The influence of two types of meal on the pharmacokinetics of a modified-release formulation of nifedipine (Adalat Retard)

OBJECTIVE

The effect of two different types of meal on the absorption of a modified-release formulation of nifedipine (Adalat Retard) was studied.

RESULTS

A light breakfast produced a delay in gastric emptying (indicated by the rate of paracetamol absorption) compared with the fasting state but did not alter the tmax or Cmax for nifedipine significantly. After a cooked breakfast, there was less delay in gastric emptying and again no delay in tmax for nifedipine. However, the Cmax for nifedipine was significantly higher than in the fasting state. Neither meal influenced the bioavailability of nifedipine.

CONCLUSION

The results suggest that the nature of the meal has an important influence on the absorption profile of this formulation of nifedipine, probably by an effect on its dissolution. This study illustrates the importance of considering the effects of different types of meal before concluding that food does not affect the pattern of drug absorption.

Evaluation of two forms of sustained release nifedipine using 24 h ambulatory blood pressure monitoring

Therapeutic interchange between the available forms of sustained release nifedipine (osmotic-pump and coat-core forms of nifedipine) is a matter of controversy. This study was initiated to determine whether there is a difference in clinical outcomes when there is interchange between the two forms of sustained release nifedipine when used for the treatment of hypertension. A total of 43 patients with a history of stage I hypertension who were receiving stable doses of the osmotic-pump form of nifedipine for > 3 months with controlled blood pressures (< 150/90 mm Hg) were enrolled. Patients were then switched to the same dose of the coat-core form of nifedipine and were followed for 3 months. In the 36 patients who completed the study, mean trough serum nifedipine concentrations were significantly higher with the osmotic-pump from (46.5 +/- 35.0 ng/mL) of nifedipine compared with the coat-core form (27.2 +/- 20.4 ng/mL) (P < .05). However, blood pressure control as determined by the indices of 24 h ambulatory blood pressure monitoring, trough blood pressures and load blood pressures were similar between the osmotic-pump and coat-core forms of nifedipine. The coat-core form of nifedipine was discontinued in four patients for possible side effects. In this group of patients with mild hypertension, there were no clinically relevant differences in blood pressure control between the two forms of nifedipine. Some patients on the coat-core form of nifedipine may need to discontinue therapy due to intolerable side effects.

Extrahepatic first-pass metabolism of nifedipine in the rat

The peroral (p.o.) bioavailability of nifedipine is reported to range from about 45 to 58% in the rat; this compares favourably to human beings. The metabolism of nifedipine is similar in rats and humans (oxidation of the dihydropyridine ring), with the liver believed to be solely responsible for the systemic clearance of the drug and the observed first-pass effect after p.o. dosing. The purpose of this study was to determine whether intestinal metabolism also contributes to the first-pass elimination of nifedipine in the rat. The systemic availabilities of nifedipine doses given by po, intracolonic (i.c.), and intraperitoneal (i.p.) routes of administration were compared to that for an intravenous (i.v.) dose (in each case a dose of 6 mg kg-1 was given) using adult male Sprague-Dawley rats (249-311 g, n = 6 or 7/group). The geometric mean of systemic nifedipine plasma clearance after i.v. dosing was 10.3 mL min-1 kg-1. The nifedipine blood-to-plasma ratio was found to be about 0.59. Therefore, the systemic blood clearance of nifedipine was about 17.5 mL min-1 kg-1; which, compared to the hepatic blood flow of rats (55 to 80 mL min-1 kg-1) showed that nifedipine is poorly extracted by the liver (0.22 < or = EH < = 0.32). The mean absolute bioavailabilities of the p.o., i.p., and i.c. doses were 61, 90, and 100%, respectively. Assuming complete absorption of the extravascular nifedipine doses these results indicate that, in addition to hepatic extraction, substantial first-pass elimination of nifedipine occurs within the wall of the small intestine but not the colon of the rat.

Human bioequivalence study of a new nifedipine containing retard filmtablet after single and repeated administration

A clinical pharmacokinetic bioequivalence study with two retard filmtablet preparations, both containing 20 mg of nifedipine (CAS 219829-25-4) was carried out. The investigated test preparation was Cordaflex 20 mg retard filmtablet. The pharmacokinetic parameters were determined after single and repeated administration in 15 and 16 healthy male volunteers, respectively, in open, randomised studies of cross-over design. Plasma levels of nifedipine were determined by HPLC with electrochemical detection using a robotic sample preparation technique. Statistical comparison of the pharmacokinetic parameters (AUC0-infinity, AUCss, tau tmax, Cmax, Css,min, Css,av, MRT, etc.) calculated from plasma concentration-time curves by ANOVAlog, confidence interval, Schuirman's, Westlake's, Anderson's and Wilcoxon's tests, furthermore the comparison of the clinical results did not show any significant difference between the two preparations. It is concluded that the two preparations are bioequivalent after repeated administration.

Effects of short-term administration of sublingual nifedipine on coronary arterial wall elastic properties: evaluation by intravascular ultrasound

Intravascular ultrasound is suited to measure coronary cross-sectional anatomy. Therefore the regional coronary wall elasticity was evaluated by examining the response to nifedipine. In 20 patients, coronary ostial pressure (P) and intravascular ultrasound images were simultaneously recorded before and after sublingual administration of 10 mg nifedipine. We identified the perimeter of the vessel wall, with normal or atherosclerotic plaque, on ultrasound image. At the atherosclerotic site, we measured segmental perimeter (S) for each normal or plaque segment. The ratio of the individual segment length (delta S/delta P) and cyclic variation of cross-sectional area (delta A/delta P) per mm Hg increase in P were calculated. Nifedipine decreased pressure (133/79-120/73 mm Hg) and increased heart rate (79-82 beats/min). After nifedipine, delta A/delta P increased from 8.5 +/- 10.2 x 10(-3) to 16.5 +/- 14.4 x 10(-3) mm2/mm Hg at 20 normal sites (p = 0.005) but was unchanged at 17 atherosclerotic sites (6.6 +/- 7.0 x 10(-3) to 6.7 +/- 7.1 x 10(-3) mm2/mm Hg). Nifedipine increased delta S/delta P in normal segments (4.5 +/- 8.7 x 10(-3) to 9.9 +/- 10.9 x 10(-3) mm/mm Hg; p = 0.02) but produced no change in segments with calcified or soft plaque (-1.1 +/- 0.3 x 10(-3) to 1.4 +/- 1.6 x 10(-3) mm/mm Hg and 5.0 +/- 3.6 x 10(-3) to 6.1 +/- 4.8 x 10(-3) mm/mm Hg, respectively). This study demonstrated that nifedipine increases regional coronary arterial elasticity at normal segments but not at that containing mildly atherosclerotic segment, and likely that the arterial wall function indicated by the response to nifedipine was impaired at an early stage of atherosclerosis.

pH dependent binding of ligands to serum lipoproteins

PURPOSE

The binding interactions of binedaline, nicardipine and darodipine with lipoproteins (HDL, LDL, VLDL) were examined as a function of pH in order to evaluate the role of lipoprotein components and ligand protonation in the binding process.

METHODS

Binding studies were performed by equilibrium dialysis with radiolabeled ligands and differential UV-visible spectroscopy.

RESULTS

Deprotonated ligands had a markedly higher affinity for lipoproteins than the protonated forms, resulting in a concomitant decrease in the pKa of bound ligands, i.e., a decrease in the basicity of the ligand in the bound state. The UV-visible difference spectra generated upon binding of auramine O to lipoproteins also showed that there was a contribution to the binding arising from the deprotonation of the ligand. Ligand binding was related to the phospholipid and cholesteryl ester content and to a lesser degree to the free cholesterol and protein content of lipoproteins, therefore to the surface monolayer components of lipoproteins. This relationship was even more accurate for the deprotonated, high-affinity, than for the protonated species.

CONCLUSIONS

It is suggested that among other possible interactions, ligand binding to lipoproteins involves proton exchange between the reactants and that the high affinity ligand species interact more specifically with the phospholipids of the lipoprotein surface monolayer.

Effect of nifedipine on fetal and maternal hemodynamics and blood gases in the pregnant ewe

OBJECTIVE

Our purpose was to determine whether the fetal acidosis and hypoxia previously demonstrated in animal models with maternal nifedipine infusion is the result of a decrease in uteroplacental or fetoplacental blood flow and whether this effect is exacerbated by a higher drug concentration and duration of infusion.

STUDY DESIGN

Ten chronically instrumented pregnant ewes (gestational age 0.9 term, term = 145 days) received nifedipine infusions (n = 7) or vehicle (95% ethanol/water, 3:7) (n = 3). Three 90-minute periods were evaluated: 5 microg/kg/min infusion (low-dose nifedipine), no infusion, and 10 microg/kg/min (high-dose nifedipine). Paired maternal and fetal blood gases, glucose, lactate, and nifedipine levels were obtained every 30 minutes while hemodynamic parameters were monitored. We determined maternal and fetal blood flows using the radioactive microsphere technique.

RESULTS

Although maternal placental blood flows decreased by 25% during low-dose nifedipine (p < 0.05), this was only transient and there were no other decreases in uteroplacental or fetoplacental blood flow. Fetal blood flow increased to the adrenals and diaphragm with high-dose nifedipine (p < 0.05). Maternal and fetal lactate levels increased with both doses (p < 0.05). In addition, fetuses exhibited significant hypoxia (oxygen content fell 0.46 mmol/L) and acidosis (pH fell 0.06 units) throughout the nifedipine infusion and recovery period. Maternal heart rate increased transiently with both doses (p < 0.05); however, there were no changes in either fetal or maternal mean arterial pressure. Infusion of the vehicle alone did not alter maternal or fetal hemodynamics. Maternal and fetal plasma nifedipine levels reached steady-state by 30 minutes, and maternal/fetal ratios were 0.4 to 0.55. The maternal metabolic clearance rates for low- and high-dose nifedipine were 80.0 and 79.8 ml/min/kg, respectively. Maternal half-life calculation revealed a two-compartment model with a calculated half-life of 2.87 +/- 3.15 and 63.57 +/- 154.03 (+/-SD) minutes for the alpha and beta components, respectively.

CONCLUSIONS

Maternal nifedipine infusion is associated with hypoxia and acidosis in the sheep fetus, without persistent decreases in uteroplacental or fetoplacental blood flows or blood pressures. These fetal blood gas changes are more severe with high-dose nifedipine and longer duration of infusion and continue to deteriorate even when recovery is allowed. The deterioration of fetal blood gases is out of proportion to the transient decreases in uteroplacental blood flow and demonstrates that another mechanism for this fetal acidosis and hypoxia exists during nifedipine infusion.

Effects of erythromycin, clarithromycin and rokitamycin on nifedipine metabolism in rats

The effects of erythromycin, clarithromycin and rokitamycin on the metabolism of nifedipine were studied in vitro and in situ. Erythromycin, clarithromycin or rokitamycin added to nifedipine did not inhibit the formation of metabolite, M-1, of nifedipine, whereas pretreatment with erythromycin or clarithromycin significantly (p < 0.05) inhibited its formation. Only erythromycin significantly (p < 0.05) inhibited the formation of M-2 from M-1. These observations agreed with the results obtained using an in situ rat intestinal loop technique. As assessed by the concentrations of nifedipine and M-2 in jugular and portal vein blood, the inhibition of nifedipine metabolism by erythromycin was greater after multiple doses than after a single dose. Moreover, our results suggest that rokitamycin is a less potent inhibitor of nifedipine metabolism.

Nifedipine pharmacological variables as risk factors for gingival overgrowth in organ-transplant patients

The prevalence and severity of gingival overgrowth in organ-transplant patients medicated with cyclosporin are greater in patients concomitantly medicated with nifedipine; however, no relationship between the gingival overgrowth and any of the nifedipine pharmacological variables has been demonstrated. The study examined the effect of five nifedipine pharmacological variables (nifedipine dosage, plasma concentration and gingival crevicular fluid concentration, M1 metabolite plasma concentration and the nifedipine: M1 ratio). The effect of the nifedipine variables on the gingival overgrowth score were examined using univariate and multivariate regression analysis. Adjustment for the effect of other risk factors was made by adding the distribution of each of the nifedipine variables in turn to a stepwise regression model containing previously identified risk factors for this condition. Despite the high levels of nifedipine sequestered in the GCF, only the plasma concentration of nifedipine was identified as a risk factor for the severity of gingival overgrowth in these patients (P = 0.01) once adjusted for other known risk factors (R2 for the model = 55%).

Metabolism and pharmacokinetics of barnidipine hydrochloride, a calcium channel blocker, in man following oral administration of its sustained release formulation

1. The metabolism and pharmacokinetics of barnidipine hydrochloride, a 1, 4-dihydropyridine calcium antagonist were evaluated following single oral administration of a sustained release formulation (SR) capsule comprising of quick and slow release pellets to healthy male volunteers. 2. Various metabolites were identified and quantitated by newly established GC-MS analytical methods. Major metabolites were the hydrolyzed product of the benzyl-pyrrolidinyl ester (M-3) in plasma and its oxidized pyridine product (M-4) in plasma and urine. The pyridine form of unchanged barnidipine and the N-debenzylated product were observed as minor metabolites. Therefore, the primary metabolic pathways in man are (a) hydrolysis of the benzylpyrrolidine ester, (b) N-debenzylation, and (c) oxidation of the dihydropyridine ring. 3. When the SR and normal capsules were administered at a dose of 10 mg to six subjects in a crossover design, AUC 0-infinity of unchanged drug, M-3 and 4 in each subject receiving the SR were 97 +/- 15, 85 +/- 31 and 76 +/- 21% respectively of those subjects receiving the normal formulation. The sum of the excretion of urinary metabolites for the SR formulation was 65 +/- 6% of that for the normal formulation. These data suggest that the absorption of the SR formulation is slightly reduced but that its bioavailability is comparable to that of the normal formulation.

[Determination of nifedipine in human plasma by gas chromatography and its pharmacokinetic study]

A gas chromatographic method for the determination of nifedipine in human plasma is presented. Nifedipine was extracted into toluene and diazepam was used as the internal standard. Chromatography was performed on an OV-101 fused-silica column by splitless injection with an electron capture detector. The minimal detectable concentration in plasma was 1 ng.ml-1. The standard curve was linear in the range 2-150 ng.ml-1 (gamma = 0.9988). The method has been applied to pharmacokinetic study.

Influence of cisapride on the pharmacokinetics and antihypertensive effect of sustained-release nifedipine

To investigate the clinical significance of interactions between cisapride and sustained-release nifedipine, we compared the plasma nifedipine concentration and blood pressure after administration of nifedipine alone (20 mg) with those obtained after administration of nifedipine cisapride (2.5 mg) in 20 patients with hypertension. The plasma nifedipine level was not altered by cisapride at one hour after administration, but was significantly increased at two (p < 0.01), three (p < 0.01), and four (p < 0.05) hours when compared with the level measured after nifedipine alone. Cisapride significantly decreased the mean blood pressure at three hours (p < 0.05) after administration of nifedipine. The acetaminophen method was used to determine gastric emptying time. The plasma concentration of acetaminophen at 45 minutes after administration was significantly increased by cisapride, suggesting that enhanced gastrointestinal motility might be the basis for the increase in the plasma nifedipine concentration. These results suggest that enhancement of the antihypertensive effect of nifedipine can occur when the drug is prescribed with cisapride, and that caution is needed when using such a combination therapy.

Sensitive high-performance liquid chromatographic determination of nifedipine in dog plasma using an automated sample preparation system with laboratory robot

Nifedipine, a calcium-channel blocking drug was analysed in dog plasma after oral dosing with two different formulations. Sample preparation was automated with a laboratory robot. Quantitative determination of the drug was performed on a reversed-phase HPLC system with electrochemical detection (ED) using an internal standard. Validation of the analytical method showed that the system is well suited for pharmacokinetic studies on dogs. The assay was linear in the range 1-50 ng/ml. Inter-day and intra-day variability were between 6.43-18.15% C.V. and 1.57-5.53% C.V., respectively.

Effect of the lipase inhibitor orlistat on the pharmacokinetics of four different antihypertensive drugs in healthy volunteers

OBJECTIVE

To study the influence of the lipase inhibitor orlistat on the pharmacokinetics of the antihypertensive drugs atenolol, furosemide, captopril and nifedipine.

METHODS

Four open-label, crossover studies were performed on six to eight healthy male volunteers. Orlistat was given in doses of 50 mg 3 times daily mid-meal for 7 (nifedipine and captopril) or 8 days (atenolol and furosemide). The four antihypertensive drugs (atenolol 100-mg tablet, furosemide 40-mg tablet, captopril 50-mg tablet and nifedipine 20-mg slow-release tablet) were administered in single doses twice, once before and once together, with orlistat at the end of the orlistat treatment period.

RESULTS

The plasma concentration time profiles and the pharmacokinetic parameters estimated for these drugs were in the expected range, except for furosemide, whose bioavailability was lower than reported in the literature. This was probably due to the fact that furosemide was given during a meal. There were minor, but statistically significant, differences in one of the pharmacokinetic parameters of furosemide and nifedipine (no difference for captopril and atenolol) when these drugs were given alone and in combination with orlistat: the half-life of furosemide was slightly longer, the time to peak plasma concentrations of nifedipine was slightly longer. None of these are considered to be clinically significant changes.

CONCLUSIONS

The lipase inhibitor orlistat given 50 mg 3 times daily does not alter the pharmacokinetics of atenolol, furosemide, nifedipine and captopril to a clinically significant extent.

Screening for cytochrome P450 3A in man: studies with midazolam and nifedipine

This report describes work directed towards the development of a screening technique for cytochrome P450 3A activity which should be valid for a variety of drugs metabolized by this enzyme. A significant correlation (P < 0.01) was found between the ratio of the plasma concentration of nifedipine to that of its oxidized metabolite and the area under the time curve for the plasma concentration of midazolam. It is suggested that the nifedipine: metabolite ratio might have general predictive value for the metabolism of orally administered cytochrome P450 3A substrates.

Digital pulse plethysmography as a non-invasive method for predicting drug-induced changes in left ventricular preload

OBJECTIVE

Changes in the contour of the plethysmographically recorded digital pulse curve after nitrate ingestion are well known, but it has not been fully established whether these changes reflect nitrate action on left ventricular (LV) preload or afterload. Therefore, we compared the pulse wave contour after administration of equieffective doses of nitroglycerin and nifedipine.

METHODS

In 20 patients with coronary artery disease we measured aortic blood pressure curve in the aorta ascendens, digital volume pulse curve with a photoelectric pulse pickup, Riva Rocci blood pressure and heart rate after administration of either 0.8 mg nitroglycerin or 10 mg nifedipine.

RESULTS

Peak plasma concentrations of nitroglycerin and nifedipine were achieved 5 min and 20 min after ingestion of the drugs. Systolic aortic blood pressure decreased after both nitroglycerin and nifedipine to 19.4 mmHg, but diastolic blood pressure decreased only after nifedipine by 10.5 mmHg (P < 0.05). Riva Rocci blood pressures showed a similar time course. Heart rate increased from 67.4 to 70.9 beats.min-1 after nitroglycerin and from 58.9 to 69.4 beats.min-1 after nifedipine. The calculated a/b ratio of the aortic pressure curve increased after both medications (nitroglycerin, from 1.66 to 1.99; nifedipine, from 1.66 to 1.93) and its time course mimicked that of the systolic blood pressure. The a/b ratio of the digital pulse curve did not change after nifedipine, but showed a pronounced rise after nitroglycerin from 1.29 to 1.84. With regard to pharmacological actions, nitroglycerin causes a reduction in LV preload and afterload, whereas nifedipine has only LV-afterload-reducing activity.

CONCLUSION

We conclude, that the reduction in afterload did not cause the typical changes in wave contour of the peripheral pulse curve which occur with organic nitrates. Most likely changes in the a/b ratio reflect changes in LV preload.

Serum nifedipine concentrations and response of patients with pulmonary hypertension

In patients with primary pulmonary hypertension who respond to nifedipine during acute drug testing, there is a significant linear correlation of serum nifedipine concentration with pulmonary artery pressure and resistance. Although most demonstrate an initial response at readily attainable nifedipine concentrations with conventional dosages, a subset of patients seem to display delayed or incomplete oral absorption; these results may facilitate the clinical use of nifedipine in patients with primary pulmonary hypertension.

Pathogenesis of drug-induced gingival overgrowth. A review of studies in the rat model

Drug-induced gingival overgrowth is a side effect associated principally with 3 types of drugs: anticonvulsant (phenytoin), immunosuppressant (cyclosporine A), and various calcium channel blockers (nifedipine, verapamil, diltiazem). In this review, we describe the features of phenytoin-, cyclosporine A- and nifedipine-induced gingival overgrowth in rats and discuss factors influencing the onset and severity of these disorders. There are several features common to the gingival overgrowth induced by these drugs: 1) gingival overgrowth is more conspicuous in the buccal than in the lingual gingiva and less severe in the maxilla than in the mandible; 2) once the blood concentration of the drug reaches a certain level as a result of increasing the dose, the incidence of gingival overgrowth is 100% and its severity is dependent on the blood level, the most severe overgrowth being induced by cyclosporine A; 3) the duration of drug administration for maximal gingival overgrowth to develop is about 40 days; 4) the gingival overgrowth regresses spontaneously after discontinuing the drug; 5) accumulation of dental plaque is not essential for the onset of overgrowth, but plays a role in its severity; and 6) more severe overgrowth is induced in young than in old rats. Furthermore, male rats are more susceptible than females to nifedipine-induced gingival overgrowth. These results suggest that drug-induced gingival overgrowth in rats is dependent on the oral drug dose, blood drug level, age, and sex and that preexisting gingival inflammation is a factor relevant to its severity. Since these factors have also been suggested to be important determinants for human drug-induced gingival overgrowth, the rat model may prove valuable in the future for elucidating the molecular pathogenesis of the disorder.

Lack of effect of orlistat on the bioavailability of a single dose of nifedipine extended-release tablets (Procardia XL) in healthy volunteers

Orlistat, a lipase inhibitor, reduces dietary fat absorption, and thus could potentially alter the absorption of some concomitantly administered drugs, such as the nifedipine gastrointestinal therapeutic system (GITS). To assess the effect of orlistat on the bioavailability of nifedipine GITS, a third party-blind, placebo-controlled, randomized, two-way crossover study was performed in 18 healthy volunteers. Each participant received single 60-mg oral doses of nifedipine GITS (Procardia XL; Pfizer Labs, New York, NY) on the fourth day of treatment with 120 mg of orlistat or placebo three times a day for 6 days. The two treatments were separated by a washout period of at least 1 week. Serial blood samples were collected before and at appropriate intervals after each nifedipine dose to determine plasma concentrations of nifedipine. The 90% confidence intervals for the ratio of geometric least-square means for maximum concentration (C(max)) and area under the concentration-time curve (AUCo-t) and for the difference of arithmetic least-square means for time to maximum concentration (t(max)) indicate that the bioavailability of nifedipine was not altered by treatment with orlistat. Therapeutic doses of 120 mg of orlistat three times daily do not significantly alter the bioavailability of a single 60-mg oral dose of nifedipine GITS in healthy volunteers.

Cyclosporin- and nifedipine-induced gingival overgrowth in renal transplant patients: correlations with periodontal and pharmacological parameters, and HLA-antigens

The factors associated with cyclosporin A (CsA)- and nifedipine (Nif)-induced gingival overgrowth were investigated in 113 renal transplant recipients receiving CsA alone (Group 1) [n = 61], CsA and Nif (Group 2) [n = 28], or azathioprine (Aza) (Control Group) [n = 24]. Periodontal and pharmacological parameters were assessed for each patient. The patients with a gingival overgrowth index (GOI) score >1 were considered responders (R); those with a score </= 1 were non-responders (NR). Gingival overgrowth occurred in 33.7% of the patients in Groups 1 and 2; 60% of the responders were receiving CsA+Nif. In R, no relationship was found between the GOI and the periodontal and pharmacological parameters, and although there was a trend towards an increased presence of HLA-A19 antigen (chi-square=4.40; P=0.04; RR=2.86), no significant difference was found between R and NR (Pc>0.05). It is concluded that the prevalence and severity of gingival overgrowth are greater in patients receiving CsA+Nif. As overgrowth appeared to be unrelated to local irritants, gingival inflammation or pharmacological parameters, it may be related to individual susceptibility.

[The pharmacokinetics of different drug forms of nifedipine when used singly and in a course as monotherapy and in combination with Cordanum and triampur preparations in patients with arterial hypertension]

Pharmacokinetics of three drugs derived from nifedipine: corinfar, corinfar retard, and SL adalate in the cases of a single and course administration in patients with arterial hypertension and the effect of cordanum and triampur on pharmacokinetics of corinfar retard in combined repeated administration have been studied. The studies were carried out in 6 groups of patients with arterial Hypertension, each group included 10 patients. Nifedipine concentration in blood plasma was determined using a special HPLC procedure within 24 h after administration of the drugs at a dose 20 mg. A pharmacokinetic characteristics of new drug adalate SL with two-step liberation of nifedipine. A possibility of autoinhibition was noted for corinfar and adalate SL in course therapy. A conclusion was made that cordanum and triampur did not affect the pharmacokinetics of corinfar retard.

Determination of barnidipine in human serum and dog plasma by HPLC with electrochemical detection

Barnidipine is a 1,4-dihydropyridine calcium antagonist. HPLC was conducted on a polybutadiene coated alumina column using an alkaline mobile phase and an electrochemical detector to determine the content of this drug in serum and plasma. A good linear relationship between barnidipine concentration and peak height was found in 5-500 ng/ml with a correlation coefficient of 0.998. The detection limit was 1 ng/ml. The within-day and day-to-day variations were examined for control human serum. Relative standard deviation of within-day assay for serum spiked with 10 ng/ml barnidipine.HCl was 6.9% and the recovery was 104%. A pharmacokinetic study was made in which the time course of barnidipine in dog plasma was followed.

Pharmacokinetic basis of nifedipine-digoxin interaction: a commentary

Elevation of plasma digoxin levels following concurrent administration of nifedipine have previously been reported. The mechanism for this interaction has not been fully explained, but may include a reduction in volume of distribution of digoxin and/or reduction in the renal or non-renal clearance of digoxin by nifedipine. The end result is probably an elevation of plasma concentrations of free (pharmacologically active) digoxin, which may lead to manifestation of side effects of digoxin. This communication highlights the possible pharmacokinetic basis of the reported digoxin-nifedipine interaction.