.

RESULTS

Pharmacokinetics of paracetamol after intravenous administration was best described by a two-compartment model with clearance of 13.2 l/h per 70 kg (between-subject variability: 30%), intercompartmental clearance of 45.7 l/h per 70 kg (both parameters standardized to a 70-kg person using allometric "1/4 power models"), central volume of distribution of 13.2 l per 70 kg (between-subject variability: 71%) and peripheral volume of distribution of 33.0 l per 70 kg. Paracetamol, the glucuronide- and sulfate conjugates as well as cysteine and mercapturic acid conjugates, both products of oxidative pathways of paracetamol, were excreted in urine.

CONCLUSIONS

Surgery, with all its potential influencing factors, together with chemotherapy given about 4 weeks previously do not seem to have a major impact on the pharmacokinetic behavior and the between-subject variability of paracetamol after intravenous administration.

Validation and application of a high-performance liquid chromatography-tandem mass spectrometry assay for mosapride in human plasma

A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for quantification of mosapride (I), a novel and potent gastroprokinetic agent that enhances the upper gastrointestinal motility by stimulating 5-HT(4) receptor. The analyte and internal standard, tamsulosin (II), were extracted by liquid-liquid extraction with diethyl ether-dichloromethane (70:30, v/v) using a Glas-Col Multi-Pulse Vortexer. The chromatographic separation was performed on a reversed-phase Waters symmetry C(18) column with a mobile phase of 0.03% formic acid-acetonitrile (10:90, v/v). The protonated analyte was quantitated in positive ionization by multiple reaction monitoring with a mass spectrometer. The mass transitions m/z 422.3 -->198.3 and m/z 409.1 -->228.1 were used to measure I and II, respectively. The assay exhibited a linear dynamic range of 0.5-100.0 ng/mL for mosapride in human plasma. The lower limit of quantitation was 500 pg/mL with a relative standard deviation of less than 15%. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. A run time of 2.0 min for each sample made it possible to analyze a throughput of more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.

Sensitive liquid chromatography-tandem mass spectrometry method for quantification of hydrochlorothiazide in human plasma

A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for quantification of hydrochlorothiazide (I), a common diuretic and anti-hypertensive agent. The analyte and internal standard, tamsulosin (II) were extracted by liquid-liquid extraction with diethyl ether-dichloromethane (70:30, v/v) using a Glas-Col Multi-Pulse Vortexer. The chromatographic separation was performed on a reversed-phase column (Waters symmetry C18) with a mobile phase of 10 mm ammonium acetate-methanol (15:85, v/v). The protonated analyte was quantitated in negative ionization by multiple reaction monitoring with a mass spectrometer. The mass transitions m/z 296.1 solidus in circle 205.0 and m/z 407.2 solidus in circle 184.9 were used to measure I and II, respectively. The assay exhibited a linear dynamic range of 0.5-200 ng/mL for hydrochlorothiazide in human plasma. The lower limit of quantitation was 500 pg/mL, with a relative standard deviation of less than 9%. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. A run time of 2.5 min for each sample made it possible to analyze a throughput of more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.

Comparative pharmacokinetics of two tablet formulations of Losartan: bioequivalence assessment

The pharmacokinetic profiles of two brands of losartan 50 mg tablets were compared in 24 healthy adult volunteers after a single oral dose in a randomized cross-over study. The study was conducted at the ACDIMA Center for Bioequivalence & Pharmaceutical Studies, Amman, Jordan. The reference (Cozaar, MSD, The Netherlands) and test (Blosart, Julphar, UAE) products were administered to fasting volunteers. Blood samples were collected at specified time intervals, and the plasma separated and analysed for losartan and its active metabolite (losartan carboxylic acid) using a validated HPLC method with fluorescence detection. Pharmacokinetic parameters AUC(0-t), AUC(0-alpha), C(max), T(max), T(1/2), elimination rate constant, MRT, Cl/F and Vss/F were determined from plasma concentration-time profiles of both formulations and found to be in good agreement with reported values. Three parameters (AUC(0-t), AUC(0-alpha), and C(max)) were compared statistically to evaluate the bioequivalence between the two brands, using statistical modules recommended by the FDA. Analysis of variance (ANOVA) did not show any significant difference between the two formulations and 90% confidence intervals fell within the acceptable range (80%-125%) for bioequivalence. Based on these statistical inferences it was concluded that the two formulations exhibited comparable pharmacokinetic profiles and that Julphar's Blosart is bioequivalent to Cozaar of MSD, The Netherlands.

Bioequivalence assessment of Lovrak (Julphar, UAE) compared with Zovirax (Glaxo Wellcome, UK)-Two brands of Acyclovir-in healthy human volunteers

Two studies were performed to assess the relative bioavailability of Lovrak (Julphar, UAE) compared with Zovirax (Glaxo Wellcome, UK) at the International Pharmaceutical Research Center (IPRC), Amman, Jordan. One study involved acyclovir tablets and the other acyclovir suspension. Each study enrolled 24 volunteers and in both studies, after an overnight fasting, the two brands of acyclovir were administered as a single dose on 2 treatment days separated by 1 week washout period. After dosing, serial blood samples were collected for a period of 16 h. Plasma harvested from blood, was analysed for acyclovir by an HPLC method with UV detection. Various pharmacokinetic parameters including AUC0-t, AUC0-infinity, Cmax, Tmax, T1/2 and Kelm were determined from plasma concentrations for both formulations and found to be in good agreement with the reported values. AUC0-t, AUC(0-proportional to), and Cmax were tested for bioequivalence after log-transformation of data. No significant difference was found based on ANOVA; 90% confidence intervals for the test/reference ratio of these parameters were found within the bioequivalence acceptance range 80%-125%. Based on these statistical inferences it was concluded that a Lovrak tablet is bioequivalent to a Zovirax tablet and that Lovrak suspension is bioequivalent to Zovirax suspension.

Development, validation, and implementation of a multiplex immunoassay for the simultaneous determination of five cytokines in human serum

Quantification of biomarkers can provide important information about the safety and efficacy of candidate drugs. Unfortunately, limited sample volume and excess costs often limit analysis of multiple biomarkers. We developed, optimized, validated, and implemented a multiplex immunoassay for simultaneous measurement of multiple circulating cytokines: IL-1beta, TNFalpha, IL-6, IL-8, and IL-10. Multiplex immuoassays were performed using the Luminex LabMAP instrument. Capture antibodies for each cytokine were covalently bound to distinct microsphere subsets distinguished by differing dye ratios. The concentration of each individual cytokine determined by measuring orange fluorescence produced by a complex of a biotinylated cytokine-specific antibody and streptavidin-phycoerythrin. The lower limit of quantification for all assays was 20 pg/mL with the exception of IL-8 which was 100 pg/mL. The inter-assay precision was less than 25%CV for all analytes at all control levels both pre-study and in-study. The percent recovery ranged from 83 to 108% pre-study and 90 to 125% in-study. In a linearity assessment, a 15,000 pg/mL multi-analyte control could be diluted 1:50 and maintain expected accuracy. We measured the cytokine concentrations in more than 2000 serum samples from patients with sepsis. Multiplex results for IL-6 were compared to a conventional commercially available ELISA kit. The degree of agreement between the two methods as measured by the concordance correlation coefficient was 84.5%. Multiplex results were 2.36-fold higher than ELISA values on the average. After adjusting for this mean difference, the 95% empirical limits of agreement for the ratio of individual sample values were 0.33, 2.65. This multiplex immunoassay provided simultaneous measurement of circulating cytokines using 80% less patient specimen compared to traditional approaches and at a significantly decreased cost. Efficient use of this platform requires process improvements to fully maximize the positive impact of multiplex assays in clinical drug development.

Simultaneous analysis of gamma-hydroxybutyric acid and its precursors in urine using liquid chromatography–tandem mass spectrometry

We have developed a rapid method that enables the simultaneous analysis of gamma-hydroxybutyrate (GHB) and its precursors, i.e. gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) in urine. The method comprised a simple dilution of the urine sample, followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Chromatographic separation was achieved using an Atlantis dC18 column, eluted with a mixture of formic acid and methanol. The method was linear from 1-80 mg/L for GHB and 1,4-BD and from 1-50 mg/L for GBL. The limit of quantification was 1 mg/L for all analytes. The procedure, which has a total analysis time (including sample preparation) of less than 12 min, was fully validated and applied to the analysis of 182 authentic urine samples; the results were correlated with a previously published GC-MS procedure and revealed a low prevalence of GHB-positive samples. Since no commercial immunoassay is available for the routine screening of GHB, this simple and rapid method should prove useful to meet the current increased demand for the measurement of GHB and its precursors.

Serum lamivudine levels in the presence of a lamivudine-resistant HBV mutant

BACKGROUND/AIMS

Lamivudine efficiently inhibits hepatitis B virus replication and has been used to treat hepatitis B virus recurrence after orthotopic liver transplantation. Although effective, its use is hampered by viral breakthrough due to the appearance of hepatitis B virus drug-resistant strains. Aims of this work were to evaluate the inter- and intra-individual variations of lamivudine serum levels and the effects on the drug levels of the lamivudine-resistant hepatitis B virus mutant infection.

METHODS

Serum lamivudine concentration was measured by high-performance liquid chromatography. Polymerase chain reaction analysis and sequencing analysis of the reverse transcriptase area of the polymerase was performed on each sample using specific primers. A polymerase chain reaction-enzyme-linked immunosorbent assay was used to differentiate between wild-type hepatitis B virus and lamivudine-resistant hepatitis B virus strain.

RESULTS

Lamivudine serum levels presented minor inter- and intra-individual fluctuations along time, with an important increase at the time of the hepatitis flare-up due to the hepatitis B virus mutant presence. When the wild-type hepatitis B virus briefly reappeared as a mixed population, the titre of lamivudine dropped to below the detection level.

CONCLUSIONS

While lamivudine serum levels appears stable when the anti-viral efficacy is fully achieved, important fluctuations are present according to the type of viral population, with a considerable decrease possibly due to the presence of the wild-type virus.

Pharmacokinetics of magnesium glycyrrhizinate following intravenous administration of magnesium glycyrrhizinate in rats

The elimination, distribution, excretion of magnesium glycyrrhizinate (MG) after intravenous (i.v.) administration in rats, and the binding rate of MG to plasma protein were investigated. The concentrations of MG in plasma, tissue, and excretion of rats after i.v. administration of MG were measured using reversed-phase high performance liquid chromatography (RP-HPLC). The concentrations of MG in plasma declined in an apparent biexponential manner. The pharmacokinetic parameters from a two-compartment model analysis of plasma samples after i.v. administration of MG 30, 60, and 120 mg/kg-, were t(1/2beta) (min): 140, 180, and 240; AUC(0 approximately 18) (g x min x L(-1)): 10212, 15432, and 50321; CL (L x kg(-1) x min(-1)): 0.0025, 0.0039, and 0.0021, respectively. The drug administered as an iv injection, were mainly cumulated in the liver. When MG was administered to bile-duct cannulated rats, about 90% of i.v. dosed MG was excreted into bile under unchanged form within 24 h after administration. The average binding rate of MG to plasma protein was 87%. The experimental results showed that the distributional property of MG in the present rats study is beneficial to its liver protective activity and liver function improvement.

Determination of MS-275, a novel histone deacetylase inhibitor, in human plasma by liquid chromatography–electrospray mass spectrometry

A rapid method was developed for the quantitative determination of the novel histone deacetylase inhibitor, MS-275, in human plasma. Calibration curves were constructed in the range of 1-100 ng/ml, and were analyzed using a weight factor proportional to the nominal concentration. Sample pretreatment involved a one-step protein precipitation with acetonitrile of 0.1 ml samples. The analysis was performed on a column (75 mm x 4.6 mm i.d.) packed with 3.5 microm Phenyl-SB material, using methanol-10mM ammonium formate (55:45 (v/v)) as the mobile phase. The column effluent was monitored by mass spectrometry with positive electrospray ionization. The values for precision and accuracy were always < or =5.58 and <11.4% relative error, respectively. The method was successfully applied to examine the pharmacokinetics of MS-275 in a cancer patient.

Biomarkers, validation and pharmacokinetic-pharmacodynamic modelling

Four elements are crucial to successful pharmacokinetic-pharmacodynamic (PK/PD) modelling and simulation for efficient and effective rational drug development: (i) mechanism-based biomarker selection and correlation to clinical endpoints; (ii) quantification of drug and/or metabolites in biological fluids under good laboratory practices (GLP); (iii) GLP-like biomarker method validation and measurements and; (iv) mechanism-based PK/PD modelling and validation. Biomarkers can provide great predictive value in early drug development if they reflect the mechanism of action for the intervention even if they do not become surrogate endpoints. PK/PD modelling and simulation can play a critical role in this process. Data from genomic and proteomics differentiating healthy versus disease states lead to biomarker discovery and identification. Multiple genes control complex diseases via hosts of gene products in biometabolic pathways and cell/organ signal transduction. Pilot exploratory studies should be conducted to identify pivotal biomarkers to be used for predictive clinical assessment of disease progression and the effect of drug intervention. Most biomarkers are endogenous macromolecules, which could be measured in biological fluids. Many exist in heterogeneous forms with varying activity and immunoreactivity, posting challenges for bioanalysis. Reliable and selective assays could be validated under a GLP-like environment for quantitative methods. While the need for consistent reference standards and quality control monitoring during sample analysis for biomarker assays are similar to that of drug molecules, many biomarkers have special requirements for sample collection that demand a well coordinated team management. Bioanalytical methods should be validated to meet study objectives at various drug development stages, and possess adequate performance to quantify biochemical responses specific to the target disease progression and drug intervention. Protocol design to produce sufficient data for PK/PD modelling would be more complex than that of PK. Knowledge of mechanism from discovery and preclinical studies are helpful for planning clinical study designs in cascade, sequential, crossover or replicate mode. The appropriate combination of biomarker identification and selection, bioanalytical methods development and validation for drugs and biomarkers, and mechanism-based PK/PD models for fitting data and predicting future clinical endpoints/outcomes provide powerful insights and guidance for effective and efficient rational drug development, toward safe and efficacious medicine for individual patients.