Methoxsalen stimulates electrogenic Cl- secretion in the mouse jejunum

We used the short-circuit current (I(sc)) and patch-clamp techniques to investigate the effects of methoxsalen (MTX) on the electrogenic Cl- secretion of the mouse jejunum. MTX stimulated a sustained increase in Isc that was dose dependent. Bumetanide inhibited MTX-stimulated Isc in a dose-dependent manner consistent with activation of Cl- secretion. MTX failed to stimulate I(sc) following maximal activation of the cAMP pathway by forskolin, but did increase Isc after a submaximal dose of forskolin. Glibenclamide, a blocker of the cystic fibrosis transmembrane conductance regulator (CFTR), reduced the MTX-stimulated increase of Isc by 59 +/- 6%. The cAMP-dependent K+ channel blocker 293B did not alter the MTX-activated I(sc); however, clotrimazole, an intermediate Ca2(+)-activated K+ channel (IK(Ca)) blocker, reduced the MTX-stimulated I(sc). MTX did not alter Na(+)-glucose cotransport across the mouse jejunum. In cell-attached membrane patches, MTX increased the open probability of the basolateral IK(Ca) channel of isolated crypts. These data suggest that the CFTR and IK(Ca) channels participate in the MTX-activated, sustained Cl- secretory response of the mouse jejunum.

Solubilization and stability of bumetanide in vehicles for intranasal administration, a pilot study

The solubility of bumetanide in vehicles of various polarities, suitable for intranasal administration in acute situations, has been investigated. The solubility at 4 degrees C in glycofurol and polyethylene glycol 200 was high (167 and 143 mg/mL, respectively), decreasing exponentially with addition of phosphate buffer or coconut oil. Vehicles containing coconut oil and glycofurol did not seem to improve the solubility relative to mixtures between glycofurol and buffer. Adequate solubility (approximately 50 mg/mL) was achieved in vehicles containing about 80% cosolvent. The stability of bumetanide was studied at 5 degrees C and 57 degrees C. No degradation was observed at low temperature. At high temperature, bumetanide decomposes in nonaqueous vehicles with half-lifes ranging from 69 to 400 days, but sufficient stability may be obtained by adjustment of pH to 7.4. It may be concluded that it is possible to prepare a clinically relevant formulation for intranasal delivery of bumetanide.

Loop diuretics alter the diurnal rhythm of endogenous parathyroid hormone secretion. A randomized-controlled study on the effects of loop- and thiazide-diuretics on the diurnal rhythms of calcitropic hormones and biochemical bone markers in postmenopausal women

BACKGROUND

Thiazide diuretics (TD) reduce urinary calcium, bone loss and fracture risk. Loop diuretics (LD) may have opposite effects. These effects could depend on induced rhythmic changes in bone and calcium homeostasis.

DESIGN

After a run-in period of 7 days, we studied (in a factorial design) the diurnal rhythms of plasma levels of calcium, phosphate, parathyroid hormone (PTH), 1,25-dihydroxyvitamin D and osteocalcin, as well as renal excretions rates of calcium, phosphate, and cross-linked N-terminal telopeptide of type 1 collagen (NTx) in 50 postmenopausal women randomized to treatment with either a thiazide diuretic (TD; bendroflumethiazide, n = 14), a loop diuretic (LD; bumetanide, n = 13), LD plus TD (bendroflumethiazide plus bumetanide, n = 11), or placebo (n = 12).

RESULTS

In all four groups, all measured quantities showed a diurnal variation. LD caused a steep increase, with a subsequent decrease, in urinary calcium and plasma PTH. The mean 24 h plasma PTH concentration was increased (8.5 +/- 0.9 mmol L-1) compared with placebo (4.4 +/- 0.4 mmol L-1), whereas net 24 h renal calcium excretion did not differ from that of the placebo group due to a rebound hypocalciuria. Compared with placebo, diurnal rhythms of plasma phosphate and osteocalcin were changed with an increase during daytime and a decrease during the night. TD did not alter the diurnal rhythm of any of the measured quantities. However, the 24-h renal calcium excretion decreased, whereas the mean 24-h plasma calcium concentration increased without PTH suppression. LD plus TD caused changes similar to those observed with LD alone.

CONCLUSION

One daily dose of LD increases parathyroid activity with alterations in the diurnal pattern of osteocalcin. This could indicate a potential anabolic effect of LD.

Cisplatin-induced apoptosis of mesothelioma cells is affected by potassium ion flux modulator amphotericin B and bumetanide

Chemotherapeutic anti-cancer drugs induce cell death by the process of apoptosis. Efflux of potassium ions (K(+)) is necessary for cell volume reduction during apoptosis and increased inward pumping of K(+) thus counteracts apoptosis. Potassium flux modulation could therefore interact with apoptosis and affect the efficiency of cancer chemotherapeutics. We explored if the K(+) efflux stimulator amphotericin B, with or without the Na(+), K(+), 2Cl(-)-cotransport (K(+) influx) blocker bumetanide, could affect cisplatin- and carboplatin-induced apoptosis and cytotoxicity in the pulmonary mesothelioma cell line (P31). Apoptosis was determined by quantifying free nucleosomes and caspase-3 activity, and cytotoxicity was determined by clone formation and a fluorometric assay. The pan-caspase enzyme inhibitor Boc-D-FMK was used to further determine the role of caspase activity in K(+)-flux-modulated cisplatin-/carboplatin-induced apoptosis and cytotoxicity. Amphotericin B (3.2 micromol/L) combined with bumetanide (100 micromol/L) potentiated cisplatin-induced free nucleosome and caspase-3 activity. The combination of the K(+) modulators did not, however, increase cisplatin cytotoxicity. The caspase inhibitor Boc-D-FMK, but unexpectedly also bumetanide, markedly reduced cisplatin cytotoxicity and annihilated the augmented cytotoxicity of cisplatin in the presence of amphotericin B. Carboplatin cytotoxicity was reduced by bumetanide, but not affected by amphotericin B. Carboplatin and carboplatin/bumetanide cytotoxicity was further reduced by Boc-D-FMK. We conclude that the ability of cisplatin, and to a lesser extent carboplatin, to induce apoptosis is indeed influenced by cellular potassium flux modulators. We suggest that K(+) ionophores such as amphotericin B, and K(+) influx blockers such as bumetanide, alone or in combination, should be further evaluated for their potential clinical usefulness in influencing tumor cell apoptosis induced by cisplatin and other cancer chemotherapeutics.

Application of multiple response optimization technique to extended release formulations design

The purpose of the present study was to apply response surface methodology and multiple response optimization utilizing superimposed contour diagrams to design extended release formulations with a preplanned release profile. Bumetanide solution was layered on sugar pellets followed by coating with various coating formulations according to a central composite statistical design using a Glatt GPCG 1 Wurster Fluid Bed. The coated pellets were tested for their release profiles and the percent of drug released after 1, 4 and 8 h were used to describe and optimize the release process. Statistical models describing the percent bumetanide released after 1, 4 and 8 h were developed and the corresponding contour diagrams were superimposed to predict the coating formulation parameters expected to produce target release profile. The pellets coated with the designed coating formulation were tested for their release profiles in comparison to the target profile. According to the model-independent approach using similarity factor (F2), the dissolution profile of the designed formulation and the expected target profile were found to be similar. It was concluded that response surface methodology and multiple response optimization could be successfully used to design and optimize extended release formulations with desired preplanned release profile.

Na+-K+-Cl- cotransporter in rat focal cerebral ischemia

In cultured neurons, the authors previously demonstrated that the Na+-K+-Cl- cotransporter is significantly stimulated by elevated extracellular potassium and glutamate, which are important factors in cerebral ischemic damage. These findings led the authors to hypothesize that stimulation of the cotransporter after ischemia might result in Na+, K+, and Cl- influx, and might contribute to neuron damage. In the current study, the authors investigated such a role of the Na+-K+-Cl- cotransporter in focal cerebral ischemia. Cerebral ischemia was induced by 2-hour occlusion of the left middle cerebral artery (MCA) and 24-hour reperfusion in male spontaneously hypertensive rats (SHRs). Immunocytochemical staining and immunoblotting revealed an up-regulation of expression of the cotransporter protein in neurons in cortex at 24 hours of reperfusion. Artificial cerebral spinal fluid (aCSF) or 100 micromol/L bumetanide (a cotransporter inhibitor) in aCSF were continuously microdialyzed through a microdialysis probe into left cortices throughout 2-hour MCA occlusion and 24-hour reperfusion. Compared with the aCSF-treated group, infarction volume was significantly reduced in the bumetanide-treated group (25%, P < 0.05). In addition, brain water content in the bumetanide-treated brains was decreased by 70% (P < 0.05). These results strongly suggest that the Na+-K+-Cl- cotransporter may play an important role in cerebral ischemic neuronal damage.

Pulmonary oedema after ophthalmic regional anaesthesia in an unfasted patient undergoing elective surgery

An elderly female patient presenting for phaco-emulsification and intra-ocular lens implant under local anaesthesia developed pulmonary oedema after surgery and underwent emergency tracheal intubation. The pulmonary oedema may have been caused by her omission of routine oral diuretic medication before surgery and having to lie flat for the procedure. The patient had not been fasted before surgery, as is accepted practice in many hospitals. This made emergency tracheal intubation potentially hazardous. The patient made a full recovery. The issues of pre-operative assessment, fasting and the withholding of diuretic medication before elective eye surgery under local anaesthesia are discussed.

Pharmacokinetics and pharmacodynamics of intravenous bumetanide in mutant Nagase analbuminemic rats: importance of globulin binding for the pharmacodynamic effects

The importance of plasma protein binding of intravenous furosemide in circulating blood for its urinary excretion and hence its diuretic effects in mutant Nagase analbuminemic rats was reported. Based on the furosemide report, the diuretic effects of another loop diuretic, bumetanide, could be expected in analbuminemic rats if plasma protein binding of bumetanide is considerable in the rats. This was proved by this study. After intravenous administration of bumetanide, 10 mg/kg, to analbuminemic rats, the plasma protein binding of bumetanide was 36.8% in the rats mainly due to considerable binding to alpha- and beta-globulins (this value, 36.8%, was considerably greater than only 12% for furosemide), and hence the percentages of intravenous dose of bumetanide excreted in 6 h urine as unchanged drug was 16.0% in the rat (this value was considerably greater than only 7% for furosemide). After intravenous administration of bumetanide to analbuminemic rats, the area under the plasma concentration-time curve from time zero to time infinity (1012 compared with 2472 microg min/mL) was significantly smaller [due to significantly faster both renal clearance (1.49 compared with 0.275 ml/min/kg) and nonrenal clearance (8.30 compared with 3.71 ml/min/kg)], terminal half-life (9.94 compared with 22.4 min) and mean residence time (4.25 compared with 5.90 min) were significantly shorter (due to faster total body clearance, 9.88 compared with 4.05 ml/min/kg), and amount of 6 h urinary excretion of unchanged bumetanide (559 compared with 261 microg, due to increase in intrinsic renal excretion) was significantly greater than that in control rats. The 6 h urine output and 6 h urinary excretions of sodium, chloride and potassium were comparable between two groups of rats although the 6 h urinary excretion of bumetanide was significantly greater in analbuminemic rats. This could be explained by the following. The amount of urinary excretion of bumetanide was significantly greater in analbuminemic rats than that in control rats only between 0 and 30 min urine collection. In both groups of rats, the urinary excretion rates of bumetanide during 0-30 min reached a upper plateau with respect to urine flow rate as well urinary excretion rates of sodium, potassium and chloride, therefore, the diuretic effects (6 h urine output and 6 h urinary excretions of sodium, potassium and chloride) were not significantly different between two groups of rats.

Intranasal administration of different liquid formulations of bumetanide to rabbits

The bioavailability of bumetanide in rabbits after intranasal administration of eight formulations intended for use in acute situations has been studied. The vehicles tested were combinations of phosphate buffer, pH 7.4, glycofurol 75. polyethylene glycol 200 and coconut oil. A mixture of 51% glycofurol in polyethylene glycol 200 was administered containing doses of 1 and 8 mg bumetanide respectively. For all other formulations the lower dose level only was studied. The tmax obtained ranged from 3 to 10 min. The vehicles resulting in the highest rate of absorption were 60% glycofurol in coconut oil and pure glycofurol. The observed bioavailability for the different formulations ranged from 16 to 37% for the time period 0-120 min. The bioavailability was also calculated omitting the initial peak seen after i.v. injection, which may be undesirable. Using this method bioavailabilities of 33-82, for the time interval 5-120 min was found. The study also demonstrated that the total amount of bumetanide absorbed increased proportionally to the dose administered. The rate of absorption of bumetanide from all formulations tested may be relevant for the treatment of acute oedematous states. The tmax obtained after intranasal administration was shorter than reported for other non-parenteral routes of administration.

The pharmacokinetics of bumetanide in the newborn infant

This study characterizes the pharmacokinetics of bumetanide after an intravenous dose of 0.05 or 0.10 mg/kg to 14 neonates (weight range 820-4,000 g; gestational age 26-40 weeks) during the first week of life. Blood samples and urine were collected for up to 12 h after dosing. Estimated serum clearance was 0.2-1.0 ml/min.kg (range), volume of distribution was 0.22 l/kg (range 0.11-0.32 l/kg), and the harmonic mean half-life was 6-7 h (range of 4-19 h). Nonrenal clearance accounted for 58-97% of the serum clearance with the presence of certain oxidative metabolites of bumetanide in the urine. These findings suggest higher dosing requirements and prolonged intervals as compared to adults. Utilizing these pharmacokinetic data, pharmacodynamic and ototoxicity studies should be conducted to establish a safe and effective neonatal dose.

Role of duration of diuretic effect in preventing sodium retention

OBJECTIVE

To determine whether the duration of diuretic effect at the active nephron site enhances ability to excrete an exogenous salt load.

METHODS

We conducted a study that involved eight patients with New York Heart Association class II to III congestive heart failure. In a randomized, crossover manner, each patient received 3.25 mg intravenous bumetanide at 0 hours and again at 6 hours or a loading dose of 0.5 mg bumetanide at 0 hours followed by a continuous infusion of 0.5 mg/hr for 6 hours. Response was followed for 12 hours; a total of 6.5 mg of bumetanide was administered in each arm of the study. Eight hours after dosing began, we administered approximately 80 mEq sodium intravenously and examined its excretion over 4 hours.

RESULTS

The percentage of the load excreted was 86% +/- 15% versus 29% +/- 30% for the infusion and bolus regimens, respectively (p = 0.0005). More bumetanide was excreted during the infusion (667 +/- 133 micrograms versus 240 +/- 121 micrograms; p = 0.0002). During the infusion, however, more sodium was excreted relative to amounts of bumetanide, indicating that the efficiency of response was greater during the infusion, 0.10 +/- 0.02 mEq sodium per microgram bumetanide versus 0.07 +/- 0.05 mEq for the bolus (p = 0.0145).

CONCLUSIONS

These data support the notions that a long-acting loop diuretic maintains its efficacy and that a longer duration of action facilitates excretion of a sodium load, such as that which might occur during dietary indiscretion.

Dose-ranging evaluation of bumetanide pharmacodynamics in critically ill infants

OBJECTIVES

Determine the diuretic effects of single intravenous doses of bumetanide in volume-overloaded critically ill infants.

METHODS

A prospective, open-label study was carried out in 56 infants aged 0 to 6 months who required diuretic therapy. Each patient received a single intravenous dose of bumetanide. Doses selected in sequential order ranged from 0.005 to 0.10 mg/kg. Determinations of urine volume, electrolytes, creatinine levels, and osmolality were performed before (collected from -2 to -4 hours to time 0) and at 1, 2, 3, 4, 6, and 12 hours after bumetanide dosing. Serum samples collected at time 0 and at 5, 15, 30, 60, 120, 180, 240, 360, and 480 minutes and urine aliquots collected at time 0, 0 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to 6, and 6 to 12 hours were analyzed for bumetanide concentration. Individual changes in urine flow rate and electrolyte excretion were plotted against corresponding bumetanide excretion rates, taken as the effective dose of the drug.

RESULTS

Peak bumetanide excretion rates increased linearly with increasing doses of drug. Time course patterns for urine flow rate and electrolyte excretion were similar for all dosage groups. Urine flow rate and electrolyte excretion increased linearly up to a bumetanide excretion rate of approximately 7 micrograms/kg/hr and either plateaued (urine flow rate) or declined at a bumetanide excretion rate of > 10 micrograms/kg/hr. Diuretic efficiency of bumetanide was maximal at doses of 0.005 to 0.010 mg/kg but decreased at higher doses.

CONCLUSIONS

Maximal diuretic responses occurred at a bumetanide excretion rate of about 7 micrograms/kg/hr, corresponding to doses of 0.035 to 0.040 mg/kg. Higher doses produced a proportionately higher bumetanide excretion rate but no increased diuretic effect. Lower doses of bumetanide had the greatest diuretic efficiency, suggesting that continuous infusion of low doses of bumetanide or intermittent low-dose boluses may produce optimal diuretic responses in critically ill infants.

Inhaled loop diuretics and basal airway responsiveness in man: evidence of a role for cyclo-oxygenase products

Inhaled frusemide protects asthmatic airways against a wide variety of bronchoconstrictor stimuli by unknown mechanisms. To investigate whether inhaled loop diuretics modulate baseline bronchial responsiveness, a randomized, double-blind, placebo-controlled study was conducted to test the ability of frusemide (40 mg) and bumetanide (2 mg) to displace concentration-response curves with methacholine in 14 healthy volunteers. In addition, separate randomized, double-blind studies were carried out to evaluate the effects of oral flurbiprofen, a potent cyclo-oxygenase inhibitor, on the protective action of frusemide against methacholine-induced bronchoconstriction. Inhaled loop diuretics significantly increased the provocative concentration of methacholine causing a 15% decrease in forced expiratory volume in one second (PC15FEV1) from the geometric mean (range) value of 58.6 (9.2-233) mg.ml-1 after placebo administration, to 129 (13.8-505) and to 106 (6.6-510) mg.ml-1 after administration of frusemide and bumetanide, respectively. Similar results were obtained when data from partial flow-volume curves were used for analysis. In the eight subjects studied, pretreatment with oral placebo and inhaled frusemide reduced airway responsiveness to methacholine, with a geometric mean (range) PC15FEV1 value of 116 (25.4-405) mg.ml-1, and premedication with oral flurbiprofen abolished this protective effect, the geometric mean (range) PC15FEV1 methacholine being reduced to a value of 50.3 (16.6-189) mg.ml-1. In addition, oral flurbiprofen alone failed to alter airway responsiveness to methacholine. In view of these findings, it is suggested that bronchoprotective prostaglandins may mediate the effects of loop diuretics against methacholine-induced bronchoconstriction in man.

Effects of the rate and composition of fluid replacement on the pharmacokinetics and pharmacodynamics of intravenous bumetanide

The effects of differences in the rate and composition of intravenous (i.v.) fluid replacement for urine loss on the pharmacokinetics and pharmacodynamics of bumetanide were evaluated with rabbit as the animal model. Each rabbit received a 4-h constant i.v. infusion of bumetanide at 1 mg/kg with 0% replacement (treatment I, n = 8), 50% replacement (treatment II, n = 6), and 100% replacement (treatment III, n = 7) with lactated Ringer's solution, in addition, another group of rabbits received 100% replacement with 5% dextrose in water (D-5-W, treatment IV, n = 4). Some pharmacokinetic parameters, such as the apparent volume of distribution at steady-state, mean residence time, and terminal half-life, remained relatively unchanged in all four treatments. Renal clearance and urinary excretion rate of the drug in treatments I-III were essentially the same, but were considerably higher than those in treatment IV. In spite of the similarities in kinetic properties (approximately 40% difference between lowest and highest values), the diuretic and/or natriuretic effects of bumetanide were markedly different among the four treatments. For example, the mean 8-h urine output values were 189, 317, 2170, and 306 mL for treatments I-IV, respectively, the corresponding 8-h sodium excretion values were 9.19, 16.5, 88.8, and 15.7 mmol, and the chloride excretion values were 10.8, 33.7, 77.4, and 11.7 mmol. Except for treatment III, diuresis and/or natriuresis were time dependent, generally decreasing with time until reaching a low plateau during later hours of infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and pharmacodynamics of bumetanide after intravenous and oral administration to rats: absorption from various GI segments

Bumetanide, 2, 8, and 20 mg/kg, was administered both intravenously and orally to determine the pharmacokinetics and pharmacodynamics of bumetanide in rats (n = 10-12). The absorption of bumetanide from various segments of GI tract and the reasons for the appearance of multiple peaks in plasma concentrations of bumetanide after oral administration were also investigated. After i.v. dose, the pharmacokinetic parameters of bumetanide, such as t1/2 (21.4, 53.8 vs. 127 min), CL (35.8, 19.1 vs. 13.4 ml/min per kg), CLNR (35.2, 17.8 vs. 12.6 ml/min per kg) and VSS (392, 250 vs. 274 ml/kg) were dose-dependent at the dose range studied. It may be due to the saturable metabolism of bumetanide in rats. After i.v. dose, 8-hr urine output per 100 g body weight increased significantly with increasing doses and it could be due to significantly increased amounts of bumetanide excreted in 8-hr urine with increasing doses. The total amount of sodium and chloride excreted in 8-hr urine per 100 g body weight also increased significantly after i.v. dose of 8 mg/kg, however, the corresponding values for potassium were dose-independent. After oral administration, the percentages of the dose excreted in 24-hr urine as unchanged bumetanide were dose-independent. Bumetanide was absorbed from all regions of GI tract studied and approximately 43.7, 50.0, and 38.4% of the orally administered dose were absorbed between 1 and 24 hr after oral doses of 2, 8, and 20 mg/kg, respectively. Therefore, the appearance of multiple peaks after oral administration could be mainly due to the gastric emptying patterns.(ABSTRACT TRUNCATED AT 250 WORDS)

Locally deposited but not inhaled frusemide reduces nasal potential difference in healthy subjects

Previous publications suggest that prolonged inhalation of frusemide (F) does not cause a fall in the nasal transepithelial potential difference (PD) whereas locally deposited F does. In an attempt to reconcile these observations, we have measured the effect of inhalation through the nose and local deposition of F, amiloride (A), bumetanide (B) and salbutamol (S) on nasal PD in 7 healthy male volunteers in a randomised, double blind study. Solutions of drugs ranging from 10(-6) M to 10(-3) M (3 x 10(-8) M to 3 x 10(-5) M for B) in phosphate buffered saline 0.5 ml (PBS) were sequentially deposited in both nostrils, and nasal PD was measured 5 min after each dose. In 10 further volunteers, 10(-2) M solutions of A, F and S (3 x 10(-4) M for B) 5 ml were nebulised through the nose for 15 min, when nasal PD was measured. Resting PD was similar in the left and right nostrils averaging -17.1 mV (lumen negative). Placebo, inhaled of deposited B and S, and inhaled F did not change nasal PD. Topically deposited F significantly lowered PDmax in a dose-dependent manner [10(-4) M, -12% from baseline; 10(-3) M, -24%] as did the more potent A [10(-5) M, -19%; 10(-4) M, -31%; 10(-3) M, -47%]. Nebulised A (10(-2) M) had the same effect on nasal PD as deposited A (10(-4) M). The effects of locally deposited F and A (10(-3) M) on nasal PD were additive.(ABSTRACT TRUNCATED AT 250 WORDS)

[Loop diuretics. Rational pharmacotherapy]

The pharmacodynamics and -kinetics as well as rational pharmacotherapy of furosemide and bumetanide is reviewed. In renal insufficiency, a reduced response to diuretics is due to altered pharmacokinetics. The optimum dose can be determined within three to four hours by titration and the effect is measured by the amount of excreted sodium. In nephrotic syndrome, both pharmaco-kinetics and--dynamics are altered. The optimum dose is established as above. Starting and ceiling doses are given in tables for both drugs in renal insufficiency and nephrotic syndrome. In congestive heart failure, the difference is greater between oral and intravenous doses than apparent from the bioavailability of the drugs. If potent diuretics are without effect, the heart failure must be treated more vigorously or a combination with thiazides tried out. Potent diuretics are seldom used in the treatment of liver cirrhosis, but, if used, large doses are necessary. Non-steroidal antiinflammatory drugs are usually considered contra-indicated in patients with severe renal insufficiency, since the pharmacodynamics of the diuretics are altered.

CONCLUSION

The general strategy when using potent diuretics is titration to an effective dose and then using this dose as frequently as needed in order to obtain the desired response.

Bioavailability and diuretic effect of bumetanide following rectal administration of suppositories containing weak acids in human subjects

The bioavailability of bumetanide following the oral administration of tablets, or the rectal administration of either macrogol suppositories or suppositories with and without weak acids were evaluated in human subjects. The absorption of bumetanide from those suppositories containing bumetanide without weak acids (control suppositories) was extremely poor, while the absorption from those suppositories containing citric acid or tartaric acid was enhanced. The mean area under the plasma concentration-time curve (AUC) following the rectal administration of the suppositories containing citric acid and tartaric acid was 52 and 62%, respectively, of that following the oral administration. On the other hand, the absorption rate constant (ka) and the mean residence time (MRT) following the rectal administration of the suppositories containing weak acids increased significantly compared to those administered orally. The time (Tmax) required to achieve the maximum plasma concentration (Cmax) in the plasma following the rectal administration of the suppositories containing weak acids was significantly shortened compared to the time of those administered orally. These results indicated that the bumetanide contained in the suppositories containing weak acids might be absorbed rapidly after administration. The diuretic effect of bumetanide following the oral and rectal administration was also evaluated. Sufficient diuretic effects were obtained following the rectal administration of the suppositories containing weak acids.

A comparison of three diuretic regimens in heart failure

Eight patients with mild heart failure were treated in random order for 1 week with 2 mg bumethanide at 0800 and 1200 (treatment 1) h, 1 mg bumethanide at 0800, 1200, 1800, 2200 (treatment 2) and 5 mg bendroflumethiazide at 0800 and 1800 (treatment 3) h. The 'quality of life' did not differ significantly between the three treatment periods. At the presumed trough of the diuretic effect the circulating blood volume was largest during treatment 1; it was 6.3% smaller during treatment 2 (P < 0.02) and 6.7% lower during treatment 3 (P < 0.05). In comparison with treatment 1, the maximal increase in rate-pressure product during physical exercise was 24.6% higher in treatment 3. Compared with treatment 1 the area under the curve (AUC) for plasma lactate during physical exercise was 14% lower during treatment 2 (P < 0.05) and 18% lower during treatment 3 (P < 0.01). These findings suggest that the type of program for diuretic therapy influences the magnitude of inevitable diurnal fluctuations in body fluids, the ability of the heart to work and the ability of the body to adjust to the oxygen demand.

Effect of intravenous infusion time on the pharmacokinetics and pharmacodynamics of the same total dose of bumetanide

The pharmacokinetics and pharmacodynamics of bumetanide were evaluated after intravenous (i.v.) administration of the same total dose of bumetanide in different lengths of infusion times, 10 s (treatment I), 1 h (treatment II), and 4 h (treatment III) to rabbits. The fluid loss in urine was immediately replaced volume for volume with i.v. infusion of lactated Ringer's solution. Some pharmacokinetic parameters of bumetanide were infusion time-dependent and it might be due to the saturable metabolism of bumetanide. For example, the mean values of CL (13.6, 25.3 vs 18.2 ml min-1 kg-1), MRT (9.70, 10.6 vs 21.8 min), Vss (128, 217 vs 378 ml kg-1), and CLNR (2.71, 9.24 vs 6.44 ml min-1 kg-1) increased when the same dose of bumetanide was infused in 1 h or 4 h. However, the mean values of t1/2, and CLR were not significantly different among three treatments. The diuretic effects (urine outputs and urinary excretions of sodium and chloride) increased significantly in 1 and 4 h of infusion although the total amounts of urinary excretion of unchanged bumetanide were 21.8 and 20.5 per cent lower in treatments II and III, respectively, when compared with the value in treatment I; the mean values of 8-h urine outputs were 373, 922, and 1030 ml for 10s, 1 h, and 4 h of infusion, respectively, and the corresponding values for 24-h sodium excretions were 49.0, 82.8, and 121 mmol, and for chloride were 47.5, 71.1, and 114 mmol. It could be due to the higher diuretic efficiencies in treatments II and III. Plasma concentrations of bumetanide, and hourly urine outputs and hourly urinary excretion rates of bumetanide, sodium, potassium, and chloride during the apparent steady state (between 1 and 4 h) in the 4 h infusion study were fairly constant.

Enhanced absorption of bumetanide from suppositories containing weak acids in rabbits

The in vitro release of bumetanide from macrogol suppositories with and without weak acids (citric acid and tartaric acid) was studied. The release of bumetanide was not affected when weak acids were added to the suppositories. The in vivo rectal absorption of bumetanide from the suppositories was evaluated in rabbits. The bioavailability (absolute), expressed as the ratio of the area under the plasma concentration-time curve (AUC) following oral administration of bumetanide, was 39% that of intravenous administration. The value in bumetanide following rectal administration of the suppositories without weak acids was 32%. Each absolute bioavailability following rectal administration of the suppositories with 5% citric acid and 5% tartaric acid was 52% and 42%, respectively. These values were significantly larger than those of rectal administration of the suppositories without weak acids. Particularly, the bioavailability following rectal administration of the suppositories containing citric acid was significantly different from even those of oral administration. The absorption rate constants of bumetanide from the suppositories with weak acids were significantly larger than those following oral administration. These results indicated the possibilities of the rectal route of administration of drugs which are weak organic acids and show low or variable bioavailability following oral administration.

Spironolactone in congestive heart failure refractory to high-dose loop diuretic and low-dose angiotensin-converting enzyme inhibitor

Patients with severe congestive heart failure (New York Heart Association [NYHA] functional classes III-IV) often can tolerate only low doses of angiotensin-converting enzyme (ACE) inhibitors because pronounced hypotension caused by additional ACE inhibitor increments may decrease renal perfusion. The use of high-dose loop diuretics is currently advised to overcome diuretic resistance in refractory congestive heart failure (CHF). In a baseline controlled study, we evaluated 21 patients with diuretic resistance and evident fluid retention for the responses to 5 days of double drug therapy consisting of high-dose loop diuretic (10 mg oral bumetanide) in combination with the maximum tolerable dose of an ACE inhibitor (individualized to blood pressure and kidney function). Five patients (24%) showed a gross natriuresis and reduction in excess weight > 25% in response to this therapy. The remaining 16 patients (76%) with insufficient responses (i.e., < 25% reduction in excess weight) subsequently received 100 mg spironolactone once a day for 7 days in addition to the double therapy. Spironolactone coadministration was highly effective in 13 of 16 patients (81%). Marked natriuresis and diuresis were achieved within the next week of treatment, and CHF symptoms regressed or disappeared. The clinical course was similar in the bumetanide-ACE inhibitor and the bumetanide-ACE inhibitor-spironolactone treatment (triple therapy) groups. Plasma aldosterone was significantly higher (p < 0.05) in the patients who needed spironolactone. The 3 patients who were considered refractory to triple therapy exhibited the highest baseline plasma aldosterone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

[The immunomodulating properties of the diuretic bufenoks]

Bufenox, a diuretic with a sodium-uretic and light potassium--uretic effect, has an immediate but short-term effect, stimulates IgM antibody production, depressed delayed-type hypersensitivity. The immunomodulating effect of bufenox may be due to changes in Na+ ions concentrations since sodium load abrogates immunoactive properties of the drug.

Na+,2Cl-,K+ cotransport system as a marker of antihypertensive activity of new torasemide derivatives

A series of compounds related to torasemide, a loop diuretic, were synthesized and examined for their diuretic potency and inhibitory activity on the erythrocyte and renal medullary thick ascending limb vesicle Na+,2Cl-,K+ cotransport in Milan hypertensive (MHS) and normotensive (MNS) rat strains, where previous studies had demonstrated an alteration of the cotransport system genetically related to hypertension. From the results of the screening, structure-activity relationships were drawn and two compounds, JDL 961 and C 2921 were selected. Their IC50 on renal vesicle cotransport were similar in the two strains (JDL 961: MHS = 1.8 microM; MNS = 1.2 microM; C 2921: MHS = 4 microM; MNS = 3.8 microM), and were 4-8 times lower than those of torasemide (MHS = 13 microM; MNS = 31 microM, P less than 0.01) and 50-60 times lower than those of bumetanide (MHS = 145 microM; MNS = 206 microM, P less than 0.05) taken as reference compounds. Their ability to reduce the development rate of hypertension was tested both in MHS and in Okamoto spontaneously hypertensive rats (SHR) strain, in which cotransport alterations are opposite to those of MHS. Both torasemide derivatives (7.5 mg.kg-1 os per day) prevented development of hypertension in the two strains. The time course of this hypotensive activity was faster and the percentage of blood pressure fall greater in MHS (20-25%) than in SHR rats (12-15%), even though the absolute value of blood pressure fall was similar in MHS (JDL 961 = -17 mm Hg; C 2921 = -30 mm Hg) and SHR (JDL 961 = -25 mm Hg; C 2921 = -20 mm Hg). A superimposable effect of bumetanide was observed in the two strains, but at 8 times higher daily dose (60 mg.kg-1). These results suggest that new loop diuretics can be selected for their antihypertensive activity on the basis of their in vitro potency in inhibiting the Na+,2Cl-,K+.