Pharmacokinetics and Bioequivalence of 2 Nifedipine Controlled-Release Tablets: A Randomized, Single-Dose, 2-Period Crossover Study in Healthy Chinese Volunteers Under Fasting and Fed Conditions

The aim of this study was to evaluate the bioequivalence of generic nifedipine controlled-release tablet compared to branded product under fasting and fed conditions. A randomized, single-dose, 2-period, crossover study with a 7-day washout period was performed in 84 healthy Chinese volunteers (fasting cohort, n = 42; fed cohort, n = 42). In each study period, volunteers were assigned to receive a single oral dose of the generic or reference product (30 mg). Blood samples were collected before dosing and up to 72 hours after administration. The plasma concentration of nifedipine was determined by a validated liquid chromatography-tandem mass spectrometry method. Pharmacokinetic parameters were obtained using a noncompartmental model and log-transformed pharmacokinetic parameters (maximum plasma concentration, area under the plasma concentration-time curve (AUC) from time 0 to the last measurable concentration, AUC from time 0 to infinity) were used to evaluate bioequivalence. The results showed that the 90% confidence interval for the geometric mean ratio of pharmacokinetic parameters of the test and reference products ranged from 80.0% to 125.0% in both the fasting and fed cohorts, meeting the criteria for bioequivalence. No serious adverse events were reported throughout the study and no adverse events led to withdrawal from the study. Food effects were found in both the test and reference products, with mean maximum plasma concentration, AUC from time 0 to the last measurable concentration, and AUC from time 0 to infinity increased by 23.7%, 20.7%, and 20.5%, respectively, for the test product and 35.2%, 13.4%, and 14.7% for the reference product after a high-fat and high-calorie breakfast.

Analysis of nifedipine in human plasma and amniotic fluid by liquid chromatography-tandem mass spectrometry and its application to clinical pharmacokinetics in hypertensive pregnant women

Nifedipine is a dihydropyridine calcium channel blocker used for the treatment of hypertension in pregnant women. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for analysis of nifedipine in human plasma and amniotic fluid. Separation of nifedipine and nitrendipine (IS) was performed using a LiChroCART(®) RP-Select B column and a mixture of water:acetonitrile:glacial acetic acid (30:70:0.5 v/v) as the mobile phase. Aliquots of 500μL of biological samples were extracted at pH 13 using dichloromethane:n-pentane (3:7 v/v). The validated method was applied to a study of the pharmacokinetics of nifedipine in human plasma and amniotic fluid samples collected up to 12h after administration of the last slow-release nifedipine (20mg/12h) dose to 12 hypertensive pregnant women. The estimated pharmacokinetic parameters of nifedipine showed a mean AUC(0-12) of 250.2ngh/mL, ClT/F of 89.2L/h, Vd/F of 600.0L and t1/2 5.1h. The mean amniotic fluid/plasma concentration ratio was 0.05. The methods proved to be highly sensitive by showing a lower quantification limit of 0.1ng/mL for both matrices. And this study reports for the first time the complete development and validation of the method to quantify nifedipine in amniotic fluid using LC-MS-MS.

Quantitative prediction of formulation-specific food effects and their population variability from in vitro data with the physiologically-based ADAM model: a case study using the BCS/BDDCS Class II drug nifedipine

Quantitative prediction of food effects (FE) upon drug pharmacokinetics, including population variability, in advance of human trials may help with trial design by optimising the number of subjects and sampling times when a clinical study is warranted or by negating the need for conduct of clinical studies. Classification and rule-based systems such as the BCS and BDDCS and statistical QSARs are widely used to anticipate the nature of FE in early drug development. However, their qualitative rather than quantitative nature makes them less appropriate for assessing the magnitude of FE. Moreover, these approaches are based upon drug properties alone and are not appropriate for estimating potential formulation-specific FE on modified or controlled release products. In contrast, physiologically-based mechanistic models can consider the scope and interplay of a range of physiological changes after food intake and, in combination with appropriate in vitro drug- and formulation-specific data, can make quantitative predictions of formulation-specific FE including the inter-individual variability of such effects. Herein the Advanced Dissolution, Absorption and Metabolism (ADAM) model is applied to the prediction of formulation-specific FE for BCS/BDDCS Class II drug and CYP3A4 substrate nifedipine using as far as possible only in vitro data. Predicted plasma concentration profiles of all three studied formulations under fasted and fed states are within 2-fold of clinically observed profiles. The % prediction error (%PE) in fed-to-fasted ratio of Cmax and AUC were less than 5% for all formulations except for the Cmax of Nifedicron (%PE=-29.6%). This successful case study should help to improve confidence in the use of mechanistic physiologically-based models coupled with in vitro data for the anticipation of FE in advance of in vivo studies. However, it is acknowledged that further studies with drugs/formulations exhibiting a wide range of properties are required to further validate this methodology.

Nifedipine serum levels in pregnant women undergoing tocolysis with nifedipine

The objective of our cross-sectional, observational study was to investigate nifedipine serum levels in pregnant women undergoing tocolysis. A total of 24 pregnant women, 22-34 weeks' gestation, who were administered nifedipine for treatment of pre-term labour, were enrolled in the study. Blood samples were taken 12 h after the oral application of 60 mg nifedipine in 'continuous release' form (Adalat CR 60). Nifedipine serum levels were measured with liquid chromatography. Nifedipine serum levels spread between 6 and 101 ng/ml (17-292 nmol/l). There was no correlation between nifedipine levels and body mass index (BMI), or between nifedipine levels and gestational age. During nifedipine tocolysis, 11 of 24 patients (45.8%) had mild side-effects, mostly headache. The side-effects were not dose-related. Despite the standardised dosage and standardised blood sampling nifedipine serum levels spread in a wide range. There is no need to adjust the dose of nifedipine to BMI or to gestational age.

Pharmacokinetics of calcium blockers in patients with renal insufficiency and in geriatric patients

Calcium antagonists have been used in the treatment of various medical disorders for more than 10 years, but their pharmacokinetics properties are poorly investigated. Available data on the pharmacokinetics of calcium antagonists in normal men are summarized in the present paper. Information on the influence of renal impairment and old age on the handling of calcium-antagonists are only available for verapamil. Patients with advanced renal disease had a significant reduction in the apparent volume of distribution, a shortened serum elimination half life, a decreased total body clearance of verapamil due to a decrease in the renal excretion of verapamil and its active metabolite norverapamil and also to a decrease in metabolic clearance. Pharmacokinetic parameters obtained after oral administration were not significantly different from those after intravenous dosing. The mean biologic availability (22.8%) was in the same range as reported for normal persons, but individual variations would seem to be greater. Elderly patients with a mean age of 87 years also had a significantly reduced volume of distribution of verapamil and decreased total body clearance of the drug, although this last change did not reach statistical significance. The biologic availability in the elderly was higher than in younger persons with a mean value of 37.69% and a wide range from 9.16 to 82.76%. These findings imply that verapamil dosage should be reduced in patients with impaired renal function and elderly patients.

[Preparation of weak cation exchange monolithic column and its applications for on-line determination of nifedipine in human plasma]

A cation exchange monolithic column was prepared with methylacrylic acid (MAA) as the functional monomer and ethylene dimethacrylate (EDMA) as the cross linker. This column was applied to remove the matrix compounds and enrich the ionic medicines in human plasma with water as the mobile phase. As a result, the human plasma samples can be directly injected into chromatographic system. The relationship between the mobile phase flow rate and back pressure was studied. The results showed that the monolithic column had good performances in lower pressure and higher permeability. In addition, the maximum adsorption of nifedipine on this monolithic column was investigated. The on-line clean-up and enrichment of samples were carried out using this column as the solid-phase extraction material and the C18 column as the analytical column. The chromatography was performed on a C18 reversed-phase high performance liquid chromatographic column with ultraviolet detection at 235 nm. The mobile phase was a mixture of methanol-water (70:30, v/v), and the flow rate was 1.0 mL/min. The linear range of nifedipine in human plasma was 5.0-75.0 microg/L. The intra- and inter-day relative standard deviations (RSDs) were both less than 5.0%. The limit of detection (LOD) was 1 microg/L and the limit of quantification (LOQ) was 4 microg/L. In this method tedious pretreatment procedure is not necessary. It is a fast, economical, reproducible and efficient method for assaying trace nifedipine in human plasma.

Pharmacokinetics of anorectal nifedipine and lidocaine (lignocaine) ointment following haemorrhoidectomy: an open-label, single-dose, phase IV clinical study

OBJECTIVES

This study aimed to assess whether topical anorectal application of an ointment containing nifedipine (0.3% w/w) and lidocaine (lignocaine) [1.5% w/w] to patients undergoing Milligan-Morgan haemorrhoidectomy achieves pharmacologically relevant serum concentrations of the active ingredients and has any haemodynamic effects or adverse effects.

METHODS

A single dose of 3 g of study ointment was circumferentially applied inside the anus to 24 patients (17 males and 7 females) aged 23-71 years (mean +/- SD: 42.9 +/- 4.9 years) during postoperative dressing after Milligan-Morgan haemorrhoidectomy from March 2007 to January 2008. Blood samples for the determination of nifedipine and lidocaine serum concentrations were drawn before surgery and at 20, 40, 60, 90, 120, 240, 360, 480 and 720 minutes after application. Serum concentrations of nifedipine and lidocaine were determined by a high-performance liquid chromatography method in order to calculate pharmacokinetic parameters. Patients' BP, heart rate and ECG readings were monitored during the study.

RESULTS

Chromatographic signals of nifedipine were sporadically observed in only five patients (20.8%), consistent with therapeutically negligible concentrations and insufficient to permit calculation of any pharmacokinetic parameters. The serum concentrations of nifedipine in these five patients ranged from 5.9 to 18.8 ng/mL. Lidocaine concentrations were detectable in all patients. The means +/- SD and medians of pharmacokinetic parameters for lidocaine were as follows: maximum serum concentration (C(max)) 245.1 +/- 370.8 ng/mL, 73.6 ng/mL; time to reach C(max) (t(max)) 69.2 +/- 78.3 minutes, 40 minutes; area under the serum concentration-time curve from 0 to 6 hours (AUC(6)) 756.5 +/- 1254.1 ng.h/mL, 238.2 ng.h/mL. Only three patients had maximum serum concentrations above 1000 ng/mL (1037.8, 1044.75 and 1364.1 ng/mL). These outlier concentrations were four to five times lower than the threshold of CNS lidocaine toxicity (5000-6000 ng/mL). No serious local or systemic adverse events were observed throughout the study, and no subjects developed arrhythmias or significant ECG changes. Neither BP nor mean heart rate varied significantly after application of a single dose.

CONCLUSIONS

This study demonstrates that single-dose topical application of an ointment containing nifedipine (0.3% w/w) and lidocaine (1.5% w/w) to patients undergoing Milligan-Morgan haemorrhoidectomy is safe to use. Following application onto damaged anorectal mucosa, nifedipine and lidocaine are absorbed into the bloodstream in small quantities that do not have any major implications for the safety of the product. Further studies are required to evaluate nifedipine and lidocaine concentrations in serum using a multiple-dose regimen.

The effect of silymarin on oral nifedipine pharmacokinetics

Silibinin, the main component of silymarin (a milk thistle extract used for treatment of liver injury), has been shown to inhibit CYP3A4 in human liver microsomes. The present study was conducted to examine whether inhibition of CYP3A4 by silymarin is also present IN VIVO. Immediate release nifedipine (10 mg) was administered as a CYP3A4 test drug either alone or with co-administration of silymarin (280 mg administered 10 hours and 1.5 hours prior to the administration of nifedipine) to 16 healthy male volunteers (mean age 27 years, mean body weight 77 kg). Nifedipine and silibinin concentrations were quantified by HPLC, heart rate and blood pressure were monitored for safety reasons. Pharmacokinetic parameters were calculated by non-compartmental methods, and the potential interaction by silymarin was handled as an equivalence problem. We found that nifedipine AUC was 1.13-fold higher (90 % CI, 0.97- to 1.32-fold) in the silymarin period, C (max) values were 0.70-fold (90 % CI, 0.39- to 1.27-fold) of those of the reference period, with a trend to delayed absorption in the silymarin period. Intraindividual variability especially for C (max) (intrasubject CV 120 %) was unexpectedly high. There was no meaningful effect on hemodynamic parameters. In conclusion, our data suggest that co-administration of silymarin does not considerably change the extent of absorption or metabolism of nifedipine but may decrease the absorption rate. Silymarin thus is not a potent CYP3A4 inhibitor IN VIVO.

Nifedipine pharmacokinetics and plasma levels in the management of preterm labor

The aim of this study was to determine if the dose regimen of nifedipine used for tocolysis was effective to achieve uterine quietness, and at which plasma concentration levels this tocolysis was achieved to optimize our dose regimen of nifedipine. In women with preterm labor, nifedipine was administered orally to achieve uterine quietness to prevent preterm birth. Patients (n = 5) were administered 10 mg nifedipine capsules (Adalat capsules, Bayer AG) orally every 15 minutes up to 40 mg in the first hour, and were subsequently given 1 tablet of 20 mg nifedipine slow release (Adalat retard, Bayer AG) t = 90 min. Plasma levels of nifedipine were measured at regular intervals during the first 4 hours after starting tocolysis. In all 5 patients tocolysis was achieved with nifedipine. Peak plasma concentration of nifedipine was 127.2 +/- 44 ng/mL at 1.2 +/- 0.1 hours. Mean plasma concentrations of nifedipine was 67.4 +/- 28.4 ng/mL. In all patients, tocolysis was achieved during the 4 hours of blood sampling. There were no adverse hemodynamic side effects seen before and after starting tocolysis with nifedipine. Initial dose regimen of 4 times 10 mg nifedipine capsule orally in the first hour, followed by 20 mg slow release nifedipine at t = 90 min is effective in achieving tocolysis in women with preterm labor. In steady state, the mean nifedipine plasma concentration to achieve tocolysis is about the half of that measured after initial tocolysis. Use of nifedipine for preterm labor was not associated with any adverse hemodynamic side effects.

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 nifedipine in human plasma and its use in bioequivalence study

A sensitive atmospheric pressure chemical ionization liquid chromatographic-mass spectrometric (APCI-LC-MS) assay with positive ion mode has been developed for the determination of nifedipine in human plasma. In this method, nifedipine was extracted from human plasma using diethyl ether with dimethoxanate as the internal standard. Analysis was achieved on a BDS C(18) column with methanol-H(2)O (66:34, v/v) as the mobile phase. Sustained-release nifedipine tablets from DiSha (test, Weihai, China) and from GuoFeng (reference, Qingdao, China) were evaluated following a single 20mg oral dose to 20 healthy volunteers. Bioequivalence between the products was determined by calculating 90% confidence intervals (90% CI) for the ratio of C(max), AUC(0-t) and AUC(0-infinity) values for the test and reference products, using logarithmic transformed data. The 90% confidence intervals for the ratio of C(max) (86.6-105.2%), AUC(0-t) (97.8-110.9%) and AUC(0-infinity) (96.5-110.4%) values for the test and reference products are within the interval (80.0-125.0% for AUC, and 70-143% for C(max)), proposed by State of Food and Drug Administration [SFDA, 2005. Guidance for Bioavailability and Bioequivalence Studies for Chemical Drug Products in Human Being. China, p. 19]. It was concluded that the two sustained-release nifedipine tablets are bioequivalent in their rate and extent of absorption and, thus, may be used interchangeably.

The use of heat treatment to eliminate drug interactions due to grapefruit juice

Grapefruit juice (GJ) contains components that may increase the bioavailability of drugs; however, approaches to the removal of these components have been little investigated. It is known that furanocoumarin derivatives (FCs), such as bergamottin (BG) and 6',7'-dihydroxybergamottin (DHB) in GJ, induce such drug interactions. In the present study, it was found that the heat treatment of grapefruit juice decreases concentrations of BG and DHB as well as their interactions both in vitro and in vivo. We incubated GJ for 10, 20, 30, 40, 50, and 60 min at 37, 62, 72, and 95 degrees C; FCs in each sample were then measured, using high-performance liquid chromatography (HPLC). The concentrations of BG and DHB were decreased in a time- and temperature-dependent manner, by 82.5 and 97.9% respectively, after incubation for 1 h at 95 degrees C. In contrast, the concentration of bergaptrol (BT) increased in a time- and temperature-dependent manner (27.7% after 60 min at 95 degrees C). In addition, the effect of each GJ sample on testosterone 6beta-oxidation in human liver microsomes was observed. The inhibitory effects of GJ heated to 95 degrees C were decreased in a time-dependent manner, as in the case of BG and DHB concentrations. Furthermore, 2 ml of GJ treated for 60 min at 95 degrees C was administered into the rat duodenum. After 30 min, nifedipine (NFP) was administered intraduodenally at a dose of 3 mg/kg body weight. The concentrations of NFP in the plasma samples were determined by HPLC. No significant increase in the AUC of NFP was observed in the rats given heat-treated GJ. These results suggest that the heat treatment of GJ reduces the concentrations of FCs, thus eliminating the potential for drug interactions.

Rapid and simultaneous determination of nifedipine and dehydronifedipine in human plasma by liquid chromatography-tandem mass spectrometry: Application to a clinical herb-drug interaction study

Nifedipine (NIF), a calcium channel antagonist, is metabolized primarily by cytochrome P450 (CYP3A4) to dehydronifedipine (DNIF). As such, NIF is often used as a probe drug for determining CYP3A4 activity in human studies. A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and validated to simultaneously determine NIF and DNIF in human plasma using nitrendipine as the internal standard (IS). After extraction of the plasma samples by ether-n-hexane (3:1, v/v), NIF, DNIF and the IS were subjected to LC/MS/MS analysis using electro-spray ionization (ESI). Chromatographic separation was performed on a Hypersil BDS C(18) column (50 mm x 2.1 mm, i.d., 3 microm). The method had a chromatographic running time of approximately 2.5 min and linear calibration curves over the concentrations of 0.5-100 ng/mL for NIF and DNIF. The recoveries of the one-step liquid extraction method were 81.3-89.1% for NIF and 71.6-80.4% for DNIF. The lower limit of quantification (LLOQ) of the analytical method was 0.5 ng/mL for both analytes. The intra- and inter-day precision was less than 15% for all quality control samples at concentrations of 2, 10, and 50 ng/mL. The validated LC/MS/MS method has been successfully used to study pharmacokinetic interactions of NIF with the herbal antidepressant St. John's wort in healthy volunteers. These results indicated that the developed LC/MS/MS method was efficient with a significantly shorter running time (2.5 min) for NIF and DNIF compared to those methods previously reported in the literature. The presented LC/MS/MS method had acceptable accuracy, precision and sensitivity and was used in a clinical pharmacokinetic interaction study of NIF with St. John's wort, a known herbal inducer of CYP3A4. St. John's wort was shown to induce NIF metabolism with increased plasma concentrations of DNIF.

1H NMR Monitoring of the Canine Metabolic Profile after Oral Administration of Xenobiotics Using Multivariate Statistics

This study describes a chemometric analysis of 1H NMR spectra of canine plasma following oral single dose administrations of two food components (lycopene and oleuropein) and of two drug products, Fungoral (ketoconazole) and Adalat (nifedipine). Due to the high interday physiological variation, 1H NMR plasma data were first filtered (by applying orthogonal signal correction) and then subjected to principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA). A distinct discrimination was achieved between samples obtained with and without administration of xenobiotics using both techniques. According to distance to model criterion and as shown by the Cooman's plots there was no overlap between the four models which proved to be specific for each xenobiotic. Moreover, it was shown that this approach has the potential to recognize subtle variations in the metabolic profile even if the administered xenobiotic itself could not be detected in the canine plasma by conventional HPLC methods.

Effect of Lactobacillus casei on the Absorption of Nifedipine from Rat Small Intestine

Lactobacillus casei Shirota strain (L. casei) has a modulating effect on the production of cytokines, which often play important roles in drug metabolism, in the inflamed intestinal mucosa. We evaluated the effect of L. casei administered orally in advance for 4 weeks on the absorption of nifedipine from the rat small intestine. The maximum concentration of nifedipine in plasma after administration into the intestinal loop (0.8 mg/kg) was significantly higher in L. casei-treated rats (3.26 microg/mL) than in those untreated rats (2.33 microg/mL) by 40%. Accordingly, the bioavailability of nifedipine was tended to be higher in the former, while the effect of L. casei on the disposition of intravenously administered nifedipine was negligible. We also found that the availability of nifedipine for the passage through the intestinal mucosa was significantly increased in L. casei-treated rats from the single-pass intestinal perfusion experiments. Therefore, it is likely that the exposure to nifedipine after its administration into rat intestine was increased by oral ingestion of L. casei due to an increase in absorption by increased intestinal availability (decreased metabolic extraction) during passage through the intestinal mucosa. This study has suggested that L. casei has some effect on the metabolic activity in the intestinal mucosa, though it seems to be only mild.

Practical application of guinea pig telemetry system for QT evaluation

The purpose of this study was to evaluate a telemetry system for examining QT evaluation in the conscious free-moving guinea pig using 10 reference compounds whose effects on human QT interval are well established: 8 positive references (bepridil, terfenadine, cisapride, haloperidol, pimozide, quinidine, E-4031 and thioridazine), and 2 negative references (propranolol and nifedipine). Pharmacokinetic experiments were also performed for the 8 positive references. Telemetry transmitters were implanted subcutaneously in male Hartley guinea pigs, and the RR and QT intervals were measured. All 8 positive references prolonged QTc (QTc = k x QT/RR(1/2)) 10% or more during the 60 min observation period. When the values of the QTc changes were plotted against the serum concentrations, the resulting curves exhibited an anticlockwise hysteresis loop for all 8 references. In guinea pigs treated with haloperidol, changes of the T-wave shape from positive to flat were observed. The 2 negative references did not prolong the QTc. These findings suggest that the present telemetry guinea pig model is useful for QT evaluation in the early stages of drug development, because of the small body size of guinea pigs and their action potential configuration, which is similar to that of humans.

Significant food interactions observed with a nifedipine modified-release formulation marketed in the European Union

The objective of this study was to compare the rate and extent of nifedipine bioavailability after single dose administration of Adalat OROS 30 (Reference) and Nifedipine Sandoz retard 30 tablets (Test). Both modified release formulations are marketed in Member States of the European Union. Prior to the clinical study the in vitro dissolution characteristics were investigated. There was a significant pH dependency observed with the Test product but drug release with the Reference product was almost independent of the experimental conditions used. In the subsequent open, randomized, controlled, 4-way crossover study both pharmaceutical products were administered to 28 healthy male volunteers, either after fasting overnight or immediately after a high-fat American breakfast. Blood sampling was performed over 48 hours post-dose for the determination of pharmacokinetic profiles of nifedipine. Considerable differences were observed between the two formulations when administered to fasted subjects where maximum nifedipine plasma concentration (C(max)) were higher in the case of the Test formulation. Differences were even more pronounced after a high-fat American breakfast. Under these conditions a significant food interaction was detected in the case of Nifedipine Sandoz retard 30 with a three-fold increase in the mean C(max) when compared to values obtained in fasting subjects. In contrast, food intake had no clinically relevant effect on bioavailability of nifedipine (rate and extent) in the case of Adalat OROS 30. The pharmacokinetic findings in this study were reflected in the adverse event pattern which indicated a potential tolerability problem in the case of Nifedipine Sandoz retard 30. The results confirm the relationship between the in vitro dissolution profile results and the effects of the drug in vivo. Dose dumping after intake of a high-fat meal could be shown. Nifedipine Sandoz retard 30 is not bioequivalent to Adalat OROS 30 and produced highly variable and poorly predictable nifedipine plasma concentrations. The differences observed between the two products investigated may have direct therapeutic relevance when switching from one formulation to the other and, in particular, when administration conditions change i.e. administration in the fasting state and administration with a meal, since the pharmacological and therapeutic actions of nifedipine are closely associated with the concentration.

Development of an HPLC method for the determination of nifedipine in human plasma by solid-phase extraction

Nifedipine, a dihydropyridine calcium channel antagonist, is widely used in the treatment of hypertension and other cardiovascular disorders. A selective, sensitive and accurate high-performance liquid chromatographic method has been developed, validated and applied for determination of nifedipine in human plasma samples. A series of studies were conducted in order to investigate the effects of mobile phase composition, buffer concentration, mobile phase pH and concentration of organic modifiers, and to develop a convenient and easy-to-use method for quantitative analysis of nifedipine. The method involves solid-phase extraction on C18 cartridges. The chromatographic separation was accomplished on a Lichrocart Lichrospher 60 RP selectB column with a mobile phase composed of 0.020 mol/L KH2PO4 (pH 4.8) and acetonitrile (42:58, v/v). UV detection was set at 240 nm. The calibration curve was linear in the concentration range of 5.0-200.0 ng/mL for nifedipine in plasma and the limit of quantification was 5.0 ng/mL.

Photostability studies for micellar liquid chromatographic determination of nifedipine in serum and urine samples

Nifedipine is a photosensitive compound that is converted into its 4-(2-nitrophenyl) pyridine and 4-(2-nitrosophenyl) pyridine homologue. In order to obtain the most adequate conditions for handling nifedipine solutions in the analytical laboratory, a number of studies on the decomposition of this compound were performed. A simple micellar liquid chromatographic procedure was described to determine nifedipine in different biological matrices such as serum and urine, and to control its decomposition. To perform the analysis, nifedipine was dissolved in 0.1 m SDS at pH 3 and chromatographed using a mobile phase containing 0.125 m SDS-3% pentanol, pH 3 on a C18 column and UV detection at 235 nm. The chromatographic analysis time was 8 min. The response of the drug for both biological matrices was linear in the 1-100 microg/mL range, with r2>0.997 at all times. Repeatability, intermediate precision (CV, %) and limits of quantification and detection (ng/mL) were 0.19, 4.3, 104 and 31 in serum and 0.81, 2.1, 136 and 41 in urine. The method developed here does not show interferences or matrix effects produced by endogenous compounds. Micellar media and mobile phases have the advantage of stabilising the compounds, thus preventing photodegradation and allowing the direct injection of biological samples.

UV-Irradiated Grapefruit Juice Loses Pharmacokinetic Interaction with Nifedipine in Rats

In the present study, UV-irradiated grapefruit juice was used to investigate the effects of UV light on nifedipine pharmacokinetics. Grapefruit juice in quartz vessels was UV irradiated (302 nm) with a transilluminator for 0 to 6 h at 4 degrees C, and furanocoumarins, potent contributors to the pharmacokinetic interaction, in each juice sample were measured using HPLC. The concentrations of all three types of furanocoumarins, bergamottin, 6',7'-dihydroxybergamottin, and bergaptol, decreased in a time-dependent manner. Concentrations of bergamottin, 6',7'-dihydroxybergamottin, and bergaptol were decreased to 1.66, 1.98, and 5.58%, respectively, after UV irradiation for 6 h. Two milliliters of untreated and UV-irradiated grapefruit juice were preadministered into the duodenum in rats to assess the effects of UV irradiation on nifedipine pharmacokinetics in vivo. After 30 min, nifedipine was intraduodenally administered at a dose of 3 mg/kg body weight. The nifedipine concentrations in the plasma samples were determined using HPLC. A significant increase in the area under the concentration-time curve of nifedipine was observed in untreated grapefruit juice to 1.6-fold that in the control group, but not in the UV-irradiated grapefruit juice. These findings suggest that UV irradiation is useful to eliminate pharmacokinetic interactions with grapefruit juice.

Determination of nifedipine in serum of women in preterm labor by high-performance liquid chromatography with diode array detection

Nifedipine (Nif) is widely used in treating cardiovascular disorders (especially hypertension) and for inhibiting preterm labor. A fully validated selective high-performance liquid chromatographic method with diode array detection, using solid-phase extraction, was developed for the determination of Nif in human serum. To assess specificity, Nif and its degradation products were separated on a Purospher RP-18 (5 microm, 125 x 4 mm) column plus a LiChrospher 100 RP-18 (5 microm, 4 x 4 mm) precolumn with a mobile phase of methanol-10 mM aqueous trifluoroacetic acid, pH 7.3 (57 + 43, v/v); chromatographic separation was followed by UV detection at 238 nm. For toxicological analysis, Nif in the presence of other calcium-channel antagonist drugs was identified under optimum chromatographic conditions. The calibration graph was constructed over the concentration range of 12.5-400 ng/mL in serum with good correlation (r = 0.9956). This method was not subject to interference by other plasma components and was successfully applied to the assay of Nif in spiked human serum and in serum of women in preterm labor after sublingual administration of 30 mg Nif per day divided into 3 equal doses. The mean recovery based on the ratio of the slopes of serum and mobile phase standard curves was 96.5%. The detection and quantification limits of the drug in spiked human serum were found to be 6 and 17.5 ng/mL, respectively. Validation of the method demonstrated good intraday and interday precision, which ranged from 2.18 to 6.67% and from 6.52 to 11.93%, respectively.

Serum Levels and Possible Haemodynamic Effects following Anorectal Application of an Ointment Containing Nifedipine and Lignocaine

OBJECTIVES

This study aimed to assess whether topical anorectal application of an ointment containing nifedipine (0.3% w/w) and lignocaine (lidocaine) [1.5% w/w] to healthy adult volunteers gives rise to pharmacologically relevant serum levels of the active ingredients and has any haemodynamic effects or side effects.

METHODS

A dose of 3g of the ointment was circumferentially applied inside the anus to 12 healthy volunteers every 12 hours for 7 days. Blood samples were collected at 0, 30, 60, 240, 480 and 720 minutes after the first application; in addition, blood samples were collected at days 1 and 7 after multiple applications. Serum concentrations of nifedipine, its main metabolites and lignocaine were determined by a new high-performance liquid chromatography method established for the purpose of the study. Volunteers' blood pressure, heart rate, ECG status and laboratory parameters were monitored throughout the study.

RESULTS

Topical application of the ointment to healthy volunteers did not produce therapeutically significant serum levels of the active ingredients and/or their active metabolites. Indeed, chromatographic signals of the active ingredients and/or nifedipine metabolites were only sporadically observed, below the quantification limits for the method, and consistent with therapeutically negligible concentrations. No serious local or systemic adverse events were observed throughout the study, and no subjects developed arrhythmias or significant ECG changes. Neither blood pressure nor mean heart rate varied significantly after application of a single dose. After multiple doses, mean systolic and diastolic blood pressure remained close to baseline levels for the duration of the study. The mean heart rate after multiple doses was about 5% below baseline level at days 1 and 7; however, these differences were not statistically significant.

CONCLUSION

This study demonstrates the safety of topical anorectal application of an ointment containing nifedipine (0.3% w/w) and lignocaine (1.5% w/w) to healthy volunteers.

[Effects of nifedipine controlled release on blood pressure and heart rate of spontaneously hypertensive rats. Comparison with nifedipine standard and with amlodipine]

BACKGROUND

Antihypertensive therapy aims to reduce long-term morbidity and mortality. Drugs characterized by controlled release show a better pharmacokinetic and pharmacodynamic profile compared to standard formulations.

METHODS

The present study evaluated the effects of nifedipine controlled release (0.33, 0.66 and 1.32 mg/kg per os), nifedipine standard (0.08, 0.165 and 0.33 mg/kg per os) and amlodipine (0.08, 0.165 and 0.33 mg/kg per os) on mean arterial blood pressure, heart rate and pressure rate index of spontaneously hypertensive rats (SHR). These were treated by gastric gavage, and analyzed after 30 min, 1, 3, 6, 12, and 24 hours. Moreover, plasma levels of nifedipine and amlodipine were also assayed by high-performance liquid chromatography.

RESULTS

Nifedipine controlled release showed a longer antihypertensive effect when compared with standard formulation and with amlodipine. The highest dose of nifedipine controlled release decreased blood pressure soon after 1 hour with a maximum decrease (-20 mmHg) at 3 hours. The effect was still significant 24 hours later (p < 0.05). Amlodipine antihypertensive effect lasted 12 hours with a maximum decrease of 18 mmHg at 6 hours. The treatment of SHR rats with nifedipine controlled release, at each of the tested doses, did not cause any significant alterations in heart rate recorded at the beginning of the experiments. Nifedipine standard (0.165 and 0.33 mg/kg) and amlodipine (0.33 mg/kg) increased heart rate in SHR rats. Interestingly enough, pressure rate index was slightly affected by nifedipine standard release and amlodipine whereas it was remarkably reduced by nifedipine controlled release (p < 0.01 vs vehicle until 9 hours). All the compounds showed maximum plasma concentrations paralleled by maximum antihypertensive effects, as evidenced at high-performance liquid chromatography method.

CONCLUSIONS

Nifedipine controlled release showed more pronounced antihypertensive effects and longer pharmacokinetic properties with respect to nifedipine standard release and amlodipine.

(-)-(9S)-9-(3-Bromo-4-fluorophenyl)-2,3,5,6,7,9-hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-dioxide (A-278637), a novel ATP-sensitive potassium channel opener: hemodynamic comparison to ZD-6169, WAY-133537, and nifedipine in the anesthetized canine

The therapeutic utility of KATP channel opening agents (KCOs) in the treatment of overactive bladder may be limited by hypotension as a result of insufficient selectivity in vivo for bladder versus vasculature smooth muscle. Recently, we demonstrated that the putative uroselective KCOs, A-278637, ZD-6169, and WAY-133537 suppress unstable bladder contraction in an in vivo pre-clinical pig model of detrusor instability secondary to partial outlet obstruction. In the present study in the anesthetized dog we targeted plasma concentrations 3-, 10-, and 30-fold above a common index of in vivo efficacy (EC35) for suppression of unstable bladder contraction in pigs, to provide a comprehensive cardiovascular profile of these compounds. When compared at similar multiples of efficacy, dose-dependent reductions in SVR were greater in ZD-6169 and WAY-133537-treated animals versus A-278637. A-278637, unlike ZD-6169 or WAY-133537, produced no effect on MAP at concentrations 10-fold above the EC35. At concentrations 30-fold above the EC35, MAP in A-278637-treated animals was reduced -11% from baseline versus -24% and -42% for ZD-6169 and WAY-133537. Accordingly, at plasma concentrations approximately 30-fold above the EC35 reflex-mediated increases in HR were modest for A-278637-treated animals (15% above baseline) versus ZD-6169 (22%) or WAY-133537 (35%). Increases in both dP/dt and cardiac output occurred at lower therapeutic multiples and were greater in magnitude for animals treated with WAY-133537 (66% and 64% above baseline, respectively, 60 minutes into compound infusion) and ZD-6169 (10% and 13%) versus A-278637 (-2% and 6%). Thus, A-278637 exerted lesser effects on cardiovascular function at equivalent multiples of the EC35 than either ZD-6169 or WAY-133537. These data suggest that A-278637 possesses a greater functional selectivity for urinary bladder versus vascular smooth muscle in vivo and that A-278637 may exhibit a more favorable therapeutic index than either ZD-6169 or WAY-133537.

Enhancement of nifedipine-induced gingival overgrowth by concomitant ketoconazole in rats

Nifedipine (NIF), a calcium channel blocker, is well known to induce gingival overgrowth (GO) as an adverse effect, and ketoconazole (KTZ), an azole antifungal agent, has been implicated in various drug interactions. We here examined the effects of concomitant KTZ on NIF-induced GO in a rat model. Fifteen-day-old male Fischer rats were fed chow with NIF, KTZ, or both. After 41 days, gingival conditions were evaluated and the concentration of NIF in serum was measured. Rats fed with NIF alone had induced GO and suppressed growth, while those given KTZ alone did not. Compared to the administration of NIF alone, concomitant KTZ significantly increased the severity of GO and the concentration of NIF in serum. These results suggest that concomitant KTZ increases the serum concentration of NIF and enhances the severity of GO.

Pharmacokinetics of a new extended-release nifedipine formulation following a single oral dose, in human volunteers

This study aimed to define the pharmacokinetics of nifedipine following oral administration of a new extended-release formulation. Twelve healthy volunteers of both sexes, aged 39 +/- 4 years, were treated with a single oral tablet of a new extended-release formulation containing 40 mg of nifedipine. Samples of venous blood were taken before dosing, after 30 min and at 1, 2, 4, 8, 12, 16, 20 and 24 h after administration. Nifedipine concentration was measured by means of a high-performance liquid chromatography method. Noncompartmental pharmacokinetics parameters were then calculated. The plasma concentration of nifedipine increased slowly and in seven subjects biphasic peaks occurred. The mean values were as follows: t(max): 8.5 +/- 1.2 h; C(max): 36.55 +/- 6.76 ng/ml; AUC: 347.06 +/- 51.61 ng/h/ml; AUC 409.99 +/- 61.08 ng/h/ml; A(half-life): 2.26 +/- 0.36 h; D(half-life): 2.43 +/- 0.44 h; E(half-life): 4.62 +/- 0.79 h. Twenty-four hours after administration nifedipine was still detectable (3.17 +/- 0.67 ng/ml). Arterial blood pressure decreased and heart rate increased concurrently and proportionally to the increase in nifedipine concentration. Extended-release nifedipine formulations have better tolerability profiles than immediate-release formulations, which are at present not recommended in the treatment of hypertension, hypertensive crises or myocardial infarction. This new extended-release formulation has interesting pharmacokinetic parameters and may be effective in conditions in which dihydropyridine calcium channel blockers are indicated.

[Toxicological analysis of selected 1,4-dihydropyridine calcium channel blockers in the diagnosis of intoxications]

This study is aimed at evaluating effective techniques of qualitative and quantitative analysis of selected 1,4-dihydropyridine calcium channel blockers, useful both for thanatological diagnosis of intoxications as well as monitoring therapy. The studies took advantage of gas chromatography (GLC) and high performance liquid chromatography (HPLC). Isolation of studied compounds from biological material was performed using classical and solid phase extraction procedures (SPE) such as Bond Elut LRC (Varian), Abselut Nexus (Varian), STRATA C - 18 E (Phenomenex). The program included analysis of nine of the most frequently prescribed derivatives: nifedipine, felodipine, amlodipine, nicardipine, nimodypine, nilvadipine, nitrendipine, nisoldipine, isradipine.

Pharmacokinetics of nifedipine in Taiwanese

To elucidate the pharmacokinetics of nifedipine in Taiwanese, a retrospective review of nifedipine bioequivalence studies completed in Taiwan in the past 5 years was conducted. A total of 198 healthy male volunteers were given a single dose of a 10 mg Adalat capsule as a reference drug after overnight fasting. Pharmacokinetic parameters derived from Adalat administration were calculated by non-compartmental analysis with the WinNonlin program. After oral administration of an immediate-release dosage form of a 10 mg nifedipine capsule to Taiwan residents, a skewed distribution with no clear evidence of bimodality of pharmacokinetic parameters was observed. The mean Cmax was 143.12+/-53.48 ng/ml, the mean AUC was 293.77+/-115.62 ng.h/ml, the mean T1/2 was 3.08+/-1.61 h, and the median value of Tmax was 0.61 h. Compared with other published studies, the Cmax and AUC of nifedipine after 10 mg administration were significantly higher in Taiwanese than in British and American subjects. However, the Cmax and AUC were similar to those of Indian and Mexican subjects. According to the antimode of AUC distribution of 22.5 ng.h/ml/mg proposed by Kleinbloesem, 69.7% of Taiwanese can be categorized as slow metabolizers. Based on the results in this study, the majority of Taiwanese show lower activity of nifedipine metabolism.

Time-release compression-coated core tablet containing nifedipine for chronopharmacotherapy

Compression-coated time-release tablets (CC tablets) containing nifedipine, dihydropyridine Ca channel blocker, in the core tablet were prepared by dry coating with different polyethylene oxide-polyethylene glycol mixtures. Each formulation showed a clear lag period before nifedipine release initiation, followed by sustained drug release lasting up to 24 h. The lag time of nifedipine release increased as the amount of polyethylene oxide in the outer layer increased. To investigate the applicability of such CC-tablets for chronopharmacotherapy, the pharmacokinetics of CC-1 and CC-2 tablets, with different in vitro lag times before drug release, were compared with the pharmacokinetics of a sustained-release (SR) tablet in dogs. The times of first nifedipine appearance (TFA) in plasma were 0.7 +/- 0.3 h for SR, 2.5 +/- 1.2 h for CC-1, and 5.3 +/- 1.0 h for CC-2. These data show a significant difference in in vivo lag time (P < 0.01) among the three formulations that correlates with the in vitro lag times. Thus, the in vivo lag time could be predicted from the in vitro lag time. Additionally, higher plasma nifedipine concentrations were observed at 8 h after administration of the CC-2 than that observed for the SR-tablet. These results indicate that a CC-tablet with a lag time before drug release is a potentially useful formulation for chronopharmacotherapy that can control the time and duration of plasma drug concentration better than existing SR technologies.

Formulation Dependent Pharmacokinetics–Does the Dosage Form Matter for Nifedipine?

This was an open-label, randomized, 3-way crossover study that compared in 25 healthy male subjects, the pharmacokinetics of a single 60-mg dose of nifedipine GITS tablet versus (1) 20-mg doses of nifedipine prolonged action tablets given q12h for a total of two doses and (2) 2 x 10 mg doses of nifedipine capsules given q8h for a total of three doses. Following capsule administration, there was a rapid rise in plasma concentration of drug achieving a peak concentration of 196(35) ng/mL (mean and coefficient of variation) within 0.7 (105) hours and an AUC(infinity) of 973(39) ng.hr/mL. After nifedipine PA there was also a rapid rise in plasma concentration of drug achieving a Cmax of 85.5 (36) ng/mL with a tmax of 1.7(58) hours and an AUC(infinity) of 879(46) ng.hr/mL. For the nifedipine GITS formulation, there was a lag in the plasma concentration time profile for approximately 2 to 3 hours, then it rose gradually achieving a Cmax of of 686(54) 30.5(63) ng/mL with a tmax of 15.0(50) hours and an AUC(infinity) ng.hr/mL. The AUC(infinity) and Cmax were significantly (P = 0.0001) greater in the capsule and PA formulations than for the GITS; however, the tmax for the GITS formulation was significantly (P = 0.001) longer than for the other formulations. This study suggests marked formulation-dependent pharmacokinetics, which may have important clinical implications.

Pharmacokinetics of mebudipine, a new calcium antagonist, following single intravenous and oral administrations in rats

The pharmacokinetics of a new calcium antagonist, mebudipine, was studied after a single intravenous (0.5 mg/kg) and oral (10 mg/kg) administration to rats. After intravenous dosing, the plasma concentration of mebudipine declined biexponentially with a terminal half-life of 2.84 h. The blood clearance was 1.67 l/h/kg and the volume of distribution at steady state was found to be 6.26 l/kg. After oral dosing (10 mg/kg), the C(max) of mebudipine was 25.9+/-9.79 ng/ml. The oral bioavailability was low (< 2%) suggesting a marked first-pass effect. The distribution of mebudipine into some tissues such as brain, heart, liver and kidney following intravenous administration (0.5 mg/kg) was studied and a rapid distribution of mebudipine into these tissues was found. It was concluded that brain, heart, liver and kidney are in the same compartment as plasma (central).

Ximelagatran, an oral direct thrombin inhibitor, has a low potential for cytochrome P450-mediated drug-drug interactions

BACKGROUND

Ximelagatran is an oral direct thrombin inhibitor currently in clinical development for the prevention and treatment of thromboembolic disorders. After oral administration, ximelagatran is rapidly absorbed and extensively bioconverted, via two intermediates (ethyl-melagatran and hydroxy-melagatran), to its active form, melagatran. In vitro studies have shown no evidence for involvement of cytochrome P450 (CYP) enzymes in either the bioactivation or the elimination of melagatran.

OBJECTIVE

To investigate the potential of ximelagatran, the intermediates ethyl-melagatran and hydroxy-melagatran, and melagatran to inhibit the CYP system in vitro and in vivo, and the influence of three CYP substrates on the pharmacokinetics of melagatran in vivo.

METHODS

The CYP inhibitory properties of ximelagatran, the intermediates and melagatran were tested in vitro by two different methods, using heterologously expressed enzymes or human liver microsomes. Diclofenac (CYP2C9), diazepam (CYP2C19) and nifedipine (CYP3A4) were chosen for coadministration with ximelagatran in healthy volunteers. Subjects received oral ximelagatran 24mg and/or diclofenac 50mg, a 10-minute intravenous infusion of diazepam 0.1 mg/kg, or nifedipine 60mg. The plasma pharmacokinetics of melagatran, diclofenac, diazepam, N-desmethyl-diazepam and nifedipine were determined when administered alone and in combination with ximelagatran.

RESULTS

No inhibition, or only minor inhibition, of CYP enzymes by ximelagatran, the intermediates or melagatran was shown in the in vitro studies, suggesting that ximelagatran would not cause CYP-mediated drug-drug interactions in vivo. This result was confirmed in the clinical studies. There were no statistically significant differences in the pharmacokinetics of diclofenac, diazepam and nifedipine on coadministration with ximelagatran. Moreover, there were no statistically significant differences in the pharmacokinetics of melagatran when ximelagatran was administered alone or in combination with diclofenac, diazepam or nifedipine.

CONCLUSION

As ximelagatran did not exert a significant effect on the hepatic CYP isoenzymes responsible for the metabolism of diclofenac, diazepam and nifedipine, it is reasonable to expect that it would have no effect on the metabolism of other drugs metabolised by these isoenzymes. Furthermore, the pharmacokinetics of melagatran after oral administration of ximelagatran are not expected to be altered by inhibition or induction of CYP2C9, CYP2C19 or CYP3A4. Together, the in vitro and in vivo studies indicate that metabolic drug-drug interactions involving the major human CYP enzymes should not be expected with ximelagatran.

Reproducibility of nifedipine absorption from GITS tablets: comparison of single-dose pharmacokinetics using 10, 20, 40 and 60 mg nifedipine

OBJECTIVE

To examine the reproducibility of nifedipine absorption from gastrointestinal therapeutic system (GITS) tablets by comparing the single-dose pharmacokinetic profiles of 4 different dosages administered orally.

METHODS

Twelve healthy male volunteers, aged between 22 and 29 years were enrolled in the open, 4-way, dose escalation study with single oral doses of 10, 20, 40 and 60 mg (two 30 mg) nifedipine GITS tablets. Each administration was separated by a 1-week washout period. Coefficients of variation (CV) of dose-corrected area under the concentration-time curve (AUC) and peak plasma drug concentrations (Cmax) were calculated from the pharmacokinetic profiles.

RESULTS

Mean AUC and mean Cmax were dose-proportional from 10 to 60 mg. Although the CV of 4 mean dose-corrected AUC and Cmax were 5.5% and 17.5%, respectively, CV of dose-corrected AUC and Cmax in each subject varied from 5.1 to 37.4% (mean 11.0%) and from 14.1% to 46.4% (mean 25.8%), respectively.

CONCLUSIONS

Whereas mean plasma nifedipine concentration remained markedly stable over a 16- to 24-hour interval and mean dose-corrected AUC showed good reproducibility with nifedipine GITS, the CV of dose-corrected AUC of the nifedipine GITS tablets in each subject showed large variability.

CYP3A5 genotype did not impact on nifedipine disposition in healthy volunteers

CYP3A5 expression is regulated by single-nucleotide polymorphisms (SNPs). The CYP3A5 genotype might contribute to a marked interindividual variation in CYP3A-mediated metabolism of drugs. Nifedipine is a typical substrate of CYP3A4 and CYP3A5 in vitro. The aim of this study was to elucidate the influence of the CYP3A5 genotype on nifedipine disposition in healthy subjects. A single capsule containing 10 mg of nifedipine was administered to 16 healthy male Japanese subjects (eight subjects: CYP3A5(*)1/(*)3; eight subjects: CYP3A5(*)3/(*)3). Blood samples were collected to analyze the pharmacokinetics of serum nifedipine and nitropyridine metabolite (M-I). The area under the plasma concentration-time curve (AUC), the peak plasma concentration (C(max)) and the terminal half-life (t(1/2)) of nifedipine, and the ratio of the nifedipine AUC to M-I AUC showed large intragroup variations, but no significant differences between the two genotypes. Based on the present findings, the functional relevance of CYP3A5 polymorphism should be re-evaluated in clinical trials.

Application of a new high performance liquid chromatography method to the pharmacokinetics of dibudipine in rats

PURPOSE

To develop a HPLC method for assay of dibudipine in biological fluids and to study its pharmacokinetics in the rat.

METHODS

HPLC: 2 microl (20 microg/ml) mebudipine as internal standard, 0.2 ml NaOH 1 M and 2 ml ethyl acetate were added to 0.2 ml of rat plasma. The mixture was shaken for 10 min, centrifuged, and the supernatant was dried under nitrogen. The dissolved residue was injected to a C18 analytical column. Mobile phase flowed at 1 ml/min with a composition of methanol--water-acetonitrile (70-25-5). The eluent was monitored at 238 nm. Pharmacokinetic study: plasma samples were collected periodically after intravenous (0.5 mg/kg) or oral (10 mg/kg) administration of dibudipine to rats (n = 4/group). In addition, separate groups of animals were administered 0.5 mg/kg doses of the drug for serial collection of brain, heart, kidney and liver (n = 4/time). The concentration of the drug in tissue or plasma was assayed using the above HPLC method.

RESULTS

Calibration curves were linear over a concentration of 10-1000 ng/ml and CV was less than 10%. Dibudipine showed a bi-exponential decline after IV injection in the rats with a t1/2 beta of 2.5 +/- 0.5(mean +/- SE) hr. Oral bioavailability was low. Distribution of dibudipine to the examined tissues was rapid, and with the exception of the brain, the concentrations of the drug in all tissues were higher than the plasma levels

CONCLUSIONS

The HPLC method was simple and convenient. Moreover, it could be applied to investigations of the pharmacokinetics of dibudipine in the rat.

Determination of nifedipine in human plasma by solid-phase extraction and high-performance liquid chromatography: validation and application to pharmacokinetic studies

Nifedipine, a dihydropyridine calcium channel antagonist, is widely used in the treatment of hypertension and other cardiovascular disorders. A simple, rapid, sensitive, precise and accurate HPLC method, using solid-phase extraction, for the quantitation of nifedipine in human plasma was developed and validated. The calibration graphs were linear in the 5-400 ng/ml concentration range (r>0.999). Recovery for nifedipine was greater than 93.9% and for internal standard nitrendipine was 96.1%. Intra-day and inter-day precision ranged from 1.4 to 4.2 and 3.9 to 5.6%, respectively. Intra-day and inter-day accuracy was ranged from 94.5 to 98.0 and 93.1 to 98.0%, respectively. The method was not interfered with by other plasma components and was applied for the determination of nifedipine in pharmacokinetic study after single oral administration of 10 mg nifedipine to 18 healthy male subjects.

Design of controlled release delivery systems using a modified pharmacokinetic approach: a case study for drugs having a short elimination half-life and a narrow therapeutic index

The objectives of peroral controlled release drug delivery systems (CRDDS) are to maintain therapeutically effective plasma drug concentration levels for a longer duration thereby reducing the dosing frequency and to minimise the plasma drug concentration fluctuations at steady state by delivering drug in a controlled and a reproducible manner. Drug delivery rate, duration of delivery and the dosing interval are the target features for any temporal CRDDS. The classical pharmacokinetic model for designing CRDDS [Drug Dev. Ind. Pharm. 15 (1989) 1073] assumes the time of drug delivery (t(del)) to be less than the dosing interval. However, termination of drug release from such a CRDDS at t(del) and/or a declining drug input function towards the terminal phase of t(del) from a first order kinetic CRDDS can have severe implications on plasma drug concentration and steady state fluctuations for a drug with very short half-life. A case study is presented in this paper, wherein by means of theoretical calculations using a classical pharmacokinetic approach, it is shown that a first order kinetic CRDDS for hypothetical drugs with short elimination half-life and different pharmacokinetic conditions would result in sub-therapeutic plasma concentrations at least for some time during the dosing interval at steady state. In order to avoid sub-therapeutic plasma drug concentrations a modification in classical pharmacokinetic model is proposed and discussed through theoretical calculations for different hypothetical pharmacokinetic situations and a practical single dose pharmacokinetic study with a first order kinetic CRDDS for nifedipine (a short half-life drug; about 2h). It is shown that improved therapeutic efficacy could be expected from a CRDDS developed based on proposed modification in the classical pharmacokinetic model.

Evidence of an interaction between nifedipine and nafcillin in humans

AIMS

Nafcillin (Wyeth Laboratories, Philadelphia, PA, USA) has been reported to induce the metabolism of cyclosporin and warfarin, which are known substrates of cytochrome P-450 (CYP). However, there has not been any report to date on its possible interaction with nifedipine, an index substrate of the enzyme, CYP3A4.

METHODS

Nine healthy normotensive subjects participated in this randomized placebo-controlled two-way crossover study examining the effects of 5 days' pretreatment of nafcillin 500 mg or placebo four times daily on the pharmacokinetics of an oral dose of nifedipine 10 mg. Plasma nifedipine concentrations were measured by gas chromatography-mass spectro.

RESULTS

The area under the plasma nifedipine concentration-time curve (AUC0-alpha) in nafcillin-pretreated subjects (80.9 +/- 32.9 micro g l-1 h-1) was significantly decreased compared with subjects who received only nifedipine (216.4 +/- 93.2 micro g l-1 h-1) (P < 0.001). Total plasma clearance of nifedipine (CL/F) was significantly increased with nafcillin pretreatment (138.5 +/- 42.0 l h-1 vs 56.5 +/- 32.0 l h-1) (P < 0.002).

CONCLUSIONS

The results show that nafcillin pretreatment markedly increased the clearance of nifedipine and suggest that nafcillin is a potent inducer of CYP enzyme.

Administration of nifedipine CR immediately after awakening prevents a morning surge in hypertensive patients. Case report of three cases

Although the blood pressure-lowering action of some long-acting calcium antagonists may last more than 24 h, some patients taking this drug still experience a morning surge, i.e. an early morning increase in blood pressure. We evaluated this morning surge in three hypertensive patients with morning surge after administration of antihypertensive drugs including nifedipine CR. Nifedipine CR is one of the once-a-day formulations of nifedipine, which after administration, results in two peaks in the plasma concentration of nifedipine. The first concentration peak of occurs 3 h after administration and the second around 12 h after intake. When the time of intake of nifedipine CR was changed from after breakfast to immediately after awakening, the morning surge was suppressed in these patients without the use of other drugs such as alpha- or beta-blockers. Administration of nifedipine CR immediately after awakening is one option that can be used to prevent morning surge as well as to control blood pressure throughout the day.

The effect of cyclosporine with and without nifedipine on gingival overgrowth in renal transplant patients

PURPOSE

This investigation was performed to evaluate the effect of cyclosporine alone and in combination with nifedipine on gingival overgrowth.

METHODS

One hundred and nineteen patients who had undergone renal transplantation at least 12 months previously were selected for the study. The patients were divided into 2 groups according to whether they had received cyclosporine alone (group 1, n = 98) or cyclosporine with nifedipine (group 2, n = 21). Periodontal and pharmacological characteristics were assessed for all patients.

RESULTS

Marked gingival overgrowth was seen in 11 (52%) of the patients in group 2 but just 6 (6%) of those in group 1. In addition, the gingival overgrowth index was significantly greater for patients who had received both nifedipine and cyclosporine (Mann-Whitney U-test, p < 0.001). However, there were no significant differences between groups with higher and lower gingival overgrowth index in terms of age, sex, cyclosporine dose, nifedipine dose or level of cyclosporine in the serum.

CONCLUSION

The combination of cyclosporine and nifedipine may increase the incidence as well as the severity of gingival overgrowth in renal transplant patients. Among patients who had received both drugs, there was a clear relationship between gingival overgrowth and duration of cyclosporine and nifedipine use.

Cathodic adsorptive stripping square-wave voltammetric determination of nifedipine drug in bulk, pharmaceutical formulation and human serum

Nifedipine is a calcium-channel antagonist drug used in the management of angina pectoris and hypertension through inhibition of calcium influx. A fully validated sensitive cathodic adsorptive stripping square-wave voltammetry procedure was optimized for the determination of the drug at trace levels. The procedure was based on the reduction of the nitrophenyl group after the interfacial accumulation of the drug onto a hanging mercury drop electrode in Britton-Robinson buffer of pH 11.0. The optimal conditions of the procedure were found to be: accumulation potential=-0.9 V vs. Ag/AgCl/KCl(s)), accumulation time=30 s, scan increment=10 mV, pulse amplitude=50 mV and frequency=120 Hz. Under these conditions, a well-defined peak was obtained; its peak current showed a linear dependence on drug concentration in the range of 2x10(-9)-2x10(-7) mol L(-1) bulk nifedipine. The mean recoveries based on eight replicate measurements for 1x10(-8) and 5x10(-8) mol L(-1) bulk nifedipine solutions were 98.46+/-0.86% and 98.23+/-0.92%, respectively. A detection limit of 3.42x10(-10) mol L(-1) bulk nifedipine was achieved. The procedure was successfully applied for assay of the drug in tablets and spiked human serum with mean recoveries of 101.95+/-1.42% and 98.70+/-0.63%, respectively. The limit of detection of the drug in spiked human serum was found to be 3.90x10(-10) mol L(-1).

Determination of nifedipine in human plasma by square wave adsorptive stripping voltammetry

A simple, sensitive and selective square-wave adsorptive stripping voltammetric method has been developed and validated for the determination of nifedipine (NIF) in plasma. The assay was performed after single extraction of NIF from alkalinised plasma into organic phase. The adsorption behaviour of NIF on a hanging mercury drop electrode (HMDE) was explored by square-wave and cyclic voltammetry. The drug was accumulated at HMDE and a well-defined peak was obtained at -730 mV versus Ag/AgCl in borate buffer of pH 9.0 including 0.01 M KCl. The linear concentration range was 2.89 x 10(-9) M-3.61 x 10(-7) M (1.00-125.01 ng ml(-1)) when using 30 s accumulation time at -300 mV. Limit of detection and limit of quantification were 1.21 x 10(-9) M (0.42 ng ml(-1)) and 2.89 x 10(-9) M (1.00 ng ml(-1)) respectively. The intra-day relative standard deviation (RSD) ranged from 1.93 to 4.12% at three concentrations and the inter-day RSDs varied from 2.53 to 6.68%. The method was applied, to the plasma of pregnant women suffering from pregnancy induced hypertension, for the determination of NIF. The percentage recoveries varied from 96.26 to 99.49%. It has been shown that NIF could be determined in the presence of its main metabolite (dehydronifedipine) by the developed method.

Improving the dissolution and bioavailability of nifedipine using solid dispersions and solubilizers

Nifedipine (NF) is a poorly water-soluble drug, of low and irregular bioavailability after oral administration. Although some reports have attempted to improve the dissolution of NF using solid dispersions and solubilizers, little literature information is available on the in vivo performance of such preparations. The aim of the present work was to improve the therapeutic efficacy of NF via incorporation into different types of carriers, and to investigate their in vitro dissolution and bioavailability in rabbits. Nifedipine solid dispersions were prepared by fusion, solvent, and freeze-drying methods with polyethylene glycol (PEG) 6000 and PEG monomethylether 5000 (PEG MME 5000). Complexation of NF with beta-cyclodextrin (beta-CyD) and solubilization by sodium lauryl sulfate (SLS) have also been studied. The dissolution was determined by the flow-through cell in order to maintain perfect sink conditions. The solid dispersions resulted in a significant increase in the dissolution rate as compare to pure drug. The highest NF dissolution rate was obtained from solid dispersions containing 95% PEG 6000 prepared by the solvent method. While, unexpectedly, the highest absorption in rabbits was obtained from 95% PEG 6000 prepared by the fusion method. Compared to SLS, beta-CyD gave higher in vitro and in vivo values. Differential scanning calorimetry (DSC) and powder x-ray diffractometry indicated that NF in solid dispersions is homogeneously distributed, and no drug crystallized out of the system. The DSC thermograms of NF-beta-CyD complex and NF/SLS solid mixture showed a decrease in the NF endothermic peak. The x-rays showed different diffraction patterns of pure NF and pure carrier, suggesting the formation of a new solid form.

The effect of food on the pharmacokinetics of nifedipine in two slow release formulations: pronounced lag-time after a high fat breakfast

AIMS

The aim of this study was to investigate the effect of concomitant food intake on the bioavailability of two nifedipine containing modified release dosage forms for once daily administration. The clinical study was performed to investigate the in vivo relevance of pH-dependent differences in the in vitro release properties of the two dosage forms.

METHODS

This was a randomized, open, 4-way crossover study in 24 healthy, male subjects. Following an overnight fast of 12 h single doses of Adalat OROS or Slofedipine XL were administered either in the fasted state or immediately after a high fat American breakfast. Nifedipine plasma concentrations in samples obtained until 48 h after drug administration were determined using a validated LC-MS/MS method. Calculation of pharmacokinetic parameters was conducted model-independently. The two dosage forms as well as the two administration conditions were compared by calculating point estimates and 90% confidence intervals for the relevant pharmacokinetic parameters. In vitro dissolution tests were performed using a paddle apparatus 3 acc. USP, a pharmacopoeial dissolution system consisting of reciprocating cylinders in flat-bottomed glass vessels, with various buffer systems covering the entire physiological pH-range of the gastrointestinal tract.

RESULTS

After fasted administration the extent of bioavailability of nifedipine as characterized by AUC(0,infinity) was slightly lower for Slofedipine XL compared with Adalat OROS with a point estimate of 82.3% primarily resulting from pronounced differences in nifedipine concentrations during the first 15 h after administration. Accordingly, maximum plasma concentrations were lower after administration of Slofedipine XL compared with Adalat OROS (point estimate: 84.3%). Under fed conditions the differences in bioavailability between the two products as characterized by the pharmacokinetic parameters AUC(0,tn) and Cmax were greater than after fasting conditions with point estimates of 69.6% and 81.0%, respectively. However, most striking was a pronounced delay in nifedipine absorption observed under fed conditions after administration of Slofedipine XL which resulted in lag-times of more than 15 h in 15 out of 24 subjects. Owing to this lag-time under fed conditions the relative bioavailability of nifedipine from Slofedipine XL compared with Adalat OROS was only 28% over the intended dosing interval of 24 h.

CONCLUSIONS

In this study a dosage form-dependent food interaction was observed which, under fed conditions, resulted in pronounced differences in the relative bioavailability of nifedipine between Slofedipine XL and Adalat OROS over the intended dosing interval of 24 h. The delay in nifedipine absorption when Slofedipine XL is administered after a high-fat breakfast may be explained by the formulation properties. Slofedipine XL is an erosive tablet with an acid resistant coating whereas Adalat OROS is designed with an osmotic push-pull system. Under fed conditions drug from the single unit enteric coated dosage form exhibits a delayed absorption probably due to an extensively prolonged gastric residence time which does not allow drug release, on the other hand the osmotically driven push-pull system is not sensitive to concomitant food intake. The observed phenomenon might be of therapeutic relevance. For example a change from taking Slofedipine XL in the fed to the fasted state might result in increased systemic concentrations of nifedipine.

Dosage form-related food interaction observed in a marketed once-daily nifedipine formulation after a high-fat American breakfast

OBJECTIVE

Objective of the study was the comparison of two nifedipine sustained-release products marketed in Europe. Maximum plasma concentration (C(max)) and area under the plasma-concentration curve (AUC) values were derived after administration of single doses (60 mg) of test product and reference product, both approved for once-a-day administration, to 24 healthy male volunteers either after an overnight fast or immediately after a high-fat American breakfast. The study was performed with a randomised, non-blinded, four-period crossover design. Within- and between-product comparisons were determined for fed versus fasted administration considering bioavailability and tolerability of all treatments. Furthermore, in vitro dissolution characteristics of both products were evaluated.

METHODS

Plasma samples were assayed using a liquid chromatography-mass spectrometry method, and resulting pharmacokinetic parameters were determined model independently according to international requirements and the current European guidelines.

RESULTS

Under fasted conditions the comparison of test and reference products showed a similar extent of bioavailability with a mean ratio of AUC((0-)(infinity)()) of 99% [95% confidence interval (CI) 86%, 114%], but significantly higher C(max) values resulting in a mean ratio of 169% (95% CI 139%, 206%). Accordingly, mean residence time and half-value duration values were smaller for the test product than the reference product. Under fed conditions, a pronounced food effect could be observed for the test product resulting in a pronounced increase of C(max) values. The affiliating point estimate was calculated as 340% with a 95% CI of 279%, 413%. However no remarkable influence of food intake was observed for the reference product.

CONCLUSION

Under fasting conditions the modified-release characteristics of the test product are less pronounced than the reference product. No relevant impact of food intake could be observed for the reference product when switching from fasted to fed state, whereas a significant loss of modified-release characteristics could be detected for the test product under fed conditions resulting in much higher maximum concentrations. Such a phenomenon has been described in literature as "dose-dumping effect".

Formulation-dependent food effects demonstrated for nifedipine modified-release preparations marketed in the European Union

The objective of this study was a comparative investigation of the influence of concomitant food intake on the bioavailability of two nifedipine-containing controlled-release formulations. Adalat OROS and CORAL were compared in a randomised, non-blind, four-way crossover design in 24 healthy, male subjects after single dose administration following a high fat American breakfast or an overnight fast of 12 h, respectively. Plasma samples were withdrawn until 48 h post-dose. In the fasted state, the bioavailability (AUC and C(max) values) was lower for CORAL than for Adalat OROS. Under fed conditions, differences in bioavailability between both products were markedly increased. With respect to the therapeutic use of both products, the most important finding was the significant dose-dumping effect observed after fed administration of CORAL, resulting in nifedipine plasma concentrations of nearly three- to four-fold in 11 of 24 volunteers. The mean ratio of C(max) was 235% comparing CORAL with Adalat OROS under these conditions. The formulation-dependent food interaction observed in this study may be therapeutically relevant, especially in the case of changing administration conditions or switching from one product to the other.

The effects of rifampicin on the pharmacokinetics and pharmacodynamics of orally administered nilvadipine to healthy subjects

AIMS

To study the effects of rifampicin on the pharmacokinetics and pharmacodynamics of nilvadipine.

METHODS

Five healthy adult volunteers received nilvadipine (4 mg) orally before and after a 6 day treatment with rifampicin. Blood and urine were collected and assayed for plasma nilvadipine and urinary 6beta-hydroxycortisol and cortisol.

RESULTS

The treatment with rifampicin reduced the mean (+/- s.d.) AUC of nilvadipine from 17.4 +/- 8.4 to 0.6 +/- 0.4 microg l-1 h (mean difference -16.8 microg l-1 h, 95% CI -9.4, 24.2 microg l-1 h). While the administration of nilvadipine alone elicited a significant (P < 0.05) hypotensive (mean difference for diastolic blood pressure -8 mmHg, 95% CI -4, -12 mmHg) and reflex tachycardia (mean difference 5 beats min-1, 95% CI 1, 9 beats min-1), the treatment with rifampicin abolished these responses. The urinary 6beta-hydroxycortisol/cortisol ratio showed a significant (P < 0.05) increase from 10.3 +/- 4.0 to 50.3 +/- 24.6 by rifampicin: mean difference 40.1, 95% CI 20.4, 59.8.

CONCLUSIONS

Because rifampicin may greatly decrease the oral bioavailability of nilvadipine, caution is needed when these two drugs are to be coadministered.

Persistence of antihypertensive efficacy after missed doses: comparison of amlodipine and nifedipine gastrointestinal therapeutic system

OBJECTIVE

In this randomized, double-blind, crossover study, the antihypertensive efficacy of amlodipine and nifedipine gastrointestinal therapeutic system (GITS) was compared following missed doses. Design and methods In a randomized crossover design, 42 patients were randomized to receive amlodipine (5-10 mg) or the GITS formulation of nifedipine (nifedipine GITS) (30-60 mg) once daily for 12 weeks, then vice versa. During weeks 8, 10 and 12 of each treatment period, compliance failures were simulated by patients missing 0, 1 or 2 doses of their medication, and ambulatory systolic (SBP) and diastolic (DBP) blood pressure measurements were obtained.

RESULTS

Following steady-state treatment (i.e. 'perfect compliance'), there was no difference between amlodipine and nifedipine GITS in SBP (140.1 versus 134.2 mmHg) or DBP (84.0 versus 85.8 mmHg) at 0-24 h post-dose. When compliance was not perfect, i.e. when one or two doses were missed, DBP was maintained at a significantly lower level with amlodipine compared with nifedipine GITS at 24-48 h post-dose (83.1 versus 86.4 mmHg, P = 0.005) and at 48-72 h post-dose (84.2 versus 89.7 mmHg, P < 0.001). Plasma concentrations of amlodipine were better maintained than those of nifedipine GITS. At 72 h post-dose, the plasma concentration of amlodipine was 61% (17.0 +/- 11.2 ng/ml) compared with < 25% (28.3 +/- 49.9 ng/ml) for nifedipine GITS.

CONCLUSION

During short periods of non-compliance, antihypertensive efficacy remains more predictable with amlodipine than with nifedipine GITS.

Carbamazepine decreases antihypertensive effect of nilvadipine

A 59-year-old male who had suffered from hypertension for 21 years was admitted because of manic and delusional symptoms. He was treated with 12 mg/day of haloperidol for psychotic symptoms and 8 mg/day of nilvadipine for hypertension. Due to insufficient effect of haloperidol on the patient's manic symptoms, carbamazepine was added to these medications. Abnormally high blood pressure was observed during carbamazepine coadministration, and it returned gradually to normal range after its discontinuation. Retrospective analyses revealed that the plasma concentrations of nilvadipine were undetectable during carbamazepine treatment. The clinical course and laboratory findings suggest that carbamazepine decreased the plasma concentration and hence the antihypertensive effect of nilvadipine probably via CYP3A induction. This interaction between nilvadipine and carbamazepine should be kept in mind when these drugs are administered concomitantly.