Pharmacokinetics of felodipine in chronic hemodialysis patients

Extracorporeal treatment for calcium channel blocker poisoning: systematic review and recommendations from the EXTRIP workgroup

BACKGROUND

Calcium channel blockers (CCBs) are commonly used to treat conditions such as arterial hypertension and supraventricular dysrhythmias. Poisoning from these drugs can lead to severe morbidity and mortality. We aimed to determine the utility of extracorporeal treatments (ECTRs) in the management of CCB poisoning.

METHODS

We conducted systematic reviews of the literature, screened studies, extracted data, summarized findings, and formulated recommendations following published EXTRIP methods.

RESULTS

A total of 83 publications (6 in vitro and 1 animal experiments, 55 case reports or case series, 19 pharmacokinetic studies, 1 cohort study and 1 systematic review) met inclusion criteria regarding the effect of ECTR. Toxicokinetic or pharmacokinetic data were available on 210 patients (including 32 for amlodipine, 20 for diltiazem, and 52 for verapamil). Regardless of the ECTR used, amlodipine, bepridil, diltiazem, felodipine, isradipine, mibefradil, nifedipine, nisoldipine, and verapamil were considered not dialyzable, with variable levels of evidence, while no dialyzability grading was possible for nicardipine and nitrendipine. Data were available for clinical analysis on 78 CCB poisoned patients (including 32 patients for amlodipine, 16 for diltiazem, and 23 for verapamil). Standard care (including high dose insulin euglycemic therapy) was not systematically administered. Clinical data did not suggest an improvement in outcomes with ECTR. Consequently, the EXTRIP workgroup recommends against using ECTR in addition to standard care for patients severely poisoned with either amlodipine, diltiazem or verapamil (strong recommendations, very low quality of the evidence (1D)). There were insufficient clinical data to draft recommendation for other CCBs, although the workgroup acknowledged the low dialyzability from, and lack of biological plausibility for, ECTR.

CONCLUSIONS

Both dialyzability and clinical data do not support a clinical benefit from ECTRs for CCB poisoning. The EXTRIP workgroup recommends against using extracorporeal methods to enhance the elimination of amlodipine, diltiazem, and verapamil in patients with severe poisoning.

Clearance of cardiovascular medications during hemodialysis

PURPOSE OF REVIEW

To review the current understanding of hemodialysis-mediated clearance of commonly used cardiovascular medications.

RECENT FINDINGS

Although cardiovascular drug dialyzability is poorly understood, many drug classes appear to include agents with substantially different degrees of dialyzability. Recent data suggest that more readily dialyzable beta-blockers associate with higher short-term mortality in patients initiating these drugs when on hemodialysis. Although this relationship was not observed in a later study with angiotensin-converting enzyme inhibitors of varying dialyzability, studies of this kind are currently limited by pharmacokinetic data that are either incomplete or no longer applicable to modern hemodialysis procedures.

SUMMARY

There are substantial deficits in our understanding of cardiovascular medication dialyzability, which relates in large part to advances in the process of hemodialysis that have rendered older studies of dialyzability irrelevant. The importance of cardiovascular disease in patients receiving hemodialysis demands a better understanding of the effect hemodialysis exerts on cardiovascular drug pharmacokinetics.

Management of hypertension in hemodialysis patients

The relationship of hypertension with adverse outcomes is uncertain in the hemodialysis population. If hypertension is an etiologically significant cardiovascular risk factor in hemodialysis patients, the first step would be to assess the level of BP accurately. BP obtained at home over a week and averaged using a validated oscillometric automatic device can prove valuable. To the extent BP lowering influences cardiovascular outcomes, home BP of 150/90 mm Hg would warrant therapy, since it correlates with target organ damage and hypertension diagnosed by ambulatory BP monitoring. To manage hypertension, limiting dietary sodium intake and individualizing dialysate sodium delivery would be first steps. The magnitude of reduction in BP with dietary sodium restriction and the whether dialysate sodium can be safely limited in those who are hypotension-prone is unclear. Antihypertensive drug therapies can effectively reduce BP and are needed by the vast majority of hemodialysis patients. Whether control of hypertension translates into better outcomes is not known, but collective evidence suggests that hypertension should be controlled in hemodialysis patients.

Calcium-channel blockers and end-stage renal disease: pharmacokinetic and pharmacodynamic considerations

PURPOSE OF REVIEW

To characterize the pharmacokinetics and pharmacodynamics of the different calcium-channel blockers.

RECENT FINDINGS

Calcium-channel blockers have been in use for some time in the end-stage renal disease population. Their primary use has been as antihypertensive and antianginal therapies. In this regard, they are effective agents. Recently, it has been noted that dialysis-related hypotension occurs less frequently in calcium-channel blocker treated patients. Also, access patency and overall patient survival are improved with calcium-channel blocker therapy.

SUMMARY

Calcium-channel blockers are useful agents for the control of hypertension in end-stage renal disease patients and appear to favorably influence survival in this population. Calcium-channel blockers are not dialyzable and their pharmacokinetics do not substantially change with renal failure therefore they do not require dose adjustment based on level of renal function. Too few studies exist to determine if individual calcium-channel blockers differ in their effects. Prospective, randomized, controlled clinical trials are needed in the end-stage renal disease population to better understand the role of calcium-channel blockers in the excess cardiovascular disease burden of this population.

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.

Felodipine. A review of the pharmacology and therapeutic use of the extended release formulation in cardiovascular disorders

Felodipine is a vascular-selective, dihydropyridine calcium antagonist previously investigated as a conventional tablet formulation administered twice daily. More recently considerable experience has been gained with an extended release (ER) formulation which has the convenience of once daily administration. Felodipine ER has been well studied in patients with essential hypertension. As monotherapy in mild to moderate essential hypertension, felodipine ER is at least as effective in reducing blood pressure as other calcium antagonists, beta-blockers, diuretics and ACE inhibitors, with some results favouring felodipine ER at a statistically significant level at the dosages used. It is also effective combined with controlled release metoprolol or enalapril in patients with mild to moderate essential hypertension. In patients with more severe forms of essential hypertension uncontrolled by beta-blocker and/or diuretic therapy, felodipine ER was effective as an 'add-on' therapy in placebo-controlled trials, and, at the dosages used, more effective than either sustained release nifedipine or nitrendipine. Felodipine produces effective control of blood pressure without negative effects on cardiac performance. In addition to its antihypertensive action, results suggest that felodipine therapy is associated with significant regression of left ventricular hypertrophy. Furthermore, it appears suitable for use in patients with concomitant diabetes, renal dysfunction or asthma, and is also being investigated for use in patients with congestive heart failure or angina pectoris. Felodipine ER is an effective drug for the treatment of all grades of essential hypertension, and can be used both as monotherapy and in combination with other antihypertensive agents. Further clinical experience should fully establish the long term tolerability of felodipine ER and consequently its place in therapy relative to other accepted antihypertensive drugs. However, with the convenience of once daily administration, felodipine ER is a worthwhile innovation in the treatment of hypertension.