Quantitation of the 5HT1D agonists MK-462 and sumatriptan in plasma by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

Electro-oxidation sensing of sumatriptan in aqueous solutions and human blood serum by Zn(II)-MOF modified electrochemical delaminated pencil graphite electrode

An electrochemical sensory platform is presented for determination of sumatriptan (SUM) in aqueous solutions and human blood serum. A pencil graphite electrode (PGE) was electrochemically delaminated by cyclic voltammetry technique, and then further modified using nanoparticles of a zinc-based metal-organic framework (Zn(II)-MOF). The fabricated Zn(II)-MOF/EDPGE electrode was utilized for sensitive electrochemical detection of SUM via an electro-oxidation reaction. The Zn(II)-MOF was hydrothermally synthesized and characterized by various techniques. The electrochemical delamination of PGE results in a porous substrate, facilitating the effective immobilization of the modifier. The designed sensor benefits from both enhanced surface area and an accelerated electron transfer rate, as evidenced by the chronocoulogram and Nyquist plots. Under optimized conditions, the developed sensor exhibited a linear response for 0.99-9.52 µM SUM solutions. A short response time of 5 s was observed for the fabricated sensor and the detection limit was found to be 0.29 μM. Selectivity of Zn(II)-MOF/EDPGE towards SUM was evaluated by examining the interference effect of codeine, epinephrine, acetaminophen, ascorbic acid, and uric acid, which are commonly found in biological samples. The developed sensor shows excellent performance with recovery values falling within the range of 96.6 to 111% for the analysis of SUM in human blood serum samples.

Development and Validation of Liquid Chromatography-Tandem Mass Spectrometry Method for Simple Analysis of Sumatriptan and its Application in Bioequivalence Study

This work demonstrated a sensitive, selective, and simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantitation of sumatriptan in human plasma samples. Terazosin was used as an internal standard to minimize the variability during sample processing and detection. Sample cleanup prior to chromatographic analysis was accomplished by liquid-liquid extraction (LLE) with tert-butyl methyl ether (t-BME). The separation was performed on a reversed-phase Symmetry^® C18 column (150 × 4.6 mm i.d., 5 µm) under a gradient mode, using a 0.2% formic acid aqueous solution and acetonitrile at a flow rate of 0.5 mL/min. Sumatriptan (m/z 296.26→251.05) and terazosin (m/z 388.10→290.25) were quantified using a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) under the positive ion mode. The method was fully validated following US-FDA and EMA guidelines. The LC-MS/MS assay had a calibration range of 0.5–50.0 ng/mL. The assay was precise and accurate with a between-run precision of <9.51%, and between-run accuracy between −7.27 to 8.30%. The developed method was subsequently applied in the determination of plasma concentration-time profile of a sumatriptan 50-mg tablet following oral administration in healthy volunteers.

Application of a Reliable LC-MS/MS Method for Determination of Rizatriptan in Healthy Subject Samples: Demonstration of Assay Reproducibility by Incurred Sample Reanalysis

A reliable, rapid, and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay has been proposed for the determination of rizatriptan in human plasma using sumatriptan as internal standard (IS). The analyte and IS were extracted from 300 μL human plasma via liquid-liquid extraction and the chromatography was achieved on Hypurity C18 (50 mm × 4.6 mm, 5 μm) column under isocratic conditions. Detection of rizatriptan and IS was done by tandem mass spectrometry, operating in positive ionization and multiple-reaction monitoring mode. The limit of detection and lower limit of quantitation of the method were 0.04 and 0.20 ng/mL, respectively, with a linear dynamic range of 0.20–60.0 ng/mL. The intrabatch and interbatch precision (% CV) was ≤8.4% while the mean extraction recovery was >78% across quality control levels. Bench top stability, freeze and thaw stability, processed sample stability, and long-term stability in plasma were evaluated at two quality control levels. It was successfully applied to a bioequivalence study of 10 mg rizatriptan orally disintegrating tablet formulation in 40 and 32 healthy Indian male subjects under fasting and fed conditions, respectively. The reproducibility in the measurement of study data was demonstrated by reanalysis of 254 incurred samples.

Development and Validation of a HPTLC Method for the Estimation of Sumatriptan in Tablet Dosage Forms

A simple, precise, accurate and rapid high performance thin layer chromatographic method has been developed and validated for the estimation of sumatriptan in tablet dosage forms. The stationary phase used was precoated silica gel 60F254. The mobile phase used was a mixture of methanol:water:glacial acetic acid (4.0:8.0:0.1, v/v/v). The detection of spots was carried out at 230 nm. The method was validated in terms of linearity, accuracy, precision and specificity. The calibration curve was found to be linear between 200 to 800 ng/spot. The limit of detection and the limit of quantification for the sumatriptan were found to be 63.87 and 193.54 ng/spot, respectively. The proposed method can be successfully used to determine the drug content of marketed formulation.

An evaporation-free solid-phase extraction method for rapid and accurate analysis of sumatriptan in human plasma by LC–MS/MS

An evaporation-free solid-phase extraction (SPE) method was developed and validated for sumatriptan. High organic washing (50% methanol) and low organic elution (20% methanol) were used and the recovery was greater than 92%. The eluate was injected into a C18 column without evaporation and reconstitution. Sumatriptan was monitored in positive ion mode with mass transition of m/z 296.4-58.1 amu. The calibration curve was 1-100 ng/mL (r>or=0.9923). The inter-day and intra-day precisions ranged from 4.53 to 9.12% and 1.72 to 6.93%, respectively. This method features reduced cost and pollution, clean extract, high speed, and most importantly overall method reliability.

Liquid chromatography–mass spectrometry method for the determination of venlafaxine in human plasma and application to a pharmacokinetic study

A sensitive and selective liquid chromatographic-mass spectrometric (LC-MS) method for the determination of venlafaxine in human plasma has been developed. Samples were prepared using liquid-liquid extraction and analyzed on a C(18) column interfaced with a triple quadrupole mass spectrometer. Positive electrospray ionization was employed as the ionization source. The mobile phase was methanol-water containing 10 mmol/L ammonium acetate, pH 7.9 adjusted with aqueous ammonia (80:20, v/v) at the flow rate of 1.0 mL/min. The analyte and internal standard clozapine were both detected by use of selected ion monitoring mode. The method was linear in the concentration range of 1.0-200.0 ng/mL. The lower limit of quantification (LLOQ) was 1.0 ng/mL. The intra- and inter-day relative standard deviation across three validation runs over the entire concentration range was less than 10.1%. The accuracy determined at three concentrations (5.0, 50.0 and 150.0 ng/mL for venlafaxine) was within +/-10.0% in terms of relative error (RE). The method was successfully applied for the evaluation of pharmacokinetic profiles of venlafaxine capsule in 20 healthy volunteers. The results show AUC, T(max), C(max) and T(1/2) between the testing formulation and reference formulation have no significant difference (p > 0.05). Relative bioavailability was 103.4 +/- 14.1%.

Development and validation of a selective and robust LC–MS/MS method for high-throughput quantifying rizatriptan in small plasma samples: Application to a clinical pharmacokinetic study

An analytical method based on liquid chromatography with positive ion electrospray ionization (ESI) coupled to tandem mass spectrometry detection (LC-MS/MS) was developed for the determination of a potent 5-HT(1B/1D) receptor agonist, rizatriptan in human plasma using granisetron as the internal standard. The analyte and internal standard were isolated from 100 microL plasma samples by liquid-liquid extraction (LLE) and chromatographed on a Lichrospher C18 column (4.6mm x 50mm, 5 microm) with a mobile phase consisting of acetonitrile-10mM aqueous ammonium acetate-acetic acid (50:50:0.5, v/v/v) pumped at 1.0 mL/min. The method had a chromatographic total run time of 2 min. A Varian 1200 L electrospray tandem mass spectrometer equipped with an electrospray ionization source was operated in selected reaction monitoring (SRM) mode with the precursor-to-product ion transitions m/z 270-->201 (rizatriptan) and 313.4-->138 (granisetron) used for quantitation. The assay was validated over the concentration range of 0.05-50 ng/mL and was found to have acceptable accuracy, precision, linearity, and selectivity. The mean extraction recovery from spiked plasma samples was above 98%. The intra-day accuracy of the assay was within 12% of nominal and intra-day precision was better than 13% C.V. Following a 10mg dose of the compound administered to human subjects, mean concentrations of rizatriptan ranged from 0.2 to 70.6 ng/mL in plasma samples collected up to 24h after dosing. Inter-day accuracy and precision results for quality control samples run over a 5-day period alongside clinical samples showed mean accuracies of within 12% of nominal and precision better than 9.5% C.V.

Development and validation of a specific stability indicating high performance liquid chromatographic method for rizatriptan benzoate

A gradient, reversed-phase liquid chromatographic (RP-LC) method was developed for the quantitative determination of rizatriptan benzoate, used to treat relieves migraine headache symptoms. The developed method can be also employed for the related substance determination in bulk samples. Forced degradation studies were performed on bulk sample of rizatriptan benzoate using acid (0.5 N hydrochloric acid), base (0.1 N sodium hydroxide), oxidation (3.0% hydrogen peroxide), water hydrolysis, heat (60 degrees C) and photolytic degradation. Mild degradation of the drug substance was observed in base hydrolysis and considerable degradation observed during oxidative stress. The chromatographic method was fine tuned using the samples generated from forced degradation studies. Good resolution between the peaks corresponds to degradation products and the analyte was achieved on Agilent Zorbax SB-CN (250 mm x 4.6 mm, 5 microm) column. The mobile phase consists of a mixture of aqueous potassium di hydrogen ortho phosphate (pH 3.4), acetonitrile and methanol. The stress sample solutions were assayed against the qualified reference standard of rizatriptan benzoate and the mass balance in each case was close to 99.7% indicating that the developed method is stability indicating. Validation of the developed method was carried out as per ICH requirements.

Simple, sensitive and rapid LC-ESI-MS method for the quantitation of lafutidine in human plasma--application to pharmacokinetic studies

A sensitive and specific liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS) method has been developed and validated for the identification and quantification of lafutidine in human plasma. Lafutidine and internal standard were isolated from plasma samples by liquid-liquid extraction with diethyl ether. The chromatographic separation was accomplished on a stainless-steel column (C18 Shim-pack 5 microm 150 mm x 2.0 mm i.d. Shimadzu) at a flow rate of 0.2 ml/min by a gradient elution. Detection was performed on a single quadrupole mass spectrometer by selected ion monitoring (SIM) mode via electrospray ionization (ESI) source. The method was proved to be sensitive and specific by testing six different plasma batches. Linearity was established for the range of concentrations 1.0-400.0 ng/ml with a coefficient of determination (r) of 0.9998 and good back-calculated accuracy and precision. The intra- and inter-day precision (R.S.D.%) was lower than 10% and accuracy ranged from 85 to 115%. The lower limit of quantification was identifiable and reproducible at 0.5 ng/ml with 0.2 ml plasma. The proposed method enables the unambiguous identification and quantification of lafutidine for pharmacokinetic, bioavailability or bioequivalence studies.

High-performance liquid chromatographic determination of sumatriptan after in vitro transdermal diffusion studies

A simple, accurate, precise and rapid HPLC method with UV detection has been validated in order to determine the in vitro transdermal absorption of sumatriptan succinate. The HPLC method is a modification of that described by Nozal et al. [M.J. Nozal, J.L. Bernal, L. Toribio, M.T. Martin, F.J. Diez, J. Pharm. Biomed. Anal. 30 (2002) 285-291]. Separation was carried out on a 250 mm Kromasil C18 column at room temperature. The detector response, at 282.7 nm, was found to be linear in a concentration range between 0.145 and 145 microM. The limit of detection (LOD) was 0.019 microM and the limit of quantification (LOQ) was 0.145 microM.

Determination of rizatriptan in human plasma by liquid chromatographic-eletrospray tandem mass spectrometry: application to a pharmacokinetic study

A sensitive liquid chromatographic-tandem mass spectrometry(LC-MS/MS) method was developed for the determination of rizatriptan in human plasma. The analytes were extracted from plasma samples by liquid-liquid extraction, separated on a Zorbax XDB C8 column (150 x 4.6 mm i.d.) and detected by tandem mass spectrometry with an electrospray ionization interface. Zomitriptan was used as the internal standard. The method had a lower limit of quantitation of 50 pg/mL for rizatriptan, which showed more sensitivity and speed of analysis compared with reported methods. The within- and between-day precision was measured to be below 11.71% and accuracy between -5.87 and 0.86% for all quality control samples. This quantitation method was successfully applied to the evaluation of the pharmacokinetic profiles of rizatriptan after single oral administration of 5, 10 and 15 mg rizatriptan tablets to 10 healthy volunteers (five males and five females).

Discovery stage pharmacokinetics using dried blood spots

Early in the discovery stage, the measurement of drug candidates in biological fluids as a function time provides important information used in decision making for lead optimization. The detection methodology primarily used is liquid chromatography coupled to triple quadrupole mass spectrometry (LC-MS). Sample preparation is an important aspect of these experiments and robotic-based automation is commonly used. The often overlooked aspect of these experiments is the sample collection itself. Typically, several hundred microliters of whole blood is collected and the plasma fraction separated for each time-point. The plasma is then transferred to an appropriate vessel for subsequent aliquoting and processing. We describe a method for performing discovery stage pharmacokinetic analysis using whole blood dried onto filter paper. The use of dried blood spots is a well established technique for neo-natal screening, and its application to early screening of drug candidates proves to be robust, reliable and reproducible.

Liquid chromatographic method for the determination of rizatriptan in human plasma

A high-performance liquid chromatographic (HPLC) method with fluorescence detection has been developed for the determination of rizatriptan in human plasma. Following a single-step liquid-liquid extraction with methyl tertiarybutyl ether, the analytes were separated using a mobile phase consisting of 0.05% (v/v) triethylamine in water (adjusting to pH 2.75 with 85% phosphoric acid) and acetonitrile (92:8, v/v). Fluorescence detection was performed at an excitation wavelength of 225nm and an emission wavelength of 360nm. The linearity for rizatriptan was within the concentration range of 0.5-50ng/ml. The intra- and inter-day precisions of the method were not more than 8.0%. The lower limit of quantification (LLOQ) was 0.5ng/ml for rizatriptan. The method was sensitive, simple and repeatable enough to be used in pharmacokinetic studies.

Stability-indicating methods for the determination of sumatriptan succinate

Four stability-indicating methods were developed for the determination of sumatriptan succinate in the presence of its degradation products. The first method depends on the quantitative densitometric evaluation of thin-layer chromatography of sumatriptan succinate in the presence of its degradation products without any interference. Cyclohexane-dichloromethane-diethylamine (50:40:10 v/v/v) was used as a mobile phase and the chromatogram was scanned at 228 nm. This method determines sumatriptan succinate in the concentration range l-8 microg per spot with mean percentage recovery 100.52+/-1.23%. The second and third methods depend on the use of first-derivative (D(1)) and second-derivative (D(2)) spectrophotometry at 234 and 238 nm, respectively. These methods determine the drug in the concentration range 1.25-10 microg x ml(-1) with mean percentage recovery 99.91+/-1.01% and 99.96+/-1.13% for (D(1)) and (D(2)), respectively. The fourth method depends on the use of ratio derivative spectrophotometric technique. The amplitude in the first derivative of the ratio spectra at 235 nm was selected to determine the cited drug in the presence of its degradation products. Calibration graph is linear in the concentration range 1.25-10 microg x ml(-1) with mean percentage recovery 100.19+/-1.19%. The suggested methods were successfully applied for determining sumatriptan succinate in bulk powder, laboratory-prepared mixtures and pharmaceutical dosage forms (Imigran tablet) with good accuracy and precision. The results obtained by applying the proposed methods were statistically analyzed and compared with those obtained by the reported method.

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

A sensitive and convenient high-performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS) assay is described for the (5-HT(lB/lD)) receptor agonist sumatriptan in human plasma. Sumatriptan was recovered from plasma (81.8 +/- 6.8%) by liquid-liquid extraction. The mobile phase flow rate was 0.3 mL/min and consisted of methanol:water:formic acid (90:10:0.1, v/v/v). The analytical column (4.6 x 100 mm) was packed with Partisil C(8) (5 micro m). The standard curve was linear from 0.7 to 70.4 ng/mL (r(2) > 0.99). The lower limit of quantitation was 0.7 ng/mL. The assay was specific, accurate (percentage deviation from nominal concentrations were <15%), precise and reproducible (within- and between-day coefficients of variation <10.3%). Sumatriptan in plasma was stable over three freeze/thaw cycles and at room temperature for one day. The utility of the assay was demonstrated by following sumatriptan plasma concentrations in two healthy subjects for 8-12 h following a single 20 mg intranasal dose.

Development and validation of an LC assay for sumatriptan succinate residues on surfaces in the manufacture of pharmaceuticals

A high performance liquid chromatographic (HPLC) method for the assay of sumatriptan succinate residues in swabs collected from manufacturing equipment surfaces was developed and validated in order to control a cleaning procedure. The swabbing procedure using two cotton swabs moistened with water was validated applying a wipe-test and a HPLC method developed to determine low quantities of the drug. The HPLC method involves a C18 column at 25 degrees C, a mixture of ammonium phosphate monobasic (0.05 M)-acetonitrile (84:16, v/v) as a mobile phase and UV detection at 228 nm. Using the proposed method, the average recoveries obtained are of 88.5% for vinyl, 94.2% for glass and 95.2% for stainless steel plates with RSD of 5.5 (n=36), 2.3 (n=36), 2.2% (n=36), respectively. The method was successfully applied to the assay of real swab samples collected from the equipment surfaces.

Determination of degradation products of sumatriptan succinate using LC-MS and LC-MS-MS

Acid, base, heat, oxidation and UV irradiation stress methods were applied to study the stability of the bulk drug form of sumatriptan succinate. Liquid chromatography coupled with mass spectrometry (LC-MS and LC-MS-MS) was used to analyze the degraded samples and tentative structural identifications were assigned based upon known reactivity of the drug, molecular weight measurements and MS-MS fragmentation patterns. Sumatriptan succinate was found to be stable to exposure of acid, base, oxidation and UV irradiation at ambient conditions, but was found to degrade under acidic, basic and oxidative conditions when heated to 90 degrees C.

Influence of beta-adrenoceptor antagonists on the pharmacokinetics of rizatriptan, a 5-HT1B/1D agonist: differential effects of propranolol, nadolol and metoprolol

AIMS

Patients with migraine may receive the 5-HT1B/1D agonist, rizatriptan (5 or 10 mg), to control acute attacks. Patients with frequent attacks may also receive propranolol or other beta-adrenoceptor antagonists for migraine prophylaxis. The present studies investigated the potential for pharmacokinetic or pharmacodynamic interaction between beta-adrenoceptor blockers and rizatriptan.

METHODS

Four double-blind, placebo-controlled, randomized crossover investigations were performed in a total of 51 healthy subjects. A single 10 mg dose of rizatriptan was administered after 7 days' administration of propranolol (60 and 120 mg twice daily), nadolol (80 mg twice daily), metoprolol (100 mg twice daily) or placebo. Rizatriptan pharmacokinetics were assessed. In vitro incubations of rizatriptan and sumatriptan with various beta-adrenoceptor blockers were performed in human S9 fraction. Production of the indole-acetic acid-MAO-A metabolite of each triptan was measured.

RESULTS

Administration of rizatriptan during propranolol treatment (120 mg twice daily for 7.5 days) increased the AUC(0, infinity) for rizatriptan by approximately 67% and the Cmax by approximately 75%. A reduction in the dose of propranolol (60 mg twice daily) and/or the incorporation of a delay (1 or 2 h) between propranolol and rizatriptan administration did not produce a statistically significant change in the effect of propranolol on rizatriptan pharmacokinetics. Administration of rizatriptan together with nadolol (80 mg twice daily) or metoprolol (100 mg twice daily) for 7 days did not significantly alter the pharmacokinetics of rizatriptan. No untoward adverse experiences attributable to the pharmacokinetic interaction between propranolol and rizatriptan were observed, and no subjects developed serious clinical, laboratory, or other significant adverse experiences during coadministration of rizatriptan with any of the beta-adrenoceptor blockers. In vitro incubations showed that propranolol, but not other beta-adrenoceptor blockers significantly inhibited the production of the indole-acetic acid metabolite of rizatriptan and sumatriptan.

CONCLUSIONS

These results suggest that propranolol increases plasma concentrations of rizatriptan by inhibiting monoamine oxidase-A. When prescribing rizatriptan to migraine patients receiving propranolol for prophylaxis, the 5 mg dose of rizatriptan is recommended. Administration with other beta-adrenoceptor blockers does not require consideration of a dose adjustment.

Reduction of animal usage by serial bleeding of mice for pharmacokinetic studies: application of robotic sample preparation and fast liquid chromatography-mass spectrometry

Typically, pharmacokinetic studies in mice require one animal per time point, thus resulting in differences due to dosing error, animal to animal variation and more importantly the euthanasia of a large number of animals. A method for the determination of pharmacokinetic data from serially bled mice to support early drug discovery is described. Sample analysis relies on liquid chromatography coupled with tandem mass spectrometry permitting robust and reproducible analysis requiring approximately 3 min per sample. Several parameters are discussed including the method of sample collection, preparation and analysis. The use of serially bled mice has lead to a remarkable reduction in animal usage and a corresponding reduction in compound required for such experiments. Using conventional methodology, a nine-point pharmacokinetic curve with four animals per time point would require 36 mice. With the method described below, only four mice in total are used and euthanasia is not required, permitting reuse after several weeks recovery and washout. Also, pharmacodynamic-pharmacokinetic correlation is possible and is demonstrated using a mouse model of diabetes.

Automating solid-phase extraction: current aspects and future prospects

This paper reviews current trends and techniques in automated solid-phase extraction. The area has shown a dramatic growth the number of manuscripts published over the last 10 years, including applications in environmental science, food science, clinical chemistry, pharmaceutical bioanalysis, forensics, analytical biochemistry and organic synthesis. This dramatic increase of more that 100% per year can be attributed to the commercial availability of higher throughput 96-well workstations and extraction plates that allow numerous samples to be processed simultaneously. These so-called parallel-processing workstations represent the highest throughput systems currently available. The advantages and limitations of other types of systems, including discrete column systems and on-line solid-phase extraction are also discussed. Discussions of how automated solid-phase extractions can be developed, generic approaches to automated solid-phase extraction, and three noteworthy examples of automated extractions are given. The last part of the review suggests possible near- and long-term directions of automated solid-phase extraction.

Determination of antimigraine compounds rizatriptan, zolmitriptan, naratriptan and sumatriptan in human serum by liquid chromatography/electrospray tandem mass spectrometry

Development of a rapid, sensitive and selective method for the determination of antimigraine drugs from human serum is essential for understanding the pharmacokinetics of these drugs when administered concurrently. Solid phase extraction (SPE) using Oasis HLB was used to extract the drugs (sumatriptan, naratriptan, zolmitriptan and rizatriptan) and the internal standard bufotenine from serum. A method based on liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed and validated to simultaneously quantitate these antimigraine drugs from human serum. The precursor and major product ions of the analytes were monitored on a triple quadrupole mass spectrometer with positive ion electrospray ionization (ESI) in the multiple reaction monitoring (MRM) mode. The base peak in all the analytes is formed by alpha cleavage associated with protonation of the secondary amine. Mechanisms for the formation of the collision-induced dissociation products of these antimigraine compounds are proposed. Linear calibration curves were generated from 1-100 ng/mL with all coefficients of determination greater than 0.99. The inter- and intraday precision (%RSD) were less than 9.3% and accuracy (%error) was less than 9.8% for all components. The limits of detection (LOD) for the method were 250 pg/mL for sumatriptan and 100 pg/mL for the remaining analytes based on a signal-to-noise ratio of 3.

The effects of moclobemide on the pharmacokinetics of the 5-HT1B/1D agonist rizatriptan in healthy volunteers

AIMS

The new 5-HT1B/1D agonist rizatriptan (MK-0462) has recently been registered for the treatment of migraine. Its primary route of metabolism is via monoamine oxidase-A (MAO-A). Antidepressants such as the MAO-A inhibitor moclobemide may be used in patients with chronic headache syndromes. Hence, this study aimed to investigate the interactions between rizatriptan and moclobemide.

METHODS

In a double-blind, randomized, placebo-controlled, two-period cross-over study 12 healthy, young volunteers (six males, six females) were treated with moclobemide (150 mg twice daily) or placebo for 4 days. On the fourth day, a single dose of rizatriptan (10 mg) was administered, and subsequently blood and urine samples were collected for assay of rizatripan and N-monodesmethyl rizatriptan. Plasma concentrates of 3,4-dihydroxyphenylglycol (DHPG), a marker of MAO-A inhibition, were also assessed. Supine and standing blood pressure were measured regularly.

RESULTS

Both treatments were well tolerated. During moclobemide, the increase in supine diastolic blood pressure following rizatriptan administration was augmented. Inhibition of MAO by moclobemide was inferred from a persistent decrease in DHPG level (43% on average). When rizatriptan was coadministered with moclobemide, the area under the plasma drug concentration-time profiles for rizatriptan and its N-monodesmethyl metabolite increased 2.2-fold (90% CI, 1.93-2.47) and 5.3-fold (90% CI, 4.81-5.91), respectively, when compared with placebo. Peak plasma drug concentrations for rizatriptan and its n-monodesmethyl metabolite increased 1.4-fold (90% CI, 1.11-1.80) and 2.6-fold (90% CI, 2.23-3.14), respectively, and half-lives of both were prolonged.

CONCLUSIONS

Moclobemide inhibited the metabolism of rizatriptan and its active N-monodesmethyl metabolite through inhibition of MAO-A. Thus, moclobemide may considerably potentiate rizatriptan action. Concurrent administration of moclobemide and rizatriptan is not recommended.

Simultaneous investigation of indinavir nonlinear pharmacokinetics and bioavailability in healthy volunteers using stable isotope labeling technique: study design and model-independent data analysis

Indinavir follows nonlinear pharmacokinetics upon oral administration at clinical doses. A study employing the stable isotope administration technique in a three-treatment design was conducted to identify the source of the nonlinearity and to determine the dose-dependency of systemic bioavailability. In treatment A, 400 mg of unlabeled indinavir (D0) was coadministered orally with 16 mg of a hexadeutero analogue of indinavir (D6) intravenously. In treatment B, 800 mg of D0 po was coadministered with 16 mg of D6 intravenously. In treatment C, 16 mg of iv D6 was infused concurrently with 16 mg iv of D0. Plasma concentrations of D0 and D6 were determined by an LC/MS/MS assay method. Concentrations of indinavir in plasma increased greater than dose-proportionally over the 400- to 800-mg dose range. No meaningful kinetic isotope effects were found in treatment C. Plasma concentrations of D6 were dependent on the coadministered D0-indinavir dose and were lowest in treatment C, higher in treatment A, and highest in treatment B. The bioavailability of indinavir was high (60-65%) and comparable between the 400- and 800-mg doses. There was a significant contribution of nonlinear kinetics in the systemic circulation to the observed disproportional increase in plasma concentrations following oral dosing. The high bioavailability at clinically relevant doses suggests a high degree of saturation of first-pass metabolism. These results further demonstrate that the concomitant administration technique in combination with the LC/MS/MS method can provide a realistic and reliable means of elucidating important pharmacokinetic properties of drug candidates during product development.

Pharmacokinetics and tolerability of oral rizatriptan in healthy male and female volunteers

AIMS

The pharmacokinetics and dose proportionality of rizatriptan single oral doses from 2.5 to 15 mg administered as solutions to healthy volunteers were studied.

METHODS

In a randomized, crossover study with four periods, twenty-four healthy volunteers (12 males and 12 females) took single oral doses of 2.5, 5, 10, and 15 mg rizatriptan in Periods 1-4. In a fifth period, subjects received 4 mg intravenous (i.v.) rizatriptan as a reference. Plasma and urine rizatriptan concentrations were determined at several timepoints/intervals for 12 and 24 h, respectively.

RESULTS

The arithmetic mean AUC values following single oral doses of 2.5, 5, 10, and 15-mg rizatriptan were 16, 33, 72, and 127 ng ml-1 h, respectively, in males; and 19, 42, 97, and 161 ng ml-1 h, respectively, in females. The overall bioavailability (F ) of rizatriptan was approximately 40% in males. Following the 4 mg reference i.v. dose, the apparent plasma clearance (CL) and renal clearance (CLr ) were 1042 and 225 ml min-1, respectively, in males; and 821 and 174 ml min-1, respectively, in females.

CONCLUSIONS

The disposition kinetics of oral rizatriptan were linear for doses of 2. 5-10 mg in males, and for doses of 2.5-5 mg in females. However, the degree of nonlinearity for higher doses was minor for both genders. The plasma concentrations of rizatriptan were slightly greater in women compared to men but the difference was not considered to be clinically meaningful. Also, the clearance of rizatriptan appeared to be mainly nonrenal.

Lack of pharmacokinetic and pharmacodynamic interaction between rizatriptan and paroxetine

Rizatriptan is a potent, oral 5-HT(1B/1D) agonist with a rapid onset of action being investigated for the acute treatment of migraine. This study examined the clinical and pharmacolinetic interaction between rizatriptan and the selective serotonin reuptake inhibitor, paroxetine. In this two-period crossover study, 12 healthy young subjects (6 males and 6 females) received 1 mg rizatriptan following 14 days of treatment with placebo or paroxetine (20 mg once daily). Plasma was sampled for rizatriptan and N-monodesmethyl rizatriptan, a minor but active metabolite of rizatriptan. Safety evaluations included monitoring for adverse events, vital signs, and visual analog scale assessment of mood. Plasma levels of rizatriptan and N-monodesmethyl rizatriptan were not altered when rizatriptan was administered with paroxetine compared to the placebo. Clinically, coadministration of rizatriptan with paroxetine was well tolerated. Blood pressure, heart rate, and temperature changes during the observation period did not differ to a clinically significant degree when rizatriptan was administered with paroxetine compared to the placebo. No effects on mood occurred following treatment with the combination compared to rizatriptan alone. Adverse events following rizatriptan administration with paroxetine were similar to those reported when rizatriptan was given with the placebo.

Simultaneous determination of omeprazole and 5'-hydroxyomeprazole in human plasma by liquid chromatography-tandem mass spectrometry

A method for the simultaneous determination of omeprazole and 5'-hydroxyomeprazole in human plasma is described. Isolation of the analytes from plasma was achieved via solid-phase extraction using a polymeric sorbent based cartridge. The analytes were chromatographed under reversed-phase conditions on a Zorbax XDB-C8 column (50 x 4.6 mm). The HPLC mobile phase consisted of a mixture of acetonitrile-water (21:79, v/v) containing 10 mM ammonium hydroxide. The apparent pH of the mobile phase was adjusted to 8.5 with formic acid prior to use. A Sciex API III+ tandem mass spectrometer equipped with a heated nebulizer atmospheric pressure chemical ionization interface was used as a detector and was operated in the positive ion mode. Multiple reaction monitoring using the precursor-->product ion combinations of m/z 362-->214, 346-->198 and 316-->147 was used to detect 5'-hydroxyomeprazole, omeprazole and internal standard, respectively. The method was validated in the concentration range of 10-500 ng/ml plasma with adequate assay precision and accuracy. The assay was used to determine the cytochrome P450 2C19 phenotype of subjects participating in clinical trials of compounds under development.

Simultaneous determination of nifedipine and dehydronifedipine in human plasma by liquid chromatography-tandem mass spectrometry

Quantitative analysis of therapeutic compounds and their metabolites in biological matrix (such as plasma, serum or urine) nowadays requires sensitive and selective methods to allow the determination of concentrations in the ng/ml range. A new on-line LC-MS-MS method using atmospheric pressure chemical ionisation (APCI) as interface for the simultaneous determination of nifedipine (NIF) and its metabolite in human plasma, dehydronifedipine (DNIF) has been developed. The compounds were extracted from plasma using solid-phase extraction (SPE) on disposable extraction cartridges (DECs). The SPE operations were performed automatically by means of a sample processor equipped with a robotic arm (ASPEC system). The DEC filled with phenyl modified silica was first conditioned with methanol and water. The washing step was performed with water. Finally, the analytes were successively eluted with methanol and water. The liquid chromatographic (LC) separation of NIF and DNIF was achieved on a RP-18 stationary phase (4 microm). The mobile phase consisted of methanol-50 mM ammonium acetate solution (50:50, v/v). The LC was then coupled to tandem mass spectrometry with an APCI interface in the positive ion mode. The method developed was validated. The absolute recoveries evaluated over the whole concentration range were 95+/-2% and 95+/-4% for NIF and DNIF, respectively. The method was found to be linear in the 0.5-100 ng/ml concentration range for the two analytes (r2 = 0.999 for both NIF and DNIF). The mean R.S.D. values for repeatability and intermediate precision were 2.9 and 3.0% for NIF and 2.2-4.7% for the metabolite. The method developed was successfully used to investigate the plasma concentration of NIF and DNIF in the pharmacokinetic studies.

Determination of molsidomine and its active metabolite in human plasma using liquid chromatography with tandem mass spectrometric detection

Pharmacokinetic studies of molsidomine require a sensitive analytical method to allow the determination of concentrations of this compound and its active metabolite 3-morpholinosydnonimine (Sin-1) in the ng/ml range in plasma. The method developed is based on on-line LC-MS-MS using pneumatically assisted electrospray ionisation as an interface, preceded by off-line solid-phase extraction (SPE) on disposable extraction cartridges (DECs). The SPE operations were performed automatically by means of a sample processor equipped with a robotic arm (automated sample preparation with extraction cartridges; ASPEC system). The DEC, filled with phenyl-modified silica, was first conditioned with methanol and water. The washing step was performed with water. Finally, the analytes were successively eluted with methanol containing formic acid (0.2%) and water. The liquid chromatographic separation of molsidomine and Sin-1 was achieved on an RP-8 stationary phase (5 microns). The mobile phase was a mixture of methanol-water-formic acid (65:35:0.1, v/v/v). The HPLC system was then coupled to a MS-MS system with an atmospheric pressure ionisation interface in the positive ion mode. The chromatographed analytes were detected in the multiple reaction monitoring mode. The MS-MS ion transitions monitored were (m/z) 243-->86 for molsidomine and 171-->86 for Sin-1. The method developed was validated. The absolute recoveries evaluated over the whole concentration range were 74 +/- 3 and 55 +/- 5% for molsidomine and Sin-1, respectively. The method was found to be linear in the 0.5-50 ng/ml concentration range for the two analytes (r2 = 0.999 for both molsidomine and Sin-1). The mean RSD values for repeatability and intermediate precision were 3.4 and 4.8% for moldsidomine and 3.1-7.7% for the metabolite. The method developed was successfully used to investigate the bioequivalence of oral doses of molsidomine between a generic tablet and a reference product.

Liquid chromatography-mass spectrometry in forensic and clinical toxicology

This paper reviews liquid chromatographic-mass spectrometric (LC-MS) procedures for the identification and/or quantification of drugs of abuse, therapeutic drugs, poisons and/or their metabolites in biosamples (whole blood, plasma, serum, urine, cerebrospinal fluid, vitreous humor, liver or hair) of humans or animals (cattle, dog, horse, mouse, pig or rat). Papers published from 1995 to early 1997, which are relevant to clinical toxicology, forensic toxicology, doping control or drug metabolism and pharmacokinetics, were taken into consideration. They cover the following analytes: amphetamines, cocaine, lysergide (LSD), opiates, anabolics, antihypertensives, benzodiazepines, cardiac glycosides, corticosteroids, immunosuppressants, neuroleptics, non-steroidal anti-inflammatory drugs (NSAID), opioids, quaternary amines, xanthins, biogenic poisons such as aconitines, aflatoxins, amanitins and nicotine, and pesticides. LC-MS interface types, mass spectral detection modes, sample preparation procedures and chromatographic systems applied in the reviewed papers are discussed. Basic information about the biosample assayed, work-up, LC column, mobile phase, interface type, mass spectral detection mode, and validation data of each procedure is summarized in tables. Examples of typical LC-MS applications are presented.

Validation of a liquid chromatographic tandem mass spectrometric method for the determination of sumatriptan in human biological fluids

A liquid chromatographic tandem mass spectrometric method for the quantitative determination of sumatriptan base in human plasma and urine has been developed and validated over the concentration range 0.2-20 ng base ml-1. Sumatriptan is a 5-HT1 receptor agonist which has found widespread use in the treatment of migraine. Sumatriptan and its internal standard (D3-sumatriptan) were extracted from human matrices using C2 solid phase cartridges. The extracts were chromatographed on a C18 column, ionised using a heated nebuliser assisted atmospheric pressure ionisation (API) interface and detected by MS/MS in the multiple reaction monitoring mode. The completed validation demonstrated the method to be robust, accurate, precise and specific for the direct quantification of sumatriptan in human fluids. The method was used on a routine basis to determine the levels of sumatriptan in human volunteers following the oral administration of a 25 mg dose of sumatriptan succinate.

A direct technique for the simultaneous determination of 10 drug candidates in plasma by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry interfaced to a Prospekt solid-phase extraction system

New drug candidates are being synthesized at an ever increasing rate and, until recently, the pharmacokinetics of only a few of these could be evaluated. Our laboratory is taking a novel approach to rapid multiple pharmacokinetic screening of potential drug candidates in which mixtures of new substances are co-administered to animals and analyzed simultaneously in plasma using liquid chromatography with tandem MS/MS detection in conjunction with a Prospekt automated on-line solid-phase extraction system. Plasma is sampled via an autosampler and extracted by the Prospekt with the eluent being introduced directly via a reverse phase HPLC column and a heated nebulizer interface to the mass spectrometer. Generic extraction and chromatographic conditions generally give good recoveries. The chromatographic run-times are less than 8 min. The accuracy and precision of these assays are carefully controlled with recoveries generally in the range 80-120% and coefficients of variation less than 20%. Lower quantifiable limits range from 2.5 to 5 ng ml-1. This approach considerably reduces the number of animals needed to screen drug candidates and its power is illustrated by determination of the pharmacokinetics of 10 substances after their simultaneous administration to dogs.

Determination of an in vivo metabolite of a human immunodeficiency virus protease-inhibitor in human plasma by high-performance liquid chromatography with tandem mass spectrometry

A method for the determination of a metabolic of the human immunodeficiency virus protease inhibitor indinavir, in human plasma is described. Isolation of the analyte and the internal standard from plasma was achieved via liquid-liquid extraction with a mixture of isopropanol-chloroform (5:95, v/v). The analytes were chromatographed under reversed-phase conditions on a Waters Symmetry C, column. A Sciex API III+ tandem mass spectrometer equipped with a heated nebulizer was used as a detector and was operated in the positive ion mode. Multiple reaction monitoring using the precursor-->production combinations of m/z, 523.4-->273.4 and 512.4-->345.2 was used to quantify analyte and internal standard, respectively. The method was validated in the concentration range of 5-500 ng/ml plasma with adequate assay precision and accuracy. The assay was used to analyze samples collected during drug interaction studies of indinavir.

Simultaneous determination of unlabeled and deuterium-labeled indinavir in human plasma by high-performance liquid chromatography with tandem mass spectrometric detection

A method for the simultaneous determination of indinavir and its hexadeuterated analog (d6-indinavir) in human plasma is described. Isolation of the analytes and internal standard from plasma was achieved via liquid-liquid extraction with methyl-t-butyl ether. The analytes were chromatographed under reversed-phase conditions on a BDS-Hypersil C8 column. A Sciex API III+ tandem mass spectrometer equipped with a turbo ion-spray interface was used as the detector. Multiple reaction monitoring using the parent-->product ion combinations of m/z 614-->465, 620-->471 and 654-->505 were used to quantify indinavir, d6-indinavir, and internal standard, respectively. The method was validated, using 1-mL aliquots of plasma, in the concentration range in plasma of 1 to 200 ng/mL. Precision of the assay, as measured by the coefficient of variation, ranged from 0.9 to 4.3% and 0.9 to 6.2% for indinavir and d6-indinavir, respectively. Indinavir assay accuracy ranged from 95.8 to 105.0% of nominal, whereas the accuracy of the assay for d6-indinavir ranged from 97.4 to 104.0% of nominal. The assay was used to support a clinical study in which the stable isotope technique was used to determine the bioavailability of indinavir.