Differential cardiovascular effects of calcium channel blocking agents: potential mechanisms

Calcium Channel Blockers in Acute Care: The Links and Missing Links Between Hemodynamic Effects and Outcome Evidence

Calcium channel blockers (CCBs) exert profound hemodynamic effects via blockage of calcium flux through voltage-gated calcium channels. CCBs are widely used in acute care to treat concerning, debilitating, or life-threatening hemodynamic changes in many patients. The overall literature suggests that, for systemic hemodynamics, although CCBs decrease blood pressure, they normally increase cardiac output; for regional hemodynamics, although they impair pressure autoregulation, they normally increase organ blood flow and tissue oxygenation. In acute care, CCBs exert therapeutic efficacy or improve outcomes in patients with aneurysmal subarachnoid hemorrhage, acute myocardial infarction and unstable angina, hypertensive crisis, perioperative hypertension, and atrial tachyarrhythmia. However, despite the clear links, there are missing links between the known hemodynamic effects and the reported outcome evidence, suggesting that further studies are needed for clarification. In this narrative review, we aim to discuss the hemodynamic effects and outcome evidence for CCBs, the links and missing links between these two domains, and the directions that merit future investigations.

A pharmacological characterization of electrocardiogram PR and QRS intervals in conscious telemetered rats

INTRODUCTION

The conscious telemetered rat is widely used as an early in vivo screening model for assessing the cardiovascular safety of novel pharmacological agents. The current study aimed to identify its utility in assessing electrocardiogram (ECG) PR and QRS interval changes.

METHOD

Male Han-Wistar rats (~250 g) were implanted with radio-telemetry devices for the recording of ECG and haemodynamic parameters. Animals (n = 4-8) were treated with single doses of calcium (nifedipine, diltiazem or verapamil; CCBs) or sodium channel blockers (quinidine or flecainide; SCBs) or their corresponding vehicles in an ascending dose design. Data was recorded continuously up to 24 h post-dose. Pharmacokinetic analysis of blood samples was performed to allow comparison of effects to published data in other species.

RESULTS

Of the CCBs, only diltiazem (300 mg/kg) prolonged the PR interval (49 ± 2 versus vehicle: 43 ± 1 ms), although this was not statistically significant (p = .11). QA interval decreased with nifedipine (30 ± 1 versus 24 ± 0 ms) and diltiazem (34 ± 1 versus 27 ± 1 ms) but increased with verapamil (30 ± 0 versus 37 ± 1 ms) demonstrating pharmacological activity of each agent. Both SCBs, caused statistically significant (p < .05) increases in both intervals - quinidine (100 mg/kg; PR: 50 ± 2 versus 43 ± 1 ms; QRS: 22 ± 2 versus 18 ± 1 ms) and flecainide (9 mg/kg; PR: 56 ± 1 versus 46 ± 1 ms; QRS: 27 ± 1 versus 21 ± 1 ms). Drug plasma exposure was confirmed in all animals.

DISCUSSION

At similar plasma concentrations to other species, the conscious telemetered rat demonstrates limited utility in assessing PR interval prolongation by CCBs, despite significant contractility effects being observed. However, results with SCBs demonstrate a potential application for evaluating drug-induced QRS prolongation.

Long-term maternal hypoxia: the role of extracellular Ca2+ entry during serotonin-mediated contractility in fetal ovine pulmonary arteries

Antenatal maternal long-term hypoxia (LTH) can alter serotonin (5-HT) and calcium (Ca(2+)) signaling in fetal pulmonary arteries (PAs) and is associated with persistent pulmonary hypertension of the newborn (PPHN). In humans, the antenatal maternal hypoxia can be secondary to smoking, anemia, and chronic obstructive pulmonary disorders. However, the mechanisms of antenatal maternal hypoxia-related PPHN are unresolved. Because both LTH and 5-HT are associated with PPHN, we tested the hypothesis that antenatal maternal LTH can increase 5-HT-mediated PA contraction and associated extracellular Ca(2+) influx through L-type Ca(2+) channels (Ca(L)), nonselective cation channels (NSCCs), and reverse-mode sodium-calcium exchanger (NCX) in the near-term fetus. We performed wire myography and confocal-Ca(2+) imaging approaches on fetal lamb PA (∼ 140 days of gestation) from normoxic ewes or those acclimatized to high-altitude LTH (3801 m) for ∼110 days. Long-term hypoxia reduced the potency but not the efficacy of 5-HT-induced PA contraction. Ketanserin (100 nmol/L), a 5-HT(2A) antagonist, shifted 5-HT potency irrespective of LTH, while GR-55562 (1 µmol/L), a 5-HT(1B/D) inhibitor, antagonized 5-HT-induced contraction in normoxic fetuses only. Various inhibitors for Ca(L), NSCC, and reverse-mode NCX were used in contraction studies. Contraction was reliant on extracellular Ca(2+) regardless of maternal hypoxia, NSCC was more important to contraction than Ca(L), and reverse-mode NCX had little or no role in contraction. Long-term hypoxia also attenuated the effects of 2-APB and flufenamic acid and reduced Ca(2+) responses observed by imaging studies. Overall, LTH reduced 5HT(1B/D) function and increased NSCC-related Ca(2+)-dependent contraction in ovine fetuses, which may compromise pulmonary vascular function in the newborn.

On the mechanism of action of calcium antagonists

A short review is given of possible mechanisms of action of the organic "calcium antagonists". Calcium antagonists comprise a chemically heterogenous group of drugs, and the term may be used to denote agents that inhibit Ca2+-dependent processes or regulatory mechanisms without acting at other sites. Such drugs may be subdivided into those that decrease the availability of Ca2+ to the myoplasm, and those that decrease the cellular effects of Ca2+ without lowering the intracellular Ca2+ concentration. Accordingly, calcium channel blockers, such as verapamil, nifedipine, and diltiazem, form a subgroup of calcium availability inhibitors, as they block influx of extracellular calcium through ion selective channels in the membrane both in cardiac and smooth muscle. However, it cannot be excluded that some of these drugs, particularly in smooth muscle, may have additional sites of action, which must be taken into consideration when they are used as investigational tools.

Assessment of hyperglycemia after calcium channel blocker overdoses involving diltiazem or verapamil

BACKGROUND

Overdoses of calcium channel blocker agents result in hyperglycemia, primarily due to the blockade of pancreatic L-type calcium channels and insulin resistance on the cellular level. The clinical significance of the hyperglycemia in this setting has not previously been described.

METHODS

This study is a retrospective review of all adult (age, >or=15 yrs) patients with a discharge diagnosis of acute verapamil or diltiazem overdose at five university-affiliated teaching hospitals. The severity of overdose was assessed by determining whether a patient met the composite end points of in-hospital mortality, the necessity for a temporary pacemaker, or the need for vasopressors. We compared the initial and peak serum glucose concentrations with hemodynamic variables between patients who did and did not meet the composite end points.

RESULTS

A total of 40 patients met inclusion criteria, with verapamil and diltiazem accounting for 27 of 40 (67.5%) and 13 of 40 (32.5%) of the ingestions, respectively. For those patients who did and did not meet the composite end points, the median initial serum glucose concentrations were 188 (interquartile range, 143.5-270.5) mg/dL and 129 (98.5-156.5) mg/dL, respectively (p = .0058). The median peak serum glucose concentrations for these two groups were 364 (267.5-408.5) mg/dL and 145 (107.5-160.5) mg/dL, respectively (p = .0001). The median increase in blood glucose was 71.2% for those who met composite end points vs. 0% for those who did not meet composite end points (p = .0067). Neither the change in the median heart rate nor the change in systolic blood pressure was significantly different in any group.

CONCLUSION

Serum glucose concentrations correlate directly with the severity of the calcium channel blocker intoxication. The percentage increase of the peak glucose concentration is a better predictor of severity of illness than hemodynamic derangements. If validated prospectively, serum glucose concentration alone might be an indicator to begin hyperinsulinemia-euglycemia therapy.

Are One or Two Dangerous? Calcium Channel Blocker Exposure in Toddlers

Unintentional pediatric ingestions of calcium channel blockers are increasing in frequency due to increased use of this antihypertensive class. Potential toxic effects include severe refractory hypotension and death; however, the true toxicity of unintentional pediatric ingestions of 1-2 pills is poorly defined. A literature review was conducted to more closely determine toxic and lethal dosages of calcium channel blockers in the pediatric population under 6 years of age. Results indicate that, although most accidental pediatric ingestions are asymptomatic, a small number do result in cardiovascular instability or even death. The dihydropyridines, particularly nifedipine, and the phenylalkylamine verapamil are most often implicated in symptomatic ingestions. There are no adequate data to identify which children are predisposed to illness, or to determine cutoffs for toxic dosages. However, ingestions of only one pill have been documented to cause severe symptoms, including death. Thus, emergency evaluation to assess potential toxicity is necessary, and gastrointestinal decontamination and in-hospital observation of at least 6 h after toxic ingestion for regular release medications, and 12-24 h after toxic ingestion for sustained release medications is recommended for all cases of unintentional calcium channel blocker ingestion in children younger than 6 years of age.

Fatality from administration of labetalol and crushed extended-release nifedipine

OBJECTIVE

To report a case in which a crushed extended-release (XL) nifedipine tablet contributed to a patient fatality.

CASE SUMMARY

A 38-year-old woman with multiple medical problems presented to the hospital in acute respiratory distress and was diagnosed with acute pulmonary edema and pneumonia. After initial stabilization, her medications were changed to oral hydralazine, labetalol, and nifedipine XL. These medications were crushed and administered through a nasogastric tube. The patient developed worsening bradycardia with hypotension and experienced asystolic cardiac arrest. She was resuscitated; however, the following morning, another dose of labetalol and nifedipine XL was crushed and administered through the nasogastric tube. She again developed worsening bradycardia with hypotension and ultimately died.

DISCUSSION

The administration of a crushed nifedipine XL tablet resulted in the patient's severe hypotension. The concurrent administration of labetalol prevented a compensatory heart rate increase. The repeat administration of nifedipine XL in the same manner underscores a fundamental problem in healthcare worker communication and drug delivery system comprehension. Use of the Naranjo probability scale indicated a highly probable relationship between the patient's hypotension and the nifedipine and labetalol therapy.

CONCLUSIONS

Simultaneous administration of a beta-blocker and a calcium-channel blocker may produce synergistic effects. The release characteristics of oral controlled-release medications are destroyed when crushed, resulting in the rapid bioavailability of the total drug amount. The importance of education and communication among nurses, physicians, and pharmacists regarding the mechanism of action of controlled-release medications and their administration needs to be emphasized.

Effect of calcium channel blockers on baroreceptor reflex in anaesthetized cats

The baroreflex-induced changes in heart rate in chloralose anaesthetized and artificially ventilated cats (2.5-4.0 kg) before and after pretreatment with calcium channel blockers (CCBs) were compared. Baroreflex mediated changes in heart rate (HR) were elicited by raising and lowering the systemic blood pressure with intravenous injections of phenylephrine and sodium nitroprusside, respectively. The effects of three CCBs, verapamil, diltiazem and nifedipine administered either intravenously (i.v.) or intracisternally (i.c.) were studied. Verapamil administration markedly inhibited the reflex bradycardia as well as the tachycardia following either i.v. or i.c. administration. Intracisternally, a relatively smaller dose of verapamil produced an effect comparable in magnitude and duration, to a higher i.v. dose. The reflex bradycardia was inhibited following i.v., but not i.c. administration of nifedipine while the reflex tachycardia was not affected significantly by either i.v. or i.c. nifedipine. Intravenous diltiazem did not appear to affect the reflex bradycardia or tachycardia significantly. It is suggested that verapamil administration interacts with central cardiovascular integrating mechanisms to reduce the gain of the baroreflex function. Nifedipine and diltiazem are relatively free from this effect.

Damaging effects of the calcium paradox are reduced in isolated hearts from ethanol-dependent rats: paradoxic effects of dihydropyridine drugs

Previous experiments showed that isolated hearts from ethanol-exposed rats show a marked increase in sensitivity to anoxic myocardial damage, and we suggested that this may be due to excess calcium entry through L-type voltage-operated calcium channels (L-VOCCs). To challenge this hypothesis, we investigated the effect of ethanol treatment ex vivo on a damaging stimulus, the "calcium paradox," which is associated with removal of calcium from the perfusate. Adult male Sprague-Dawley rats were exposed to intoxicating concentrations of ethanol for 6-10 days by inhalation. Isolated hearts from these animals were perfused with Krebs-Henseleit buffer by using a modified Langendorff technique, and the calcium paradox induced by a 10-min period of perfusion with calcium-free buffer, followed by reperfusion with calcium-containing buffer. Compared with controls, hearts from ethanol-exposed rats were significantly protected against myocardial damage, as shown by a marked reduction in release of intracellular proteins (lactate dehydrogenase, creatine phosphokinase, and myoglobin) during the reperfusion phase. These indices of myocardial damage were modified by the presence of the dihydropyridine (DHP) calcium channel antagonist nitrendipine (10(-6) M) and the DHP L-VOCC activator Bay K 8644 (10(-7) M) in the perfusate during the calcium paradox. Paradoxically, both drugs appeared to increase the damaging effects of calcium-free perfusion, with this effect being generally greater in the preparations from ethanol-exposed rats. As a result, the difference between these hearts and those from control rats was reduced, although a significant degree of protection against the calcium paradox remained. The results support the hypothesis that long-term exposure to ethanol in vivo produces marked alterations in the toxic effects of changes in myocardial calcium concentration. The increased sensitivity to DHP drugs of isolated hearts from ethanol-treated rats is consistent with previous experiments showing increased DHP radioligand-binding sites in these tissues.

Increased sensitivity to damaging effects of hypoxia and anoxia of isolated hearts from rats after prolonged exposure to ethanol: apparent protection by nitrendipine

The studies described here investigate whether pathologic states that are thought to cause myocardial damage through excess calcium entry (i.e., hypoxia and anoxia) indeed cause greater damage in hearts from ethanol-exposed animals, and whether L-type voltage-operated calcium channels (L-VOCCs) are implicated. Adult male Sprague-Dawley rats were exposed to intoxicating concentrations of ethanol vapor for 6-10 days, and their isolated hearts compared with those of control animals in a Langendorff perfusion system. Hypoxia was induced by perfusion with Krebs-Henseleit buffer, which had not previously been bubbled with oxygen; anoxia was produced by perfusion with buffer bubbled with nitrogen. On reperfusion with oxygenated buffer, evidence of myocardial damage during the hypoxic/anoxic period was obtained by the release of intracellular proteins into the perfusate. After hypoxia, release of myoglobin (MYO) was significantly greater from hearts from ethanol-exposed rats than from controls; other indices of myocardial damage also were increased by hypoxia but did not differ significantly between treatment groups. After anoxic perfusion, release of lactate dehydrogenase (LDH) and creatine phosphokinase (CPK) as well as MYO were all markedly and significantly increased from ethanol-exposed hearts compared with those from control rats. The role of L-VOCCs in this damage was assessed with the calcium channel antagonist nitrendipine (10(-6) M) present in the perfusing buffer immediately before and during the anoxic stimulus. This completely reversed the situation so that preparations from ethanol-exposed rats now showed a reduced release of intracellular proteins compared with hearts from controls. Comparisons with absolute values from the previous experiments suggest that nitrendipine increased release of LDH and CPK from control hearts with little effect on these indices from ethanol-exposed hearts. However, in the case of anoxia-induced MYO release, nitrendipine markedly and significantly reduced this in hearts from ethanol-treated rats but had only a very small effect on the same parameter in controls. The results strongly suggest increased pathologic effects of hypoxia/anoxia in hearts from ethanol-exposed rats. This increased sensitivity may be at least partly a consequence of increased numbers of L-VOCCs in this tissue.

Novel calcium antagonists with both calcium overload inhibition and antioxidant activity. 1. 2-(3, 5-di-tert-butyl-4-hydroxyphenyl)-3-(aminopropyl)thiazolidinones

A series of 2-(3, 5-di-tert-butyl-4-hydroxyphenyl)-3-(aminopropyl)thiazolidinones was synthesized in order to explore novel calcium antagonists with potent antiischemic activity. These compounds were designed to have, in addition to Ca2+ antagonistic activity, both Ca2+ overload prevention and antioxidant activity in one molecule. These three kinds of activity were evaluated by using a K+-depolarized rat aorta, a veratridine-induced Ca2+ overload model of rat cardiomyocytes, and a soybean lipoxygenase-induced lipid peroxidation model of rabbit low-density lipoprotein, respectively. In particular, 2-(3, 5-di-tert-butyl-4-hydroxyphenyl)-3-[3-[N-methyl-N-[2-[3, 4-(methylenedioxy)phenoxy]ethyl]amino]propyl]-1,3-thiazolidin-4-on e (7o) was found to be highly potent and possessed a well-balanced combination of these actions in vitro.

Effects of the optical isomers of verapamil on electrophysiological properties of the heart in conscious dogs

We compared the cumulative dose-response relations of verapamil (0.1, 0.2 and 0.4 mg kg(-1)) in different R/S enantiomer ratios (100/0, 90/10, 80/20, 50/50 and 20/80) on the electrophysiological and hemodynamic characteristics of the heart using the conscious dogs. A reduction of mean arterial pressure occurred with 20R/80S producing a 3-times greater decrease than 100R/0S, but an increase in heart rate occurred with 20R/80S producing a 9-times greater increase than 100R/0S. Increased heart rate was concurrent with decreased mean arterial pressure most prevalent with a higher ratio of S-isomer that produced a greater reduction in mean arterial pressure and increase in heart rate at lower overall verapamil doses. Atrio-ventricular conduction time increased 3-5 min after each infusion, with 20R/80S producing a 4-times greater effect than 100R/0S. These results indicate that the peripheral and cardiac electrophysiologic properties of various nonracemic verapamil mixtures are mainly attributable to the concentration of S-isomer.

Effects of the calcium channel antagonist mibefradil on haemodynamic and morphological parameters in myocardial infarction-induced cardiac failure in rats

OBJECTIVE

Calcium channel antagonists (CCA) have been proposed for the prevention of cardiac events after myocardial infarction (MI). Mibefradil is a CCA featuring a selective blockade of T-type Ca2(+)-channels. The aim of the study was to characterize the effects of mibefradil on haemodynamic and morphological parameters in a model of postMI chronic heart failure and to establish the "therapeutic window" for the start of therapy.

METHODS

MI was induced by permanent ligation of the left coronary artery in male normotensive Wistar rats. Animals were assigned to placebo- or mibefradil-treated (10 mg/kg/day p.o.) groups as follows: (1) sham operation; (2) MI placebo treatment; (3) 7 days preMI start of treatment; (4) 3 h postMI start of treatment; (5) 24 h postMI start of treatment; (6) 3 days postMI start of treatment; (7) 7 days postMI start of treatment. Treatment was continued for 6 weeks postMI. At this time point, mean arterial blood pressure (MAP), heart rate, left ventricular enddiastolic pressure (LVEDP) and contraction force (dP/dtmax) were measured in conscious rats at baseline and after methoxamine (MEX; 0.5-1.0 mg/h i.v.) stimulation to increase afterload. The hearts were subjected to histological determination of infarct size (IS), infarct length (IL), noninfarcted length (NL), left ventricular circumference (LVC), inner LV-diameter (LVD) and septal thickness (ST).

RESULTS

Six weeks after MI, MAP was lowered, LVEDP increased and dP/dtmax reduced. Mibefradil treatment increased basal MAP in groups 3-5 compared to the placebo-treated MI group. Under mibefradil, LVEDP was reduced at baseline in groups 3-6 and, after MEX, in all groups. dP/dtmax was increased in groups 3-4 at baseline and after MEX. In the placebo-treated MI group, the infarcted area was 39% of the LV and heart weight, LVD and LVC were increased. Heart weights of mibefradil-treated rats (groups 3-6) did not differ from those of the placebo-treated group. Early onset of treatment with mibefradil reduced IS and IL and increased NL in groups 3-4. LVD and LVC were decreased in group 3 only. ST was increased in groups 3-5.

CONCLUSION

Chronic treatment with mibefradil exerts beneficial actions on cardiac structure and performance in postMI cardiac failure in rats, especially when the onset of treatment is either prior to or within hours after the acute ischemic event.

Cardiovascular effects of verapamil enantiomer combinations in conscious dogs

We examined the systemic and coronary hemodynamic effects of five combinations of R- and S-verapamil enantiomers (R/S; 100/0, 90/10, 80/20, 50/50, and 20/80%, respectively) in conscious dogs chronically instrumented for measurement of aortic and LV pressure, +dP/dt, subendocardial segment length, coronary blood flow velocity, and aortic blood flow. Dogs received escalating doses (0.1, 0.2, and 0.4 mg kg(-1)) of each verapamil combination over 2 min at 30 min intervals on different experimental days and peak changes in hemodynamics were recorded 2 min after each dose. All verapamil combinations increased heart rate, mean aortic blood flow, and coronary blood flow velocity and decreased calculated systemic and coronary vascular resistance. Alterations in coronary hemodynamics were most pronounced with 20/80 R/S verapamil. Racemic and 20/80 R/S verapamil decreased mean arterial and left ventricular systolic pressure, in contrast to combinations with greater concentrations of the R enantiomer. Left ventricular function was unchanged during administration of 100/0, 90/10, and 80/20 R/S verapamil. Direct negative inotropic and lusitropic effects occurred with 50/50 and 20/80 R/S verapamil. The high dose of 20/80 R/S verapamil also increased left ventricular end-diastolic pressure and the regional chamber stiffness constant, consistent with diastolic dysfunction. The results indicate that combinations of R- and S-verapamil produce differential hemodynamic and left ventricular functional effects in conscious, unsedated dogs that are dependent on the relative ratio of these enantiomers.

Effects of amlodipine in patients with chronic heart failure

The role of calcium antagonists in patients with ischemic heart failure is currently unclear. We examined the effects of amlodipine on exercise capacity and central and regional hemodynamics in 32 patients with mild to moderate chronic heart failure in a single-center, double-blind, randomized placebo-controlled trial. All were taking at least 40 mg of furosemide daily with an angiotensin-converting enzyme inhibitor. Ischemic heart disease was the most common cause of heart failure, but no patient had symptom-limiting angina. Mean treadmill exercise capacity in patients taking amlodipine increased by 96 seconds (95% confidence interval -23 to 215) and 50 seconds (-34 to 135) in the placebo group; mean difference in change between treatments was 70 seconds (-90 to 233), p = 0.38. Active treatment with amlodipine did not affect self-paced corridor walking times. Similarly, there were no significant effects on cardiac output, oxygen uptake, heart rate, and mean arterial pressure at rest or during exercise. Calf and renal blood flow were also unchanged by treatment. The lack of significant effect demonstrated by these data suggests a limited role for amlodipine in patients with ischemic cardiomyopathy, although it may prove beneficial in those with nonischemic disease. More data are required before amlodipine can be recommended for all patients with chronic heart failure.

Pharmacological studies on a new antihypertensive agent, S-2150, a benzothiazepine derivative: 3. Hypotensive and antimyocardial-stunning effects in dogs

The hypotensive and antimyocardial-stunning effects of a new 1,5-benzothiazepine antihypertensive agent, S-2150, were investigated in dogs. S-2150 (30 mg/kg, p.o.) decreased the blood pressure in conscious renal hypertensive dogs. Although the maximal hypotensive effect of S-2150 was observed at 5-9 h after administration, the effect of diltiazem was seen at 2.0 h. Arrhythmia was not observed as a hypotensive effects of S-2150 but was markedly induced by diltiazem. In anesthetized open-chest dogs, S-2150 (20 micrograms/kg/min, i.v.) caused by hypotensive effect similar to that of diltiazem but decreased myocardial work (double product) by much less than did diltiazem. S-2150 more promptly improved the local myocardial stunning caused by occlusion of the left anterior descending coronary artery and its reperfusion. This effect did not accompany the energy-sparing action in ischemic/reperfused myocardium, which was different from the case of diltiazem. In isolated dog mesenteric arteries, S-2150 relaxed KCl and phenylephrine contracture. These results suggest that S-2150 is a favorable hypotensive agent for hypertensive patients with ischemic heart disease. Blockage of both Ca2+ channels and alpha 1-adrenoceptors by S-2150 seems to lead to cardiovascular effects different from those of diltiazem.

Preconditioning to improve myocardial protection

Major advances in the composition and delivery of cardioplegia have helped to reduce the morbidity and mortality associated with coronary bypass surgery. The discovery of the preconditioning response should facilitate the development of more powerful myocardial protective agents. These new agents may act to directly stimulate the preconditioning response or may act in a supplementary fashion to either augment the response or provide protection from alternate pathways. As new techniques of myocardial protection continue to be developed, the risk-to-benefit ratio of coronary bypass surgery will continue to improve. As a result of these improvements, surgeons will be able to offer surgery to an increasingly high risk patient population without increasing the morbidity or mortality currently associated with coronary bypass.

Dual calcium-channel blocker therapy in the treatment of hypertension

OBJECTIVE

To review the in vitro receptor binding data of calcium-channel blockers (CCBs) and in vivo studies in humans regarding the use of dual calcium-channel blocker therapy, with a focus on the use of this therapy for hypertension.

DATA SOURCE

A MEDLINE search was conducted to identify literature pertaining to CCBs.

STUDY SELECTION

In vitro studies and investigations that evaluated CCB receptor binding and the interactions between subclasses of CCBs were chosen. All studies in humans and clinical trials that evaluated the use of dual CCB therapy in the treatment of cardiovascular diseases were selected for review. Also, case reports describing the use of dual CCB therapy were included in this article.

DATA EXTRACTION

The methodology, results, and conclusions of the selected data were evaluated. Data regarding the in vitro receptor binding kinetics of CCBs, as well as interactions, were reported. Because there is limited information on dual CCB therapy for hypertension, clinical studies using this treatment for ischemic heart disease were also reviewed. They were summarized and compared on the basis of the degree of disease control (e.g., blood pressure, exercise tolerance), adverse effects, and other clinical endpoints of pharmacologic therapy.

DATA SYNTHESIS

In vitro studies have identified binding sites for the dihydropyridine (nifedipine), diphenylalkylamine (verapamil), and benzothiazepine (diltiazem) subclasses of CCBs, and indicate that they are allosterically related to each other within the voltage-sensitive calcium-channel receptor. Dihydropyridine binding affinity is decreased with concomitant verapamil binding, but is enhanced by concomitant diltiazem binding. Dual CCB therapy has been shown to be efficacious in patients with ischemic heart disease. Although this therapy is limited by dose-related adverse effects, it appears to have an important role in patients with ischemia that is refractory to conventional therapy, or for those whose therapeutic options are limited by contraindications. Theoretically, many patients with hypertension may benefit similarly from dual CCB therapy. Because data evaluating this treatment option are sparse, recommendations regarding safety, efficacy, and the role of dual CCB therapy for hypertension would be premature.

CONCLUSIONS

Controlled data evaluating dual CCB therapy for the treatment of hypertension are lacking. This treatment modality may be beneficial in the future, but requires further investigation to determine safety and efficacy.

Comparison of nifedipine alone and with diltiazem or verapamil in hypertension

Receptor binding studies suggest that combinations of calcium channel blockers may result in either enhanced or diminished pharmacological effects, but clinical data in hypertension are incomplete. In this study, we compared blood pressure reductions using nifedipine alone, nifedipine plus diltiazem, and nifedipine plus verapamil and determined whether combinations alter nifedipine pharmacokinetics. After determination of baseline blood pressures. 16 subjects with essential hypertension (12 men, 4 women; mean age, 48 years) received 30 mg/d open-label, sustained release nifedipine for 2 weeks. If still hypertensive (n = 16), they were randomized (double-blind) to receive either additional sustained release diltiazem or sustained release verapamil, both 180 mg/d, for 2 weeks and were then crossed-over for the final 2 weeks of the study. All medications were once-daily, extended-release formulations. Blood pressures and nifedipine plasma concentrations were measured during the final day of each treatment. Overall, each combination lowered mean systolic and diastolic pressures more than nifedipine alone. Mean supine diastolic pressures were significantly lower at 8 hours (77.6 versus 84.6 mm Hg, P = .001) and 12 hours (81.5 versus 87.1 mm Hg, P = .04) with nifedipine plus diltiazem than nifedipine plus verapamil. Mean nifedipine concentrations were inversely correlated with mean blood pressures. Mean nifedipine area under the curve values were greater with diltiazem than verapamil (1430 versus 1134 ng.h/mL, P = .026), with each greater than nifedipine alone (957 ng.h/mL). Nifedipine plus diltiazem had a greater antihypertensive effect than nifedipine plus verapamil. Diltiazem caused greater increases in nifedipine plasma concentrations than did verapamil. These data suggest that combined calcium channel blockers result in additive antihypertensive effects, perhaps because of a pharmacokinetic interaction.

The force-interval relationship in human myocardium

The force-interval relationship is an important modulator of contractility in mammalian myocardium. In a number of mammalian species, increasing the frequency of stimulation results in an increase in force of contraction. Over the last 10 years, the effects of atrial pacing have been closely examined in normal human subjects and in patients with dilated cardiomyopathy, and the effects of the stimulation frequency have been investigated in isolated preparations from nonfailing and failing human hearts. An abnormal force-interval relationship in vivo and in vitro has been a consistent finding in patients with dilated cardiomyopathy, whereby an increase in stimulation frequency fails to increase the contractile response. The force-interval relationship of cardiac muscle has been shown to reflect intracellular calcium cycling and sarcoplasmic reticulum function. Therefore, agents that affect excitation-contraction coupling, in particular intracellular calcium mobilization and sarcoplasmic reticulum function, modulate the response of contraction force to stimulation frequency.

Effects of the calcium channel blockers, diltiazem and Ro 40-5967, on systemic haemodynamics and plasma noradrenaline levels in conscious dogs with pacing-induced heart failure

1. Calcium channel blockers increase cardiovascular morbidity and mortality in patients with left ventricular dysfunction. These adverse effects are probably related to the negative inotropic effect of calcium channel blockers and/or a neurohormonal activation. 2. The present study was designed to examine, in conscious dogs, the acute haemodynamic and sympathetic effects of diltiazem and Ro 40-5967 (a novel calcium channel blocker) in the control state and in heart failure. 3. Thirteen dogs were instrumented with a micromanometer and an aortic catheter. After completion of experiments in the control state, heart failure was induced by right ventricular pacing (250 beats min-1, 3 weeks). Diltiazem and Ro 40-5967 were given intravenously (0.8 mg kg-1 and 1.0 mg kg-1 respectively). Cardiac output was measured by a thermodilution technique. 4. In the control state, both agents decreased similarly mean aortic pressure with significant increases in heart rate, cardiac output (both +1.0 l min-1 and P < 0.001) and plasma noradrenaline (both +55%) without changes in left ventricular dP/dtmax. In heart failure, for matched decreases in mean aortic pressure, neither diltiazem nor Ro 40-5967 changed heart rate significantly; diltiazem decreased cardiac output (-0.3 l min-1, P < 0.02) and dP/dtmax (-14%, P < 0.001) while Ro 40-5967 still increased cardiac output (+0.3 l min-1, P < 0.02) although the increased amount was smaller than in the control state. Plasma noradrenaline level was increased more during diltiazem infusion (+120%) than during Ro 40-5967 infusion (+38%, P < 0.001). 5. Diltiazem and Ro 40-5967 have similar haemodynamic and sympathetic effects in the control state.Heart failure alters haemodynamic and sympathetic responses to both calcium channel blockers but the magnitude of the alteration appears to be different. Diltiazem exerts a depressant effect on cardiac function which cannot be overcome by its vasodilator effect and sympathetic stimulation, while Ro 40-5967 has little effect on cardiac function. These data suggest that novel calcium channel blockers with less depressant effect may not be detrimental in heart failure.

Electrophysiologic effects of amlodipine vs. diltiazem in patients with coronary artery disease and beta-blocking therapy

This study compares the electrophysiologic effects of amlodipine and diltiazem in patients with coronary artery disease concomitantly treated with background beta-blocking therapy. Thirty patients were included in an open-label parallel study in two phases. During phase 1, patients were screened and placed on maintenance atenolol therapy at 50 or 100 mg/day, while phase 2 consisted of right-sided catheterization and randomization of patients to either amlodipine (10 mg i.v.) or diltiazem (10 mg i.v.). Following treatment with amlodipine, no significant alteration in markers of electrophysiological activity was observed. Treatment with diltiazem resulted in a significant lengthening of sinus cycle length (SCL, p < 0.04), AH interval (p < 0.02), and Wenckebach CL (WCL, p < 0.001), and a trend towards an increase in sinus node recovery time (SNRT, p = 0.057). No effects were observed with regard to HV interval and corrected SNRT. The results of this study indicate that 10 mg intravenous amlodipine has no significant electrophysiological action on sinus or AV node function in patients receiving beta-blocker therapy with atenolol, suggesting that amlodipine can be added to beta-blockers to treat patients with myocardial ischemia and/or hypertension without any significant increase in the risk of bradyarrhythmias.

Noncardiogenic pulmonary edema complicating massive verapamil overdose

Noncardiogenic pulmonary edema has not been (to our knowledge) previously reported associated with a verapamil overdose. We describe a 27-year-old woman who developed this complication after an overdose of 15, 120-mg verapamil tablets (total of 1,800 mg). This report illustrates the possibility of serious pulmonary embarrassment in the course of a verapamil overdose and the need to avoid excessive crystalloid administration during the hypotensive period.

Vascular versus myocardial effects of calcium antagonists

As vascular smooth muscle tone and myocardial contractility both depend on calcium entry, the calcium antagonists are not only potent arterial vasodilators, but may also have important negative inotropic effects. For example, verapamil is nearly equipotent in reducing vascular smooth muscle tone and myocardial contraction in isolated tissue preparations. In contrast, felodipine has high vascular selectivity in such preparations, and drug concentrations required to depress myocardial contraction are more than 100 times greater than those required to relax vascular smooth muscle. In the isolated, isovolumetrically contracting canine left ventricle, clinically relevant concentrations of felodipine (14 nmol/L) produce coronary vasodilation and a mild positive inotropic response. Using left ventricular (LV) pressure-volume analysis, we evaluated a similar dose of felodipine (plasma drug concentration 16 nmol/L) in conscious dogs. Felodipine produced a 25mm Hg fall in arterial pressure and a 10% reduction in peripheral vascular resistance. There was no negative inotropic effect. Instead, myocardial contractile performance was slightly but significantly enhanced. These results were not altered by adrenergic blockade. Further studies in our laboratory showed that doses of amlodipine and nifedipine producing arterial vasodilation of a magnitude similar to that produced by felodipine had negative inotropic effects in the conscious dog. Only felodipine enhanced the rate of LV relaxation and the rate of early diastolic filling. Thus, felodipine was significantly more vasoselective than amlodipine and nifedipine. The direct inotropic effects of calcium antagonists are difficult to evaluate in clinical studies because of the load-dependence of most conventional measures of LV performance. However, no negative inotropic effects are clinically relevant doses of felodipine have been identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of calcium chloride on verapamil- and diltiazem-pretreated isolated rat hearts

The effects of calcium chloride on cardiac responses to verapamil and diltiazem were investigated using isolated and perfused rat hearts with a Langendorff technique. Ionized calcium concentrations were increased approximately from 0.5 mM to 2.2 mM when the hearts were pretreated with 0.2 mg/L of verapamil or 0.28 mg/L of diltiazem, or were untreated with calcium blockers. Calcium significantly counteracted the negative inotropic effect produced by diltiazem and verapamil. In contrast, the negative chronotropic effects of both diltiazem and verapamil were potentiated by increasing concentrations of ionized calcium, and this potentiation was not eliminated by 1.0 mg/L of atropine. An atrioventricular block was induced by both verapamil and diltiazem when ionized calcium concentrations were lower than normal. It is suggested from this study that, although calcium chloride counteracts the negative inotropic effects of verapamil and diltiazem, abruptly increased ionized calcium may cause severe bradycardia clinically.

Verapamil intoxication: a literature review of overdoses and discussion of therapeutic options

Calcium channel antagonists can be quite toxic. In the management of poisoning, early recognition is critical. Calcium channel antagonists are frequently prescribed, and the potential for serious morbidity and mortality with overdosage is significant. Ingestion of these agents should be suspected in any patient who presents in an overdose situation with unexplained hypotension and conduction abnormalities. The potential for toxicity should be noted in patients with underlying hepatic or renal dysfunction who are receiving therapeutic doses. Because there is no specific antidote, decontamination of the gastrointestinal tract is crucial. Intravenous calcium should be administered to symptomatic patients because it is relatively innocuous and may be beneficial. Volume expansion should be the initial approach to hypotension unrelated to bradycardia. Patients who have had a verapamil overdose should be observed in intensive care units where Swan-Ganz catheterization and ventricular pacing are routinely available. The choice of sympathomimetic agents for treatment remains controversial. According to the published literature, isoproterenol, epinephrine, and norepinephrine may be more effective in improving bradycardia and the resultant hypotension than dopamine. However, none of these agents is universally effective. A more logical approach may be to improve cardiac output with agents like amrinone. Bay K 8644 and 4-aminopyridine show promise as potential antidotes but at present are still experimental.

Hemodynamic tolerability and anti-ischemic efficacy of high dose intravenous diltiazem in patients with normal versus impaired ventricular function

OBJECTIVES

This study was designed to compare the acute systemic and coronary hemodynamic effects of high doses of intravenous diltiazem in patients with normal versus impaired left ventricular function, investigate the safety of this drug and compare its anti-ischemic potential in these two patient groups during pacing-induced stress.

BACKGROUND

Because coronary hemodynamic effects and negative inotropic properties of diltiazem are dose related, high dose intravenous diltiazem may improve anti-ischemic efficacy but may not be tolerated in patients with impaired cardiac function.

METHODS

High dose intravenous diltiazem, 0.4 mg/kg for 5 min followed by 0.4 mg/kg for 10 min, was administered to 23 normotensive patients with coronary artery disease, 11 (group A) with normal and 12 (group B) with impaired ventricular function (ejection fraction < 45%) during two identical arterial pacing stress tests performed 30 min before (pacing test I) and immediately after diltiazem (pacing test II).

RESULTS

Diltiazem was well tolerated despite high peak plasma levels, 869 +/- 152 micrograms/liter (group A) and 926 +/- 169 micrograms/liter (group B). It resulted in immediate but similar reductions in systemic resistance from 1,321 +/- 136 (control value) to 963 +/- 113 dynes.s.cm-5 (group A) and from 1,267 +/- 106 to 865 +/- 58 dynes.s.cm-5 (group B) and in mean arterial pressure from 107 +/- 3 to 93 +/- 4 mm Hg (group A) and from 103 +/- 4 to 86 +/- 4 mm Hg (group B), at 5 min after diltiazem (all p < 0.05 vs. control value). Diltiazem improved stroke output from 36 +/- 3 (control value) to 46 +/- 4 ml/beat per m2 in group B and from 44 +/- 4 (control value) to 49 +/- 5 ml/beat per m2 in group A, an effect that was significantly greater and more prolonged in group B than in group A. Although neither heart rate nor contractility was affected in either group, left ventricular end-diastolic pressure increased in group A (9 +/- 2 mm Hg to 12 +/- 1 mm Hg, p < 0.05) but not in group B. Despite similar reductions in coronary resistance and improvements in coronary flow, diltiazem consistently reduced myocardial oxygen extraction, but only in group B. Also, the anti-ischemic effects of diltiazem were more pronounced in group B. During pacing test II, myocardial lactate extraction normalized in group B (7 +/- 5% vs. -6 +/- 12% [pacing test I]) but not in group A, contractility indexes improved more and the increase in left ventricular filling pressure was reduced to a greater extent in group B. Moreover, the ischemia-induced increase in arterial pressures, observed in both groups during pacing test I, was prevented in group B but recurred in group A during pacing test II.

CONCLUSIONS

High dose intravenous diltiazem is well tolerated, augments coronary flow and improves left ventricular pump function, particularly in patients with preexisting ventricular dysfunction. As its anti-ischemic effects also appear more pronounced in the latter group, high dose diltiazem may be particularly useful when ventricular function is depressed, for example, during prolonged ischemia at rest.

A one-year evaluation of calcium channel blocker overdoses: toxicity and treatment

STUDY OBJECTIVE

To examine the cardiovascular toxicity of calcium channel blockers and the efficacy of various treatments.

DESIGN

Case series collected prospectively over one year.

SETTING

Three regional poison control centers.

TYPE OF PARTICIPANTS

One hundred thirty-nine hospitalized patients who had ingested a calcium channel blocker.

INTERVENTIONS

Calcium, dopamine, atropine, isoproterenol, glucagon, and pacemakers.

MAIN RESULTS

Hypotension, sinus node suppression, and dysrhythmias often occur with calcium channel blocker overdoses, but atrioventricular nodal block occurs more often with verapamil (chi 2 test, P < .025). Calcium was administered to 23 patients and was efficacious in reversing depression of cardiac conduction and increasing blood pressure. Dopamine was administered to ten patients and was efficacious in increasing blood pressure. Atropine was administered to eight patients, but only two had a positive response.

CONCLUSION

Atrioventricular nodal depression is more common with verapamil overdoses. Calcium and dopamine are useful in treating toxicity from calcium channel blocker overdose, whereas atropine is sometimes useful.

Influences of changes in calcium concentration and verapamil on the cardiac depressant effect of ethanol in cat papillary muscle

1. In isolated cat heart papillary muscle electrically driven at a constant rate the depressant effects of increasing concentrations of ethanol on peak tension developed (PTD) was studied in Ringer-Locke solution with different calcium concentrations and with the addition of verapamil. 2. Ethanol induced a concentration dependent decrease in PTD that was significantly greater for each concentration of ethanol in hypocalcic medium (1.1 mM) than in normocalcic medium (2.2 mM). 3. In normocalcic (2.2 mM) medium, verapamil (5.1 x 10(-4) mM) plus ethanol (48.6 and 97.2 mM) produced a decrease in PTD to values significantly greater than those obtained by the addition of ethanol and verapamil alone. Therefore a potentiation of the effects of ethanol by verapamil was observed when both drugs act simultaneously. 4. In hypercalcic medium (4.4 mM), verapamil plus ethanol (48.6 and 97.2 mM) produced a slight decrease in PTD that was significantly less than that observed in normocalcic and hypocalcic mediums. 5. In hypocalcic medium (1.1 mM) verapamil plus ethanol (48.6 and 97.2 mM) produced a decrease in PTD that was of the same relative magnitude (%) as that observed in normocalcic medium. However no potentiation of the combined effects of verapamil plus ethanol was observed in hypocalcic medium.

Acute hemodynamic and electrophysiologic effects and safety of high-dose intravenous diltiazem in patients receiving metoprolol

The anti-ischemic efficacy of diltiazem may improve with increments in dosage and with additional beta-blocking therapy. However, the combined administration could lead to adverse effects through amplification of negative inotropic and chronotropic properties. To evaluate hemodynamic tolerability and safety of high-dose intravenous diltiazem in patients with coronary artery disease receiving long-term metoprolol treatment, 9 such patients were studied for 30 minutes after onset of intravenous diltiazem administration (0.5 mg/kg for 5 minutes, followed by 15 mg/hour). Diltiazem plasma levels peaked at 5 minutes (641 +/- 74 micrograms/liter), decreasing to 177 micrograms/liter at 30 minutes. Average metoprolol levels (43 +/- 12 micrograms/liter) did not change. Diltiazem immediately decreased systemic vascular resistance, left ventricular systolic and mean aortic pressures (29, 21 and 20%, respectively, at 5 minutes), and they remained significantly reduced at 30 minutes. Heart rate initially increased by 11% during the bolus infusion (p < 0.05). Concomitantly, contractility indexes Vmax and Vce40, measured at fixed heart rates, also increased significantly by 11%. Both heart rate and contractility indexes returned to baseline levels thereafter. Cardiac output increased by 10% (p = not significant), stroke index remained unchanged, but stroke work decreased significantly by 20%. Also, the tension-time index was significantly reduced (23%). Diltiazem induced moderate negative lusitropic effects, the first derivative of negative left ventricular pressure decline decreased by 12% and Tau 2 lengthened by 13%. Concomitantly, left ventricular filling pressure increased from 19 +/- 2 to 23 +/- 3 mm Hg, but only at 5 and 15 minutes. PQ, QRS and QTc intervals were not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of semotiadil (SD-3211), a benzothiazine calcium antagonist, on blood pressure and atrioventricular conductivity in anesthetized dogs

We investigated the effects of semotiadil (SD-3211), a novel calcium antagonist, on blood pressure and the atrioventricular (AV) conduction time and functional refractory period (FRP) of the AV conduction system (AV conductivity) in anesthetized open-chest dogs. The heart was electrically stimulated at a constant rate. In dogs with an intact nerve supply to the heart, i.v.-injections of semotiadil (0.03 to 0.3 mg/kg) produced a fall of blood pressure in a dose-dependent manner. AV conduction time and FRP were prolonged by rather higher doses (0.3 mg/kg), and second-degree AV block occurred only with the highest dose (1 mg/kg). In dogs with the nerve supply to the heart interrupted, the vasodepressor effects and suppressant effects of semotiadil on AV conductivity were slightly enhanced. The suppressant effects on AV conductivity became marked as pacing rates were increased. These results suggest that semotiadil at appropriate doses produces a vasodepressor effect without affecting AV conductivity even in the heart deprived of nervous control, e.g., the heart with beta-adrenoceptors blocked. The frequency-dependent suppressant effect on FRP of semotiadil is also noteworthy in the treatment of reentrant supraventricular tachycardia that involves the AV node.

Evidence for verapamil-induced functional inhibition of noradrenergic neurotransmission in vivo

Contractions of the cat nictitating membrane have been used to explore the effects of calcium channel blockers on neurotransmission in vivo, by comparing the effects of verapamil and nifedipine on contractions of nictitating membrane following either electrical stimulation of the superior cervical ganglion or intravenous injection of the alpha-adrenoceptor agonist phenylephrine. Verapamil (0.3, 0.6 and 1.2 mg/kg, iv) produced a dose related and reversible inhibition of stimulation induced contractions but did not affect phenylephrine responses of nictitating membrane. Intravenous nifedipine (10, 20 and 40 micrograms/kg) produced inconsistent effects on both stimulation- and phenylephrine-induced contractions of the nictitating membrane. Thus only verapamil appears to selectively affect noradrenergic neurotransmission in this model, possibly by altering the neurotransmitter release from the terminals innervating the nictitating membrane in the cat.

Responses of murine natural killer cells to binding of the fungal target Cryptococcus neoformans

Natural killer (NK) cells bind to and inhibit the growth of the fungal target Cryptococcus neoformans. Since C. neoformans is structurally and chemically distinct from the standard tumor cell target used in the model of NK cell-mediated cytotoxicity, this study was designed to investigate the NK cell response after binding to cryptococci. Transmission electron micrographs and three-dimensional reconstructions of NK cell-cryptococci conjugates demonstrated focusing of the NK cell centrioles and Golgi apparatus toward the cryptococcal attachment site. NK cell cytoskeletal changes after cryptococcal binding were confirmed by immunofluorescence studies in which NK cells were allowed to bind to cryptococci in Mg2(+)-containing, Ca2(+)-free medium. One hour after the addition of Ca2+ to the preformed conjugates, the bound NK cells demonstrated a significant increase in the percentage of microtubule organizing centers focused toward the cryptococcal binding site. Colchicine, a drug that inhibits microtubule assembly, did not affect NK cell-cryptococci binding but abrogated NK cell-mediated cryptococcal growth inhibition, indicating that microtubule assembly, an important prerequisite for the secretory process, is not required for NK cell-cryptococci binding but is essential for inhibition of cryptococcal growth. In addition, the Ca2+ channel-blocking reagents, lidocaine and verapamil, did not affect NK cell-cryptococci binding but blocked the NK cell-mediated anticryptococcal activity, suggesting that a Ca2+ flux is essential for inhibition of cryptococcal growth. Considered together, these data indicate that NK cells respond to binding of a target cell that has a capsule and cell wall, in addition to a cell membrane, in a manner similar to that seen following binding to target cells that are surrounded by only a cell membrane; however, the response of the NK cells to the binding of C. neoformans is slower and possibly less efficient than the response after tumor cell binding.

A prospective, randomized, double-blind, crossover study to compare the efficacy and safety of chronic nifedipine therapy with that of isosorbide dinitrate and their combination in the treatment of chronic congestive heart failure

We performed a prospective, randomized, double-blind, crossover study to compare the efficacy and safety of vasodilation with the calcium entry blocker nifedipine with that of isosorbide dinitrate (ISDN) and their combination as treatment for heart failure. Twenty-eight patients with New York Heart Association Functional class II or III chronic heart failure due to left ventricular systolic dysfunction were studied. All patients were maintained on a constant dose of digitalis and diuretics throughout the study. Eight weeks of therapy with nifedipine alone or in combination with ISDN resulted in a significantly higher incidence of heart failure deterioration necessitating hospitalizations and/or additional diuretics. Twenty-four percent of patients required hospitalization during nifedipine therapy and 26% required hospitalization during nifedipine-ISDN combination therapy in comparison to 0% requiring hospitalization during ISDN therapy alone. The total number of heart failure-worsening episodes was nine among patients on nifedipine, three among patients on ISDN (p less than 0.09 versus nifedipine), and 21 among patients on nifedipine-ISDN combination (p less than 0.001 versus nifedipine, p less than 0.0001 versus ISDN). Premature discontinuation of drug administration due to clinical deterioration or other side effects occurred in 29% of patients during nifedipine therapy, 5% of patients during ISDN therapy (p = 0.05 versus nifedipine), and 19% of patients during the combination therapy. A comparison of eight patients who demonstrated clinical deterioration on nifedipine with the remainder of the patients demonstrated no significant difference in left ventricular ejection fraction (0.24 +/- 0.06 versus 0.23 +/- 0.07) or maximal oxygen uptake during exercise (13 +/- 3 versus 14 +/- 2 ml/kg/min).(ABSTRACT TRUNCATED AT 250 WORDS)

The cardiovascular effects of oral nifedipine and nicardipine: a double-blind comparison in healthy volunteers using transthoracic bioimpedance cardiography

The cardiovascular effects of single oral doses of nifedipine (5 and 10 mg) and nicardipine (20 and 30 mg) were compared in a placebo controlled double-blind crossover study involving 8 healthy male volunteers. Two hours following drug administration stroke volume and cardiac index were measured non-invasively using transthoracic electrical bioimpedance cardiography during passive tilting, graded bicycle exercise, and recovery from exercise. Two separate experiments were performed in the absence of active drug to allow the reproducibility of the measurements to be assessed. Coefficients of variation (within experiment/between experiments) for cardiac index were 7.0%/19.9% at rest and 11.5%/9.3% at 180 W exercise. Both nifedipine and nicardipine increased stroke volume and cardiac index and reduced total peripheral resistance (mean blood pressure/cardiac index) at all times in the experiment. Reductions in peripheral resistance were similar for nifedipine 10 mg and nicardipine 20 mg but in these doses slightly larger increases in heart rate were produced by nifedipine, and in stroke volume and cardiac index with nicardipine. The study shows that the cardiovascular effects of nifedipine and nicardipine can be detected using impedance cardiography which is a simple, safe, and inexpensive technique. The differences between the effects of the two drugs were small. Although some were of statistical significance and are consistent with a less marked cardiodepressant effect for nicardipine, the clinical importance of these observations is uncertain. Further studies to examine the effect of oral nifedipine and nicardipine in patients with impaired ventricular function may be helpful in clarifying this tissue.

Different negative inotropic activity of Ca2(+)-antagonists in human myocardial tissue

To evaluate the negative inotropic effect of various Ca2(+)-antagonists in human myocardium without additional influences of preload, afterload, or frequency, we examined their effects on isometric force of contraction in isolated human papillary muscle strips and in auricular trabeculae. The 1,4-dihydropyridines isradipine, nitrendipine, and nifedipine, the phenylalkylamine verapamil, and the benzothiazepine diltiazem exerted concentration-dependent negative inotropic effects. The potency of the investigated Ca2(+)-antagonists was identical in papillary muscle strips of patients with only moderate clinical signs of heart failure undergoing mitral valve replacement-operation (NYHA II-III) and in terminally failing (heart transplantation, NYHA IV) human hearts. The IC50 values were lower in auricular trabeculae than in papillary muscle strips. The difference was significant for nifedipine, nitrendipine, and verapamil. The restorative effects of external Ca2+ after pretreatment with Ca2(+)-antagonists were significantly less strong after pretreatment with 1,4-dihydropyridine than with non-dihydropyridines in papillary muscle strips. It is concluded that 1,4-dihydropyridines and verapamil and diltiazem did differently influence Ca2(+)-mediated increase in force of contraction. Moreover, a relation between the therapeutically active free plasma concentration in vivo and the negative inotropic potency in vitro can be found. This relation follows a rank order of potency for negative inotropism (isradipine less than or equal to nitrendipine less than diltiazem less than nifedipine less than verapamil) and might have clinical relevance in the treatment of patients with compromised cardiac function.

Calcium channel blocker toxicity

A retrospective review was conducted of all patients who were reported to a regional poison control center after "overdose" of a calcium channel blocker during a two-year period (1987 and 1988). An analysis of 91 patient cases is presented after excluding allergic reactions, cases involving coingestants, and patients lost to follow-up. Patients who developed any symptoms after ingestion were defined as manifesting toxicity. There were 38 cases of verapamil ingestion with toxicity developing in 18 patients. The mean nontoxic dose was 320 mg, whereas the mean toxic ingestion was 3.2 g. Nine patients became hypotensive, 13 developed conduction system abnormalities (sinus node suppression, atrioventricular nodal block, or bundle branch block), and 11 manifested arrhythmias. Ten developed neurological symptoms. There were 31 cases of nifedipine ingestion with toxicity developing in seven patients. The mean nontoxic dose was 19 mg, while the mean toxic ingestion was 340 mg. Four patients were hypotensive, only one developed cardiac conduction abnormalities, and four developed arrhythmias. Three had neurological symptoms. There were 24 cases of diltiazem ingestion with only minor toxicity developing in four patients. There was no statistically significant difference in the frequency of hypotension, arrhythmias, or neurological symptoms in patients who overdosed with verapamil as compared with nifedipine (by Fisher's exact test). However, conduction system abnormalities were more common with verapamil ingestion (P less than .05). Toxic manifestations after diltiazem over-dose were uncommon in our study. Eighteen of the 29 patients who developed toxicity required treatment in excess of gastrointestinal decontamination. Calcium was administered to 14 patients and was helpful in five.

Hemodynamic mechanisms of antianginal action of calcium channel blocker nisoldipine in dynamic exercise-induced angina

To investigate the mechanism of antianginal action of the calcium channel blocker nisoldipine and to determine the reproducibility of the clinical and hemodynamic events induced by supine leg exercise, 30 patients with stable effort angina pectoris were studied. They were divided into two groups; one group of 19 patients received a single 10-mg dose of nisoldipine orally, and the other group of 11 patients received a single dose of placebo orally. Chest pain was induced in all of 30 patients during the control exercise test. After nisoldipine administration, chest pain was not induced in 13 of 19 patients and was of lessened severity in five patients with the same work load as those performing control exercise. ST segment at peak exercise showed less severe depression after nisoldipine. Systemic vascular resistance was reduced by 38% (p less than 0.001) at rest and 22% (p less than 0.001) at peak exercise, and coronary vascular resistance was reduced by 31% (p less than 0.01) at rest and 18% (p less than 0.01) at peak exercise. Pulmonary artery wedge pressure fell from 6 +/- 1 to 3 +/- 1 mm Hg (p less than 0.001) at rest and from 28 +/- 3 to 11 +/- 2 mm Hg (p less than 0.001) at peak exercise. Coronary sinus flow at rest and myocardial oxygen uptake both at rest and during exercise was not modified by nisoldipine. However, coronary sinus flow at peak exercise increased significantly from 219 +/- 24 to 249 +/- 31 ml/min (p less than 0.01) after nisoldipine, and myocardial oxygen uptake was not significantly changed despite decreased coronary vascular resistance. The clinical and hemodynamic events induced by the exercise during invasive studies (except pulmonary artery wedge pressure at rest) were reproducible after placebo administration. Our data demonstrate that increased coronary blood flow could be the major mechanism of the antianginal action of nisoldipine in supine leg exercise-induced angina.

Effect of diltiazem on the oxymyoglobin level of myocardial cells in the isolated, perfused rat heart during hypoxia

The effect of diltiazem on the oxymyoglobin level was studied in the isolated rat heart during hypoxia. The heart was perfused with Krebs-Henseleit solution equilibrated with a gas mixture containing 95% O2 + 5% CO2 (normoxic perfusion solution) at a constant flow rate (9 ml/min) according to Langendorff's method. All the hearts were paced at 300 beats/min. The myocardial oxymyoglobin level (i.e., intracellular oxygen level) of the left ventricular surface was continuously measured by means of an optical technique. Diltiazem (infused into the aortic cannula for 10 minutes at concentrations of 0.72, 2.41, or 4.82 microM, expressed as the final concentration in the solution) decreased the left ventricular pressure (LVP) and perfusion pressure (PP) dose dependently, and did not change the oxymyoglobin (MbO2) level during normoxic perfusion. Hypoxic perfusion (using a gas mixture containing 30% O2 + 5% CO2 + 65% N2) decreased the MbO2, LVP, and PP. Diltiazem (infused 5 minutes after the hypoxic perfusion) at a concentration of 2.41 or 4.82 microM increased the MbO2 level and further decreased the LVP, without affecting the PP. The low concentration of 2.41 or 4.82 microM increased the MbO2 level and further decreased the LVP, without affecting the PP. The low concentration (0.72 microM) of diltiazem, however, had practically no effect on these parameters. In summary, diltiazem in high concentrations decreased the LVP and increased the intracellular oxygen level of the myocardial cells during hypoxia, but not during normoxia.

Nimodipine: evidence for clinically significant gastrointestinal side-effects

Nimodipine, now widely used for treatment and prevention of cerebrovascular spasm, is regarded as a safe drug. Despite a preferential action on cerebral vessels, there is clinical and experimental evidence of effects on systemic vascular and intestinal smooth muscle cells. Gastro-intestinal side-effects, however, have not been reported in clinical studies dealing with treatment of vasospasm following subarachnoid haemorrhage. We report on a patient with subarachnoid haemorrhage who developed an acute life-threatening pseudo-obstruction of the colon, a variant of adynamic ileus, while being treated with intravenous nimodipine. The relationship between this complication and calcium antagonist therapy is discussed and therapeutic strategies are presented. We conclude that neurosurgeons and neurologists should be aware of calcium antagonist--related ileus in patients treated with nimodipine.

Electrophysiological effects of bepridil and its quaternary derivative CERM 11888 in closed chest anaesthetized dogs: a comparison with verapamil and diltiazem

1. The electrophysiological effects of bepridil, its quaternary derivative, CERM 11888 (methylpyrrolidinium bromide) (both 2.5 mg kg-1 i.v.) and those of verapamil and diltiazem (0.2 mg kg-1 i.v.) were studied in closed chest anaesthetized dogs at doses used in clinical studies. 2. The four drugs caused a bradycardia with the following order of potency: bepridil greater than CERM 11888 greater than diltiazem greater than verapamil. 3. All the compounds slowed conduction in the AV node, increased the refractory period (RP) and decreased Wenckebach rates with the following order: verapamil much greater than diltiazem greater than bepridil greater than CERM 11888. 4. Verapamil and diltiazem did not affect conduction or the RP in atria while bepridil weakly slowed the former and markedly increased the latter. CERM 11888 caused a lengthening of RP but this was a delayed effect. 5. In the ventricle, bepridil and CERM 11888 caused a small increase in the QRS and a more pronounced increase in the RP. Both compounds increased QTc but did not modify HV. Verapamil and diltiazem had no significant effects at the ventricular level. 6. Our results confirm that the main sites of action of calcium antagonists are the SA and AV nodes. Bepridil has a broader spectrum of activity and also acts at the atrial and ventricular levels. A comparison of the effects of bepridil with those of its quaternary derivative suggests the involvement of an intracellular action in the electrophysiological effects of bepridil.

Arterial baroreceptor reflex and calcium antagonists

The tachycardia elicited by decreases in aortic pressure produced by various calcium antagonists, regardless of their chemical structures, is not always simply related to the reduction in pressure. Several experimental and clinical experiments have clearly demonstrated that some of these compounds interfer with the baroreceptor reflex control of heart rate. The voltage-dependent calcium channel blockade induced by these antagonists is probably not involved in the baroreceptor mechanotransduction, but central modulation of the baroreceptor reflex is probably an important site for action of these drugs at therapeutic levels. During chronic treatment of hypertension with calcium antagonists, a resetting of the reflex occurred with parallel shift of the set-point and of the baroreceptor reflex-response curve towards lower pressures, thus explaining the lack of change in heart rate despite a permanent reduction in blood pressure under these conditions. However, these effects of calcium antagonists on the baroreceptor reflex do not provide evidence that such interactions could play a role in their antihypertensive action during chronic therapy.