Diuretic treatment of resistant hypertension

Hypertension meets osteoarthritis - revisiting the vascular aetiology hypothesis

Osteoarthritis (OA) is a whole-joint disease characterized by subchondral bone perfusion abnormalities and neovascular invasion into the synovium and articular cartilage. In addition to local vascular disturbance, mounting evidence suggests a pivotal role for systemic vascular pathology in the aetiology of OA. This Review outlines the current understanding of the close relationship between high blood pressure (hypertension) and OA at the crossroads of epidemiology and molecular biology. As one of the most common comorbidities in patients with OA, hypertension can disrupt joint homeostasis both biophysically and biochemically. High blood pressure can increase intraosseous pressure and cause hypoxia, which in turn triggers subchondral bone and osteochondral junction remodelling. Furthermore, systemic activation of the renin-angiotensin and endothelin systems can affect the Wnt-β-catenin signalling pathway locally to govern joint disease. The intimate relationship between hypertension and OA indicates that endothelium-targeted strategies, including re-purposed FDA-approved antihypertensive drugs, could be useful in the treatment of OA.

Maintenance of negative fluid balance can improve endothelial and cardiac functions in primary hypertensive patients

PURPOSE

The issue of unidentified volume expansion is well recognized as a cause for resistance to antihypertensive therapy. The aim of study is to identify contribution of negative fluid balance to hypertension control and impact on endothelial and cardiac functions among primary hypertensive patients who do not have kidney failure.

MATERIALS AND METHODS

This is a prospective interventional study with one-year follow-up. Preceded by volume status measurements were performed by a body composition monitor (BCM), the patients were put on ambulatory blood pressure monitoring for 24 hours. Then, echocardiographic assessments and flow-mediated dilation (FMD) and carotid intima-media thickness (CIMT) measurements were completed. Patients in one of the two groups were kept negative hydrated during trial with diuretic treatment.

RESULTS

At the end of one-year follow-up, patients in negative hydrated group were found to have significantly lower CIMT, left ventricle mass index, left ventricular end-diastolic diameter, mean systolic and diastolic BP, non-dipper patient ratio, and higher FMD. In negatively hydrated group, target organ damage significantly reduced during trial.

CONCLUSIONS

The significance of negative hydration status with respect to blood pressure control, endothelial and cardiac functions within primary hypertensive patients who do not suffer from kidney failure has been demonstrated.

Loop Diuretics in the Treatment of Hypertension

Loop diuretics are not recommended in current hypertension guidelines largely due to the lack of outcome data. Nevertheless, they have been shown to lower blood pressure and to offer potential advantages over thiazide-type diuretics. Torsemide offers advantages of longer duration of action and once daily dosing (vs. furosemide and bumetanide) and more reliable bioavailability (vs. furosemide). Studies show that the previously employed high doses of thiazide-type diuretics lower BP more than furosemide. Loop diuretics appear to have a preferable side effect profile (less hyponatremia, hypokalemia, and possibly less glucose intolerance). Studies comparing efficacy and side effect profiles of loop diuretics with the lower, currently widely prescribed, thiazide doses are needed. Research is needed to fill gaps in knowledge and common misconceptions about loop diuretic use in hypertension and to determine their rightful place in the antihypertensive arsenal.

Individualizing antihypertensive combination therapies: clinical and hemodynamic considerations

While there are strong trial data to guide the selection of initial hypertension treatment choice and limited data to support second agent choice, beyond the first two agents, subsequent steps are empiric. As medications are added, the resulting polypharmacy may be complex, inefficient and poorly tolerated, resulting in low treatment adherence rates. The selection of antihypertensive drug therapy based on hemodynamic mechanisms is not new but became practical with the availability of noninvasive hemodynamic parameters using impedance cardiography. Individualized therapy based on hormonal or hemodynamic measurements can effectively control hypertension as shown in several small clinical trials. Hemodynamic measurements are obtained quickly, painlessly and can be used in a serial fashion to guide treatment adjustments. Current limitations relate to availability of the measurement device and personnel trained in its use, reimbursement for the measurements, expertise in interpretation of the measurements and systems to adjust medication and repeat measurements in a serial fashion until targets are attained. The potential utility of this approach increases with greater complexity of the medication regimen. Further studies are indicated and may advance options for individualized treatment of hypertensive patients.

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.

Common secondary causes of resistant hypertension and rational for treatment

Resistant hypertension is defined as uncontrolled blood pressure despite the use of three antihypertensive drugs, including a diuretic, in optimal doses. Treatment resistance can be attributed to poor adherence to antihypertensive drugs, excessive salt intake, physician inertia, inappropriate or inadequate medication, and secondary hypertension. Drug-induced hypertension, obstructive sleep apnoea, primary aldosteronism, and chronic kidney disease represent the most common secondary causes of resistant hypertension. Several drugs can induce or exacerbate pre-existing hypertension, with non-steroidal anti-inflammatory drugs being the most common due to their wide use. Obstructive sleep apnoea and primary aldosteronism are frequently encountered in patients with resistant hypertension and require expert management. Hypertension is commonly found in patients with chronic kidney disease and is frequently resistant to treatment, while the management of renovascular hypertension remains controversial. A step-by-step approach of patients with resistant hypertension is proposed at the end of this review paper.

The role of aldosterone in resistant hypertension: Implications for pathogenesis and therapy

Resistant hypertension constitutes an increasingly common medical disorder. Although the exact incidence is not precisely known, estimates derived from recent outcome studies emphasize that resistant hypertension is much more common than previously thought. A major advance in our understanding of its pathogenesis and management is the recent recognition of the importance of aldosterone excess or autonomy as an important mechanism for drug resistance in hypertension. Recent studies of the effects of aldosterone on vascular smooth muscle have delineated several extra-renal mechanisms whereby aldosterone produces hypertension primarily by its direct vasoconstrictor effects and by altering vascular compliance. Consequently, aldosterone blockade constitutes an effective intervention for treating resistant hypertension.

Low-Dose Aldosterone Blockade as a New Treatment Paradigm for Controlling Resistant Hypertension

Treatment of resistant hypertension requires confirmation of true resistance, diagnosis and treatment of secondary causes of hypertension, adoption of appropriate lifestyle modifications, and effective use of multidrug antihypertensive regimens. Excessive volume retention often underlies resistant hypertension, so diuretics are generally necessary to achieve blood pressure (BP) goals. Although treatment regimens consisting of 3 or more agents have not been systematically evaluated, the author has found a triple regimen consisting of a thiazide diuretic, a calcium channel blocker, and an angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) to be generally effective and well tolerated. Although hydrochlorothiazide is more widely used, chlorthalidone provides better BP reduction and should be preferentially used in patients with resistant hypertension, particularly if the patient remains uncontrolled on hydrochlorothiazide. Recent studies have demonstrated that low doses of aldosterone antagonists, when added to multidrug regimens that include a thiazide diuretic and an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker, provide significant additional BP reduction, seemingly exceeding what would be expected with addition of alternative classes of agents. The degree of BP reduction induced by aldosterone blockade has been similar in patients with and without evidence of aldosterone excess. Aldosterone antagonists are generally safe and well tolerated. The most common adverse effect of low-dose spironolactone has been breast tenderness, occurring in about 10% of men. Hyperkalemia is uncommon, but can occur, necessitating biochemical monitoring. Risk of hyperkalemia is increased in patients with chronic kidney disease or diabetes, elderly patients, and patients already receiving an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker.

Can the dextroenantiomer of the aromatase inhibitor fadrozole be useful for clinical investigation of aldosterone-synthase inhibition?

The beneficial effects of spironolactone, eplerenone, amiloride and potassium in preventing cardiovascular damage in various experimental models of salt-induced hypertension can be dissociated from blood pressure effects, and have drawn attention to the direct genomic and non-genomic actions of aldosterone at the level of the vessels, the heart and the kidneys. Exposure to endogenous aldosterone could be decreased by direct and specific aldosterone-synthase inhibition. FAD 286A, the dextroenantiomer of the aromatase inhibitor fadrozole, might be a first candidate to investigate in humans, the physiological impact and therapeutic properties of aldosterone-synthase inhibition, especially in various forms of primary aldosteronism.

Treatment of resistant hypertension

Although the true prevalence of resistant hypertension is not known, it is likely that this condition will become increasingly common, driven by an aging population, obesity, nonadherence trends, and effects of target-organ disease. Current approaches focus on two goals: evaluation and correction of contributing causes, then selection of an effective drug regimen. Lifestyle factors contribute to resistance, particularly high sodium intake and weight gain. Secondary causes should be considered and corrected if feasible. Recent efforts have focused on the development of clinical pathways to guide treatment, based on plasma renin activity, aldosterone production, or hemodynamic measurements. The components of drug combinations beyond the second agent remain empiric. Although volume expansion plays a key role in drug resistance, clinical assessment of volume status is often difficult, frustrating efforts to achieve blood pressure control. Determination of the most effective approaches will require clinical trials using combination therapy.

Resistant hypertension, obesity, sleep apnea, and aldosterone: theory and therapy

Hypertension resistant to 2 antihypertensive drugs is more common among obese patients than among lean patients. The case we describe and the observations we report suggest that refractoriness among obese hypertensives is frequently caused by obstructive sleep apnea and/or inappropriately high plasma aldosterone levels. In other words, obese hypertensives may have sleep apnea, obese hypertensives without sleep apnea may have inappropriately elevated levels of plasma aldosterone, and a surprising number of obese patients with sleep apnea also have elevated levels of aldosterone. The mechanisms by which obesity and obstructive sleep apnea increase aldosterone levels and raise blood pressure are not understood, but sympathetic nervous system activation and production of nonclassical adrenal stimuli are two possibilities. Obstructive sleep apnea can be detected with a careful history and various sleep studies. Inappropriately elevated aldosterone levels can be detected by measuring the ratio of plasma aldosterone concentration to plasma renin activity. Successful treatment of these resistant hypertensives often can be achieved by devices that provide positive pressure to the upper airway to correct obstructive sleep apnea and by incorporating an aldosterone antagonist in the therapeutic regimen.

Resistant hypertension: comparing hemodynamic management to specialist care

Although resistant hypertension affects a minority of all hypertensives, this group continues to experience disproportionately high cardiovascular event rates despite newer antihypertensive agents. Hypertension represents an imbalance of hemodynamic forces within the circulation, usually characterized by elevated systemic vascular resistance. We studied the utility of serial hemodynamic parameters in the selection and titration of antihypertensive medication in resistant hypertensive patients using highly reproducible noninvasive measurements by thoracic bioimpedance. Resistant hypertension patients (n=104) were randomized to drug selection based either on serial hemodynamic (HD) measurements and a predefined algorithm or on drug selection directed by a hypertension specialist (SC) in a 3-month intensive treatment program. Blood pressure was lowered by intensified drug therapy in both treatment groups (169+/-3/87+/-2 to 139+/-2/72+/-1 mm Hg HD versus 173+/-3/91+/-2 to 147+/-2/79+/-1 mm Hg SC, P<0.01 for systolic and diastolic BP), using similar numbers and intensity of antihypertensive medications. Blood pressures were reduced further for those treated according to hemodynamic measurements, resulting in improved control rates (56% HD versus 33% SC controlled to </=140/90 mm Hg, P<0.05) and incremental reduction in systemic vascular resistance measurements. Although the number of patients taking diuretics did not differ between groups, final diuretic dosage was higher in the hemodynamic cohort. Our results demonstrate superior blood pressure control using a treatment algorithm and serial hemodynamic measurements compared with clinical judgment alone in a randomized prospective study. Our measurements of thoracic fluid volume support occult volume expansion as a mediator of antihypertensive drug resistance and use of impedance measurements to guide advancing diuretic dose and adjustment of multidrug antihypertensive treatment.

Prognosis in therapy-resistant hypertension

OBJECTIVES

To study the prognosis in therapy-resistant hypertension (RH).

DESIGN

Patients with RH and age- and sex-matched responding hypertensives, were followed-up for a period of 7 years.

SETTING

All subjects were outpatients at a secondary referral centre for hypertension.

SUBJECTS

(i) Age < or = 65 years; (ii) no prior diagnosis of secondary hypertension; (iii) on antihypertensive triple-drug therapy of optimal dosage; (iv) diastolic blood pressure remaining 5 mmHg above their (age-related) target pressure; (v) no history of renal failure, heart failure, stroke or myocardial infarction; and (vi) no record of noncompliance. A total of 800 patients were screened. Thirty-six were finally included. For each study patient, two control patients were randomly selected.

INTERVENTIONS

Continuous efforts to optimize blood pressure control were made in all patients.

MAIN OUTCOME MEASURES

Transient ischaemic attack or stroke, myocardial infarction, congestive heart failure, renal failure, and death. Development of non-insulin-dependent diabetes mellitus (NIDDM).

RESULTS

At the end of the follow-up period, RH had a casual functional blood pressure 2/6 mmHg higher than the control hypertensives. RH exhibited an increased incidence of stroke (P < 0.05), renal insufficiency (P < 0.05) and NIDDM (P < 0.05). RH patients had an increased risk of suffering an event during the 7 years [odds ratio (OR) 2.71; P < 0.05].

CONCLUSIONS

Resistance to antihypertensive therapy may persist even when therapy is aggressively applied in compliant patients. RH is associated to an increased risk of stroke and of target organ damage, foremost renal insufficiency. The apparent association between RH, obesity and NIDDM may imply that hyperinsulinaemia is involved in therapy resistance.

Diuretics. Clinical pharmacology and therapeutic use (Part II)

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 a 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. The metabolic consequences of continued diuretic usage are considered along with non-metabolic sequelae such as ototoxicity or interactions with other concurrent treatments. The relationships between the clinical benefits conferred and the potential harms generated by long term diuretic therapy are also discussed.

Preliminary evaluation of pinacidil in hypertension

In a balanced single-blind placebo controlled study in six hypertensive patients treated with diuretic and beta-adrenoceptor blocker, a single oral dose of 10 mg pinacidil lowered blood pressure significantly, by a maximum of 26/13 mm Hg lying and 15/12 mm Hg standing at 3 h. The duration of action was less than 6 h. Chronic treatment of four patients (mean dose 20 mg twice daily for 3--7 weeks) lowered blood pressure by only 15/7 mm Hg. All four patients experienced side-effects of the type often observed during treatment with potent vasodilators. In the formulation studied pinacidil is unlikely to offer any advantage over the antihypertensive drugs currently available.