Clinical relevance of verapamil plasma levels in stable angina pectoris

Ion Transport Modulators Differentially Modulate Inflammatory Responses in THP-1-Derived Macrophages

Ion transport modulators are most commonly used to treat various noncommunicable diseases including diabetes and hypertension. They are also known to bind to receptors on various immune cells, but the immunomodulatory properties of most ion transport modulators have not been fully elucidated. We assessed the effects of thirteen FDA-approved ion transport modulators, namely, ambroxol HCl, amiloride HCl, diazoxide, digoxin, furosemide, hydrochlorothiazide, metformin, omeprazole, pantoprazole, phenytoin, verapamil, drug X, and drug Y on superoxide production, nitric oxide production, and cytokine expression by THP-1-derived macrophages that had been stimulated with ethanol-inactivated Mycobacterium bovis BCG. Ambroxol HCl, diazoxide, digoxin, furosemide, hydrochlorothiazide, metformin, pantoprazole, phenytoin, verapamil, and drug Y had an inhibitory effect on nitric oxide production, while all the test drugs had an inhibitory effect on superoxide production. Amiloride HCl, diazoxide, digoxin, furosemide, phenytoin, verapamil, drug X, and drug Y enhanced the expression of IL-1β and TNF-α. Unlike most immunomodulatory compounds currently in clinical use, most of the test drugs inhibited some inflammatory processes while promoting others. Ion pumps and ion channels could therefore serve as targets for more selective immunomodulatory agents which do not cause overt immunosuppression.

Ion Transport Modulators as Antimycobacterial Agents

There is an urgent need for better and safer therapeutic interventions for tuberculosis (TB). We assessed the effects of FDA-approved ion transport modulators, namely, ambroxol HCl, amiloride HCl, diazoxide, digoxin, furosemide, hydrochlorothiazide (HCTZ), metformin, omeprazole, pantoprazole, phenytoin, verapamil, and drug X and Y on the growth of free and intracellular Mycobacterium bovis BCG. Free and intracellular M. bovis BCG were cultured in the presence or absence of the test drugs for 3 to 9 days and then quantified. For both free and intracellular bacteria, cultures that were exposed to furosemide, phenytoin, or drug Y yielded lower bacteria counts compared to drug-free controls (p < 0.05). The same was observed with diazoxide, HCTZ, verapamil, and drug X, but only for intracellular M. bovis BCG (p < 0.05). To assess the effects of the drugs on bactericidal activity of rifampicin, free and intracellular M. bovis BCG were treated with rifampicin alone or in combination with each of the thirteen test drugs for 3 to 9 days. For extracellular bacteria, higher bacteria clearance rates were observed in cultures exposed to rifampicin in combination with amiloride HCl, diazoxide, digoxin, furosemide, HCTZ, metformin, pantoprazole, phenytoin, drug X, or drug Y than those exposed to rifampicin alone, indicating that rifampicin had a synergistic effect with these test drugs. Rifampicin was also synergistic with ambroxol HCl, diazoxide, digoxin, furosemide, HCTZ, omeprazole, pantoprazole, phenytoin, verapamil, and drug X against intracellular M. bovis BCG. The antimycobacterial properties exhibited by the ion transport modulators in this study make them viable candidates as adjuncts to the current anti-TB regimens.

4'Epidoxorubicin Plus Verapamil in Anthracycline - Refractory Cancer Patients

Four patients refractory to doxorubicin (DX) and 9 patients refractory to 4'epidoxorubicin (4'EpiDX) were treated with verapamil (VRP) (120 mg every 6 h for 3 days) plus 4'EpiDX (80 mg/m2 i.v. bolus, together with the 6th VRP administration). Three patients had partial remissions lasting 3, 3.5 and 7 months, respectively. Toxicity grading did not exceed usual levels. The study demonstrates that VRP, when added at conventional doses to 4'EpiDX, can induce objective responses in some patients refractory to anthracyclines.

Cardiac Arrhythmias and Antiarrhythmic Drugs: An Autophagic Perspective

Degradation of cellular material by lysosomes is known as autophagy, and its main function is to maintain cellular homeostasis for growth, proliferation and survival of the cell. In recent years, research has focused on the characterization of autophagy pathways. Targeting of autophagy mediators has been described predominantly in cancer treatment, but also in neurological and cardiovascular diseases. Although the number of studies is still limited, there are indications that activity of autophagy pathways increases under arrhythmic conditions. Moreover, an increasing number of antiarrhythmic and non-cardiac drugs are found to affect autophagy pathways. We, therefore, suggest that future work should recognize the largely unaddressed effects of antiarrhythmic agents and other classes of drugs on autophagy pathway activation and inhibition.

New Verapamil Analogs Inhibit Intracellular Mycobacteria without Affecting the Functions of Mycobacterium-Specific T Cells

There is a growing interest in repurposing mycobacterial efflux pump inhibitors, such as verapamil, for tuberculosis (TB) treatment. To aid in the design of better analogs, we studied the effects of verapamil on macrophages and Mycobacterium tuberculosis-specific T cells. Macrophage activation was evaluated by measuring levels of nitric oxide, tumor necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β), and gamma interferon (IFN-γ). Since verapamil is a known autophagy inducer, the roles of autophagy induction in the antimycobacterial activities of verapamil and norverapamil were studied using bone marrow-derived macrophages from ATG5(flox/flox) (control) and ATG5(flox/flox) Lyz-Cre mice. Our results showed that despite the well-recognized effects of verapamil on calcium channels and autophagy, its action on intracellular M. tuberculosis does not involve macrophage activation or autophagy induction. Next, the effects of verapamil and norverapamil on M. tuberculosis-specific T cells were assessed using flow cytometry following the stimulation of peripheral blood mononuclear cells from TB-skin-test-positive donors with M. tuberculosis whole-cell lysate for 7 days in the presence or absence of drugs. We found that verapamil and norverapamil inhibit the expansion of M. tuberculosis-specific T cells. Additionally, three new verapamil analogs were found to inhibit intracellular Mycobacterium bovis BCG, and one of the three analogs (KSV21) inhibited intracellular M. tuberculosis replication at concentrations that did not inhibit M. tuberculosis-specific T cell expansion. KSV21 also inhibited mycobacterial efflux pumps to the same degree as verapamil. More interestingly, the new analog enhances the inhibitory activities of isoniazid and rifampin on intracellular M. tuberculosis. In conclusion, KSV21 is a promising verapamil analog on which to base structure-activity relationship studies aimed at identifying more effective analogs.

Human lymphatic vessel contractile activity is inhibited in vitro but not in vivo by the calcium channel blocker nifedipine

Calcium channel blockers (CCB) are widely prescribed anti-hypertensive agents. The commonest side-effect, peripheral oedema, is attributed to a larger arterial than venous dilatation causing increased fluid filtration. Whether CCB treatment is detrimental to human lymphatic vessel function and thereby exacerbates oedema formation is unknown. We observed that spontaneous lymphatic contractions in isolated human vessels (thoracic duct and mesenteric lymphatics) maintained under isometric conditions were inhibited by therapeutic concentrations (nanomolar) of the CCB nifedipine while higher than therapeutic concentrations of verapamil (micromolar) were necessary to inhibit activity. Nifedipine also inhibited spontaneous action potentials measured by sharp microelectrodes. Furthermore, noradrenaline did not elicit normal increases in lymphatic vessel tone when maximal constriction was reduced to 29.4 ± 4.9% of control in the presence of 20 nmol l(-1) nifedipine. Transcripts for the L-type calcium channel gene CACNA1C were consistently detected from human thoracic duct samples examined and the CaV1.2 protein was localized by immunoreactivity to lymphatic smooth muscle cells. While human lymphatics ex vivo were highly sensitive to nifedipine, this was not apparent in vivo when nifedipine was compared to placebo in a randomized, double-blinded clinical trial: conversely, lymphatic vessel contraction frequency was increased and refill time was faster despite all subjects achieving target nifedipine plasma concentrations. We conclude that human lymphatic vessels are highly sensitive to nifedipine in vitro but that care must be taken when extrapolating in vitro observations of lymphatic vessel function to the clinical situation, as similar changes in lymphatic function were not evident in our clinical trial comparing nifedipine treatment to placebo.

Re-evaluation of cytostatic therapies for meningiomas in vitro

PURPOSE

The purpose was to re-evaluate in cell culture models the therapeutic usefulness of some discussed chemotherapies or targeted therapies for meningiomas with a special emphasis on the role of the neurofibromatosis type 2 (NF2) tumor suppressor, which had been neglected so far. In addition, the study intended to evaluate a potential benefit from a treatment with drugs which are well established in other fields of medicine and have been linked recently with tumor disease by epidemiological studies.

METHODS

Meningioma cell lines corresponding to various subtypes and pairs of syngenic meningioma cell lines with or without shRNA-induced NF2 knockdown were analyzed for their dose-dependent response to the drugs in microtiter tetrazolium assays, BrdU assays and for selected cases in ELISAs measuring nucleosome liberation to specifically separate cell death from pure inhibition of cell proliferation.

RESULTS

We confirmed a moderate efficacy of hydroxyurea (HU) in clinically relevant concentrations. Under appropriate dosing, we neither detected major responses to the alkylating compound temozolomide nor to various drugs targeting membrane receptors or enzymes (tamoxifen, erlotinib, mifepristone, losartan, metformin and verapamil). Only concentrations far beyond achievable serum levels generated significant effects with the exception of losartan, which showed no effects at all. Chemosensitivity varied markedly among meningioma cell lines. Importantly, cells with NF2 loss exhibited a significantly higher induction of cell death by HU.

CONCLUSIONS

Alternative chemotherapeutic or targeted approaches besides HU have still to be evaluated in further studies, and the role of NF2 must be taken into account.

I(CaL) inhibition prevents arrhythmogenic Ca(2+) waves caused by abnormal Ca(2+) sensitivity of RyR or SR Ca(2+) accumulation

AIMS

Arrhythmogenic Ca(2+) waves result from uncontrolled Ca(2+) release from the sarcoplasmic reticulum (SR) that occurs with increased Ca(2+) sensitivity of the ryanodine receptor (RyR) or excessive Ca(2+) accumulation during β-adrenergic stimulation. We hypothesized that inhibition of the L-type Ca(2+) current (I(CaL)) could prevent such Ca(2+) waves in both situations.

METHODS AND RESULTS

Ca(2+) waves were induced in mouse left ventricular cardiomyocytes by isoproterenol combined with caffeine to increase RyR Ca(2+) sensitivity. I(CaL) inhibition by verapamil (0.5 µM) reduced Ca(2+) wave probability in cardiomyocytes during electrostimulation, and during a 10 s rest period after ceasing stimulation. A separate type of Ca(2+) release events occurred during the decay phase of the Ca(2+) transient and was not prevented by verapamil. Verapamil decreased Ca(2+) spark frequency, but not in permeabilized cells, indicating that this was not due to direct effects on RyR. The antiarrhythmic effect of verapamil was due to reduced SR Ca(2+) content following I(CaL) inhibition. Computational modelling supported that the level of I(CaL) inhibition obtained experimentally was sufficient to reduce the SR Ca(2+) content. Ca(2+) wave prevention through reduced SR Ca(2+) content was also effective in heterozygous ankyrin B knockout mice with excessive SR Ca(2+) accumulation during β-adrenergic stimulation.

CONCLUSION

I(CaL) inhibition prevents diastolic Ca(2+) waves caused by increased Ca(2+) sensitivity of RyR or excessive SR Ca(2+) accumulation during β-adrenergic stimulation. In contrast, unstimulated early Ca(2+) release during the decay of the Ca(2+) transient is not prevented, and merits further study to understand the full antiarrhythmic potential of I(CaL) inhibition.

Inhibitory effects of verapamil isomers on the proliferation of choroidal endothelial cells

PURPOSE

To evaluate the effects of verapamil isomers on in vitro proliferation of bovine choroidal endothelial cells (CECs).

MATERIALS AND METHODS

CECs were isolated from bovine eyes and cultured in endothelial growth medium (EGM). For the proliferation assays, CECs were exposed to verapamil isomers (0.1-100 microM) in EGM with 2% fetal bovine serum or basic fibroblast growth factor (bFGF) (10 ng/ml). After 72 h of incubation with the desired drug, the cellular proliferation was determined by an MTT assay and a BrdU assay. In addition, the drug toxicity on CECs stimulated with EGM was evaluated by cell counting with trypan blue.

RESULTS

All verapamil isomers inhibited the bFGF- or medium-stimulated growth significantly in a concentration range of 10-40 microM without toxicity. No significant differences were seen between the inhibitory effects of the various isomers. Cell toxicity was detected at a concentration of 100 microM verapamil isomers on EGM-stimulated CECs.

CONCLUSION

The results demonstrate the efficacy of all verapamil isomers in inhibiting CEC proliferation involved in the process of choroidal neovascularization. D: -(+)-Verapamil may be recommended for further in vivo evaluation in an animal model of exudative AMD; it has fewer systemic and local side effects because calcium channels are not blocked.

Calcium channel antagonists inhibit growth of subcutaneous xenograft meningiomas in nude mice

BACKGROUND

We have previously shown that calcium channel antagonists inhibit in vitro meningioma growth. This study examines the effect of calcium channel antagonists on in vivo xenograft meningioma growth.

METHODS

Meningioma cells taken from human patients were mixed with Matrigel and injected into the subcutaneous space in the flank of nude mice. These animals were treated with calcium channel antagonists in their drinking water. Tumor volumes were measured over time; comparison was made between control and treatment groups. Daily weights, average daily water consumption, and serum calcium channel antagonist levels were determined. Comparison of histology and proliferation index was made between control and treatment groups.

RESULTS

Diltiazem treatment decreased tumor growth over time compared to control groups. Increased tumor growth inhibition was seen with increasing doses (p > 0.05). Treatment with verapamil had similar effects; however, there are no statistically significant dose dependent decreases in growth with increasing verapamil doses. There were no tumor "cures" or spontaneous regression of tumor in any group including the control groups. Animal daily weight and average daily water consumption was unaffected by increasing calcium channel antagonist doses compared to control groups. Mouse serum drug levels increased with increasing doses of drug in the drinking water of treatment groups (p > 0.05). Histology and proliferative index of treatment groups were similar to control groups.

CONCLUSION

Calcium channel antagonists decrease but do not completely inhibit the growth of meningiomas in nude mice. Clinical correlations and potential applications are discussed.

Verapamil inhibits proliferation, migration and protein kinase C activity in human retinal pigment epithelial cells

The effects of three calcium channel blockers, verapamil, diltiazem and nifedipine, were examined on in vitro proliferation and migration of human retinal pigment epithelial cells. Human retinal pigment epithelial cells were seeded in Dulbecco's modified essential medium with 10% fetal bovine serum and different concentrations of the three calcium channel blockers. After 3 days of treatment, cell proliferation was determined by cell counting and by [3H]-thymidine uptake. Cell viability was determined with trypan blue exclusion. For determination of cell migration, retinal pigment epithelial cells were grown to confluence and then growth-inhibited with mitomycin C. After a 3 mm zone was denuded, the cells were treated with different concentrations of the calcium channel antagonists. After 24 hr, the cells that had migrated over the wound edge were counted. To determine the involvement of protein kinase C in the verapamil effect, its activity was measured in both verapamil-treated and untreated cells. Verapamil dose dependently inhibited serum-induced proliferation of retinal pigment epithelial cells, when measured by cell number (IC50 14.6 microM) or [3H]-thymidine incorporation (IC50 11.3 microM). At concentrations of 15 microM and below, there was no effect on cell viability, as determined by morphology and trypan blue exclusion. Diltiazem inhibited cell proliferation at a concentration of 100 microM; however, 100 microM nifedipine had no effect. Verapamil showed a significant inhibition of serum-induced migration in the range of 10 microM to 0.1 microM. The IC50 of the inhibition of retinal pigment epithelial cell proliferation and migration by verapamil is significantly higher than that seen for effects on calcium channel blockage. Eight micromolar verapamil reversibly inhibited total protein kinase-C activity in retinal pigment epithelial cells suggesting the possibility that the drug may act by inhibiting the protein kinase-C pathway. These data suggest the potential of the calcium channel blocker verapamil as a pharmacological modulator of disorders such as proliferative vitreoretinopathy in which there is increased retinal pigment epithelial cell proliferation and migration.

Clinical pharmacokinetics of vasodilators. Part I

Understanding the mechanism of action and the pharmacokinetic properties of vasodilatory drugs facilitates optimal use in clinical practice. It should be kept in mind that a drug belongs to a class but is a distinct entity, sometimes derived from a prototype to achieve a specific effect. The most common pharmacokinetic drug improvement is the development of a drug with a half-life sufficiently long to allow an adequate once-daily dosage. Developing a controlled release preparation can increase the apparent half-life of a drug. Altering the molecular structure may also increase the half-life of a prototype drug. Another desirable improvement is increasing the specificity of a drug, which may result in fewer adverse effects, or more efficacy at the target site. This is especially important for vasodilatory drugs which may be administered over decades for the treatment of hypertension, which usually does not interfere with subjective well-being. Compliance is greatly increased with once-daily dosing. Vasodilatory agents cause relaxation by either a decrease in cytoplasmic calcium, an increase in nitric oxide (NO) or by inhibiting myosin light chain kinase. They are divided into 9 classes: calcium antagonists, potassium channel openers, ACE inhibitors, angiotensin-II receptor antagonists, alpha-adrenergic and imidazole receptor antagonists, beta 1-adrenergic agonist, phosphodiesterase inhibitors, eicosanoids and NO donors. Despite chemical differences, the pharmacokinetic properties of calcium antagonists are similar. Absorption from the gastrointestinal tract is high, with all substances undergoing considerable first-pass metabolism by the liver, resulting in low bioavailability and pronounced individual variation in pharmacokinetics. Renal impairment has little effect on pharmacokinetics since renal elimination of these agents is minimal. Except for the newer drugs of the dihydropyridine type, amlodipine, felodipine, isradipine, nilvadipine, nisoldipine and nitrendipine, the half-life of calcium antagonists is short. Maintaining an effective drug concentration for the remainder of these agents requires multiple daily dosing, in some cases even with controlled release formulations. However, a coat-core preparation of nifedipine has been developed to allow once-daily administration. Adverse effects are directly correlated to the potency of the individual calcium antagonists. Treatment with the potassium channel opener minoxidil is reserved for patients with moderately severe to severe hypertension which is refractory to other treatment. Diazoxide and hydralazine are chiefly used to treat severe hypertensive emergencies, primary pulmonary and malignant hypertension and in severe preeclampsia. ACE inhibitors prevent conversion of angiotensin-I to angiotensin-II and are most effective when renin production is increased. Since ACE is identical to kininase-II, which inactivates the potent endogenous vasodilator bradykinin, ACE inhibition causes a reduction in bradykinin degradation. ACE inhibitors exert cardioprotective and cardioreparative effects by preventing and reversing cardiac fibrosis and ventricular hypertrophy in animal models. The predominant elimination pathway of most ACE inhibitors is via renal excretion. Therefore, renal impairment is associated with reduced elimination and a dosage reduction of 25 to 50% is recommended in patients with moderate to severe renal impairment. Separating angiotensin-II inhibition from bradykinin potentiation has been the goal in developing angiotensin-II receptor antagonists. The incidence of adverse effects of such an agent, losartan, is comparable to that encountered with placebo treatment, and the troublesome cough associated with ACE inhibitors is absent.

Human hepatoma cells rich in P-glycoprotein are sensitive to aclarubicin and resistant to three other anthracyclines

Drug resistance is a major obstacle to successful chemotherapy of primary liver cancer, which is associated with high expression of the multidrug resistance (MDR) gene product P-glycoprotein (Pgp), a multidrug efflux transporter. The most effective single agents in treatment of primary liver carcinoma belong to the anthracycline family, yet several anthracyclines are known to be substrates for Pgp. In the present study, we compared four anthracyclines with respect to cell growth inhibition, intracellular accumulation and cellular efflux using the HB8065/R human hepatoma cell line which is rich in Pgp, and the Pgp-poor parental line HB8065/S. The anthracyclines were also administered in conjunction with the Pgp-modifying agents verapamil and SDZ PSC 833 to assess modulation of resistance. The HB8065/R cells were sensitive to aclarubicin (ACL) and highly resistant to epirubicin (EPI), doxorubicin (DOX) and daunorubicin (DNR). SDZ PSC 833 enhanced accumulation, decreased efflux and increased cytotoxicity of EPI, DOX and DNR in the HB8065/R cells, but none of these effects was seen with ACL. In conclusion, ACL is apparently not transported by Pgp and retains its activity in a multidrug-resistant human hepatoma cell line; such properties can be exploited for clinical purposes.

Age and severe adverse drug reactions caused by nifedipine and verapamil. Gruppo Italiano di Farmacovigilanza nell' Anziano (GIFA)

The association of age with risk for severe adverse drug reactions (SADRs) was studied in 2371 and 862 hospitalized patients taking nifedipine and verapamil, respectively. Nifedipine caused hypotension (n = 22), tachycardia (n = 3), and acute renal failure (n = 1) (total SADR rate, 1.1%, 26/2371). Verapamil caused hypotension (n = 3), bradycardia (n = 9), and atrioventricular blocks (n = 2) (total SADR rate, 1.6%, 14/862). The mean age of patients with and without SADRs was for nifedipine 77.1 +/- 1.7 and 71.8 +/- 0.8 years, respectively (p < 0.05), and for verapamil 73.4 +/- 2.9 and 73.1 +/- 0.4 years, respectively. Sex, length of stay, comorbidity, polypharmacy, intake of slow-release preparations, daily dosage, and new intake of calcium antagonists were examined as potential confounders of the age-SADR association. After adjusting for potential confounders, age was significantly and independently associated with SADRs caused by nifedipine, but not with SADRs caused by verapamil (OR = 1.69, 95% CI = 1.05-2.72 and OR = 1.06, 95% CI = 0.63-1.68 for 10-year increase, respectively). Although nifedipine and verapamil did not have significantly different rates of SADRs, an age-related gradient was found only for nifedipine.

Inhibition of in vitro meningioma proliferation after growth factor stimulation by calcium channel antagonists: Part II--Additional growth factors, growth factor receptor immunohistochemistry, and intracellular calcium measurements

We have previously reported that calcium channel antagonists can block both the growth of meningiomas in culture and the potent growth stimulation of meningioma cells by epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). This study further defines the nature of this growth inhibition. Primary meningioma cultures were established, and cells were characterized. Fibroblast growth factor or insulin-like growth factor-I growth stimulation in the presence of calcium channel antagonists was examined. In addition, the effects of ethylene glycol-bis-(aminoethylether) N,N,N',N"-tetraacetic acid and Bay K 8644, a calcium channel agonist, on the growth factors were analyzed. Growth factor receptor immunohistochemistry was performed on the original tumors and the in vitro meningioma cells. Twelve of 17 (71%) meningiomas in this study were positive for the EGF receptor, and 14 of 17 (82%) were positive for the PDGF receptor. Five of six (83%) of the culture cells were positive for the EGF receptor, and four of five (80%) were positive for the PDGF receptor. Intracellular calcium changes were quantified using the intracellular calcium-chelating, fluorescent dye, Fura-2. The growth stimulation of fibroblast growth factor and insulin-like growth factor-I on meningioma cells in culture was decreased in a dose-dependent manner by calcium channel antagonists. The growth stimulation of fibroblast growth factor and insulin-like growth factor-I was not affected by a reduction of extracellular calcium, whereas the growth stimulation of EGF and PDGF was. Interestingly, intracellular calcium was not increased after exposure to growth factors but was increased after serum stimulation. This increase could be blocked by preincubation with verapamil. Calcium channel antagonists can inhibit proliferation of meningioma cells in culture after stimulation with a number of growth factors. These drugs might disrupt intracellular calcium homeostasis or interfere with key elements of the growth factor signal transduction pathways. These mechanisms as well as the potential clinical relevance of these findings are discussed.

In vitro growth inhibition of growth factor-stimulated meningioma cells by calcium channel antagonists

Studies have shown that a majority of meningiomas contain receptors for platelet-derived growth factor and epidermal growth factor and that these growth factors promote the proliferation of meningioma cells in culture. Although the mechanism of action has not been elucidated, intracellular calcium appears to be part of the signal transduction mechanism. Because alterations in intracellular calcium could interrupt this pathway and decrease cellular proliferation, we investigated the effects of calcium channel-blocking agents on the growth of meningioma cells in vitro. Primary meningioma cell cultures were established, and the cells were characterized by light and electron microscopy and by immunohistochemical studies. Then, the cultures were given growth factors and/or various calcium channel antagonists, and growth rates were measured. A dose-response decrease in cell growth was seen when verapamil, nifedipine, or diltiazem (voltage-dependent calcium channel-blocking agents) was added to serum-containing media. Also, these drugs blocked the growth stimulation of epidermal growth factor and platelet-derived growth factor in a similar fashion. Dantrolene, which inhibits the release of sequestered intracellular calcium, was also an effective blocker of the mitogenic stimulation of these growth factors.

A double-blind, placebo-controlled crossover trial of nadolol and verapamil in mild and moderately symptomatic hypertrophic cardiomyopathy

OBJECTIVES

The aim of this study was to determine whether therapy with a beta-adrenergic or calcium channel blocking agent can improve the functional capacity and quality of life of patients with mild or moderately symptomatic hypertrophic cardiomyopathy.

BACKGROUND

Both beta-blockers and calcium channel blockers may alleviate symptoms in hypertrophic cardiomyopathy, but previous studies have been performed in hospitalized patients or have been open studies without control subjects.

METHODS

A randomized, double-blind crossover trial of nadolol, verapamil and placebo, administered for periods of 4 weeks each, was performed in 18 patients with mild or moderately symptomatic hypertrophic cardiomyopathy (10 men, 8 women; mean age +/- SD 39 +/- 17 years). A detailed symptom assessment, bicycle exercise testing, echocardiography and Holter monitoring were performed in each period.

RESULTS

Two patients withdrew from the study owing to symptomatic sinus bradycardia during nadolol therapy. Neither drug improved maximal oxygen consumption (placebo 26 +/- 8, verapamil 23 +/- 6, nadolol 21 +/- 7 ml/kg per min; p = 0.1). Peak exercise work load was reduced by > or = 10 W in 13 patients (81%) during nadolol therapy and in 4 patients (25%) during verapamil therapy (p = 0.005, nadolol vs. verapamil). Despite the effects on exercise capacity, 13 patients (81%) preferred drug treatment (8 verapamil, 5 nadolol) over placebo (p = 0.001). Verapamil improved reported performance at work compared with nadolol (p = 0.01) and tended to improve other measures of health-related behavior and symptoms compared with nadolol and placebo.

CONCLUSIONS

In patients with mild or moderately symptomatic hypertrophic cardiomyopathy, exercise capacity was not improved by nadolol or verapamil, and individuals were more often impaired by nadolol than with verapamil. Nevertheless, many patients derived symptomatic benefit from drug therapy, especially with verapamil.

Sustained-release verapamil formulations for treating hypertension

Verapamil, the first calcium-channel blocker to be introduced for clinical use, is a major drug used for the treatment of systemic hypertension. During the past 10 years, the use of verapamil for hypertension has produced a considerable clinical database to support the efficacy and safety of the agent in many patients. Because of its short half-life, verapamil was originally administered 3 to 4 times daily. During the past decade, a sustained-release formulation of verapamil has been marketed in the US. This product allows for once-daily dosing up to 240 mg/d; however, when higher doses are needed, this sustained-release formulation should be administered twice daily. In addition, the medicine should be taken with food to avoid the high peak blood levels of verapamil, which appears to be related to the delivery system. A new pellet-filled capsule formulation of verapamil (Verelan, Lederle, Wayne, NJ and Wyeth-Ayerst, Philadelphia, PA) is available and provides controlled absorption, 24-hour blood pressure control, improved peak-to-trough plasma levels, and once-daily dosing regardless of dosage size. Prolonged-release verapamil can be taken without food.

Differences in response to single dose and steady-state therapy with verapamil in stable angina

Ten patients with stable effort angina were studied in a randomized double-blind and placebo-controlled trial to compare the antianginal efficacy of "acute" and "chronic" (after reaching a steady-state level) treatment with verapamil. Efficacy was assessed by exercise testing after a 120 mg single-dose and at the end of a seven-dose course of 120 mg of verapamil given thrice daily. Three daily exercise tests were performed the first, second and fifth day of the study protocol at 8, 12 and 16 hours. Eight hours after the last dose was given, exercise time increased by 54 +/- 30 sec after a single-dose of verapamil and by 156 +/- 31 sec after seven-doses of verapamil (P less than 0.05 as compared to single-dose verapamil). The time to 1 mm depression of the ST segment increased by 30 +/- 20 sec after a single-dose of verapamil and by 66 +/- 28 sec after seven-doses of verapamil (P less than 0.01 as compared to single dose verapamil). Six of the ten patients became free from angina on treadmill exercise after a seven-dose course of verapamil, but only one patient became free from angina after acute testing with a single-dose of verapamil. It is concluded that several doses of verapamil are required to achieve an optimal anti-ischemic effect, as suggested by the pharmacodynamic properties of this drug. Once steady-state is achieved, the effects of verapamil remain for at least 8 hours, so that an administration schedule of three times daily protects the patient for a 24-hour period.

A phase II study of epidoxorubicin in colorectal cancer and the use of cyclosporin-A in an attempt to reverse multidrug resistance

We determined the ability of the multidrug resistance (MDR) reversal agent cyclosporin-A to increase anthracycline drug accumulation in colorectal tumour cells in vitro, using the technique of on-line flow cytometry. Data of four previously untreated patients showed that cyclosporin-A can increase intracellular net-uptake of daunorubicin. A phase II study was initiated in 24 colorectal cancer patients. They received cyclosporin-A at a dose of 3 mg kg-1 over 1 h as i.v. infusion, at 7 h and at 1 h preceding cytotoxic drug administration. At the end of the second cyclosporin-A administration epidoxorubicin 90 mg m-2 was administered as i.v. bolus. Cycles were repeated every 3 weeks. Median cyclosporin-A peak blood levels and levels at 18 h after cytotoxic drug administration appeared to be 6248 ng ml-1 and 1012 ng ml-1 respectively. Only one partial response was observed, despite these high cyclosporin-A levels. Cyclosporin-A did not cause major toxicity, only a 29% incidence of hot flushes was observed. Epidoxorubicin toxicities were as expected but the frequency of severe leucocytopenia was striking. This treatment schedule can not be considered active in colorectal cancer.

Double-blind randomised placebo-controlled dose-efficacy study of sustained release verapamil in chronic stable angina

The efficacy and tolerability of sustained release verapamil (Securon SR) was investigated in twenty-four patients with chronic stable angina. Patients entered four randomised, double-blind treatment periods, each lasting one week of verapamil-SR 240 mg once daily, 360 mg once daily, 240 mg twice daily, and matching placebo. Four patients were withdrawn, but in one instance this was attributable to side effects from verapamil. Among the remaining twenty patients, mean frequency of angina fell from 4.25 episodes during the last five days of placebo to 2.35, 2.6 and 1.3 episodes during respective active treatments (all P less than 0.001). Compared with placebo the median percentage increase in time to 1 mV ST depression during treadmill exercise (12 hours post dose) was significant only with the regimen of verapamil-SR 240 mg given twice daily at +11% (P = 0.04). Total duration of exercise was also significantly longer and maximum ST depression significantly less only with the twice daily treatment (704 + 186 sec vs 648 + 203 sec; P = 0.03, and 1.75 + 0.73 mm vs 2.15 +/- 0.62 mm; P = 0.02). Side effects, predominantly constipation, breathlessness, and swollen ankles, occurred most frequently with verapamil-SR 360 mg. Thus, sustained release verapamil is well tolerated and effective in the treatment of angina. A regimen of 240 mg given twice daily emerges as superior to once daily treatments for 24-hour prophylaxis of angina.

Inhibition by calcium channel blockers of the binding of platelet-activating factor to human neutrophil granulocytes

The inhibitory action of calcium channel blockers on platelet-activating factor (PAF)-induced activation of human polymorphonuclear granulocytes (PMNL) and on the binding of [3H]PAF to neutrophils was studied. Verapamil and diltiazem inhibited PAF (10(-8)-10(-15) M)-induced degranulation and superoxide production in a dose-dependent manner, with pA2 values of 5.6 and 6.1 for verapamil and 5.9 and 6.2 for diltiazem, respectively. Both channel blockers inhibited the specific binding of [3H]PAF to PMNL in dose-dependent fashion, with Ki values of 3.9 +/- 0.6 X 10(-5) M and 3.2 +/- 0.4 X 10(-5) M for verapamil and diltiazem, respectively. Scatchard analysis of the binding data revealed that both calcium channel blockers decreased the receptor binding affinity and slightly increased the number of high-affinity PAF receptors, whereas they did not affect the binding affinity and number of low-affinity receptors. These results indicate that calcium channel blockers can inhibit neutrophil responses elicited by PAF by a mechanism other than inhibition of calcium influx and suggest that the PAF receptor may be closely associated with calcium channels.

Verapamil potentiates 4'-epidoxorubicin cytotoxicity in a rat hepatoma cell line and in a substrain resistant to 4'-epidoxorubicin

We have examined the influence of verapamil (VP) on the in vitro effect of 4'-epidoxorubicin (Epi-A) in a rat hepatocarcinoma cell line (MHlCl) and in an Epi-A resistant substrain. A VP concentration of 500 ng/ml (1.1 mumol/l) markedly potentiated the cytotoxic effect of Epi-A in the parent line. The resistant cells grow at an Epi-A concentration of 7500 ng/ml (12.9 mumol/l). This is approximately 15-fold higher than the concentration tolerated by parental cells. In these cells VP reversed the acquired resistance to Epi-A in a concentration dependent manner; thus, a concentration in the range of 500-750 ng/ml (1.1-1.7 mumol/l) of VP restored the sensitivity to Epi-A in the resistant cells. Our results demonstrate that VP increases the sensitivity to Epi-A in hepatocarcinoma cells never exposed to this drug, as well as in hepatocarcinoma cells with acquired Epi-A resistance.

Effects of calcium channel blockers on the development of early rat postimplantation embryos in culture

Rat embryos (9.5-day-old) were cultured for 48 h in the presence of nifedipine (NIF), nimodipine (NIM), nitrendipine (NIT), gallopamil HCl (GAL), verapamil HCl (VER) and diltiazem HCl (DIL). The effects on growth and morphogenetic differentiation in vitro were monitored. Dose-response relationships were evaluated, including an assessment of the "no-observed-effect-level" (NOEL) or the "lowest-observed-effect-level" (LOEL), and the lowest concentration tested inducing abnormalities in 100% of the embryos ("100% EL"). The morphological alterations observed at the highest concentrations were very similar for all six drugs. The abnormalities concerned yolk sac circulation and morphology, as well as heartbeat, the morphology of the heart, head, neural tube, or forelimbs, and the shape of the embryo. The abnormal embryos were also growth retarded (decrease in protein content and crown-rump length). Interference with calcium channel functions seems to represent an interesting model for studying a special kind of abnormal prenatal development, especially the differentiation of certain mesenchymal structures. The concentration ranges between NOELs and 100% ELs were found to be: NIM = 0.1-1 microgram/ml; NIT and VER = 1-10 micrograms/ml; DIL = 1-30 micrograms/ml, and LOELs-100% ELs were: GAL = 1-10 micrograms/ml; NIF = 10-30 micrograms/ml.

Addition of verapamil and tamoxifen to the initial chemotherapy of small cell lung cancer. A phase I/II study

Based on experimental observations that verapamil and tamoxifen reverse multiple drug resistance, the authors investigated the feasibility of combining both agents with the initial chemotherapy of extensive small cell lung cancer. Overall, in a consecutive series of 58 patients the most important toxicity was myelosuppression, and there was a 24% rate of severe infections. Therapeutic results included 24% complete and 34% partial response rates, median time to disease progression of 32 weeks, and median survival of 46 weeks. In three consecutive cohorts of patients the dose of either tamoxifen or verapamil were escalated by 25% and 33%, respectively. The cohort of patients receiving verapamil 360 mg/day and tamoxifen 100 mg/day (level 2) had slightly more toxicity but also more responses than the other groups. Therefore, the authors recommend that these doses be used in controlled trials to confirm the promising results of their study.

Requirements for drug monitoring of verapamil: experience from an unselected group of patients with cardiovascular disease

Serum verapamil and metabolite concentrations were determined by HPLC in 29 patients in routine treatment with verapamil, and 23 were in steady state. Dosage levels and corresponding mean trough levels (+/- S.D.) were as follows: 120 mg daily: 79.1 (+/- 77) nmol/l, 240 mg daily: 173.3 (+/- 200.1) nmol/l, 360 mg daily: 204 (+/- 110.2) nmol/l and 480 mg daily: 361.0 (+/- 231.4) nmol/l. The variation coefficients were 97.3, 115.4, 54.0, and 62.1, respectively, thus showing considerable interpatient variation. Repeated determination of trough levels showed, in contrast, only small intrapatient variation (variation coefficient 35.8, 1.9, and 7.4, at the dosage levels 120, 240 and 340 mg per day). No significant correlation was found between serum verapamil levels age, sex, or weight. No significant effect of digoxin on the concentration of serum verapamil was found. No relation was observed between serum verapamil concentrations and desired effect or side-effects. Two patients showed no measurable serum verapamil, but one of these had detectable levels of metabolites. Such patients may represent subgroups of fast metabolizers or non-absorbers. Measurements of the metabolites nor-verapamil, D 620 and D 617 indicated saturation of the first-pass metabolism. In conclusion, therapeutic drug monitoring is not indicated during routine verapamil treatment, whereas single measurements of verapamil may be warranted in patients not responding to treatment in order to identify fast metabolizers or non-absorbers.

Massive verapamil ingestion: a report of two cases and a review of the literature

This report describes two patients who were victims of massive verapamil ingestion and then reviews the available literature. Because verapamil blocks the slow calcium channels of the heart and blood vessels, the use of calcium as a treatment would be logical. In the two cases reported here, calcium was only transiently effective in maintaining cardiac output and blood pressure. Several other agents were then used and most were ineffective. This is similar to experience reported in the literature that suggests that no single agent is capable of reversing verapamil's negative inotropic, dromotropic, chronotropic, and vascular smooth muscle effects.

In vitro modulation of human neutrophil superoxide anion generation by various calcium channel antagonists used in ischemia-reperfusion resuscitation

Generation of toxic oxygen species by activated polymorphonuclear leukocytes (PMNs) may represent an important mechanism of ischemia-reperfusion injury. Concentration-response data concerning inhibition of superoxide anion (O2-) generation by NADPH oxidoreductase (NADPH OR) from isolated human PMN were generated for five calcium channel antagonists commonly utilized in ischemia-reperfusion investigational therapeutics. Regression analysis derived IC50 values for verapamil, nimodipine, nicardipine and lidoflazine were 45, 20, 12 and 7 microM respectively. Inhibition of the extent of reaction at 5 min paralleled inhibition of initial velocity. No inhibition by flunarizine was noted at concentrations less than or equal to 25 microM (where it did not alter reaction mixture composition). Only nicardipine demonstrated a significant concentration-response effect relative to prolonging lag time preceding O2- synthesis. Inhibition appeared at least partially reversible for all five agents. Neither PMN activation/desensitization, free-radical scavenging, nor PMN cytotoxicity appeared to be involved in the inhibition of PMN O2- synthesis by these agents. Ca2+ antagonist inhibition of PMN NADPH OR appears to involve more than simple inhibition of Ca2+ flux across the PMN plasma membrane. Direct inhibition of the intracellular events involved in the activation and/or activity of NADPH OR may be operative.

Calcium channel antagonists: Part VI: Clinical pharmacokinetics of first and second-generation agents

A survey of the pharmacokinetic properties of the three prototypical calcium antagonist agents shows that they have in common a very high rate of hepatic first-pass metabolism with, in the case of verapamil and diltiazem, the formation of an active metabolite that affects the dose during chronic therapy. Therefore, the major factor altering the pharmacokinetic properties and the dose of the drug required is the capacity of the liver to metabolize the drug, which in turn depends on the hepatic blood flow and the activity of the hepatic metabolizing systems. Hence liver disease, a low cardiac output, and coadministration of certain drugs inducing or inhibiting the hepatic enzymes, all indirectly affect the pharmacokinetic properties of the calcium antagonists. There are also other potential drug interactions of a kinetic or dynamic nature that may arise. In general, renal disease has little effect on the pharmacokinetics of calcium antagonists.

Clinical utility of nifedipine and diltiazem plasma levels in patients with angina pectoris receiving monotherapy and combination treatment

The clinical utility of nifedipine and diltiazem blood levels in patients with angina pectoris receiving monotherapy (N = 14) and combination treatment (N = 9) were assessed in a placebo run-in, double blind, randomized, crossover study. Compared to placebo, diltiazem (mean daily dose 360 mg), nifedipine (mean daily dose 90 mg) and combination diltiazem-nifedipine therapy (mean daily dose 55 mg of nifedipine, 360 mg of diltiazem) were associated with reductions in weekly angina attacks and nitroglycerin consumption. Although both drugs used as monotherapy and in combination were also associated with significant increments in exercise tolerance and other improved angina parameters, these changes were not related to the plasma levels of either drug. Nifedipine plasma levels were measured by gas chromatography and diltiazem plasma levels measured by reverse high-pressure liquid chromatography from specimens obtained 2-5 hours after the last previous dose, after 1, 2 and 3 weeks of treatment, and during baseline placebo and placebo washout periods. With combination therapy, there was no effect on the diltiazem plasma level compared to monotherapy. The significant decrease in the nifedipine dose in patients on combination therapy did not significantly change nifedipine plasma levels. Determinations of plasma levels of diltiazem and nifedipine in the management of patients is of no value in the management of patients with angina pectoris except for monitoring treatment compliance and overdosage.

Diltiazem, nifedipine, and their combination in patients with stable angina pectoris: effects on angina, exercise tolerance, and the ambulatory electrocardiographic ST segment

The efficacy and safety of oral nifedipine and diltiazem were compared in 20 patients with stable angina pectoris with use of a placebo run-in, randomized, double-blind titration to maximal effect crossover protocol. The effects of treatment withdrawal were also analyzed. All patients received placebo for 2 weeks and were then randomly assigned to receive either diltiazem or nifedipine. A 2 week drug titration phase in which patients received either diltiazem (180 to 360 mg/day) or nifedipine (30 to 120 mg/day) in three divided doses was followed by a 1 week maintenance phase. Patients then received placebo for 1 to 2 weeks, followed by crossover to the other treatment regimen and a second placebo washout period of 1 week. Patients (n = 13) who remained symptomatic on both diltiazem and nifedipine during the monotherapy periods entered a 3 week combination treatment phase, followed by a final 1 week placebo washout period. Frequency of angina, nitroglycerin consumption, exercise tolerance (Naughton protocol), and frequency of daily episodes of ST segment deviations on the electrocardiogram (1 mm of ST segment depression persisting for at least 1 min with and without chest pain) on an ambulatory electrocardiographic monitor were assessed during the baseline placebo, active monotherapy, placebo withdrawal, and combination treatment phases. Plasma drug levels were also measured. Compared with initial placebo values, the frequency of angina and the amount of nitroglycerin treatment were reduced by both diltiazem (p less than .001) and nifedipine (p less than .02). Diltiazem was more effective than nifedipine in reducing angina (p less than .02). Exercise duration increased with both drugs (p less than .0001). Diltiazem was significantly better than nifedipine in reducing the episodes of ST segment depression on the ambulatory monitor (p less than .01). Diltiazem reduced the resting heart rate (p less than .01); both drugs reduced the resting blood pressure and rate-pressure product. Overall, combination therapy was more effective in patients who did not maximally respond to diltiazem or nifedipine alone with respect to anginal and exercise variables and in reducing blood pressure at rest and during exercise. Plasma drug levels could not predict an individual patient's treatment response. Diltiazem may increase nifedipine drug levels when the drugs are combined. Fewer side effects were observed with diltiazem than nifedipine; the most side effects were seen with combination treatment. There were no apparent withdrawal effects observed with either treatment regimen.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium channel blockers

The calcium channel blockers initially were approved for the treatment of classical and variant angina pectoris. Recent studies indicate that these agents also are useful in such diverse conditions as pulmonary and systemic hypertension, hypertrophic cardiomyopathy, arrhythmias, asthma, Raynaud's syndrome, esophageal spasm, myometrial hyperactivity, cerebral arterial spasm, and migraine.

The effects of slow channel blockers and beta blockers on atrioventricular nodal conduction

The PR interval on the electrocardiogram represents the time that it takes an impulse to travel through the atrium and atrioventricular (AV) conduction system to the ventricles. Normally, activation is slowest in the AV node, and variations in PR interval most commonly parallel changes in AV nodal activation time. The AV nodal conduction time and effective refractory period are rate dependent and, in adult humans, are usually prolonged with increasing atrial paced rates. In addition, alterations in autonomic tone effect AV nodal conduction as well as sinus rate. The effect is usually in the same direction but often to different degrees. In patients with normal AV nodal function, parasympathetic and sympathetic tone are balanced at rest, but in patients with abnormal AV conduction, the effect of the parasympathetic system is more marked. Drugs including the slow channel blockers and beta blockers, affect AV nodal function. Slow channel blockers inhibit the slow inward calcium current, which may prolong conduction and refractoriness in the AV node. However, whereas diltiazem and verapamil have been shown to prolong AV nodal conduction and refractoriness in humans, nifedipine, a potent vasodilator, cannot be used in doses large enough to affect the AV node. The increase in PR interval caused by verapamil is minimal, and at doses of less than 480 mg/d, AV block occurs infrequently. When AV block occurs, it is first degree block in most patients, and it is usually asymptomatic. The electrophysiologic effects of diltiazem are similar to those of verapamil. Beta blockers also have a negative dromotropic effect on the AV node. They prolong the AH interval and AV nodal refractory periods and may lengthen the PR interval. The prolonged PR interval rarely results in more than first degree AV block in patients receiving maintenance therapy. In selected patients, combination therapy with a slow channel blocker and a beta blocker rarely causes second-degree AV block.

A double blind placebo controlled comparison of verapamil, atenolol, and their combination in patients with chronic stable angina pectoris

The efficacy and effect on cardiac function of verapamil 120 mg three times a day and atenolol 100 mg once a day, singly and in combination, were evaluated in 15 patients with angina pectoris. While they were on the combination treatment four patients withdrew from the study. Episodes of angina pectoris and glyceryl trinitrate consumption were significantly reduced only on the combination. On the combination only four patients developed evidence of ischaemia during exercise compared with seven on verapamil and ten on atenolol. ST segment depression at peak exercise, assessed by 16 point precordial mapping, was reduced by all active treatments from 7.1 on placebo to 2.7, 0.9, and 0.6 mm on atenolol, verapamil, and the combination respectively. Mean left ventricular ejection fraction fell significantly from 60% on placebo to 53% on the combination but was unchanged on verapamil and atenolol. Verapamil was an effective alternative to atenolol; the combination was the most effective treatment but was associated with a significant morbidity.

Efficacy of sustained-release verapamil in chronic stable angina pectoris

The effectiveness of a sustained-release preparation of verapamil (verapamil-SR) was compared with the regular formulation of verapamil and with placebo in 12 patients with chronic stable angina pectoris. All patients completed an 8-week, double-blind, double-crossover, randomized protocol with 2-week treatment periods of verapamil-SR, 240 mg twice daily; regular-formulation verapamil, 120 mg 4 times daily; and 2 placebo therapies. The frequency of weekly anginal episodes was reduced from 7.6 +/- 10.0 with placebo to 3.1 +/- 4.2 after the regular formulation of verapamil (p = 0.09) and from 6.4 +/- 7.6 with placebo to 2.8 +/- 4.8 after verapamil-SR (p = 0.06). Treadmill time increased from 384 +/- 144 seconds during the first placebo phase to 468 +/- 138 seconds after the regular formulation of verapamil (p less than 0.01) and from 354 +/- 102 seconds during the second placebo phase to 462 +/- 138 seconds after verapamil-SR (p less than 0.01). Time to the onset of angina was similarly prolonged by formulations of verapamil. There were no significant adverse effects after 1 year in any patient taking verapamil-SR, 240 mg twice daily. Thus, a twice-a-day verapamil-SR dose regimen is safe and is as effective for treatment of angina of effort as the regular formulation given 4 times a day.

New therapeutic modalities for the treatment of elderly patients with ischemic heart disease

In developing a treatment plan for elderly patients with ischemic heart disease, it is important to appreciate that the pathophysiologic process and aging influence the type of response produced by various drugs. The aging process also alters the way drugs are absorbed, distributed, and eliminated. Each of these variables must be considered in deciding which drugs should be used and how they should be administered.

Controlled-release formulations of propranolol and verapamil

The in vitro and clinical behavior of new controlled-release formulations of propranolol and verapamil are reviewed. In vitro dissolution studies have proved to be of little value in determining the clinical activity of these new dosage forms. There is a difference between the blood levels found with the new formulations and those of the reference products. The once-daily verapamil product was evaluated in black hypertensive patients with promising results and suggests that this dosage form of verapamil may be successful as monotherapy for treating this patient population.

The effect of oral verapamil therapy on antipyrine clearance

The influence of chronic verapamil treatment on antipyrine elimination was studied in eight angina patients. Antipyrine half-life (mean +/- s.d.) was 13.1 +/- 1.15 h at the start of therapy and 16.6 +/- 3.05 h (P less than 0.05) during chronic oral administration of verapamil (80-120 mg four or three times daily for 4 to 7 months). There was a significant decrease in antipyrine clearance (mean +/- s.d, 43.2 +/- 16.8 ml min-1 vs 28.7 +/- 16.6 ml min-1, P less than 0.01) while the change of distribution volume was insignificant. Verapamil elimination was also found to be impaired after chronic dosing as compared to single administration. Half-lives measured from the concentration vs time and urinary excretion rate vs time curves were both prolonged and oral clearance was decreased. Our results suggest that the inhibition of drug-metabolizing enzymes accounts for the impairment of verapamil elimination on chronic administration.

Kinetics and dynamics of calcium entry antagonists in systemic hypertension

The calcium-entry antagonists verapamil, diltiazem and nifedipine (and their analogs) are all eliminated by hepatic metabolism and the rate of disposition is dependent on the rate of liver blood flow. During long-term administration, the profound hemodynamic effects of these agents result in changes in hepatic blood flow in association with decreases in arterial pressure, and either increases or decreases in measured cardiac output. This alters the drug's rate of delivery to the site of elimination, with concomitant changes in systemic clearance and a prolongation in elimination half-life. The pharmacokinetic data determined after initial single doses, therefore, only suggest the kinetic characteristics during long-term administration, because this profile depends on the drugs' sustained effects on liver blood flow. The elimination half-life of all 3 prototypical calcium antagonists is probably significantly prolonged during long-term dosing with clinically effective regimens. Patients with hepatic disorders in which liver blood flow is altered, such as cirrhosis, have profound changes in pharmacokinetics with both short- and long-term administration of verapamil and are likely to have similar changes with other calcium antagonists. During short-term administration, the plasma concentrations of verapamil and other calcium antagonists relate closely to the observed hemodynamic (and electrophysiologic) effects. With long-term administration, however, these correlations are much less impressive. When given in tablet form, nifedipine lowers blood pressure roughly in proportion to plasma levels between 20 and 200 ng/ml; verapamil plasma levels between 80 and 800 ng/ml are associated with antihypertensive efficacy. Plasma level measurements, therefore, are not of clinical importance as guides to antihypertensive therapy, except to identify noncompliance or abnormal patterns of drug handling.

Cardiovascular and pharmacokinetic consequences of combined administration of verapamil and propranolol in dogs

Verapamil and propranolol, alone and in combination, were given intravenously to anesthetized dogs to analyze the interaction between drug-induced cardiovascular effects and the resulting changes in pharmacokinetics. Dosing regimens were used that produced steady state plasma levels of both drugs, and the observed effects were clearly related to the plasma concentrations of the agents. When given alone, at stable "therapeutic" levels in plasma, verapamil or propranolol decreased spontaneous heart rate, increased atrioventricular conduction time, and had opposite effects on cardiac output. At the same doses, the combined infusion of the 2 drugs rapidly resulted in profound depression in cardiac function; in addition, plasma concentrations of both agents increased into ranges associated with cardiovascular toxicity. When verapamil doses were reduced, combined infusion with propranolol decreased atrioventricular conduction and cardiac output, but drug plasma concentrations (and associated effects) remained stable. When reduced doses of propranolol were added to infusion of verapamil, similar effects on cardiovascular function occurred, but plasma drug levels increased progressively throughout the remainder of the study period. In all combinations studied, beta blockade with propranolol decreased liver plasma flow and, therefore, the systemic clearance of verapamil. The in vitro effects of propranolol on verapamil metabolism were small, although significant, and not clinically relevant. These acute studies suggest that the hemodynamic effects resulting from verapamil and propranolol in combination may significantly diminish clearance of 1 or both drugs, thereby resulting in accumulation during continued administration, increased drug effects with increasing plasma concentrations, and potentially lethal drug toxicity.