Quantification of nitrendipine by stable isotope dilution and electron-capture negative ion chemical ionization

Development and validation of a reversed-phase HPLC method for determination of nitrendipine in rat plasma: application to pharmacokinetic studies

A simple and sensitive method for the determination of nitrendipine in rat plasma was developed using high-performance liquid chromatography (HPLC). The procedure involves extraction of nitrendipine in dichloromethane/sodium hydroxide, followed by reversed phase HPLC using a Waters, Spherisorb ODS2 (250 x 4.6 mm, 5 microm) column and UV detection at 238 nm. The retention times of nitrendipine and internal standard (felodipine) were 5.0 min and 7.5 min, respectively. The calibration curves were linear over the range of 5 ng/mL (lower limit of quantification, LOQ) to 200 ng/mL for nitrendipine. The intra- and inter-day coefficients of variation for all criteria of validation were less than 15% over the linearity range. The sensitivity and precision of the method were within the accepted limits (< 15%) throughout the validation period. The present method was also successfully applied for the study of plasma pharmacokinetics of nitrendipine loaded solid lipid nanoparticles (SLN) in rats.

Quantitative Determination of the Calcium Channel Antagonists Amlodipine, Lercanidipine, Nitrendipine, Felodipine, and Lacidipine in Human Plasma Using Liquid Chromatography-Tandem Mass Spectrometry

A sensitive and specific liquid chromatography-tandem mass spectrometric method has been developed and validated for the quantification of the five 1,4-dihydropyridine calcium channel antagonists amlodipine, lercanidipine, nitrendipine, felodipine, and lacidipine in human plasma. Sample preparation involved solid-phase extraction on RP-C18 cartridges with good recovery for all the compounds. Sample analysis was performed on a Luna RP-C18 analytical column (15 mm x 2 mm ID, 3.0 microm) with a Sciex API 365 triple quadrupole mass spectrometer with turboionspray source and multiple reaction monitoring. The method is sensitive with a limit of detection below 1 ng/mL for each drug in plasma, with good linearity (r(2) > 0.998), over the therapeutic concentration range (1 to 40 ng/mL). All the validation data, such as accuracy, precision, and interday repeatability, were within the required limits. The method can be used for pharmacokinetic studies and therapeutic drug monitoring of the compounds in humans.

High-performance liquid chromatographic analysis of nitrendipine in human plasma using ultraviolet detection and single-step solid-phase sample preparation

A high-performance liquid chromatographic (HPLC) method was developed for the determination of nitrendipine in human plasma using solid-phase extraction (SPE) and ultraviolet detection. A 30-microl aliquot of methanol (containing 2 microg/ml of the internal standard, nimodipine) was added to a 1-ml aliquot of biological sample. After vortex-mixing, the mixture was loaded on C(18) SPE cartridge which was conditioned with methanol and distilled water. After washing with distilled water, the SPE cartridge was eluted with 1-ml aliquot of diethyl ether. The organic phase was collected and evaporated under nitrogen gas. The residue was then reconstituted with a 100 microl aliquot of mobile phase, and a 50 microl aliquot was injected onto the C(18) reverse-phased column. The mobile phase, 10 mM phosphate buffer (pH 4.5):acetonitrile (50:50, v/v), was run at a flow rate of 1.2 ml/min. The column effluent was monitored using ultraviolet detector at 238 nm. The retention times for nitrendipine and the internal standard were approximately 10.1 and 12.6 min, respectively. The detection limit of nitrendipine in human plasma was 2.0 ng/ml. The coefficients of variation (CV) of the assay were below 16.5% for human plasma, and no interferences from endogenous substances were found. This specific, accurate and precise assay was useful in the study for the pharmacokinetic characteristics of nitrendipine.

Oxidative degradation study of nitrendipine using stability indicating, HPLC, HPTLC and spectrophotometric method

The objective of this study is to develop validated stability indicating HPLC (A), HPTLC (B) and spectrophotometric (C) method for the estimation of nitrendipine. The stability indicating capability of the assays is proved using forced degradation, by exposing drug solution to sunlight, acidic and alkaline medium. The chromatogram and UV spectrum showed nitrendipine well resolved from the degradation product. Degradation of drug is found faster in acidic (0.1 N hydrochloric acid) medium as compared to alkaline (0.1 N sodium hydroxide) medium at 100 degrees C. Also, photodegradation is studied, with special emphasis on the effect of solvents like methanol (1), chloroform (2), dichloromethane (3), acetone (4) and ethyl acetate (5), on the rate of photodegradation. The degradation of title compound followed first order kinetics in all cases. Estimation of the drug is carried out by the stability indicating methods mentioned, using one point standardization within the linearity range of interest. The methods are compared in respect of performance precision and accuracy. Major route of degradation in all cases is found to be oxidation and degradation product is confirmed as dehydronitrendipine by the use of relevant UV, IR and 1H NMR spectrometry.

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.

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.

Use of pseudoracemic nitrendipine to elucidate the metabolic steps responsible for stereoselective disposition of nitrendipine enantiomers

1. The pharmacokinetics, protein binding, bioavailability and metabolism of (+)-R- and (-)-S-nitrendipine were studied in six healthy subjects following random oral administration of 20 mg (+)-R-, 20 mg (-)-S- and 20 mg R,S-nitrendipine (pseudoracemic mixture of 10 mg [13C4)-(+)-R- and 10 mg (-)-S-enantiomer). 2. After administration of the enantiomers pronounced differences in AUC (R: 29.9 +/- 20.1; S: 123.8 +/- 63.7 ng ml-1 h; P less than 0.05), bioavailability (R: 10.7 +/- 7.4%; S: 44.6 +/- 23.1%; P less than 0.05) and Cmax (R: 14.4 +/- 7.7; S: 72.5 +/- 40.5 ng ml-1; P less than 0.05) were observed between R- and S-nitrendipine. When racemic nitrendipine was given bioavailability and dose normalized AUC and Cmax values of the S-enantiomer were not different from the values after S-nitrendipine-administration. In contrast, bioavailability (R: 10.7% R,S: 22.1%) and dose normalized AUC (R: 15.0; R,S: 29.5 ng ml-1 h and Cmax (R: 7.2; R,S: 16.8 ng ml-1) of R-nitrendipine were doubled following R,S- as compared with R-nitrendipine administration. t1/2 (R: 9.8; S: 9.1 h) and tmax were not different between the enantiomers nor were the values different after administration of the enantiomers or racemate. The fraction unbound in serum of R-nitrendipine was 0.0098 +/- 0.0032 (s.d.) and that of S-nitrendipine was 0.0083 +/- 0.0015 (s.d.). 3. The AUC values of the major pyridine metabolite M1 were similar after administration of R- and S-nitrendipine (S: 114.7 +/- 48.5; R: 71.7 +/- 29.9 ng ml-1 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics, bioavailability, metabolism and acute and chronic antihypertensive effects of nitrendipine in patients with chronic renal failure and moderate to severe hypertension

1. The pharmacokinetics, bioavailability, metabolism and antihypertensive effects of nitrendipine have been studied in 12 patients with impaired renal function and moderate to severe hypertension. The drug was administered simultaneously by the i.v. [13C4] and oral (commercial tablet 20 mg) routes. 2. No differences in the pharmacokinetic parameters were observed between the two routes of administration. The systemic clearance after i.v. administration in patients with renal impairment (18.2 +/- 6.1 ml min-1 kg-1) was similar to that observed in healthy volunteers. Despite complete absorption of drug from the tablet the bioavailability of the parent compound was 21.2 +/- 12.5%. Cumulative urinary excretion of nitrendipine metabolites was correlated with the creatinine clearance (r = 0.946). 3. Significant reductions in mean arterial blood pressure (mean: 23.6%) at the end of the nitrendipine infusion and after oral administration of 20 mg (mean: 17.5%) were observed. The blood pressure lowering effect of nitrendipine could be correlated within individuals with serum nitrendipine concentrations using a log linear model. 4. Following 4 weeks of therapy an average dose of 77 mg nitrendipine day-1 was required to achieve a systolic blood pressure below 160 mm Hg or a diastolic blood pressure below 90 mm Hg. The reduction in blood pressure during multiple dosing was related to the nitrendipine steady-state concentration. There was a significant relationship between the nitrendipine bioavailability and the dose required for sufficient blood pressure control. 5. No accumulation of nitrendipine caused by impaired renal function was observed during multiple dosing. Thus, no reduction of the nitrendipine dose in patients with renal impairment is necessary.

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.

Lack of effect of nitrendipine on the pharmacokinetics and pharmacodynamics of midazolam during steady state

1. The possible interaction (as indicated by rat experiments) between calcium channel blocking agents and benzodiazepines has been evaluated in nine healthy subjects. 2. Subsequently to an intravenous loading dose (0.07 mg kg-1) midazolam was infused for 6 h (0.035 mg kg-1 h-1) and steady state plasma levels between 54 to 114 micrograms l-1 were achieved. Two hours after the bolus of midazolam a solution of 20 mg nitrendipine or placebo was administered in a randomized, double-blind crossover fashion. 3. The marked sedative-hypnotic effects of midazolam as assessed by visual analogue scales (about four fold increase in the sedation index) and choice reaction time (100% prolongation) indicated some form of adaptation or tolerance towards the end of the infusion. However, the midazolam-induced impairments were not affected by nitrendipine. 4. EEG-data indicated stabile benzodiazepine-like effects during the complete infusion period of midazolam (e.g. decrease in alpha activity, increase in sigma, delta 2 and beta 1 activity). Again, these alterations were not modified by nitrendipine. 5. There was also no pharmacokinetic interaction between both agents, since elimination of midazolam (t 1/2 = 2.5 +/- 0.8 h; CL = 548 +/- 143 ml min-1) was in close agreement with control values (t 1/2 = 2.4 +/- 0.6 h; CL = 512 +/- 102 ml min-1). Likewise, plasma levels of nitrendipine were comparable to literature data. 6. Thus, it could be concluded that nitrendipine does not affect the action of midazolam and therefore a direct involvement of calcium at the benzodiazepine receptor site is unlikely under our clinical conditions.

Application of stable isotope methodology to study the pharmacokinetics, bioavailability and metabolism of nitrendipine after i.v. and p.o. administration

1. The pharmacokinetics, bioavailability and metabolism of nitrendipine were studied in six healthy volunteers (three females, three males) using [13C4]-nitrendipine as a biological internal standard. In the first study the drug was administered simultaneously by the i.v. [13C4] and p.o. (solution) routes and in a second study two oral preparations (13C4-solution and commercial tablet) were administered, also simultaneously. 2. The mean terminal elimination half-life was 8.3 +/- 3.2 h (range 3.4 to 16 h) with no differences between the intravenous and oral route of administration. Total plasma clearance averaged 18.7 +/- 0.6 ml min-1 kg-1 and volume of distribution at steady state 5.4 +/- 2.4 1 kg-1. 3. Following oral administration of nitrendipine solution the percentage of dose absorbed was 88.4 +/- 16.0% based on urinary excretion of metabolites. Despite its almost complete absorption, absolute bioavailability of the solution was only 22.6 +/- 6.7% due to extensive presystemic elimination. The bioavailability of the commercial tablet relative to the solution was 82.2 +/- 20.3%. 4. Both after i.v. and oral administration the drug was extensively metabolized with less than 0.5% of the dose excreted as unchanged drug in urine. Cleavage of the two ester functions in position 3 and 5, respectively, to carboxylic acids and further hydroxylation of the methyl groups in position 2 and 6 of the pyridine ring to the corresponding hydroxymethyl carboxylic acids constituted the major urinary metabolites accounting for 35.0 +/- 16.5% (i.v.) and 32.8 +/- 20.4% (p.o.), respectively, of the dose administered. 5. Binding of nitrendipine to plasma proteins was high with a fraction unbound of only 0.02 +/- 0.012 (range 0.011 to 0.036).