Electrophysiologic and hemodynamic actions of diltiazem: disparate temporal effects shown by experimental dose-response studies

Pharmacodynamics and pharmacokinetics of clentiazem and diltiazem in closed-chest anesthetized dogs

In the present study we investigated the relationship between pharmacodynamic and pharmacokinetic properties of the benzothiazepine-like calcium antagonists, clentiazem and diltiazem. Experiments were carried out in closed-chest anesthetized dogs, instrumented for hemodynamic recording and blood sampling. Clentiazem and diltiazem bolus injections (400 micrograms/kg) were administered intravenously, and subgroups of animals were sacrificed at 15, 30, 60, or 120 minutes Clentiazem and diltiazem plasma and myocardial levels were determined by high performance liquid chromatography (HPLC). Clentiazem elicited a more marked reduction in mean arterial pressure (-17% for clentiazem vs. -12% for diltiazem), along with an attenuation of the expected positive reflex chronotropic response. Pharmacokinetic analysis revealed that clentiazem had a greater volume of distribution (33 +/- 16 l vs. 15 +/- 9 l for diltiazem), while the half-life of elimination (t1/2 beta) was similar (55 +/- 21 minutes vs. 59 +/- 23 minutes). The kinetic disposition profile of both drugs was analyzed through myocardial/plasma concentration ratios. In the distribution phase (0-15 minutes), this ratio was similar (26 +/- 2 for clentiazem vs. 18 +/- 5 diltiazem), suggesting that the myocardium was not a preferential site of distribution for either drugs. Data collected within the elimination phase indicate significant myocardial retention for clentiazem; at the end of the study period, the myocardial/plasma concentration ratio was twofold higher for clentiazem. The observed retention of clentiazem in the myocardium may be responsible for attenuation of the baroreflex. Clentiazem increased potency was confirmed by the fact that its hypotensive and cardioinhibitory effects were observed at lower plasma concentrations.

Effects of combined intravenous nicardipine and diltiazem administration on the circulatory response to laryngoscopy and tracheal intubation

To evaluate the effect of combined intravenous administration of the calcium antagonists, nicardipine and diltiazem, on the circulatory responses to tracheal intubation, the mean arterial pressure (MAP) and rate pressure product (RPP) in response to laryngoscopy following tracheal intubation were compared in patients receiving saline placebo or nicardipine 10 μg·kg^-1 and diltiazem 0.1 mg·kg^-1 60 s before the initiation of laryngoscopy. Each group was comprised of ten patients undergoing elective surgery. The patients receiving saline showed a significant increase in MAP and RPP associated with tracheal intubation. However, these increases were significantly attenuated (P<0.05) in the patients to whom nicardipine and diltiazem were administered concurrently.

Effect of diltiazem on hypoxic pulmonary vasoconstriction in dogs

We have examined the effect of diltiazem upon the pulmonary vascular response to the left lower lobe (LLL) hypoxia in dogs. Without diltiazem, the fraction of cardiac output perfusing the LLL (QLLL/QT) measured by the ultrasonic doppler rheometer in the hypoxic phase was 21.0 +/- 11.7(%) of the ratio in the first normoxic phase. When diltiazem was given as a 0.48 mg/kg intravenous bolus followed by an intravenous infusion of 0.48 mg/kg/hr and 0.96 mg/kg intravenous bolus followed by an intravenous infusion of 0.96 mg/kg/hr, QLLL/QT in the hypoxic phase were 34.0 +/- 14.0, 48.6 +/- 16.1(%) of the ratio in the first normoxic phase respectively. Significant difference was observed at all diltiazem concentrations. With respect to PaO2, significant difference was not observed at all diltiazem concentrations in the ratio of the hypoxic phase to the first control phase. So we concluded that diltiazem obviously attenuated hypoxic pulmonary vasoconstriction (HPV) response but did not decrease PaO2 because of keeping myocardial oxygen balance and better ventilation/perfusing relationship.

Reversal of the adverse cardiovascular effects of intravenous diltiazem in anesthetized dogs

Intravenous diltiazem can be used to treat myocardial ischemia, hypertension, and supraventricular dysrhythmias, but significant adverse effects including atrioventricular block and hypotension have been reported. At the present time, there is controversy as to which drug is most effective in reversing these sequelae. This study was designed to assess the effectiveness of calcium chloride v epinephrine in reversing these side effects. The hemodynamic and electrophysiologic effects of diltiazem infusion were investigated in eight dogs anesthetized with fentanyl and nitrous oxide/oxygen. This study confirmed that diltiazem infusions in high concentrations produced predominantly atrioventricular conduction depression followed by profound hypotension. Epinephrine infusion proved to be most effective in attenuating and eliminating each of these deleterious side effects. In contrast, calcium chloride did not significantly increase heart rate or blood pressure or reverse atrioventricular block. In two instances calcium chloride produced further depression of atrioventricular conduction, leading to severe bradycardia and sinus arrest. Although calcium chloride increased left ventricular contractile force (LV dP/ dt) and cardiac index (CI), mean arterial pressure was not affected and SVR was further decreased. This study indicates that calcium chloride should not be given to reverse the side effects of diltiazem in the presence of atrioventricular conduction block or profound hypotension. Calcium chloride is indicated only when isolated myocardial depression is present and after the calcium channels have been reopened by epinephrine.

Interaction between diltiazem and halothane or enflurane in the canine blood-perfused papillary muscle and sinoatrial node preparations cross-circulated by chronically instrumented conscious donor dog

Interaction of cardiovascular effects of diltiazem with those of halothane or enflurane was estimated in the canine isolated papillary muscle and sinoatrial node preparations perfused by arterial blood of the chronically instrumented conscious and halothane- or enflurane-anesthetized donor dog, into which diltiazem was infused i.v. at a rate of 20 micro g/kg/min for 60 min. One hour after diltiazem infusion, in the conscious donor dog, mean arterial pressure (MAP) and heart rate (DHR) were decreased to 84 +/- 3 and 84 +/- 2% and PQ interval (PQ) was prolonged to 148 +/- 5%, while in the isolated preparations, developed tension (DT) of the papillary muscle and sinoatrial rate (SAR) were decreased to 68 +/- 3 and 74 +/- 3% and blood flow (BF) was increased to 155 +/- 5% (n = 10). On the other hand, halothane (0.8%) anesthesia per se decreased MAP, DHR, DT and SAR to 89 +/- 8, 84 +/- 3, 79 +/- 3 and 89 +/- 5% (n = 7) of each basal value in conscious state 20 min after the inhalation. During halothane anesthesia, the same dose of diltiazem infused decreased MAP to 74 +/- 4 (n = 7), DHR to 66 +/- 4 (n = 6), DT to 62 +/- 7 (n = 7) and SAR to 69 +/- 1% (n = 3) of each value suppressed by halothane itself. Meanwhile, enflurane (1.7%) anesthesia itself decreased MAP, DHR, DT and SAR to 81 +/- 3, 85 +/- 2, 81 +/- 2 and 88 +/- 2% (n = 10) of each basal value in conscious state 30 min after enflurane inhalation. During enflurane anesthesia diltiazem decreased MAP to 74 +/- 3 (n = 10), DHR to 67 +/- 3 (n = 8), DT to 45 +/- 5 (n = 10) and SAR to 74 +/- 6% (n = 3) of each value under enflurane anesthesia alone. PQ interval of the donor dog heart was prolonged by halothane alone to 111 +/- 5% (n = 7) and by enflurane alone to 110 +/- 2% (n = 10) of the value before each anesthesia, and then diltiazem prolonged PQ interval to 160 +/- 8% (n = 6) and 174 +/- 10% (n = 8) of each value suppressed by the anesthetic itself during halothane- or enflurane-anesthesia, respectively. The second degree AV conduction block was induced in 1 of 7 halothane- and in 2 of 10 enflurane-anesthetized donor dogs, respectively. The sinus arrest was induced by diltiazem in 4 of 7 sinoatrial node preparations under halothane and in 7 of 10 ones during enflurane anesthesia. Moreover, plasma concentration of diltiazem 60 min after the start of infusion was 556 +/- 121 ng/ml in conscious dogs and tended to increase to 752 +/- 101 ng/ml in enflurane anesthetized donor dogs (n = 4), but there was no significant difference between two values (0.05 < P < 0.1). These results indicate that effects of diltiazem could be potentiated during halothane or enflurane anesthesia by elimination of compensatory reflex noted in conscious state, and that the negative inotropic effect of diltiazem was enhanced by enflurane anesthesia due to unknown mechanisms which probably include a slight but insignificant increase in plasma concentration.

Effect of diltiazem-induced hypotension on normal and increased intracranial pressure of cats

The commonly used vasodilators sodium nitroprusside and nitroglycerin increase intracranial pressure (ICP) and cause tachycardia. Since diltiazem is also a vasodilator, we designed this experiment in cats to study its effect on intracranial pressure and heart rate (HR). Twelve cats were assigned to two equal groups. One group had normal ICP (N-ICP), while in the other the ICP was raised artificially (AR-ICP) by placing a balloon into the intracranial extradural space. Both groups received an infusion of diltiazem to decrease the mean blood pressure (BP), which was maintained 30 per cent below the baseline value for 15 minutes. Diltiazem caused no significant change in ICP (5.7 +/- 1 to 6.7 +/- 1.5 mmHg, p less than 0.01) in cats with N-ICP while in cats with AR-ICP, the increase from 26.9 +/- 0.5 to 34.0 +/- 1.9 mmHg was significant (p less than 0.006). HR decreased significantly during the diltiazem infusion in both groups.

Hypotensive actions of diltiazem and nitroprusside compared during fentanyl anaesthesia for total hip arthroplasty

The potential for inducing hypotension during fentanyl anaesthesia by administering either diltiazem (n = 7) or sodium nitroprusside (n = 7) was investigated during total hip arthroplasty. Haemodynamic variables were obtained in the lateral position before, during and after administration of the hypotensive agent. Diltiazem 0.15 mg X kg-1 given as an IV bolus followed by a 12.5 +/- 3 micrograms X kg-1 X min-1 continuous infusion decreased mean arterial pressure (MAP) from 77 +/- 11 mmHg to 63 +/- 16 mmHg (p less than 0.05) while other haemodynamic parameters showed only minor and insignificant changes. Hypotension continued for at least 30 min after the cessation of diltiazem. With sodium nitroprusside MAP decreased immediately from 81 +/- 11 mmHg to 59 +/- 9 mmHg (p less than 0.01) and rapidly returned to its control value after cessation of the infusion. CI and Qs/Qt rose significantly (p less than 0.05) while the systemic vascular resistance index (SVRI) (p less than 0.01) and pulmonary vascular resistance index (PVRI) (p less than 0.05) fell significantly. The haemodynamic profile was significantly different between hypotensive agents for MAP (p less than 0.02), heart rate (HR) (p less than 0.01), SVRI (p less than 0.05), and PVRI (p less than 0.05). HR was lower with diltiazem than with nitroprusside. A bradycardia less than 50 beats/min was observed in five patients in the diltiazem group. MAP, SVRI and PVRI were lower with nitroprusside than with diltiazem. Diltiazem can induce and maintain moderate hypotension without tachycardia and decreased cardiac output in humans during fentanyl anaesthesia but the modulation of the level of arterial pressure and the depression of atrioventricular conduction are unpredictable.

Hemodynamic effects of antiarrhythmic drugs

In order to use antiarrhythmic drugs safely, one must understand their hemodynamic effects. Quinidine and the calcium antagonists have direct cardiac effects and frequently opposing autonomically mediated or indirect cardiac effects. Lidocaine is exceptionally well tolerated, even by patients with severe left ventricular dysfunction. Phenytoin and procainamide have the potential for serious adverse effects, but are generally well tolerated at usual doses. Disopyramide causes serious depression of left ventricular function in many patients because of its direct myocardial depressant and peripheral vasoconstricting actions. Although bretylium causes an immediate increase in contractility, it can ultimately result in important hypotension. In this review the in vitro and in vivo hemodynamic effects of these and other antiarrhythmic drugs are discussed to provide information that will assist the clinician in using these drugs properly.

Clinical applications of slow channel blocking compounds

The slow-channel blockers constitute a structurally diverse group of drugs with varying mechanisms of action, propensities for site of greatest cardiovascular activity, and clinical efficacy. They share however the property of blocking the slow inward channel in heart muscle and of inhibiting calcium fluxes in smooth muscle. Their in vivo and in vitro actions must be distinguished. The overall actions represent a balance of direct and autonomically-mediated reflex actions interacting with the compounds' varying degrees of intrinsic non-competitive sympathetic antagonism. A knowledge of the pharmacodynamic differences between these drugs allows the physician to select the most appropriate agent for a given clinical situation. The central role of calcium in the cellular processes in the heart and the vascular system forms the basis for the utility of this class of drugs in a wide variety of cardiovascular disorders. Current intensive experimental and clinical investigations are likely to further define the roles of nifedipine, verapamil and diltiazem and their congeners in cardiovascular therapeutics. The prospect of development of newer compounds with greater selectivity of action is real. As pointed out by Braunwald (1982 a,b), with further clarification of the mechanisms of actions of these compounds and elucidation of the role of calcium fluxes throughout the body, more specific and potent agents may be developed. The apparent efficacy of the nifedipine congener nimodipine, in the treatment of cerebral vasospasm associated with subarachnoid hemorrhage (Allen et al., 1983) may simply be the first of a large number of 'specific' or targeted slow channel blockers. The development of such compounds may offer further therapeutic possibilities in the control of a variety of cardiocirculatory diseases.

Efficacy of diltiazem in angina on effort: a multicenter trial

During a multicenter study 57 patients with exercise-induced angina were evaluated with serial exercise testing to assess the efficacy of diltiazem, a calcium slow channel blocking agent, compared with a placebo. The study consisted of a 1 week single-blind placebo stabilization period followed by a double-blind triple crossover between diltiazem and placebo. Three dose levels were tested (120, 180 and 240 mg/day) in each patient. For the three time-related variables there was a significant dose-related response, with 240 mg/day being the most effective. The increases, over the washout placebo stabilization values, of the time-related variables for the 240 mg/day week compared with the corresponding placebo week were total duration of exercise 1.87 versus 1.05 minutes (p less than 0.002), time to onset of angina 1.81 versus 1.17 minutes (p less than 0.01) and time to appearance of 1 mm S-T segment depression 1.81 versus 1.01 minutes (p less than 0.002). Analysis of exercise variables indicated a significant reduction in heart rate, diastolic blood pressure, and pressure-rate product at submaximal exercise after administration of diltiazem. Diastolic blood pressure was significantly reduced at maximal exercise. Heart rate and pressure-rate product were unchanged at rest during submaximal or maximal exercise. Submaximal and maximal exercise S-T depression was not significantly altered by diltiazem. The reduction in pressure-rate product at submaximal exercise was a possible mechanism for the drug's beneficial effect in enhancing the three time-related variables.