Pharmacokinetics and pharmacodynamics of two commercial oral nifedipine products

Nifedipine, a calcium channel blocker, is widely used in the management of hypertension, angina and cardiac arrhythmias. In this study, the bioequivalence of two pharmaceutical formulations of nifedipine, Nifecard (10 mg capsules) manufactured by Dar Al-Dawa Development and Investment Co, Ltd. and Adalat (10 mg capsules) manufactured by Bayer Pharmaceutical Company, was assessed in twelve healthy male subjects. Nifecard or Adalat was given orally on two occasions separated by one week wash-out interval. Blood samples for the determination of plasma nifedipine concentration were taken for 8 hours following drug administration. Blood pressure and pulse were also measured after each treatment. Plasma nifedipine concentrations were measured by a simple, sensitive and reproducible HPLC method. There were no significant differences in oral absorption, Cmax, tmax, t1/2 and AUC between Nifecard and Adalat. Also, Nifecard and Adalat produced similar hemodynamic profiles (blood pressure and pulse). In conclusion, our results demonstrate that both Adalat and Nifecard are bioequivalent and produced similar pharmacological effects.

Two deaths from intravenous nifedipine abuse

An incident is reported in which 2 intravenous drug abusers died as the result of uncontrolled experimentation with intravenous injection of the common anti-hypertensive and anti-anginal drug Nifedipine (Adalat t.m. Bayer), probably in mistake for the commonly abused short-acting benzodiazepine drug Temazepam. Large quantities of Nifedipine were identified in the blood of both decreased men by gas chromatography. Apart from intense gastric mucosal congestion, pulmonary oedema and general visceral congestion, the autopsy findings were entirely nonspecific. The similarity in colour, shape and texture between capsules of Nifedipine and those of Temazepam is likely to have prompted the mistake.

Efficacy of slow-release nifedipine on myocardial ischemic episodes in variant angina pectoris

To evaluate the efficacy of slow-release nifedipine (a single dose of 20 mg given at 10 P.M. or 2 doses of 20 mg at 10 P.M. and 6 A.M.) on ischemic episodes in patients with variant angina, a single-blind crossover study with ambulatory electrocardiographic monitoring was performed in 15 patients (13 men and 2 women, mean age 63 years). In all, there were 646 ischemic episodes detected with ambulatory electrocardiographic monitoring during the study period, and 618 episodes of them occurred during placebo periods with a circadian variation. Sixty-nine percent of the episodes in placebo periods were asymptomatic. The number of anginal attacks, nitroglycerin tablets taken, ST-segment elevation and the total ischemic duration significantly decreased during nifedipine therapy compared with results after the placebo therapy period, respectively (p less than 0.01 or 0.05). Twenty-eight ischemic episodes occurred during nifedipine therapy when the plasma level of nifedipine was low. Thus, asymptomatic ischemic episodes more frequently occur than symptomatic episodes and the administration of slow-release nifedipine is highly effective in suppressing not only symptomatic but also asymptomatic myocardial ischemia in patients with variant angina. The timing of the administration of slow-release nifedipine is an important factor in suppressing ischemic episodes.

Effect of nifedipine on oxygen delivery in patients with angina pectoris: relation between blood viscosity and hematocrit

The effect of nifedipine on blood viscosity and hematocrit was investigated. Blood was sampled from eight patients with angina pectoris (mean age: 59 +/- 8 yr) treated with nifedipine (20-30 mg/day) for 5 months. Using a cone-plate type viscometer, blood viscosity was determined at the shear rates of 37.5 and 375 sec-1 at 37 degrees C. Hematocrit was also measured at the same time. Since the ratio of hematocrit to blood viscosity at a shear rate of 375 sec-1 can be considered to reflect oxygen delivery, this ratio (oxygen delivery index) was also calculated. Blood viscosity at a shear rate of 37.5 sec-1 was significantly (P less than .05) decreased by nifedipine treatment, but hematocrit and the blood viscosity at a shear rate of 375 sec-1 were not changed. The oxygen delivery index, however, was significantly (P less than .01) increased after the administration of nifedipine. These results suggest that oxygen delivery increased by the treatment with nifedipine and inhibited erythrocyte aggregation by decreasing blood viscosity at low shear rate.

High-performance liquid chromatographic determination of the polar metabolites of nifedipine in plasma, blood and urine

A relatively simple reversed-phase high-performance liquid chromatographic method for the determination of the polar metabolites of nifedipine in biological fluids is described. After conversion of 2-hydroxymethyl-6-methyl-4-(2-nitrophenyl)pyridine-3,5-dicarboxylic acid 5-methyl ester (IV) into 5,7-dihydro-2-methyl-4-(2-nitrophenyl)-5-oxofuro[3,4-b] pyridine-3-carboxylic acid methyl ester (V) by heating under acidic conditions, V was extracted with n-pentane-dichloromethane (7:3) and analysed on a C18 column with ultraviolet detection. Subsequently, 2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinedicarboxylic acid monomethyl ester (III) was extracted with chloroform and analysed on the same system. Limits of determination in blood were 0.1 microgram/ml for III and 0.05 microgram/ml for IV and V; these limits were two to ten times higher for urine. This inter-assay variability was always less than 7.5%.

Effects of amlodipine on urinary sodium excretion, renin-angiotensin-aldosterone system, atrial natriuretic peptide and blood pressure in essential hypertension

We studied the effect of amlodipine, a long-acting dihydropyridine calcium antagonist, on blood pressure, urinary sodium excretion, plasma renin activity, aldosterone and atrial natriuretic peptide in six patients (aged 47-63 yrs) with essential hypertension. Patients were placed on a fixed sodium intake of 150 mmol/day. After a control period, amlodipine 10 mg/day was given for two weeks. There was a gradual reduction in supine BP over the first two days of treatment, from 165/103 +/- 5/4 mmHg to 137/92 +/- 6/4 mmHg (P less than 0.001) and BP remained at this level during treatment. Three days after amlodipine was stopped the BP was still reduced at 136/87 +/- 5/4 mmHg but was back to pretreatment levels two weeks later. Plasma amlodipine rose after two weeks of treatment to 29.7 +/- 4.7 ng/ml but had only decreased to 15.0 +/- 3.4 ng/ml three days after the treatment was withdrawn. During the first two days of treatment there was no evidence of an increase in urinary sodium excretion and when amlodipine was withdrawn there was no evidence of sodium retention. Plasma renin activity increased from 1.26 +/- 0.30 to 2.99 +/- 0.68 ng/ml/h (P less than 0.001) and plasma atrial natriuretic peptide fell from 19.3 +/- 7.0 to 11.4 +/- 3.8 pg/ml (P less than 0.03) with two weeks of treatment. This study demonstrates that amlodipine is a long-acting calcium antagonist with a slow onset of action and a slow end of action after withdrawal. This makes it difficult to detect alterations in sodium balance when assessed by changes in urinary sodium excretion. However, one explanation for the increase in plasma renin activity and fall in atrial natriuretic peptide is a small reduction in total body sodium.

Interaction of citrus juices with felodipine and nifedipine

Six men with borderline hypertension took felodipine 5 mg with water, grapefruit juice, or orange juice. The mean felodipine bioavailability with grapefruit juice was 284 (range 164-469)% of that with water. The dehydrofelodipine/felodipine AUC ratio was lower, diastolic blood pressure lower, and heart rate higher with grapefruit juice than with water. Vasodilatation-related side-effects were more frequent. Orange juice had no such effects. Six healthy men took nifedipine 10 mg with water or grapefruit juice; the bioavailability with grapefruit juice was 134 (108-169)% of that with water.

[Comparative study of effects of diltiazem, nifedipine and their combination on exercise stable angina]

Diltiazem and Nifedipine could be synergic. The aim of this study was to investigate the benefits of their association. Eighteen patients, 15 men and 3 women, average age 61 +/- 6 years, with stable angina on effort, were studied. Eight patients had single vessel disease and 10 patients had multivessel disease. The patients underwent a randomised double-blind trial with 4 successive treatment periods each lasting one week: placebo; 360 mg/day of Diltiazem; 60 mg/day of Nifedipine; 180 mg/day of Diltiazem with 30 mg/day of Nifedipine. The benefits were evaluated clinically, by exercise stress testing and with drug plasma concentrations at the end of each sequence. The results at the end of the 3 treatment periods were significantly better than with placebo. Diltiazem was significantly better than Nifedipine with respect to the development of angina during exercise testing (1 patient compared with 7 patients) and to maximum load (118.3 +/- 33.3 watts compared with 105.9 +/- 35.4 watts) (p less than 0.05). The association of the two drugs did not give better results than Diltiazem alone. Compared with placebo, the total duration of exercise testing and the duration of 1 mm ST depression were significantly longer during the 3 treatment sequences but there were no significant differences between each of them. Secondary effects were significantly more common with Nifedipine (7 patients) and with the drug association (9 patients) than with Diltiazem alone (3 patients) or placebo (1 patient). Plasma concentrations of Diltiazem were 328 +/- 35 ng/l with the 360 mg/day dosage and 137 +/- 52 ng/l with the 180 mg/day dosage.(ABSTRACT TRUNCATED AT 250 WORDS)

High-performance liquid chromatographic determination of nifedipine, nicardipine and pindolol using a carbon fibre flow-through amperometric detector

The electrochemical properties of the calcium-channel blockers, nifedipine and nicardipine, and the beta-blocking agent, pindolol, have been exploited for the determination of their concentrations in plasma samples. High-performance liquid chromatography (HPLC) separation was carried out on a cyanopropyl modified column and the drugs were detected in a flow-through carbon fibre microelectrode cell. The chromatographic system was coupled to a column-switching arrangement in order to perform on-line solid-phase extraction of the drugs from spiked human plasma. Preliminary investigations showed the response of the method to be linear over a range of 20-500 ng ml-1 in plasma with a limit of detection of approximately 15 ng ml-1 for each compound.

Analysis of nifedipine and its pyridine metabolite dehydronifedipine in blood and plasma: review and improved high-performance liquid chromatographic methodology

A reversed-phase HPLC method is described for the simultaneous determination of nifedipine and its primary pyridine metabolite dehydronifedipine in blood and plasma, that involves UV detection and neutral (blood) or alkaline (plasma) extraction. The limit of reliable determination is found to be 3 ng ml-1 with an inter-assay RSD of below 11%. In the presence of haemoglobin, nifedipine is unstable at pH greater than 10, necessitating neutral extraction for the measurement of nifedipine in haemolysed blood. Published methods for analysis of nifedipine are reviewed, emphasizing the lack of specificity and sensitivity which render many of them unsuitable for the investigation of nifedipine disposition in man.

Lack of effect of co-trimoxazole on the pharmacokinetics and pharmacodynamics of nifedipine

The pharmacokinetics of nifedipine and its primary oxidised metabolite, M-I were studied in nine healthy volunteers following a single oral dose of 20 mg nifedipine alone or after pretreatment with oral co-trimoxazole. Following pretreatment with co-trimoxazole, no significant effect was detected on maximum plasma concentration, elimination half-life, or area under the plasma concentration-time curve of either nifedipine or M-I, nor on the blood pressure response to nifedipine.

Interaction between nifedipine and cardioactive drugs

Nifedipine (N) and dehydronifedipine (DHN) plasma levels were measured by gas chromatography in 37 patients before and 2 h after the intake of 20 mg N. They suffered from cardiovascular diseases and were treated with N in daily doses of 30 or 60 mg in combination with nitrates, beta-receptor blocking agents, digitoxin, saluretics and/or vasodilators for several weeks or months. Simultaneously, blood pressure and heart rate were measured. For comparison, six healthy volunteers between the ages of 25 and 46 years took 20 mg N on an empty stomach. Their mean plasma N level amounted to 47.7 (SD: 13.6) ng.ml-1, the DHN level reached a mean value of 46.7 (SD: 22.8) ng.ml-1 2 h after administration. The mean plasma N level of the patients rose from 14.1 to 34.1 ng.ml-1 and that of DHN, from 5.4 to 16.0 ng.ml-1. In 26 of 37 patients the heart rate increased without correlating with the altitude of the N level. The ratio DHN/N was 0.83 (SD 0.24) in the volunteers, while in the patients it amounted to 0.59 (SD 0.30). If the criterion DHN/N plasma level reached values greater than 1.0 the N degradation was enhanced (n = 4), and if it reached values less than 0.2, N degradation was depressed (n = 9). The results did not indicate inhibition of N degradation under long-term treatment with simultaneously administered cardioactive drugs.

Antiischemic and hemodynamic effects of intravenous isradipine, a new calcium antagonist, in coronary heart disease: a comparative double-blind cross-over study with nifedipine

In a double-blind cross-over study, 10 patients with stable angina pectoris owing to coronary heart disease were investigated in supine position during rest and bicycle exercise for the effect of 0.4 mg of intravenous (i.v.) isradipine in comparison to 2 mg i.v. nifedipine on cardiac hemodynamics and myocardial ischemia. At rest, both drugs significantly decreased total peripheral resistance (TPR) and mean arterial blood pressure (MAP), whereas heart rate (HR) increased. The pressures and resistance of the pulmonary circulation remained uninfluenced at rest. During symptom limited-exercise, both medications reduced TPR despite an unchanged MAP. Mean pulmonary artery pressure decreased significantly after both medications, whereas right atrial pressure (RAP), pulmonary capillary wedge pressure (PCWP), and pulmonary vascular resistance (PVR) decreased significantly only after nifedipine. The improvement of mean ischemic ST-segment depression averaged 44 +/- 6% (mean +/- SEM, p less than or equal to 0.01) after nifedipine and 45 +/- 7% (p less than or equal to 0.01) after isradipine. The time until angina appeared increased after isradipine by 89 +/- 28% (p less than or equal to 0.05) and after nifedipine by 105 +/- 42% (p less than or equal to 0.01). Significant differences between the two medications appeared only for cardiac output (CO) at rest (p less than or equal to 0.05), during which state the increase after isradipine was higher than after nifedipine, and for exercise HR (p less than or equal to 0.01), during which state only nifedipine induced a significant increase in frequency. We conclude that at the chosen dosages the hemodynamic and antiischemic effects of isradipine are similar to the effects that occur after nifedipine.

Effect of cardiopulmonary bypass on plasma levels of nifedipine

Blood levels of many medications are acutely lowered by cardiopulmonary bypass (CPB). Because nifedipine is often used to provide protection from coronary ischemia, a determination of the effect of CPB on plasma nifedipine levels might help to determine the potential clinical benefit of nifedipine during and after bypass. Four samples of blood were drawn from each of eight patients undergoing cardiac surgery: one before, two during, and one after CPB. Although plasma levels of nifedipine declined during and after bypass (P less than 0.05, analysis of variance), the time-course and slope of the decline indicate that this was an effect of normal metabolism of the drug rather than an effect of physiologic changes occurring during CPB. An important additional finding was that the majority of patients had subtherapeutic levels of nifedipine before bypass, suggesting that additional nifedipine given during and after surgery might be of benefit. The effect of the CPB circuit itself was also examined in vitro by mixing nifedipine into a pump prime solution that was then recirculated with 2 U of outdated blood while levels of nifedipine were measured for 3 h. Plasma levels did not change in either a CPB circuit exposed to light or kept in a darkened room.

Pharmacokinetics of nifedipine derived from a new retard tablet formulation

A nifedipine retard tablet formation (Glopir, 20mg) was developed to reduce the number of daily doses required in the treatment of hypertension. The plasma pharmacokinetics of this oral formulation were examined, in a single study, on 12 healthy volunteers. Single 20 mg doses of nifedipine retard tablet (Glopir, GAP & Co. Athens, Greece) were given after an overnight fast and 10 blood samples were drawn during the first 24 h after administration. Plasma concentrations of nifedipine were measured by high performance liquid chromatography. The mean peak plasma nifedipine concentration was 27.6 ng/ml at a maximum time of 24 h, after tablet ingestion. The mean apparent nifedipine elimination half-life was 16.0 +/- 7.5 h and the mean area under the plasma concentration time curve (0-24 h) 404.1 +/- 134.0 ng/ml.h. The data suggest that the tablet form has properties of a sustained-release preparation, with slow accumulation and elimination phases and can appropriately be given in a twice-daily regimen.

Vascular pressor responses in treated and untreated essential hypertension

Thirty-seven essential hypertensives received placebo for 3 weeks followed by nifedipine retard (n = 14) or enalapril (n = 13) or doxazosin (n = 10) as monotherapy for 6 weeks and attended study days to evaluate the effects of placebo, first dose, and chronic (1-6 weeks) treatment. On each study day, pressor responses to i.v. infusions of phenylephrine (PE) and angiotensin II (AII) were measured 1.5-3 h after drug administration and the derived PD20 values (dose required to increase mean blood pressure by 20 mm Hg) compared. Each treatment produced comparable reductions in BP. Nifedipine significantly attenuated the pressor responses to AII and PE: for AII, the mean PD20 (ng/kg/min) increased from 8.2 (placebo) to 9.9 (first dose), 13.9 (1 week), and 17.4 (6 weeks). Pressor responsiveness to both AII and PE was unchanged following enalapril: for PE, the mean PD20 (micrograms/kg/min) was 2.1 (placebo), 1.5 (first dose), and 1.5 (6 weeks). Doxazosin produced rightward shifts of the PE pressor dose-response curves but had no effect on responses to AII. The relationship between the simultaneous BP and HR changes during the infusion of PE was used as an index of cardiac baroreflex activity. In contrast to enalapril and doxazosin, which had no effect, nifedipine reduced the slope of the HR/BP relationship from -0.62 (placebo) to -0.38 (first dose) and -0.31 beats/min/mm Hg (6 weeks). For comparable reductions in BP, doxazosin only affects adrenergic mechanisms whereas nifedipine affects both adrenergic and non-adrenergically mediated vasoconstriction. The ACE inhibitor enalapril had no effect on pressor responses to AII and PE.

Acute and long-term treatment of hypertension with nifedipine in the elderly

The acute hypotensive effect of nifedipine was evaluated, and the possibility of its long-term use in hypertensives over 60 years of age was studied. Sublingual nifedipine in a dose of 20 mg was given to 28 patients, mean age 73.1 yrs, and blood pressure, heart rate, and plasma drug concentration were monitored at 15 min, and every 30 min thereafter for 3 hrs. Systolic and diastolic blood pressure decreased at 15 min by 22.1 and 7.0 mmHg, respectively, reaching a maximal decrease two hours after drug administration. The decrease in blood pressure level did not correlate with nifedipine plasma concentration, but only with the initial systolic blood pressure. Long-term treatment with nifedipine was initiated in 60 patients, with 45 patients completing the study. Mean age was 66.2 years. An initial dose of 30 mg daily had to be increased to 60-80 mg in one-third of the patients. Monotherapy was not satisfactory in some patients. Blood pressure gradually decreased from 173/99 to 148/85 mmHg at three months, and to 141/84 mmHg at six months. Drug tolerance was fairly good. Nifedipine was withdrawn due to a considerable increase in heart rate in three patients and skin allergy in one. The most frequent adverse symptoms were: rash, headache, and leg oedema. Laboratory tests revealed no changes in urea and creatinine, and an increase in fasting glycaemia. Lipid parameters did not change significantly. These data proved that a single dose of 20 mg of nifedipine produced therapeutic plasma concentration of the drug and good hypotensive effect, positively correlating with initial systolic blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum concentrations and effects of (+/-)-nicardipine compared with nifedipine in a population of healthy subjects

The dihydropyridine calcium antagonist (+/-)-nicardipine shares some of the pharmacologic properties of the dihydropyridine prototype nifedipine. To compare them, serum concentrations and cardiovascular effects of 10 mg nifedipine and 20 mg (+/-)-nicardipine were evaluated at 1, 2, and 3 hours after oral intake in a randomized, crossover, single-blind study involving 79 healthy volunteers. (+/-)-Nicardipine serum concentrations were much lower than those of nifedipine, indicating a greater hepatic first-pass metabolism of (+/-)-nicardipine. There was a significant correlation between serum concentrations of both drugs. The frequency distributions of nifedipine and (+/-)-nicardipine AUC (0-3), heart rate increase, and mean arterial pressure decrease showed no bimodality. This does not confirm the proposed polymorphism of nifedipine oxidation. Concentration-effect plots indicate that (+/-)-nicardipine is more potent than nifedipine but shows comparable efficacy in blood pressure reduction.

Retardation of angiographic progression of coronary artery disease by nifedipine. Results of the International Nifedipine Trial on Antiatherosclerotic Therapy (INTACT). INTACT Group Investigators

425 patients showing mild coronary artery disease (CAD) on arteriography were enrolled in a multicentre trial and randomised to treatment with nifedipine (80 mg/day) or placebo. The two groups were well matched for age, sex, and risk factors. 348 patients (82%) underwent repeat arteriography 3 years later; 282 (134 nifedipine, 148 placebo) had received treatment throughout, but treatment had been stopped in 39 nifedipine-treated and 27 placebo-treated patients after average periods of 354 and 467 days. Computer-assisted measurements of arteriograms from all restudied patients (175 placebo, 173 nifedipine) showed no significant differences in the number or severity of lesions on initial arteriograms, or in the progression or regression of existing lesions over 3 years. In contrast, the number of new lesions per patient was significantly lower in the nifedipine group than in the placebo group (0.59 vs 0.82 lesions per patient, a 28% reduction). Thus in patients with mild CAD nifedipine substantially suppresses disease progression as shown by the appearance of new lesions detectable by quantitative coronary arteriography.

Evaluation of the clinical pharmacology of nilvadipine in patients with mild to moderate essential hypertension

Eighty-four patients with diastolic blood pressure ranging from 100-115 mm Hg were randomized into a multicenter, parallel, double-blind, placebo-controlled, dose response study with nilvadipine (6 mg, 8 mg, 10 mg tid for 28 days). The hypotensive response pattern to nilvadipine was similar with all three doses although duration of response was dose dependent. Maximal decreases in diastolic blood pressure occurred at 1 hour when assessed on days 1 and 15 (16.0, 17.4, and 15.8 mm Hg, vs 17.2, 18.7, and 17.5 mm Hg, respectively). The hypotensive effect remained significant compared to placebo for at least 4 hours after dosing. The increase in heart rate associated with the maximal hypotensive response was minimal and not clinically significant (day 1: 7.6, 5.2, and 4.0 beats/min with 6, 8, and 10 mg; day 15: 4.0, 5.1, 2.6 beats/min with 6, 8, 9, and 10 mg, respectively). Finally, a correlation between plasma drug concentrations and nilvadipine-induced hypotensive response was observed (r = 0.48). Black and white hypertensive patients had similar hypotensive responses. Plasma nilvadipine concentrations on day 15 were similar to those on day 1 suggesting no accumulation of drug with a tid regimen. The most common drug related side effect was headache; less frequently seen were dizziness, edema, palpitations, and abdominal pain. Nilvadipine was well tolerated (only three patients were discontinued due to side effects). The efficacy, lack of tachycardia, and side effect profile observed in this study suggest that nilvadipine may be an important addition to the treatment of hypertension.

Negative inotropic effect of intravenous nifedipine in coronary artery disease: relation to plasma levels

The relative extent of the vasodilator versus direct negative inotropic effects of nifedipine was studied in 15 male patients with documented coronary artery disease and normal left ventricular function. At the time of diagnostic cardiac catheterization, three groups of five patients received dose of 1, 2, and 3 mg intravenous nifedipine at a rate of 0.33 mg/min. Hemodynamic measurements and blood collections were made before, during, and every 5 minutes for 30 minutes after infusion of nifedipine. Heart rate increased and mean arterial pressure decreased significantly after the 2 and 3 mg doses of nifedipine. Systemic vascular resistance was significantly decreased and cardiac index increased after all doses of nifedipine. Maximal left ventricular dp/dt (dp/dtmax) was significantly decreased after the 3 mg infusion. The reduction in dp/dtmax was most consistent with a reduction in left ventricular contractility as opposed to changes in loading conditions. Plasma concentrations of nifedipine were significantly correlated with bidirectional changes in dp/dtmax (r = 0.86). Nifedipine concentrations below 28.2 ng/ml were associated with a rise in dp/dtmax, whereas concentrations above that level were associated with a reduction in dp/dtmax. These data indicate that intravenous nifedipine produces dose- and concentration-dependent depression of myocardial contractility in patients with coronary artery disease. Nifedipine concentrations associated with negative inotropic effects are readily achievable with common oral and sublingual doses.

Is nifedipine phototoxic?

Circumstantial evidence of phototoxicity of nifedipine is poor, being based only on uncontrolled clinical evidence. The authors have assessed nifedipine phototoxicity in vitro by photohemolysis and Candida albicans tests and found it measurable at 10 and 100 micrograms/ml. These dosages exceed the 0.1 microgram/ml blood levels that are usually attained in vivo.

Dose adjustment of nifedipine in hypertensive patients

Ten patients with essential hypertension (WHO grade I-II) were treated in an open dose-adjustment study with the standard regimen of slow-release nifedipine 20 mg b.d. for 2 weeks and with an individualized dose for 6 weeks. The optimum dose, defined as that producing a pre-dose diastolic blood pressure (dBP) of 90 mm Hg at steady state, was determined from the individual concentration-effect relationship after a test-dose of 20 mg. On standard therapy, the reduction in pre-dose dBP was inadequate in 4 patients and it was excessive in 1 patient. After 2 weeks of individualized treatment, the required pre-dose antihypertensive effect was obtained in all patients. The individual doses required were 10 mg b.d., 10 mg t.d.s. 20 mg b.d., 20 mg t.d.s. and 20 mg q.d.s. One patient dropped out of the study because of side effects. Loss of the antihypertensive effect was observed in one patient after 6 weeks of treatment. On the optimized dose, the average value of the pre- and 2 h post-dose steady state nifedipine concentrations (27.6 micrograms/l) compared well with model-derived optimum concentrations (28.6 microliters/l) (r = 0.9210). The results show that the dose of nifedipine can be accurately predicted using the individual concentration-effect relationship after a single dose.