Clinicopharmacological reappraisal of the potency of diuretics

Meta-analysis of dose-response relationships for hydrochlorothiazide, chlorthalidone, and bendroflumethiazide on blood pressure, serum potassium, and urate

Thiazide and thiazide-like diuretics are widely used in the management of hypertension, but recently the equivalence of hydrochlorothiazide and chlorthalidone for blood pressure (BP) lowering and prevention of cardiovascular disease has been questioned. We performed a meta-analysis to characterize the dose-response relationships for 3 commonly prescribed thiazide diuretics, hydrochlorothiazide, chlorthalidone, and bendroflumethiazide, on BP, serum potassium, and urate. Randomized, double-blind, parallel placebo-controlled trials meeting the following criteria, ≥ 2 different monotherapy dose arms, follow-up duration ≥ 4 weeks, and baseline washout of medication ≥ 2 weeks, were identified using Embase (1980-2010 week 50), Medline (1950-2010 November week 3), metaRegister of Controlled Trials, and Cochrane Central. A total of 26 trials examined hydrochlorothiazide, 3 examined chlorthalidone, and 1 examined bendroflumethiazide. Studies included a total of 4683 subjects in >53 comparison arms. Meta-regression of the effect of thiazides on systolic BP showed a log-linear relationship with a potency series: bendroflumethiazide>chlorthalidone>hydrochlorothiazide. The estimated dose of each drug predicted to reduce systolic BP by 10 mm Hg was 1.4, 8.6, and 26.4 mg, respectively, and there was no evidence of a difference in maximum reduction of systolic BP by high doses of different thiazides. Potency series for diastolic BP, serum potassium, and urate were similar to those seen for systolic BP. Hydrochlorothiazide, chlorthalidone, and bendroflumethiazide have markedly different potency. This may account for differences in the antihypertensive effect between hydrochlorothiazide and chlorthalidone using standard dose ranges.

Pharmacokinetic and pharmacodynamic interaction between tolvaptan, a non-peptide AVP antagonist, and furosemide or hydrochlorothiazide

The pharmacokinetic and pharmacodynamic interactions between tolvaptan and furosemide or hydrochlorothiazide (HCTZ) were determined in a single-center, randomized, open-label, parallel-arm, 3-period crossover study conducted in healthy white (Caucasian) men. A total of 12 subjects were enrolled in the study, with 6 subjects assigned to each of two treatment arms. Subjects in Arm 1 received 30 mg of tolvaptan, 80 mg of furosemide, and 30 mg of tolvaptan + 80 mg of furosemide. Subjects in Arm 2 received 30 mg of tolvaptan, 100 mg of HCTZ, and 30 mg pf tolvaptan + 100 mg of HCTZ. Doses were separated by a 48-hour washout. Blood and urine samples were collected at scheduled timepoints during the 24 hours after administration of study drug for the determination of pharmacokinetic and pharmacodynamic parameters. No clinically significant changes were noted in the pharmacokinetic profiles of tolvaptan and furosemide or tolvaptan and HCTZ when coadministered. Free water clearance, 24-hour urine volume, plasma sodium and argentine vasopressin concentrations, and plasma osmolality were higher, and urine osmolality was lower when tolvaptan was administered either alone or in combination with furosemide or HCTZ, compared with furosemide or HCTZ administered alone. At 24 hours postdose, plasma renin activity was increased after furosemide or HCTZ administered alone or with tolvaptan, but it was unchanged after tolvaptan alone. Tolvaptan did not significantly affect the natriuretic activity of furosemide or HCTZ. Furosemide and HCTZ did not significantly affect the aquaretic activity of tolvaptan. Tolvaptan administered alone or in combination with furosemide or HCTZ was safe and well tolerated at the given doses.

Diuretics in the therapy of hypertension

Antihypertensive monopharmacotherapy with diuretics renders blood pressure (BP) values under control in a large percentage of patients suffering from essential hypertension, and it reduces cardiovascular morbidity and mortality. Diuretics are effective in adult and elderly hypertensive subjects, independently of their race. Treatments with classic (high) doses of antihypertensive diuretics, such as 25 mg hydrochlorothiazide once daily, raise the activity of the RAA system, decrease plasma potassium and magnesium concentrations, and cause untoward changes in carbohydrate metabolism and in the plasma lipid profile. These changes appear to limit the positive response of cardiovascular prognosis to antihypertensive therapy with classic doses of diuretics. Lower doses of diuretics reduce high BP to the sought extent in many patients, and they do not elicit or cause only mild unfavourable neuroendocrine and metabolic changes. When a low dose of an antihypertensive diuretic substance is used as monopharmacotherapy, it may take 12-14 weeks after the initiation of treatment for BP to attain final stable values. The following low-dose oral formulations of diuretics constitute effective once-daily monopharmacotherapies for mild-to-moderate uncomplicated essential hypertension: bendrofluazide 1.25 mg, chlorthalidone 12.5 and 15 mg, cicletanine 50 mg, cyclopenthiazide 0.125 mg, HCTZ 12.5 mg, and torasemide 2.5 and 5 mg. These formulations are safer than classically used high-dose formulations such as hydrochlorothiazide 25 and 50 mg.

Clinical consequences of the biphasic elimination kinetics for the diuretic effect of furosemide and its acyl glucuronide in humans

This review discusses the possibility of whether furosemide acyl glucuronide, a metabolite of furosemide, contributes to the clinical effect of diuresis. First an analytical method (e.g. HPLC) must be available to measure both parent drug and furosemide acyl glucuronide. Then, with correctly treated plasma and urine samples (light protected, pH 5) from volunteers and furosemide-treated patients, the kinetic curves of both furosemide as well as its acyl glucuronide can be measured. The acyl glucuronide is formed in part by the kidney tubules and it is possible that the compound is pharmacologically active through inhibition of the Na+/2Cl-/K+ co-transport system; up to now the mechanism of action has been solely attributed to furosemide. The total body clearance of furosemide occurs by hepatic and renal glucuronidation (50%) and by renal excretion (50%). Enterohepatic cycling of furosemide acyl glucuronide, followed by hydrolysis, results in a second and slow elimination phase with a half-life of 20-30 h. This slow elimination phase coincides with a pharmacodynamic rebound phase of urine retention. After each dosage of furosemide, there is first a short stimulation of urine flow (4 h), which is followed by a 3-day recovery period of the body. The following clinical implications arise from study of the elimination kinetics of furosemide. Repetitive dosing must result in accumulation of the recovery period. Accumulation of furosemide and its acyl glucuronide in patients with end-stage renal failure results from infinite hepatic cycling. Impaired kidney function may result in impaired glucuronidation and diuresis. While kidney impairment normally requires a dose reduction for those compounds which are mainly eliminated by renal excretion, for diuretics, a dose increment is required in order to maintain a required level of diuresis. The full clinical impact of the accumulation of furosemide and its acyl glucuronide in patients with end-stage renal failure has to be determined.

Edema and principles of diuretic use

Diuretics have changed the approach to many disease and have turned once fatal conditions into tolerable ones. Treatment of salt and water overload and edema can be quite satisfying for the clinician as long as the patient is closely watched for side effects. Thiazide diuretics have their greatest use in hypertension, loop diuretics in edema and congestive heart failure, CA inhibitors in glaucoma and altitude sickness, potassium-sparing diuretics in hypokalemia induced by other diuretics and ascites, and osmotic diuretics in acute renal failure and dialysis. They are among the most widely prescribed medications in the world today and rightly have a prominent place in the armamentarium against disease.

Antihypertensive drugs and endothelial cell function

Arterial hypertension is associated with increased capillary permeability, a possible contributor to the vascular remodeling process which could be involved in certain pathological conditions arising from elevated blood pressure. This study evaluated the effects of various antihypertensive drugs on capillary permeability in the normal rat, using Evan's blue dye (EB) as a marker of albumin extravasation. The results reveal that acute injection of certain diuretics (furosemide, indapamide, hydrochlorothiazide) increase while others (amiloride, cicletanine) decrease capillary permeability via stimulation of the cyclooxygenase pathway. 10 day gavage with indapamide, amiloride and cicletanine, as well as angiotensin-converting enzyme (ACE) inhibitor perindopril and calcium channel blockers nifedipine and verapamil decreases capillary permeability, whereas furosemide, hydrochlorothiazide, ACE inhibitor captopril and calcium channel blocker clentiazem do not modify or increase EB extravasation. Hence, selected antihypertensive agents reduce capillary permeability and could therefore have a supplemental protective vascular effect, in addition to their lowering arterial pressure.

Loop diuretics versus others in the treatment of congestive heart failure after myocardial infarction

Most frequently, diuretic therapy in congestive heart failure has as its main objective ridding the lungs of water. The work of the muscles of external respiration is thus decreased, the fraction of cardiac output that is distributed to vascular beds other than that of the respiratory muscles is consequently increased, and the functional and clinical condition of the patient improves. Diuretic therapy does not change cardiac output significantly in most cases; in some circumstances diuretic therapy may increase cardiac output in a clinically relevant fashion, and in some other cases diuretic therapy may lower cardiac output to the extent of impairing the overall functional situation. The dose of diuretics should be the minimal compatible with the prosecution of the main clinical objective (class betterment), to minimize possible increases in the afterload to the left ventricle (intravenous administration), to minimize hemodynamically detrimental decreases in the preload, and to minimize the likelihood of development or the severity of undesired changes in plasma biochemistry (hyponatremia, hypokalemia, hypomagnesemia, hyperuricemia, etc.). Loop diuretics are preferred shortly after myocardial infarction, given the ample dose-effect range of these substances and their relatively benign effect on renal blood flow. During chronic therapy, loop diuretics at low doses may be tried first, and the dose may be increased if necessary, provided higher doses do not cause symptomatic falls in cardiac output through the striking renal excretory response that these drugs elicit shortly after dosing.(ABSTRACT TRUNCATED AT 250 WORDS)