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

Development and Validation of RP-HPLC and an Ecofriendly HPTLC Method for Simultaneous Determination of Felodipine and Metoprolol Succinate, and their Major Metabolites in Human Spiked Plasma

BACKGROUND

Felodipine is a calcium channel blocker used together with metoprolol succinate for treatment of hypertension.

OBJECTIVE

Two chromatographic methods were developed for simultaneous determination of felodipine (FEL) and metoprolol succinate (MET), and their major metabolites, dehydrofelodipine and metoprolol acid, respectively.

METHODS

The first method was RP-HPLC which comprised separation of the studied components by gradient elution using a Phenomenex C8 column and a mobile phase composed of water (adjusted to pH 3.5 with o-phosphoric acid)-acetonitrile - methanol (45:40:15, by volume) for the first 6 min and (30:60:10, by volume) for the next 4 min at a flow rate of 1 mL/min followed by UV detection of the eluted peaks at 225 nm. The second method was an HPTLC method where separation was achieved using a mobile phase consisting of toluene-ethyl acetate-methanol-ammonia-formic acid (10:5:2.5:0.3:0.1, by volume) and scanning of the separated bands at 225 nm.

RESULTS

Validation of the developed methods was done according to ICH guidelines. Successful application of the developed methods was carried out for determination of the studied drugs in human spiked plasma and in Logimax® tablets.

CONCLUSIONS

The developed RP-HPLC and HPTLC methods can be further applied for quality control testing of the studied drugs.

HIGHLIGHTS

RP-HPLC and HPTLC methods for determination of FEL, MET and their major metabolites. The developed methods were successfully applied for determination of FEL and MET in Logimax® tablets.

Coffee inhibition of CYP3A4 in vitro was not translated to a grapefruit-like pharmacokinetic interaction clinically

Grapefruit can augment oral medication bioavailability through irreversible (mechanism‐based) inhibition of intestinal CYP3A4. Supplementary data from our recent coffee–drug interaction clinical study showed some subjects had higher area under the plasma drug concentration ‐ time curve (AUC) and plasma peak drug concentration (Cmax) of the CYP3A4 probe felodipine compared to aqueous control. It was hypothesized that coffee might interact like grapefruit in responsive individuals. Beans from six geographical locations were consistently brewed into coffee that was separated chromatographically to a methanolic fraction for in vitro inhibition testing of CYP3A4 metabolism of felodipine at 1% coffee strength. The effect of simultaneous incubation and 10‐min preincubation with coffee fractions determined whether coffee had direct and mechanism‐based inhibitory activity. A subsequent five‐way randomized balanced controlled crossover clinical study evaluated the clinical pharmacokinetic interaction with single‐dose felodipine. Grapefruit juice, water, or three of the in vitro tested coffees were ingested at 300 mL alone 1 h before and then with felodipine. In vitro, all six coffees decreased felodipine metabolism for both simultaneous and preincubation exposure compared to corresponding control. Five coffees demonstrated mechanism‐based inhibition. Grapefruit increased felodipine AUC_0–8 (25 vs. 13 ng.h/mL, P < 0.001) and Cmax (5.8 vs. 2.7 ng/mL, P < 0.001) and decreased dehydrofelodipine/felodipine AUC_0–8 ratio (0.84 vs. 1.29, P < 0.001), while the three coffees caused no change in these parameters compared to water. Despite high in vitro potency of CYP3A4 inhibition, the coffees did not cause a clinical pharmacokinetic interaction possibly from insufficient amount of inhibitor(s) in coffee reaching intestinal CYP3A4 during the absorption phase of felodipine. The results of this study highlight the need for follow‐up clinical testing when in vitro results indicate the possibility of an interaction.

Spectrofluorimetric and micelle-enhanced spectrofluorimetric methods for determination of Felodipine and Nimodipine in pharmaceutical preparations and human plasma

Rapid, simple and sensitive two spectrofluorimetric methods have been developed for determination of Felodipine (FLD) and Nimodipine (NDP). The first method is based on measuring the native fluorescence of either Felodipine or Nimodipine at 426 nm after excitation at 385 nm. The fluorescence intensity-concentration plots of Felodipine and Nimodipine were rectilinear over the concentration ranges (0.2-3.0) and (0.5-4.0) μg ml(-1), respectively. The second method is based on measuring the fluorescence intensity of the studied drugs in micellar media (0.3% Tween-80) at λex=385 nm and λem=423 nm. In the presence of 0.3% Tween-80, about 1.6-fold and 2.1-fold enhancement can be achieved in the relative fluorescence intensity (RFI) of Felodipine and Nimodipine, respectively. The fluorescence intensity-concentration plots of Felodipine and Nimodipine with Tween-80 were rectilinear over the concentration ranges (0.05-4.0) and (0.1-4.0) μg ml(-1), respectively with determination coefficients (r(2)) of 0.9981 and 0.9990, and limit of quantitation of 0.05 and 0.027μg ml(-1) for FLD and NDP, respectively. The proposed methods were validated according to ICH guidelines and have been successfully applied to the analysis of these drugs in their commercial tablets with high accuracy (97.6-98.8±0.50-1.42%, n=5). The high sensitivity of micellar method permits its application for determination of the cited drugs in spiked human plasma with % recovery (91.9-106.6±0.66-1.7%, n=6).

Development of a high-performance liquid chromatography method for simultaneous determination of pioglitazone and felodipine in pig serum: application to pharmacokinetic study

A simple and sensitive high-performance liquid chromatographic method was developed and validated for simultaneous estimation of pioglitazone and felodipine in pig serum. The present method consists of protein precipitation, extraction of analytes from pig serum into dichloromethane and separation using reversed-phase C(18) column. Nitrendipine was used as an internal standard and the eluent was monitored by UV detector at 240 nm. The mobile phase used was acetonitrile and 50 mm ammonium acetate buffer at a flow rate of 1 mL/min. The retention times for pioglitazone, felodipine and nitrendipine were found to be 5.12, 10.53 and 7.14 min, respectively. The intraday and inter-day coefficient of variation and percent error values of assay method were less than 7% and mean recovery was more than 94% for each analyte, and the method was found to be precise, accurate and specific during study. The method was successfully applied for pharmacokinetic study of pioglitazone and felodipine from bioadhesive buccal tablet after buccal administration to pigs. The C(Max) , T(Max) , and AUC(0-24) of pioglitazone and felodipine from buccal tablet were found to be 394.6 ng/mL, 5.6 h, 2624.2 ng h/mL and 44.4 ng/mL, 5.5 h, 275.8 ng h/mL, respectively.

Effect of menthol on the pharmacokinetics and pharmacodynamics of felodipine in healthy subjects

OBJECTIVES

The present study was undertaken to determine whether menthol affects the metabolism of and pharmacological responses to the calcium channel antagonist felodipine in people.

METHODS

Eleven healthy subjects (ten female, one male) participated in a randomized, double-blind, two-way crossover study, comparing the kinetics and effects of a single oral dose of felodipine ER tablet (Plendil, 10 mg) with menthol (test) or placebo (reference) capsules. Ten subjects completed the study. At the beginning of the study, a 10-mg felodipine ER tablet and a 100-mg menthol or placebo capsule were given. During the 2nd, 5th and 7th hours of the study, 50, 25 and 25 mg menthol or placebo capsules were given, respectively. Blood samples and cardiovascular measurements were obtained at frequent intervals. Serum felodipine and dehydrofelodipine concentrations were determined by means of gas chromatography/mass spectrometry.

RESULTS

Pharmacokinetic parameters of felodipine and dehydrofelodipine (AUC0-24, Cmax, t(max), dehydrofelodipine/felodipine AUC0-24 ratio) were not markedly changed with menthol coadministration. Only eight female subjects' cardiovascular data were included in the analysis because of technical problems during the measurements. There were no statistically significant differences in blood pressures and heart rates between the two treatments.

CONCLUSIONS

We conclude that the pharmacokinetics and pharmacodynamics of felodipine were essentially unaltered by menthol.

Sensitive spectrophotometric determination of amlodipine and felodipine using iron(III) and ferricyanide

A simple, accurate, sensitive and economical procedure for the estimation of amlodipine besylate and felodipine, both in pure form and in formulations has been developed. The method is based on the reduction of iron(III) by the studied drugs in acid medium and subsequent interaction of iron(II) with ferricyanide to form Prussian blue. The product exhibits absorption maximum at 760 nm in both cases. Beer's law is obeyed in the concentration ranges 5.0-15.0 and 1.5-5.0 microg/ml, for amlodipine and felodipine, respectively. The molar absorptivities are 1.76 x 10(4) and 4.24 x 10(4) l/mol cm. The corresponding Sandell sensitivities are 23.18 and 9.06 ng/cm(2). The limits of detection as well as quantification are reported. Seven replicate analyses of solutions containing three different concentrations of each drug were carried out and the percent error and the RSD values have been reported. The proposed method was applied to the determination of these drugs in pharmaceutical formulations and the results demonstrate that the method is equally accurate and precise as the official methods as found from the t- and F-values. The reliability of the method was established by recovery studies using standard-addition technique.

A stability indicating LC method for felodipine

A stability indicating reversed-phase liquid chromatographic (RP-LC) method was developed for the assay of felodipine as a bulk drug and in pharmaceuticals. The chromatography was performed on a C18 column. Eluents were monitored by UV detection at 238 nm using the mobile phase methanol-potassium dihydrogen orthophosphate (pH 3.5; 0.01 M) (75:25, v/v). The method was statistically validated for linearity, accuracy, precision and specificity. The linearity of felodipine peak area responses was demonstrated within the concentration range of 1-7 microg/ml. The limits of detection and quantitation were 150 and 500 ng/ml, respectively. The method was demonstrated to be precise, accurate and specific with no interference from the tablet excipients and separation of the drug peak from the peaks of the degradation products (oxidative degradation, photodegradation, acid and base degradation). The results indicated that the proposed method could be used in a stability assay.

Calcium channel blockade with felodipine does not affect metabolic coronary vasodilation in patients with coronary artery disease

The effect of calcium channel blockers may affect the feedback mechanism between myocardial metabolic activity and coronary blood flow. To test this hypothesis the effect of calcium channel blockade on metabolic coronary flow regulation was studied. In 10 patients with stable coronary artery disease, coronary sinus blood flow and myocardial oxygen supply and consumption (MVO2) were measured both at sinus rhythm and during atrial pacing (30 beats/min above sinus rate), at control and during infusion of felodipine, a vasoselective dihydropyridine. The myocardial oxygen supply-consumption ratio at control (i.e., the slope of the regression line characterizing normal metabolic flow regulation) was 1.58 (95% CI, 1.38-1.80). Following infusion of felodipine, systemic and coronary vascular resistance during sinus rhythm decreased by 20 +/- 11% and 23 +/- 15%, respectively, and coronary venous oxygen saturation increased from 36 +/- 6% at control to 42 +/- 7% (p = 0.047) during infusion of felodipine. The myocardial oxygen supply-consumption ratio, characterizing metabolic flow regulation during felodipine, was 1.52 (95% CI, 1.26-1.78) and thus not different from control. Metabolic coronary flow regulation was not affected by administration of felodipine, although the setpoint of this regulation mechanism might have been offset by the initial drug-induced coronary vasodilation, which persisted during pacing.

Enantioselective determination of felodipine in human plasma by chiral normal-phase liquid chromatography and electrospray ionisation mass spectrometry

An analytical method was developed for the determination of the enantiomers of felodipine, a dihydropyridine-type calcium antagonist, in human blood plasma. Felodipine was extracted from plasma using toluene as extraction solvent. The enantiomers were separated on a cellulose tris(4-methyl benzoate) stationary phase (Chiralcel OJ-R) using 2-propanol-iso-hexane (11:89) as mobile phase. Post-column addition of ammonium acetate in ethanol-water (95:5) allowed sensitive detection of the ammonium adduct by electrospray ionisation and selected reaction monitoring. Deuterated felodipine racemate was used as internal standard. Within-run repeatability was determined and a coefficient of variation below 2% was achieved at 22 nmol/l and below 10% at 0.27 nmol/l. Between-day precision was evaluated and a coefficient of variation of 3.6% at 4 nmol/l plasma was obtained. Limit of quantification (LOQ) was set at 0.25 nmol/l (0.10 microg/l). The method proved adequate for pharmacokinetic studies of R- and S-felodipine after oral administration of therapeutic doses of felodipine.

Influence of hydrodynamics and particle size on the absorption of felodipine in labradors

PURPOSE

To study the influence of GI hydrodynamics and drug particle size on felodipine absorption in the dog.

METHODS

Labradors fistulated at midjejunum were used to selectively study the influence of hydrodynamics and particle size on the in vivo dissolution and absorption of the poorly soluble, lipophilic drug felodipine. A combination of infusion and oral administration of either normal saline or a 5% glucose solution was used to maintain "fasted" and establish "fed" state motility patterns, respectively. The absorption characteristics of both a micronized (8 microm) and a coarse fraction (125 micom) of felodipine were subsequently studied under these two motility patterns.

RESULTS

A reduction in particle size led up to an approximate 22-fold increase in maximum plasma concentration and up to an approximate 14-fold increase in area under the curve, with a commensurate decrease in the time at which the maximum plasma concentration occurred. Although the absorption of felodipine from the solution and micronized suspension was not influenced by a change in the hydrodynamics, felodipine was absorbed from the coarse suspension almost twice as well in the "fed" state as under "fasted" conditions.

CONCLUSIONS

Absorption from coarse suspensions of felodipine was sensitive to luminal hydrodynamics, whereas micronized suspensions were not. However, the particle size seems to have a much more important influence on the bioavailability of felodipine than the hydrodynamics per se.

Renal hypoxanthine balance in cardiac surgery: effects of felodipine

OBJECTIVE

To test the hypothesis that felodipine, a renal vasodilator, can prevent a release of hypoxanthine during rewarming after moderate hypothermic cardiopulmonary bypass and that this is related to improved renal oxygen supply.

DESIGN

A prospective, randomized, and controlled study.

SETTING

Operating room in the cardiothoracic surgery department of a university hospital.

PARTICIPANTS

Twenty-two patients submitted to elective first-time coronary bypass surgery.

INTERVENTIONS

A catheter was placed in the left renal vein for thermodilution renal blood flow (RBF) measurement and blood sampling. In 11 patients, felodipine was infused during the hypothermic period of cardiopulmonary bypass.

MEASUREMENTS AND MAIN RESULTS

Renal uptake (renal arteriovenous concentration difference x RBF) of hypoxanthine was maintained during rewarming in felodipine-treated patients but not in control patients (55+/-28 v. -39+/-1 nmol/min, p<0.05). Oxygen consumption was higher after felodipine infusion despite unchanged total RBF. A positive correlation between renal oxygen consumption and hypoxanthine uptake and release (r = 0.74, p<0.01) was observed.

CONCLUSIONS

Felodipine maintained renal uptake of hypoxanthine during rewarming after hypothermic cardiopulmonary bypass. This maintenance is the effect of improved renal oxygen supply secondary to improved nutritive blood flow at the expense of nonnutritive renal blood flow.

Sensitive and specific liquid chromatographic-tandem mass spectrometric assay for barnidipine in human plasma

A sensitive and specific LC-MS-MS assay has been developed and validated for barnidipine (1-benzyl-3-pyrrolidinyl)methyl-2,6-dimethyl-4(m-nitrophenyl)-1,4-dihydr opyridine-3,5-dicarboxylate). The assay involves a simple and rapid solid-phase extraction procedure. Sample analysis was on a Spherisorb S3ODS2 100 mmX2 mm I.D. column, with a Finnigan TSQ 7000 mass spectrometer, using an electrospray interface and selective reaction monitoring (SRM). The intra- and inter-day precision and accuracy, determined as the coefficient of variation and relative error, respectively, were 11.8% or less. The limit of quantitation was 0.03 ng/ml, and the calibration was linear between 0.03 and 3.0 ng/ml. The method has been used successfully for the measurement of over two thousand human plasma samples from pharmacokinetic clinical trials.

Grapefruit juice-felodipine interaction: effect of naringin and 6',7'-dihydroxybergamottin in humans

OBJECTIVE

To test whether naringin or 6',7'-dihydroxybergamottin is a major active substance in grapefruit juice-felodipine interaction in humans.

METHODS

Grapefruit juice was separated by means of centrifugation and filtration into supernatant and particulate fractions, which were then assayed for naringin and 6',7'-dihydroxybergamottin. The effect of these fractions, grapefruit juice (containing comparable amounts of both fractions), and water on the pharmacokinetics of oral felodipine were assessed in 12 healthy men in a randomized, 4-way crossover study.

RESULTS

The amounts of naringin and 6',7'-dihydroxybergamottin in the supernatant fraction (148 mg and 1.85 mg) were greater than in the particulate fraction (7 mg and 0.60 mg). The area under the plasma concentration-time curve (AUC) and the peak concentration (Cmax) of felodipine were higher with supernatant fraction (81 nmol.h/L and 20 nmol/L), particulate fraction (117 nmol.h/L and 24 nmol/L), and grapefruit juice (130 nmol.h/L and 33 nmol/L) compared with water (53 nmol.h/L and 11 nmol/L). However, the supernatant fraction had a lower AUC for felodipine and a similar Cmax of felodipine relative to the particulate fraction. The supernatant fraction neither augmented the AUC of the primary metabolite dehydrofelodipine nor decreased the AUC ratio of dehydrofelodipine to felodipine compared with water. Individually the supernatant fraction consistently produced lower felodipine AUC and Cmax compared with grapefruit juice. In contrast, the particulate fraction had values ranging from more than grapefruit juice to less than supernatant fraction.

CONCLUSIONS

Naringin and 6',7'-dihydroxybergamottin are not the major active ingredients, although they may contribute to the grapefruit juice-felodipine interaction. The variable effect with the particulate fraction may result from erratic bioavailability of unidentified primary active substances. The findings show the importance of in vivo testing to determine the ingredients in grapefruit juice responsible for inhibition of cytochrome P450 3A4 in humans.

Drug absorption from nifedipine hydrophilic matrix extended-release (ER) tablet-comparison with an osmotic pump tablet and effect of food

The aim of the present study was to compare the bioavailability of nifedipine when administered as a hydrophilic matrix tablet (ER) and a push-pull osmotic pump tablet (XL) administrated after fasting, and to evaluate the effect of food for the hydrophilic matrix tablet. For this purpose, three separate studies were performed on healthy volunteers (n = 58) including gammascintigraphic monitoring of tablet erosion and localisation in the gastrointestinal tract for ER in one study. Both ER and XL provided almost constant drug delivery over 24 h, after administration under fasting conditions, and bioequivalence was obtained according to 90% confidence intervals of the difference between formulations within 80-125% for Cmax and AUC. Food significantly increased AUC for ER but no significant difference was obtained between ER and XL with food with respect to extent of bioavailability. The rate of absorption was increased to a higher degree for ER than for XL, as indicated by a Cmax which was almost twice as high for ER compared with XL. This finding was shown to be related to an increased tablet-erosion rate for ER, leading to more rapid drug release.

Grapefruit juice increases felodipine oral availability in humans by decreasing intestinal CYP3A protein expression

The increase in oral availability of felodipine and other commonly used medications when taken with grapefruit juice has been assumed to be due to inhibition of CYP3A4, a cytochrome P450 that is present in liver and intestine. To evaluate the effect of repeated grapefruit juice ingestion on CYP3A4 expression, 10 healthy men were given 8 oz of grapefruit juice three times a day for 6 d. Before and after receiving grapefruit juice, small bowel and colon mucosal biopsies were obtained endoscopically, oral felodipine kinetics were determined, and liver CYP3A4 activity was measured with the [14C N-methyl] erythromycin breath test in each subject. Grapefruit juice did not alter liver CYP3A4 activity, colon levels of CYP3A5, or small bowel concentrations of P-glycoprotein, villin, CYP1A1, and CYP2D6. In contrast, the concentration of CYP3A4 in small bowel epithelia (enterocytes) fell 62% (P = 0.0006) with no corresponding change in CYP3A4 mRNA levels. In addition, enterocyte concentrations of CYP3A4 measured before grapefruit juice consumption correlated with the increase in Cmax when felodipine was taken with either the 1st or the 16th glass of grapefruit juice relative to water (r = 0. 67, P = 0.043, and r = 0.71, P = 0.022, respectively). We conclude that a mechanism for the effect of grapefruit juice on oral felodipine kinetics is its selective downregulation of CYP3A4 in the small intestine.

Itraconazole greatly increases plasma concentrations and effects of felodipine

BACKGROUND

Felodipine, a dihydropyridine calcium antagonist, is extensively metabolized by CYP3A4. Itraconazole strongly interacts with some of the substrates of CYP3A4 (e.g., terfenadine, triazolam and lovastatin); hence it is important to uncover the possible interaction of itraconazole with felodipine.

METHODS

A double-blind, randomized, two-phase crossover design was used to investigate the interaction between felodipine and itraconazole. Nine healthy volunteers received either 200 mg itraconazole or placebo orally once a day for 4 days. On day 4, each ingested a single 5 mg oral dose of felodipine. Plasma concentrations of felodipine and itraconazole were determined and systolic and diastolic blood pressures and heart rate were measured up to 32 hours.

RESULTS

On average, itraconazole increased the peak plasma concentration (Cmax) of felodipine nearly eightfold (p < 0.001), the areas under the felodipine concentration-time curve [AUC(0-32) and AUC(0-infinity)] about sixfold (p < 0.001), and the elimination half-life twofold (p < 0.05). In seven of the nine subjects, even the Cmax of felodipine was lower without itraconazole than the 32-hour concentrations during the itraconazole phase. The decreases in blood pressure and the increases in heart rate were significantly greater during the itraconazole phase than during the placebo phase.

CONCLUSIONS

Itraconazole greatly increases plasma concentrations and effects of oral felodipine. The inhibition of CYP3A4 during the first-pass and elimination phases of felodipine seems to be the mechanism of the observed interaction. The concomitant use of itraconazole and some other azole antifungals with felodipine and other dihydropyridine calcium antagonists should be avoided or their doses should be reduced accordingly.

Erythromycin-felodipine interaction: magnitude, mechanism, and comparison with grapefruit juice

OBJECTIVE

To investigate a potentially marked effect by erythromycin on felodipine pharmacokinetics, to characterize the mechanism, and to compare the interaction with that between grapefruit juice and felodipine.

METHODS

Felodipine, 10 mg extended release, was administered with 250 ml water, 250 mg erythromycin, or 250 ml grapefruit juice in a randomized crossover study of 12 healthy men. Erythromycin base, 250 mg four times a day, was started the day before and continued on that study day. Pharmacokinetic values of felodipine, the primary metabolite dehydrofelodipine, and the major secondary derivative M3 metabolite were studied.

RESULTS

Compared with water, erythromycin produced severalfold higher felodipine area under the plasma drug concentration-time profile (AUC), plasma peak drug concentration (Cmax), and apparent elimination half-life (t1/2); however, the effect was variable among individuals. Erythromycin augmented dehydrofelodipine AUC, Cmax, and t1/2 but decreased dehydrofelodipine/felodipine ratios. The AUC of the M3 metabolite and the M3 metabolite/dehydrofelodipine ratios were reduced. These findings support inhibition of both metabolic pathways likely mediated by CYP3A4. Grapefruit juice produced similar mean effects but did not prolong felodipine or dehydrofelodipine t1/2. Individually, felodipine AUC with erythromycin was greater than or similar to that with grapefruit juice. Relative felodipine AUC (erythromycin compared with grapefruit juice) correlated with relative felodipine Cmax but not with relative felodipine t1/2, suggesting felodipine AUC differed between these treatments, mainly from factors affecting presystemic drug elimination.

CONCLUSIONS

Erythromycin produced an important pharmacokinetic interaction with felodipine by inhibition of drug metabolism. Although erythromycin and grapefruit juice shared a common mechanism, erythromycin likely reduced felodipine biotransformation at the gut wall and liver, whereas single-dose grapefruit juice had an effect mainly at the gut wall.

Renal function during cardiopulmonary bypass: influence of the calcium entry blocker felodipine

Glomerular filtration and tubular activity are decreased during hypothermic cardiopulmonary bypass (CPB). The role of vasoconstriction to explain these changes is not known. The calcium entry blocking drug felodipine dilates constricted arterioles and reduces renal vascular resistance during noncardiac surgery. The present study was initiated to evaluate the effects of felodipine on renal perfusion and function during hypothermic, low pressure CPB. Twenty-two male patients (aged 61.7 +/- 2.3 y) were included in a prospective, randomized, controlled study. Renal blood flow was measured with thermodilution technique; renal extraction of 51Cr-EDTA and p-aminohippurate (PAH) were used to evaluate glomerular and tubular function. Systemic blood flow during hypothermic CPB was varied experimentally between 1.45 and 2.2 L.min-1.m-2. Felodipine reduced systemic vascular resistance but did not reduce the total renal vascular resistance during CPB. On the contrary, renal vascular resistance was increased at low CPB flow rates. The extraction of PAH (signifying tubular activity) was higher during felodipine infusion (0.74 +/- 0.04 vs 0.64 +/- 0.03 during low CPB flow, and 0.64 +/- 0.03 vs 0.57 +/- 0.05 during high CPB flow), whereas 51Cr-EDTA extraction was not influenced. The mechanism of enhanced PAH extraction may involve reduced regional vasoconstriction in PAH-extracting areas.

Relationship between time of intake of grapefruit juice and its effect on pharmacokinetics and pharmacodynamics of felodipine in healthy subjects

In this randomised, cross-over study, in nine healthy males given felodipine ER 10 mg PO 200 ml grapefruit juice was found to increase the plasma levels of felodipine even when the juice was taken 24 hours before the drug. Grapefruit juice drunk simultaneously with and 1, 4, 10 or 24 hours before the drug administration resulted in a 32-99% increase in mean Cmax values of felodipine, relative to concomitant water and felodipine intake. The effect on AUC was also significant when juice was taken up to 10 h before the drug. The effect of the interaction decreased with increasing time between juice and drug intake. All treatments produced a significant decrease in diastolic blood pressure and an increase in heart rate in comparison with morning basal values. The change in haemodynamic variables was approximately the same after all treatment combinations. Headache was reported more frequently after treatments including grapefruit juice.

Felodipine population dose-response and concentration-response relationships in patients with essential hypertension

OBJECTIVES

To characterize the population dose-response and concentration-response relationships of felodipine and to investigate the influence of patient variables on these relationships.

METHODS

We studied 239 evaluable patients with mild to moderate essential hypertension in a multicenter, randomized, double-blind dose-escalation trial, followed by an optional open-label maintenance phase for the remainder of 1 year. Extended-release felodipine (2.5 to 20 mg) monotherapy was given once daily. Felodipine plasma concentration and sitting diastolic blood pressure were measured at approximately 2 and 24 hours after drug administration. Analysis, performed with use of the population approach (NONMEM program), accounted for baseline and placebo effects.

RESULTS

A saturation (Emax) model best described both felodipine dose response (only 24-hour postdose data) and concentration response. The maximum effect (Emax) characterizing dose response was found to increase linearly with age and was estimated to be 20.6 mm Hg in the typical individual (60 years of age). The dose at which 50% of the maximum effect is achieved (D50) was estimated to be 11.1 mg. The Emax characterizing concentration response also increased linearly with age and was estimated to be 27.8 mm Hg for the typical individual. The concentration at which 50% of the maximum effect is achieved (C50) was related to plasma renin activity (PRA) by the following: (21.6.PRA)/(0.25 + PRA) nmol/L; its value in the typical individual was estimated to be about 16.9 nmol/L. Felodipine (oral) clearance decreased with increasing age, up to 60 years, and was larger in black patients.

CONCLUSIONS

The effects of age on felodipine pharmacokinetics and pharmacodynamics lead to a heightened antihypertensive response in the elderly. A starting dose of 2.5 mg daily is recommended, especially in elderly patients.

Determination of felodipine, its enantiomers, and a pyridine metabolite in human plasma by capillary gas chromatography with mass spectrometric detection

Sensitive methods based on capillary gas chromatography (GC) with mass spectrometric (MS) detection in a selected-ion monitoring mode (SIM) for the determination of racemic felodipine, its enantiomers, and a pyridine metabolite in human plasma are described. Following liquid-liquid extraction from plasma, enantiomers of felodipine were separated on a chiral HPLC column (Chiralcel OJ) and fractions containing each isomer were collected on a continuous basis using a fraction collector. These fractions were later analyzed by GC-MS-SIM. A similar method based on GC-MS-SIM detection was developed for the determination of racemic felodipine and its pyridine metabolite with a minor modification of sample preparation. The limits of quantitation in plasma were 0.1 ng/ml for both the R(+)- and S(-)-enantiomers of felodipine and 0.5 ng/ml for both racemic felodipine and its pyridine metabolite. The stereoselective assay was used to support a clinical study with racemic felodipine, and was capable of analyzing more than 30 plasma samples per day.

Stereoselective pharmacokinetics of dihydropyridine calcium antagonists

Many dihydropyridine calcium antagonists are widely used for the treatment of angina and hypertension, and many more are under development. Most of these drugs have one or more chiral centre, and the pharmacological activity between the enantiomers for these drugs is known to be markedly different. First, the stereospecific assay methods for these drugs in plasma or serum are reviewed with emphasis on chiral stationary phase high-performance liquid chromatography for their determination. Next, the stereoselective pharmacokinetics of these drugs (nilvadipine, nitrendipine, felodipine, nimodipine, manidipine, benidipine and nisoldipine) in animals, healthy subjects and patients with hepatic disease is reviewed. Enantiomer-enantiomer interaction, enantiomeric inversion and the stereochemical aspects of pharmacokinetic drug interactions in these drugs are also described.

Natriuretic and diuretic effects of felodipine and hydrochlorothiazide after single and repeated doses

The effects of the calcium antagonist, felodipine, and hydrochlorothiazide (HCTZ) on natriuresis/diuresis and blood pressure were evaluated in 12 healthy subjects. The investigation was designed as a double-blind, three-way, randomised, crossover study, and all comparisons were performed against placebo. Urine volume, urine sodium excretion, heart rate and blood pressure were measured after a single dose of felodipine 10 mg, HCTZ 12.5 mg or placebo as well as during steady-state conditions (6 days of treatment with felodipine 10 mg b.i.d., HCTZ 12.5 mg b.i.d. or placebo). A significant increase in natriuresis was seen in the first 4 h after a single dose of felodipine and HCTZ, and the effect of felodipine was approximately 40% that of HCTZ. When the entire 24-h period after a single dose was studied, there was a significant increase in natriuresis after HCTZ, but not after felodipine, compared with placebo. A significant increase in diuresis was found in the first 4 h after a single dose of HCTZ, but not after felodipine, compared with placebo. Under steady-state conditions, there were no statistically significant differences between felodipine and placebo or HCTZ and placebo when the 24-h period, as a whole was considered. Potassium excretion was not affected by any of the drugs. Felodipine caused a significant decrease in diastolic blood pressure in this study. This was not the case for HCTZ or placebo.

Metoclopramide stimulates kaliuresis during felodipine without affecting its natriuresis

Calcium entry blockers such as felodipine induce natriuresis without a parallel rise of potassium excretion. Previous studies with exogenous aldosterone and felodipine have suggested that the absence of kaliuresis might be explained by a felodipine-induced inhibition of aldosterone release. The natriuresis with calcium entry blockers could not be attributed to a similar mechanism but might be due to the stimulation of intrarenal natriuretic systems such as the dopaminergic system. We studied whether the aselective dopamine antagonist metoclopramide prevents the natriuresis with low and therapeutic felodipine doses and whether metoclopramide-induced aldosterone release promotes kaliuresis with felodipine. Twelve healthy male volunteers participated in a randomized, placebo-controlled, crossover study comparing felodipine infusion during metoclopramide with felodipine alone. Metoclopramide had no significant influence on the pronounced and dose-dependent increases of renal plasma flow and urinary sodium excretion with felodipine. Metoclopramide increased plasma aldosterone concentration from 0.17 +/- 0.03 to 0.60 +/- 0.14 nmol/L, and subsequent felodipine infusion clearly increased urinary potassium excretion by 23 +/- 6 and 35 +/- 8 mumol/min (low and therapeutic doses, respectively). In contrast, potassium excretion remained stable with felodipine alone (+5 +/- 4 and +7 +/- 5 mumol/min, respectively). In conclusion, the natriuretic action of calcium entry blockers cannot be blocked by the aselective dopamine antagonist metoclopramide. This natriuresis is accompanied by kaliuresis only in the presence of elevated endogenous aldosterone concentrations. The ability of calcium entry blockers to prevent a rise of plasma aldosterone thus seems essential for the prevention of urinary potassium losses.

Acute and chronic calcium antagonist treatment elevates sympathetic activity in primary hypertension

Eleven men with mild to moderate primary hypertension were studied at rest and during mental stress before and during intravenous infusion of the calcium antagonist felodipine. Eight of them were restudied during long-term treatment (extended-release felodipine, 10 mg daily). For comparison, 10 normotensive control subjects were studied with the short-term protocol. Heart rate, cardiac output, central cardiovascular pressures, and forearm blood flow were registered. Arterial and venous sampling was performed. Norepinephrine spillovers to arterial plasma and from the forearm were assessed with the use of radiotracer methodology. In the hypertensive patients, felodipine lowered mean arterial blood pressure acutely by 8% (P < .01). Systemic vascular resistance decreased by 22% (P < .001), cardiac output increased by 20% (P < .01), and norepinephrine spillover to arterial plasma increased by 61% (P < .001). Forearm vascular resistance fell by 30% (P < .001), but norepinephrine overflow from the forearm increased by 115% (P < .001). These forearm responses were not seen in normotensive subjects despite similar systemic responses to felodipine infusion. After 8 weeks of treatment, mean arterial pressure decreased to 15% below baseline (P < .001), cardiac output returned toward pretreatment levels, and systemic vascular resistance remained low. Forearm blood flow returned toward basal levels, but forearm vascular resistance remained lowered. Total body and forearm norepinephrine spillover values were as elevated as in the acute situation. The hemodynamic "defense reaction" and the sympathoadrenal response to mental stress were essentially unaffected by felodipine. Stress-induced small elevations of neuropeptide Y-like immunoreactivity persisted during felodipine. Thus, the vasodilatation induced by felodipine elicits sympathetic counterregulation, which persists in the long term with respect to peripheral and total sympathetic activities, despite resetting of the baroreflex control of heart rate.

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

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

Evaluation of solubilizers in the drug release testing of hydrophilic matrix extended-release tablets of felodipine

The drug release of felodipine, a water-insoluble drug, was tested by using sodium lauryl sulphate (SLS), polyoxyethylene 20 sorbitan monooleate (Tween) or cetyltrimethylammonium bromide (CTAB) in the test medium as solubilizers. Three slightly different felodipine extended-release (ER) tablets 10 mg based on the gel matrix principle were evaluated under different solubilizer concentrations, agitation intensities and pH. These tablets were also tested in a bioavailability study together with an oral solution. All three solubilizers substantially enhanced the drug solubility and sink conditions were obtained. The choice of solubilizer affected the drug release rate. This is most probably due to physico-chemical interactions between the gel-forming agent and the solubilizers. All in vitro test conditions provided a good correlation (r2 = 0.94-0.97) to in vivo dissolution, as determined by moment analysis. However, a much steeper in vitro/in vivo relationship was obtained for SLS compared to Tween and CTAB reflecting an inferior discrimination between the tablets by use of this anionic solubilizer.

Short-term effects of felodipine in hypertensive type II diabetic males on sulfonylurea treatment

OBJECTIVES

To study the effects on blood pressure and glucose homeostasis of felodipine, a calcium antagonist.

DESIGN

A double-blind randomized cross-over study comparing felodipine ER and placebo.

SETTING

A university centre of diabetic care in Malmö, Sweden.

SUBJECTS

Seventeen hypertensive type II diabetic males on oral sulfonylurea (glibenclamide) treatment.

INTERVENTIONS

Four-week treatment periods separated by a 2-week wash-out period. Felodipine 10-20 mg once daily was given.

MAIN OUTCOME MEASURES

Blood pressure, heart rate, HbA1c and response to oral glucose tolerance test; glucose, insulin and c-peptide. Measured before randomization and at the end of each double-blind treatment period.

RESULTS

Blood pressure was significantly reduced during felodipine treatment and heart rate slightly increased. Felodipine did not influence insulin or c-peptide levels. There was no significant change in glucose levels but an increase in HbA1c.

CONCLUSION

The study demonstrated that felodipine is an effective agent for type II diabetic patients on glibenclamide treatment. The effect on HbA1c is noteworthy even if not of clinical significance in the short term. Controlled long-term studies in diabetic patients are needed to fully evaluate antihypertensive agents.

A comparative assessment of amlodipine and felodipine ER: pharmacokinetic and pharmacodynamic indices

This study investigated potential therapeutic differences between Amlodipine 5 mg and Felodipine ER 10 mg in 12 normotensive/borderline hypertensive subjects by comparison of the plasma drug concentration-time profiles and the blood pressure and heart rate responses. There was significantly less trough-to-peak variability in plasma drug concentrations with amlodipine with a ratio of 67%, compared to 37% for felodipine. Correspondingly there was less variability with amlodipine in the blood pressure reductions across the dosage interval. Overall, amlodipine displayed a more consistent hypotensive effect across 24 hours and lower blood pressure values at trough, i.e. 24 hours post-dose.

Absorption, gastrointestinal transit, and tablet erosion of felodipine extended-release (ER) tablets

The gastrointestinal transit and tablet erosion of felodipine extended release (ER) tablets 10 mg were studied by gamma scintigraphy in eight healthy young males after administration under fasting and nonfasting conditions. Plasma concentrations of felodipine were also measured. Gastric emptying after administration together with food (mean, 3.2 hr) was slower in all subjects compared to emptying under fasting conditions (mean, 0.6 hr). The mean small intestinal transit times for the two study conditions did not differ significantly (5.1 and 4.7 hr, respectively). Tablets did not leave the colon in any subject within 14 hr after administration. Felodipine was shown to be absorbed in the colon, although the major part of the dose was absorbed in the small intestine. The absorption rate of felodipine was related to erosion of the hydrophilic matrix tablet. Tablet erosion and hence drug absorption were slower in the more distal parts of the gastrointestinal tract. Administration together with food did not significantly affect tablet erosion.

The effect of felodipine on the uptake and degradation of acetylated LDL in mouse peritoneal cells and on the distribution of acetylated LDL in macrophage-rich organs of the rat

The effect of felodipine on lipoprotein metabolism ex vivo and in vivo was investigated. In the ex vivo studies mice were given felodipine (40-125 mumol/kg body weight) or vehicle for one week. Peritoneal macrophages from these animals and controls were isolated and used in binding and degradation studies with human iodinated acetylated LDL (Ac-LDL). Macrophages from felodipine-treated mice showed a significant decrease of binding and degradation of Ac-LDL compared to macrophages from control animals (P < 0.05). The in vivo studies were performed in rats pretreated with felodipine or vehicle. To determine the distribution and plasma turnover of LDL and Ac-LDL, 125I-tyramine cellobiose labelled LDL or Ac-LDL were given i.v. No differences in the removal rate of Ac-LDL or LDL were observed between felodipine-treated or untreated rats. However, an increased uptake of Ac-LDL could be seen in the liver of the felodipine-treated rats. This increased uptake could be ascribed to the parenchymal cells because no differences in uptake could be seen in the liver endothelial cells. However, a significant decreased uptake was seen in the Kupffer cells and in the spleen, a macrophage-rich organ, of the felodipine-treated rats. The present study suggests a possible mechanism behind the antiatherogenic effects of calcium antagonists, a decreased uptake of atherogenic modified lipoproteins by peripheral macrophages and an increased uptake by the liver.

Effects of felodipine on utero-placental blood flow in normotensive rabbits

The utero-placental blood flow was investigated in anaesthetized normotensive pregnant rabbits after repeated administration of a high dose of the antihypertensive calcium antagonist felodipine and in untreated controls. By means of the microsphere technique blood flow was also determined in the lungs, skin, intestine, skeletal muscle and kidneys during chloralose anaesthesia. Felodipine reduced mean arterial blood pressure, which was associated with a marked reduction in vascular resistance in the skeletal muscle vascular bed, where blood flow was increased seven-fold. In contrast, blood flow to placentae and kidneys were reduced. The pronounced reduction in placental blood flow may limit foetal nutrition and hence explain reported foetal digital defects after administration of high doses of felodipine to pregnant normotensive rabbits.

Clinical pharmacokinetics of calcium antagonists. An update

The calcium antagonists are valuable and widely used agents in the management of essential hypertension and angina. There is an increasing number of new agents to add to the 3 prototype substances nifedipine, diltiazem and verapamil. These new agents are dihydropyridines structurally related to nifedipine. However, they tend to have longer elimination half-lives (t 1/2 beta) and may be suitable for twice-daily administration. Amlodipine is an exception with a t 1/2 beta in excess of 30h. Apart from elimination rates, however, the pharmacokinetic characteristics of the newer agents have a notable tendency to resemble those of the established agents. They are highly cleared drugs, are relatively highly protein bound. As they are subject to significant first-pass metabolism, old age and hepatic impairment will increase their plasma concentrations due to a reduced first-pass effect. Renal impairment does little to their pharmacokinetics since the fraction eliminated unchanged by the kidney is small. For most agents, plasma concentration-response relationships have been described. Interesting areas for further research include chronopharmacokinetics, stereoselective pharmacokinetics and lipid solubility. Drugs affecting hepatic blood flow and drug metabolising capacity have predictable interaction potential. Some of the newer calcium antagonists will, like verapamil, increase plasma digoxin concentrations. Verapamil and diltiazem decrease phenazone (antipyrine) metabolism and therefore tend to decrease the metabolism of other drugs.

Acute effects of drinking grapefruit juice on the pharmacokinetics and dynamics of felodipine--and its potential clinical relevance

The effect of drinking grapefruit juice on the acute pharmacokinetic and haemodynamic actions of the dihydropyridine calcium antagonist felodipine given as a 5 mg plain tablet has been studied in nine, healthy, middle-aged males. Compared to water, grapefruit juice caused an increase in Cmax from mean 6 to 16 nmol.l-1, and in the AUC from 23 to 65 nmol.h.l-1. The change in AUC corresponded to an increase in the systemic availability of felodipine from 15 to 45%, assuming no change in its clearance. This change was probably caused by inhibition of the oxidation of felodipine to the inactive dehydrofelodipine by flavonoids in grapefruit juice. The interaction with grapefruit juice is believed to be a class effect for the dihydropyridines, as oxidation of the dihydropyridine ring to the corresponding pyridine derivative is a major metabolic route for all these drugs. The higher plasma concentrations of felodipine taken with grapefruit juice resulted in a greater change in blood pressure measured in the morning 3 h after dosing (-9%) than did water (0%).

Twenty-four hour blood pressure profiles in hypertensive patients following various formulations and dosage regimens of felodipine

The blood pressure lowering capacity of felodipine administered either as extended release tablets once or twice daily or as plain tablets twice daily has been compared in a double-blind, three-way cross-over study in 16 hypertensive patients. All the patients were on long-term treatment with 10 or 20 mg felodipine daily and other antihypertensive therapy (mainly beta-blockers) was allowed if it was kept unchanged. Non-invasive blood pressure and heart rate recordings were obtained throughout 24 hour periods using an Accutracker ambulatory system. The 24 h mean systolic and diastolic blood pressures after extended release tablets o.m. did not differ significantly from those after extended release tablets b.d. or plain tablets b.d. There was a tendency for the extended release tablets given o.m. to reduce blood pressure somewhat more in the morning, and for the extended release tablets b.d. to reduce blood pressure more during the night than the other treatments. Mean 24 h heart rate after all treatments was comparable. Manual recordings confirmed these results. Blood pressure was well-controlled throughout the 24 h period by all three treatments. The extended release tablets tended to give less extreme plasma concentrations of felodipine. This may be of value for patients with adverse vasodilator effects. For a majority of hypertensive patients the adequacy of blood pressure control and the simplicity of once daily dosing will favour the extended release tablet given once daily.

Felodipine clinical pharmacokinetics

Absorption of felodipine is rapid and complete. A pronounced first-pass metabolism results in a bioavailability of 15%, irrespective of the oral formulation used. The peak plasma concentrations and area under the plasma concentration-time curve are linearly related to the dose. The variability in plasma concentrations is wide, and individualization of the dosage is recommended. Plasma felodipine concentrations are increased in the elderly, and in patients with congestive heart failure or liver cirrhosis; in these patients felodipine should be started at a low dosage. Food intake has no clinically significant effect on felodipine absorption. Serum digoxin concentrations are increased by felodipine in plain tablet form, but not when it is administered as extended release tablets. Activators, inducers and inhibitors of the cytochrome P450 system affect the plasma concentrations of felodipine. No displacement reactions with high affinity protein binding drugs have been observed. There is a significant correlation between plasma concentration and haemodynamic effect. The mean elimination half-life of 24h together with the extended release formulation of felodipine favours once-daily dosage in patients with hypertension.

Central and peripheral haemodynamic responses to felodipine in congestive heart failure

Using non-invasive radionuclide techniques, we studied the arterial and venous effects of 0.1 mg/kg oral felodipine in 12 men with heart failure due to ischaemic heart disease aged 37-72 y. All were in New York Heart Association Class II or III, required frusemide 40-120 mg daily and were clinically stable. Felodipine produced significant falls in blood pressure (-19%) and systemic vascular resistance (-39%) with increases in cardiac index (+34%), heart rate (+12%) and left ventricular ejection fraction (from 0.25 to 0.32). Peripheral venous volume fell by 10.6% after felodipine indicating venoconstriction rather than venodilatation and may be caused by an acute sympathetic reflex associated with the increase in heart rate. Our results confirm that felodipine is an arterial vasodilator. The previously observed changes in cardiac filling pressures may simply represent improved ventricular function as a consequence of reduced afterload, not venodilatation.

Pharmacokinetics of felodipine in chronic hemodialysis patients

Five chronic hemodialysis patients (1 woman and 4 men, aged, 46-68 yr) were given an oral dose of 10 mg felodipine followed by 0.057 mg [3H] felodipine IV. After 5 hours, a hemodialysis treatment lasting 4 hours was performed. Blood and dialysate flows were 200 mL/min and 500 mL/min, respectively. Capillary dialyzers with 1.3 m2 cellulose acetate membrane were used. The pharmacokinetic characteristics and reduction in diastolic BP were similar to those in hypertensive patients with normal renal function and in uremic patients who were not treated with dialysis. There was no measurable removal of felodipine by hemodialysis. Dialyzer clearance of radioactive metabolites was about 10 mL/min, and only 8.9% of the dose was eliminated by the treatment. The half-life of radioactive metabolites was 10 days (6-14 days) in three patients dialyzed thrice weekly. Since the metabolites are biologically inactive, no adjustment of dose is required in hemodialysis patients.

Evaluation of the antianginal effect of nifedipine: influence of formulation dependent pharmacokinetics

Nifedipine capsules t.d.s. and an extended release formulation of nifedipine, nifedipine-ER tablets, given once daily in corresponding daily doses, have been compared with placebo in a double-blind, three-way cross-over study in 24 patients with stable angina pectoris. The objective was to study the influence on the antianginal effect of the different pharmacokinetics of several preparations of nifedipine. All patients received concomitant treatment with beta-adrenoceptor blockers. Antianginal efficacy was assessed by a dynamic exercise test at the end of the dosage intervals, i.e. 8 and 24 h after nifedipine capsules and nifedipine-ER, respectively, as well as 6 h after dosing. Six h after dosing the time of onset of chest pain and total exercise time were longer and total work was significantly higher during both nifedipine-ER (plasma concentration 260 nmol/l) and placebo treatment than after nifedipine capsules (plasma concentration 78 nmol/l). Time to 1 mm ST depression was longer during nifedipine-ER than during nifedipine capsule treatment. No significant difference was seen between nifedipine-ER and placebo. At the end of the dosage interval (24 and 8 h after nifedipine-ER and nifedipine capsules, respectively), no significant difference was found between nifedipine-ER (plasma concentration 75 nmol/l) and the other two treatments. However, placebo was superior to nifedipine capsules (plasma concentration 58 nmol/l) both in the time to onset of chest pain and total exercise time. The lack of effect at the end of the dosage interval was probably due to the subtherapeutic plasma nifedipine level.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of felodipine and its metabolites in plasma using capillary gas chromatography with electron-capture detection and their identification by gas chromatography-mass spectrometry

A novel method for the determination of felodipine and its metabolites in plasma by capillary gas chromatography (GC) with electron capture detection was developed. Felodipine and its oxidized metabolite were assayed by capillary GC after solid-phase extraction with the aid of a cool on-column injection technique. Acid metabolites, methyl monoacid and ethyl monoacid and diacid, were extracted with diethyl ether and propylated with 1-n-propyl-3-p-tolyltriazene before being submitted to capillary GC. These methods were very sensitive and useful for the pharmacokinetic study of felodipine. Felodipine and its metabolites were identified by GC-mass spectrometry. The mass spectral patterns of the peaks of extracts from human plasma samples after oral administration of felodipine were in good agreement with those of reference compounds.

Attenuation of renal ischaemic injury by felodipine

Felodipine is a vasodilating calcium channel blocker of the dihydropyridine type. The effects of felodipine on post-ischaemic renal function were evaluated in rats subjected to bilateral renal artery occlusion for 30 or 60 min. In a first set of experiments the recovery of renal function after 30 or 60 min of renal artery occlusion was followed intermittently for 16 days by endogenous creatinine clearance. Renal function was better preserved in rats given felodipine (45 nmol/kg i.v.) during the occlusion period than in vehicle-treated control rats. The survival rate after 60-min occlusion was 11% in controls but 70% in the felodipine-treated rats. After occlusion for 30 min the survival rate was similar in the two groups, but renal function recovered faster in the felodipine group than in the controls. In a second series, acute renal damage was evaluated by the extent of erythrocytes trapped in the kidney after 30-min reperfusion following 60-min renal artery occlusion. Felodipine administration (45 nmol/kg) during the occlusion reduced renal damage compared with vehicle controls. Kidney weight and systemic haematocrit were also better maintained in the felodipine-treated rats. Furthermore, renal damage was reduced by the t-butyl analogue or felodipine. H 186/86, which is devoid of vasodilatory effects. The results demonstrate that treatment with the vasodilator calcium channel blocker felodipine protects the kidney from ischaemic/reperfusion injuries. The tissue protection is not related to the haemodynamic effects alone, since the haemodynamically inactive dihydropyridine H 186/86 also reduced the extent of renal damage. An additional antiperoxidant or scavcnger-like effect inherent in the dihydropyridine molecule is suggested.