Prolongation of verapamil elimination kinetics during chronic oral administration

Variability of blood pressure in ambulatory hypertensive patients: effects of verapamil on twice and thrice daily dose regimens

The antihypertensive effects of verapamil over 24 hours were assessed on twice and thrice daily dose regimens on 12 patients (25-65 years of age; mean age 50) with essential hypertension (WHO stages I-II) in a randomised, double-blind, cross-over trial. After a dose titration period starting with either verapamil 80 mg tid or 120 mg bid the patients kept their maintenance dose (240, 360 or 480 mg daily) for 4 weeks before crossing over to the other administration schedule. Repeated ambulatory blood pressure (BP) curves were recorded in 10 patients with a non-invasive portable device (Pressurometer III, Del Mar Avionics). The BP reductions (causal BP values) obtained by 2- and 3-dose regimens were of similar magnitude (from 170 +/- 19/105 +/- 8 on placebo to 140 +/- 17/87 +/- 7 and to 146 +/- 14/88 +/- 8 by 2-and 3-dose respectively). Analyses of BP curves revealed close similarity in profiles on the two dose regimens, although DBP was significantly (p less than 0.05) lower by 3-dose as compared to 2-dose regimen during the period 0.00-2.59 a.m. Long-term (circadian rhythm) and short-term variability did not differ between the regimens. Despite the slight difference in DBP curves after midnight, the overall impression is that verapamil given both twice and thrice daily provides adequate BP control throughout 24 hours.

Pharmacokinetics of calcium channel blocking agents

Verapamil and nifedipine are the most frequently used calcium channel blocking agents in Sweden at present time. The pharmacokinetics of verapamil has been described both in healthy volunteers as well as in patients with supraventricular arrhythmias, angina pectoris, liver cirrhosis, hypertrophic cardiomyopathy or hypertension. Intravenous pharmacokinetics of nifedipine has been investigated in healthy volunteers and oral pharmacokinetics in healthy volunteers as well as in patients with hypertension. The pharmacokinetics of verapamil and of one of its metabolites, norverapamil, is changed after multiple oral dosing as has been described in patients with supraventricular tachyarrhythmias, angina pectoris or in patients with essential hypertension. Plasma concentration-effect relationships have been established for verapamil in different clinical situations and in a few cases also for nifedipine. An update of the pharmacokinetics of these two important calcium channel blocking agents is presented.

Cardiovascular effects of (R)- and (S)-verapamil and racemic verapamil in humans: a placebo-controlled study

OBJECTIVE

To characterise the comparative potency of optically pure (R)- and (S)-verapamil as regards negative dromotropic effects on atrioventricular (AV) node conduction and to compare the hemodynamic effects of single doses of the enantiomers in healthy volunteers.

METHODS

Eight healthy volunteers received a single oral dose of 120 mg (S)-verapamil, 480 mg (R)-verapamil, 240 mg racemic verapamil (rac-verapamil) or placebo on 4 separate occasions. Serum concentrations of (R)- and (S)-verapamil were measured up to 24 h. Cardiovascular effects were assessed by electrocardiography, measurement of blood pressure and transthoracic impedance cardiography (cardiac output and total peripheral resistance). The comparative potency of (R)- and (S)-verapamil with regard to prolongation of the PR interval in the surface ECG was estimated by use of the areas under the effect-time and serum concentration-time curves and linear regression analyses of per cent change in PR interval from baseline versus the logarithm of serum (R)- or (S)-verapamil concentration.

RESULTS

The PR interval was significantly prolonged after all verapamil treatments as compared with placebo. (S)-verapamil was 20.6-21.8 times more potent than (R)-verapamil with regard to negative dromotropic effects. (R)-verapamil caused a significantly greater maximum reduction in the mean arterial pressure (MAP) than placebo [15.9+/-6.8 versus 8.7+/-3.2 mmHg (mean+/-SD); 95% CI on the difference, 0.79-13.7 mmHg; p<0.05], whereas MAP was not affected by the other verapamil treatments. No significant changes were observed in heart rate, cardiac output and total peripheral resistance after any verapamil treatment as compared with placebo.

CONCLUSIONS

(S)-verapamil was about 20 times more potent than (R)-verapamil with regard to negative dromotropic effects on AV node conduction. (R)-verapamil but not (S)-verapamil significantly reduced the MAP as compared with placebo.

Rapid induction of P-glycoprotein expression by high permeability compounds in colonic cells in vitro: a possible source of transporter mediated drug interactions?

P-glycoprotein (PGP) substrates with high membrane permeability, such as propranolol and verapamil, are considered to be essentially "transparent" to PGP since the transporter does not significantly limit their absorption or elimination. However, the question of whether such compounds can modulate PGP expression in epithelial cells following short-term exposure, with potential consequences for drug interactions, has not been addressed. LS180 colonic epithelial cells were exposed to propranolol or verapamil at concentrations (50-300 microM) consistent with those likely to be present in the gut lumen during oral dosing. Both compounds stimulated four to six-fold increases in MDR1 mRNA and PGP protein expression measured by quantitative real-time PCR and immunoblotting, respectively. These changes were accompanied by an induction in transporter activity measured by rhodamine 123 efflux. In contrast, metoprolol, a compound with similar permeability but no affinity for PGP had no effect on PGP expression. The induction of PGP by propranolol and verapamil was rapid with significant increases occurring within 3h with maximal stimulation after 6h exposure. Rifampicin, shown to cause clinical drug interactions via a PXR-mediated increase in PGP expression, exhibited a very similar time-course and extent of induction. In conclusion, verapamil and propranolol, whose trans-epithelial permeability are unaffected by PGP, appear to be effective inducers of PGP expression in gut epithelial cells in vitro. While the in vivo significance of these observations is unknown, this questions whether high permeability, "PGP-transparent" compounds, currently favoured in drug selection strategies, should be evaluated in terms of their potential for transporter-mediated drug interactions.

First line drugs in chronic stable effort angina--the case for newer, longer-acting calcium channel blocking agents

The American College of Cardiology-American Heart Association Committee recommends first line beta-adrenergic blocking agents for chronic stable effort angina. This article reassesses some critical evidence that is new or could have been neglected by the Committee. In particular, the putative role of calcium channel blocking agents (CCBs) is reexamined. Additional evidence is culled from articles not cited by the Committee, together with added reference to recent trials. Safety, side-effects and tolerability are issues that are evaluated. Mortality data are reviewed with the aid of a meta-analysis of all placebo-controlled trials on long acting CCBs. The advice of the committee may need to be reconsidered in view of recent evidence on the tolerability and benefits in hypertension of newer, longer-acting, second-generation CCBs. Of the older agents, verapamil has been shown to be the best with regard to safety and efficacy. Especially in the elderly, angina is often associated with hypertension, with evidence showing dihydropyridine CCBs and beta-adrenergic blocking agents to be similarly effective. Beta-blockers may have undesirable side effects such impotence and impaired exercise ability, despite their proven protective effects in postinfarct patients and in heart failure. The choice of drug should be keyed to the needs and the pathophysiology of the individual patient.

Current status of safety and efficacy of calcium channel blockers in cardiovascular diseases: a critical analysis based on 100 studies

Recently, serious concerns have been expressed about the long-term safety of the calcium channel blockers (CCBs) as a group. Safety and efficacy are, however, ultimately linked to each other; therefore both must be evaluated especially in the therapy of angina and hypertension, the main clinical indications for CCBs. The structural, functional, and pharmacokinetic heterogeneity of CCBs means that the efficacy and dangers of one subclass, such as the short-acting dihydropyridines (DHPs), in one situation, such as unstable angina, do not necessarily apply in other clinical situations. One hundred studies are reviewed according to their methods of data collection: case series, case control, cohort, randomized controlled trials (RCTs), and meta-analyses. Large, well-designed RCTs and the meta-analyses based on these trials remain the gold standard. Observational studies, though potentially less reliable sources of information because of selection bias, may nevertheless produce hypotheses that must then be tested in RCTs. Regarding safety, both observational studies and RCTs suggest that adverse effects of CCBs may be linked to short-acting agents, specifically short-acting nifedipine. Two good studies favor the safety of verapamil, even in short-acting form. Incomplete but increasing overall evidence favors the safety of longer-acting DHPs. Heart failure remains a class contraindication to the use of all CCBs, with some exceptions. Regarding efficacy, there are positive results of RCTs with CCBs in 2 specific clinical situations, namely, verapamil in postinfarct protection in the absence of pre-existing heart failure, and 2 outcome studies on hypertension with longer acting DHPs. These results cannot automatically be applied to other clinical situations and to other CCBs. For example, there is no evidence for the safety or efficacy of DHPs used without beta blockers in postinfarct patients. In diabetic hypertensives, 2 relatively large RCTs show that the blood pressure can be reduced by DHP-based therapy in diabetics, with a reduction in hard end points. To achieve current blood pressure goals, combination therapy is almost always necessary, and in diabetics there is strong evidence that 1 essential component should be an angiotensin converting enzyme inhibitor. The future aim with CCBs must be to obtain a large database gathered from RCTs, which will give the same certainty about efficacy and safety that already holds for use of the diuretics in hypertension, beta-blockers in postmyocardial infarction patients, and the angiotensin converting enzyme inhibitors in heart failure.

Postabsorption concentration peaks with brand-name and generic verapamil: a double-blind, crossover study in elderly hypertensive patients

The pharmacokinetic actions, bioequivalence, and cardiovascular effects of two verapamil products were studied in a randomized, double-blind, crossover study in eight elderly hypertensive patients (median age, 69.5 years; range, 60-79 years) given brand-name or generic immediate-release verapamil in 120-mg twice-daily doses for 14 days. Blood pressures, heart rates, P-R intervals; and serum concentrations of R-/S-verapamil and norverapamil were measured multiple times in patients during the last day of each therapy. Median blood pressure decreased more with generic verapamil than with the brand-name drug, with the largest difference occurring at 0.5 hours (137/74 mmHg versus 144.5/80.5 mmHg; P = 0.05 and 0.091, respectively). Pharmacokinetic parameters were not different for the two products (P < 0.01). However, the generic product, compared with the brand-name drug, had mean area under the concentration-time curve (time 0 to 12 hours) ratios (90% CI) of 1.09 (0.78-1.52), 1.16 (0.87-1.55) and 1.11 (0.81-1.52) for R-, S-, and total verapamil. Seventy concentration peaks (31 with the brand-name drug, 39 with the generic drug) appeared between 8 and 24 hours. Median percentages of increase of these peaks, compared with those of previous concentrations, were 48.3% and 36.3% for brand-name and generic drugs, respectively. Fifty of the 70 peaks (71%) were associated with a stereospecific concentration peak of norverapamil and, temporally, with meals. Our findings suggest that whereas the two verapamil products may not be bioequivalent by Food and Drug Administration criteria, the observed differences in effects were not clinically significant in this elderly population. Multiple concentration peaks after absorption were observed in all patients with both verapamil products and were perhaps related to enterohepatic recirculation.

Verapamil stereoisomerism: enantiomeric ratios in plasma dependent on peak concentrations, oral input rate, or both

OBJECTIVE

To determine if R/S enantiomeric ratios of verapamil in plasma are affected by the changes in plasma concentration-time profiles of total verapamil, which result from administration of oral formulations with different input rates.

METHODS

Twelve young (19 to 37 years old) healthy men received 240 mg single oral doses of racemic verapamil as immediate-release (fasting) and sustained-release (fed) formulations in a randomized, crossover (7-day washout) study. Serial blood samples were taken over a 48-hour period, and PR intervals were measured at times close to blood drawings for the first 16 hours.

RESULTS

Marked enantiospecific disposition of verapamil occurred, with oral clearance values of 40.8, 25.3, and 121 ml/min/kg for the total verapamil, R-verapamil, and S-verapamil, respectively. Wide input-rate differences also occurred between the immediate- and sustained-release formulations (mean [% coefficient of variation]; peak concentration [Cmax] [total], 327 [44%] versus 73 [58%] ng/ml; time to reach Cmax [total], 1.71 [36%] versus 10.8 [62%] hours). The mean extent of total verapamil bioavailability from the sustained-release formulation was 73.3% of the immediate-release formulation. The R/S ratios at Cmax (total) and at several other time periods were lower, with the immediate-release formulation for both verapamil (R/S = 4.52 [13%] versus 5.83 [18%]; p < 0.01) and norverapamil (R/S = 2.48 [16%] versus 3.04 [19%]; p < 0.01).

CONCLUSIONS

Significantly different R/S ratios of verapamil occurred in the plasma with oral formulations that had substantially different rates of input. With the immediate-release formulation the total verapamil Cmax was higher than that observed with the sustained-release formulation, and the percentage of the pharmacologically more active S-verapamil in the total was also higher (lower R/S ratio). These findings were attributed to the concentration- and/or input-rate-related saturable hepatic first-pass metabolism of the S-verapamil.

Pharmacokinetics of the enantiomers of verapamil in the dog

The intravenous (0.5 mg/kg) and oral (5 mg/kg) dose kinetics of verapamil were studied in 6 dogs during steady-state oral verapamil dosing (5 mg/kg every 8 h for 3 days). Racemic verapamil and norverapamil, a metabolite of verapamil, were quantitated in plasma by HPLC-fluorescence detection. The verapamil peaks eluting off the column were collected and rechromatographed on an Ultron-OVM column, which resolved the two verapamil enantiomers. After intravenous administration, the systemic clearance and apparent volume of distribution of (-)-(S)-verapamil were nearly twice that of the (+)-(R)-isomer. There was no difference in the elimination half-lives between the two isomers. After oral administration, the oral clearance of (-)-(S)-verapamil was 20 times that of the (+)-(R)-isomer. The apparent bioavailability of (+)-(R)-verapamil was over 14 times that of (-)-(S)-verapamil. The plasma protein binding of the (+)-(R)-isomer was slightly higher by 5% than (-)-(S)-verapamil; however, this effect was not enough to account for the difference between the apparent volume of distribution of the enantiomers, indicating that the tissue binding of (-)-(S)-verapamil was greater than that of the (+)-(R)-isomer. This data on the disposition of the enantiomers of verapamil in the dog is similar to that reported for man and demonstrates that the dog may be an appropriate animal model for man in future studies on the disposition of the enantiomers of verapamil.

Interaction between ethanol and calcium channel blockers in humans

The purpose of this study was to test the hypothesis that pretreatment with Ca2+ channel blockers would antagonize the effects of ethanol intoxication in humans. The Ca2+ channel blockers verapamil and nifedipine were chosen because preclinical research has shown them to decrease certain behavioral effects of ethanol in animals. Sixteen healthy, male, paid volunteers, moderate users of ethanol, participated in the study (six in the verapamil and 10 in the nifedipine paradigms). Gelatin capsules containing verapamil (80 mg, 160 mg, or placebo) were administered orally 90 min before ethanol ingestion; whereas, gelatin capsules containing nifedipine (10 mg, 20 mg, or placebo) were administered 30 min before ethanol ingestion. Ethanol (0.85 g/kg or placebo) was administered over a 30-min interval. Subjects were tested in a single-blind, latin-square, cross-over design with each of the following six conditions: placebo ethanol-placebo blocker, placebo ethanol-low dose blocker, placebo ethanol-high dose blocker, ethanol-placebo blocker, ethanol-low dose blocker, and ethanol-high dose blocker. The variables measured in this study were subjective rating of ethanol intoxication, Addiction Research Center Inventory alcohol scale, heart rate, blood pressure, short-term memory, accuracy and latency of response in the Simulator Evaluation of Drug Impairment task, and blood ethanol concentrations by breath analyzer. Results indicate that pretreatment with either verapamil or nifedipine failed to antagonize the inebriating effects of ethanol including its decremental effects on short-term memory and psychomotor performance.

Pharmacokinetic interactions with calcium channel antagonists (Part II)

Since calcium channel antagonists are a diverse class of drugs frequently administered in combination with other agents, the potential for clinically significant pharmacokinetic drug interactions exists. These interactions occur most frequently via altered hepatic blood flow and impaired hepatic enzyme activity. Part I of the article, which appeared in the previous issue of the Journal, dealt with interactions between calcium antagonists and marker compounds, theophylline, midazolam, lithium, doxorubicin, oral hypoglycaemics and cardiac drugs. Part II examines interactions with cyclosporin, anaesthetics, carbamazepine and cardiovascular agents.

Plasma level monitoring of D,L-verapamil and three of its metabolites by reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic assay was developed for determination of verapamil, norverapamil (M1) and its N-dealkylated metabolites (M2 and M3) in plasma. Plasma samples were vortex-mixed, deproteinized and centrifuged. The analysis was performed on a C18 reversed-phase column with fluorimetric detection. Since the polarity of verapamil and norverapamil differs considerably from that of M2 and M3, two different eluents were used for rapid high-performance liquid chromatographic separation. The eluent for the separation of verapamil and norverapamil was acetonitrile-0.07% orthophosphoric acid (33:67, v/v), and for M2 and M3 acetonitrile-0.07% orthophosphoric acid (25:75, v/v). The high-performance liquid chromatographic assay allowed rapid, sensitive and reliable quantitation of verapamil and three of its metabolites in plasma without an extraction procedure. The limit of detection was less than 5 ng/ml (plasma) for all compounds. No interferences with other commonly co-administered drugs was observed. Plasma concentrations of verapamil and its metabolites were determined in 21 patients receiving a continuous infusion of verapamil for tachyarrhythmia of acute onset. The steady-state plasma concentration data of verapamil and its three main metabolites in these patients gave evidence that the plasma concentration of verapamil and its active metabolite norverapamil was primarily determined by the extent of the formation of M2.

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.

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.

Stability of plasma amiodarone levels during chronic oral therapy

The variability of plasma amiodarone levels in 51 patients receiving chronic oral therapy over 4-53 (median 19) months was examined; 3-14 (median 5) plasma samples were obtained. After a loading dose, most patients received either 200 mg or 400 mg a day. Mean plasma amiodarone concentration was 1.2 +/- 0.6 mg/l and mean plasma desethylamiodarone concentration was 1.2 +/- 0.5 mg/l. No relationship was seen between height and weight and plasma concentrations. Dose was a significant predictor of plasma level (p less than 0.01) although it was a poor predictor of steady state amiodarone concentration.

Enzyme induction and inhibition

The rate and extent of drug metabolism significantly influences drug effect. Enzyme induction by increasing the metabolism of drugs may result in important drug interactions. Other implications of enzyme induction include alterations in the metabolism of endogenous substrates, vitamins and activity of extrahepatic enzyme systems. Similarly a wide range of drugs may produce clinically significant drug interactions following enzyme inhibition. Assessment of enzyme induction and inhibition in man involves diverse methods including the use of model drugs.

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.

Effects of cardiovascular disease on pharmacokinetics

The pathophysiologic changes occurring in cardiovascular disease can affect the kinetics of drugs in several different ways. The present review examines these modifications and the underlying mechanisms. The kinetics of specific agents, such as antiarrhythmic, antihypertensive, cardiotonic, and other drugs are considered, and the clinical implications are outlined. The clinician should be aware of these modifications, because they require an adjustment of the dosage regimen. A rational basis for a correct therapeutic choice can be provided by adequate knowledge of these modifications.

The effects of encainide versus diltiazem on the oxidative metabolic pathways of antipyrine

The effects of diltiazem and encainide on the pharmacokinetics and metabolism of antipyrine were compared in nine healthy male volunteers. Diltiazem 90 mg every 8 hours for 5 days decreased the oral clearance of antipyrine from 2.34 to 1.86 L/hour (p less than 0.05) and increased half-life from 12.7 to 15.9 hours (p less than 0.05). Diltiazem reduced the formation rate constants for 3-hydroxymethylantipyrine by 27% (p less than 0.05) and 4-hydroxyantipyrine by 37% (p less than 0.05). There was also a 21% reduction in the formation rate constant for norantipyrine (0.05 less than p less than 0.10). Encainide 25 mg every 8 hours for 5 days had no apparent effect on the oral clearance or half-life of antipyrine, or on the formation rate constants for metabolites of antipyrine. In contrast to a previously published report in rats, encainide, unlike diltiazem, does not inhibit the oxidative metabolism of antipyrine in humans.

Serum binding of nifedipine and verapamil in patients with ischaemic heart disease on monotherapy

Serum free fractions of nifedipine, verapamil and some of their metabolites were measured in patients with ischaemic heart disease receiving single oral dose and chronic monotherapy and were compared with those obtained in vitro. The percentages of unbound nifedipine and verapamil in vitro (concentration range 50-200 and 150-400 ng ml-1, respectively) were 2.51 and 7.23%, respectively, and did not differ from those found on monotherapy with these drugs (2.05 and 8.08%, respectively), and after single dosing. It is suggested that, during treatment with nifedipine or verapamil, their serum metabolites do not affect binding of the parent drugs to serum proteins.

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.

Antihypertensive therapy in the geriatric patient. I: A review of the role of calcium channel blockers

Animal and clinical studies have demonstrated the efficacy of calcium channel blockers in reducing blood pressure, especially in older patients whose hypertension is characterized by increased peripheral vascular resistance. Their chemical heterogeneity, which permits targeted therapy, as well as their minimal side effects, drug interactions, and clinical utility in numerous pathophysiologic states common to the elderly, enhance the suitability of calcium channel blockers in treating mild to moderate hypertension in this subgroup. This is particularly relevant for those patients who have concomitant conditions, such as diabetes, chronic obstructive pulmonary disease, or peripheral vascular disease, and for whom many of the more traditional antihypertensive drugs are either contraindicated or might cause a worsening of the disease.

Pharmacokinetic characterization of the antiarrhythmic drug diprafenone in man

The pharmacokinetics of the antiarrhythmic drug diprafenone have been investigated in 6 healthy volunteers following single intravenous (50 mg) and oral doses (50 and 150 mg). Diprafenone was mainly eliminated by metabolism in the liver. Following i.v. infusion of 50 mg diprafenone, the terminal half-life of elimination was 1.50 h, the volume of distribution at steady-state was 1.23 l.kg-1, and the free fraction in plasma was 1.68%. Mean total plasma clearance was 741 ml.min-1.70 kg-1, which approaches normal liver blood flow after correction for the blood/plasma concentration ratio. Thus, diprafenone can be classified as a high extraction drug. Following oral administration, a dose-dependent increase in bioavailability from 10.9 (50 mg dose) to 32.5% (150 mg dose) was observed. The data suggest that diprafenone is subject to saturable hepatic first-pass metabolism.

Twenty-four-hour blood pressure monitoring after a single dose of sustained-release verapamil

The antihypertensive effect of a single dose of 240 mg sustained-release (S-R) verapamil was investigated by ambulatory blood pressure (BP) monitoring in 13 patients with mild to moderate essential hypertension. Following a 2-week washout period, 24-hour BP monitoring was carried out with a Spacelabs ICR 5300 device following random administration of a tablet of S-R verapamil or placebo; BP recording was repeated after crossover 3 to 7 days later. Average whole-day systolic and diastolic BPs were significantly lower after verapamil (130.1 +/- 2.6/87.1 +/- 1.2 mmHg) than after placebo (142.1 +/- 3.3/95.8 +/- 2.1 mmHg) (p less than 0.01). Mean waking BP was 146.4 +/- 3.6/99.1 +/- 2.2 mmHg after placebo and 135.2 +/- 3.3/90.5 +/- 1.7 mmHg after verapamil (p less than 0.01); during sleeping hours BP was 133.8 +/- 3.1/88.7 +/- 2.6 mmHg following placebo and 122.2 +/- 2.3/80.9 +/- 1.8 mmHg following verapamil (p less than 0.01). Blood pressure profile was significantly reduced by verapamil up to 20 hours after tablet administration, while from 21 to 24 hours after drug intake BP values were similar to placebo. Response to verapamil was not correlated to the pretreatment BP values and to the patient's age. In summary, this study suggests that acute administration of 240 mg S-R verapamil in hypertensive patients produces a BP reduction during 24-hour, daytime, and nighttime periods. The hypotensive efficacy is preserved for many hours after tablet intake and seems to be due to individual variation in cardiovascular reactivity to the drug.

Calcium channel antagonists. Part V: Second-generation agents

Second-generation agents include new dihydropyridines, such as amlodipine, felodipine, isradipine, nicardipine, nimodipine, nisoldipine, and nitrendipine. Verapamil-like agents include tiapamil, gallopamil, and anipamil. Among the diphenylalkylamines, bepridil is of special interest. New preparations of existing agents include slow-release formulations of nifedipine, verapamil, and diltiazem. From all these agents will be selected those that are longer-acting and provide higher vascular selectivity.

The effect of combined therapy on the pharmacokinetics and pharmacodynamics of verapamil and propranolol in patients with angina pectoris

1. The pharmacokinetics and pharmacodynamics of oral verapamil and propranolol were studied in patients with stable angina pectoris during chronic mono- and dual therapy. 2. The peak plasma concentrations (Cmax) and areas under the plasma concentration-time curves (AUC) of verapamil were similar during combined treatment with propranolol (mean +/- s.d.: Cmax = 491 +/- 397 ng ml-1; AUC = 2075 +/- 1524 ng ml-1 h) or atenolol (mean +/- s.d.: Cmax = 372 +/- 320 ng ml-1; AUC = 1985 +/- 1660 ng ml-1 h). 3. No differences in Cmax and AUC were observed during verapamil monotherapy (mean +/- s.d.: Cmax = 287 +/- 105 ng ml-1; AUC = 1375 +/- 455 ng ml-1 h) vs combined treatment with propranolol (mean +/- s.d.: Cmax = 312 +/- 55 ng ml-1; AUC = 1566 +/- 486 ng ml-1 h). 4. Treatment with verapamil increased the Cmax (mean +/- s.d.: 227 +/- 117 vs 116 +/- 62 ng ml-1, P less than 0.05) and AUC (1389 +/- 617 vs 837 +/- 316 ng ml-1 h, P = 0.0625) of propranolol in all subjects. 5. Transient atrioventricular dissociation occurred in two patients 2 h after dosing with verapamil and propranolol or atenolol. 6. Close observation of patients is essential when beta-adrenoceptor antagonists and verapamil are used together.

Pharmacokinetics and pharmacodynamics of two formulations of verapamil

The pharmacokinetics and pharmacodynamics of sustained release verapamil were compared with the conventional formulation in 10 healthy adult volunteers after single and multiple dosing. The mean time of maximum plasma concentrations of verapamil were significantly prolonged and the absorption rate constants significantly reduced after sustained release verapamil on both day 1 and day 10. On day 10 there was no significant difference between formulations in the relative bioavailability of verapamil. However, the area under the plasma concentration-time curve and maximum concentration (Cmax) for both formulations increased significantly with repeat dosing. On day 10, the difference in Cmax between formulations was significant. The day 10 mean peak/trough plasma verapamil concentration ratio was significantly less following the sustained release dose form. The mean PR interval was significantly prolonged by both formulations on day 1 and day 10. There were no differences between formulations other than a significantly longer PR interval following the conventional formulation 2 h after dosing on day 10.

Verapamil prophylaxis for postoperative atrial dysrhythmias: a prospective, randomized, double-blind study using drug level monitoring

Orally administered verapamil hydrochloride (80 mg every 8 hours) or a placebo was given to 109 patients after coronary artery bypass grafting in a randomized, double-blind manner to test the efficacy of verapamil in preventing postoperative atrial dysrhythmias. The test drug was given through a nasogastric tube beginning 4 to 6 hours after operation until oral ingestion was possible. Serum levels of verapamil were measured at selected times after operation and when postoperative atrial dysrhythmias occurred. Postoperative atrial dysrhythmias occurred in 10 of the 53 verapamil-treated patients and in 20 of the 56 placebo-treated patients. Patients with verapamil drug levels higher than 150 ng/ml had fewer postoperative atrial dysrhythmias than those with lesser verapamil levels (p = .034) or than placebo-treated patients (p = .012). Only 2 of 31 patients with drug levels higher than 150 ng/ml experienced postoperative atrial dysrhythmias. Approximately 40% of verapamil-treated patients had drug levels lower than 150 ng/ml at 48 hours after operation. It is concluded that oral administration of verapamil prevents postoperative atrial dysrhythmias in a dose-dependent fashion.

Efficacy of oral diltiazem to control ventricular response in chronic atrial fibrillation at rest and during exercise

Although digoxin is often the first choice for control of ventricular response in chronic atrial fibrillation, it fails to slow exercise rates. Diltiazem, a calcium channel antagonist that slows atrioventricular conduction, was administered to 16 patients who failed to achieve adequate rate control on low level exercise testing despite digoxin therapy. Therapeutic response to diltiazem was assessed with submaximal and maximal exercise tests and 24 hour ambulatory electrocardiographic monitoring. During the diltiazem treatment phase, ventricular response at rest diminished (96 +/- 17 versus 69 +/- 10 beats/min, p less than 0.001) as did rate during submaximal exercise (155 +/- 28 versus 116 +/- 26, p less than 0.001), maximal exercise (163 +/- 14 versus 133 +/- 26, p less than 0.001) and average ventricular response during 24 hour monitoring (87 +/- 13 versus 69 +/- 10, p less than 0.001). Rate at rest decreased 26 +/- 15% and submaximal exercise rate diminished 24 +/- 12%. Thirteen (81%) of the 16 patients exhibited at least 15% slowing of rate at rest and during submaximal exercise. Eleven patients (69%) reported alleviation of symptoms. There was no change in serum digoxin levels during diltiazem treatment (1.3 +/- 0.5 versus 1.3 +/- 0.6 ng/ml, p = NS). On withdrawal of diltiazem, ventricular response returned to baseline values. Diltiazem is an effective agent for control of ventricular response, both at rest and during exercise, in digoxin-treated patients with chronic atrial fibrillation.

24-hour antiarrhythmic effect of conventional and slow-release verapamil in chronic atrial fibrillation

Twenty-four-hour heart rate control by verapamil given as conventional tablets t.d.s., or as a new slow release formulation once daily, has been compared in an open cross-over trial. Eight patients with chronic atrial fibrillation and one with chronic atrial flutter were studied outside hospital. Trough serum concentration of verapamil did not differ during the two dosage regimens (59 ng/ml - conventional formulation and 49.3 ng/ml - slow release tablet). The average serum concentration of digoxin in the patients was not changed. Compared to the control phase, both dosage regimens significantly and equally reduced individual and average heart rates throughout the entire 24-h period. A positive correlation between the serum concentration of verapamil and the relative increase in average R-R interval was demonstrated. It is concluded that dosage t.d.s. with conventional tablets of verapamil or once daily with the slow release formulation gave the same antiarrhythmic efficacy over 24 h, and was associated with equal trough serum concentrations of verapamil.

Verapamil and norverapamil in plasma and breast milk during breast feeding

The concentrations of verapamil and norverapamil have been measured in milk and plasma samples from a 32 year-old woman treated with verapamil 80 mg tds while breast-feeding her child. The average steady-state concentrations of verapamil and noverapamil in milk were, respectively, 60% and 16% of the concentrations in plasma. The breast-fed child received less than 0.01% of the dose of verapamil given to the mother. No verapamil or norverapamil (less than 1 ng/ml) could be detected in the plasma from the child.

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.

The pharmacodynamic and pharmacokinetic differences of the D- and L-isomers of verapamil: implications in the treatment of paroxysmal supraventricular tachycardia

There is increasing interest in defining the pharmacodynamic and pharmacokinetic characteristics of drugs that are marketed as racemic mixtures. Verapamil is one such drug that is commercially available as a mixture of D- and L-isomers. The L-isomer of verapamil has a greater-negative inotropic, negative chronotropic, and negative dromotropic potency than the D-isomer. The values for fraction unbound in serum, distribution volume, and systemic clearance are substantially greater for the L-isomer after intravenous dosing. After oral dosing, the D-isomer achieves peak plasma concentrations five times greater than the L-isomer. The pharmacodynamic and pharmacokinetic characteristics of each isomer are reviewed. The differences in the concentrations of the D- and L-isomers after oral vs intravenous dosing may contribute to the relatively lower efficacy of orally administered verapamil in the treatment of PSVT.

Advances in calcium blocker therapy

Calcium blockers are drugs that interfere with the entry of calcium ions into cells of a variety of tissues. Three calcium blockers, verapamil, nifedipine, and diltiazem, are currently approved for clinical use in the United States and many others are undergoing clinical trials. All calcium blockers share the effect of dilating blood vessels, although some agents are selective dilators of certain vascular beds, such as the coronary or cerebral circulation. There exist major differences among these drugs in their ability to depress myocardial contraction and inhibit cardiac impulse conduction, as well as other properties. The therapeutic actions of the agents in use, as well as the actions of the investigational calcium blockers, have been reviewed. Although calcium blockers are generally well tolerated and have fewer side effects than many alternative drugs, serious adverse effects are possible in certain clinical settings. The clinical indications for these drugs continue to expand and will likely find many uses in surgical patients, especially in the areas of cardiac surgery, neurosurgery, vascular surgery, and general surgery.

Pharmacokinetics of verapamil in patients with hypertension

Twelve hypertensive patients (WHO Stage I-II) were given oral verapamil (Isoptin) b.d. or t.d.s. as long-term treatment. The pharmacokinetics of verapamil and norverapamil were studied both after single and b.d. and t.d.s. doses of verapamil 240, 360 or 480 mg daily adjusted according to the blood pressure response. The apparent oral clearance of verapamil was decreased after both the twice and thrice daily dosage regimens (1.38 and 1.841/min, respectively) as compared to the single dose (4.391/min). The plasma half-life of verapamil was increased from 3.34 h (single dose) to 4.65 h (b.i.d.). Decreased elimination of norverapamil was also found after multiple doses of verapamil, as shown by an increase in the adjusted AUC of norverapamil (adjusted to a verapamil dose of 80 mg), namely from 574.9 h X ng X ml-1 (single dose) to 1172 h X ng X ml-1 (b.d.) and to 841 h X ng X ml-1 (t.d.s.). The plasma half-life of norverapamil increase from 5.68 h to 7.34 h during twice daily dosing. During thrice daily verapamil, no increase in plasma half-life was found either for verapamil or norverapamil, probably due to the relatively short sampling time (6 h). The plasma concentration of verapamil and the reduction in supine systolic and diastolic blood pressure were correlated. The mean decrease in supine systolic blood pressure was 5.8 mm Hg per 100 ng verapamil/ml plasma, and for diastolic pressure 2.9 mm Hg per 100 ng verapamil/ml plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Individualization of calcium entry-blocker dosage for systemic hypertension

The calcium entry blockers are used in a wide variety of clinical situations. Coexisting disease states, such as renal or hepatic dysfunction, may require individualized dosing of these agents. The physiologic changes associated with aging may also affect the pharmacokinetic properties of the drugs. If calcium entry blockers are used concurrently with other medications, dosage adjustment or selection of an alternative drug may be needed. Drug interactions between calcium entry blockers and cimetidine, digoxin and quinidine appear to be clinically significant. Individualized dosing in patients who have coexisting disease or who are using other medications is essential to achieve an adequate therapeutic response and avoid adverse effects. Considerations to attain an optimal response in such situations are presented.

Hemodynamic effects of verapamil in left ventricular valvular volume overload

The hemodynamic consequences of aortic and mitral insufficiency may be influenced by the high systemic vascular resistance often seen in these patients. Since the calcium antagonists have been shown to reduce systemic vascular resistance, we evaluated the effects of intravenous verapamil in 23 patients. In 11 patients with aortic insufficiency, verapamil resulted in a 20% increase in cardiac index (p less than 0.001), 18% increase in forward stroke volume index (p less than 0.001), and a 24% decrease in regurgitant fraction (p less than 0.005). In the 12 patients with mitral insufficiency, verapamil resulted in a 19% increase in both cardiac index (p = 0.004), and forward stroke volume index (p less than 0.001), while there was a 19% decrease in regurgitant fraction (p less than 0.02). Left ventricular end-systolic stress decreased significantly in both groups as did end-diastolic stress in the mitral insufficiency group. There was no significant change in several measures of contractile performance, though the end-systolic stress-to-volume index ratio fell significantly (p less than 0.04) in the mitral insufficiency group. Our findings suggest that the vasodilatory effects of intravenous verapamil predominate over the negative inotropic effects in patients with aortic and mitral insufficiency. Verapamil may be of use in patients intolerant to other vasodilators, patients with concomitant ischemic heart disease, or those with supraventricular arrhythmias.

Verapamil pharmacokinetics and apparent hepatic and renal blood flow

The effect of acute and continued administration of verapamil on pharmacokinetics and regional blood flow has been studied in eight normotensive subjects. Continued administration resulted in a significant decrease in verapamil clearance, compared to that following acute dosing, as assessed by increases in both terminal elimination half-life (from a mean +/- s.d. of 5.2 +/- 2.3 h to 6.7 +/- 2.0 h) and AUC (from a mean +/- s.d. of 800 +/- 353 ng ml-1 h to 1455 +/- 244 ng ml-1 h). The relative clearance of norverapamil was not changed. Acute administration of verapamil resulted in a significant increase (P less than 0.005) in apparent liver blood flow which with continued administration fell significantly (P less than 0.01) towards placebo values. Effective renal plasma flow similarly increased with acute verapamil administration (P less than 0.05) and with chronic administration reduced again to be not significantly different from placebo. Acute and chronic verapamil administration did not significantly alter glomerular filtration rates. These results suggest that there may be a relationship between the acute increase in liver blood flow and the relatively increased clearance of verapamil following acute dosing.

Pharmacokinetics of verapamil in patients with renal failure

The pharmacokinetics of verapamil was studied in patients with end-stage chronic renal failure and in normal subjects after i.v. injection of 3 mg and a single oral dose of 80 mg. Plasma levels of verapamil and its active metabolite norverapamil were measured by HPLC. After i.v. injection, the terminal phase half-life and total plasma clearance of verapamil in both groups were similar. Haemodialysis did not change the time course of plasma verapamil levels after i.v. administration. After a single oral dose, the plasma levels of verapamil and norverapamil in both groups of subjects were similar. Subsequently, normal volunteers and patients with renal failure were treated for 5 days with oral verapamil 80 mg t.d.s. There was no difference between the 2 groups of subjects in the trough and peak levels of verapamil or of norverapamil. Intravenous and oral administration of the calcium channel blocking agent had similar effects on blood pressure, heart rate and the PR-interval in the electrocardiogram in both groups. The study demonstrated that the disposition of verapamil was similar in normal subjects and in patients with renal failure.

Verapamil-rifampin interaction

A case of verapamil-rifampin interaction is presented in a patient receiving verapamil for supraventricular tachycardia (SVT) and rifampin for pulmonary tuberculosis. The patient experienced recurrent symptomatic SVT, despite receiving verapamil 480 mg po q6h. Serum verapamil concentrations were determined to be extremely low. Discontinuation of rifampin and substitution of ethambutol resulted in an almost four-fold increase in verapamil levels with concurrent control of SVT. Rifampin may have increased the metabolism of verapamil by inducing hepatic microsomal enzymes resulting in low verapamil levels and failure to control SVT.

Prophylaxis of supraventricular tachyarrhythmia after coronary bypass surgery with oral verapamil: a randomized, double-blind trial

This study investigated the efficacy of oral administration of verapamil, started 24 hours after coronary artery bypass grafting (CABG), in reducing the incidence of postoperative supraventricular tachyarrhythmia (SVT). Two hundred patients were randomly assigned in a double-blind fashion to receive a one-week course of either a placebo or 80 mg of verapamil every 6 hours. Overall, SVT developed in 23 control and 14 verapamil-treated patients, a 39% reduction in incidence (p less than 0.10). Of the patients who received at least four doses and continued to receive the study drug, 17 in the control and 7 in the verapamil group experienced SVT, a 53% decrease in incidence (p less than 0.06). Atrial fibrillation constituted 34 of the 37 SVT episodes and was associated with a slower ventricular response in the group given verapamil (115 +/- 8 versus 156 +/- 4 beats per minute; p less than 0.001). No evidence was found linking postoperative SVT with the withdrawal of beta-blocking drugs. Adverse effects required that 20 patients in the verapamil and 6 in the placebo group be removed from the study. Hypotension or pulmonary edema or both developed in 13 of the patients receiving verapamil, but in only 1 of the control patients (p less than 0.001). We conclude that although verapamil has potential merit for the prophylaxis of SVT after CABG, its use in this setting is associated with a high incidence of unacceptable hemodynamic side effects.

An investigation of the cause of accumulation of verapamil during regular dosing in patients

The accumulation of verapamil during regular dosing conditions was studied. Plasma concentrations of verapamil (V) and norverapamil (NV) were measured as were urinary concentrations of verapamil, norverapamil, and four other N- and O-dealkylated metabolites in nine patients after an initial single dose and after chronic oral verapamil administration to steady-state plasma concentrations. Indocyanine green (ICG) clearance was determined immediately prior to the initial verapamil dose and prior to the verapamil washout from regular dosing. An approximately two-fold accumulation of V had occurred during regular dosing. The area under the plasma concentration-time curve (AUC1) after the first dose was 417.4 +/- 276.7 ng ml-1 h (mean +/- s.d.) and increased to 786.5 +/- 54 ng ml-1 h (P less than 0.01) during one dosage interval at steady-state (AUCss). NV also tended to accumulate from an AUC1 of 552.6 +/- 411 to an AUCss 668.7 +/- 332 ng ml-1 h (P less than 0.09). The ratio of AUC-V to AUC-NV was unchanged. The verapamil elimination half-life (t 1/2) increased from 8.4 +/- 4.2 to 12.0 +/- 3.6 h (P less than 0.01) whereas the norverapamil t 1/2 was unchanged. ICG clearance was unchanged. Urinary excretion of NV increased slightly but the ratio of urinary V/NV concentrations was not significantly altered nor was the ratio of four other metabolites to verapamil or the ratio of the combined o-demethylated to the N-dealkylated metabolites.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium channel blockers in emergency medicine

Diltiazem, nifedipine, and verapamil inhibit calcium entry into cells via different mechanisms with different pharmacologies. They display different relative effects on different cardiovascular functions, a complex interplay of direct actions and adrenergic reflexes. Peripheral arterial vasorelaxation causes adrenergic reflex activity which opposes their direct negative chronotropic, dromotropic, inotropic, and hypotensive actions. Verapamil's most potent activity is electrophysiologic, and nifedipine's effects are hemodynamic; diltiazem acts like a less-potent combination of verapamil and nifedipine. All three drugs are efficacious in angina. These three drugs may not be interchangeable in all patients, but individualization of therapy is possible. Future indications for calcium channel blocker therapy may include hypertrophic cardiomyopathy, cerebral vasospasm, migraine headaches, pulmonary hypertension, asthma, esophageal spasm, intestinal ischemia, Raynaud's phenomenon, dysmenorrhea, and premature labor.