Antiatherosclerotic effects of calcium channel blockers.

Hypertension is a constellation of abnormalities, including metabolic disorders. The current approach to treatment of hypertension should not be dictated solely by measures to lower blood pressure. It must also take into consideration the effect of antihypertensive drug treatment on the development of atherosclerosis and many other important factors. Evidence from rabbit models and cell cultures indicates that calcium channel blockers are antiatherogenic through a variety of mechanisms. In addition to preserving endothelial function, these agents inhibit the following: Platelet aggregation Migration of monocytes and smooth-muscle cells into the intima Incorporation of low-density lipoprotein cholesterol into these cells Matrix formation Calcium overload in atherosclerotic lesions However, additional studies are needed to delineate the antiatherogenic effects of these and other antihypertensive agents.     

The porphyrogenic effects of calcium channel blocking drugs

Treatment of monolayers of chick embryo hepatocytes with the calcium channel blocking drugs nifedipine and verapamil resulted in a decrease in the activity of uroporphyrinogen decarboxylase, an increase in the activity of delta-aminolaevulinate synthase and accumulation of porphyrins with uroporphyrin and heptacarboxylic porphyrin predominating. Diltiazem, another calcium channel blocking drug, did not affect uroporphyrinogen decarboxylase activity and had a slight effect only on the accumulation of porphyrins. Experiments with nifedipine and verapamil in the presence of various concentrations of calcium indicate that the porphyrogenic effect is apparently not related to blocking of calcium channels.     

Fetal safety of calcium channel blockers

Question

Many of my pregnant or lactating patients are taking calcium channel blockers (CCBs) for hypertension. How safe is maternal use of CCBs for fetuses and nursing infants?

Answer

Generally, CCBs have not been shown to increase teratogenic risk. Information regarding the safety of CCBs during lactation is limited, although they are not likely to pose a risk to the nursing infant.     

氯通道阻断剂对血小板胞浆游离钙和血小板聚集的影响

目的　探讨氯通道在血小板胞浆游离钙和血小板聚集功能调节中的作用。方法　新鲜分离人血小板,以凝血酶为诱导剂,观察氯通道阻断剂DIDS、NFA和钙通道阻断剂SK&F96365、Nife dipine对血小板胞浆游离钙和血小板聚集的单独作用和相互作用。结果　氯通道阻断剂DIDS、NFA可以浓度依赖性地抑制凝血酶 ( 1U/ml)诱导的血小板聚集,对静息血小板胞浆游离钙无明显影响;DIDS、SK&F96365、Nifedipine可以明显降低凝血酶诱导的血小板聚集、钙释放和钙内流,与对照组比较,P<0. 05;DIDS与SK&F96365联合,对凝血酶诱导的血小板聚集、钙释放和钙内流的抑制比各自单独抑制作用明显增高(P<0. 05),两者的作用相互增强;DIDS与Nifedipine联合,对凝血酶诱导的血小板钙释放的抑制比各自单独抑制作用明显增高 (P<0. 05 ),两者可相互增强;NFA与SK&F96365联合,对凝血酶诱导的血小板钙释放的抑制比各自的单独作用明显降低 (P<0. 05 ),两者可相互减弱;NFA与Nifedipine联合,对凝血酶诱导的血小板聚集、钙释放和钙内流的抑制比各自的单独作用明显降低(P<0. 05),两者可相互减弱。结论　氯通道阻断剂DIDS、NFA对人静息血小板胞浆钙浓度无影响;DIDS可抑制凝血酶诱导的血小板聚集、钙释放和钙内流,NFA仅抑制凝血酶诱导的钙释放;氯通道阻断剂和     

Comparative clinical pharmacology of calcium channel blockers

Calcium channel blockers are effective antihypertensive agents, both as initial monotherapy and in combination with other antihypertensive agents. These drugs are also effective in the treatment of chronic, stable angina, variant angina and supraventricular arrhythmias. Drugs in this class have different affinities for calcium channels in vascular smooth muscle, cardiac muscle, cardiac sinus and atrioventricular node. They are all useful in hypertension and angina, but only verapamil and diltiazem are also useful in the control of heart rate and supraventricular arrhythmias. Nimodipine may control vascular spasm following subarachnoid hemorrhage. Calcium channel blockers have also been used in the treatment of migraine headache and Raynaud's phenomenon.     

Time-dependent protective effects of calcium channel blockers on anoxia- and hypoxia-induced proximal tubule injury.

The effects of anoxia or hypoxia on Ca++ uptake and lactic dehydrogenase (LDH) release were examined in freshly isolated rat proximal tubules (rPT). Both Ca++ uptake and LDH release were increased above control after only 10 min of either anoxia or hypoxia in rPT. The increase in Ca++ uptake was through voltage-sensitive, slow Ca++ channels, because pretreatment with chemically dissimilar calcium channel blockers (CCB), either verapamil or flunarizine, prevented the increased Ca++ uptake and reduced the LDH release from the anoxic and hypoxic rPT. After 20 min of hypoxia, however, verapamil pretreatment did not significantly reduce the high Ca++ uptake rate, thus, suggesting that this increase in Ca++ permeability was occurring through pathways other than the slow Ca++ channels. The increase in LDH release was only slightly decreased by verapamil after 20 min of hypoxia. After 20 min of anoxia in rPT, Ca++ uptake was no longer increased, but the increased LDH release persisted. These effects of anoxia were unaltered by verapamil. These results, thus, suggest that early membrane injury to isolated rPT in suspension, which is associated with 10 min of either anoxia or hypoxia, involves increased cellular Ca++ uptake through voltage-sensitive Ca++ channels and protection is afforded by CCB. In contrast, after 20 min of anoxia or hypoxia, rPT membrane damage persisted and was only partially reversed by CCB. The rPT injury induced by 20 min of O2 deprivation, thus, involves factors independent of voltage-sensitive Ca++ channels.     

Effects of calcium channel blockers on the pharmacokinetics of propranolol stereoisomers

Diltiazem and verapamil inhibit oxidative drug metabolism both in vivo and in vitro. We compared their effects on the stereoselective pharmacokinetics and protein binding of propranolol in 12 subjects. After 6 days of coadministration with racemic propranolol, diltiazem caused decreases of 27% and 24% in d-propranolol and 1-propranolol oral clearances, respectively (p less than 0.05 versus control). With verapamil, d-propranolol oral clearance decreased 32% (p less than 0.05), and 1-propranolol oral clearance decreased 26% (p less than 0.05). The unbound fraction of d-propranolol was higher than that of 1-propranolol (p less than 0.05), but the protein binding was not altered by diltiazem or verapamil. Both drugs therefore decreased the unbound oral clearance of each propranolol enantiomer (p less than 0.05). Verapamil caused a stereoselective effect and increased the d/l ratio of propranolol serum concentrations (p less than 0.05) and decreased the d/l ratio of oral clearance (p less than 0.05).     

Antihypertensive effects of long-acting calcium channel blockers on hemodialysis days--a randomized crossover trial between benidipine and nifedipine CR

A variety of dietary and metabolic factors may contribute or cause stone formation in idiopathic calcium oxalate nephrolithiasis. Dietary factors include a high intake of animal proteins, oxalate and sodium, and a low intake of fluids and potassium-containing citrus products. Some of the metabolic causes of stones are hypercalciuria, hypocitraturia, gouty diathesis, hyperoxaluria, and hyperuricosuria. Dietary modification, to be applied in all patients with stones includes a high fluid intake, restriction of oxalate and sodium, and balanced diet with animal proteins complemented by adequate intake of fruits and vegetables. When dietary modification is ineffective in controlling stone formation or in the presence of severe metabolic derangements, a pharmacologic intervention may be necessary. In a simple approach, thiazide or indapamide with potassium citrate is recommended for patients with hypercalciuria, and potassium citrate alone for the remaining normocalciuric subjects.     

Pharmacokinetic interactions between indinavir plus ritonavir and calcium channel blockers

BACKGROUND: Hypertension is an important modifiable cardiac risk factor in human immunodeficiency virus (HIV)-infected patients. Calcium channel blockers are substrates of cytochrome P450 3A and are commonly prescribed for hypertension. We evaluated potential bidirectional pharmacokinetic interactions between calcium channel blockers and coadministered indinavir and ritonavir. METHODS: Healthy HIV- seronegative subjects received 120 mg diltiazem daily or 5 mg amlodipine daily for days 1 to 7 and 20 to 26. All subjects received 100 mg ritonavir and 800 mg indinavir every 12 hours on days 8 to 26. Twenty-four-hour pharmacokinetic collection was performed on days 7 and 26, with 12-hour collection on day 19. RESULTS: Indinavir plus ritonavir increased the median amlodipine area under the curve from 0 to 24 hours (AUC) by 89.8%, from 122 to 230 ng.h/mL (n = 18, P < .0001), and increased the median diltiazem AUC by 26.5%, from 800 to 1060 ng.h/mL (n = 13, P = .06). Of 13 subjects, 2 (15%) had greater than 4-fold increases in diltiazem AUC. Desacetyldiltiazem AUC increased by 102.2% (P = .001), and desmethyldiltiazem AUC decreased by 27.4% (P = .01). Neither amlodipine nor diltiazem affected steady-state AUCs of the protease inhibitors. No serious cardiovascular adverse effects were observed. CONCLUSIONS: Indinavir plus ritonavir increases the AUCs of both amlodipine and diltiazem, which may result in an increased response. If coadministration is indicated, amlodipine or diltiazem should be initiated at low doses with careful titration to response and side effects.     

Cocaine toxicity and the calcium channel blockers nifedipine and nimodipine in rats

Two dihydropyridine type calcium channel blockers (CCBs) were studied for any protective or therapeutic effect upon cocaine-induced toxicity and death in rats. To test for the protective effects, rats were pretreated with vehicle (control), nifedipine or nimodipine, intraperitoneally (IP) 30 minutes prior to an LD₈₅ of cocaine, or intravenously (IV) 10 minutes prior to cocaine administration. Anumals receiving EP control vehicle developed seizures in 5.6 ± 1.0 minutes and respiratory arrest in 9.8 ± 1.4 minutes. Animals pretreated EP with nifedipine or nimodipine developed seizures and respiratory arrest significantly sooner than the controls, although the overall incidences of seizures and respiratory arrest were not significantly different. Pretreatment with IV CCBs resulted in similar findings. To test the therapeutic effect of CCBs given following cocaine overdose, rats were administered cocaine EP and then treated with IV nifedipine or nimodipine once seizures occurred. In these animals, there was no significant difference in the Incidence or time to respiratory arrest compared to vehicle controls. This study demonstrates that neither pretreatment nor posttreatment with the CCBs nifethpine or nimodipine reduces cocaine toxicity in this rodent model.     

Reversal of experimental neuropathic pain by T-type calcium channel blockers

Experimental nerve injury results in exaggerated responses to tactile and thermal stimuli that resemble some aspects of human neuropathic pain. Neuronal hyperexcitability and neurotransmitter release have been suggested to promote such increased responses to sensory stimuli. Enhanced activity of Ca(2+) current is associated with increased neuronal activity and blockade of N- and P-types, but not L-type, calcium channels have been found to block experimental neuropathic pain. While T-type currents are believed to promote neuronal excitability and transmitter release, it is unclear whether these channels may also contribute to the neuropathic state. Rats were prepared with L(5)/L(6) spinal nerve ligation, and tactile and thermal hypersensitivities were established. Mibefradil or ethosuximide was administered either intraperitoneally, intrathecally (i.th.), or locally into the plantar aspect of the injured hindpaw. Systemic mibefradil or ethosuximide produced a dose-dependent blockade of both tactile and thermal hypersensitivities in nerve-injured rats; responses of sham-operated rats were unchanged. Local injection of mibefradil also blocked both end points. Ethosuximide, however, was inactive after local administration, perhaps reflecting its low potency when compared with mibefradil. Neither mibefradil nor ethosuximide given i.th. produced any blockade of neuropathic behaviors. The results presented here suggest that T-type calcium channels may play a role in the expression of the neuropathic state. The data support the view that selective T-type calcium channel blockers may have significant potential in the treatment of neuropathic pain states.     

Slow-infusion of calcium channel blockers in the emergency management of supraventricular tachycardia

OBJECTIVE: To compare the efficacy of verapamil and diltiazem as slow infusions in terminating spontaneous supraventricular tachycardia (SVT) in the emergency department (ED). METHOD: Patients of at least 10 years of age who presented to our ED with regular narrow complex tachycardia not converted with a vagal manoeuvre with an ECG diagnosis of SVT were included. Those who were haemodynamically unstable were excluded. Patients were randomized to undergo either verapamil infusion at a rate of 1 mg/min to a maximum of 20 mg or diltiazem infusion at a rate of 2.5 mg/min to a maximum of 50 mg. RESULTS: Eighty-one patients were randomized to receive verapamil infusion and 80 were randomized to receive the diltiazem infusion. There is no difference in success rate between verapamil (98.8%) and diltiazem (96.3%) infusion. The dose of medication required to convert 25,50 and 75% of SVTs were 4.0,5.0 and 8.0 mg for the verapamil infusion and 10.0,12.5 and 17.5 mg for the diltiazem infusion. There was one complication in each group. CONCLUSION: Calcium channel blockers infusions were safe and efficacious in terminating spontaneous SVT. There was no difference between the success rates of verapamil and diltiazem infusions.     

Effects of calcium channel blockers on cloned cardiac K+ channels IKr and IKs

Cloned HERG and KvLQT1-IsK K+ channels have been expressed in mammalian cells and assayed as a target for calcium channel blockers. These channels generate the rapid and slow components of the cardiac delayed rectifier K+ current, and mutations can affect them that lead to long QT syndromes. HERG is blocked by bepridil (EC50 = 0.55 microM), verapamil (EC50 = 0.83 microM) and mibefradil (EC50 = 1.43 microM), whereas nitrendipine and diltiazem have negligible effects. Steady-state activation and inactivation parameters are shifted to more negative values in the presence of the blockers. Similarly, KvLQT1-IsK is inhibited by bepridil (EC50 = 10.0 microM) and mibefradil (EC50 = 11.8 microM), whilst being insensitive to nitrendipine, diltiazem or verapamil. This work may help to understand the mechanisms of action of verapamil in certain ventricular tachycardias as well as some of the deleterious adverse cardiac events associated with bepridil and mibefradil.