β-adrenergic Receptor Polymorphisms and Responses during Titration of Metoprolol Controlled Release/extended Release in Heart Failure*

OBJECTIVE

beta-Blockers require careful initiation and titration when used in patients with heart failure. Some patients tolerate beta-blocker therapy initiation without difficulty, whereas in other patients this period presents clinical challenges. We tested the hypothesis that polymorphisms at codons 389 (Arg389Gly) and 49 (Ser49Gly) of the beta(1)-adrenergic receptor would be associated with differences in initial tolerability of beta-blocker therapy in patients with heart failure. We also tested whether polymorphisms in the beta(2)-adrenergic receptor, G-protein alpha s subunit (G(s)alpha), and cytochrome P450 (CYP) 2D6 genes or S-metoprolol plasma concentrations were associated with beta-blocker tolerability.

METHODS

Sixty-one beta-blocker-naive patients with systolic heart failure were prospectively enrolled. Patients began taking 12.5 to 25 mg metoprolol controlled release/extended release with titration every 2 weeks (as tolerated) to 200 mg/d or the maximum tolerated dose over a period of 8 to 10 weeks. Decompensation was the composite of death, heart failure hospitalization, increase in other heart failure medications, or need to discontinue metoprolol. End points were assessed during the titration period.

RESULTS

The overall rate of decompensation was not different between the codon 49 or 389 genotypes. However, a significantly greater percentage of patients with the Gly389 variant required increases in heart failure medications as compared with Arg389 homozygotes (48% versus 14%, respectively; P = .006). Similarly, patients with the Ser49 homozygous genotype were significantly more likely to require increases in concomitant heart failure therapy as compared with Gly49 carriers (41% versus 11%, respectively; P = .03). Neither CYP2D6 genotypes nor metoprolol pharmacokinetics differed between patients with and those without a decompensation event. There was no association between the beta(2)-adrenergic receptor or G(s)alpha polymorphisms with decompensated heart failure.

CONCLUSIONS

Patients with the Gly389 variant and Ser49Ser genotype were significantly more likely to require increases in heart failure medications during beta-blocker titration and thus may require more frequent follow-up during titration.

High-Impact Articles Related to the Pharmacotherapeutic Management of Systolic Heart Failure

This compilation is part of a series of five articles identifying important literature in cardiovascular pharmacotherapy. This list focuses on pharmacotherapeutic management of acute decompensated and chronic heart failure. Most of the cited works present the results of landmark clinical studies that have shaped the management of patients with left ventricular systolic dysfunction. Limited primary literature is available for some topics; thus, pertinent review articles also are listed. In addition, consensus documents formed by expert panels in the United States and Europe are reviewed. This compilation may serve as a teaching tool, reference resource, or update of the literature for pharmacy clinicians, physicians, and students.

Vasopressin: a new target for the treatment of heart failure

BACKGROUND

Arginine vasopressin is a peptide hormone that modulates a number of processes implicated in the pathogenesis of heart failure. Numerous vasopressin antagonists are currently under development for the treatment of this syndrome.

METHODS

Preclinical and clinical data describing the effects of vasopressin and the vasopressin antagonists on both normal physiology and heart failure were reviewed.

RESULTS

Through activation of V(1a) and V(2) receptors, vasopressin regulates various physiological processes including body fluid regulation, vascular tone regulation, and cardiovascular contractility. Vasopressin synthesis is significantly and chronically elevated in patients with heart failure despite the volume overload and reductions in plasma osmolality often observed in these patients. Vasopressin also appears to adversely effect hemodynamics and cardiac remodeling, while potentiating the effects of norepinephrine and angiotensin II. The selective V(2) and dual V(1a)/V(2) receptor antagonists tolvaptan and conivaptan, respectively, substantially increase free water excretion and plasma osmolality, reduce body weight, improve symptoms of congestion, and moderately increase serum sodium concentrations in patients with heart failure who present with symptoms of fluid overload. Tolvaptan effectively normalizes serum sodium concentrations in hyponatremic heart failure patients. Conivaptan significantly reduces pulmonary capillary wedge pressure without affecting systemic vascular resistance or cardiac output. The clinical significance of V(1a) receptor antagonism requires further investigation.

CONCLUSIONS

Current preclinical and clinical findings with the vasopressin antagonists appear promising, however further evaluation in phase III clinical trials is necessary to define the role of vasopressin antagonism in the treatment of heart failure.

Extended-release metoprolol succinate in chronic heart failure

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and tolerability of extended-release (ER) metoprolol succinate and its role in the management of chronic heart failure.

DATA SOURCES

A MEDLINE search of English-language literature (1990-October 2002) was conducted using congestive heart failure and metoprolol CR/XL or metoprolol CR/ZOK as search terms to identify pertinent studies.

STUDY SELECTION/DATA EXTRACTION

All of the articles identified from the data sources were evaluated, with priority given to randomized, double-blind, placebo-controlled studies.

DATA SYNTHESIS

ER metoprolol succinate is a controlled-release tablet designed to produce even and consistent beta(1)-blockade throughout the 24-hour dosing interval, with less fluctuation in metoprolol plasma concentrations compared with immediate-release metoprolol. Three randomized, double-blind, placebo-controlled trials have evaluated the efficacy of ER metoprolol succinate in the treatment of patients with chronic heart failure. The MERIT-HF (Metoprolol CR/XL Randomized Intervention Trial in Congestive Heart Failure) study, the largest of these trials and the largest randomized mortality trial with beta-blockers in heart failure to date, demonstrated that ER metoprolol succinate reduced the relative risk of all-cause mortality by 34% versus placebo. Furthermore, the relative risk of the combined endpoint of mortality plus all-cause hospitalizations was reduced by 19% and sudden death was reduced by 41%. The benefits of therapy were evident in various patient subgroups, including elderly patients and those with diabetes mellitus. ER metoprolol succinate was generally well tolerated, with a similar proportion of patients discontinuing therapy due to adverse events relative to placebo (9.8% and 11.7%, respectively).

CONCLUSIONS

ER metoprolol succinate therapy provides substantial mortality and morbidity benefits in patients with New York Heart Association class II and III heart failure who are stabilized on angiotensin-converting enzyme inhibitors and diuretics. ER metoprolol succinate is administered once daily, is well tolerated, and provides consistent beta(1)-blockade over the 24-hour dosing interval.

Expanding role of beta-blockade in the management of chronic heart failure

Although recent advances have been made in the treatment of heart failure, this disease continues to result in significant morbidity and mortality. Among the negative effects associated with progression of heart failure are decline in myocardial reserve, decreased exercise tolerance, decreased contractile function, and altered cardiac gene expression. Guidelines recommend neurohormonal antagonists for treatment and stress the importance of angiotensin-converting enzyme inhibition and beta-blockade in reversing the cardiac remodeling process. beta-Blockade slows or reverses the adverse effects resulting from chronic adrenergic stimulation. Traditionally, beta-blockers were reserved for mild-to-moderate heart failure, based on evidence from large, randomized clinical trials showing their positive effects on myocardial function and clinical outcomes. More recently, clinical data reveal that the agents can be expanded to patients with severe heart failure and those with left ventricular systolic dysfunction after myocardial infarction. Individual beta-blocking agents vary in their pharmacology and dosing requirements. These variations may influence treatment decisions and affect clinical measurements of left ventricular function and ventricular remodeling.

Angiotensin II receptor blockers in heart failure

Heart failure remains a significant cause of morbidity and mortality, despite major advances in therapy. Angiotensin II, the principal mediator of the renin-angiotensin system, exerts both short-term (e.g., hemodynamic, renal) and long-term (e.g., inflammation, cardiac remodeling) effects in the pathophysiology of cardiovascular disease. The effects of angiotensin II appear to be more completely inhibited by angiotensin II receptor blockers (ARBs), which act at the subtype 1 receptor level, than by angiotensin-converting enzyme (ACE) inhibitors because pathways other than that of ACE contribute to the generation of angiotensin II. Evidence demonstrates that ARBs, when added to conventional treatment for patients with heart failure, are associated with a reduction in morbidity and mortality as well as an improvement in quality of life. Clinical trials of ARB therapy indicate that these agents are generally well tolerated, both alone and in combination with other neurohormonal inhibitors. The current role of ARBs in heart failure is as an alternative for patients who cannot tolerate therapy with an ACE inhibitor. A number of ongoing clinical studies are likely to further define or expand the role of ARBs in the treatment of cardiovascular disease.

Evaluation of potential losartan-phenytoin drug interactions in healthy volunteers

BACKGROUND

Phenytoin, a cytochrome P450 (CYP) 2C9 substrate, has a narrow therapeutic index and nonlinear pharmacokinetics. Therefore there is the potential for significant concentration-related adverse effects when phenytoin is coadministered with other CYP2C9 substrates. Losartan, an antihypertensive agent, is also a substrate for CYP2C9.

OBJECTIVE

Our objective was to assess the effects of losartan on the pharmacokinetics of phenytoin and the effects of phenytoin on the pharmacokinetics of losartan in a healthy population of volunteers.

METHODS

A prospective, randomized, 3-period crossover study was conducted in 16 healthy volunteers with phenytoin alone, phenytoin in combination with losartan, and losartan alone. Each treatment was given for 10 days with a 3-week washout period between treatments. On day 10, plasma concentrations of phenytoin and plasma and urine concentrations of losartan and its active carboxylic-acid metabolite E3174 were measured to determine steady-state pharmacokinetic parameters.

RESULTS

Coadministration of losartan had no effect on the pharmacokinetics of phenytoin. Coadministration of phenytoin increased the mean area under the concentration-time curve from time zero to 24 hours [AUC(0-24)] of losartan by 17% (355 +/- 220 ng x h/mL versus 427 +/- 177 ng x h/mL; P =.1), but this difference was not statistically significant. In the 14 CYP2C9*1/*1 subjects, the mean AUC(0-24) of losartan was increased by 29% (284 +/- 84 ng x h/mL versus 402 +/- 128 ng x h/mL; P =.008). Coadministration of phenytoin significantly reduced the AUC(0-24) of E3174 by 63% (1254 +/- 256 ng x h/mL versus 466 +/- 174 ng x h/mL; P =.0001) and the formation clearance of losartan to E3174 (1.91 +/- 0.8 mL/h per kilogram versus 0.62 +/- 0.4 mL/h per kilogram; P =.0001).

CONCLUSIONS

Losartan, a CYP2C9 substrate, had no effect on the pharmacokinetics of phenytoin. However, phenytoin inhibited the CYP2C9-mediated conversion of losartan to E3174.

Clinical benefits of low serum digoxin concentrations in heart failure

OBJECTIVES

We sought to determine whether there was a relationship between serum digoxin concentration (SDC), including SDCs typically regarded as low, and clinical efficacy related to digoxin in patients with symptomatic left ventricular dysfunction.

BACKGROUND

Digitalis glycosides have been used for 200 years in the treatment of heart failure (HF), but the SDC required for optimal clinical efficacy and acceptable toxicity remains controversial.

METHODS

This relationship was investigated by utilizing data from two randomized, double-blinded, placebo-controlled, digoxin-withdrawal trials: the Prospective Randomized study Of Ventricular failure and Efficacy of Digoxin (PROVED) and the Randomized Assessment of Digoxin on Inhibitors of Angiotensin-Converting Enzyme (RADIANCE). Major end points were worsening HF, change in left ventricular ejection fraction and treadmill time after randomization. The primary analysis investigated the relationship between SDC at randomization and these end points. A secondary categorical analysis compared these end points in patients who discontinued digoxin versus patients who continued digoxin and had low (0.5 to 0.9 ng/ml), moderate (0.9 to 1.2 ng/ml) or high (>1.2 ng/ml) SDCs at randomization.

RESULTS

Multiple regression analysis failed to find a relationship between randomization SDC, considered as a continuous variable, and any study end point (all p > 0.236). Multivariable Cox analysis found that the risk of worsening HF was significantly less (all p < 0.02) for patients in any category of SDC who continued digoxin, as compared with patients withdrawn from digoxin. Specifically, patients in the low SDC category were significantly less likely than placebo patients to experience worsening HF during follow-up (p = 0.018).

CONCLUSIONS

The beneficial effects of digoxin on common clinical end points in patients with HF were similar, regardless of SDC.

Surrogate end points in heart failure

OBJECTIVE

To describe the potential utility of a true surrogate marker of heart failure outcomes, historically investigate the validity of surrogates most commonly evaluated in heart failure, and identify specific end points offering the most potential for future use.

DATA SOURCES

A MEDLINE search (1966-June 2001) was completed to identify relevant literature. Additional references were also retrieved from selected articles. Search terms included b-type natriuretic peptide, cardiac remodeling, end-diastolic volume, heart failure, and surrogate end points.

DATA SYNTHESIS

By definition, true surrogate end points must predict outcomes associated with disease progression and response to therapy. A validated surrogate measure of mortality would render significant utility in both heart failure drug development and clinical practice. Improvements in traditional functional markers of heart failure, including ejection fraction and exercise capacity, have produced inconsistent results in regard to mortality in a number of clinical trials. Numerous measures of cardiac remodeling and neurohormonal activation, however, have proven to be reliable predictors of disease progression and therapeutic response. These findings have contributed significantly to the current understanding of heart failure pathophysiology and approach to treatment. Specifically, measures such as left-ventricular end-diastolic volume (LVEDV) and, potentially, b-type natriuretic peptide (BNP) concentrations may correlate with disease progression and parallel the mortality reductions observed with angiotensin-converting enzyme inhibitor and beta-blocker therapy.

CONCLUSIONS

Currently, LVEDV and plasma BNP offer the greatest potential as surrogate end points in heart failure. Further investigation of these measures is required before routine implementation in drug development and clinical practice can be justified.

Angiotensin II-receptor blockers: clinical relevance and therapeutic role

The limitations of angiotensin-converting-enzyme (ACE) inhibitors and the role of angiotensin II-receptor blockers (ARBs) in the treatment of hypertension, heart failure, and diabetic nephropathy are discussed. Although ACE inhibitors are generally well tolerated, two important class-related adverse effects are cough, which is common, and angioedema, which is rare but serious. Cough and angioedema appear to be less frequent with ARBs than with ACE inhibitors. ARBs seem to be as capable as ACE inhibitors of producing renal dysfunction. ARBs may offer more complete inhibition of angiotensin II than ACE inhibitors. The mechanism of action is based on selective binding to angiotensin type 1 receptors. Many clinical studies have shown that ARBs lower blood pressure as effectively as other antihypertensive agents, including ACE inhibitors. ARBs do not appear to have a greater clinical effect than ACE inhibitors in patients with heart failure. Some studies of combination ARB and ACE inhibitor therapy for heart failure indicate advantages of the combination over therapy with either class. ARBs may exert renal protective effects in diabetic nephropathy. ARBs offer an alternative to ACE inhibitors in the management of hypertension, especially for ACE-inhibitor-intolerant patients. ACE inhibitors remain the drugs of choice for patients with heart failure, left ventricular dysfunction after MI, and diabetic nephropathy; ARBs offer these patients an alternative when ACE inhibitor therapy is not tolerated.

Effect of fluoxetine on carvedilol pharmacokinetics, CYP2D6 activity, and autonomic balance in heart failure patients

The objective of this study was to examine the pharmacokinetic and pharmacodynamic consequences of concomitant administration of fluoxetine and carvedilol in heart failure patients. Fluoxetine (20 mg) or matching placebo was administered in a randomized, double-blind, two-period crossover study to 10 patients previously identified as extensive metabolizers of CYP2D6 substrates. Patients were maintained on a carvedilol dose of 25 or 50 mg bid and given fluoxetine/placebo for a minimum of 28 days. Plasma was collected over the 12-hour carvedilol dosing interval, and the concentrations of the R(+) and S(-) enantiomers of carvedilol were measured. CYP2D6 phenotype was assessed during each study period using dextromethorphan (30 mg). Changes in autonomic modulation between study periods were measured by heart rate variability in the time and frequency domains using ambulatory electrocardiographic monitoring. Compared to placebo, fluoxetine coadministration resulted in a 77% increase in mean (+/- SD) R(+) enantiomer AUC0-12 (522 +/- 413 vs. 927 +/- 506 ng.h/mL, p = 0.01) and a nonsignificant increase in S(-) enantiomer AUC (244 +/- 185 vs. 330 +/- 179 ng.h/mL, p = 0.17). Mean apparent oral clearance for both enantiomers decreased significantly with fluoxetine administration (R(+): 10.3 +/- 7.2 vs. 4.5 +/- 2.2 mL/min/kg; S(-): 22.5 +/- 12.3 vs. 12.6 +/- 7.4 mL/min/kg; p = 0.004 and 0.03, respectively). No differences in adverse effects, blood pressure, or heart rate were noted between treatment groups, and there were no consistent changes in heart rate variability parameters. In conclusion, fluoxetine administration resulted in a stereospecific inhibition of carvedilol metabolism, with the R(+) enantiomer increasing to a greater extent than the S(-) enantiomer. However, this interaction was of little clinical significance in our sample population.

The role of the renin-angiotensin-aldosterone system in the management of heart failure

Numerous clinical trials have highlighted the role of the renin-angiotensin-aldosterone (RAA) system in the development and progression of heart failure. Over 30 randomized, controlled trials have evaluated the effects of angiotensin-converting enzyme (ACE) inhibitors on morbidity and mortality in over 7,000 patients with heart failure. Cumulative evidence from these trials shows that these agents significantly reduce mortality and hospitalizations, slow disease progression, and improve exercise tolerance and New York Heart Association class. The Heart Failure Society of America guidelines recommend ACE inhibitors as standard therapy for patients with left ventricular systolic dysfunction. The angiotensin receptor blockers and spironolactone offer alternative and perhaps complimentary mechanisms by which the RAA system may be therapeutically manipulated. The role of these therapies in treating heart failure is discussed.

Identification of a methyltransferase from Mycobacterium smegmatis involved in glycopeptidolipid synthesis

Glycopeptidolipids (GPLs) are major components of the cell walls of several species of mycobacteria. We have isolated a transposon mutant of Mycobacterium smegmatis that is unable to synthesize mature GPLs and that displays a rough colony morphology. The disrupted gene, mtf1, shares a high degree of homology with several S-adenosylmethionine-dependent methyltransferases. The enzyme encoded by mtf1 is required for the methylation of a single rhamnose residue that forms part of the conserved GPL core structure. This conclusion is supported by the finding that (a) the mutant synthesized only GPLs with undermethylated (either mono- or nonmethylated instead of di- or trimethylated) rhamnose residues; (b) complementation of the mutant with a wild-type copy of mtf1 restored high levels of synthesis of GPLs containing di- and trimethylated rhamnose; and (c) S-adenosylmethionine-dependent methylation of rhamnosylated GPLs could be detected in cell lysates of wild-type cells and mtf1-complemented mutant cells, but not in mutant cells lacking intact mtf1. Structural analysis of wild-type and mutant GPLs suggests that disruption of mtf1 specifically inhibits addition of O-methyl groups to the 3 (or 2)-position of the rhamnose. In the absence of 3-O-methylation, further methylation of GPL rhamnose is apparently inhibited, and overall GPL synthesis is down-regulated by 90%.

The major surface antigens of Entamoeba histolytica trophozoites are GPI-anchored proteophosphoglycans

Trophozoites of the parasitic protozoa, Entamoeba histolytica, synthesize a cell surface lipoglycoconjugate, termed lipophosphoglycan, which is thought to be an important virulence factor and potential vaccine candidate against invasive amebiasis. Here, we show that the E. histolytica lipophosphoglycans are in fact glycosylphosphatidylinositol (GPI)-anchored proteophosphoglycans (PPGs). These PPGs contain a highly acidic polypeptide component which is rich in Asp, Glu and phosphoserine residues. This polypeptide component is extensively modified with linear glycan chains having the general structure, [Glcalpha1-6](n)Glcbeta1-6Gal (where n=2-23). These glycan chains can be released after mild-acid hydrolysis with trifluoroacetic or hydrofluoric acid and are probably attached to phosphoserine residues in the polypeptide backbone. The PPGs are further modified with a GPI anchor which differs from all other eukaryotic GPI anchors so far characterized in containing a glycan core with the structure, Gal(1)Man(2)GlcN-myo-inositol, and in being heterogeneously modified with chains of alpha-galactose. Trophozoites of the pathogenic HM-1:IMSS strain synthesize two distinct classes of PPG which have polydisperse molecular masses of 50-180 kDa (PPG-1) and 35-60 kDa (PPG-2) and are modified with glucan side-chains of different average lengths. In contrast, the non-pathogenic Rahman strain synthesizes one class of PPG which is only elaborated with short disaccharide side-chains (i.e. Glcbeta1-6Gal). However, the PPGs are abundant in all strains (8x10(7) copies per cell) and are likely to form a protective surface coat.

The effects of fluvastatin, a CYP2C9 inhibitor, on losartan pharmacokinetics in healthy volunteers

Losartan is an angiotensin II receptor antagonist that is metabolized by CYP2C9 and CYP3A4 to a more potent antihypertensive metabolite, E3174. Interaction studies with inhibitors of CYP3A4 have not demonstrated significant changes in the pharmacokinetics of losartan or E3174. The authors assessed the steady-state pharmacokinetics of losartan and E3174 when administered alone and concomitantly with fluvastatin, a specific CYP2C9 inhibitor. A prospective, open-label, crossover study was conducted in 12 healthy volunteers with losartan alone and in combination with fluvastatin. The baseline phase was 7 days of losartan (50 mg QAM), and the inhibition phase was 14 total days of fluvastatin (40 mg QHS), with the final 7 days including losartan. The authors found that fluvastatin did not significantly change the steady-state AUC0-24 or half-life of losartan or E3174. Losartan apparent oral clearance was not affected by fluvastatin. Inhibition of losartan metabolism appears to require both CYP2C9 and CYP3A4 inhibition.

Digoxin toxicity: an evaluation in current clinical practice

BACKGROUND

Serum digoxin concentrations (SDCs) are frequently sampled before completion of drug distribution. If elevated, these concentrations may be misinterpreted, potentially leading to a misdiagnosis of digoxin toxicity.

OBJECTIVES

To determine the frequency of elevated SDCs (>2.6 nmol/L [>2.0 ng/mL]) obtained at appropriate postdosing intervals and to evaluate the frequency of clinically defined digoxin toxicity in patients with elevated SDCs.

METHODS

The medical records of adult patients with SDCs assayed at 5 general hospitals in North Carolina during a 3-month period (May 1 through July 31, 1996) were prospectively evaluated. Data on SDC, inpatient or outpatient status, and medical or surgical service were collected for all patients. Data on patient demographics, serum chemistry values, indication for digoxin treatment, clinical evidence of digoxin toxicity, and timing of the blood sample relative to administration of the last dose of digoxin were collected for patients with SDCs higher than 2.6 nmol/L (>2.0 ng/mL).

RESULTS

Of 3434 SDCs assayed in 2009 patients, 320 (9.3%) were higher than 2.6 nmol/L (>2.0 ng/mL). Fifty-one (15.9%) of the 320 SDCs were drawn at 6 hours or less following a digoxin dose. Sampling time relative to the digoxin dose could not be determined in 70 (21.9%) of the 320 elevated SDCs, leaving 199 (62.2%) of 320 SDCs in 138 patients evaluable for digoxin toxicity. Eighty-three of the 138 patients had clinical evidence of digoxin toxicity for an overall incidence of 4.1%.

CONCLUSIONS

Digoxin toxicity occurs less frequently than historically reported. Continued emphasis needs to be placed on obtaining appropriately timed SDCs.

Superiority of "triple" drug therapy in heart failure: insights from the PROVED and RADIANCE trials. Prospective Randomized Study of Ventricular Function and Efficacy of Digoxin. Randomized Assessment of Digoxin and Inhibitors of Angiotensin-Converting Enzyme

OBJECTIVES

We sought to study the efficacy of "triple" therapy with digoxin, diuretic and angiotensin-converting enzyme inhibitor (ACEI) compared to other combinations of these drugs in patients with symptomatic left ventricular systolic dysfunction.

BACKGROUND

Controversy continues concerning the role of combining digoxin with diuretic and ACEI in the initial management of patients with heart failure.

METHODS

The study utilized data from two studies of digoxin efficacy: Prospective Randomized Study of Ventricular Function and Efficacy of Digoxin (PROVED) and Randomized Assessment of Digoxin and Inhibitors of Angiotensin-Converting Enzyme (RADIANCE). Worsening heart failure defined as augmentation of heart failure therapy or an emergency room visit or hospitalization for increased heart failure was the main outcome measure.

RESULTS

A total of 266 patients comprising the four treatment groups of the combined PROVED (diuretic alone or digoxin and diuretic) and RADIANCE (ACEI and diuretic, or digoxin, diuretic and ACEI) trials were analyzed. Worsening heart failure occurred in only 4 of the 85 patients who continued digoxin, diuretic and ACEI therapy (4.7%) compared to 18 of the 42 patients (19%) on digoxin and diuretic therapy (p=0.009), to 23 of the 93 patients (25%) on ACEI and diuretic therapy (p=0.001) and to 18 of the 46 patients (39%) on diuretic alone (p < 0.001). Life table and multivariate analysis also demonstrated that worsening heart failure was least likely in patients treated with triple therapy (p < 0.01 vs. all other groups).

CONCLUSION

Pending definitive, prospective clinical trials, our results argue for triple therapy as the initial management of patients with symptomatic heart failure due to systolic dysfunction.

Effects of erythromycin or rifampin on losartan pharmacokinetics in healthy volunteers

BACKGROUND

Losartan is metabolized by CYP2C9 and CYP3A4 to an active metabolite, E3174, which has greater antihypertensive activity than the parent compound. Coadministered drugs that inhibit or induce metabolic processes may therefore alter the pharmacokinetics and pharmacologic response of losartan and E3174.

OBJECTIVE AND METHODS

Ten healthy volunteers were studied to assess the effects of CYP3A4 inhibition and nonspecific P450 enzyme induction on the pharmacokinetics of losartan and E3174. Subjects completed three 1-week phases separated by 6 days: 50 mg losartan every morning, losartan plus 500 mg erythromycin four times a day, and losartan plus 300 mg rifampin (INN, rifampicin) twice a day. On the eighth day of each phase, serial plasma concentrations of losartan and E3174 were obtained over 32 hours and steady-state pharmacokinetics were determined.

RESULTS

Rifampin decreased the area under the concentration-time curve from time zero to 24 hours after the dose (AUC[0-24]) of losartan by 35% (349 +/- 246 versus 225 +/- 130; p = 0.0001) and decreased the AUC(0-24) of E3174 by 40% (1336 +/- 445 versus 792 +/- 302; p < 0.005). Losartan oral clearance was increased by 44% (p = 0.0001). The half-life values of both compounds were decreased by 50% (p < 0.005). In contrast, erythromycin did not significantly affect the AUC(0-24) or half-life of either losartan or E3174.

CONCLUSIONS

Rifampin is a potent inducer of losartan and E3174 elimination. Given the magnitude of the effect, this interaction is likely to be clinically significant. On the basis of the minimal inhibitory effects observed with erythromycin, CYP3A4 appears to play a minor role in the in vivo metabolism of losartan to E3174. Further studies are needed to define the contribution of other isozymes, particularly CYP2C9, to the pharmacokinetics of losartan and E3174.

Clinical predictors of worsening heart failure during withdrawal from digoxin therapy

Previous work provides limited information concerning predictors of clinical deterioration after digoxin withdrawal. We investigated the association between selected baseline clinical characteristics and symptomatic deterioration in two similarly designed trials: Prospective Randomized Study of Ventricular Function and Efficacy of Digoxin (PROVED) and Randomized Assessment of Digoxin and Inhibitors of Angiotensin-Converting Enzyme (RADIANCE). Cox proportional-hazards analysis found the following independent predictors of worsening during follow-up in the combined PROVED and RADIANCE patients: heart failure score, left ventricular ejection fraction, cardiothoracic ratio, use of an angiotensin-converting enzyme inhibitor, use of digoxin, and age. When these factors, except for digoxin use, were tested in the subgroup of patients withdrawn from digoxin, they all were significant independent predictors of worsening heart failure. In contrast, only use of angiotensin-converting enzyme inhibitor predicted deterioration in patients who continued digoxin. Patients with more congestive symptoms, worse ventricular function, greater cardiac enlargement, or who were not taking an angiotensin-converting enzyme inhibitor were significantly more likely to worsen early after digoxin discontinuation than patients without these characteristics.

The AHCPR clinical practice guideline for heart failure revisited

OBJECTIVE

To review the Agency for Health Care Policy and Research (AHCPR) clinical practice guideline for heart failure and comment on the guideline regarding pharmacotherapy from the perspective of the latest clinical trial data and the authors' clinical experience.

DATA SOURCES

A MEDLINE search (1966 to June 1997) of English-language literature pertaining to the pharmacotherapy of heart failure was performed. Special emphasis was placed on literature published in the last 5 years. Additional literature was obtained from reference lists of key articles identified through the search.

DATA SYNTHESIS

Pertinent clinical trials were reviewed and considered along with information from the authors' database of over 800 patients with heart failure. Evidence concerning the use of angiotensin-converting enzyme inhibitors at appropriate dosages in all New York Heart Association classes of heart failure and the inclusion of digoxin as part of triple therapy in all symptomatic patients with left ventricular systolic dysfunction are reviewed. Strategies to circumvent clinical problems that may limit the proper application of standard therapeutic agents are considered, and the possible future role of beta-blockers as the therapeutic agents in patients with heart failure is discussed.

CONCLUSIONS

The AHCPR guideline provides the clinician with an excellent framework for treating the patient with heart failure. Building on the fundamentals of the guideline, the clinician can carefully apply current therapy at appropriate dosages and in the best combinations to individualize and thereby optimize pharmacologic therapy for this patient population.

Blast overpressure induced structural and functional changes in the auditory system

Blast overpressure of sufficient intensity can produce injury to various organ systems. Unprotected ears result in the auditory system being the most susceptible. The injuries to the auditory system include: rupture of the tympanic membrane, dislocation or fracture of the ossicular chain, and damage to the sensory structures on the basilar membrane. All these injuries can be characterized as a form of mechanical damage to the affected structure. Injury to the sensory structures on the basilar membrane leads to temporary and permanent loss of hearing sensitivity. The temporary component of the hearing loss shows a time course after removal from the noise which frequently will include an initial increase in hearing loss followed by a recovery period during which threshold may return to preexposure levels or stabilize at a higher level which represents a permanent loss of hearing sensitivity. This type of recovery function suggests that there are damage processes which continue after the traumatic event and that intervention might mitigate some of the damage and hearing loss.

Is there an expanded role for digoxin in patients with heart failure and sinus rhythm? A protagonist viewpoint

The evidence supporting the efficacy of digoxin in patients with heart failure who are in sinus rhythm is substantial. Digoxin improves hemodynamics, exercise capacity, symptoms, and quality of life and reduces hospitalizations. All of this is accomplished with a drug that is very inexpensive and can be given once daily. Its safety has been established through the DIG trial. Although digoxin does not decrease mortality beyond that of diuretics and ACE inhibitors, it does not increase mortality, unlike many positive inotropes. Furthermore, digoxin, in addition to ACE inhibitors and a diuretic, decreases the hospitalization rate due to worsening of heart failure. From a managed care perspective, as well as that of the patient, this is of enormous benefit. A pharmacoeconomic analysis estimated that continuation of digoxin in patients with stable congestive heart failure could save the healthcare system an estimated $ 400 million, based on costs from one hospital. The issue is not whether to use digoxin in these patients, but rather, how early to initiate therapy. From some of the recent data in patients with systolic dysfunction and mild heart failure, as well as knowledge of the neurohormonal activation that occurs early in these patients, it could be suggested that early use of neurohormonal modulators, including digoxin, would decrease the progression of heart failure. Thus, rather than waiting for symptoms despite optimal doses of an ACE inhibitor and diuretic, as suggested by the AHCPR practice guideline for heart failure, initiation of digoxin therapy in patients as early as NYHA class II at a dosage that will achieve a serum concentration of 1.0 ng/mL or less should occur. With the understanding of digoxin's effect on the neurohormonal systems, its role in patients with preserved systolic function needs to be reexplored. The debate can now focus on asymptomatic patients or those with preserved systolic function. Could these patients benefit from therapy with digoxin as well?