Pharmacokinetic studies with chlorthalidone (Hygroton) in man

Effect of the combination of bumetanide plus chlorthalidone on hypertension and volume overload in patients with chronic kidney disease stage 4-5 KDIGO without renal replacement therapy: a double-blind randomized HEBE-CKD trial

Background

The co-administration of loop diuretics with thiazide diuretics is a therapeutic strategy in patients with hypertension and volume overload. The aim of this study was to assess the efficacy and safety of treatment with bumetanide plus chlorthalidone in patients with chronic kidney disease (CKD) stage 4–5 KDIGO.

Methods

A double-blind randomized study was conducted. Patients were randomized into two groups: bumetanide plus chlorthalidone group (intervention) and the bumetanide plus placebo group (control) to evaluate differences in TBW, ECW and ECW/TBW between baseline and 30 Days of follow-up. Volume overload was defined as ‘bioelectrical impedance analysis as fluid volume above the 90th percentile of a presumed healthy reference population. The study’s registration number was NCT03923933.

Results

Thirty-two patients with a mean age of 57.2 ± 9.34 years and a median estimated glomerular filtration rate (eGFR) of 16.7 ml/min/1.73 m² (2.2–29) were included. There was decreased volume overload in the liters of total body water (TBW) on Day 7 (intervention: -2.5 vs. control: -0.59, p = 0.003) and Day 30 (intervention: -5.3 vs. control: -0.07, p = 0.016); and in liters of extracellular water (ECW) on Day 7 (intervention: -1.58 vs. control: -0.43, p < 0.001) and Day 30 (intervention: -3.05 vs. control: -0.15, p < 0.000). There was also a decrease in systolic blood pressure on Day 7 (intervention: -18 vs. control: -7.5, p = 0.073) and Day 30 (intervention: -26.1 vs. control: -10, p = 0.028) and in diastolic blood pressure on Day 7 (intervention: -8.5 vs. control: -2.25, p = 0.059) and Day 30 (intervention: -13.5 vs. control: -3.4, p = 0.018).

Conclusion

In CKD stage 4–5 KDIGO without renal replacement therapy, bumetanide in combination with chlorthalidone is more effective in treating volume overload and hypertension than bumetanide with placebo.

Thiazide diuretics are back in CKD: the case of chlorthalidone

Sodium and volume excess is the fundamental risk factor underlying hypertension in chronic kidney disease (CKD) patients, who represent the prototypical population characterized by salt-sensitive hypertension. Low salt diets and diuretics constitute the centrepiece for blood pressure control in CKD. In patients with CKD stage 4, loop diuretics are generally preferred to thiazides. Furthermore, thiazide diuretics have long been held as being of limited efficacy in this population. In this review, by systematically appraising published randomized trials of thiazides in CKD, we show that this class of drugs may be useful even among people with advanced CKD. Thiazides cause a negative sodium balance and reduce body fluids by 1-2 l within the first 2-4 weeks and these effects go along with improvement in hypertension control. The recent CLICK trial has documented the antihypertensive efficacy of chlorthalidone, a long-acting thiazide-like diuretic, in stage 4 CKD patients with poorly controlled hypertension. Overall, chlorthalidone use could be considered in patients with treatment-resistant hypertension when spironolactone cannot be administered or must be withdrawn due to side effects. Hyponatremia, hypokalaemia, volume depletion and acute kidney injury are side effects that demand a vigilant attitude by physicians prescribing these drugs. Well-powered randomized trials assessing hard outcomes are still necessary to more confidently recommend the use of these drugs in advanced CKD.

Thiazide and the Thiazide-Like Diuretics: Review of Hydrochlorothiazide, Chlorthalidone, and Indapamide

The term thiazide is universally understood to refer to diuretics that exert their principal action in the distal tubule. The thiazide class is heterogenous and can be further subdivided into compounds containing the benzothiadiazine ring structure-the thiazide-type (e.g., hydrochlorothiazide)-and those lacking the benzothiadiazine ring-the thiazide-like (e.g., chlorthalidone and indapamide) drugs. Thiazide-like agents are longer acting and constitute the diuretics used in most of the cardiovascular outcome trials that established benefits of treatment with diuretics, but pragmatic aspects, such as lack of availability in convenient formulations, limit their use. Regardless of class heterogeneity, thiazides have retained importance in the management of hypertension for over 60 years. They are reliably effective as monotherapy in a majority of hypertensive patients, and augment the efficacy of other classes of antihypertensives when used in combination. Importantly, a thiazide-based treatment regimen lowers cardiovascular events, and their sturdy effect reinforces their place among the recommended first-line agents to treat hypertension in major domestic and international hypertension guidelines. There are few head-to-head comparisons within the class, but potential differences have been explored indirectly as well as in non-blood pressure mechanisms and potential pleiotropic properties. Until proven otherwise, the importance of these differences remains speculative, and clinicians should assume that cardiovascular events will be lowered similarly across agents when equivalent blood pressure reduction occurs. Thiazides remain underutilized, with only about one-third of hypertensive patients receiving them. For many patients, however, a thiazide is an indispensable component of their regimen to achieve adequate blood pressure control.

Monotherapy treatment with chlorthalidone or amlodipine in the systolic blood pressure intervention trial (SPRINT)

This post hoc analysis of the Systolic Blood Pressure Intervention Trial (SPRINT) examined the performance of chlorthalidone (C) versus amlodipine (A) monotherapies. ANOVA was used to analyze the differences in systolic blood pressure (SBP) response between C and A. Logistic regression was used to examine monotherapy failure (adding a second antihypertensive agent or switching to a different antihypertensive agent) rates. Four hundred ninety-one participants were treated with C monotherapy (n = 210, mean dose = 22 mg/day) or A monotherapy (n = 281, mean dose = 7 mg/day). There was a significant difference in mean SBP reduction between the C and A monotherapies at the third visit (higher reduction with A, adjusted p = .018). Unadjusted analysis showed a higher failure with C in the standard treatment group. Although the average SBP at failure was higher and above the 140 mm Hg cutoff that indicated monotherapy failure with A (142.60) compared with C (138.40), more participants on C failed despite having SBP below the 140 cutoff. This was probably due to decisions made by the investigative teams to change the antihypertensive regimen, because, in their opinion, the clinical picture required it. After adjusting for baseline characteristics, C had higher failure than A only in the standard treatment group (1.64 odds ratio [OR], 95% CI 1.06-2.56, p = .028). A sub-analysis including participants who had never used antihypertensive treatment before randomization had similar results (2.57 OR, 95% CI 1.34-5.02, p = .004). Overall, in SPRINT chlorthalidone was associated with higher monotherapy failure than amlodipine in the standard treatment group because of decisions of the investigative teams.

Antioxidant properties of drugs used in Type 2 diabetes management: could they contribute to, confound or conceal effects of antioxidant therapy?

Objectives: This is a narrative review, investigating the antioxidant properties of drugs used in the management of diabetes, and discusses whether these antioxidant effects contribute to, confound, or conceal the effects of antioxidant therapy.

Methods: A systematic search for articles reporting trials, or observational studies on the antioxidant effect of drugs used in the treatment of diabetes in humans or animals was performed using Web of Science, PubMed, and Ovid. Data were extracted, including data on a number of subjects, type of treatment (and duration) received, and primary and secondary outcomes. The primary outcomes were reporting on changes in biomarkers of antioxidants concentrations and secondary outcomes were reporting on changes in biomarkers of oxidative stress.

Results: Diabetes Mellitus is a disease characterized by increased oxidative stress. It is often accompanied by a spectrum of other metabolic disturbances, including elevated plasma lipids, elevated uric acid, hypertension, endothelial dysfunction, and central obesity. This review shows evidence that some of the drugs in diabetes management have both in vivo and in vitro antioxidant properties through mechanisms such as scavenging free radicals and upregulating antioxidant gene expression.

Conclusion: Pharmaceutical agents used in the treatment of type 2 diabetes has been shown to exert an antioxidant effect..

Pathophysiology and treatment of resistant hypertension: the role of aldosterone and amiloride-sensitive sodium channels

Resistant hypertension is a clinically distinct subgroup of hypertension defined by the failure to achieve blood pressure control on optimal dosing of at least 3 antihypertensive medications of different classes, including a diuretic. The pathophysiology of hypertension can be attributed to aldosterone excess in more than 20% of patients with resistant hypertension. Existing dogma attributes the increase in blood pressure seen with increases in aldosterone to its antinatriuretic effects in the distal nephron. However, emerging research, which has identified and has begun to define the function of amiloride-sensitive sodium channels and mineralocorticoid receptors in the systemic vasculature, challenges impaired natriuresis as the sole cause of aldosterone-mediated resistant hypertension. This review integrates these findings to better define the role of the vasculature and aldosterone in the pathophysiology of resistant hypertension. In addition, a brief guide to the treatment of resistant hypertension is presented.

Risk of hyponatremia with diuretics: chlorthalidone versus hydrochlorothiazide

BACKGROUND

Chlorthalidone and hydrochlorothiazide are often considered as interchangeable. However, greater (nighttime) blood pressure reduction, and alleged pleiotropic effects have renewed the interest in chlorthalidone. A recent study showed an increased risk of adverse events with chlorthalidone, including hyponatremia.

METHODS

To investigate differences in risk of hyponatremia between chlorthalidone and hydrochlorothiazide, adjusted for daily dose, we conducted a population-based case-control study within the Dutch IPCI (Integrated Primary Care Information) database. The study population included all subjects ≥18 years without diabetes mellitus, heart failure, liver failure, and malignancy, who were registered in the IPCI database from 1996 to 2011. Cases were subjects with a serum sodium <130 millimoles per liter or hospitalization due to hyponatremia. Controls were matched on practice, age within 5 years, sex, and date of onset.

RESULTS

A total of 1033 cases of hyponatremia were identified. Hyponatremia was more common with chlorthalidone than with hydrochlorothiazide at equal dose per day: adjusted odds ratio was 2.09 (95% confidence interval [CI], 1.13-3.88) for 12.5 milligrams per day and 1.72 (95% CI, 1.15-2.57) for 25 milligrams per day. Risks were not significantly increased with chlorthalidone compared with twice the dose per day of hydrochlorothiazide.

CONCLUSIONS

This is the first study that shows an increased risk of hyponatremia with chlorthalidone relative to hydrochlorothiazide at equal milligram-to-milligram dose per day. The need for a lower dose of chlorthalidone than hydrochlorothiazide to achieve similar blood pressure reduction likely compensates for the increased risk of hyponatremia at equal dose.

Blood pressure-lowering efficacy of monotherapy with thiazide diuretics for primary hypertension

BACKGROUND

Hypertension is a modifiable cardiovascular risk factor. Although it is established that low-dose thiazides reduce mortality as well as cardiovascular morbidity, the dose-related effect of thiazides in decreasing blood pressure has not been subject to a rigorous systematic review. It is not known whether individual drugs within the thiazide diuretic class differ in their blood pressure-lowering effects and adverse effects.

OBJECTIVES

To determine the dose-related decrease in systolic and/or diastolic blood pressure due to thiazide diuretics compared with placebo control in the treatment of patients with primary hypertension. Secondary outcomes included the dose-related adverse events leading to patient withdrawal and adverse biochemical effects on serum potassium, uric acid, creatinine, glucose and lipids.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2014, Issue 1), Ovid MEDLINE (1946 to February 2014), Ovid EMBASE (1974 to February 2014) and ClinicalTrials.gov.

SELECTION CRITERIA

We included double-blind, randomized controlled trials (RCTs) comparing fixed-dose thiazide diuretic monotherapy with placebo for a duration of 3 to 12 weeks in the treatment of adult patients with primary hypertension.

DATA COLLECTION AND ANALYSIS

Two authors independently screened articles, assessed trial eligibility, extracted data and determined risk of bias. We combined data for continuous variables using a mean difference (MD) and for dichotomous outcomes we calculated the relative risk ratio (RR) with 95% confidence interval (CI).

MAIN RESULTS

We included 60 randomized, double-blind trials that evaluated the dose-related trough blood pressure-lowering efficacy of six different thiazide diuretics in 11,282 participants treated for a mean duration of eight weeks. The mean age of the participants was 55 years and baseline blood pressure was 158/99 mmHg. Adequate blood pressure-lowering efficacy data were available for hydrochlorothiazide, chlorthalidone and indapamide. We judged 54 (90%) included trials to have unclear or high risk of bias, which impacted on our confidence in the results for some of our outcomes.In 33 trials with a baseline blood pressure of 155/100 mmHg, hydrochlorothiazide lowered blood pressure based on dose, with doses of 6.25 mg, 12.5 mg, 25 mg and 50 mg/day lowering blood pressure compared to placebo by 4 mmHg (95% CI 2 to 6, moderate-quality evidence)/2 mmHg (95% CI 1 to 4, moderate-quality evidence), 6 mmHg (95% CI 5 to 7, high-quality evidence)/3 mmHg (95% CI 3 to 4, high-quality evidence), 8 mmHg (95% CI 7 to 9, high-quality evidence)/3 mmHg (95% CI 3 to 4, high-quality evidence) and 11 mmHg (95% CI 6 to 15, low-quality evidence)/5 mmHg (95% CI 3 to 7, low-quality evidence), respectively.Direct comparison of doses did not show evidence of dose dependence for blood pressure-lowering for any of the other thiazides for which RCT data were available: bendrofluazide, chlorthalidone, cyclopenthiazide, metolazone or indapamide.In seven trials with a baseline blood pressure of 163/88 mmHg, chlorthalidone at doses of 12.5 mg to 75 mg/day reduced average blood pressure compared to placebo by 12.0 mmHg (95% CI 10 to 14, low-quality evidence)/4 mmHg (95% CI 3 to 5, low-quality evidence).In 10 trials with a baseline blood pressure of 161/98 mmHg, indapamide at doses of 1.0 mg to 5.0 mg/day reduced blood pressure compared to placebo by 9 mmHg (95% CI 7 to 10, low-quality evidence)/4 (95% CI 3 to 5, low-quality evidence).We judged the maximal blood pressure-lowering effect of the different thiazides to be similar. Overall, thiazides reduced average blood pressure compared to placebo by 9 mmHg (95% CI 9 to 10, high-quality evidence)/4 mmHg (95% CI 3 to 4, high-quality evidence).Thiazides as a class have a greater effect on systolic than on diastolic blood pressure, therefore thiazides lower pulse pressure by 4 mmHg to 6 mmHg, an amount that is greater than the 3 mmHg seen with angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs) and renin inhibitors, and the 2 mmHg seen with non-selective beta-blockers. This is based on an informal indirect comparison of results observed in other Cochrane reviews on ACE inhibitors, ARBs and renin inhibitors compared with placebo, which used similar inclusion/exclusion criteria to the present review.Thiazides reduced potassium, increased uric acid and increased total cholesterol and triglycerides. These effects were dose-related and were least for hydrochlorothiazide. Chlorthalidone increased serum glucose but the evidence was unclear for other thiazides. There is a high risk of bias in the metabolic data. This review does not provide a good assessment of the adverse effects of these drugs because there was a high risk of bias in the reporting of withdrawals due to adverse effects.

AUTHORS' CONCLUSIONS

This systematic review shows that hydrochlorothiazide has a dose-related blood pressure-lowering effect. The mean blood pressure-lowering effect over the dose range 6.25 mg, 12.5 mg, 25 mg and 50 mg/day is 4/2 mmHg, 6/3 mmHg, 8/3 mmHg and 11/5 mmHg, respectively. For other thiazide drugs, the lowest doses studied lowered blood pressure maximally and higher doses did not lower it more. Due to the greater effect on systolic than on diastolic blood pressure, thiazides lower pulse pressure by 4 mmHg to 6 mmHg. This exceeds the mean 3 mmHg pulse pressure reduction achieved by ACE inhibitors, ARBs and renin inhibitors, and the 2 mmHg pulse pressure reduction with non-selective beta-blockers as shown in other Cochrane reviews, which compared these antihypertensive drug classes with placebo and used similar inclusion/exclusion criteria.Thiazides did not increase withdrawals due to adverse effects in these short-term trials but there is a high risk of bias for that outcome. Thiazides reduced potassium, increased uric acid and increased total cholesterol and triglycerides.

Azilsartan medoxomil in the treatment of hypertension: the definitive angiotensin receptor blocker?

INTRODUCTION

Azilsartan medoxomil is the newest angiotensin receptor blocker marketed for the treatment of arterial hypertension. The aim of this article was to review the available evidence about this drug alone or combined with other antihypertensive agents in the treatment of hypertensive population.

AREAS COVERED

For this purpose, a search on MEDLINE and EMBASE databases was performed. The MEDLINE and EMBASE search included both medical subject headings (MeSHs) and keywords including azilsartan or azilsartan medoxomil or angiotensin receptor blockers or renin angiotensin system or chlorthalidone and hypertension. References of the retrieved articles were also screened for additional studies. There were no language restrictions.

EXPERT OPINION

Azilsartan medoxomil has a potent and persistent ability to inhibit binding of angiotensin II to AT1 receptors, which may play a role in its superior blood pressure (BP) -lowering efficacy compared with other drugs, including ramipril, candesartan, valsartan or olmesartan, without an increase of side effects. Chlortalidone is a diuretic which significantly differs from other classic thiazides and has largely demonstrated clinical benefits in outcome trials. The fixed-dose combination of azilsartan and chlorthalidone has been shown to be more effective than other potent combinations of angiotensin receptor blockers plus hydrochlorothiazide, with a good tolerability profile.

Nocturia in arterial hypertension: a prevalent, underreported, and sometimes underestimated association

Nocturia is a risk factor for morbidity and mortality but is frequently overlooked and underreported by patients and unrecognized by physicians. Epidemiologic studies reported that nocturnal voiding is associated not only with aging and benign prostatic hyperplasia, but also with many other clinical conditions. The majority of epidemiologic studies reported a significant relationship between nocturia and hypertension. However, the cause-and-effect relationship between them has not been established. Some physiopathological changes in hypertension are conducive to result in nocturia. These include the effects of hypertension on glomerular filtration and tubular transport, resetting of the kidney pressure-natriuresis relationship, atrial stretch and release of atrial natriuretic peptide when congestive heart failure complicates hypertension, and peripheral edema. Another link between hypertension and nocturia is obstructive sleep apnea. Furthermore, some evidence supports the relationship between nondipping behavior of blood pressure and an increased prevalence of nocturia. The use of some classes of antihypertensive agents may result in nocturia. The present review aims to provide a comprehensive evaluation of the epidemiologic evidence and physiopathological links that correlate hypertension and nocturia. Emphasis is placed on the need to take a pro-active attitude to detect and treat this hazardous condition.

Azilsartan/chlorthalidone combination therapy for blood pressure control

BACKGROUND

Edarbyclor(®) is a combined angiotensin receptor blocker (ARB) and thiazide-like diuretic (azilsartan and chlorthalidone), and was approved on December 20, 2011 by the US Food and Drug Administration (FDA) for hypertension management.

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, safety, tolerability, and role of azilsartan plus chlorthalidone for hypertension management.

METHODS

Peer-reviewed clinical trials, review articles, and relevant treatment guidelines, were identified from the databases MEDLINE and Current Contents (both 1966 to February 15, 2013, inclusive) using search terms "azilsartan", "chlorthalidone", "pharmacology", "pharmacokinetics", "pharmacodynamics", "pharmacoeconomics", and "cost-effectiveness". The FDA website, as well as manufacturer prescribing information, was also reviewed to identify other relevant information.

RESULTS

Azilsartan is a new ARB with high affinity for the angiotensin 1 receptor, approved by the FDA for hypertension management. Unlike other ARBs, azilsartan has no clinical data supporting improvement in cardiovascular outcomes, and is not approved for indications other than hypertension, which a select few other ARBs may be used for (eg, diabetic nephropathy and heart failure). Chlorthalidone is a longer acting thiazide-like diuretic that has been demonstrated to improve cardiovascular outcomes. Combination treatment with azilsartan/chlorthalidone is effective for reducing blood pressure. Compared to olmesartan/hydrochlorothiazide and azilsartan/hydrochlorothiazide combinations, azilsartan/chlorthalidone appears to be more efficacious for reducing blood pressure.

CONCLUSIONS

Azilsartan/chlorthalidone can be considered an antihypertensive therapy option in patients for whom combination therapy is required (blood pressure >20 mmHg systolic or >10 mmHg diastolic above goal). Cost to patients and insurance coverage will probably determine whether azilsartan/chlorthalidone will be the most appropriate combination therapy for an individual patient.

Sustained blood pressure-lowering effect of aliskiren compared with telmisartan after a single missed dose

Poor adherence to antihypertensive drug treatment is common and is often associated with marked prolongations of the dosing interval. Hence, selecting a treatment that has the potential to provide a sustained blood pressure (BP)-lowering effect is important. The objective of this analysis is to compare the sustained efficacy of aliskiren with telmisartan after a single missed dose. This is part of a 12-week double-blind study conducted in patients with mild to moderate hypertension randomized to once-daily aliskiren 150 mg or telmisartan 40 mg for 2 weeks, force-titrated to double the doses for 10 weeks, followed by placebo for 1 week. The changes in BP from the end of active treatment (EOA) to 48 hours after treatment withdrawal (day 2) were analyzed. Demographic and baseline characteristics were comparable between the treatment groups. Aliskiren continued to show significantly greater reductions in mean sitting systolic BP (-0.7 vs +1.3 mm Hg; P<.05), 24-hour mean ambulatory systolic BP (-3.6 vs +2.6 mm Hg; P<.01), and 24-hour mean ambulatory diastolic BP (-3.7 vs +0.4 mm Hg; P<.01) compared with telmisartan from EOA to day 2, despite the similar BP reductions from randomization to EOA. In conclusion, aliskiren sustained the BP-lowering efficacy better than telmisartan after a single missed dose.

Blood pressure-lowering efficacy of the fixed-dose combination of azilsartan medoxomil and chlorthalidone: a factorial study

This study compared the efficacy and safety of fixed-dose combinations (FDCs) of the angiotensin II receptor blocker azilsartan medoxomil (AZL-M) and the thiazide-like diuretic chlorthalidone (CLD) with the individual monotherapies in a double-blind factorial study. A total of 1714 patients with clinic systolic blood pressure (SBP) 160 mm Hg to 190 mm Hg inclusive were randomized to AZL-M 0 mg, 20 mg, 40 mg, or 80 mg and/or chlorthalidone 0 mg, 12.5 mg, or 25 mg. The primary efficacy end point was change from baseline to 8 weeks in trough (hour 22-24) SBP by ambulatory blood pressure (BP) monitoring (ABPM). Patients' mean age was 57 years; 47% were men and 20% were black. Baseline trough BP was approximately 165/95 mm Hg and 151/91 mm Hg by clinic and ABPM measurements, respectively. For the pooled AZL-M/CLD 40/25-mg and 80/25-mg FDC groups, SBP reduction by ABPM at trough was 28.9 mm Hg and exceeded AZL-M 80 mg and CLD 25 mg monotherapies by 13.8 mm Hg and 13 mm Hg, respectively (P<.001 for both comparisons). Discontinuation rates and elevations in serum creatinine were dose-dependent and occurred more often in the AZL-M/CLD groups. In patients with stage 2 hypertension, treatment with the combination of AZL-M and CLD resulted in substantially greater SBP reduction compared with either agent alone.

Older blood pressure medications-do they still have a place?

Hypertension is a major risk factor for cardiovascular disease, but control of hypertension remains inadequate, often because of poor patient adherence to prescribed medical regimens that are viewed as poorly tolerated and expensive. Physicians have largely stopped using some older blood pressure medications in favor of newer agents, mostly because of a presumed more favorable side effect profile. The investigators reviewed the pharmacologic properties and the evidence supporting the effectiveness and tolerability of several older blood pressure drugs: sympatholytic agents such as reserpine, methyldopa, and clonidine; diuretics such as chlorthalidone, ethacrynic acid and spironolactone; the vasodilators hydralazine and minoxidil; and others. In conclusion, some of these drugs are well studied and represent alternatives for patients who cannot afford or tolerate newer medications.

Masking and manipulation

The list of prohibited substances in sports includes a group of masking agents that are forbidden in both in- and out-of-competition doping tests. This group consists of a series of compounds that are misused in sports to mask the administration of other doping agents, and includes: diuretics, used to reduce the concentration in urine of other doping agents either by increasing the urine volume or by reducing the excretion of basic doping agents by increasing the urinary pH; probenecid, used to reduce the concentration in urine of acidic compounds, such as glucuronoconjugates of some doping agents; 5alpha-reductase inhibitors, used to reduce the formation of 5alpha-reduced metabolites of anabolic androgenic steroids; plasma expanders, used to maintain the plasma volume after misuse of erythropoietin or red blood cells concentrates; and epitestosterone, used to mask the detection of the administration of testosterone. Diuretics may be also misused to achieve acute weight loss before competition in sports with weight categories. In this chapter, pharmacological modes of action, intended pharmacological effects for doping purposes, main routes of biotransformation and analytical procedures used for anti-doping controls to screen and confirm these substances will be reviewed and discussed.

Chlorthalidone - a renaissance in use?

Diuretic therapy remains a mainstay of hypertension treatment, either given as monotherapy or used in combination with other antihypertensive compounds. Several issues have complicated the issue of diuretic use with that of class effect being the one that has proven most difficult. Hydrochlorothiazide is a commonly used thiazide diuretic; whereas chlorthalidone is a structurally similar compound, quite dissimilar pharmacokinetically with a much longer half-life for effect and a wider volume of distribution with heavy partitioning in red blood cells. These pharmacokinetic features afford chlorthalidone a unique advantage in its capacity to act as an effective diuretic and blood-pressure-lowering agent, as well as a compound that improves cardiovascular outcomes in the patient with hypertension. Chlorthalidone has been used sparingly in clinical practice in large measure because it is not readily available in many fixed-dose combination products. Fixed-dose combinations containing chlorthalidone and an angiotensin-receptor blocker are now in development. It remains to be determined how well these two therapies will reduce blood pressure in the general population while keeping compound-specific side effects to a minimum.

Aspects on pharmacokinetics of some diuretics

This review summarizes the present knowledge of some commonly used diuretics. Bendroflumethiazide and bumetanide are completely absorbed from the gut while the uptake of hydrochlorothiazide, chlorthalidone and furosemide averages about 65%. The degree of uptake of amiloride and spironolactone is unknown but exceeds 50%. Plasma t 1/2 of bumetanide and furosemide are approximately 1 h. The clinically important phase of the plasma concentration of bendroflumethiazide has a t 1/2 of 3 h, although a slower phase with a t 1/2 of 9 h has been described. Hydrochlorothiazide and amiloride, often used in combination, both have a t 1/2 of about 10 h. Canrenone, an active metabolite of spironolactone, has a t 1/2 of 15-20 h. Chlorthalidone is eliminated very slowly with a t 1/2 of about two days. This is partly caused by an extensive binding to carbonic anhydrase in the erythrocytes. The protein binding of bendroflumethiazide, bumetanide, canrenone and furosemide is approximately 95%. The binding of chlorthalidone and hydrochlorothiazide is about 75 and 40% respectively. All mentioned diuretics except spironolactone are in part eliminated renally, mainly via tubular secretion. This is the major elimination route for amiloride and hydrochlorothiazide, while it constitutes one third to two thirds for bendroflumethiazide, bumetanide and furosemide. Spironolactone is exclusively eliminated as metabolites.

Hydrochlorothiazide versus chlorthalidone: evidence supporting their interchangeability

Thiazide diuretics are one of the preferred pharmacologic treatments for hypertension. Hydrochlorothiazide and chlorthalidone have been the 2 most commonly used diuretics in major clinical trials. Treatment guidelines and compendia often consider these 2 drugs interchangeable agents within the class of thiazide or thiazide-like diuretics. Many sources list them as equipotent. Despite these beliefs, there is some suggestion that cardiovascular outcomes are not necessarily the same with these 2 drugs. We conducted a literature search from 1960 to 2003 to identify studies that evaluated the pharmacokinetic and blood pressure-lowering effects of these 2 agents. There are significant pharmacokinetic and pharmacodynamic differences between these diuretics. Chlorthalidone is approximately 1.5 to 2.0 times as potent as hydrochlorothiazide, and the former has a much longer duration of action. Whether these pharmacokinetic and pharmacodynamic features cause differences in outcomes is not known.

Simultaneous determination of atenolol and chlorthalidone in plasma by high-performance liquid chromatography. Application to pharmacokinetic studies in man

An HPLC method developed to detect in a single run both atenolol and chlorthalidone, extracted from plasma, using two detectors (UV for chlorthalidone and fluorometric for atenolol) connected in series, is described. The drugs were separated on an ODS column at room temperature using a 0.05 M sodium dodecyl sulphate in phosphate buffer (pH 5.8)-n-propanol (95:5, v/v) solution, delivered at a flow-rate of 1.3 ml/min. Having ascertained the sensitivity (10 ng/ml of both drugs) and the intra-day reproducibility (pre-study validation), the reliability of the method was verified by inter-day assays (within-study validation) carried out during the analysis of plasma samples collected from healthy volunteers after single-dose treatment with atenolol+chlorthalidone tablets (pharmaceutical preparations containing 100+25 mg and 50+12.5 mg of the two drugs, respectively).

Detection of diuretic agents in doping control

Since the inclusion of diuretics in the list of banned substances in sports in 1988, a large number of screening and confirmation procedures to detect the presence of these substances in urine samples have been developed. In this paper, a review of the analytical methodology described to analyze diuretics is presented. The paper has been focused on the needs of doping control and mainly screening procedures including sample preparation and liquid or gas chromatographic separation have been considered. More relevant papers using capillary zone electrophoresis have been also considered. Mass spectrometry is mandatory in doping control for confirmation purposes, and finally, mass spectrometric techniques described for diuretics have been reviewed.

Diuretics. Clinical pharmacology and therapeutic use (Part I)

25 years have elapsed since the introduction of the first effective oral diuretic, chlorothiazide. Diuretics are now amongst the most widely prescribed drugs in clinical practice worldwide. Availability of these drugs has not only brought therapeutic benefit to countless numbers of patients but it has at the same time provided valuable research tools with which to investigate the functional behaviour of the kidney and other electrolyte-transporting tissues. Despite many remaining gaps in our knowledge of the biochemical processes involved in diuretic drug action, available compounds can be divided into 5 groups on the basis of their preferential effects on different segments of the nephron involved in tubular reabsorption of sodium chloride and water. Firstly, there is heterogeneous group of chemicals that share the common property of powerful, short-lived diuretic effects that are complete within 4 to 6 hours. These agents act on the thick ascending limb of Henle's loop and are known as 'high ceiling' or 'loop' diuretics. The second group are the benzothiadiazines and their many related heterocyclic variants, all of which localise their effects to the early portion of the distal tubule. The third group comprises the potassium-sparing diuretics which act exclusively on the Na+-K+/H+ exchange mechanisms in the late distal tubule and cortical collecting duct. The action of drugs in groups 2 and 3 is prolonged to between 12 and 24 hours. The fourth group consists of diuretics that are chemically related to ethacrynic acid but have the unusual property of combining within the same molecule the property of saluresis and uricosuria. These compounds have actions, to different individual extents, in the proximal tubule, thick ascending limb, and early distal tubule and are known as 'polyvalent' diuretics. Finally, there is a mixed group of weak or adjunctive diuretics which includes the vasodilator xanthines such as aminophylline, and the osmotically active compounds such as mannitol. Available evidence on the molecular mechanisms of action of diuretics in each group is reviewed. The haemodynamic, humoral and physical factors involved in control of electrolyte and fluid handling by the kidney in normal conditions and pathological states are discussed in relation to rational choices of different diuretics in the treatment of various oedematous and non-oedematous conditions.

Comparative pharmacokinetic profiles of metoprolol and chlorthalidone administered alone or in combination to healthy volunteers

A potential pharmacokinetic interaction between the beta-blocking drug, metoprolol, and the diuretic, chlorthalidone, has been investigated in three single or multiple dose studies in healthy volunteers. The pharmacokinetic profile of metoprolol 100 mg was not affected by pretreatment with or co-administration of chlorthalidone 25 mg twice daily. Similarly, the pre-dosing steady-state level of chlorthalidone during chronic treatment and its blood level profile after a single 25 mg dose were not affected by metoprolol. The bioavailabilities of the 2 drugs administered in combination were identical to those observed when each drug was administered alone. These studies demonstrate that there is no pharmacokinetic interaction between metoprolol and chlorthalidone when doses of 100 and 25 mg, respectively, are co-administered twice daily.

Pharmacokinetics of hydroflumethiazide during repeated administration in congestive heart failure

The renal elimination and accumulation of hydroflumethiazide (HFT) during repeated oral administration was investigated in patients with congestive heart failure (CHF). When four doses of HFT wee given with 24 hr intervals, the mean 24 hr urinary excretion of HFT was 55-65% of the dose after 75 mg and 53-57% after 150 mg. 24 hr excretion of HFT was not significantly higher after the fourth dose as compared with the first. The renal plasma clearance of HFT was significantly correlated with creatinine clearance (P less than 0.01). The biological half-life (t1/2 beta) of HFT ranged from 6.5-27.9 hrs. Mean t1/2 beta was shorter (P less than 0.05) after 75 mg (9.2 hrs) than after 150 mg doses (14.1 hrs). The disposition rate constant of HFT was not significantly correlated with creatinine clearance or with renal plasma clearance of HFT, indicating that the volume of distribution was reduced at reduced renal function.

Relative bioavailability of chlorthalidone in humans: adverse influence of polyethylene glycol

The bioavailability of two commercial preparations of chlorthalidone was studied in healthy male subjects. Reference solutions/suspensions for the two products were chlorthalidone dissolved in a solution of water-polyethylene glycol and a solution/suspension of chlorthalidone. Bioavailability of the chlorthalidone in water-polyethylene glycol solution was significantly reduced in comparison to one of the commercial preparations, and trends in the data suggested that it was less well absorbed than either the chlorthalidone in water solution/suspension or the other commercial preparation of chlorthalidone. These data, together with previous reports indicating that polyethylene glycol may retard the absorption of some drugs in vitro, suggest that this compound should not be used to aid dissolution of drug in a reference standard for bioavailability investigations.

A pharmacokinetic and pharmacodynamic assessment of a combined slow-release metoprolol-chlorthalidone preparation

Beta adrenoceptor blocking drugs and diuretics are frequently given together to control hypertension and increasingly the two agents are being combined in a single preparation. Possible interactions between the two agents are therefore of interest. In this study the addition of chlorthalidone has been shown not to influence the plasma levels or beta-blocking action of a sustained release form of metoprolol. In addition, when the combination product containing sustained release metoprolol and chlorthalidone is given over 21 days, the plasma levels of each drug are similar to those reported for each drug when given alone.

Biliary excretion of chlorthalidone in humans

A single oral dose of the diuretic chlorthalidone (100 or 200 mg) was given to six cholecystectomized patients with T-tube drainage of the common bile duct, and the 24 h bile and urine were collected during 3--7 days. Urinary recovery of chlorthalidone was 23--27 per cent of the dose, which is in the range of that in healthy volunteers. Chlorthalidone concentration in bile was 11--44 times lower than urine concentration in corresponding periods, and biliary recovery was only 0.6--1.4 per cent of the dose. When compared from equal periods of sampling of bile and urine, the same relative amount of drug was found in bile, whether the 100 or 200 mg dose had been given (viz., a fraction of 2.5--4.7 per cent and 2.5--5.7 per cent of corresponding urinary amounts respectively). It was concluded that excretion into bile constitutes only a minor route of elimination for unchanged chlorthalidone. Bile samples treated with glucuronidase and sulphatase showed no increase of chlorthalidone concentration. The open acid analogue of chlorthalidone, 3-(4-chloro-3-sulphamoylbenzoyl)-benzoic acid, was apparently not formed as a human metabolite, as evidenced by gas chromatographic analysis of both urine and bile.

Pharmacokinetics of chlorthalidone. Dependence of biological half life on blood carbonic anhydrase levels

The relationship between the whole blood concentration of carbonic anhydrase and the biological half life of chlorthalidone has been investigated in six volunteers. A linear relationship was observed and on the basis of this, a pharmacokinetic model to explain the long and variable biological half life of chlorthalidone is proposed and discussed.

Antihypertensive effect of oxprenolol and chlorthalidone in fixed combination, given once daily

In a multicentre, single-blind, within-patient study, the effectiveness and tolerability of the fixed combination oxprenolol 80 mg + chlorthalidone 10 mg per tablet given once daily, compared to the well established b.i.d. schedule, has been investigated in forty out-patients with mild to moderate hypertension. After a two-weeks placebo wash-out, twenty patients were given 1 tablet b.i.d. of the fixed combination for 4 weeks and thereafter 2 tablets once-daily for a further 4 weeks; the remaining twenty patients were given the fixed combination in the reverse order. There was no significant difference in clinical response between the two treatment regimes, which were equally effective and well tolerated. However, patient compliance might be considerably improved with the once-daily dosage schedule of the fixed combination.

Automated analysis of chlorthalidone

Chlorthalidone inhibition of the enzymatic hydrolysis rate of p-nitrophenyl acetate by bovine erythrocyte carbonic anhydrase was used as a basis for chlorthalidone determination in plasma and urine. For urinary samples, a completely automated, continuous flow system was developed to extract the samples and perform the enzymatic reaction. Over 100 samples per day could be assayed by one person. The assay had a sensitivity of 0.5 micrograms/ml and thus could determine urinary concentrations after a therapeutic chlorthalidone dose. To determine plasma concentrations after a therapeutic dose, a manual extraction procedure was used in combination with a second continuous flow system for the enzymatic reaction. This system was optimized to detect the lowest chlorthalidone concentration allowed by the enzymatic inhibition constant and could detect 25 ng/ml.

Absolute bioavailability of chlorthalidone in man: a cross-over study after intravenous and oral administration

Seven normal human volunteers each received a constant-rate infusion of chlorthalidone for 2 h, and the same (commonly 50 mg) single oral dose on separate occasions. The concentration of unchanged chlorthalidone was analyzed over a 100 to 220 h period in plasma, red blood cells, urine and faeces after both dosage forms. A three compartment model was required to describe the intravenous plasma concentrations in five of the subjects. A two compartment model sufficed to account for the decay of the oral plasma concentrations in all seven subjects. The mean plasma t1/2 after i.v. dosing was 36.5 h (+/- 10.5 SD), and the mean plasma t1/2 after oral doses was 44.1 h (+/- 9.6 SD). The mean red blood cell concentration t1/2 after i.v. doses was 46.4 h (+/- 9.9 SD), and the mean red blood cell t1/2 after the oral doses was 52.7 h (+/- 9.0 SD). The shorter i.v. half-live was not equally manifest in all subjects, being mainly apparent in three of them. In all cases the urinary excretion rate plots were parallel to the plasma concentration curves. As the faster decay after i.v. administration was not accompanied by increased renal clearance, the difference must have been due to non-renal mechanism. The mean total of 65.4 (+/- 8.6 SD) % of the intranvenous dose was excreted in urine over infinite time, whereas the mean total excretion after the oral dose was 43.8 (+/- 8.5 SD) %. Faecal excretion ranged from 1.3--8.5% of dose in the i.v. study to 17.5--31.2% of dose in the oral study. The sum of the amounts present in urine plus faeces pointed strongly to an important metabolic route of elimination of chlorthalidone. Bioavailability estimates (F) from three sets of data were--a mean F of 0.61 from plasma concentrations, 0.67 from urinary excretion measurements and 0.72 from the erythrocyte concentrations. Simulations with a non-linear model indicated lesser validity of the estimate from erythrocyte concentrations. It was concluded that the average of plasma and urine data, F = 0.64, yielded the best estimate of the oral availability of chlorthalidone 50 mg in man.