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.

Regulation of magnesium sulfate combined with nifedipine and labetalol on disease-related molecules in serum and placenta in the treatment of preeclampsia.

OBJECTIVE: To explore the regulatory effect of magnesium sulfate combined with nifedipine and labetalol on disease-related molecules in serum and placenta in the treatment of preeclampsia. PATIENTS AND METHODS: Altogether 100 patients with preeclampsia admitted to the Children & Women's Healthcare of Laiwu City were selected. They were divided into control group and experimental group according to different treatment methods. Among them, 51 patients in the control group were treated with magnesium sulfate combined with nifedipine, and 49 patients in the experimental group were treated with labetalol on the basis of the treatment in the control group. The therapeutic effects of the two methods were compared. The levels of the following factors in the two groups were compared: kallikrein expression, pregnancy-associated plasma protein A (PAPP-A), pregnancy-specific ß1 glycoprotein (SPI), placental growth factor (PLGF), human placental prolactin (HPL), transforming growth factor ß1(TGF-ß1), vascular cell adhesion molecule 1 (VCAM-1) and E-selectin in serum and placenta tissues. RESULTS: After treatment, the blood pressure in the experimental group was lower than that in the control group (p<0.05). The expression of kallikrein in serum and placental tissue of the patients in the experimental group was higher than that of the patients in the control group (p<0.05); PAPP-A level was lower than that in the control group (p<0.05); TGF-ß1 level was higher than that in the control group (p<0.05); VCAM-1 and E-selectin were lower than those in the control group (p<0.05), and kallikrein and TGF-ß1 in serum and placenta in the non-occurrence group were higher than those in the occurrence group (p<0.05). The serum and placenta PAPP-A, VCAM-1, and E-selectin in the non-occurrence group were lower than those in the occurrence group (p<0.05). CONCLUSIONS: Magnesium sulfate combined with nifedipine and labetalol has good efficacy in the treatment of preeclampsia. They can promote the expression of endogenous kallikrein, reduce the level of pregnancy-related hypertension predictors, and weaken the infiltration ability of cytotrophoblasts.

Microminipig: A suitable animal model to estimate oral absorption of sustained-release formulation in humans.

We investigated the gastrointestinal absorption characteristics of oral sustained-release formulations in microminipigs, dogs, and monkeys in order to clarify the similarities in absorption properties between these animals and humans. Time profiles of oral absorption of nifedipine and valproic acid were calculated from the plasma concentration-time profiles of the drugs by a deconvolution method. The curves for both drugs in microminipigs were close to or slightly higher than those in humans, whereas those in monkeys were lower. Furthermore, the plasma concentration-time profiles of the drugs were subjected to non-compartmental analysis. The fractions of a dose absorbed into the portal vein (FaFg) in microminipigs ranged from 50 to 100% of the human values, whereas those in monkeys were less than half the human values. In addition, the other absorption-related parameters for the sustained-release formulation in microminipigs, as well as monkeys, were comparable to those in humans. In conclusion, the oral absorption properties of microminipigs and humans were similar regarding the sustained-release formulations. Therefore, microminipig is a suitable animal model to estimate the oral absorption of sustained-release formulations in humans.

Formulation, Optimization, and In vivo Evaluation of Gastroretentive Drug Delivery System of Nifedipine for the Treatment of Preeclampsia.

The study aimed to develop gastroretentive drug delivery system of nifedipine, its optimization, and in vivo evaluation. Bilayered tablet of nifedipine was prepared using central composite design with 3 factors, 5 responses, and 15 experimental trials. Response surface methodology along with numerical and graphical optimization was used to select the best formulation. Scanning electron microscopy study of optimized tablet at different time interval was carried out which showed formation of porous structure on the tablet surface. In vivo studies for optimized formulation were carried out on 10 healthy human volunteers and obtained pharmacokinetic parameters were compared with the marketed formulation, "Nicardia XL." Optimized formulation containing 3.083 mg HPMC K15M, 29.859 mg HPMC E15LV, and 3.541 mg Carbopol 974P releases the drug in a desired manner and remain buoyant for more than 12 h in human stomach. Both the formulations were found to have similar in vitro release profile (f1 4.5089 and f2 55.8274) and also were found to be bioequivalent. Finally, the stability study of the optimized formulation proved the integrity of the optimized formulation. Hence, the data suggest gastroretention as a promising approach to enhance bioavailability of nifedipine.

Development of a HPLC-MS/MS method for the simultaneous determination of nifedipine and lidocaine in human plasma.

The method for simultaneous determination of nifedipine (NIF) and lidocaine (LID) in human plasma by one-step sample preparation has been developed for the first time. Due to the photosensitivity of nifedipine and its low plasma concentrations a precise and reliable method was required. The method involved liquid-liquid extraction (methyl tert-butyl ether, MTBE), and 10µL of the resulting sample was analyzed by HPLC-MS/MS. Chromatographic separation was achieved on an YMC-Triart C18 HPLC column (100×2.0mm; S-5µm 12nm). The mobile phase was methanol:water, 60:40 (v/v) and contained 0.15% acetic acid. The linearity of the method was established in the concentration ranges of 0.5-50ng/mL for NIF and 1.0-500ng/mL for LID. Photodestruction of NIF under ambient light was evaluated. The validated method was successfully applied to analyze human plasma samples after rectal application of the drug (1g) containing 2.0% LID and 0.3% NIF.

Pharmacokinetic-pharmacodynamic analyses of antihypertensive drugs, nifedipine and propranolol, in spontaneously hypertensive rats to investigate characteristics of effect and side effects.

To investigate the relationship between the pharmacokinetics (PK) and effects and/or side-effects of nifedipine and propranolol, simultaneous examination of their PK and pharmacodynamics (PD), namely blood pressure (BP), heart rate (HR), and QT interval (QT), were assessed in spontaneously hypertensive rats as a disease model. Drugs were infused intravenously for 30 min, then plasma PK and hemodynamic effects were monitored. After general two-compartmental analysis was applied to the plasma data, PD parameters were calculated by fitting the data to PK-PD models. After nifedipine administration, the maximal hypotensive effect appeared about 10 min after starting the infusion, then BP started to elevate although the plasma concentration increased, supposedly because of a negative feedback mechanism generated from the homeostatic mechanism. After propranolol administration, HR decreased by half, and this bradycardic effect was greater than that with nifedipine. Wide variation in QT was observed when the propranolol concentration exceeded 700 ng/mL. This variation may have been caused by arrhythmia. Prolongation of QT with propranolol was greater than that with nifedipine, and bradycardia was slower than the concentration increase and QT prolongation. The characteristically designed PK-PD model incorporating a negative feedback system could be adequately and simultaneously fitted to both observed effect and side-effects.

Deciphering nifedipine in vivo delivery from modified release dosage forms: Identification of food effect.

With the increased reliance on in vitro dissolution testing as an indicator of in vivo drug behavior and the trend towards the in silico modeling of dosage form performance, the need for bioperformance dissolution methodology development has been enhanced. Determination of the in vivo drug delivery profile is essential for the bioperformance dissolution test development and in vitro/in vivo correlation modeling, as well as the understanding of absorption mechanisms. The aim of this study was to compare different methods in terms of their usefulness and applicability in deciphering in vivo delivery of nifedipine administered in modified release dosage forms. A detailed survey of publications on nifedipine pharmacokinetics was done and used to identify the magnitude of food effect. In vitro dissolution testing was performed under various experimental conditions. Obtained results indicate the potential for using the developed in silico model coupled with discriminative in vitro dissolution data for identification of the in vivo drug product behavior.

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.

Pharmacokinetics of nifedipine slow-release during sustained tocolysis.

OBJECTIVE: The pharmacokinetics of nifedipine as a tocolytic agent has not been studied in great detail in pregnant women and has instead focused on immediate release tablets and gastrointestinal therapeutic system (GITS) tablets. The aim of this study was to determine nifedipine slow-release half-life and distribution volume in pregnant women and to compare these with pharmacokinetic parameters of nifedipine in non-pregnant subjects described in the literature. MATERIALS: This is a study parallel to a trial studying women with threatened preterm labor between 26 + 0 and 32 + 2 weeks after initial tocolysis and a completed course of corticosteroids, who were randomly allocated to maintenance nifedipine (slow-release tablets 20 mg 4 times daily) or placebo. Exclusion criteria for the pharmacokinetic study were contra-indications for nifedipine, impaired liver function, and concomitant intake of inhibitors or inducers of the cytochrome P450 3A4 isoenzyme. Blood samples for measuring nifedipine plasma concentrations were drawn at t = 0, t = 12 hours, t = 24 hours, t = 48 hours, t = 72 hours, t = 7 days, and t = 9 days. METHODS: Pharmacokinetic parameters were estimated using iterative two-stage Bayesian population pharmacokinetic analysis by MWPharm© software. The study was designed to establish a correlation between body weight and nifedipine plasma level. RESULTS: The pharmacokinetic parameters of nifedipine slow-release tablets were determined from the data of 8 pregnant women. Nifedipine slow-release had a half-life of 2 - 5 hours, a mean distribution volume of 6.2 ± 1.9 L/kg (calculated while using a fixed biological availability of 0.45 taken from the literature due to lack of intravenous data in this population) compared to a half-life of 6 - 11 hours, and a distribution volume of 1.2 - 1.3 L/kg described in non-pregnant subjects in the literature. None of the women delivered during study medication. Study medication was continued for the duration of the pharmacokinetic study (9 days) in all women. A correlation between nifedipine plasma levels and maternal body weight was not demonstrated. This may have been caused by lack of power. CONCLUSION: Pregnant subjects in this study, using nifedipine slow-release tablets, showed a larger volume of distribution and a shorter elimination half-life than for non-pregnant subjects as published in the literature.

Species differences and substrate specificity of CYP3A heteroactivation by efavirenz.

1. The purpose of this study was to clarify species differences in the heteroactivation of CYP3A substrates by efavirenz, which is known from clinical studies to activate midazolam 1'-hydroxylation, and to assess the feasibility of an animal model. 2. In monkey and human liver microsomes, efavirenz activated CYP3A-mediated midazolam 1'-hydroxylation, but had no effect in rat liver microsomes. The activating effect of efavirenz was also observed with recombinant human CYP3A4 and CYP3A5. Midazolam 4-hydroxylation, testosterone 6ß-hydroxylation and the oxidation of nifedipine were not activated by efavirenz in any of the microsomes. 3. In an in vivo study using monkeys, the AUC ratio of midazolam/1'-hydroxymidazolam was reduced from 0.85 to 0.30 by efavirenz treatment, which was comparable to that obtained in clinical studies. However, the AUC changes of midazolam caused by efavirenz were smaller than those observed in clinical results, therefore the effect of efavirenz on monkeys was not completely consistent with that seen in humans. 4. In conclusion, this is the first report that efavirenz specifically activates midazolam 1'-hydroxylation only in monkey and human liver microsomes, revealing marked species differences and high substrate specificity in the heteroactivation. A further study is required to clarify whether this in vitro result reflects the in vivo situation.

In vitro--in silico--in vivo drug absorption model development based on mechanistic gastrointestinal simulation and artificial neural networks: nifedipine osmotic release tablets case study.

In vitro--in vivo correlations (IVIVC) are generally accepted as a valuable tool in modified release formulation development aimed at (i) quantifying the in vivo drug delivery profile and formulation related effects on absorption; (ii) establishing clinically relevant dissolution specifications and (iii) supporting the biowaiver claims. The aim of the present study was to develop relevant IVIVC models based on mechanistic gastrointestinal simulation (GIS) and artificial neural network (ANN) analysis and to evaluate their applicability and usefulness in biopharmaceutical drug characterisation. Nifedipine osmotic release tablets were selected as model drug product on the basis of their robustness, dissolution limited drug absorption and the availability of relevant literature data. Although the osmotic release tablets have been designed to be robust against the influence of physiological conditions in the gastrointestinal tract, notable differences in nifedipine dissolution kinetics were observed depending on the in vitro experimental conditions employed. The results obtained indicate that both GIS and ANN model developed were sensitive to input kinetics represented by the in vitro profiles obtained under various experimental conditions. Different in silico approaches may be successfully employed in the in vitro--in silico--in vivo model development. However, the results obtained may differ and relevant outcomes are sensitive to the methodology employed.

Desirability function approach for the optimization of an in-syringe ultrasound-assisted emulsification-microextraction method for the simultaneous determination of amlodipine and nifedipine in plasma samples.

In the present study, an in-syringe ultrasound-assisted emulsification-microextraction using a low-density organic solvent was developed for simultaneous extraction and pre-concentration of amlodipine besylate and nifedipine from plasma samples. The extracts were analyzed by high-performance liquid chromatography with UV detection. Central composite design combined with desirability function was applied to find out the optimal experimental conditions providing the highest global extraction efficiency. The optimal conditions identified were volume of the extracting solvent 45 µL, ionic strength 18.95% w/v, sonication time 2.58 min, and centrifugation time 3 min. Under the optimal conditions, the proposed method was evaluated, and applied to the analysis of amlodipine besylate and nifedipine in plasma samples. The validation results of the method indicated a wide linear range (2-1200 ng/mL) with a good linearity (r(2) >0.9991) and low detection limits (0.17 ng/mL for amlodipine besylate and 0.15 ng/mL for nifedipine) with RSD less than 5.2% for both components, both in intra- and inter-day precision studies. The applicability of the proposed in-syringe ultrasound-assisted emulsification-microextraction coupled to high-performance liquid chromatography with UV detection method was demonstrated by analyzing the drugs in spiked plasma samples.

Physiologically based pharmacokinetic modeling of CYP3A4 induction by rifampicin in human: influence of time between substrate and inducer administration.

The induction of cytochrome P450 enzymes (CYPs) is an important source of drug-drug interaction (DDI) and can result in pronounced changes in pharmacokinetics (PK). Rifampicin (RIF) is a potent inducer of CYP3A4 and also acts as a competitive inhibitor which can partially mask the induction. The objective of this study was to determine a clinical DDI study design for RIF resulting in maximum CYP3A4 induction. A physiologically based pharmacokinetic (PBPK) model was developed to project the dynamics and magnitude of CYP3A4 induction in vivo from in vitro data generated with primary human hepatocytes. The interaction model included both inductive and inhibitory effects of RIF on CYP3A4 in gut and liver and accounting for the observed RIF auto-induction. The model has been verified for 4 CYP3A4 substrates: midazolam, triazolam, alfentanil and nifedipine using plasma concentration data from 20 clinical study designs with intravenous (n=7) and oral (n=13) administrations. Finally, the influence of the time between RIF and substrate administration was explored for the interaction between midazolam and RIF. The model integrating in vitro induction parameters correctly predicted intravenous induction but underestimated oral induction with 30% of simulated concentrations more than 2-fold higher than of observed data. The use of a 1.6-fold higher value for the maximum induction effect (Emax) improved significantly the accuracy and precision of oral induction with 82% of simulated concentrations and all predicted PK parameters within 2-fold of observed data. Our simulations suggested that a concomitant administration of RIF and midazolam resulted in significant competitive inhibition limited to intestinal enzyme. Accordingly, a maximum induction effect could be achieved with a RIF pretreatment of 600 mg/day during 5 days and a substrate administration at least 2 h after the last RIF dose. A period of 2 weeks after RIF removal was found sufficient to allow return to baseline levels of enzyme.

Determination of nifedipine in dog plasma by high-performance liquid chromatography with tandem mass spectrometric detection.

Nifedipine is a dihydropyridine calcium channel blocker used widely in the management of hypertension and other cardiovascular disorders. In this work, a simple, rapid and sensitive liquid chromatography/tandem mass spectrometry method was developed and validated to determine nifedipine in dog plasma using nimodipine as the internal standard. Chromatographic separation was carried out on a C8 column. The mobile phase consisted of a mixture of acetonitrile, water and formic acid (60:40:0.2, v/v/v) at a flow rate of 0.5 mL/min. Detection was performed on a triple quadrupole tandem mass spectrometer in selected reaction monitoring mode via an atmospheric pressure chemical ionization source. The method has a lower limit of quantification of 0.20 ng/mL with consumption of plasma as low as 0.05 mL. The linear calibration curves were obtained in the concentration range of 0.20-50.0 ng/mL (r = 0.9948). The recoveries of the liquid extraction method were 74.5-84.1%. Intra-day and inter-day precisions were 4.1-8.8 and 6.7-7.4%, respectively. The quantification was not interfered with by other plasma components and the method was applied to determine nifedipine in plasma after a single oral administration of two controlled-release nifedipine tablets to beagle dogs.

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.

Utilizing in vitro and PBPK tools to link ADME characteristics to plasma profiles: case example nifedipine immediate release formulation.

One of the most prominent food-drug interactions is the inhibition of intestinal cytochrome P450 (CYP) 3A enzymes by grapefruit juice ingredients, and, as many drugs are metabolized via CYP 3A, this interaction can be of clinical importance. Calcium channel-blocking agents of the dihydropyridine type, such as felodipine and nifedipine, are subject to extensive intestinal first pass metabolism via CYP 3A, thus resulting in significantly enhanced in vivo exposure of the drug when administered together with grapefruit juice. Physiologically based pharmacokinetic (PBPK) modeling was used to simulate pharmacokinetics of a nifedipine immediate release formulation following concomitant grapefruit juice ingestion, that is, after inhibition of small intestinal CYP 3A enzymes. For this purpose, detailed data about CYP 3A levels were collected from the literature and implemented into commercial PBPK software. As literature reports show that grapefruit juice (i) leads to a marked delay in gastric emptying, and (ii) rapidly lowers the levels of intestinal CYP 3A enzymes, inhibition of intestinal first pass metabolism following ingestion of grapefruit juice was simulated by altering the intestinal CYP 3A enzyme levels and simultaneously decelerating the gastric emptying rate. To estimate the in vivo dispersion and dissolution behavior of the formulation, dissolution tests in several media simulating both the fasted and fed state stomach and small intestine were conducted, and the results from the in vitro dissolution tests were used as input function to describe the in vivo dissolution of the drug. Plasma concentration-time profiles of the nifedipine immediate release formulation both with and without simultaneous CYP 3A inhibition were simulated, and the results were compared with data gathered from the literature. Using this approach, nifedipine plasma profiles could be simulated well both with and without enzyme inhibition. A reduction in small intestinal CYP 3A levels by 60% was found to yield the best results, with simulated nifedipine concentration-time profiles within 20% of the in vivo observed results. By additionally varying the dissolution input of the PBPK model, a link between the dissolution characteristics of the formulation and its in vivo performance could be established.

A more rapid, sensitive, and specific HPLC-MS/MS method for nifedipine analysis in human plasma and application to a pharmacokinetic study.

A more rapid, sensitive and specific high-performance liquid chromatography coupled to -tandem mass spectrometry (HPLC-MS/MS) was developed and validated for the quantification of nifedipine in human plasma, and applied to the pharmacokinetic study of nifedipine in Chinese healthy volunteers. Nifedipine and internal standard (IS) acetaminophen in plasma were extracted with ethyl acetate, separated on a C18 (150 mm×4.6 mm, 5 µm) reversed-phase column, eluted with acetonitrile mixed with 5 mM ammonium acetate solution (pH=6.62) (60:40, v/v), ionized by negative ion pneumatically assisted electrospray and detected in the multi-reaction monitoring mode using precursor→product ions of m/z 354.1→222.2 for nifedipine and 150.1→107.1 for the IS. A single oral dose of 20 mg nifedipine sustained release tablets and blood samples (4 mL) was collected before and 1, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 8, 12, 24, and 36 h after administration. The main pharmacokinetic parameters of nifedipine, as Tmax, t1/2α, t1/2ß, t1/2z, Cmax, AUC0~36, AUC0~∞ were 2.80±0.50 h, 6.78±2.52 h, 6.82±2.53 h, 6.69±2.22 h, 76.69±19.51 (ng/mL), 546.49±162.28 (ng · h/mL) and 564.05±176.74 (ng · h/mL), respectively. The calibration curve was linear over the concentration range of 0.17-102 ng/mL (r2>0.99, n=5) with a lower limit of quantification (LLOQ) of 0.17 ng/mL. The intra- and inter-day precision was less than 15% for all quality control samples at concentrations of 0.42, 6.53 and 81.60 ng/mL and the accuracy (relative error, RE) was - 3.92% to 7.31% at 3 quality control levels. The specificity, matrix effect, recovery, sensitivity, linearity, accuracy, precision and stabilities were validated, and can fulfill the requirement of pharmacokinetic study of nifedipine sustained release tablets in Chinese volunteers.

Sensitive LC-MS/MS-ESI method for simultaneous determination of nifedipine and atenolol in human plasma and its application to a human pharmacokinetic study.

A rapid, simple, sensitive and selective LC-MS/MS method has been developed and validated for quantification of nifedipine (NF) and atenolol (AT) in human plasma (250 µL). The analytical procedure involves a one-step liquid-liquid extraction method using carbamazepine as an internal standard (IS). The chromatographic resolution was achieved on a Hypurity Advance C(18) column using an isocratic mobile phase consisting of 5 mm ammonium acetate-acetonitrile (15:85, v/v) at flow rate of 1.0 mL/min. The LC-MS/MS was operated under the multiple-reaction monitoring mode using electrospray ionization. The total run time of analysis was 2 min and elution of NF, AT and IS occurred at 0.79, 1.04 and 0.76 min, respectively. A detailed method validation was performed as per the FDA guidelines and the standard curves found to be linear in the range of 1.02-101 ng/mL for NF and 5.05-503 ng/mL for AT, with a coefficient of correlation of ≥ 0.99 for both the drugs. NF and AT were found to be stable in a battery of stability studies, viz. bench-top, auto-sampler and repeated freeze-thaw cycles. The validated assay method was successfully applied to a pharmacokinetic study in humans.

Capsaicin induces CYP3A4 expression via pregnane X receptor and CCAAT/enhancer-binding protein ß activation.

SCOPE: Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is the principal pungent ingredient in hot red and chili peppers. Many studies have focused on the anticarcinogenic or chemopreventive activities of capsaicin. However, the influence of capsaicin on CYP3A4, its involvement in drug metabolism, and the underlying mechanisms remain unclear. METHODS AND RESULTS: Here, we examined the effect of capsaicin on CYP3A4 expression and the metabolism of CYP3A1 substrate, nifedipine in male Sprague-Dawley rats. Capsaicin induced the enzymatic activity and expression of CYP3A4 in HepG2 cells. Treatment with a human pregnane X receptor (hPXR) inhibitor reduced the inductive effects of capsaicin on CYP3A4 expression. Capsaicin also induced the activation of CCAAT/enhancer-binding protein ß (C/EBPß). Moreover, capsaicin increased the activation of the transient receptor potential vanilloid type-1 receptor downstream signaling components Ca²âº/calmodulin-dependent protein kinase and Akt. Capsaicin elevated the level of CYP3A1 in rat liver and significantly increased the biotransformation of nifedipine to dehydronifedipine. CONCLUSION: From these data, we conclude that capsaicin induces CYP3A4 expression in vitro and in vivo. This induction was achieved by the activation of hPXR and C/EBPß. Our results suggest that capsaicin might induce CYP3A4 expression; thus, exposure to capsaicin may increase the metabolism of CYP3A4 substrate and potentially cause food-drug interactions.

Highly sensitive and rapid ultra-performance liquid chromatography-tandem mass spectrometry method for the determination of nifedipine in human plasma and its application to a bioequivalence study.

An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method has been developed for the determination of nifedipine in human plasma using nifedipine-d6 as the internal standard (IS). The plasma samples were prepared by solid-phase extraction on Phenomenex Strata-X cartridges employing 200 µL human plasma. Chromatography was carried out on Waters Acquity UPLC BEH C18 (50 × 2.1 mm, 1.7 µm particle size) analytical column under isocratic conditions using a mobile phase consisting of 4.0 mm ammonium acetate-acetonitrile (15:85, v/v). The precursor → product ion transitions for nifedipine (m/z 347.2 → 315.2) and IS (m/z 353.1 → 318.1) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and positive-ion mode. The method was validated over a wide dynamic concentration range of 0.050-150 ng/mL. Matrix effect was assessed by post-column analyte infusion and the mean extraction recovery was 95.6% across four quality control levels. The method is rugged and rapid with a total run time of 1.2 min and was applied to a bioequivalence study of 20 mg nifedipine tablet formulation in 30 healthy Indian subjects under fasting condition. Assay reproducibility was confirmed by reanalysis of 116 incurred samples.