Simultaneous assessment of the intravenous and oral disposition of the enantiomers of racemic nimodipine by chiral stationary-phase high-performance liquid chromatography and gas chromatography/mass spectroscopy combined with a stable isotope technique

Nimodipine systemic exposure and outcomes following aneurysmal subarachnoid hemorrhage: a pilot prospective observational study (ASH-1 study)

Background

Nimodipine improves outcomes following aneurysmal subarachnoid hemorrhage (aSAH). Guidelines recommend that all patients should receive a fixed-dose nimodipine for 21 days. However, studies reported variability of nimodipine concentrations in aSAH. It is not clear if reduced systemic exposure contributes to worsening outcomes. The aim of this study was to compare nimodipine systemic exposure in those who experienced poor outcomes to those who experienced favorable outcomes.

Methods

This was a pilot prospective observational study in 30 adult patients admitted to the University of Alberta Hospital with aSAH. Data were collected from the electronic health records following enrollment. Blood samples were collected around one nimodipine 60 mg dose at a steady state, and nimodipine [total, (+)-R and (-)-S enantiomers] plasma concentrations were determined. The poor outcome was defined as a modified Rankin Scale (mRS) score at 90 days of 3-6, while the favorable outcome was an mRS score of 0-2. The correlation between nimodipine concentrations and percent changes in mean arterial pressure (MAP) before and after nimodipine administration was also determined. Furthermore, covariates potentially associated with nimodipine exposure were explored.

Results

In total, 20 (69%) participants had favorable outcomes and 9 (31%) had poor outcomes. Following the exclusion of those with delayed presentation (>96 h from aSAH onset), among those presented with the World Federation of Neurological Surgeons (WFNS) grade 3-5, nimodipine median (interquartile range) area under the concentration time curve (AUC0-3h) in those with favorable outcomes were 4-fold higher than in those with poor outcomes [136 (52-192) vs. 33 (23-39) ng.h/mL, respectively, value of p = 0.2]. On the other hand, among those presented with WFNS grade 1-2, nimodipine AUC0-3h in those with favorable outcomes were significantly lower than in those with poor outcomes [30 (28-36) vs. 172 (117-308) ng.h/mL, respectively, value of p = 0.03)]. (+)-R-nimodipine AUC0-3h in those who did not develop vasospasm were 4-fold significantly higher than those who had vasospasm (value of p = 0.047). (-)-S-nimodipine was significantly correlated with percentage MAP reduction. Similar results were obtained when the whole cohort was analyzed.

Conclusion

The study was the first to investigate the potential association between nimodipine exposure following oral dosing and outcomes. In addition, it suggests differential effects of nimodipine enantiomers, shedding light on the potential utility of nimodipine enantiomers. Larger studies are needed.

Nimodipine Pharmacokinetic Variability in Various Patient Populations

Nimodipine has been shown to improve outcomes following aneurysmal subarachnoid hemorrhage. Guidelines recommend that all patients receive a fixed dose of oral nimodipine for 21 days. However, pharmacokinetic studies have suggested variability of nimodipine pharmacokinetics in subarachnoid hemorrhage and in other patient populations. The clinical relevance of such variability is unknown. Therefore, the objective of the present review is, first, to conduct a literature review and summarize nimodipine pharmacokinetic data and sources of variability in various patient groups. Second, to determine if there is any evidence reporting an association between nimodipine exposure and clinical outcomes in patients with subarachnoid hemorrhage. A systematic literature search was performed in MEDLINE and EMBASE. The following keywords were used: ("nimodipine" OR "nymalize" OR "nimotop") AND ("pharmacokinetic*", OR "PK"). The search results were limited to English language and human studies. A large interpatient variability in nimodipine pharmacokinetics has been reported. Patient-specific factors that had an influence on pharmacokinetic parameters are age, comorbidities, variabilities in metabolism due to genetic polymorphism and co-administered medications, as well as nimodipine administration technique. The association between nimodipine exposure and clinical outcomes remains unclear and data available are too scarce to reach a firm conclusion. Here, we present a narrative review with a systematic literature search discussing nimodipine pharmacokinetic variability in various patient populations. It is not clear if minimal or lack of systemic exposure to nimodipine denies its benefit and contributes to worsening outcomes in patients with subarachnoid hemorrhage. Further studies are needed to determine if such an association exists.

Enantioselective assay of nimodipine in human plasma using liquid chromatography-tandem mass spectrometry

Nimodipine is a dihydropyridine calcium channel blocker that exhibits higher selectivity toward cerebral blood vessels compared with other members of the same class. It has been shown to improve outcomes and prevent delayed cerebral ischemia in the setting of aneurysmal subarachnoid hemorrhage, a life-threatening brain bleed. Nimodipine is a chiral compound and it is marketed as a racemic mixture of (+)-R and (-)-S enantiomers. (-)-S-Nimodipine is approximately twice as potent a vasorelaxant as the racemic mixture and is more rapidly eliminated than the (+)-R counterpart following oral dosing. Few analytical procedures have been reported to determine nimodipine enantiomers in biological samples; however, the reported methods were time-consuming, involved multistep extraction procedures and required large sample volumes. Herein, we present an LC-MS/MS method for quantifying nimodipine enantiomers in human plasma using a small sample volume (0.3 ml) and a single liquid-liquid extraction step. The peak area ratios were linear over the tested concentration ranges (1.5-75 ng/ml) with r²  > 0.99. The intraday CV and percentage error were within ±14% while the interday values were within ±13%, making this analytical method feasible for research purposes and pharmacokinetic studies.

Determination of nimodipine in plasma by HPLC-MS/MS and pharmacokinetic application

To develop and validate a rapid, specific and highly sensitive method to quantify nimodipine in human plasma using dibucaine as the internal standard (IS). The analyte and IS were extracted from plasma samples by liquid-liquid extraction using hexane-ethyl acetate (1:1 v/v). The chromatographic separation was performed on a Varian® Polaris C18 analytical column (3 μm, 50 x 2.0 mm) and pre-column SecurityguardTM C18 (4.0 x 3.0 mm) with a mobile phase of Acetonitrile-Ammonium acetate 0.02 ml/L (80:20v/v). The method had a chromatographic run time of 4.5 min and linear calibration curve over the range of 0.1- 40 ng/mL (r > 0.9938). The limit of quantification was 100 pg/mL. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. This validated method was successfully applied in determining the pharmacokinetic profile of nimodipine tablets of 30 mg administered to 24 healthy volunteers. The proposed method of analysis provided a sensitive and specific assay for nimodipine determination in human plasma. The time for the determination of one plasma sample was 4.5 min. This method is suitable for the analysis of nimodipine in human plasma samples collected for pharmacokinetic, bioavailability or bioequivalence studies in humans.

Enantioselective determination of azelnidipine in human plasma using liquid chromatography–tandem mass spectrometry

A sensitive and simple method was developed for determination of the enantiomers of azelnidipine, (R)-(-)-azelnidipine and (S)-(+)-azelnidipine, in human plasma using chiral liquid chromatography with positive ion atmospheric pressure chemical ionization tandem mass spectrometry. Plasma samples spiked with stable isotope-labeled azelnidipine, [(2)H(6)]-azelnidipine, as an internal standard, were processed for analysis using a solid-phase extraction in a 96-well plate format. The azelnidipine enantiomers were separated on a chiral column containing alpha(1)-acid glycoprotein as a chiral selector under isocratic mobile phase conditions. Acquisition of mass spectrometric data was performed in multiple reaction monitoring mode, monitoring the transitions from m/z 583-->167 for (R)-(-)-azelnidipine and (S)-(+)-azelnidipine, and from m/z 589-->167 for [(2)H(6)]-azelnidipine. The standard curve was linear over the studied range (0.05-20 ng/mL), with r(2)>0.997 using weighted (1/x(2)) quadratic regression, and the chromatographic run time was 5.0 min/injection. The intra- and inter-assay precision (coefficient of variation), calculated from the assay data of the quality control samples, was 1.2-8.2% and 2.4-5.8% for (R)-(-)-azelnidipine and (S)-(+)-azelnidipine, respectively. The accuracy was 101.2-117.0% for (R)-(-)-azelnidipine and 100.0-107.0% for (S)-(+)-azelnidipine. The overall recoveries for (R)-(-)-azelnidipine and (S)-(+)-azelnidipine were 71.4-79.7% and 71.7-84.2%, respectively. The lower limit of quantification for both enantiomers was 0.05 ng/mL using 1.0 mL of plasma. All the analytes showed acceptable short-term, long-term, auto-sampler and stock solution stability. Furthermore, the method described above was used to separately measure the concentrations of the azelnidipine enantiomers in plasma samples collected from healthy subjects who had received a single oral dose of 16 mg of azelnidipine.

The difference between nicardipine and its enantiomers on inhibiting vasoconstriction of isolated rabbit thoracic artery

The present study was designed to study the difference effects between nicardipine and its two enantiomers on thoracic artery of rabbit. A high-performance liquid chromatographic method was used to prepare the two enantiomers of nicardipine. The thoracic artery of rabbit was removed. The vessels were cut into 3 mm in width and 15 mm in length spiral strips and immersed into tissue baths. The concentration-response curves of nicardipine and its enantiomers were obtained by cumulative administration of the vasoconstrictors. Nicardipine and the enantiomers could shift the dose-response curves of NE, KCl or CaCl2 to right in a nonparallel manner and decrease the maximum effective in a concentration-depended manner, respectively. The pD2' value of R-(-)-nicardipine showed significantly effective than that of nicardipine and S-(+)-nicardipine (P<0.01). There was not obviouse difference between the pD2' value of nicardipine and S-(+)-nicardipine (P>0.05). The results demonstrate that the stereoselective interaction between R-(-)-nicardipine and L-calcium channel receptor is more stronger than that of S-(+)-nicardipine.

Determination of nimodipine in human plasma by a sensitive and selective liquid chromatography–tandem mass spectrometry method

A sensitive and highly selective liquid chromatography-tandem mass spectrometry (LC-MS-MS) method was developed to determine nimodipine in human plasma. The analyte and internal standard nitrendipine were extracted from plasma samples by n-hexane-dichloromethane-isopropanol (300:150:4, v/v/v), and chromatographed on a C(18) column. The mobile phase consisted of methanol-water-formic acid (80:20:1, v/v/v). Detection was performed on a triple quadrupole tandem mass spectrometer by selected reaction monitoring (SRM) mode via atmospheric pressure chemical ionization (APCI) source. The method has a limit of quantification of 0.24 ng/ml. The linear calibration curves were obtained in the concentration range of 0.24-80 ng/ml. The intra- and inter-day precisions were lower than 4.4% in terms of relative standard deviation (R.S.D.), and the accuracy ranged from 0.0 to 5.8% in terms of relative error (RE). This validated method was successfully applied for the evaluation of pharmacokinetic profiles of nimodipine tablets administered to 18 healthy volunteers.

Enantioselective determination of lercanidipine in human plasma for pharmacokinetic studies by normal-phase liquid chromatography–tandem mass spectrometry

We describe here the first method for the enantioselective analysis of the calcium antagonist lercanidipine in human plasma by high performance liquid chromatography (HPLC) employing tandem mass spectrometric (MS) detection. Routine determination of lercanidipine enantiomers in human plasma in the working range of 0.025-50.0 ng ml(-1) plasma for each enantiomer with an accuracy and precision less than 15% was possible. Application of the method to a stereospecific study of the pharmacokinetics showed that plasma levels after an oral dose of rac-lercanidipine administered to a healthy volunteer were found to be higher for the (S)-enantiomer.

Stereoselective determination and pharmacokinetics of dihydropyridines: an updated review

All dihydropyridines, except nifedipine, have at least one chiral center, and their pharmacokinetics and clinical effects differ from one enantiomer to another. Chiral separation methods for dihydropyridines using chromatographic techniques are discussed. The stereoselective pharmacokinetics of dihydropyridine calcium antagonists were reviewed in detail in 1995. The present review article updates the methods for the stereoselective determination of dihydropyridines using chromatographic techniques and summarizes the pharmacokinetics of the dihydropyridines, including the newest drugs under development.

Enantiomeric determination of amlodipine in human plasma by liquid chromatography coupled to tandem mass spectrometry

A sensitive method for the separation and determination of amlodipine enantiomers in plasma has been developed based on solid-phase extraction (SPE) with disposable extraction cartridges (DECs) in combination with chiral liquid chromatography (LC). The SPE technique is used to isolate the drug from the biological matrix and to prepare a cleaner sample before injection and analysis by HPLC coupled to mass spectrometry. The DEC is filled with ethyl silica (50 mg) and is first conditioned with a 2.5% ammonia in methanol solution and then with ammonium acetate buffer. A 1.0-ml volume of plasma is then applied on the DEC. The washing step is first performed with ammonium acetate buffer and secondly with a mixture of water and methanol (65:35, v/v), while the final elution step is obtained by dispensing methanol containing 2.5% of ammonia. The eluate is then collected and evaporated to dryness before being dissolved in the LC mobile phase and injected into the LC system. The stereoselective analysis of amlodipine is achieved on a Chiral AGP column containing alpha(1)-acid glycoprotein as chiral selector by using a mobile phase consisting of a 10-mM acetate buffer (pH 4.5) and 1-propanol (99:1, v/v). The LC system is coupled to tandem mass spectrometry with an APCI interface in the positive-ion mode. The chromatographed analytes are detected in the selected reaction monitoring mode (SRM). The MS/MS ion transitions monitored are 409 to 238 for amlodipine, and 260 to 116 for S-(-)-propranolol used as internal standard (IS). The method was validated considering different parameters, such as linearity, precision and accuracy. The limit of quantitation was found to be 0.1 ng/ml for each amlodipine enantiomer.

Normal-phase TLC separation of enantiomers of 1.4-dihydropyridine derivatives

A new TLC-based method was proposed for the separation of enantiomers and mixtures of racemic DHP derivatives differing in the kind of substituent in the phenyl ring. The conditions for the effective determination of the substances involved and the mechanism of their sorption were also studied. For the separation of felodipine, nilvadipine, and isradipine enantiomers, thin-layer chromatography was used, with a chiral stationary phase of the ligand exchange type, and developing phases of a different concentration of methanol (phi) as an organic modifier. The retention coefficient values k' were used to make the plots log k' = f(log phi) and log k' = f(phi). The processes taking place in the chromatographic systems were shown to be described by the Snyder-Soczewiński equation.

Studies on concentration-time profiles of nimodipine enantiomers following intravenous and oral administration of nimodipine in patients with subarachnoid hemorrhage

After i.v. and oral administration of nimodipine the concentration-time profiles of the drug and its enantiomers were studied in seven patients with subarachnoid hemorrhage. Concentrations of nimodipine, (+)-(R)-, and (-)-(S)-nimodipine were analyzed using a new stereoselective high-performance liquid chromatographic method. During the first 3 h after oral administration the concentrations of (+)-(R)- and (-)-(S)-nimodipine were significantly different, the (-)-(S)-enantiomer being found in much lesser concentrations compared to the (+)-(R)-enantiomer. The results indicate that if uptake from the gastrointestinal system is equal for the two enantiomers, then (-)-(S)-nimodipine is metabolized at a much faster rate compared to (+)-(R)-nimodipine after oral administration of the drug in patients with subarachnoid bleeding. After i.v. administration; no significant differences between the concentrations of the (-)-(S) and the (+)-(R) isomers were demonstrated.

Chronopharmacology of intravenous and oral modified release verapamil

AIMS

Using a stable isotope technique which allows simultaneous and differential measuring of orally and intravenously administered drugs we compared the pharmacokinetics and pharmacodynamics of unlabelled modified release verapamil p.o. (steady state) and deuterated verapamil i.v. (single dose) following morning and evening administration.

METHODS

Twelve female and 12 male healthy volunteers were studied in a randomized, crossover design. During the last day of each treatment period (day 6 and day 10) pharmacokinetics and pharmacodynamics (PR interval) of verapamil were assessed; 1 h before ingestion of a new R/S-verapamil 240 mg modified release formulation (08.00 h vs 20.00 h) a single dose of 10 mg d7-R/S-verapamil was administered intravenously. Serum levels of unlabelled and labelled R/S-verapamil were measured by gas chromatography/mass spectrometry. In selected samples of serum which were chosen at tmin,po and tmax,po the enantiomers were separated by chiral high-performance liquid chromatography in order to calculate R- to S-verapamil serum concentration ratios.

RESULTS

We observed no significant differences in pharmacokinetics (AUCpo, Cmax, tmax, CLo, F and R/S enantiomer ratio) between morning and evening treatment with modified release verapamil and there was no influence of time of dosing on mean prolongation of PR interval. AUCiv, CL, Vss and d7-R/d7-S enantiomer ratio following verapamil i.v. did not show circadian variation. t1/2 was slightly but statistically significantly increased after the morning infusion. PR-prolongation was significantly greater after verapamil i.v. in the morning than in the evening. The 90% confidence intervals of the differences between morning and evening administration in AUCpo, Cmax and AUCiv were within the equivalence range of 0.8-1.25.

CONCLUSIONS

Time of dosing has no significant influence on pharmacokinetics and pharmacodynamics of this new modified release formulation of verapamil. Circadian variation in presystemic metabolism of verapamil was not observed.

Modulation by dietary salt of verapamil disposition in humans

BACKGROUND

The intestine is an increasingly well-recognized site of first-pass drug metabolism. In this study, we determined the influence of dietary salt on the steady-state disposition of verapamil, a drug that undergoes extensive first-pass metabolism.

METHODS AND RESULTS

Eight normal volunteers received 120 mg of racemic verapamil orally twice a day for 21 days. The disposition kinetics of verapamil enantiomers were determined after coadministration of intravenous deuterated verapamil with the morning oral dose on days 7, 14, and 21. Each study day was preceded by 7 days on a fixed-salt diet: in 5 subjects, the initial study was conducted during a low-salt (10 mEq/d) diet, the second study during a high-salt (400 mEq/d) diet, and the third during a low-salt diet, whereas in the other 3 subjects, the sequence of diets was reversed. Plasma concentrations of both unlabeled enantiomers (ie, from oral therapy) were significantly (P<0.05) lower during the high-salt phase (eg, mean area under the time-concentration curve [0 to 12 hours] for S-verapamil: 7765+/-2591 ng. min. mL-1 [high salt] versus 12 514+/-3527 ng. min. mL-1 [low salt], P<0.05). Peak plasma concentrations were significantly lower and the extent of PR interval prolongation significantly blunted with the high-salt diet. In contrast, data with labeled drug (ie, reflecting the intravenous route) were nearly identical for the 2 diets.

CONCLUSIONS

These data indicate that a clinically important component of presystemic drug disposition occurs at the prehepatic (presumably intestinal) level and is sensitive to dietary salt.

Gut wall metabolism of verapamil in older people: effects of rifampicin-mediated enzyme induction

AIMS

To investigate prehepatic metabolism of verapamil and its inducibility by rifampicin in older subjects.

METHODS

Eight older subjects (67.1 +/- 1.2 years mean +/- s.d.) received racemic, unlabelled verapamil orally for 16 days (120 mg twice daily). Rifampicin (600 mg daily) was coadministered from day 5 to 16. Using stable isotope technology (i.e. intravenous coadministration of 10 mg deuterated verapamil) during verapamil steady-state without (day 4) and with rifampicin (day 16) bioavailability, prehepatic and hepatic extraction of verapamil were determined. The effects of verapamil on AV-conduction were measured by the maximum PR interval prolongation (%).

RESULTS

Bioavailability of the cardiovascularly more active S-verapamil decreased from 14.2 +/- 4.3% on day 4 to 0.6 +/- 0.5% on day 16 (P < 0.001). As a consequence, effects of orally administered verapamil on the AV-conduction were nearly abolished (14.4 +/- 9.4% vs 2.7 +/- 2.6%, P < 0.01). This could be attributed to a considerable increase of prehepatic extraction during treatment with rifampicin (41.7 +/- 22.1% vs 91.6 +/- 6.6%, P < 0.01) and to a minor extent to induction of hepatic metabolism (73.7 +/- 9.4% vs 91.6 +/- 5.3%, P < 0.01).

CONCLUSIONS

Prehepatic metabolism of verapamil occurred in the group of older people investigated. Induction of gut wall metabolism most likely was the major reason for the loss of verapamil effect during treatment with rifampicin in this group of older subjects.

Absorption, distribution, metabolism and excretion of 14C-labelled enantiomers of the calcium channel blocker benidipine after oral administration to rat

1. Each of the 14C-labelled optical isomers of benidipine, a new calcium antagonist, was separately administered orally to the male rat at a dose of 0.5 or 1 mg/kg. The absorption, distribution, metabolism and excretion of the 14C-labelled optical isomers were investigated. 2. Plasma concentrations of radioactivity after administration of the (-)-alpha isomer were higher than those after administration of the (+)-alpha isomer. 3. The highest radioactivity was found in liver and high levels of radioactivity were found in the kidney, adrenal gland and lung after administration of the (+)- or (-)-alpha isomers of benidipine. Up to 72 h, the tissue concentration of radioactivity fell from 1.4 to 9.2% of the highest level in each tissue for the (+)-alpha isomer and from 1.8 to 13.0% for the (-)-alpha isomer. 4. The ratios of the area under the time-curve of each tissue concentration to that of the corresponding plasma concentration were almost equal after the separate administrations of both isomers. 5. The dominant urinary and biliary metabolic pathways of the (+)-isomer were the hydrolysis of 1-benzyl 3-piperidylester followed by the oxidation of the dihydropyridine ring and N-dealkylation followed by hydrolysis of the methylester. Those of the (-)-isomer were the hydrolysis of 1-benzyl 3-piperidylester followed by the oxidation of dihydropyridine ring and of the oxidation methyl group, N-dealkylation followed by hydrolysis of the methylester, decarboxylation and glucuronidation of the piperidyl moiety after the oxidation of the dihydropyridine ring. 6. The cumulative excretion of radioactivity in urine and faeces up to 72 h after administration of the (+)-alpha isomer was 8.8 and 90.7% of the dose respectively. The corresponding values of the (-)-alpha isomer were 19.7 and 72.9% of the dose respectively. 7. The excretion of radioactivity in bile up to 48 h after administration of the (+)- and (-)-alpha isomer was 42.1 and 46.7% of the dose respectively.

Enantioselective high-performance liquid chromatographic determination of nicardipine in human plasma

A sensitive method for the enantioselective high-performance liquid chromatography (HPLC) determination of nicardipine in human plasma is described. (+)-Nicardipine, (-)-nicardipine and (+)-barnidipine as an internal standard are detected by an ultraviolet detector at 254 nm. Racemic nicardipine in human plasma was extracted by a rapid and simple procedure based on C18 bonded-phase extraction. The extraction samples were purified and concentrated on a pre-column using a C1 stationary phase and the enantiomers of nicardipine are quantitatively separated by HPLC on a Sumichiral OA-4500 column, containing a chemically modified Pirkle-type stationary phase. Determination of (+)- and (-)-nicardipine was possible in a concentration range of 5-100 ng ml(-1) and the limit of detection in plasma was 2.5 ng ml(-1). The recoveries of (+)- and (-)-nicardipine added to plasma were 91.4-98.4% and 93.3-96.7%, respectively, with coefficients of variation of less than 9.0 and 9.4% respectively. The method was applied to low level monitoring of (+)- and (-)-nicardipine in plasma from healthy volunteers.

Critical issues in chiral drug analysis in biological fluids by high-performance liquid chromatography

This review article focuses on the specificities of chiral liquid chromatography, with particular emphasis on stability, stereoconversion, enantiomeric separation, recovery and drug concentration determinations. In addition, the paper presents an overview of the different steps which have to be followed for a chiral method to be validated. Sensitivity, selectivity, linearity, precision and accuracy all have to be ensured for three chemical entities, the two enantiomers and the racemate. Only accurate and precise concentrations of the parent drug and its metabolites will lead to the reliable description of their in vitro stability and in vivo body disposition.

Coupled-column chromatography on a Chiral-AGP phase for determination of amlodipine enantiomers in human plasma: an HPLC assay with electrochemical detection

A sensitive enantioselective high performance liquid chromatographic assay for determination of the dihydropyridine-type calcium antagonist amlodipine in human plasma samples is described. Chiral chromatography is performed on an alpha 1-acid glycoprotein column (i.e. Chiral-AGP) and the eluted enantiomers are trapped and compressed on two short columns before final achiral chromatography on a narrow bore column (i.e. Zorbax SB-Ph) using electrochemical detection. Both stereoselective quantitative analysis and enantiomeric ratio analysis, for samples with a known total concentration of amlodipine are described. The quantitative assay shows linearity over the range 0.5-10 ng ml-1 for the two enantiomers and the limit of detection is about 0.2 ng ml-1. The method has been applied to a pharmacokinetic study of the enantiomers of amlodipine in human subjects.

Enantiospecific determination of nimodipine in human plasma by liquid chromatography-tandem mass spectrometry

A direct enantiospecific HPLC assay using tandem mass spectrometric (MS-MS) detection via pneumatically-assisted electrospray has been developed for the determination of the calcium antagonist nimodipine in human plasma. By the addition of ammonium acetate (2 mM) to the purely organic eluent ethanol-n-heptane (20:80, v/v) charged species (M+NH4+) were producible by electrospray ionization at sufficient sensitivity. Routine determination of nimodipine enantiomers in human plasma in the working range of 0.5-75 microgram/l plasma for each isomer with an accuracy < or = +/- 10% and a precision of about 10% (20% close to the limit of quantification) was possible. This was comparable to the available LC-GC-MS assay, however, the time required for routine analysis of ca. 150 unknowns could be reduced from 4 weeks to 1 week.

Stereoselective pharmacokinetics of dihydropyridine calcium antagonists

Many dihydropyridine calcium antagonists are widely used for the treatment of angina and hypertension, and many more are under development. Most of these drugs have one or more chiral centre, and the pharmacological activity between the enantiomers for these drugs is known to be markedly different. First, the stereospecific assay methods for these drugs in plasma or serum are reviewed with emphasis on chiral stationary phase high-performance liquid chromatography for their determination. Next, the stereoselective pharmacokinetics of these drugs (nilvadipine, nitrendipine, felodipine, nimodipine, manidipine, benidipine and nisoldipine) in animals, healthy subjects and patients with hepatic disease is reviewed. Enantiomer-enantiomer interaction, enantiomeric inversion and the stereochemical aspects of pharmacokinetic drug interactions in these drugs are also described.

Determination of the enantiomers of nisoldipine in human plasma using high-performance liquid chromatography on a chiral stationary phase and gas chromatography with mass-selective detection

A method is described that combines chiral HPLC and off-line GC with mass-selective detection for the quantitation of the enantiomers of nisoldipine [(+/-)-I] in human plasma. An isotope-labelled internal standard [nine-fold deuterated (+/-)-I] is used throughout the assay. The limit of quantification is 0.1 microgram/l for each enantiomer. Data on the precision, accuracy and selectivity of the method are presented. Enantioselective analysis was performed in subjects receiving the racemic drug in tablet form. In healthy volunteers the maximum concentration and the area under the curve of the pharmacologically more active (+)-enantiomer were greater by 9-fold and 13-fold, respectively, compared to those of the (-)-enantiomer. In elderly hypertensive patients plasma concentrations of (+)-I were ca. five times as high as those of the (-)-enantiomer. Stereoselectivity was not affected by hepatic impairment. After intravenous administration of (+/-)-I there were no relevant differences between the plasma concentrations of the enantiomers.