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

The Impact of Paediatric Obesity on Drug Pharmacokinetics: A Virtual Clinical Trials Case Study with Amlodipine

The incidence of paediatric obesity continues to rise worldwide and contributes to a range of diseases including cardiovascular disease. Obesity in children has been shown to impact upon the plasma concentrations of various compounds, including amlodipine. Nonetheless, information on the influence of obesity on amlodipine pharmacokinetics and the need for dose adjustment has not been studied previously. This study applied the physiologically based pharmacokinetic modelling and established a paediatric obesity population to assess the impact of obesity on amlodipine pharmacokinetics in children and explore the possible dose adjustments required to reach the same plasma concentration as non-obese paediatrics. The difference in predicted maximum concentration (Cmax) and area under the curve (AUC) were significant between children with and without obesity across the age group 2 to 18 years old when a fixed-dose regimen was used. On the contrary, a weight-based dose regimen showed no difference in Cmax between obese and non-obese from 2 to 9 years old. Thus, when a fixed-dose regimen is to be administered, a 1.25- to 1.5-fold increase in dose is required in obese children to achieve the same Cmax concentration as non-obese children, specifically for children aged 5 years and above.

Medication adherence during laboratory workup for primary aldosteronism: pilot study

PURPOSE

Current hypertension guidelines stipulate that all incompatible medications be stopped before performing laboratory screening for aldosteronism, but patient adherence is unclear. We measured plasma drug concentrations to determine drug adherence and potential drug bias during biochemical tests.

PATIENTS AND METHODS

Plasma concentrations of 10 antihypertensive drugs were quantified by mass spectrometry in 24 consecutive ambulatory patients with uncontrolled hypertension routinely evaluated for aldosteronism. Drug screening was done before (first visit), and on the day of biochemical tests (second visit) after stopping all incompatible medications. Concentrations above those expected at trough dosing interval defined same-day dose intake.

RESULTS

On the first and second visits, 76% vs 77% of prescribed antihypertensive doses could be verified in plasma. A total of 33% of patients were found to be nonadherent and showed divergent plasma drug results relative to prescriptions (21% drugs not detected/13% unprescribed drugs found) on first visit, 25% on the second (0%/25%), and 46% for both. A total of 21% used medication incompatible with the biochemical tests on the second visit. Moreover, 17% of drug concentrations were below expected trough levels on the first vs 15% on the second visit. This analysis revealed additional four (17%) vs three (13%) nonadherent patients who failed same-day dose intake and remained undetected by qualitative drug tests.

CONCLUSION

Nonadherence was frequent during laboratory evaluations for aldosteronism advocating cautious interpretation of results. A multicenter study is desirable to set the stage for new screening protocols that should incorporate also incentives and checks of drug adherence.

Review of nifedipine GITS in the treatment of high risk patients with coronary artery disease and hypertension

Nifedipine is a dihydropyridine calcium-channel blocker (CCB) introduced approximately 30 years ago for the prophylaxis of angina symptoms, and then later utilized as an anti-hypertensive agent. In the 1990s, several meta-analyses and a case-control study were published which raised concern regarding increased mortality and increased risk for myocardial infarction with short-acting nifedipine. Further evaluation of these meta-analyses and case control study underscores some important limitations and the need to further elucidate the role of this class of medications in high-risk patients. Until 2000, there was a paucity of data on the long-term effects as well as the long-term outcomes of CCBs in the treatment of stable coronary disease or in patients with manifestations of the disease such as hypertension or angina. While it has been well established that nifedipine and other dihydropyridines lower blood pressure and improve symptoms of angina, several studies were designed to evaluate the effect of dihydropyridines on "hard" outcomes, specifically cardiovascular and cerebrovascular events. In this review, we describe the clinical studies evaluating the use of nifedipine when compared to placebo as well as other anti-hypertensive therapies in an attempt to identify the most appropriate place in therapy for this class of medications and to further clarify its utilization in high-risk patients.

Sympatho-excitatory responses to once-daily dihydropyridines in young versus older hypertensive patients: amlodipine versus felodipine extended release

BACKGROUND

Once-daily dihydropyridines exert both indirect sympatho-excitatory and direct central sympatho-inhibitory effects. Age may affect this balance by influencing blood pressure (BP) or renin responses.

METHODS

We evaluated BP, sympathetic and cardiac responses after the first dose and after 8 weeks of treatment with placebo, amlodipine 5 mg/day or felodipine extended release (ER) 5 mg/day in 29 young (22-50 years) versus 37 older (60-77 years) hypertensive patients, using a double-blind, parallel group design.

RESULTS

In the young group, neither dihydropyridine dose decreased BP after the first dose and both caused decreases by 5-10 mmHg after chronic treatment. In the older group, felodipine ER decreased BP rapidly and amlodipine more gradually, and after chronic treatment, systolic BP decreased by 20-25 mmHg. Felodipine ER increased the heart rate by 5-10 bpm after the first dose in both age groups and caused persistent increases in the cardiac index (by 0.2 l/min per square metre) and the ejection fraction only in the older group. Amlodipine did not affect cardiac function in the young, and with chronic dosing decreased the heart rate by 3-5 bpm and the cardiac index by 0.2 l/min per square metre in the older group. In the young hypertensive patients, both dihydropyridines increased plasma norepinephrine (NE) after chronic dosing, with little effect after the first dose. In contrast, in the older group felodipine ER increased plasma NE after the first dose but not with chronic dosing, whereas amlodipine had no effect after the first dose, and after chronic dosing tended to decrease plasma NE.

CONCLUSION

We conclude that age is a major determinant not only of the BP but also of the cardiac and sympathetic responses to once-daily dihydropyridines.

Assessment of sex differences in pharmacokinetics and pharmacodynamics of amlodipine in a bioequivalence study

AIMS

This study was conducted to assess the bioequivalence between two 10-mg amlodipine tablet formulations. As secondary objectives, sex-related differences and tolerability profile were evaluated.

METHODS

Thirty-six healthy volunteers (18 males and 18 females; age 20-32 years, weight 49.5-98.0 kg) were included in a randomised crossover study. Subjects were administered a single 10-mg oral dose of each formulation separated by a 14-day washout period. Plasma amlodipine levels were determined by a high performance liquid chromatographic method with tandem mass spectrometry detection.

RESULTS

All subjects completed the study and 90% confidence intervals for relevant pharmacokinetic parameters were within the ranges defined by European and US Regulatory Authorities: the geometric mean and the 90% confidence interval test/reference ratios calculated from log-transformed values were 104.54 (101.46-107.72%) for AUC(0-infinity) and 100.32 (97.41-103.33%) for Cmax. There were no serious or severe adverse events. The tolerability profile appeared to be comparable for the two products. On average, bioavailability of amlodipine was slightly higher in females than in males, but these differences could be explained by the lower body weight of women. There were no sex-related differences in drug clearance. Bioequivalence was also demonstrated within each gender group. Amlodipine treatment produced a slight decrease of systolic blood pressure and an increased in heart rate, which were more pronounced in women. The incidence of adverse events was similar in men and women.

CONCLUSIONS

The two formulations were considered bioequivalent. Although there were no relevant gender-related differences in the pharmacokinetics of amlodipine, women reached higher amlodipine concentrations most likely because of their lower body weight, and therefore, the reported pharmacodynamic effects were higher within this gender group.

Dihydropyridine calcium channel blockers: basic pharmacological similarities but fundamental therapeutic differences

Recent trials indicate that treatment with calcium channel blockers (CCBs) reduces cardiovascular morbidity and mortality in hypertensive patients (including those with significant coronary artery disease). Since the fundamental mechanism of action of all CCBs is the same, it might be assumed that the findings of these outcome studies can be generalized to all types of CCB. However, in the light of the well-recognized clinical pharmacological differences between the 'rate-limiting' agents, verapamil and diltiazem, and the dihydropyridine group of CCBs, this must be considered to be a misconception. Less well-recognized, and often ignored, are the significant differences between agents within the dihydropyridine group. These differences translate to distinct differences in the therapeutic profiles and may well translate into differences in outcome during long-term treatment. Thus, the differences in pharmacokinetic, pharmacodynamic and therapeutic profiles make it clear that caution should be exercised in assuming that all dihydropyridine CCBs licensed for once-daily administration are equivalent in terms of their durations of action and overall antihypertensive efficacy.

Human variability in CYP3A4 metabolism and CYP3A4-related uncertainty factors for risk assessment

CYP3A4 constitutes the major liver cytochrome P450 isoenzyme and is responsible for the oxidation of more than 50% of all known drugs. Human variability in kinetics for this pathway has been quantified using a database of 15 compounds metabolised extensively (>60%) by this CYP isoform in order to develop CYP3A4-related uncertainty factors for the risk assessment of environmental contaminants handled via this route. Data were analysed from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration-time curve (AUC)] and acute exposure (Cmax). Interindividual variability in kinetics was greater for the oral route (46%, 12 compounds) than for the intravenous route (32%, 14 compounds). The physiological and molecular basis for the difference between these two routes of exposure is discussed. In relation to the uncertainty factors used for risk assessment, the default kinetic factor of 3.16 would be adequate for adults, whereas a CYP3A4-related factor of 12 would be required to cover up to 99% of neonates, which have lower CYP3A4 activity.

Amlodipine reduces blood pressure and headache frequency in cocaine-dependent outpatients

Blood pressure and headache frequency were evaluated in normotensive male and female cocaine-dependent patients (N=43) participating in a placebo-controlled, double-blind trial of amlodipine for the treatment of cocaine dependence. Amlodipine produced a significant reduction in both systolic (p=0.04) and diastolic (p=0.01) blood pressures without producing dizziness or faintness. Placebo subjects had about three times the frequency of headaches compared to the amlodipine-treated subjects (p=0.004). The high frequency of headaches reported by cocaine-dependent individuals was significantly reduced by amlodipine and may reflect improved cerebrovascular tone.

Comparative effects of amlodipine and nifedipine GITS during treatment and after missing two doses

OBJECTIVE

To compare the antihypertensive efficacy of amlodipine and nifedipine gastrointestinal therapeutic system (GITS) measured by office and ambulatory blood pressure monitoring (ABPM) during treatment and, after patients have missed two doses.

METHOD

After a single blind run-in 4-week placebo period, 58 patients were randomly allocated to amlodipine (5mg/daily, n=30) or nifedipine GITS (30mg/daily; n=28) in a double-blind, double dummy fashion. Patients received active medication for 4 weeks. Then, to simulate failure of compliance, patients received two single blinded doses of placebo. Ambulatory blood pressure monitoring was carried out at the end of run-in placebo phase, the first day, the last day of active treatment and up to 72h after the last active dose.

RESULTS

Diastolic blood pressure was controlled in 61.9% patients on amlodipine and 52.9% on nifedipine GITS. Reductions in blood pressure were similar in both groups. ABPM showed significant reduction in blood pressure from the first day in the nifedipine GITS group, while amlodipine group had marginal effect. Peak reduction in systolic/diastolic blood pressure was 26/15mmHg at 5-6h after ingestion of amlodipine tablets. The trough reduction was 22/13mmHg; with a trough-to-peak ratio of 84.61% for systolic and 86.67% for diastolic blood pressure. Peak reduction in systolic/diastolic blood pressure with nifedipine GITS was 19/15mmHg and the trough reduction was 21/17mmHg, giving a trough-to-peak ratio of 100% for both systolic and diastolic blood pressure. When patients received placebo after 4 weeks of active treatment, simulating a compliance failure, amlodipine maintained reduction in systolic and diastolic blood pressure for at least up to 72h after the last active dose, maintaining 57.71% of the effect for systolic blood pressure and 60.00% for diastolic blood pressure. In contrast, nifedipine GITS effect was rapidly lost during this study phase, with a reduction in systolic and diastolic blood pressure of only 14-16%, 72h after the last active dose.

CONCLUSION

This study showed that amlodipine and nifedipine GITS reduce blood pressure to about the same extent during chronic treatment. In the case of compliance failure, such as missing one or two doses, amlodipine maintained significant and important antihypertensive effect with the trough-to-peak ratio still over 50% 72h after the last active dose. On the other hand, the coverage of nifedipine GITS was limited to about 36h after the last active dose.

Retrospective evaluation of the conversion of amlodipine to alternative calcium channel blockers

STUDY OBJECTIVE

To evaluate the effectiveness, safety, and costs associated with a formulary conversion from amlodipine to alternative calcium channel blockers.

DESIGN

Retrospective study.

SETTING

Veterans Affairs Medical Center.

PATIENTS

One hundred patients with hypertension who were receiving amlodipine.

INTERVENTION

Data from a random sample of 100 patients who were taking amlodipine and converted to a formulary calcium channel blocker from February 1, 1999-October 30, 1999, were entered into an Excel database for evaluation of the conversion.

MEASUREMENTS AND MAIN RESULTS

Patients were required to have a diagnosis of hypertension and have had two consecutive clinic visits with blood pressure measurements (and no changes in antihypertensive therapy) before conversion. End points were changes in average systolic blood pressure, diastolic blood pressure, and mean arterial pressure (MAP) from the two clinic visits before and after conversion. In addition, data were collected and analyzed with regard to adverse drug reactions, average dosage of the alternative calcium channel blocker, number of additional antihypertensives begun or discontinued, and number of dosage changes in antihypertensives within the two visits after conversion, and the overall cost impact of conversion. Average systolic blood pressure was reduced from 141.6 +/- 15.1 to 139.2 +/- 15.3 mm Hg after the conversion (NS). Average diastolic blood pressure was significantly reduced from 74 +/- 9.5 to 72.6 +/- 10.1 mm Hg after conversion (p=0.032), as was MAP (97.0 +/-q 9.3 to 94.8 +/- 10.0 mm Hg, p=0.026). Five patients had other changes in therapy made concurrently at the time of conversion, and 19 had changes after conversion. When these patients were excluded from analysis, the reduction in systolic blood pressure after conversion was significant (141.4 +/- 14.5 to 137.7 +/- 14.3 mm Hg, p=0.022), as were reductions in diastolic blood pressure (74.4 +/- 9.4 to 71.7 +/- 9.8 mm Hg, p=0.014) and MAP (96.7 +/- 9.1 to 93.7 +/- 9.3 mm Hg, p=0.007). Of patients who had postconversion changes in therapy, 8 (42%) were converted to diltiazem ER, nifedipine CC, or doses of felodipine that were 50% of the original dose of amlodipine. The overall cost impact of the conversion was a net savings of $14,858/year for each 100 patients converted.

CONCLUSION

Conversion from amlodipine to other calcium channel blockers resulted in statistically significant reductions in diastolic blood pressure and MAP, and was safe as well as cost-effective. Conversion to calcium channel antagonists other than felodipine or less than equal dosages of felodipine may require dosage titration. When converting patients from amlodipine, dosages usually should be equal to those of felodipine; if converting to other calcium channel antagonists, the need for adjustments should be anticipated.

Amlodipine, felodipine, and isradipine in the treatment of Chinese patients with mild-to-moderate hypertension

Optimal treatment of hypertension requires the use of effective antihypertensive drugs. Calcium channel blockers are widely used in the treatment of hypertension and appear to be particularly efficacious in ethnic Chinese patients. The aim of this open-label study was to prospectively investigate the efficacy and tolerability of three dihydropyridine calcium channel blockers in sequence, using the same protocol for each. After 2 weeks of placebo treatment, 73 males and 45 females (mean age, 45 +/- 10 years; mean weight, 67 +/- 10 kg) with essential hypertension (diastolic blood pressure, 95 to 115 mm Hg) were treated with amlodipine (n = 41), felodipine (n = 38), or isradipine (n = 39) for 8 weeks, with dose titration after 4 weeks. Mean seated systolic and diastolic blood pressure decreased by 23/17, 30/17, and 20/15 mm Hg after 8 weeks of treatment with amlodipine, felodipine, and isradipine, respectively. These reductions were all statistically significant. Blood pressure was controlled (defined as diastolic pressure < 90 mm Hg at the final visit or a decrease from baseline of > or = 10 mm Hg) in 85%, 74%, and 74% of patients receiving amlodipine, felodipine, and isradipine, respectively. There were no significant changes in heart rate, plasma lipid levels, or serum biochemistry markers with any of the three treatments. No serious adverse events occurred, but mild adverse effects, including headaches, flushing, tachycardia, dizziness, and edema, were reported; 1 (2%), 6 (16%), and 5 (13%) patients receiving amlodipine, felodipine, and isradipine, respectively, withdrew from the study (P < 0.05). The results of this study indicate that all three drugs are highly effective in lowering blood pressure and are well tolerated in Chinese patients with mild-to-moderate hypertension.

Lacidipine: effects on vascular pressor responses throughout the dosage interval in normotensive subjects

AIMS

To assess the duration and consistency of the pharmacological activity of the dihydropyridine calcium antagonist drug, lacidipine.

METHODS

Eight healthy normotensive young males participated in a double-blind randomised crossover comparison of single and multiple doses (for 2 weeks) of lacidipine and placebo. The calcium antagonist effects were quantified at 2, 6 and 24 h post dose by the extent of the attenuation of the pressor responses to the intravenous administration of the vasoconstrictors angiotensin II and noradrenaline.

RESULTS

After 2 weeks of treatment, lacidipine consistently and significantly attenuated the pressor responses to both agents at 2 h post dose. At 6 and 24 h post dose there was a significant and progressive decline in the effectiveness of lacidipine in attenuating the pressor responses and for the response to angiotensin II there was no statistically significant effect at either 6 or 24 h post dose.

CONCLUSIONS

These results indicate that there is an obvious 'peak' in the pharmacological activity of lacidipine at about 2 h post dose and that this activity is not fully and consistently maintained throughout 24 h.

Clinical pharmacokinetics of nifedipine. Implications for the care of the elderly

Nifedipine, the prototype for the dihydropyridine class of calcium antagonists, has been available for 20 years and its efficacy as a vasodilator and an antihypertensive agent is well recognised. The development of the so-called nifedipine gastrointestinal therapeutic system (GITS), which allows once-daily administration, has modified and improved the overall therapeutic profile of nifedipine to such a significant extent that it might almost be considered a new drug entity. The nifedipine GITS is associated with distinct improvements in terms of patient compliance and convenience, and a reduced incidence of adverse effects. With regard to the care of the elderly, this 'new' drug offers the prospect of a well tolerated and effective treatment without major cost implications.

A comparison of two long-acting vasoselective calcium antagonists in pulmonary hypertension secondary to COPD

STUDY OBJECTIVES AND PATIENTS: Pulmonary hypertension (PH) is common in COPD and may predict mortality in this disorder. We have compared the pulmonary vasodilator effects, dose-response characteristics, and tolerability of two calcium channel blockers, amlodipine and extended-release (ER) felodipine, in 10 patients (seven men, age 68+/-4.8 [SD] years) with clinically stable COPD and PH.

DESIGN

Drugs were given in equal single daily oral doses (2.5, 5, and 10 mg), increasing weekly for 3 weeks, in a randomized investigator-blinded crossover manner with a 1-week wash-out period between the two treatments.

MEASUREMENTS

Doppler measurements of pulmonary hemodynamics were made on the seventh day of treatment at each drug dose. Lung function, arterial blood gases, and adverse events were also monitored weekly.

RESULTS

A dose-dependent decline of pulmonary artery pressure (PAP) was observed with each drug. A dose of 2.5 mg produced a significant decrease in PAP compared with baseline (20% amlodipine, 17% felodipine ER). Additional decreases in PAP were observed at 5 mg and 10 mg that were similar for both drugs, but did not reach statistical significance compared with 2.5 mg. There was a dose-related decrease in pulmonary vascular resistance and increase in oxygen delivery with amlodipine and felodipine ER. Lung function and blood gas values were stable throughout. Side effects (headache and ankle edema) were less frequent during amlodipine treatment (p<0.05).

CONCLUSIONS

Both amlodipine and felodipine ER, given as a single daily oral dose of > or = 2.5 mg, are effective pulmonary vasodilators in COPD patients with PH. Their dose-response characteristics are similar, but amlodipine treatment was associated with fewer side effects.

Twenty-four-hour antihypertensive efficacy of felodipine 10 mg extended-release: the Italian inter-university study

We assessed the 24-h antihypertensive efficacy of an extended-release (ER) 10-mg formulation of the dihydropyridine felodipine in mild-to-moderate essential hypertension [World Health Organization (WHO) stage I-II]. Thirty patients, 23 men and 7 women, aged 37-70 years (mean 53 +/- 9 years) participated in a double-blind, randomized, cross-over study of felodipine 10 mg ER versus placebo. An ambulatory daytime diastolic blood pressure (DBP) >90 mm Hg at the end of a 4-week run-in period was necessary to enter the 10-week treatment phase. Twenty-nine patients completed the treatment phase. Twenty-two underwent a 2-day single-blind placebo follow-up to assess residual drug effects. All patients underwent ambulatory BP monitoring (ABPM) by Spacelabs 90207 recorders. Recorders were programmed to make automatic BP and heart rate (HR) measurements every 15 min throughout the 24 h. Felodipine 10 mg ER significantly (p < 0.01) reduced ambulatory systolic BP (SBP) and DBP values throughout the 24-h, day (7 a.m. to 11 p.m.) and night (11 p.m. to 7 a.m.) periods, but not influencing average ambulatory HR values. Trough-to-peak (T/P) ratios, calculated on the average ambulatory BP values measured in the 7-9 a.m. 2-h interval of the second day of ABPM (before the new drug administration: trough) and in the 10 a.m. to 12 noon 2-h interval of the first day of ABPM (peak BP-lowering effect), were 0.71 and 0.58 for SBP and DBP, respectively. Individual T/P calculations, after post hoc selection of nonresponders, gave superimposable results, the consistency of which was judged on mean, median, and confidence intervals (CI). However, the wide variability of the individual T/P ratios suggests that this method cannot be the only means to evaluate the duration of action of an antihypertensive drug by ABPM. The long-acting BP-lowering drug effect was clearly shown by the ABPM performed in the follow-up when SBP and DBP average values of the 24-h, day, and night periods were still reduced. Felodipine 10 mg ER effectively reduced BP in patients with mild-to-moderate hypertension, showing prolonged duration of its antihypertensive action beyond the time of the next dose.

The trough-to-peak ratio as an instrument to evaluate antihypertensive drugs. The APTH Investigators. Ambulatory Blood Pressure and Treatment of Hypertension Trial

The U.S. Food and Drug Administration designed the trough-to-peak ratio as an instrument for the evaluation of long-acting antihypertensive drugs, but the ratios are usually reported without accounting for interindividual variability. This study investigated how the trough-to-peak ratio would be affected by interindividual and intraindividual variability and by smoothing of the diurnal blood pressure profiles. The ambulatory blood pressure was recorded on placebo in 143 hypertensive patients (diastolic pressure on conventional measurement > 95 mm Hg). After 2 months, the recordings were repeated on 10 mg (n = 66) or 20 mg (n = 77) lisinopril given once daily between 7 and 11 PM. The baseline-adjusted trough-to-peak ratios were determined from diurnal blood pressure profiles with 1-hour precision. Lisinopril reduced (+/- SD) the 24-hour pressure by 16 +/- 17 mm Hg for systolic and 10 +/- 10 mm Hg for diastolic (P < .001). According to the usual approach, disregarding interindividual variability, the trough-to-peak ratio was 0.72 for systolic pressure and 0.67 for diastolic pressure. In the 143 patients the ratios were not normally distributed. They were the same on both lisinopril doses. When interindividual variability was accounted for, the median trough-to-peak ratio was 0.34 (P5 to P95 interval, -0.46 to 0.87) for systolic pressure and 0.26 (-0.44 to 0.84) for diastolic pressure. In 66 patients examined twice on 10 mg lisinopril at a median interval of 32 days, the trough-to-peak ratios were characterized by large intraindividual variability.(ABSTRACT TRUNCATED AT 250 WORDS)