Pharmacokinetic interactions of nifedipine and quinidine

Several clinical investigations have been published regarding the interaction of nifedipine and quinidine. The results of these studies are contradictory. In vitro studies indicate that the 3-hydroxylation and N-oxigenation of quinidine appear to involve the P4503A4 family, a form of cytochrome that predominantly catalyzes the aromatization of nifedipine, too. The aim of our study was to investigate the effect of oral intake of 200 mg quinidine on the kinetics of 20 mg nifedipine as a retarded formulation and vice versa. Twelve healthy male volunteers between 18 and 40 years were treated. Each subject was studied on three occasions each separated by a one week washout period. Drug administration consisted of one oral dose of nifedipine (Adalat retard 20 mg), one oral dose of quinidine (Chinidin sulfuricum "Buchler" 200 mg) or a combination of both (20 mg nifedipine and 200 mg quinidine) in a randomised 3 way crossover. Administration of the test drugs in combination slightly increased the bioavailability of both--nifedipine [N] to 18% and quinidine [Q] to 16%--and decreased the clearance of both drugs. The results were not statistically significant. Based on our data, the combination of nifedipine and quinidine seems to lack a clinically relevant interaction.

Iatrogenic gingival overgrowth in cardiac transplantation

It is well established that both cyclosporin and nifedipine are associated with gingival overgrowth. Although both drugs are widely used in the management of organ transplant patients, there is little information on the prevalence and severity of this unwanted effect in cardiac transplant patients. This study evaluated the gingival health of 94 dentate cardiac transplant patients, all of whom were medicated with cyclosporin as a component of their immunosuppressive therapy. Sixty-three (63) of the patients were also medicated with nifedipine. Significantly higher gingival overgrowth scores (P < 0.0001) and periodontal probing depths (P = 0.001) were observed in patients medicated with the combination of cyclosporin and nifedipine than those medicated with cyclosporin alone. Likewise, there was a significantly greater need to carry out gingival surgery on patients taking the combination (62%), than those medicated with cyclosporin alone (25.8%) (P = 0.001). Patient's age, sex, duration of therapy, gingival bleeding index, and nifedipine therapy were important determinants for both the expression of gingival overgrowth and the need for surgery. Significant sequestration of nifedipine in the gingival crevicular fluid (GCF) was observed. The concentration of nifedipine in GCF did not relate to either the gingival changes or plasma concentration of the drug. Cardiac transplant patients are at risk of developing gingival overgrowth and approximately 50% require surgical intervention. This risk increases significantly when patients are medicated concomitantly with nifedipine.

Factors affecting the absolute bioavailability of nifedipine

1. Nifedipine was administered to eight volunteers (seven Caucasian, one East Asian of Chinese origin) as a single 10 mg capsule orally and as 2.5 mg intravenously. The pharmacokinetics were determined under fasting conditions and following 200 ml double strength grapefruit juice taken orally both 2 h before and at the time of dosing. 2. In a separate study, the pharmacokinetics of nifedipine were defined in eight South Asian volunteers (with both parents originating from the Indian subcontinent) following 10 mg nifedipine orally and 2.5 mg intravenously. 3. The administration of grapefruit juice did not alter the pharmacokinetics of intravenous nifedipine, but resulted in a significantly increased area under the plasma concentration-time curve (AUC) (191 +/- 59 c.f. 301 +/- 95 ng ml-1 h, P < 0.05) and bioavailability (0.63 +/- 0.18 c.f. 0.86 +/- 0.15, P < 0.05) following oral nifedipine. The elimination half-life was unchanged by administration of grapefruit juice and there was no evidence of decreased formation of the nitropyridine first-pass metabolite. 4. The AUC of nifedipine after intravenous administration was significantly higher in South Asian subjects than in Caucasians (146 +/- 39 c.f. 74 +/- 18 ng ml-1 h, P < 0.002). This was due to a lower systemic clearance in the South Asians which was 50% of that in the Caucasians. The half-life was markedly prolonged in South Asians (4.1 +/- 1.9 c.f. 1.7 +/- 0.5 h, P < 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of slow-release nifedipine on ST-segment depression induced by effort test. Correlations with serum levels

To study the anti-ischemic effect of slow-release nifedipine ten patients with stable angina pectoris and a positive effort test were selected. Nifedipinemia was measured by a gas chromatographic method. At the peak level of effort intensity slow-release nifedipine significantly decreased the mean ST-segment depression (p < 0.05) and the ischemic score (p < 0.01) when compared to the control effort test, without decreasing the double product. Nifedipine induced no more tachycardia additional to that produced by effort. At the beginning of the effort test the level of nifedipine (15.9 +/- 2.51 ng/ml) was superior to the value considered as minimal effective and was positively correlated with the ischemic score (r = 0.67; p < 0.05). A worsening of ischemia was noted in 2 patients probably due to a steal phenomenon.

Factors influencing nifedipine-induced gingival overgrowth in rats

Factors such as age, the dose of nifedipine administered in the diet, serum drug level, duration of drug administration, and sex which may influence nifedipine-induced gingival overgrowth were examined in a rat model using 20-, 50-, and 90-days-old male and female rats. Oral administration of nifedipine (50 to 250 mg/kg diet) increased the serum level of the drug in a dose-dependent manner in both males and females. However, a higher serum level was required in females than males to attain the same degree of gingival overgrowth. The minimum dietary concentrations of the drug required to elicit gingival overgrowth in males and females were 150 and 100 mg/kg, respectively, which gave respective minimum serum levels of 800 and 1100 ng/ml. The degree of overgrowth depended on the serum concentration of the drug after it had reached the required minimum in male and female animals. Administration of nifedipine (250 mg/kg diet) for 20 days was enough to induce maximal overgrowth, but this induction occurred only in rats that started to receive the drug when they were 20 days old, not in those that started at 50 and 90 days of age for the same administration period of 55 days, and the overgrowth regressed and the gingiva were normal 40 days after ceasing drug administration. These results suggest that gingival overgrowth occurred in accordance with the drug concentration in the diet, as well as that in the serum, and was more likely to occur in males and younger individuals.

Differences in nifedipine concentration-effect relationship between capsule and slow release tablet administration

The relationships between nifedipine plasma concentrations and its hypotensive and positive chronotropic effects were studied in healthy volunteers who received either a 10 mg capsule (CAP) or a 20 mg slow release tablet (SRT). Plasma concentrations rose more rapidly after CAP than after SRT, Cmax being 131 +/- 39 and 40 +/- 7 ng/ml and tmax being 0.5 +/- 0.07 and 1.8 +/- 0.4 h, respectively. Both formulations produced a reduction in diastolic blood pressure which exhibited a significant linear correlation (p < 0.01) with nifedipine plasma concentration. However, the slope obtained with SRT was significantly higher than that of CAP (0.24 +/- 0.05 vs 0.07 +/- 0.01, p < 0.01). That is, a similar hypotensive effect was produced at a lower concentration with SRT than with CAP. A positive chronotropic effect which exhibited a highly significant correlation with nifedipine plasma concentration (p < 0.0001) was observed with CAP. Conversely, with SRT heart rate increase was smaller and there was no significant correlation with nifedipine plasma concentration (p > 0.45). Since the measured decrease in blood pressure is the outcome of nifedipine-induced vasodilation and of homeostatic responses, results are interpreted as follows. Fast nifedipine input after CAP induced a brisk change in physiological conditions and hence triggered an important homeostatic response, visualized as heart rate increase, which partially offset the hypotensive effect. With SRT, there was a gradual change in blood pressure producing lesser activation of compensatory mechanisms and therefore the hypotensive effect of nifedipine was less antagonized than with CAP. Nifedipine SRT does not only exhibit pharmacokinetic advantages, but also a more favorable pharmacodynamic profile than CAP.

[A pharmacokinetic study of korinfar-retard in monotherapy and in combination with cordanum and triampur in patients with arterial hypertension]

The long-acting corinfar formulation, corinfar-retard tablets, 20 mg (AWD, Germany), was studied for pharmacokinetics in single and course use in 40 patients with arterial hypertension, as well as for its effects of cordanum and triampur. Patients' plasma corinfar was measured by high performance liquid chromatography. There were no changes in the pharmacokinetics of the agent when it was used in its course use. Cordanum and triampur was demonstrated to have no effects on the pharmacokinetics of corinfar during their application.

Determination of nifedipine in human serum by gas chromatography-mass spectrometry: validation of the method and its use in bioavailability studies

A procedure for the determination of nifedipine in human serum is described. The light-sensitive substance is isolated from serum by liquid-liquid extraction and analyzed using capillary gas chromatography with a mass-selective detector. The validation of the method shows that the extraction recovery is ca. 85%, the limit of detection is 2 ng/ml and the standard deviations of the intra-day precision test range from 5.8 to 7.4% with respect to the concentration. The procedure is highly selective and sensitive. It is especially suited for bioavailability studies because of its stability and high sampling rate.

Prediction and optimisation of the antihypertensive response to nifedipine

The predictability of the long term antihypertensive response to nifedipine in individual patients has been assessed by an analysis based upon the concentration-effect parameters defined following the first dose administration of 20 mg nifedipine (Retard). The predicted and measured reductions in blood pressure during steady state nifedipine treatment were compared for the trough and peak responses and there was reasonable agreement for the group of patients as a whole. However, when the measured and predicted blood pressure profiles were compared for each individual patient there was close agreement for the majority of patients but there were significant discrepancies in a few cases. Further analysis of the steady state concentrations in these cases revealed that there was no change in their responsiveness to nifedipine and that discrepancies were directly attributable to inappropriate compliance with the drug regimen. The analysis was further extended to simulate the blood pressure responses to alternative fixed dosage regimens. Assessment of these simulations suggests that blood pressure control with nifedipine Retard is significantly improved by three times daily drug administration.

Controlled study with a new sustained-release formulation of nifedipine in essential hypertensive patients

The authors studied the antihypertensive effect and tolerability of a new sustained-release formulation of nifedipine 50 mg once a day, in comparison with nifedipine retard 20 mg twice a day in patients with mild or moderate primary arterial hypertension. Both treatments significantly lowered blood pressure with no difference in daily blood pressure profile. At steady state, the two drugs determined comparable plasma levels of nifedipine as measured immediately before the morning dose. After a 12-month treatment, the new formulation of nifedipine still displayed satisfactory blood pressure control in both supine and standing positions, with no change in tolerability throughout the study. In conclusion, this new sustained-release formulation of nifedipine has similar efficacy and tolerability to conventional treatment with nifedipine retard 20 mg twice a day.

Relative bioavailability of four controlled-release nifedipine products

Four controlled-release nifedipine products were investigated in two clinical studies. In study 1, 22 healthy male volunteers took part in an open, multiple-dose, randomized, crossover study to determine the relative bioavailability of two 10 mg controlled-release nifedipine tablets (Adalat Retard, Bayer), administered 12 hourly, and one 20 mg controlled-release nifedipine tablet (Adalat Retard, Bayer) administered 12 hourly. In study 2, 24 healthy male volunteers took part in an open, multiple-dose, randomized, three-period, crossover study to determine the relative bioavailability of (i) two 30 mg nifedipine gastro-intestinal therapeutic system (GITS) tablets (Adalat XL, Bayer) administered once daily; (ii) one 60 mg nifedipine GITS tablet (Adalat XL, Bayer) administered once daily; and (iii) one 20 mg plus one 10 mg nifedipine controlled-release tablet (Adalat Retard, Bayer), administered 12 hourly. In both studies detailed pharmacokinetic data, in particular with respect to the controlled-release characteristics of the different formulations, were collected. Results of both studies indicate that all nifedipine products investigated are bioequivalent with respect to the extent of absorption of nifedipine. The nifedipine GITS products (Adalat XL) have better controlled-release properties than the Adalat Retard product, and are suitable for once-a-day administration.

Influence of grapefruit juice on the pharmacokinetics of a slow release nifedipine formulation

The objective of this study was to investigate in a twoway randomized crossover whether repeated uptake of grapefruit juice (200 ml at 0, 2, 4, 8 and 12 h enhances bioavailability of a nifedipine (1) slow release formulation (20 mg) in ten healthy volunteers. Grapefruit juice increased the AUC and cmax of 1 statistically significantly by 103 (SD 73, range 48 to 265)% and 94 (SD 83, range -23 to 259)%, respectively. AUC of dehydronifedipine (2) was also higher during grapefruit phase, but to a lesser extent (mean increase 66, SD 106, range -30 to 236)%. Half lives of neither 1 nor 2 were altered by grapefruit juice. Because 2/1-ratio was not lowered by grapefruit juice in comparison to control, a selective inhibition of cytochrome P450 3A based on the presented in vivo data is not very likely. In the light of other reports concerning grapefruit juice induced increase in bioavailability our data contradict the assumption of a selective inhibition of only one cytochrome P450 subfamily. The observed effect could be clinically significant, especially if other factors affecting the elimination of 1 occur.

Sublingual nifedipine: the continuing controversy

Sublingual, as opposed to oral, administration of Nifedipine (Adalat) has gained wide popularity as the method of choice when the most rapid onset of anti-hypertensive action is required. However recent research indicates that this delivery method may be without scientific validation, and may in fact delay the attainment of peak plasma concentrations of the drug. Peak Nifedipine serum concentrations have been shown to be less following sublingual administration than following oral administration, and the time to peak concentration has been shown to be longer following sublingual administration than with the oral dose. The lack of a standardised technique for the administration of sublingual Nifedipine means that in many cases the patient may be receiving sub-therapeutic doses of the drug.

Nifedipine kinetics and dynamics in hypertensive patients: a new approach

Nifedipine tablet in a 20 mg dose was administered orally to 44 patients with arterial hypertension. Nifedipine pharmacokinetics showed wide interindividual variation, for instance maximal concentration varied from 10-90 ng/ml, elimination half-life from 2-9 hours, etc. Cluster analysis classified all variants of nifedipine concentration profiles into 3 more homogeneous groups. Group A was characterized by small maximal nifedipine concentrations and its fast elimination; in group C nifedipine concentration reached high level in plasma and elimination half-life was more than 5.5 hours; in group B intermediate variants of nifedipine concentration profiles were separated. Nifedipine effects on mean blood pressure and platelet aggregation differed between these groups significantly. There were no changes in these parameters in patients from group A whereas in group C nifedipine produced profound and long-term reduction of both blood pressure and platelet aggregation. Using cluster analysis it appears to be possible to objectively classify a variant of nifedipine concentration profile to one of these homogeneous groups using only 3 measurements of nifedipine concentration in plasma at 1, 2 and 3 hours after the administration. It has been suggested that this approach simplifies the estimation of nifedipine pharmacokinetics and it might be useful for introducing the pharmacokinetic investigations to clinical practice.

Evaluation of chromatographic methods for the determination of nifedipine in human serum

Gas-liquid chromatography and high-performance liquid chromatography were compared for the identification and determination of nifedipine in biological samples and the elaboration of the optimum liquid-liquid extraction procedure. The determination limits were 2 and 10 ng/ml, respectively, and the detection limits were 1 and 5 ng/ml, respectively. The calibration graphs were linear in the ranges 2-300 and 10-500 ng/ml, respectively. Recoveries based on three different concentrations were 88.7-95.8% and 93.7-104.2%, respectively. Both methods are sensitive, specific and reproducible enough for pharmacokinetic studies and therapeutic drug monitoring.

Sensitive high-performance liquid chromatographic assay for nifedipine in human plasma utilizing ultraviolet detection

A rapid, simple, sensitive and selective reversed-phase high-performance liquid chromatographic (HPLC) technique is reported for the determination of nifedipine in human plasma. The procedure involves extraction of nifedipine from plasma under alkaline conditions (pH 12), separation via reversed-phase HPLC and ultraviolet detection (350 nm). The peak corresponding to nifedipine was free of interference from its photodegradation products or metabolites. The method was validated over the range 5-250 ng/ml nifedipine using weighted least-squares linear regression analysis. Accuracy and precision were within approximately 10% or less over the concentration range, except for the lowest concentration point which, nonetheless, was acceptable and approached 15%. The minimum quantifiable concentration of nifedipine was determined to be 5 ng/ml. The minimum detectable concentration was in the order of 1 ng/ml. Analysis of plasma samples collected from healthy volunteers demonstrate that this assay is applicable to clinical and pharmacokinetic studies.

Effect of nilvadipine on the development of neurological deficits in stroke-prone spontaneously hypertensive rats

BACKGROUND AND PURPOSE

Several types of antihypertensive drugs have been reported to protect stroke-prone spontaneously hypertensive rats from stroke. However, the clinical relevance remains unclear. This study was performed to investigate the effect of nilvadipine, a calcium channel blocker, on the development of neurological deficits in stroke-prone spontaneously hypertensive rats. In addition, plasma levels of nilvadipine were measured to determine the clinical relevance.

METHODS

Salt-loaded stroke-prone spontaneously hypertensive rats were orally administered nilvadipine mixed with a powder diet (0.01% and 0.03%, wt/wt). Non-salt-loaded rats were maintained on tap water. Chronological changes in neurological deficit scores and systolic blood pressure were recorded. After 6 weeks of medication, measurement of plasma levels of nilvadipine, serum biochemical analysis, and pathological observation of both the brain and the kidney were performed.

RESULTS

In the salt-loaded control group, both severe hypertension and neurological deficit developed, and the final survival rate was 30%. Systolic blood pressure decreased significantly in the high-dose nilvadipine-treated group but not in the low-dose nilvadipine-treated group. However, the development of neurological deficit was almost completely inhibited in both nilvadipine-treated groups that had no deaths (P < .01). The mean plasma levels of nilvadipine in the low-dose group and in the high-dose group at the time of death were 0.21 ng/mL and 0.61 ng/mL, respectively.

CONCLUSIONS

Nilvadipine inhibited the development of neurological deficit in stroke-prone spontaneously hypertensive rats at plasma concentrations lower than that in clinical use. Thus, nilvadipine might prevent cerebral vascular disorders at doses routinely used for essential hypertension.

[The pharmacokinetic interaction of propranolol and nifedipine in patients with angina of effort]

A comprehensive study was undertaken to examine the pharmacokinetic and pharmacodynamic interaction of propranolol and nifedipine in 11 patients with stable angina of effort who were treated for a long time. It was shown that when the agents were given in combination, the patient's plasma generated the same profiles of their concentrations as used alone. This suggests that the propranolol + nifedipine combination is safe from the point of their pharmacokinetic interaction. The latter occurs at the level of their pharmacodynamic effects.

Quantitative analysis of nifedipine in plasma by high-performance liquid chromatography

A rapid, sensitive and specific high-performance liquid chromatographic assay for the quantification of nifedipine in human plasma was developed, satisfactorily validated and applied to samples of plasma from healthy volunteers. The sample pre-treatment incorporating protein denaturation by urea and ethyl acetate extraction compared favourably in terms of selectivity with previously published methods. The limit of quantitation of this reversed-phase LC method was 7.0 ng ml-1 for the analysis of 0.5 ml samples.

A comparative assessment of the duration of action of amlodipine and nifedipine GITS in normotensive subjects

1 This study in normotensive subjects compared the duration and consistency of action of amlodipine (5 mg) and nifedipine GITS (60 mg) by assessment of the attenuation of pressor responses to noradrenaline and angiotensin II. 2 Both drugs significantly attenuated pressor responses to both vasoconstrictors at 6 and 24 h post-dose with rightward shifts of up to 2.3-fold in the dose-response curves. 3 There was significantly less pharmacokinetic variability with amlodipine: for example, intra-subject variability was 33% with amlodipine and 59% with nifedipine GITS. 4 There were no significant differences in the pressor dose ratios up to 48 h post-dose with amlodipine whereas there was a significant and progressive reduction in the pressor dose ratios with nifedipine. 5 These results suggest that both drugs are broadly comparable as once daily treatments but amlodipine displayed less intra- and inter-subject variability and provided a significantly more sustained effect with a reserve of pharmacological activity up to 48 h post-dose.

Effects of dihydropyridines on cerebral blood vessels

AIM

To evaluate the effects of dihydropyridine calcium antagonists on the cerebral circulation in stroke patients. DESIGN OF STUDIES: Mean cerebral circulation parameters were studied in chronic stroke patients with hypertension and treated acutely or chronically (2 weeks) with nicardipine or nifedipine retard. The effects of nicardipine on local cerebral blood flow were also studied in patients with a subacute brain infarction.

RESULTS

Mean cerebral blood flow was significantly increased after a single oral administration of nicardipine but not after nifedipine retard. Both calcium antagonists reduced mean arterial pressure. Nifedipine retard acted mainly by reducing blood pressure and nicardipine mainly by reducing cerebrovascular resistance.

CONCLUSION

Dihydropyridines have a beneficial effect in the control of hypertension in stroke patients.

Determination of nifedipine in gingival crevicular fluid: a capillary gas chromatographic method for nifedipine in microlitre volumes of biological fluid

This paper describes a sensitive capillary gas chromatographic (GC) method for the determination of nifedipine in sub-microliter samples of gingival crevicular fluid (GCF) in order to assess if nifedipine is present in the GCF and if so, whether the local tissue concentrations of this drug are an important determinant in the development of gingival overgrowth. Liquid-liquid and solid-phase extraction were combined to give adequate sample clean-up and concentration for measurement by automated capillary GC with electron capture detection. Nifedipine and its principal metabolite, M-I, were analysed in both plasma and GCF in 9 adult male patients who had been taking nifedipine for over six months. M-I could not be measured in GCF. Plasma nifedipine and M-I levels were normal, but the nifedipine levels found in the GCF of 7 patients (including all those with overgrowth) were remarkably elevated, 15 to 316-fold greater. This massive concentration of nifedipine into the GCF is therefore linked with gingival overgrowth. This is the first time that a GC method has been developed which permits determination of GCF pharmacokinetics of a drug which causes gingival overgrowth, and further investigation will lead to a better understanding of the tissue mechanisms involved.

The efficacy and safety of once-daily nifedipine coat-core in the treatment of mild-to-moderate hypertension. Adalat CC Cooperative Study Group

The efficacy and safety of once-daily nifedipine coat-core, a new, extended-release formulation, were examined in 245 patients with essential hypertension in this 10-week, multicenter, randomized, double-blind, placebo-controlled, parallel-group study. Mean net reductions in trough supine diastolic blood pressure at endpoint were 6.5 mmHg, 7.7 mmHg, and 11.7 mmHg at 30, 60, and 90 mg/day of nifedipine, respectively. All reductions were statistically significant, compared with placebo. Trough-to-peak ratios for supine diastolic blood pressure change following the 30, 60, and 90 mg/day doses were 49%, 67%, and 61%, respectively. Adverse events were generally mild or moderate, and most reflected the vasodilatory properties of the drug (eg, headache, edema). Reports of adverse events decreased as treatment progressed. The nifedipine coat-core tablet provided good control of blood pressure for the entire 24-hour dosing interval and was well tolerated by the majority of patients in the study.

The safety and efficacy of once-daily nifedipine coat-core in combination with atenolol in hypertensive patients. Adalat CC Cooperative Study Group

The efficacy and safety of once-daily nifedipine coat-core when added to a regimen of atenolol (ATN; 50 mg/day) were compared with ATN and placebo in 251 patients with essential hypertension in this 12-week, multicenter, randomized, double-blind, placebo-controlled, parallel-group study. Mean net reductions (ATN effect subtracted) in supine diastolic blood pressure at endpoint were 7.9 mmHg, 9.4 mmHg, and 9.9 mmHg at 30, 60, and 90 mg/day of nifedipine coat-core, respectively, and 4.1 mmHg on ATN+placebo. Beyond the first week of double-blind therapy, all reductions produced by nifedipine coat-core combined with ATN were statistically significant (P < 0.05) compared with ATN+placebo. On ambulatory blood pressure monitoring, trough-to-peak ratios of the change in diastolic blood pressure for the 30, 60, and 90 mg/day doses were 41%, 68%, and 78%, respectively. Adverse events were generally mild or moderate and most reflected the vasodilatory properties of nifedipine (eg, edema, headache). Nifedipine coat-core, when combined with ATN in patients not controlled by ATN alone, had significant antihypertensive activity for the entire 24-hour dosing interval and was well tolerated by the majority of patients in the study.