Determination of nimodipine by gas chromatography using electron-capture detection; external factors influencing nimodipine concentrations during intravenous administration

Exploring novel electroanalytical approach using MWCNT nanostructures to quantify nimodipine

A new type of buckypaper of MWCNT with entrapped Nimodipine (NMD) drug was constructed. NMD features a nitroaromatic group that is electroreducible, and a dihydropyridine ring that can be electrooxidized. From the perspective of the nitroaromatic group's reductive capability, we have devised amperometric and voltammetric analytical strategies, including both differential pulse and linear voltammetric techniques. These methods are implemented using glassy carbon electrodes (GCE) modified with buckypaper (BP) disks composed of multiwalled carbon nanotubes (MWCNT), which are capable of adsorbing NMD. Furthermore, by capitalizing on the oxidative capacity of the dihydropyridine ring, we have designed strategies that involve amperometry using screen-printed electrodes (SPE) modified with BP-MWCNT mini discs within a Batch Injection Analysis Cell (BIAS) designed for SPE. The developed sensor was applied successfully to determine the drug in commercial tablets. The analytical parameters of this sensor were adequate, with a recovery value of 98.24 % and detection and quantification limits of 7.01 mgL-1 and 23.35 mgL-1, respectively using the DPV method.

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.

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.

Nimodipine semi-solid capsules containing solid dispersion for improving dissolution

The aim of this study was to improve the dissolution and, therefore, bioavailability of the poorly water-soluble and highly permeable drug nimodipine (NMD). Present research involved the preparation of a solid dispersion (SD) consisting of NMD, Eudragit-E100 and Plasdone-S630 by hot-melt extrusion (HME). Compared with pure drug and physical mixture, the dissolution of NMD was enhanced dramatically (about 80% within 30min). Adding the nimodipine solid dispersion (NMD-SD) powder to a mixture of Plasdone-S630 and PEG400, and then transferring it to hard HPMC capsules, resulted in nimodipine semi-solid capsules (NMD-SSC). The dissolution from NMD-SSC was increased further (about 95% in 20min). In addition, the relative bioavailability of the NMD-SSC (test) and Nimotop (reference) was determined in beagle dogs after a single dose (120mg NMD) in a randomized crossover, own-control study. The results suggested that there was no significant difference in the areas under the plasma concentration-time curve and the mean peak concentration between NMD-SSC (AUC(0-infinity)=2488+/-433nghmL(-1), Cmax=321+/-78ngml(-1)) and Nimotop (AUC0-infinity=2272+/-398nghmL(-1), Cmax=293+/-73ngmL(-1)) (P>0.05). However, the apparent rate of absorption of NMD from NMD-SSC (tmax=1.3h) was markedly faster than that from Nimotop (tmax=3.1h) (P<0.05), which indicates that as a fast release preparation, NMD-SSC is well absorbed.

Simultaneous determination of nitrendipine and one of its metabolites in plasma samples by gas chromatography with electron-capture detection

A sensitive method for GC-ECD simultaneous determination of nitrendipine and its pyridine metabolite M1 in human plasma is described. Felodipine was used as the internal standard. The plasma samples were extracted with toluene. One microlitre of the extract was injected onto the capillary column (polymethylsiloxane) and measured with electron-capture detector. The developed method showed to be linear over the range 0.25-70 for nitrendipine and 0.3-61 ng/ml for its metabolite M1 with an inter-day and intra-day precision in terms of R.S.D. lower than 8% except the concentrations near lowest limit of quantification (LLOQ) (<11% R.S.D.). The LLOQ for nitrendipine was 0.25 and 0.3 ng/ml for its metabolite, respectively. The analytical recovery was 94% for nitrendipine and 89% for its pyridine metabolite M1. This GC-ECD method was developed for being used in clinical pharmacokinetic studies.

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.

Evaluation of modified gum karaya as carrier for the dissolution enhancement of poorly water-soluble drug nimodipine

Modified gum karaya (MGK), a recently developed excipient was evaluated as carrier for dissolution enhancement of poorly soluble drug, nimodipine (NM). The advantages of MGK over the parent gum karaya (GK) were illustrated by differences in the in vitro dissolution profiles of respective solid mixtures prepared by co-grinding technique. The influence of process variable, such as polysaccharide concentration and method of preparation of solid mixture on dissolution rate was studied. Solubility studies were also performed to explain the differences in dissolution rate. Solid mixtures were characterized by differential scanning calorimetry (DSC), X-ray diffraction studies (XRD) and scanning electron microscopy (SEM). The dissolution rate of NM was increased as the MGK concentration increased and optimum ratio was found to be 1:9 w/w ratio (NM:MGK). It is found that method of preparation of solid mixtures was significantly effected the dissolution rate of NM from solid mixtures. The order of method of preparation in according to their Dissolution Efficiency is physical mixture < co-grinding mixture < swollen carrier mixture < kneading mixture (water as kneading agent) < kneading mixture (70% v/v ethanol as kneading agent) < solid dispersion. Though, the solid mixtures prepared by other methods like solid dispersion, swollen carrier mixture and kneading technique gave faster release, co-grinding mixture prepared in 1:9 w/w ratio (NM:MGK) was found to exhibit a significant improvement in dissolution rate without requiring addition of organic solvents or high temperatures for its preparation and the process is less cumbersome. Hence, co-grinding technique appears to be more easier and the most convenient method from a practical point of view.

High-performance liquid chromatography with ultraviolet and fluorimetric detection for the simultaneous determination of tacrine, nimodipine, and their respective metabolites in the plasma of patients with Alzheimer disease

A new high-performance liquid chromatography (HPLC) assay was developed for the simultaneous determination of tacrine (THA), nimodipine, and their three metabolites (MI, MII, and MIII) using a 1-ml plasma sample volume. A liquid-liquid extraction procedure was coupled with a reverse-phase HPLC separation. Quantification was performed by fluorometric detection for THA and metabolites and by ultraviolet detection for nimodipine and metabolites. Peak-height ratios were linear across the ranges 0.5 to 100 micro/l for THA and its three metabolites; 2 to 500 microg/l for nimodipine, MII, and MIII; and 4 to 500 microg/l for MI. Correlation coefficients were better than 0.998 for all compounds. Accuracy and precision were less than 12% for the entire concentration range for each substance. This method is sensitive and selective. Analysis of plasma samples collected from patients with Alzheimer disease demonstrated that the assay is suitable for clinical and pharmacokinetic trials including drug-drug interactions studies.

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.

Safety and tolerance of intravenous nimodipine

OBJECTIVE

To evaluate the safety and tolerance of intravenous nimodipine administered via a peripheral vein in healthy male volunteers.

DESIGN

Double-blind, placebo- and vehicle-controlled trial with three fixed-dose panels.

SETTING

Inpatient infusion and observation periods.

SUBJECTS

61 healthy male volunteers, aged 18-40 years.

METHODS

Subjects in panel 1 received nimodipine 0.4 mg/h, vehicle 2 mL/h, or placebo 2 mL/h; subjects in panel 2 received nimodipine 1 mg/h, vehicle 5 mL/h, or placebo 5 mL/h; subjects in panel 3 received nimodipine 2 mg/h, vehicle 10 mL/h, or placebo 10 mL/h. All infusions were administered intravenously for 48 hours and volunteers were observed for 48 hours after cessation of the infusion. In addition to standard safety assessments (physical examination, electrocardiogram, laboratory studies, and adverse event reporting), supine and standing blood pressures and pulse rates were measured frequently. Plasma samples were also analyzed for nimodipine and its two demethylated metabolites.

RESULTS

Of 61 subjects, 55 completed the 48-hour infusion and 6 discontinued the study because of adverse events. Intravenous nimodipine was well tolerated at 0.4 and 1 mg/h. However, all six subjects who received nimodipine 2 mg/h experienced moderate-to-severe adverse events, and one subject was discontinued because of dizziness, diaphoresis, and postural hypotension. The matched vehicle (10 mL/h) also was not well tolerated, with three subjects who discontinued because of phlebitis. Two subjects who received placebo were also discontinued during the study. Small (2 mm Hg) decreases in mean supine diastolic blood pressure were observed in the 0.4- and 1-mg/h nimodipine groups, but the 2-mg/h group showed a slight (5 mm Hg) increase in blood pressure. These changes were not clinically significant. Clearance and half-life of nimodipine and its metabolites were similar at all three dosages.

CONCLUSIONS

Using peripheral vein administration, nimodipine 2 mg/h and matched vehicle at 10 mL/h were not well tolerated in this healthy normal population. The maximum tolerated dose of nimodipine was found to be 1 mg/h.

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

An enantioselective method of high specificity and sensitivity for the determination of the enantiomers of two racemic 1,4-dihydropyridine compounds after simultaneous oral (po) and intravenous (iv) administration is reported. The method is suitable for the simultaneous administration by two different routes of a racemic drug labeled with stable isotopes and unlabeled racemate. For workup, an internal racemic standard labeled with a different number of stable isotopes is added. After separation of the enantiomers by chiral stationary-phase high-performance liquid chromatography and subsequent analysis by gas chromatography/mass spectroscopy (GC/MS) with selected ion detection, the R and S enantiomer concentrations arising from i.v. and p.o. administration can be precisely measured because of their mass difference. This method has been applied to assess the disposition of the R and S enantiomers of nimodipine and nitrendipine after simultaneous i.v. and p.o. administration. The assay is highly specific and sensitive, with a limit of quantification per enantiomer of 0.1 ng/mL after extraction of 0.5 mL of human serum samples and monitoring the M- ions in the electron capture, negative ion chemical ionization mode. The calibration curve was linear in the range 0.1-100 ng/mL. Within- and between-day precision were satisfactory (coefficient of variation, < 10%). Enantiomeric excess in the range 0-100% could be accurately determined. Comparison of the enantioselective method with the achiral method (GC/MS only) gave good agreement.

High-performance liquid chromatographic determination of the calcium channel blocker nimodipine in monkey plasma

A new high-performance liquid chromatographic (HPLC) assay was developed for the determination of nimodipine in monkey plasma. An ethyl acetate extraction procedure was employed with a reversed-phase HPLC separation for the analysis. Absolute recovery of nimodipine from plasma was over 95% with a lower limit of quantitation of 10 ng/ml. This method was applied to a preliminary pharmacokinetic study in which 0.25 mg/kg nimodipine was administered intravenously to three monkeys. Protein binding and stability of nimodipine in monkey plasma were also examined. The pharmacokinetic parameters of nimodipine in monkeys were similar to those obtained in humans and indicate that monkeys are an appropriate animal model for further pharmacokinetic investigations.

Clinical pharmacokinetics of calcium antagonists. An update

The calcium antagonists are valuable and widely used agents in the management of essential hypertension and angina. There is an increasing number of new agents to add to the 3 prototype substances nifedipine, diltiazem and verapamil. These new agents are dihydropyridines structurally related to nifedipine. However, they tend to have longer elimination half-lives (t 1/2 beta) and may be suitable for twice-daily administration. Amlodipine is an exception with a t 1/2 beta in excess of 30h. Apart from elimination rates, however, the pharmacokinetic characteristics of the newer agents have a notable tendency to resemble those of the established agents. They are highly cleared drugs, are relatively highly protein bound. As they are subject to significant first-pass metabolism, old age and hepatic impairment will increase their plasma concentrations due to a reduced first-pass effect. Renal impairment does little to their pharmacokinetics since the fraction eliminated unchanged by the kidney is small. For most agents, plasma concentration-response relationships have been described. Interesting areas for further research include chronopharmacokinetics, stereoselective pharmacokinetics and lipid solubility. Drugs affecting hepatic blood flow and drug metabolising capacity have predictable interaction potential. Some of the newer calcium antagonists will, like verapamil, increase plasma digoxin concentrations. Verapamil and diltiazem decrease phenazone (antipyrine) metabolism and therefore tend to decrease the metabolism of other drugs.

Chromatography of calcium channel blockers

Numerous publications during the past ten years have described the determination of various calcium channel blockers in biological fluids, using gas and liquid chromatographic techniques. Diltiazem, verapamil, flunarizine and a growing number of dihydropyridines belong to this group of drugs, which in most instances are active at low plasma concentrations. From a bioanalytical point of view these compounds have many features in common, such as high lipophilicity and favourable detection properties.

Enantioselective determination of felodipine and other chiral dihydropyridine calcium entry blockers in human plasma

A sensitive method for the enantioselective determination of felodipine in human plasma is described. Following alkaline extraction with dichloromethane-pentane, racemic felodipine and its primary pyridine metabolite are simultaneously assayed using capillary gas chromatography on a DB-1 column, with electron-capture detection. The enantiomers of felodipine are quantitatively separated by high-performance liquid chromatography on a Chiralcel OJ column, containing tris(4-methylbenzoate)-modified cellulose coated on silica, and off-line detection using the same gas chromatographic system is applied. The limits of determination in plasma (and the inter-assay coefficient of variation (C.V.) at levels below 1 ng/ml) were 0.1 ng/ml (C.V. 13%) for felodipine, 0.1 ng/ml (C.V. 15%) for the enantiomers of felodipine and 0.3 ng/ml (C.V. 7%) for its pyridine metabolite. The method has proved to be applicable to several other chiral dihydropyridine calcium entry blockers, including nitrendipine, with comparable sensitivities.

The availability of diltiazem: a study on the sorption by intravenous delivery systems and on the stability of the drug

The stability and the sorption by intravenous delivery systems of the calcium antagonist diltiazem dissolved into either 5% dextrose or 0.9% sodium chloride solutions have been investigated, under conditions simulating current clinical practice. Static experiments showed an excellent stability and no sorption after 48 h. Dynamic experiments, at a perfusion rate of 20 mg h-1, showed no sorption of the drug by infusion fluid containers, burettes or administration sets. For end-line filters a temporary decrease of the recovered amount of diltiazem was observed but only with the 0.9% NaCl solution. It is concluded that the stability and the sorption of diltiazem offers no problem with regard to clinical efficacy.

Assay of isradipine and of its major metabolites in biological fluids by capillary gas chromatography and chemical ionization mass spectrometry

A method is described for the determination of isradipine, a dihydropyridine calcium antagonist, and five of its metabolites in plasma and urine. The neutral compounds were extracted in toluene and analysed in a wide-bore silica capillary column. The acidic compounds were extracted in two steps, then esterified with diazomethane and assayed separately using the same column. Detection was performed by negative-ion mass spectrometry with chemical ionization. The limit of detection of isradipine was 0.04 ng/ml when the compound was determined alone and 0.7 ng/ml when its oxidized metabolite was determined simultaneously. The limits of detection of the metabolites in plasma ranged from 0.15 to 2 ng/ml. The method was successfully used in conventional pharmacokinetic studies and in a multicentre study of population pharmacokinetics.

The influence of infusion rate on the pharmacokinetics and haemodynamic effects of nisoldipine in man

1. The pharmacokinetics and haemodynamic effects of nisoldipine on long term i.v. infusion of 2.40 mg and 9.59 mg in 25 h were studied in six healthy subjects. Liver blood flow at 0.8 and 24 h was assessed by measuring indocyanine green (ICG) clearance. 2. After high-dose nisoldipine, systemic clearance was 0.99 +/- 0.16 1 min-1, volume of distribution was 5.8 +/- 1.5 1 kg-1 and elimination half-life was 10.7 +/- 2.4 h. The pharmacokinetic parameters were similar after low-dose nisoldipine. 3. No significant changes in apparent liver blood flow were observed after either high-dose or low-dose nisoldipine. 4. Systolic blood pressure did not change, whereas diastolic blood pressure decreased by approximately 10% during both treatments. Maximal increase in heart rate was approximately 37% at high-dose infusion, whereas this was one half lower during the low-dose regimen. 5. Increased infusion rate results in an unfavourable shift in the haemodynamic effect profile of nisoldipine.

Nimodipine treatment of subarachnoid hemorrhage

In a pilot study of 6 patients with subarachnoid hemorrhage caused by a ruptured intracranial (grade IV (Hunt and Hess) aneurysm the hemodynamics and plasma-nimodipine concentrations have been observed during a 3-week period of treatment. We found that 3 patients developed reversible hypotension during the nimodipine treatment and that the hypotension tendency could be related to the plasma-nimodipine level and not to a more or less severe sensitivity to nimodipine. Repeated measurements of blood pressure, plasma-nimodipine and regional cerebral blood flow (rCBF) are necessary for the purpose of obtaining the optimum treatment and for evaluating the effect of treatment.

Survey of clinical experience with nimodipine in patients with subarachnoid hemorrhage

The present studies show that nimodipine prevents and/or improves permanent ischemic neurological deficits in patients with subarachnoid hemorrhage. This was particularly marked in four double-blind, placebo-controlled studies in which statistically significant reductions in mortality and morbidity as consequence of cerebral vasospasm were found. The drug has been shown to increase cerebral blood flow, to reduce vasoconstriction, although not to fully prevent angiographic vasospasm, and to improve central conduction time. Nimodipine did not increase the rate of rebleeding. Its administration during anesthesia does not result in management problems. In general, nimodipine was well tolerated. Side effects were recorded mainly in open studies using the intravenous formulation and consisted mainly of decreases in blood pressure and headaches. Transient increases in liver enzymes may be due to the organic solvent. Hence, all results indicate that patients with subarachnoid hemorrhage will benefit from preventive or therapeutic nimodipine treatment.