High performance liquid chromatography of mebudipine: application to pharmacokinetic study

PURPOSE

To develop a high performance liquid chromatography system for the determination of a new 1,4-dihydropyridine, mebudipine, in rabbit plasma.

METHODS

To 1 ml of rabbit plasma was added internal standard (dibudipine) and 0.5 ml of 1 M NaOH. Mebudipine and internal standard were extracted to 5 ml ethyl acetate, evaporated under slow stream of nitrogen. The residue was reconstituted in 200 microl mobile phase and 20 microl of aliquots were injected into a HPLC system equipped with 4.6 x 250 mm i.d. C18 analytical column. Mobile phase consisted of methanol (70%), water (25%) and acetonitril (5%) and its flow rate was 1 ml/min.

RESULTS

There were no interfering peaks from endogenous components in blank plasma chromatograms. Standard curves were linear (r(2)>0.99) over 10 to 500 ng/ml. The extraction efficiency was >90% and the minimum quantifiable concentration was 10 ng/ml (CV<10%).

CONCLUSION

A suitable, convenient and simple HPLC assay for pharmacokinetic study of mebudipine in rabbits was developed.

A double masked placebo controlled study on the effect of nifedipine on optic nerve blood flow and visual field function in patients with open angle glaucoma

AIMS

To investigate whether nifedipine affects ocular perfusion or visual fields in open angle glaucoma patients.

METHODS

In a parallel group study nifedipine or placebo was administered for 3 months (n = 30). Ocular fundus pulsation amplitude (FPA), cup blood flow (Flowcup) and visual field mean deviation (MD) were measured.

RESULTS

Five patients receiving nifedipine discontinued due to adverse events. Nifedipine did not affect FPA [difference: 0.3 microm (95% CI -0.3,0.9); P = 0.70], Flowcup: [difference: -9 rel.units (95% CI -133,114); P = 0.99], or MD [difference: 0.2dB (95% CI -2.2,2.7); P = 0.51] vs placebo.

CONCLUSIONS

Systemic nifedipine is not well tolerated in glaucoma patients and exerts no effect on visual fields or ocular perfusion.

Fatal nifedipine ingestions in children

Nifedipine is a prototypical dihydropyridine calcium channel "blocker" that can cause hypotension and cardiac conduction abnormalities. When compared to other calcium channel antagonists, overdoses have been reported to be relatively benign with treatment consisting mainly of supportive care. We report two pediatric cases of death secondary to accidental ingestion of long acting nifedipine (Adalat). Both cases did not respond to aggressive supportive care that included calcium, atropine, epinephrine, glucagon, sodium bicarbonate, and transthoracic pacing.

Race and sex influence clearance of nifedipine: results of a population study

OBJECTIVE

To estimate oral clearance of nifedipine and to determine demographic and clinical covariates that affect nifedipine clearance in a clinical population.

METHODS

Apparent oral clearance of nifedipine and protein binding were measured in 226 patients receiving sustained-release nifedipine formulations for hypertension and coronary artery disease (black men, n = 111; black women, n = 27; white men, n = 64; white women, n = 24). Mean age +/- SD was 71 +/- 11 years, and mean weight was 86 +/- 17 kg. Nifedipine concentrations were analyzed by HPLC, protein binding was measured by equilibrium dialysis, clearance and covariate effects were estimated by a nonlinear mixed effects population model, and statistical analyses were performed by a nonlinear mixed-effects model (clearance) and ANOVA (protein binding).

RESULTS

Clearance was significantly slower in black subjects (8.9 +/- 0.7 mL/min/kg; mean +/- SE) compared with white subjects (11.6 +/- 0.8 mL/min/kg; P = .00004) and in men compared with women (9.3 +/- 0.6 versus 12.1 +/- 1.5 mL/min/kg; P = .0021). Reported alcohol use (alcohol, 8.6 +/- 1.1 versus no alcohol, 10.8 +/- 0.6 mL/min/kg; P = .0002) and smoking status (smoker, 8.8 +/- 2.0 versus nonsmoker, 10.2 +/- 0.6 mL/min/kg; P = .0362) also affected nifedipine clearance. Race and sex had no effect on protein binding of nifedipine (P = .29 and P = .44, respectively). No effects of age, stable coronary artery disease, or reported intake of beta-blockers on nifedipine clearance were detected in this primarily elderly population with hypertension.

CONCLUSIONS

The data suggest that race, sex, and environmental factors are identifiable sources of interindividual variation in the oral clearance of nifedipine, a CYP3A substrate. Our experience also suggests that data from clinical populations may be biased with regard to age, sex, and formulation selection, and covariates may not be independently distributed, which can limit analyses.

Effect of hydroxypropylmethylcellulose (HPMC) on the release profiles and bioavailability of a poorly water-soluble drug from tablets prepared using macrogol and HPMC

The aim of the present study was to investigate the effect of hydroxypropylmethylcellulose (HPMC-2208), used as an excipient for controlled release of drug, on the release profiles and bioavailability of the poorly water-soluble nifedipine (NP) from a tablet prepared using macrogol 6000 (PEG) and HPMC. The crushing tolerance of the NP tablet prepared using PEG and HPMC (NP-PEG-HPMC tablet) was markedly increased with increasing compression force used during the preparation from 20 to 200 MPa. The values reached their maximal levels (approximately 13 kg for the NP-PEG-HPMC tablet and 8 kg for the PEG tablet) at the compression force of 100 MPa. Although NP is a poorly water-soluble drug, it was rapidly dissolved from the NP-PEG tablet (without HPMC) due to the improvement of its dissolution rate in the presence of PEG. NP dissolution was complete at the latest within 1 h. On the other hand, dissolution of NP from the NP-PEG-HPMC tablet was significantly delayed with an increase in the concentration of HPMC in the tablet. The dissolution of NP from the NP-PEG-HPMC tablet containing 50% HPMC-2208 was markedly delayed as the viscosity of HPMC also increased. Interestingly, the same peak plasma NP concentration (C(max)) and the area under the plasma NP concentration-time curve (AUC(0-10)) were observed for both the NP-PEG tablet and NP-PEG-HPMC tablets, however, the time to C(max) (t(max)) for the NP-PEG-HPMC tablet was significantly higher when the NP-PEG-HPMC tablet was orally administered to rabbits. We describe here a preparation method of a new sustained-release NP-PEG-HPMC tablet using a mixture of NP-PEG granules (prepared with PEG) and HPMC.

Trace-level determination of nifedipine in human serum by reversed phase high performance liquid chromatography

A rapid, simple, specific and sensitive high performance liquid chromatographic method has been developed for the determination of nifedipine (adalate) in human serum using diazepam (valium) as an internal standard (I.S.). The method utilized a 5 microm nonpolar C18 reversed phase Hypersil (ODS) column (250 x 3 mm i.d.). The mobile phase consisted of 60% v/v, acetonitrile in water, adjusted to pH 3.7 with glacial acetic acid and ammonium acetate, and pumped at a flow rate of 2 ml/min. The effluent was monitored by UV detection at 340 nm and a sensitivity fixed at 0.02 aufs. Each analysis required no longer than 4 min. The minimum detectable amount of nifedipine in serum was 3 ng/ml, and the mean absolute recovery was 93.5%. The within and between-day coefficients of variation at three different concentrations from 15-160 ng/ml ranged from 2.07 to 7.76%, and from 3.15 to 7.98% respectively. Calibration graphs for 10 to 200 ng/ml were linear with a mean correlation coefficient, r (n = 36) of 0.9991. The method was validated for accuracy, sensitivity, selectivity and reproducibility and finally was utilized and proved to be suitable in a bioavailability study of two products of nifedipine following oral administration to healthy male subjects.

The effect of whole-body sunbed ultraviolet A exposure on the pharmacokinetics of the photolabile drug nifedipine

The calcium antagonist nifedipine absorbs ultraviolet A (UVA) radiation and readily photodegrades in vitro to a toxic nitroso-pyridine photoproduct. We examined whether whole body exposure of normal subjects to sunbed UVA radiation would affect the pharmacokinetics of nifedipine. Eight healthy, male, Caucasian volunteers (phototypes I-III) participated in this ethically approved, randomised, cross-over study. Each subject attended on 2 occasions, one week apart, and on each occasion was given a single oral dose (10 mg) of nifedipine following which blood samples were collected at 0, 0.5, 1. 1.5, 2, 2.5, 3, 3.5, 4, 5, 6 and 7 h. During one of the visits, 15 min after nifedipine ingestion, a whole-body UVA (sunbed comprising Philips R-UVA lamps) dose of 70% of the individual's predetermined minimal phototoxic dose was delivered over a period of 17-36 min. Plasma nifedipine levels were measured using a standard reverse-phase high-performance liquid chromatography method. The area under the plasma concentration-time curve (AUC) of nifedipine during the UVA irradiation session (median 206 ng x ml(-1) x h(-1)) was significantly higher than during the non-irradiation control session (median 174.5 ng x ml(-1) x h(-1)) (P=0.03; 95% C.I. for difference in medians 9.9 to 55.9 ng x ml(-1) x h(-1)). UVA irradiation did not significantly affect any of the other measured pharmacokinetic parameters (Cmax, t 1/2, tmax). We demonstrate that sunbed UVA irradiation does not lead to in vivo photodegradation of nifedipine in healthy humans after a single dose. The apparent increase in AUC during UVA irradiation may be due to slightly slower metabolism of nifedipine in the presence of toxic photoproduct(s) or due to blood distribution changes affecting liver blood flow.

Assessment of bioavailability of experimental controlled release microcapsules of nifedipine

Experimental controlled release nifedipine microcapsules composed of ethylcellulose and eudragit RL were explored for the assessment of bioavailability on rabbit. The pharmacokinetic parameters were compared between the formulations and with the pure drug material. A statistically significant difference between the formulations was noticed in the parameters, K, T1/2, AUC (0-->infinity), MRT and bioavailability but not in Vd, Cmax and Tmax and in each case a highly significant difference was observed with reference drug material. Controlled release absorption profiles in vivo were observed from the experimental microcapsules as revealed by the Wagner-Nelson method. The absorption lag time, absorption rate constant, and absorption half life were calculated by using the back projection method of residuals. A good correlation demonstrated between in vivo absorption and in vitro release data for both the products merits specific attention. There was no loss in bioavailability of the experimental ethylcellulose microcapsule (drug content 75.8%), even though nifedipine undergoes extensive first pass metabolism.

Effects of combined oral treatments with cyclosporine A and nifedipine or diltiazem on drug-induced gingival overgrowth in rats

BACKGROUND

Cyclosporine A (CsA) and calcium channel blockers induce gingival overgrowth in humans and animals. Recently, nifedipine and diltiazem have often been used to control CsA-related hypertension in organ transplant patients. The purpose of this study was to examine the effects of a combined oral treatment of CsA and nifedipine or diltiazem on the severity of gingival overgrowth in rats.

METHODS

Fifteen-day-old Fischer rats were treated orally with single or combined applications of CsA, nifedipine, and/or diltiazem for 40 days; and induced gingival overgrowth, rat growth, and blood drug levels were compared among the different experimental groups. The experiment consisted of 6 groups: one control group (group A) and 5 test groups treated with CsA (group B), nifedipine (group C), and diltiazem (group D), as well as those concurrently treated with CsA and nifedipine (group E), and CsA and diltiazem (group F). Gingival overgrowth was determined by measuring the depth of the gingival sulcus.

RESULTS

The mandibular buccal gingival sulcus depth of group A was 365 +/- 41.2 microm. Among the test groups, the most remarkable gingival overgrowth was seen in group E (1,020 +/- 63.3 microm), followed by group F (895 +/- 43.8 microm), group B (870 +/- 48.3 microm), group C (525 +/- 116 microm), and then group D (505 +/- 83.2 microm). Rat body weight gain was reduced significantly by oral CsA treatment. Neither nifedipine nor diltiazem suppressed rat growth when used independently; however, rat growth reduced by CsA was further suppressed by a combined use of diltiazem, but not nifedipine. CsA blood levels were reduced by concurrent oral treatment with nifedipine or diltiazem along with the blood levels of those calcium channel blockers when treatment was in combination with CsA.

CONCLUSIONS

These results suggest that gingival overgrowth is induced in rats as a side effect of CsA, nifedipine, or diltiazem, and the combined use of these drugs influences rat growth, blood drug levels, and the severity of gingival overgrowth.

Liquid chromatographic assay of nifedipine in human plasma and its application to pharmacokinetic studies

A highly sensitive, selective and reproducible reversed-phase high-performance liquid chromatographic method has been developed for the determination of nifedipine in human plasma with minimum sample preparation. The method is sensitive to 3 ng/ml in plasma, with acceptable within- and between-day reproducibilities and linearity (r2 > 0.99) over a concentration range from 10-200 ng/ml. Acidified plasma samples were extracted using diethyether containing diazepam as internal standard and chromatographic separation was accomplished on C18 column using a mobile phase consisting of acetonitrile, methanol and water (35:17:48, v/v). The within-day precision ranged from 2.22 to 4.64% and accuracy ranged from 102.4-106.4%. The day-to-day precision ranged from 2.34-7.07% and accuracy from 95.1-100.1%. The relative recoveries of nifedipine from plasma ranged from 91.0-107.3% whereas extraction recoveries were 88.6-93.3%. Following eight 6-week freeze-thaw cycles, nifedipine in plasma samples proved to be stable with accuracy ranging from 0.64 to 3.0% and precision ranging from 3.6 to 4.15%. Nifedipine was also found to be photostable for at least 120 min in plasma, 30 min in blood and for 60 min in aqueous solutions after exposure to light. The method is sensitive and reliable for pharmacokinetic studies and therapeutic drug monitoring of nifedipine in humans after the oral administration of immediate-release capsules and sustained-release tablets to five healthy subjects.

Quantitation of nifedipine in human plasma by on-line solid-phase extraction and high-performance liquid chromatography

An analytical methodology for nifedipine quantitation in plasma by on-line solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) is described. The SPE cartridges contain C2 and the analytes nifedipine and nitrendipine (internal standard) are separated on a C18 column with a mobile phase consisting of acetonitrile-13 mM phosphate buffer pH 7 (65:35, v/v) followed by UV detection at 338 nm. Validation of the method demonstrated good recoveries (>90%), sensitivity (limit of quantification, 2 ng/ml), based on a 500 microl sample volume, accuracy and precision (<5.5% in concentrations greater than the limit of quantitation). This methodology has been used for bioequivalence studies.

Sympathoinhibition by central and peripheral infusion of nifedipine in spontaneously hypertensive rats

The present study assessed whether central mechanisms may contribute to the hypotensive effect of the calcium channel blocker nifedipine. In conscious, spontaneously hypertensive rats (SHR) on a high-salt diet, hemodynamic (mean arterial pressure [MAP] and heart rate) and sympathetic (renal sympathetic nerve activity) responses to low, central, intracerebroventricular infusion rates (25 microg. kg(-1). h(-1) for 2 hours) and peripheral intravenous rates (50 microg. kg(-1). h(-1) for 3 hours and then 100 microg. kg(-1). h(-1) for 2 hours) of nifedipine were evaluated. The distribution of nifedipine in the blood and tissues was assessed at the end of the infusions. Nifedipine significantly inhibited renal sympathetic nerve activity and lowered MAP in SHR beginning 30 minutes after the start of the intracerebroventricular infusion. The decrease of MAP by intravenous infusion began at 60 minutes and was more profound with 100 microg. kg(-1). h(-1). Inhibition of sympathetic activity preceded and then paralleled the decrease in blood pressure; it occurred earlier with central (15 to 30 minutes) than with peripheral (30 to 60 minutes) infusion. Intravenous infusion resulted in concentrations of nifedipine in brain structures (brain stem, midbrain, and cortex) that were 30% to 40% of those in the heart, kidneys, and liver. From the hemodynamic and sympathetic responses and the distribution of nifedipine into the central nervous system, we conclude that the peripheral infusion of nifedipine at relatively low rates may evoke a hypotensive response in SHR, not only via peripheral mechanisms, but also through central mechanisms, which will lead to an inhibition of sympathetic outflow and, therefore, a lowering of blood pressure.

Rosiglitazone has no clinically significant effect on nifedipine pharmacokinetics

To examine the effects of repeat oral dosing of rosiglitazone on the pharmacokinetics of nifedipine, a prototype CYP3A4 substrate, a randomized, open-label, crossover study was performed with two treatment phases separated by a washout period of at least 14 days. Twenty-eight healthy male volunteers received either a single 20 mg oral nifedipine dose or rosiglitazone 8 mg orally once daily for 14 days with a single 20 mg oral nifedipine dose administered on day 14. Plasma nifedipine concentrations were determined over the 24-hour period following administration of the nifedipine doses. Lack of effect was defined as the demonstration that the 90% CI was contained entirely within a symmetrical 30% range either side of unity on the loge-scale. Following rosiglitazone + nifedipine administration, the area under the nifedipine concentration-time curve from time zero to infinity (AUC(0-infinity)) was 13% lower than that after administration of nifedipine alone. This difference in nifedipine AUC(0-infinity) was not deemed to be clinically significant since the 90% CI was contained within the protocol-defined 30% range (point estimate for ratio of geometric means 0.87; 90% CI: 0.79, 0.96). Rosiglitazone had no marked effect on nifedipine peak plasma concentration (point estimate: 0.99; 90% CI: 0.73, 1.34) or time to peak concentration compared with nifedipine alone. Rosiglitazone coadministration produced a small decrease in the mean nifedipine half-life (point estimate: -0.77; 90% CI: mean difference -1.29 h, -0.25 h). Both treatment regimens were well tolerated and associated with a favorable safety profile. Rosiglitazone, at the highest dose used in clinical studies, produced a small, clinically insignificant decrease in nifedipine exposure. The very small effect on nifedipine pharmacokinetics suggests that rosiglitazone is an extremely weak inducer of CYP3A4, a characteristic that distinguishes rosiglitazone from troglitazone.

Plasma concentration and CNS effects of Ca antagonists darodipine and nimodipine after single-dose oral administration to healthy volunteers

The dynamics at the brain level (quantitative EEG), plasma kinetics and effects on blood pressure and heart rate of the Ca antagonists, darodipine (slow-release, 50- 200 mg) and nimodipine (30 mg), were compared in a double-blind cross-over study on healthy volunteers during a 9-hour period following single drug/placebo administration. Increased EEG total power was observed after 100 and 200 mg daropidine; a concomitant decrease of 14.5-32.0 Hz relative power was observed at 100 mg. The 50-mg dose proved ineffective. These effects were correlated with the darodipine plasma concentration only at the 100-mg dose, with indications of an active concentration interval at approximately 5-10 ng/ml; a reduction in diastolic blood pressure and increased heart rate proved to be linearly correlated with the drug plasma concentration throughout the entire concentration range. Comparable EEG effects were observed after nimodipine, but they did not correlate with the plasma concentration. Implications of the predictability of the brain effect from the drug plasma concentration and differential thresholds for the brain action and effects on (peripheral) circulation are suggested.

Sensitive high-performance liquid chromatographic determination of nifedipine in cat plasma following improved sample treatment

A simple, easy and accurate reversed-phase high-performance liquid chromatographic method is described for the determination of nifedipine in cat plasma. The procedure involves extraction of nifedipine from plasma using a Sep-Pak C18 cartridge and ultraviolet detection at 350 nm. The present method provides the required reproducibility and sensitivity for the determination of low concentrations of nifedipine without interference from plasma components or photodegradation products. The method was validated over the range 1-50 ng/ml nifedipine. Accuracy and precision were, respectively, 97% or more and 5% or less over the concentration range examined. The minimum quantifiable concentration of nifedipine was found to be 1 ng/ml.

Effect of Ca2+ channel blockers on arterial hypertension and heart ischaemic lesions induced by chronic blockade of nitric oxide in the rat

The effects of the Ca2+ channel blockers diltiazem, nifedipine and amlodipine were investigated on both arterial hypertension and myocardial changes induced by chronic blockade of nitric oxide synthesis. Control male Wistar rats received Nomega-nitro-L-arginine methyl ester (L-NAME; 20 mg rat(-1) day(-1)) in the drinking water for 8 weeks; blood pressure and body weight were monitored weekly. The Ca2+ channel blockers were given concomitantly to L-NAME, as follows: diltiazem (13.5 mg rat(-1) day(-1)) and amlodipine (6.25 mg rat(-1) day(-1)) were administered in the drinking water whereas nifedipine (6.25 mg rat(-1) day(-1)) was given in the chow. Nomega-nitro-L-arginine methyl ester induced a time-dependent increase in blood pressure which was significantly attenuated by diltiazem (154+/-1.6 vs. 139+/-1.6 mm Hg, p < 0.05), nifedipine (166+/-2.7 vs. 150+/-2.1 mm Hg, p < 0.05) and amlodipine (208+/-5.8 vs. 158+/-1.8 mm Hg, p < 0.05) at the last week of the treatment. Rats treated with the L-NAME also developed myocardial ischaemia, as indicated by the increased percentage of fibrous tissue found in the left ventricles of these animals (10.9+/-0.1%, p < 0.01) when compared to control ones (6.3+/-0.1%). Neither diltiazem (14.9+/-1.2%) nor nifedipine (11.1+/-1.5%) prevented this effect whereas amlodipine (6.9+/-1.1%, p < 0.01) virtually abolished the increase in fibrous tissue induced by L-NAME. The plasma concentration of the Ca2+ channel blockers was measured by liquid chromatography coupled to mass spectrometry at two different time points (morning and afternoon). Only amlodipine treatment was able to maintain constant levels (186+/-46 ng ml(-1) in the morning and 110+/-19 ng ml(-1) in the evening) compared to nifedipine (3003+/-578 ng ml(-1) in the morning and 436+/-100 ng ml(-1) in the evening) and diltiazem (77+/-51 ng ml(-1) in the morning and not detectable in the evening). In conclusion, our results indicate that amlodipine (but not diltiazem and nifedipine) can efficiently control myocardial ischaemia in nitric oxide deficient rats, probably due to its intrinsically long half-life.

Pharmacokinetics of chlorpheniramine, phenytoin, glipizide and nifedipine in an individual homozygous for the CYP2C9*3 allele

Genetic polymorphisms in the cytochrome P450 (CYP) family are widely known to contribute to interindividual differences in the pharmacokinetics of many drugs. Several alleles for the CYP2C9 gene have been reported. Individuals homozygous for the Leu359 variant (CYP2C9*3) have been shown to have significantly lower drug clearances compared with Ile359 (CYP2C9*1) homozygous individuals. A male Caucasian who participated in six bioavailability studies in our laboratory over a period of several years showed extremely low clearance of two drugs: phenytoin and glipizide (both substrates of CYP2C9), but not for nifedipine (a CYP3A4 substrate) and chlorpheniramine (a CYP2D6 substrate). His oral clearance of phenytoin was 21% of the mean of the other 11 individuals participating in the study, and his oral clearance of glipizide, a second generation sulfonylurea structurally similar to tolbutamide, was only 188% of the mean of the other 10 individuals. However, his oral clearance of nifedipine and chlorpheniramine did not differ from individuals in other studies performed at our laboratories. An additional blood sample was obtained from this individual to determine if he possessed any of the known CYP2C9 or CYP2C19 allelic variants that would account for his poor clearance of the CYP2C9 substrates (phenytoin and glipizide) compared with the CYP3A4 (nifedipine) and CYP2D6 (chlorpheniramine) substrates. The results of the genotype testing showed that this individual was homozygous for the CYP2C9*3 allele and did not possess any of the known defective CYP2C19 alleles. This study establishes that the Leu359 mutation is responsible for the phenytoin and glipizide/tolbutamide poor metabolizer phenotype.

Pharmacokinetic interaction of Diabecon (D-400) with rifampicin and nifedipine

In the present study, Diabecon (D-400), a herbomineral anti-diabetic preparation, was studied for its pharmacokinetic interaction with the commonly used drugs rifampicin and nifedipine. Interaction of Diabecon with rifampicin: The pharmacokinetic interaction of rifampicin and Diabecon (D-400) was studied in animal models as well as in healthy human volunteers. Twelve rabbits were divided into two groups of six each. Animals in group I were treated with rifampicin (100 mg/kg body weight, p.o.) and group II with rifampicin (100 mg/kg body weight, p.o.) and Diabecon (D-400) (1 g/kg body weight, p.o.) for a period of 8 days. Rifampicin levels in plasma were estimated on day 1 and day 8 at 2, 4, 6 and 8 h after drug administration. On the basis of these findings, a clinical study in 9 healthy human volunteers aged 25-35 years and weighing 50-75 kg was initiated. They were given 450 mg of rifampicin once only on day 1 and from the second day onwards were given 2 tablets of Diabecon (D-400) twice daily for 7 days. On day 9, another dose of rifampicin (450 mg) was given along with 2 tablets of Diabecon (D-400). Blood samples were collected at 2, 4, 6 and 8 h after drug administration on day 1 and day 9 to estimate the rifampicin levels in plasma. Interaction of Diabecon with nifedipine: In another study, 12 rabbits were divided into two groups of 6 each. Group I animals were treated with nifedipine (2.5 mg/kg body weight, p.o.) and Group II animals were treated with nifedipine (2.5 mg/kg body weight, p.o.) and Diabecon (D-400) (1 g/kg body weight, p.o.) for a period of 8 days. On day 1 and day 8, blood samples were collected at 1, 2, 4 and 6 h after drug administration and plasma nifedipine levels were estimated. The results of these three studies revealed that Diabecon (D-400) did not alter the pharmacokinetic profiles of rifampicin and nifedipine.

Simultaneous determination of nifedipine and dehydronifedipine in human plasma by liquid chromatography-tandem mass spectrometry

Quantitative analysis of therapeutic compounds and their metabolites in biological matrix (such as plasma, serum or urine) nowadays requires sensitive and selective methods to allow the determination of concentrations in the ng/ml range. A new on-line LC-MS-MS method using atmospheric pressure chemical ionisation (APCI) as interface for the simultaneous determination of nifedipine (NIF) and its metabolite in human plasma, dehydronifedipine (DNIF) has been developed. The compounds were extracted from plasma using solid-phase extraction (SPE) on disposable extraction cartridges (DECs). The SPE operations were performed automatically by means of a sample processor equipped with a robotic arm (ASPEC system). The DEC filled with phenyl modified silica was first conditioned with methanol and water. The washing step was performed with water. Finally, the analytes were successively eluted with methanol and water. The liquid chromatographic (LC) separation of NIF and DNIF was achieved on a RP-18 stationary phase (4 microm). The mobile phase consisted of methanol-50 mM ammonium acetate solution (50:50, v/v). The LC was then coupled to tandem mass spectrometry with an APCI interface in the positive ion mode. The method developed was validated. The absolute recoveries evaluated over the whole concentration range were 95+/-2% and 95+/-4% for NIF and DNIF, respectively. The method was found to be linear in the 0.5-100 ng/ml concentration range for the two analytes (r2 = 0.999 for both NIF and DNIF). The mean R.S.D. values for repeatability and intermediate precision were 2.9 and 3.0% for NIF and 2.2-4.7% for the metabolite. The method developed was successfully used to investigate the plasma concentration of NIF and DNIF in the pharmacokinetic studies.

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.

Effects of treatment with nilvadipine on cerebral ischemia in rats

The protective effects of a Ca2+ antagonist, nilvadipine, on focal cerebral ischemia were studied in male spontaneously hypertensive rats. The animals received either nilvadipine (3mg x kg(-1) x day(-1)) or a vehicle subcutaneously. Group 1 (n=11) was treated for 7 days, and Group 2 (n=11) for 14 days. The middle cerebral artery was occluded on the 6th (Group 1) or 13th (Group 2) day of the treatment, and neuropathological outcomes were quantified 24 hours later. The mean arterial blood pressure was significantly reduced with nilvadipine to normal levels. The % infarct volumes of Groups 1 (37+/-2) and 2 (34+/-3) were significantly less than those of their controls (39+/-3 [n=11] and 40+/-4 [n=12], respectively), although the difference between Groups 1 and 2 was not significant. When infarct areas were compared in each of 8 coronal sections, the infarct size had decreased in the 5 posterior sections in Group 2, but only in 2 sections of Group 1. A significant decrease in the edema volumes was observed in Group 2, but not in Group 1. Thus, nilvadipine provided protective effects against cerebral ischemia in rats having chronic hypertension, and the effects were dependent on the duration of treatment.

Determination of nifedipine in human plasma by flow-injection tandem mass spectrometry

For use in clinical studies, a fast and sensitive assay method was developed for the determination of nifedipine in human plasma samples. The assay method is based on tandem mass spectrometry detection (HPLC-MS-MS). The effect of flow injection as well as HPLC separation on the results of the nifedipine determination were evaluated. The limit of quantification is 0.5 ng/ml and the accuracy (as determined by spiking recovery) was found to be good.

Food interaction pharmacokinetic study of cordaflex 20 mg retard filmtablet in healthy volunteers

The aim of the present study was to investigate the effect of food consumption on the pharmacokinetics of Cordaflex 20 mg retard filmtablet in healthy volunteers through measuring nifedipine plasma levels by an HPLC-ED method both after fasting and food ingestion. The food interaction pharmacokinetic study of Cordaflex 20 mg retard filmtablet was carried out in 12 healthy male volunteers treated with a single dose of the preparation both after fasting and after food ingestion, in a crossover design allowing 1 week of wash-out period between the 2 treatments. Nifedipine concentration of plasma samples were determined by an isocratic HPLC-ED method [Horvai et al. 1994] with robotic sample processing [Horváth et al. 1995, 1996]. The pharmacokinetic parameters (AUC0-infinity, AUC0-t, Cmax, MRT) were analyzed by calculating 90% confidence interval for logarithmic transformed test/reference ratio values, and Schuirmann's statistical tests, the tmax and HVD values were analyzed by Wilcoxon's nonparametric statistical test. The above statistical tests of the present food interaction study indicated significant differences for each one of the respective pharmacokinetic parameter pairs calculated for treatments after fasting and after food ingestion. On the basis of the above findings and also by comparing the mean pharmacokinetic curves, it was evident, that, in agreement with the data of literature [Kleinbloesem et al. 1993, Schall et al. 1994], food ingestion increased the relative bioavailability and maximum plasma concentration (Cmax). Considering the average of the parameter values and also the respective statistical tests, it was also apparent that the time to maximum plasma concentration (tmax), the mean residence time (MRT), and the half-value duration (HVD) all decreased significantly upon the effect of food ingestion.

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.

Steady-state trough plasma mibefradil concentrations and correlation to blood pressure response in hypertensive patients with chronic renal disease

Mibefradil is a calcium antagonist approved for the treatment of hypertension and chronic stable angina pectoris. To investigate the relationship between steady state, trough plasma concentrations and blood pressure response in patients with renal dysfunction, data from a multicenter, multiple-dose mibefradil study were analyzed. Changes in sitting diastolic blood pressure from baseline were linearly related to trough plasma mibefradil concentrations. Renal function did not affect plasma mibefradil concentrations. Consequently, mibefradil dosage adjustment is not required for patients with renal impairment.