Chlorthalidone: Mechanisms of Action and Effect on Cardiovascular Events

The Evolving Role of Chlorthalidone and Hydrochlorothiazide as First-Line Treatments for Hypertensive Patients

Hypertension is attributable long-term to various negative health outcomes, including atherosclerotic cardiovascular disease and, more broadly, to cardiovascular events such as congestive heart disease, myocardial infarction, heart failure, and stroke. Effective hypertension treatment is essential to lower the risk of these outcomes. Treatment of hypertension includes both nonpharmacologic and, if necessary, pharmacologic interventions. The drug classes proven in trials to decrease the risk of cardiovascular disease events in cases with hypertension include angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, thiazide diuretics, and calcium channel blockers. When considering thiazide diuretics as a first-line treatment, chlorthalidone (CTD) is currently recommended by the American College of Cardiology over hydrochlorothiazide (HCTZ). Previous studies have demonstrated that CTD is superior to HCTZ in preventing cardiovascular disease events. However, more recent studies have revealed that there is no significant difference in the results of patients treated with HCTZ versus those treated with CTD. Additionally, studies have revealed CTD has worse outcomes regarding side effects when compared to HCTZ. In this regard, it is essential to carefully consider which medication will best improve the outcomes of patients with hypertension while also causing few or easily manageable side effects.

Comparative antiplatelet effects of chlorthalidone and hydrochlorothiazide

Chlorthalidone (CTD) may be superior to hydrochlorothiazide (HCTZ) in the reduction of adverse cardiovascular events in hypertensive patients. The mechanism of the potential benefit of CTD could be related to antiplatelet effects. The objective of this study was to determine if CTD or HCTZ have antiplatelet effects. This study was a prospective, double‐blind, randomized, three‐way crossover comparison evaluating the antiplatelet effects of CTD, HCTZ, and aspirin (ASA) in healthy volunteers. The effects of these treatments on platelet activation and aggregation were assessed using a well‐established method with five standard platelet agonists. Thirty‐four patients completed the three‐way crossover comparing pre‐ and post‐treatment changes in platelet activation and aggregation studies. There were statistically significant antiplatelet effects with ASA but not with CTD or HCTZ. Hypokalemia occurred in 0 (0%), 10 (30%), and 6 (18%) of the ASA, CTD, and HCTZ patients, respectively. The results of our study suggest that the benefits of CTD and HCTZ in reducing adverse cardiovascular events in patients with hypertension is not a result of an antiplatelet effect. In our study, hypokalemia with CTD was more prevalent than that reported in a large outcome trial in patients with hypertension. The clinical relevance of this finding is uncertain.

Genetic Contributors of Efficacy and Adverse Metabolic Effects of Chlorthalidone in African Americans from the Genetics of Hypertension Associated Treatments (GenHAT) Study

Hypertension is a leading risk factor for cardiovascular disease mortality. African Americans (AAs) have the highest prevalence of hypertension in the United States, and to alleviate the burden of hypertension in this population, better control of blood pressure (BP) is needed. Previous studies have shown considerable interpersonal differences in BP response to antihypertensive treatment, suggesting a genetic component. Utilizing data from 4297 AA participants randomized to chlorthalidone from the Genetics of Hypertension Associated Treatments (GenHAT) study, we aimed to identify variants associated with the efficacy of chlorthalidone. An additional aim was to find variants that contributed to changes in fasting glucose (FG) in these individuals. We performed genome-wide association analyses on the change of systolic and diastolic BP (SBP and DBP) over six months and FG levels over 24 months of treatment. We sought replication in the International Consortia of Pharmacogenomics Studies. We identified eight variants statistically associated with BP response and nine variants associated with FG response. One suggestive LINC02211-CDH9 intergenic variant was marginally replicated with the same direction of effect. Given the impact of hypertension in AAs, this study implies that understanding the genetic background for BP control and glucose changes during chlorthalidone treatment may help prevent adverse cardiovascular events in this population.

Exploration of 1, 2-naphthoquinone-4-sulfonate derivatizing reagent for determination of chlorthalidone in tablets: a spectrophotometric investigation

Background

Chlorthalidone is a diuretic medicinal agent used to treat hypertension. Lowering hypertension results in the prevention of strokes, heart attacks and kidney-related problems.

Results

In this work, the spectrophotometric investigation was employed to examine the reaction between chlorthalidone and 1, 2-naphthoquinone-4-sulfonate. A reaction is performed at the alkaline environment (pH 9.2) and heated at a moderate temperature of 60 ± 1 °C using a water bath. The red colour product was produced, and it displayed a maximum absorbance at 440.50 nm. Further, the advancement of response conditions was explored by UV/visible spectrophotometer. The stoichiometric of the reaction was considered by using Job’s plot and the reaction mechanism of the proposed work was drawn. The established approach obeyed the calibration curve in the concentration range of 2–12 μg/mL with a regression coefficient superior to 0.994. The accuracy of the method, assessed by employing the % recovery, was in the range of 99.06–99.60% with the % relative standard deviation being less than 2%. The limit of detection and limit of quantification were 0.58 μg/mL and 1.72 μg/mL, respectively.

Conclusion

A UV/visible spectrophotometric investigation for the analysis of the chlorthalidone in the tablet matrix was successfully established and validated. The established investigation was found to be simple and accurate, and because of its ease of use, the proposed strategy could be applied for quality control investigation of chlorthalidone in pharmaceutical matrices.

Hydrochlorothiazide Reduces Cardiac Hypertrophy, Fibrosis and Rho-Kinase Activation in DOCA-Salt Induced Hypertension

BACKGROUND

Thiazides are one of the most common antihypertensive drugs used for hypertension treatment and hydrochlorothiazide (HCTZ) is the most frequently used diuretic for hypertension treatment. The Rho/Rho-kinase (ROCK) path plays a key function in cardiovascular remodeling. We hypothesized that in preclinical hypertension HCTZ reduces myocardial ROCK activation and consequent myocardial remodeling.

METHODS

The preclinical model of deoxycorticosterone (DOCA)-salt hypertension was used (Sprague-Dawley male rats). After 3 weeks, in 3 different groups: HCTZ, the ROCK inhibitor fasudil or spironolactone was added (3 weeks). After 6 weeks myocardial hypertrophy and fibrosis, cardiac levels of profibrotic proteins, mRNA levels (RT PCR) of pro remodeling and pro oxidative molecules and ROCK activity were determined.

RESULTS

Blood pressure, myocardial hypertrophy and fibrosis were reduced significantly by HCTZ, fasudil and spironolactone. In the heart, increased levels of the pro-fibrotic proteins Col-I, Col-III and TGF-β1 and gene expression of pro-remodeling molecules TGF-β1, CTGF, MCP-1 and PAI-1 and the pro-oxidative molecules gp91phox and p22phox were significantly reduced by HCTZ, fasudil and spironolactone. ROCK activity in the myocardium was increased by 54% (P < 0.05) as related to the sham group and HCTZ, spironolactone and fasudil, reduced ROCK activation to control levels.

CONCLUSIONS

HCTZ reduced pathologic LVH by controlling blood pressure, hypertrophy and myocardial fibrosis and by decreasing myocardial ROCK activation, expression of pro remodeling, pro fibrotic and pro oxidative genes. In hypertension, the observed effects of HCTZ on the myocardium might explain preventive outcomes of thiazides in hypertension, specifically on LVH regression and incident heart failure.

Thiazide and other Cl-benzenesulfonamide-bearing clinical drug affinities for human carbonic anhydrases

Twelve carbonic anhydrase (CA) isoforms catalyze carbon dioxide hydration to bicarbonate and acid protons and are responsible for many biological functions in human body. Despite their vital functions, they are also responsible for, or implicated in, numerous ailments and diseases such as glaucoma, high altitude sickness, and cancer. Because CA isoforms are highly homologous, clinical drugs designed to inhibit enzymatic activity of a particular isoform, can also bind to others with similar affinity causing toxic side effects. In this study, the affinities of twelve CA isoforms have been determined for nineteen clinically used drugs used to treat hypertension related diseases, i.e. thiazides, indapamide, and metolazone. Their affinities were determined using a fluorescent thermal shift assay. Stopped flow assay and isothermal titration calorimetry were also employed on a subset of compounds and proteins to confirm inhibition of CA enzymatic activity and verify the quantitative agreement between different assays. The findings of this study showed that pharmaceuticals could bind to human CA isoforms with variable affinities and inhibit their catalytic activity, even though the drug was intended to interact with a different (non-CA) protein target. Relatively minor structural changes of the compounds may cause significant changes in affinity and selectivity for a particular CA isoform.

Pharmacokinetics of a Fixed-Dose Combination of Amlodipine/Losartan and Chlorthalidone Compared to Concurrent Administration of the Separate Components

Hypertension is more effectively treated with coadministration of 2 or more antihypertensive drugs than with high-dose monotherapy. Therefore, calcium channel blockers, angiotensin II receptor blockers, and thiazides are coadministered to treat hypertension. The objective of this study was to compare the pharmacokinetic (PK) profiles of HCP1401, a fixed-dose combination of amlodipine 5 mg, losartan 100 mg, and chlorthalidone 25 mg, with the separate components (loose combination) of amlodipine/losartan 5/100 mg and chlorthalidone 25 mg. A randomized, open-label, single-dose, 2-way crossover study was conducted. Blood samples for amlodipine and chlorthalidone were collected for up to 144 hours after dosing, whereas those for losartan were collected up to 48 hours after dosing. The PK parameters of these drugs were calculated using a noncompartmental method. Sixty subjects completed the study. The geometric mean ratios and 90% confidence intervals of maximum plasma concentration and area under the concentration-time curve to the last measurable point for amlodipine, losartan, and chlorthalidone were within the conventional bioequivalence range of 0.80 to 1.25. There were no clinically significant changes in safety assessments, and the treatments were well tolerated. The PK characteristics and tolerability profiles of a single oral FDC of amlodipine, losartan, and chlorthalidone were equivalent to those of individual tablets in a loose combination.

Chlorthalidone versus hydrochlorothiazide: major cardiovascular events, blood pressure, left ventricular mass, and adverse effects

BACKGROUND

There is continuous debate whether chlorthalidone (CTD) and hydrochlorothiazide (HCTZ) differ in reducing major cardiovascular events (MACE). HCTZ is prescribed 10 times more commonly than CTD.

METHOD

A systematic literature search yielded 14 references, including two network meta-analyses of randomized trials with MACE and left ventricular mass as outcomes.

RESULTS

The network meta-analysis of randomized trials showed CTD reducing MACE more than HCTZ, hazard ratio = 0.79 (0.72-0.88), P < 0.0001, and an observational cohort study gave an identical point estimate: hazard ratio = 0.79 (0.68-0.92), P = 0.002. In contrast, two observational cohort studies reported no differences between CTD and HCTZ. However, in the studies showing the superiority of CTD median follow-up was 4.3 and 7.0 years, respectively, whereas in the latter studies showing no difference between the two drugs follow-up was only 0.95 and 0.25 years. As differences in outcomes for MACE in hypertension trials with various interventions only emerge after prolonged (>1 year) therapy, differences in follow-up explain these discrepant results. CTD also more effectively reduced left ventricular mass in observational data and network analysis of trials. These advantages of CTD over HCTZ are consistent with greater reductions in night-time blood pressure, greater reductions in oxidative stress and platelet aggregation, and greater improvements in endothelial function.

CONCLUSION

Over the short-term there were no differences in the net clinical benefit between HCTZ and CTD. However, long-term available data document CTD to be significantly more effective in reducing MACE than HCTZ. The Veterans Administration's trial in progress may provide definitive answer to these questions.

Network meta-analysis of efficacy and safety of chlorthalidone and hydrochlorothiazide in hypertensive patients

Hypertension is a chronic condition leading to increased stress on the heart and blood vessels, a critical risk factor for clinically significant events such as myocardial infarction heart failure, stroke and death. Chlorthalidone and hydrochlorothiazide are first-line antihypertensive agents for most patients with hypertension. The aim of our meta-analysis was to compare the efficacy and safety of both therapies in patients with hypertension. Searches of electronic databases PubMed, MEDLINE, Scopus, PsycInfo and eLIBRARY.ru, were performed. We used network meta-analysis to combine direct and indirect evidence. Forest plots and closed loops depict estimated results from studies included in our meta-analysis. Of 1289 identified sources, only 37 were included in our meta-analysis. Our analysis has demonstrated a slight superiority for chlorthalidone regarding SBP and not statistically significant differences regarding DBP. Simultaneously, hydrochlorothiazide seems to be a safer choice of therapy, as evidenced by the levels of serum potassium. The two diuretics can be used interchangeably.

Prevention of Heart Failure in Hypertension-Disentangling the Role of Evolving Left Ventricular Hypertrophy and Blood Pressure Lowering: The ALLHAT Study

Background

Hypertension is a known risk factor for heart failure (HF), possibly via the mechanism of cardiac remodeling and left ventricular hypertrophy (LVH). We studied the extent to which blood pressure (BP) change and evolving LVH contribute to the effect that lisinopril, doxazosin, and amlodipine have on HF compared with chlorthalidone.

Methods and Results

We conducted causal mediation analysis of ALLHAT (Antihypertensive and Lipid‐Lowering Treatment to Prevent Heart Attack Trial) data (1994‐2002; in‐trial follow‐up). ALLHAT participants with available serial ECGs and BP measurements were included (n=29 892; mean age 67±4 years; 32% black; 56% men): 11 008 were randomized to chlorthalidone, 5967 to doxazosin, 6593 to amlodipine, and 6324 to lisinopril. Evolving ECG LVH and BP lowering served as mediators. Incident symptomatic HF was the primary outcome. Linear regression (for mediator) and logistic regression (for outcome) models were adjusted for mediator‐outcome confounders (demographic and clinical characteristics known to be associated both with both LVH/hypertension and HF). A large majority of participants (96%) had ECG LVH status unchanged, but 4% developed evolving ECG LVH. On average, BP decreased by 11/7 mm Hg. In adjusted Cox regression analyses, progressing ECG LVH (hazard ratio [HR] 1.78 [95% CI 1.43‐2.22]), resolving ECG LVH (HR 1.33 [95% CI 1.03‐1.70]), and baseline ECG LVH (1.17 [95% CI 1.04‐1.31]) carried risk of incident HF. After full adjustment, evolving ECG LVH mediated 4% of the effect of doxazosin on HF. Systolic BP lowering mediated 12% of the effect of doxazosin, and diastolic BP lowering mediated 10% of the effect of doxazosin, 7% of the effect of amlodipine, and borderline 9% of the effect of lisinopril on HF.

Conclusions

Evolving ECG LVH and BP change account for 4% to 13% of the mechanism by which antihypertensive medications prevent HF.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00000542.

See Editorial Ferdinand and Maraboto

Stability Indicating Method to Analyze Benidipine and Chlorthalidone Using HPLC Technique: Establishment, Validation and Application to Tablets

Background : The combination of chlorthalidone and benidipine was used to manage hypertension. The mixture of chlorthalidone and benidipine in tablet dosage form has not been previously determined by any method. A stability indicating HPLC method was developed for the simultaneous determination of benidipine and chlorthalidone in bulk and tablets. Methods: Chromatographic separation was accomplished in a reverse phase system using an isocratic elution with a mobile phase composed of methanol-0.1M dipotassium hydrogen phosphate buffer (40:60, v/v), at 1 ml/min flow rate. The photodiode array (PDA) detector set at 260 nm was used to detect and quantify benidipine and chlorthalidone. Benidipine and chlorthalidone tablet samples were subjected to degradation under acid, neutral, alkali, thermal, photo and oxidative. The proposed method was effectively adapted to quantify benidipine and chlorthalidone in the combined tablet formulation. Results: The elution times for benidipine and chlorthalidone were approximately 4.573 min and 6.422 min, respectively. The method was validated within a concentration range of 2 - 6 μg/ml (R2 = 0.9997) for benidipine and 6.25 - 18.75 μg/ml (R2 = 0.9998) for chlorthalidone. Adequate results were obtained for precision (RSD% = 0.106% for benidipine and RSD% = 0.031% for chlorthalidone) and accuracy (99.95 - 100.25 % mean recovery for benidipine and 99.60 - 99.63% mean recovery for chlorthalidone). Robustness has also been found to be acceptable. During the degradation study, interference was not noticed in the analysis of studied drugs. Conclusion: The findings demonstrated that the method could be useful for determination of the selected drug combination in routine analysis.

Is Electrocardiography-Left Ventricular Hypertrophy an Obsolete Marker for Determining Heart Failure Risk With Hypertension?

See Article Johnson et al.

Compelling therapy of LVH: straight (and not-so-straight) inferences from evidence

We have read with interest the Korean Society of Hypertension guidelines for the management of hypertension and congratulate the Society for an extensive review of literature while drafting the guidelines. The guidelines indicate preferring ACE-I and CCB over diuretics in patients with left ventricle hypertrophy. However, in landmark head-to-head comparison trials, the thiazide-like diuretic chlorthalidone has been shown to be superior to ACE-I and CCB in decreasing left ventricle mass and preventing heart failure in hypertensive patients. Also, we put forth the paradoxical finding that mere regression of LVH may not always translate into reduction in risk of HF; and that the pleiotropic effects of chlorthalidone may be the explanation behind its beneficial action in HF.

Approach to Antihypertensive Therapy

Antihypertensive agents are commonly prescribed by physicians to prevent the long-term mortality from chronic hypertension. They are also given to improve survival in a number of conditions (eg, heart failure, coronary artery disease), independent of the effect on blood pressure. Several classes of antihypertensives are available with unique pharmacologic characteristics and adverse effects. Not all agents in the same class have identical effects, and careful selection of drugs based on the comorbid conditions is recommended.

Hypertension subtypes modify metabolic response to thiazide diuretics

BACKGROUND

Blood pressure (BP) and metabolic response to thiazide diuretics might be varied in patients with different hypertension subtypes and ethnicities. This study aimed to investigate the response of BP and metabolic profiles to short-term thiazide treatment in an Asian cohort with different hypertension subtypes.

DESIGN

Serial ethnic Chinese nondiabetic subjects with hypertension were evaluated. After diet instruction and lifestyle modification for 2 weeks, patients who still had elevated systolic BP (SBP≥140 mmHg) and/or diastolic BP (DBP≥90 mmHg) were given 50 mg of hydrochlorothiazide daily for 2 weeks. The responses of BP and metabolic profiles were evaluated before and after treatment according to the patient's baseline BP subtype - isolated systolic hypertension (ISH), systo-diastolic hypertension (SDH) and isolated diastolic hypertension (IDH).

RESULTS

Hydrochlorothiazide treatment significantly reduced the BP in all 92 patients (62 males, aged 45·7 ± 9·6 years), irrespective of their baseline BP subtypes. In patients with SDH (n = 39) or IDH (n = 40), hydrochlorothiazide treatment significantly increased serum adiponectin (P = 0·001 and 0·007, respectively) and reduced asymmetric dimethylarginine levels (P < 0·001, in both groups). Serum cholesterol (P = 0·027) and fasting blood sugar levels (P = 0·044) were significantly improved only in the IDH patients. Furthermore, IDH was independently associated with changes in fasting blood sugar (β = -11·178, P = 0·022) and cholesterol (β = -22·654, P = 0·027).

CONCLUSIONS

The characteristics of the Asian hypertensive patients with diastolic hypertension can present a favourable metabolic response to the short-term hydrochlorothiazide treatment. The potential positive effect on cardiovascular risk should be validated in long-term studies in this diastolic type of hypertension.

New insights into carbonic anhydrase inhibition, vasodilation, and treatment of hypertensive-related diseases

Carbonic anhydrase (CA) and its inhibitors are relevant to many physiological processes and diseases. The enzyme is differentially expressed throughout the body, in concentration and subcellular location, and as 13 catalytically active isoforms. Blood vessels contain small amounts of CA, but the enzyme's role in vascular physiology and blood pressure regulation is uncertain. However, considerable recent evidence points to vasodilation by CA inhibitors. CA inhibition in vascular smooth muscle, endothelium, heart, blood cells, and nervous system could all contribute. It is equally plausible that other targets besides CA for all known CA inhibitors may account for their vascular effects. I will review this knowledge and important remaining gaps relating to treatment of hypertensive-related diseases with potent sulfonamide inhibitors, such as acetazolamide; but also the possibility that CA inhibition by thiazides and loop diuretics, although generally weaker, may have antihypertensive effects beyond their inhibition of renal sodium transporters.

Pharmacogenetic effects of 'candidate gene complexes' on stroke in the GenHAT study

OBJECTIVE

The aim of this study was to investigate whether there is a genotype-by-treatment interaction in patients experiencing stroke and treated with one of three antihypertensive drugs, that is chlorthalidone, amlodipine, or lisinopril.

PARTICIPANTS AND METHODS

A population of 436 African Americans and 539 whites who had experienced stroke in the GenHAT study were genotyped for 768 single nucleotide polymorphisms (SNPs) in 280 candidate genes. To detect a genotype-by-treatment interaction, we used the Pearson's χ-test to assess whether the genotype frequencies differed at the single SNP level for the three drug treatment groups. From these single SNP analyses, we derived a summary statistic for the degree of association at the gene and gene complex levels. This was done by grouping SNPs using information on gene locations and defining gene complexes on the basis of protein-protein interactions. To assess the statistical significance of the observed test statistic, we derived an empirical P-value by simulating data under the null hypothesis.

RESULTS

We found that, in patients who have experienced stroke, there is a significant genetic difference between hypertension drug treatment groups. In African Americans, SNP rs12143842 showed a significant association (P<0.001) with drug treatment. At the gene level, HNRNPA1P4 and NOS1AP in African Americans and PRICKLE1 and NINJ2 in non-Hispanic whites were significantly associated (P<0.01) with drug treatment, whereas none of the gene complexes tested showed significance.

CONCLUSION

On the basis of the genetic differences between drug treatment groups, we conclude that there may be an interaction between certain genotypes and antihypertensive treatment in stroke patients. This needs to be replicated in other studies.

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.

Which thiazide to choose as add-on therapy for hypertension?

Combined therapy is required in the majority of patients with hypertension to achieve blood pressure (BP) targets. Although different antihypertensive drugs can be combined, not all combinations are equally effective and safe. In this context, the combination of a renin angiotensin system inhibitor with a diuretic, usually a thiazide, particularly hydrochlorothiazide (HCTZ) or thiazide-like diuretics, such as chlorthalidone or indapamide, is recommended. However, not all diuretics are equal. Although HCTZ, chlorthalidone, and indapamide as add-on therapy effectively reduce BP levels, the majority of studies have obtained greater BP reductions with chlorthalidone or indapamide than with HCTZ. Moreover, there are data showing benefits with chlorthalidone or indapamide beyond BP. Thus, chlorthalidone seems to have pleiotropic effects beyond BP reduction. Moreover, compared with placebo, chlorthalidone has small effects on fasting glucose and total cholesterol, and compared with HCTZ, chlorthalidone achieves significantly lower total cholesterol and low-density lipoprotein cholesterol levels. Similarly, indapamide has demonstrated no negative impact on glucose or lipid metabolism. More importantly, although head-to-head clinical trials comparing the effects of indapamide or chlorthalidone with HCTZ are not available, indirect comparisons and post hoc analyses suggest that the use of chlorthalidone or indapamide is associated with a reduction in cardiovascular events. Despite this, the most frequent diuretic used in clinical practice as add-on therapy for hypertension is HCTZ. The purpose of this review is to update the published data on the efficacy and safety of HCTZ, chlorthalidone, and indapamide as add-on therapy in patients with hypertension.

Safety of carbonic anhydrase inhibitors

INTRODUCTION

Carbonic anhydrase (CA) inhibitors have an impressive safety record despite the multiple functions that CA isozymes serve because they are not fully inhibited with most dosing. While reducing the targeted CA-dependent process sufficiently for disease control, residual activity and uncatalyzed rates in combination with compensations are adequate to avoid lethal consequences. Some drugs have in vitro selectivity differences against the 13 active isozymes, but none are convincingly selective in vivo or clinically. Efforts to synthesize selective inhibitors should result in safer drugs with fewer side effects.

AREAS COVERED

This review will focus on approved drugs with CA-inhibiting activity, whether used directly for this purpose or others. Side effects are discussed in relation to various organ systems and the disease being treated. Causes of side effects are considered, and strategies for symptom reduction are given.

EXPERT OPINION

Common side effects of paresthesias, dyspepsia, lassitude and fatigue in 30 - 40% of patients are generally tolerable or abate, but if not can be partially relieved by bicarbonate supplementation. The most important safety concerns are severe acidosis, respiratory failure and encephalopathy in patients with renal, pulmonary and hepatic disease where caution is critical, as is also the case in persons with sulfa drug allergies.