Calcium antagonists and the kidney: future therapeutic perspectives

Can we prevent acute kidney injury?

OBJECTIVE

To review the literature on prevention of acute kidney injury (AKI).

DATA SOURCE

MEDLINE- and PubMed-based review of literature published from 1965 to 2007.

CONCLUSIONS

AKI is very common among critically ill patients. Even mild forms of AKI have significant attributable mortality. Hence, it is imperative that every effort to prevent AKI be made in clinical practice. However, there are very few interventions that have been shown to consistently prevent AKI. Measures such as adequate hydration, maintenance of adequate circulating blood volume and mean arterial pressure, and avoidance of nephrotoxins are still the mainstay of prevention. Loop diuretics and "renal-dose" dopamine have been clearly shown not to prevent AKI and may, in fact, do harm. Among the remaining pharmacologic options, N-acetylcysteine has the strongest evidence in prevention of AKI. Fenoldopam and theophylline need further investigation before being used to prevent septic AKI and contrast nephropathy, respectively. The role of prophylactic dialysis in preventing contrast nephropathy needs to be investigated further.

Emerging drugs for renal failure

Renal failure involves a significant impairment of the essential functions of the kidney, which can be either acute with sudden and rapid onset (acute renal failure [ARF]) or chronic with gradual onset (chronic renal failure [CRF]). ARF, if detected early, may be halted or reversed, whereas CRF is generally irreversible. Without treatment or intervention, both forms of renal failure lead to end stage renal failure (ESRF) or end stage renal disease (ESRD), requiring renal replacement therapy (RRT) in the form of dialysis or renal transplantation for survival. However, provision of RRT requires expert teams working in specialised units, making therapy of patients with renal failure expensive; furthermore, RRT is complex, with its own complications. Although pharmacological interventions have shown promise in experimental models, these have not been as successful in the clinical setting (e.g., administration of atrial natriuretic peptide, low-dose dopamine). At present, drugs are administered during CRF to either reduce one of the many risk factors of CRF (e.g., angiotensin-converting enzyme inhibitors, statins) or to deal with the consequences of CRF (e.g., erythropoietin, calcitriol). Recent evidence suggests that some of these interventions may provide further direct beneficial effects via reduction of renal inflammation. Although these interventions have greatly improved the prospects for patients suffering ESRF, the development of novel drugs and therapies with which to reduce the consequences of renal failure and ESRD remain topics of great interest. This article reviews the therapies available for the prevention and management of renal failure in adults and describes, in detail, emerging drugs and novel interventions that may soon become available for the treatment or prevention of ESRF.

Calcium antagonists

Calcium antagonists were introduced for the treatment of hypertension in the 1980s. Their use was subsequently expanded to additional disorders, such as angina pectoris, paroxysmal supraventricular tachycardias, hypertrophic cardiomyopathy, Raynaud phenomenon, pulmonary hypertension, diffuse esophageal spasms, and migraine. Calcium antagonists as a group are heterogeneous and include 3 main classes--phenylalkylamines, benzothiazepines, and dihydropyridines--that differ in their molecular structure, sites and modes of action, and effects on various other cardiovascular functions. Calcium antagonists lower blood pressure mainly through vasodilation and reduction of peripheral resistance. They maintain blood flow to vital organs, and are safe in patients with renal impairment. Unlike diuretics and beta-blockers, calcium antagonists do not impair glucose metabolism or lipid profile and may even attenuate the development of arteriosclerotic lesions. In long-term follow-up, patients treated with calcium antagonists had development of less overt diabetes mellitus than those who were treated with diuretics and beta-blockers. Moreover, calcium antagonists are able to reduce left ventricular mass and are effective in improving anginal pain. Recent prospective randomized studies attested to the beneficial effects of calcium antagonists in hypertensive patients. In comparison with placebo, calcium antagonist-based therapy reduced major cardiovascular events and cardiovascular death significantly in elderly hypertensive patients and in diabetic patients. In several comparative studies in hypertensive patients, treatment with calcium antagonists was equally effective as treatment with diuretics, beta-blockers, or angiotensin-converting enzyme inhibitors. From these studies, it seems that a calcium antagonist-based regimen is superior to other regimens in preventing stroke, equivalent in preventing ischemic heart disease, and inferior in preventing congestive heart failure. Calcium antagonists are also safe and effective as first-line or add-on therapy in diabetic hypertensive patients. Heart rate-lowering calcium antagonists (verapamil, diltiazem) may have an edge over the dihydropyridines in post-myocardial infarction patients and in diabetic nephropathy. Thus, calcium antagonists may be safely used in the management of hypertension and angina pectoris.

Acute renal failure--which treatment modality is the best?

Despite the progress in animal research concerning the pathophysiology and the progress in clinical practice regarding the methods of therapy, the incidence and mortality of acute renal failure remain high, especially when other organs are involved. New pharmacological interventions have led to the perspective that in the near future it may be possible to prevent and/or ameliorate this devastating syndrome. Continuous dialysis therapy and the selection of a biocompatible membrane may possibly help the critically ill patient especially when parenteral nutrition and correction of electrolyte and acid-base disturbances are important. Nevertheless, more solid data are needed and one should take into consideration that acute renal failure is a multifactorial syndrome. The type of dialysis itself is not the only matter which has to be evaluated since the mortality rate can be correlated with the number of involved organs before or after the initiation of acute renal failure and with the severity of the original disease. In clinical practice, a large number of prospective studies and more sophisticated statistical methodology are needed in order to evaluate the proper treatment modality.

Calcium antagonists and the progression of chronic renal failure

End-stage renal disease, which signifies irreversible renal failure, constitutes a major and growing public health problem worldwide. The striking increase in end-stage renal disease has catalyzed clinical and investigative focus on pharmacologic interventions to retard progression to this condition. Increasing evidence indicates that some classes of antihypertensive medications may confer a greater effect than others in slowing progression of renal disease despite similar levels of blood pressure reduction. Substantive data indicate that angiotensin converting enzyme inhibition preferentially retards the progression of renal disease, primarily by protecting the injured kidney from hemodynamically mediated glomerular damage. Newer studies suggest that calcium antagonists also have diverse properties, which are independent of their renal microcirculatory effects that might afford renal protection.

Deleterious effects of calcium channel blockade on pressure transmission and glomerular injury in rat remnant kidneys

Hypertensive mechanisms are postulated to play a major role in the progressive glomerulosclerosis (GS) after renal mass reduction. But, in contrast to converting enzyme inhibitors, BP reduction by calcium channel blockers, has not provided consistent protection. Radiotelemetric BP monitoring for 7 wk was used to compare nifedipine (N) and enalapril (E) in the rat approximately 5/6 renal ablation model. After the first week, rats received N, E, or no treatment (C). The overall averaged systolic BP in C (173 +/- 7 mmHg) was reduced by both E and N (P < 0.001), but E was more effective (113 +/- 2 vs. 134 +/- 3 mmHg, P < 0.01). GS was prevented by E (2 +/- 1 vs. 26 +/- 5% in C) but not by N (25 +/- 6%). GS correlated well with the overall averaged BP in individual animals of all groups, but the slope of the relationship was significantly steeper in N compared with C+E rats (P < 0.02), suggesting greater pressure transmission to the glomeruli and GS for any given BP. Since autoregulatory mechanisms provide the primary protection against pressure transmission, renal autoregulation was examined at 3 wk in additional rats. Autoregulation was impaired in C rats, was not additionally altered by E, but was completely abolished by N. These data demonstrate the importance of autoregulatory mechanisms in the pathogenesis of hypertensive injury and suggest that calcium channel blockers which adversely affect pressure transmission may not provide protection despite significant BP reduction.

Renal and hemodynamic effects of diltiazem after elective major vascular surgery--a potential renoprotective agent?

A postoperative study was done of the effects of an infusion of diltiazem (DTZ), 1 microgram.kg-1.min-1 after a bolus dose of 0.28 mg.kg-1 on renal function and hemodynamics in 10 patients who were operated with insertion of an abdominal aortic graft. Urine flow, glomerular filtration rate (GFR) by inulin clearance, and renal plasma flow (RPF) by PAH clearance and fractional excretion of electrolytes and osmols were measured for three periods of 20 min during infusion of DTZ, in the morning after surgery. Systemic hemodynamic studies were conducted and serum levels of catecholamines were measured. GFR increased during the initial period of DTZ infusion. There were no significant changes during the study period in any of the other parameters, compared to baseline, except for a decrease in heart rate from 84 to 77 beats per minute. The absence of a sustained increase in GFR and a natriuretic and diuretic effect may possibly be ascribed to a preexisting nonconstricted status of the renal vasculature. The authors conclude that the dose of DTZ used in this study can be safely used for further investigations to elucidate the effects of peroperative infusion of DTZ on renal function in connection with major vascular surgery.

Calcium-channel blockers for prophylaxis of radiocontrast-associated nephrotoxicity

Because of both an absence of sufficient data and the concern for increased toxicity in certain patient populations, the use of CCBs to reduce radiocontrast-associated nephrotoxicity is not recommended. Additional prospective, randomized trials are needed.

Acute renal failure

Preview An abrupt decrease in the kidneys' ability to excrete waste products is a common cause of severe morbidity and death in critically ill patients. This complication may result from prerenal, renal parenchymal, or postrenal causes. The authors describe the clinical and laboratory evaluation of acute renal failure and offer an approach to prevention and appropriate management.