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.