Determination of a new cerebral vasodilator 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-[2-(N-benzyl-N-methylamino)]-ethyl ester 5-methyl ester hydrochloride (YC-93) in plasma by electron capture gas chromatography

Determination of felodipine in plasma by capillary gas chromatography with electron capture detection

Felodipine in plasma was extracted with toluene and determined by automated capillary gas chromatography with electron capture detection. Undesirable oxidation of the dihydropyridine derivative in the injector and in the column was avoided by the use of glass materials with the inner surfaces treated by high-temperature silylation. The day-to-day reproducibility of the method was represented by a relative standard deviation (RSD) of 5% for a felodipine concentration of 25 nmol/l. The minimum determinable concentration (giving better than 15% RSD) was 1-2 nmol/l (0.4-0.8 ng/ml).

A simple method for nicardipine hydrochloride quantification in plasma using solid-phase extraction and reversed-phase high-performance liquid chromatography

A simple and sensitive reversed-phase liquid chromatography method was developed and validated for the determination of nicardipine hydrochloride (NC) in rabbit plasma. Nicardipine hydrochloride and nimodipine, used as internal standard, were initially extracted from plasma by a rapid solid-phase extraction using C(18) cartridges. After extraction, nicardipine hydrochloride was separated by HPLC on a C(18) column and quantified by ultraviolet detection at 254 nm. A mixture of acetonitrile-0.02 M sodium phosphate buffer-methanol (45:40:15) with 0.2% of triethylamine of pH of 6.1 was used as mobile phase. The mean (+/-SD) extraction efficiency of NC was 77.56 +/- 5.4, 84.23 +/- 4.32 and 83.94 +/- 3.87% for drug concentrations of 5, 25 and 100 ng/mL, respectively. The method proved to be linear in the range of 5-100 ng/mL with a regression coefficient of 0.9993. The relative standard deviations of intra- and inter-day analysis for NC in plasma were 3.26-6.52% (n = 5) and 4.71-9.38% (n = 5), respectively. The differences of the mean value measured from the concentration prepared, expressed in percentages (bias percentage), were only - 5.2, 0.4 and 0.8% at NC 5, 25 and 50 ng/mL, which confirmed the accuracy of the method. The analytical technique was used to determine NC plasma concentration after drug oral administration to rabbits. The results inferred that NC is rapidly absorbed in rabbits and has a short half-life (t(1/2) = 1.34 h).

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.

Fluorenone 1,4-dihydropyridine derivatives with cardiodepressant activity: enantiomeric separation by chiral HPLC and conformational aspects

The direct HPLC enantiomeric separation of five fluorenone-1,4-dihydropyridine-3,5-dicarboxylic diesters has been achieved using a Chiralpak AD stationary phase obtaining simultaneously good enantioselectivities, resolution factors, and elution times. CD spectra of the individual enantiomers for two compounds were measured. Thermodynamic parameters associated with the adsorption equilibria of the enantiomers with the chiral stationary phase were obtained from HLPC runs at various temperatures. The conformational preferences of the synperiplanar fluorenone group and of the cis/cis ester groups were obtained by 1H NMR spectra, including NOE experiments.

Analysis of felodipine by packed column supercritical fluid chromatography with electron capture and ultraviolet absorbance detection

A reproducible and selective supercritical fluid chromatography (SFC) method was developed for the analysis of felodipine, a drug indicated for the treatment of hypertension. Methanol-modified carbon dioxide was employed as the SFC mobile phase with both electron capture detection (ECD) and multi-wavelength detection (MWD) being used simultaneously for analyte determination. Chromatography limit of detection (LOD) and limit of quantitation (LOQ), linear dynamic range (LDR) and injection precision were obtained in order to assess chromatographic and detector performance for both the SFC/MWD and SFC/ECD/MWD systems. The method was shown to be stability indicating since felodipine could be separated from its potential oxidative degradation product, H152/37, in under 6 min (felodipine k' = 2.44). Sample throughput was increased by 60% with the SFC assay vs LC. The optimized SFC method was shown to be equivalent to an existing LC/UV procedure for the analysis of a sustained-release tablet while realizing a 92% saving in disposable solvent waste. In order to achieve further solvent savings overall, supercritical fluid extraction (SFE) with 8% methanol-modified carbon dioxide as the extraction fluid was used to extract felodipine from a sustained-release tablet (as opposed to traditional solvent extraction). Comparable drug recoveries were obtained with SFE sample preparation technique when either SFC or LC extract analysis was utilized.

Capillary gas chromatographic determination with nitrogen-phosphorus detection of the calcium antagonist nicardipine and its pyridine metabolite M-5 in plasma

A capillary gas chromatographic method with nitrogen-phosphorus detection for the simultaneous determination of nicardipine and its pyridine metabolite M-5 was developed. The method involves extraction of the plasma with hexane-methylene chloride (1:1, v/v), followed by evaporation of the organic phase. The extract is injected into a fused-silica capillary column coated with cross-linked 5% phenyl-methylsilicone. A temperature gradient (85-285 degrees C) is applied and the two products and the internal standard can be separated within 22 min. The limit of detection is 0.5 ng/ml for both products. The method is suitable for pharmacokinetic studies in humans.

Determination of a new calcium antagonist and its main metabolite in plasma by thermospray liquid chromatography-mass spectrometry

A highly sensitive thermospray liquid chromatographic-mass spectrometric method has been developed for the simultaneous determination of FRC-8653 (I), a new calcium antagonist, and its main metabolite (M-4) in plasma. A deuterated analogue of I was added to the plasma as the internal standard. After the purification and concentration of the plasma sample on bonded-phase disposable columns, the extract was injected into the thermospray liquid chromatograph and analysed by selected-ion monitoring mass spectrometry. The calibration curves obtained were linear over the concentration range 0.5-100 ng/ml. The limits of quantification are 0.5 ng/ml for I and 1 ng/ml for M-4 in plasma, which are sufficient to evaluate plasma concentrations after oral administration to rats.

Use of a carrier for quantitation of a new dihydropyridine calcium antagonist (OPC-13340) in human plasma by highly sensitive gas chromatography with negative-ion chemical ionization mass spectrometry

A sensitive gas chromatographic-mass spectrometric method for the quantitation of (+/-)-methyl 3-phenyl-2(E)-propenyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate (OPC-13340, I), a new dihydropyridine calcium antagonist with a potent and long-acting antihypertensive and antianginal effect, was developed in order to elucidate its pharmacokinetics. Dihydropyridine calcium antagonist have been usually quantifed by this technique in the negative-ion chemical ionization mode. However, direct application of this method to quantify trace amounts of I in biological fluids completely failed, owing to its adsorption on the column and oxidation of its dihydropyridine ring. Human plasma containing I and (+/-)-[2H3]methyl 3-phenyl-2(E)-propenyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate (II), the internal standard, was extracted with n-hexane-diethyl ether under weakly basic conditions (pH 8). In order to prevent adsorption of the compounds on the column, (+/-)-[2H5]ethyl 3-phenyl-2(E)-propenyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate (III), an analogue of I, was added to the extracts as a carrier. In addition, this carrier was also effective in preventing the oxidation of I. The quantitation limit of I in human plasma by this method was found to be less than 30 pg/ml. Thus, the method is sufficiently sensitive to study the pharmacokinetics of I in humans.

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.

Modulation by external Ca2+ and nicardipine of Ca2+ influx and cytosolic concentration in human erythrocytes

Variations of Ca2+ influx (evaluated by the initial rate of 45Ca2+ uptake) and cytosolic free Ca2+ concentration ([Ca2+]i, measured with fura-2) were investigated in human erythrocytes. When external Ca2+ concentration ([Ca2+]o) rose from 1 to 2 mM, the initial rate of Ca2+ influx nearly doubled whereas [Ca2+]i increased only by 15%. Nicardipine dose-dependently decreased both initial rate of Ca2+ influx and [Ca2+]i (up to 53 and 18%. respectively at 10(-6) M). The less marked changes in [Ca2+]i than in Ca2+ influx indicate a partial adjustment of the Ca2+ extruding-pump activity to of Ca2+ influx. In vivo administration of nicardipine reduced [Ca2+]i only when its initial value exceeded 80 nM and prevented the rise in [Ca2+]i induced by the increase in [Ca2+]o. Our results indicate that nicardipine may reduce Ca2+ influx in human erythrocytes and participate in the control of [Ca2+]i when elevated.

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.

Radio high-performance liquid chromatographic determination of 14C-labelled LF 2-0254, A 1,4-dihydropyridine calcium antagonist, in rat and dog plasma using off-line liquid scintillation counting

LF 2-0254 is a 1,4-dihydropyridine calcium antagonist with a slow onset of action. The pharmacokinetics of [14C]LF 2-0254 were studied in rats and dogs. A sensitive high-performance liquid chromatographic method using liquid scintillation counting was developed for the quantitation of labelled LF 2-0254 in plasma. The peak height of the internal standard in the chromatogram was measured by UV detection and the mobile phase containing the chromatographic peak of [14C]LF 2-0254 was collected and counted for radioactivity. The concentration of labelled drug in the plasma was then determined using a calibration graph constructed from the determination of [14C]LF 2-0254 of known specific activities. The limit of determination was dependent on the specific activity of the drug administered. This method permits the measurement of the radioactive drug in biological fluids.

Selected ion monitoring analysis of NB-818, a new calcium entry blocker in a series of dihydropyridines, in human plasma

NB-818 is expected in clinical use to produce an antihypertensive effect and simultaneously to promote an increase in cerebral blood flow, owing to its vasodilator activity. To determine NB-818 levels in human plasma for pharmacokinetic studies, a capillary column gas chromatography/mass spectrometry/selected ion monitoring (GC/MS/SIM) method was employed. Because NB-818 was degraded under GC conditions, stable derivatives had to be prepared for GC/MS measurements. Reaction of NB-818 with silylation agents produced derivatives quantitatively. In the silylation, however, the carbomoyl group of NB-818 was replaced by silyl moieties. NB-818 is possibly metabolized at the carbamate moiety alone, giving a compound with a hydroxymethyl group in place of the carbamoyloxymethyl group. Since this compound and NB-818 gave the same derivative, efforts were devoted to separating them. A detection limit below 0.1 ng ml-1 was attained. The calibration curve was linear in the concentration range 0.1-10 ng ml-1 (r = 0.9998), and the coefficient of variation was 5.5% and 3.1% at concentrations of 1 and 10 ng ml-1, respectively.

Hemodynamic and cardiac metabolic changes during nicardipine-induced myocardial ischemia

After 10 mg nicardipine IV a patient with stable angina developed chest pain and ST-segment depression accompanied by excessive tachycardia, low arterial blood pressure, and initially decreased coronary sinus blood flow. Measurements of arterial concentrations and cardiac exchanges of lactate, glucose, free fatty acids, glutamate, and alanine showed alterations indicative of severe ischemia.

Nicardipine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy, in the treatment of angina pectoris, hypertension and related cardiovascular disorders

Nicardipine is an antagonist of calcium influx through the slow channel of the cell membrane and has been shown to be an effective and relatively well-tolerated treatment for stable effort angina and rest angina due to coronary artery spasm, and mild to moderate hypertension. Although its exact mechanism of action in these disease states has not been precisely defined, the potent coronary and peripheral arterial dilator properties of nicardipine, with concomitant improvements in oxygen supply/demand and reductions in systemic vascular resistance, are of major importance. Clinical studies have shown that nicardipine appears to be effective in the treatment of chronic stable exercise-induced angina pectoris and possibly in angina at rest due to coronary artery spasm. In the treatment of stable angina, nicardipine has proved to be equally as effective as nifedipine. However, haemodynamic and clinical studies indicate that nicardipine may have a further advantage of not depressing cardiac conduction or left ventricular function, even in patients with compromised cardiac pumping ability. Nicardipine also appears to be useful as initial monotherapy or in combination with other antihypertensive drugs when used in the treatment of mild to moderate hypertension, and may have some advantages over other vasodilators in this regard in that it may not be as frequently associated with fluid retention or weight gain as other similar drugs. In the treatment of hypertension nicardipine has been shown to be as effective as drugs such as hydrochlorothiazide, cyclopenthiazide, propranolol and verapamil in short term studies although confirmation of its long term usefulness in well-designed clinical trials is still required. Similarly, although the use of nicardipine in other disorders such as congestive heart failure and cerebrovascular disease has provided encouraging preliminary results, more studies are needed to clarify its place in their treatment. Side effects appear to be dose related and more frequent within the first few weeks of therapy. Most of these effects are minor and transient in nature and include headache, flushing and peripheral oedema. Thus, there is no doubt that nicardipine provides a suitable alternative to other drugs available for the treatment of angina and hypertension. However, further well-designed comparative clinical trials are needed to clarify its relative place in the long term management of these disorders.

Capillary column gas chromatographic method using electron-capture detection for the simultaneous determination of nicardipine and its pyridine metabolite II in plasma

A rapid, specific and direct method based on capillary column gas chromatography with electron-capture detection is described for the simultaneous determination of nicardipine, a new calcium antagonist, and its pyridine metabolite II in human plasma. In this method, the nicardipine, its pyridine metabolite II and internal standard are extracted from the plasma and then partially purified by acid-base partitioning prior to the final injection onto the capillary column gas chromatograph for quantification by means of an electron-capture detector. The quantification limit of the method is 1 ng/ml of plasma for both nicardipine and its pyridine metabolite II. The coefficients of variation for nicardipine and the pyridine metabolite II at concentrations of 1-50 ng/ml are less than 7% and less than 9% (n = 4), respectively. The method has been validated against a previously developed high-performance liquid chromatographic method (sensitivity 5 ng/ml).

Metabolic and hemodynamic effects of nicardipine during pacing-induced angina pectoris

During repeat exercise testing in 10 patients with stable angina, individual optimal doses of nicardipine were determined. Hemodynamic values and cardiac metabolism were studied during 2 pacing periods carried out before and after this dose (mean 5.3 mg). Postpacing ST-segment depression diminished (1 mm) after nicardipine administration (p less than 0.05), whereas pacing time to onset of angina did not change. Nicardipine administration increased heart rate 16% (p less than 0.005) and reduced systolic (10%) and diastolic (8%) blood pressures (both p less than 0.005). Coronary blood flow increased 16% (p less than 0.05) and coronary vascular resistance decreased 24% (p less than 0.01). Myocardial oxygen consumption was unchanged despite an 11% decrease in rate-pressure product during pacing (p less than 0.02). In the control state before nicardipine administration, metabolic signs of ischemia included release of lactate across the heart in 7 patients, decreased mean free fatty acid and glutamate uptake and alanine release during pacing, together with increased glucose uptake and citrate release during recovery. After nicardipine lactate release decreased in 5 of the 7 patients, pacing no longer changed free fatty acid, glutamate and alanine uptake/release from the level at rest. During recovery glucose uptake was reduced and citrate release was unaffected. The hemodynamic data indicate that nicardipine is a systemic and coronary vasodilator, increasing oxygen supply to the ischemic myocardium. The metabolic results indicate a change in substrate utilization toward that of normal heart, suggesting improved aerobic energy supply.

Combined capillary column gas chromatography/electron capture negative ion chemical ionization mass spectrometry of dihydropyridine calcium antagonists

Several dihydropyridine calcium antagonists showed intense [M]-. ion peaks as the base peaks and a few fragment peaks in the electron capture negative ion chemical ionization mass spectra. The peak intensities of the [M]-. ion of these antagonists were about 100 times as high as those of the most abundant positive ion. The use of a capillary column connected directly to the ion source prevents the oxidation of these agents in the column and the transfer line. Furthermore, the presence of plasma extract decreases the oxidation of these agents in the injection port. The limits of sensitivity with this technique are 500 fg-5 pg on the column. Combined capillary column gas chromatography/electron capture negative ion chemical ionization mass spectrometry should be suitable for sensitive and specific assays of dihydropyridine calcium antagonists in biological fluids.

Determination of nilvadipine in human plasma by capillary column gas chromatography-negative-ion chemical-ionization mass spectrometry

A highly sensitive and specific method for the determination of nilvadipine, a new dihydropyridine calcium antagonist, in human plasma is described. A deuterated analogue of nilvadipine is added to the plasma as an internal standard. The agent and its internal standard are extracted at pH 9 from the plasma into a benzene--n-hexane (1:1) mixture. The extract is analysed by fused-silica capillary column gas chromatography--negative-ion chemical-ionization mass spectrometry with methane as the reagent gas. The mass spectrometer is set to monitor the negative molecular ions of the agent and internal standard. Quantitation is possible down to 0.01 ng/ml using 1 ml of plasma. The coefficients of variation of the method are 6.4 and 2.1% at the 0.01 and 0.1 ng/ml levels, respectively. Plasma levels obtained with this method are given for four healthy volunteers who had received a 6-mg oral dose of nilvadipine.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.

The metabolism and pharmacokinetics of nicardipine hydrochloride in man

Studies have been carried out to investigate the disposition of nicardipine hydrochloride following intravenous and oral administration to male volunteers. Following oral administration of a radiolabelled dose, nicardipine was shown to be rapidly and extensively metabolised and to be rapidly eliminated from plasma. After intravenous infusion of nicardipine at 5 mg-1 for 3 h, plasma levels declined biexponentially, and clearance values were of the same order as hepatic blood flow. With repeated oral administration, 20 mg three times daily for 28 days, plasma levels rose over the first 3 days of administration and then declined to some extent. Possible reasons for this decline are discussed. Steady-state plasma levels and bioavailability show a nonlinear relationship with doses over the range 10-40 mg three times daily. Food consumption has been shown to reduce the bioavailability of nicardipine when the food is taken before or at the same time as nicardipine administration.

Nicardipine: pharmacokinetics and effects on carotid and brachial blood flows in normal volunteers

The effects of nicardipine, 20 mg, three times daily, nicardipine slow release, 30 mg, twice daily and a placebo on brachial and carotid arteries diameters and flows have been investigated by the pulsed Doppler technique during a single blind and cross-over study performed in six healthy volunteers. Simultaneously, nicardipine plasma levels and relative bioavailability were determined. Nicardipine significantly increased brachial and carotid arteries diameters (by 16 and 10% respectively) and flows (by 60 and 35% respectively). These effects peaked after 4 h and lasted no longer than 6 h. Forearm vascular resistance was significantly decreased. Hence nicardipine dilated both large and small arteries. Nicardipine slow release elicited the same effects on brachial and carotid arteries diameters and flows as nicardipine. These effects peaked at 6 h and lasted up to 10 h. Although the profiles of the pharmacodynamic effects and of the kinetics of nicardipine were almost parallel in each individual after administration of both nicardipine formulations, there was no correlation between the nicardipine plasma relative bioavailability and its effects on brachial and carotid arteries blood flows when considering all subjects together.

A high-performance liquid chromatographic method for the simultaneous determination of nicardipine and its pyridine metabolite II in plasma

A rapid and specific method in which reverse-phase high-performance liquid chromatography (HPLC) with UV detection was used for the simultaneous determination of nicardipine and its pyridine metabolite II in human plasma is described. Nicardipine, its pyridine metabolite II, and the internal standard were extracted from plasma and partially purified by acid-base partitioning. Final purification and quantitation were achieved by HPLC by using a reverse-phase column and a UV detector (254 nm). The extraction efficiencies for nicardipine and its pyridine metabolite II from 1 mL of plasma were 77.4 and 81.1%, respectively. The sensitivity of the assay was 5 ng/mL for both nicardipine and its pyridine metabolite II, and the linear concentration range of the assay was 5-150 ng/mL for both compounds. The low coefficients of variation (less than or equal to 5%) for samples spiked with nicardipine and its pyridine metabolite II in this concentration range demonstrate good reliability and reproducibility of the assay. The HPLC procedure has been validated by comparison with a GC-electron-capture detection (ECD) procedure, which gives the combined concentration of nicardipine-its pyridine metabolite II (total) and with an HPLC/GC-ECD procedure, which gives the concentration of its pyridine metabolite II. All three methods, which were developed in our laboratory, were used to analyze nicardipine and its pyridine metabolite II in specimens of plasma from subjects treated with nicardipine hydrochloride. Good correlations were found for concentrations of nicardipine, its pyridine metabolite II, and nicardipine plus the metabolite determined by these three procedures. The HPLC procedure is suitable for use in pharmacokinetic studies following administration of nicardipine hydrochloride to humans.

Gas and liquid chromatographic analyses of nimodipine calcium antagonist in blood plasma and cerebrospinal fluid

Gas (GC) and liquid chromatographic (LC) assay procedures were developed for analysis of nimodipine (1,4-dihydropyridine calcium antagonist, BAY e 9736) in blood plasma at low nanogram concentration levels. To avoid decomposition during gas chromatography, nimodipine was oxidized to nimodipine pyridine (P) analogue before it was chromatographed on the OV-17 column and quantitated using an electron-capture detector. In contrast, the LC procedure involved chromatographic separation and quantitation of the underivatized nimodipine and of the endogenous P analogue using a 3-micron Spherisorb ODS column and UV detection. The same plasma extract and three alternative internal standards were used for both assays. Taking into consideration the fact that the GC assay result includes endogenous P analogue as well as nimodipine, good correlation between GC and LC assay data was obtained. Comparison of the results observed with the two procedures confirmed the accuracy of each procedure and provided an alternative when one of the assay results was subject to patient plasma constituent interference. The LC assay was also used for analysis of the demethylated metabolites of nimodipine. To detect sub-nanogram concentrations of nimodipine in cerebrospinal fluid a combined LC-GC procedure using an LC clean-up step and a GC quantitation step was also developed. The above GC and LC procedures were used to obtain preliminary pharmacokinetic data.

Nifedipine serum concentration; effects upon blood pressure and heart rate in normotensive volunteers

Nifedipine (10 mg) was administered orally to 8 normotensive volunteers. Various measurements such as concentration in serum, blood pressure, and heart rate, were made at 0, 20', 40', 1, 2, 3, 4, 6, 8 and 24 h after administration. The sample serum, internal standard (diethyl 2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinedicarboxylate), HCl and NaNO2 were allowed to react and GLC-ECD was carried out after extration with organic solvent. The retention time was 3 min for nifedipine and 4 min for internal standard. Absorption curves were classified into 3 types: a rapid absorption rate (2 subjects) in which the maximum measured nifedipine concentration (70-80 ng/ml) was obtained, within 20-40 min after administration, a slower absorption rate (3 subjects) and an intermediate absorption rate (3 subjects) and an intermediate absorption rate (3 subjects). A decrease in systolic blood pressure was observed, but no significant difference in diastolic blood pressure and heart rate could be noted among the volunteers.

Specific determination of plasma nicardipine hydrochloride levels by gas chromatography-mass spectrometry

A highly specific method for the determination of the plasma level of the potent vasodilator 2-(N-benzyl-N-methylamino)ethyl methyl 2,6-dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine carboxylate hydrochloride (nicardipine hydrochloride) in rats, dogs and humans is described. N-d3-Methyl derivative was added as an internal standard, then the plasma was extracted with diethyl ether and subjected to thin-layer chromatography (TLC) to remove the pyridine analogue, one of the drug's metabolites. The area corresponding to the unchanged drug was identified with simultaneously run N-d7-benzyl derivative under UV light. The unchanged drug with a 1,4-dihydropyridine structure was oxidized with nitrous acid to its pyridine anlogue, which was stable for gas chromatography, and subjected to mass spectrometry at m/e 134 (nicardipine) and m/e 137 (N-d3-methyl derivative). The sensitivity limit was 5 g ml-1. The ratio of the unchanged drug to the value obtained by the method without TLC separation was 100% for rats and 80% for dogs and humans at almost all times investigated after dosing. These results demonstrate that in these species, the amount of pyridine analogue in plasma was very small compared with that of the parent drug.

Pharmacokinetic studies on nicardipine hydrochloride, a new vasodilator, after repeated administration to rats, dogs and humans

1. Various doses of [14C]nicardipine HCl were administered orally at different intervals for different periods to rats and dogs, and cumulative excretion, plasma concn. of unchanged drug, plasma clearance, tissue distribution, and AUC determined. 2. Plasma concn. in 12 patients with cerebrovascular disease receiving 20 mg three times per day for 28 (6 patients) or 365 days (6 patients) was determined on various days 1 h after the third dose. 3. In tissues of rats receiving 3 mg/kg/day for 21 days, distribution 1 h after administration on day 14 was 1.4-2.5 times higher than on day one; there was no statistical difference between day 14 and 21, suggesting that a steady state had been established within 14 days. 4. In rats receiving 3 mg/kg/day for seven days, cumulative excretion was 97.3% administered drug, indicating no tendency to accumulation. 5. Doses of 10 mg/kg three times at 3 h intervals to dogs significantly increased the plasma concn. on repeated administration, but this was not the case if the drug was administered at 6 h intervals or if the dose was decreased to 2 mg/kg. These non-linear pharmacokinetics may be ascribable to saturation of the hepatic drug-metabolizing enzyme activity. 6. In dogs given 5 mg/kg three times per day at 3 h intervals for seven days, max. plasma concn. and AUC on day 4 were 1.8 and 1.6 times higher, respectively, than on day 1. On days 4 and 7, these values were similar, suggesting that a steady state had been established within 4 days. 7. In six patients receiving the drug for 28 days, the mean plasma concn. on day 1, 7, 14, and 28 was approx. 0.1 microgram/ml, similar to the value on day 365 in the other six patients. This indicates that during long periods of administration, the plasma concn. of the drug shows no tendency to increase.

Metabolic fate of nicardipine hydrochloride, a new vasodilator, by various species in vitro

1. The metabolic fate of nicarpidine hydrochloride by rats, dogs and monkeys in vitro has been compared with previously reported in vivo studies. 2. The rate of metabolism of the drug in rat liver was 1.76 mumol/g tissue per 20 min, while the values in the intestine, kidney, lung and blood were less than 0.1 mumol/g tissue per 20 min, suggesting that the first-pass effect observed in vivo was due mainly to metabolism of the drug in the liver. 3. The rates of liver metabolism were 1.76, 0.45 and 0.55 mumol/g tissue per 20 min in rats, dogs and monkeys, respectively. This species difference correlates well with the differences in plasma clearance values, which were 197, 37 and 27 ml/min per kg in rats, dogs and monkeys, respectively, after i.v. administration of nicardipine hydrochloride (0.4 mg/kg). 4. Urinary metabolites were qualitatively similar, but the proportions of each were slightly different, among rats, dogs, monkeys and humans. The most abundant urinary metabolite was derived from debenzylation of the N-benzyl-N-methylaminoethyl ester side-chain in dogs and humans, and from hydrolysis of the same side-chain to the carboxylic acid, together with oxidation of the dihydropyridine nucleus to pyridine, in rats and monkeys. The metabolites produced in vitro were also qualitatively similar in the animal species examined. 5. More than 90% of the drug was reversibly bound to the plasma protein at 0.1 microgram/ml in the three animal species and humans. The extent of binding decreased with increased drug concentration in rats and humans, but not in dog and monkeys.

Application of the stable isotope technique to the elucidation of the saturation phenomenon of nicardipine hydrochloride metabolizing enzyme activity in dogs

The pharmacokinetics of 2-(N-benzyl-N-methylamino)ethyl methyl 2,6-dimethyl 4-(m-nitrophenyl)-1, 4-dihydropyridine-3, 5-dicarboxylate hydrochloride (nicardipine hydrochloride) was studied in dogs by using two deuterium labelled compounds (N-[2H3]methyl and N-[2H7]benzyl derivatives). The biological isotope effect of the [2H7]derivative, which was calculated from the half-lives in vivo and the metabolic rates in vitro, was 1.37 and 1.36, respectively, suggesting that debenzylation in the liver was one of the rate limiting steps of elimination of the drug, while the [2H3] derivative did not show this effect. The [2H3] derivative was administered orally or intravenously to dogs 2 h after oral administration of the non-labelled compound, and the plasma concentration of the [2H3] derivative was determined by the selected ion monitoring method. The biological half-lives, AUC and systemic availability increased with increasing doses of non-labelled nicardipine hydrochloride, while plasma clearance decreased, suggesting that the hepatic enzyme activity metabolizing the drug was partly saturated by the drug or its metabolites.

Comparative pharmacokinetics of nicardipine hydrochloride, a new vasodilator, in various species

1. The pharmacokinetics of a new potent vasodilator, 2-(N-benzyl-N-methylamino)-ethyl methyl 2,6-dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate hydrochloride (nicardipine hydrochloride), were studied after oral and i.v. dosage to rats, dogs, monkeys and humans. 2. The plasma half-life and volume of distribution in humans after i.v. administration did not change with dosage in clinical range. In rats and dogs these parameters increased with higher doses, probably because of the potent vasodilative effect of the drug. 3. The plasma clearance in dogs and humans was not affected by dosage, but in rats tended to increase slightly with higher doses. 4. Systemic availability after oral administration was low in spite of excellent absorption, indicating a marked first-pass effect. Increased systemic availability with increased dose indicates that the metabolic activity of the liver may become partly saturated with the drug or its metabolites. 5. Disappearance of the drug from the plasma after i.v. administration was fastest in rats > dogs approximately monkeys > humans. The terminal half-life of the drug after i.v. administration to humans was about 1 h.

Quantitative determination of nifedipine in human plasma by selected ion monitoring

A highly sensitive and specific method for the determination of nifedipine in plasma is described. Nifedipine was oxidized to its pyridine analogue with nitrous acid and determined by selected ion monitoring. Deuterium labeled nifedipine was used as an internal standard. Plasma levels as low as 5 ng ml-1 were measured. The usefulness of the method was demonstrated by obtaining plasma concentration curves for humans after an oral dose of 10 mg.