Binding of diuretic antihypertensive bendroflumethiazide to human serum albumin studied by ¹9F nuclear magnetic resonance method.

Simultaneous specific and nonspecific binding of bendroflumethiazide (BFZ) to human serum albumin (HSA) and concentration profile of BFZ in HSA buffer (pH 7.40) solution were investigated by ¹9F nuclear magnetic resonance (NMR) method. The ¹9F NMR spectrum of BFZ (200 µM) in a buffer solution showed a sharp signal of its CF3 group at 17.8 ppm from the reference trifluoroethanol. Addition of 0.60mM HSA to the sample solution caused the CF(3) signal splitting into three broadened peaks at 18.4 (A), 17.9 (B) and 17.4 ppm (C). By its chemical shift and spectral behavior, B was assigned to unbound BFZ. Competition experiments with Site I and II ligands lead to C being assigned to Site II bound BFZ. However, the peak intensity (areas) of A was not reduced by these ligands, suggesting that A arises from nonspecific binding. Using the peak intensities at several total concentrations of BFZ, Scatchard plot was performed. The plot for A provided a straight line parallel to the x-axis confirming nonspecific binding and that for C was consistent with specific binding. The binding constants for nonspecific and specific Site II binding were 1.02 and 1.00 × 104 (M⁻¹) (n=1.1), respectively. The presence of 0.10 M Cl⁻ in the sample solution affected the binding constant of Site II binding, but not that of nonspecific binding. The concentration profile of BFZ calculated using the binding constants revealed that nonspecific binding is more effective than Site II binding for the binding of BFZ to HSA. It was also confirmed that considerable amounts of BFZ liberated from Site II by the Site II ligands or Cl⁻ ions bind again nonspecifically.

Doxazosin versus bendrofluazide: a comparison of the metabolic effects in British South Asians with hypertension.

BACKGROUND: People from British South Asian communities have an increased risk of mortality from coronary heart disease (CHD). Doxazosin, a selective alpha(1)-adrenergic blocker, in addition to lowering blood pressure, has been shown to have positive effects on glucose metabolism and lipid profiles in patients with hypertension. AIM: We studied doxazosin (1-8 mg) and bendrofluazide (2.5 mg) in patients of British South Asian origin with existing mild to moderate hypertension (doxazosin n = 78; bendrofluazide n = 82), to compare their effects on glucose and lipid metabolism in this group. DESIGN OF STUDY: A 34-week randomised, double-blind, parallel-group, multicentre study. SETTING: Primary care in the UK. METHOD: All doxazosin patients started with an initial dose of 1 mg once daily, titrated to a maximum 8 mg once daily if diastolic blood pressure was >90 mmHg or was not <5 mmHg of the baseline value. The primary efficacy variables were mean glucose and total cholesterol concentrations at week 21. RESULT: Doxazosin reduced glucose, total cholesterol, low-density lipoprotein-cholesterol and triglycerides and increased high-density lipoprotein-cholesterol. There were significant differences between doxazosin and bendrofluazide for glucose concentrations at week 21 (P = 0.029) and week 34 (P = 0.015), total cholesterol at week 21 (P = 0.048) and triglycerides at week 21 (P = 0.047) and week 34 (P = 0.009). There was no significant difference in blood pressure lowering between the two treatments. CONCLUSION: Doxazosin exhibits beneficial effects on glucose concentrations and lipid profile, in particular in lowering triglyceride concentrations in British South Asians. Whether these desirable characteristics translate to improved overall cardiovascular risk requires formal evaluation.

Interaction of human serum albumin with bendroflumethiazide studied by fluorescence spectroscopy.

The interactions between bendroflumethiazide (BFTZ) and human serum albumin (HSA) have been studied by fluorescence spectroscopy. Binding constants for drug attachment to the various binding sites of HSA have been measured at different temperatures in physiological buffer solution. The effect of metal ions on BFTZ interaction with HSA was also investigated. The thermodynamic parameters, DeltaH and DeltaS, have been calculated to be 49.28kJmol(-1)>0, and 258.83Jmol(-1)K(-1)>0, respectively. The distance between HSA and BFTZ, r, was determined to be 1.47nm based on Förster's non-radiative energy transfer theory. The experimental results reveal that BFTZ has a strong ability to quench the intrinsic fluorescence of HSA through a static quenching mechanism. Furthermore, the binding constants between BFTZ and HSA are remarkably independent of temperature, and decrease in the presence of various ions, usually by about 30-55%. Hydrophobic interaction occurs between BFTZ and the sub-domain II A of HSA.

Characterization of the thiazide-sensitive Na(+)-Cl(-) cotransporter: a new model for ions and diuretics interaction.

The thiazide-sensitive Na(+)-Cl(-) cotransporter (TSC) is the major pathway for salt reabsorption in the apical membrane of the mammalian distal convoluted tubule. When expressed in Xenopus laevis oocytes, rat TSC exhibits high affinity for both cotransported ions, with the Michaelis-Menten constant (K(m)) for Na(+) of 7.6 +/- 1.6 mM and for Cl(-) of 6.3 +/- 1.1 mM, and Hill coefficients for Na(+) and Cl(-) consistent with electroneutrality. The affinities of both Na(+) and Cl(-) were increased by increasing concentration of the counterion. The IC(50) values for thiazides were affected by both extracellular Na(+) and Cl(-). The higher the Na(+) or Cl(-) concentration, the lower the inhibitory effect of thiazides. Finally, rTSC function is affected by extracellular osmolarity. We propose a transport model featuring a random order of binding in which the binding of each ion facilitates the binding of the counterion. Both ion binding sites alter thiazide-mediated inhibition of transport, indicating that the thiazide-binding site is either shared or modified by both Na(+) and Cl(-).

[Pharmacokinetic studies and bioavailability of bendroflumethiazide in combination with spironolactone]. / Untersuchungen zur Pharmakokinetik und Bioverfügbarkeit von Bendroflumethiazid in Kombination mit Spironolacton.

An intraindividual comparative multiple-dose study (6 days) was carried out under controlled conditions on 10 healthy volunteers in order to establish the bioavailability of bendroflumethiazide (Bft; 3-benzyl-6-trifluoromethyl-7-sulfamyl-3,4-dihydro-1,2,4-benzoth iad iazine-1, 1-oxide), the sum of the fluorogenic metabolites of spironolactone (3-[3-oxo-7-alpha-acetylthio-17 beta-hydroxy-4-androstene-17-alpha-yl]-propionic acid-gamma-lactone) and canrenone, the main spironolactone metabolite from a fixed combination of Bft with spironolactone vs. the commercial preparations of the single drugs. Canrenone was assayed from plasma by high-performance liquid chromatography (HPLC) whereas Bft and the total aldosterone antagonistically acting spironolactone metabolites were determined fluorometrically. Both the fixed and the monosubstance formulation can be considered as bioequivalent for canrenone and the total fluorescence. Bft, in contrast, shows a reduced systemic availability of 61% when administered as the single drug formulation. A 2-compartment model was taken as the basis for the calculation of the steady-state plasma concentration curves and the pharmacokinetic parameters of Bft, canrenone and the sum of the fluorogenic spironolactone metabolites. Following oral multiple administration of 2.5 mg Bft (b.i.d.), the terminal elimination half-life, the steady-state volume of distribution and the total plasma clearance were determined to be 8.6-8.2 h, 0.88 l/kg and 269.4 ml/min, resp. In contrast to Bft, the AUC(120,tlast)-values for post-steady-state elimination, starting with the final spironolactone dose on day 6 were comparable.(ABSTRACT TRUNCATED AT 250 WORDS)

Skin blister fluid--an access to the peripheral compartment. Implications of a study on the behaviour of bendroflumethiazide in rats.

Pharmacokinetics of bendroflumethiazide (bft) were investigated in blood and skin suction blister fluid (SBF) in rats dosed 10 mg/kg intravenously. Additionally tissue levels were determined. Mean volume of skin blisters amounted to 10 or 20 microliters, respectively. While blood levels were best described according to a three-compartment model (terminal half-life 152 min) bft concentrations in SBF raised to a maximum 60 min post administration and thereafter declined (half-life 143 min). There was no significant effect of blister volume on SBF level-time course. A close relation between bft concentrations in SBF and the calculated amount of drug in the deep compartment was observed (r = 0.987). Plasma protein binding of bft was 84% while binding to SBF amounted to 76%. The drug is evenly distributed between plasma and erythrocytes. Therefore concentrations of unbound drug in SBF exceed those in plasma during the terminal phase. The determination of tissue levels showed bft concentrations in liver, kidney, lung and heart to follow blood levels whereas the pharmacokinetic behaviour of skin and muscle is rather close to that of the deep compartment. The results suggest the determination of skin blister fluid levels to be valuable if a drug acts from the tissue compartment then SBF being closer to the biophase than blood.

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.

Does cantharides blister fluid provide access to the peripheral compartment?

The pharmacokinetics of bendroflumethiazide (BFT) was investigated following the oral administration of 10 mg to 3 healthy volunteers. Each subject participated twice in the study. BFT was determined in plasma and cantharides blister fluid from 1/2 to 30 h post administration. Blister fluid was obtained from blisters 10-22 h old. Plasma levels were fitted to a tri-exponential equation and the concentration of the drug in the peripheral compartment was calculated from the microscopic rate constants. In 5 of 6 cases investigated, cantharides blister fluid levels paralleled the concentration of the drug in the peripheral compartment. The mean blister fluid levels exceeded the calculated concentration in Compartment 2 1.46 fold. In one case, the blister fluid level paralleled the plasma level. This subject clearly differed from the others as more than 10 h were required for blister formation in her. The results suggest that following the administration of BFT, cantharides blister fluid behaves as part of the peripheral compartment. The possible value of studying blister fluid levels in pharmacokinetic investigations is discussed.

Pharmacokinetics of bendroflumethiazide alone and in combination with propranolol and hydralazine.

Bendroflumethiazide (Bft) was administered to 6 healthy subjects at 3 different dose levels (2.5, 5 and 10mg) in a cross-over design, either as capsules (2.5mg) or as tablets (5mg). Its pharmacokinetics were evaluated then and following administration of a fixed combination of Bft and propranolol and hydralazine to a further 7 volunteers. Plasma and urinary concentrations of Bft were determined by a new fluorimetric - thin-layer chromatography procedure. Peak plasma levels occurred after 2-3h and averaged 15, 27 and 45 microgram/l in the three dose groups. Areas under the plasma concentration - time curves (AUC0 leads to 12), which were 75, 147 and 250 microgram 1(-1)h respectively, and cumulative urinary recovery (20%) were independent of the dose administered and the type of formulation. Thus Bft kinetics proved to be linear within the dose range evaluated. The plasma clearance was calculated to be 505 ml/min, renal clearance 108 ml/min and nonrenal clearance 396 ml/min. Bioavailability of Bft was not altered following administration of the fixed combination. The amount of propranolol found in the circulation did not change, whereas that of hydralazine (determined as apparent hydralazine) increased by 59% when the fixed combination was administered.

Pharmacokinetics of bendroflumethiazide after low oral doses.

The pharmacokinetics of bendroflumethiazide after oral administration of 1.25, 2.5, and 5.0 mg were studied in nine healthy male volunteers. Bendroflumethiazide was analyzed by GLC after extractive alkylation. After the lowest dose, the plasma concentration, could be followed to 14 hr, and the data were adequately fitted by a one-compartment model; the half-life was 3.1 hr. After the 2.5 and 5.0 mg doses, the plasma concentration was followed for 24 hr, and the data were fitted by a two-compartment model with half-lives of 8.9 hr. The urinary sodium concentration was doubled after bendroflumethiazide intake, but the urinary potassium concentration remained almost constant. The renal clearance of bendroflumethiazide was around 30 ml . min-1.

Bioavailability of propranolol and bendrofluazide formulations.

In this comparative bioavailability study in 12 healthy volunteers the blood level profiles of both propranolol and bendrofluazide were studied following the multiple oral administration of the drugs as a fixed combination (Inderetic) and as a free combination at doses of 80 mg propranolol twice daily and 2.5 mg bendrofluazide twice daily. There were no statistically significant differences between the two regimens in terms of individual propranolol blood levels, half-lives and areas under the curve. The half-lives were between 5 and 8 h. Thus the bioavailability of propranolol from the fixed combination is equivalent to that from the free combination. The mean peak bendrofluazide blood levels were slightly higher following the administration of the fixed combination. This difference was statistically significant only at 1 and 2 h after the first dose. There were no statistically significant differences between these two bendrofluazide regimens in terms of half-life and area under the curve. Thus the bioavailability of bendrofluazide from the fixed combination is equivalent to that from the free combination. It is concluded therefore that by combining bendrofluazide and propranolol in a fixed capsule formulation does not affect significantly the systemic bioavailability of either component.

Effect of food on the bioavailability of bendroflumethiazide.

Bendroflumethiazide (BFT), 10 mg, was given orally to eight subjects after fasting overnight and together with a meal. Concentrations of the diuretic in plasma and urine were determined by GLC. As judged by AUC and urinary recovery of BFT, the bioavailability of the diuretic was not influenced by concomitant intake of a meal.

Pharmacokinetics of bendroflumethiazide.

Bendroflumethiazide (bft), 10 mg, was administered orally to 9 healthy volunteers. The concentrations of the diuretic in plasma and urine were determined by gas-liquid chromatography (GLC). Peak plasma levels (86 +/- 18 ng/ml) of bft were reached at 2 +/- 0.4 hr. The concentration declined with a mean t1/2 of 3.0 hr. The apparent volume of distribution averaged 1.48 L/kg. The major part of the drug was eliminated via nonrenal mechanisms, the nonrenal clearance being estimated to 269 +/- 77 ml/min and renal clearance to 105 +/- 24 ml/min. Urinary recovery of the thiazide averaged 30%.