Blocking early GABA depolarization with bumetanide results in permanent alterations in cortical circuits and sensorimotor gating deficits.

A high incidence of seizures occurs during the neonatal period when immature networks are hyperexcitable and susceptible to hypersyncrhonous activity. During development, γ-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in adults, typically excites neurons due to high expression of the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1). NKCC1 facilitates seizures because it renders GABA activity excitatory through intracellular Cl(-) accumulation, while blocking NKCC1 with bumetanide suppresses seizures. Bumetanide is currently being tested in clinical trials for treatment of neonatal seizures. By blocking NKCC1 with bumetanide during cortical development, we found a critical period for the development of α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate synapses. Disruption of GABA signaling during this window resulted in permanent decreases in excitatory synaptic transmission and sensorimotor gating deficits, a common feature in schizophrenia. Our study identifies an essential role for GABA-mediated depolarization in regulating the balance between cortical excitation and inhibition during a critical period and suggests a cautionary approach for using bumetanide in treating neonatal seizures.

Rapid hair cell loss: a mouse model for cochlear lesions.

In comparison to other mammals, mice have proved extremely resistant to aminoglycoside-induced hair cell ablation in vivo. In this paper we examine the pattern and extent of cochlear lesions rapidly induced with a combination of a single dose of aminoglycoside (kanamycin) followed by a loop diuretic (bumetanide). With this protocol, the vestibular system was unaffected, but in the cochlea, there was extensive loss of outer hair cells (OHC) that commenced in the basal coil and progressed apically so that, by 48 h, OHC loss was almost complete. TUNEL-positive nuclei and activated caspase-3 labeling demonstrated that most OHC died via a classical apoptotic pathway. However, scattered debris within the OHC region suggested that many apoptotic cells ruptured prior to completion of apoptosis. Following lesion repair, supporting cells retained characteristics of differentiated cells but positional shift occurred. In comparison to OHC loss, inner hair cell (IHC) death was delayed and only observed in 50% of all cochleae examined even after extensive reorganization of the tissue. The coadmininstration of diuretic with FM1-43, used as a tracer for aminoglycoside uptake, indicated entry into IHC as readily as OHC, suggesting that the differential response to aminoglycoside was not due to differential uptake. Where IHC death was ongoing, there were indications of different modes of cell death: cells with morphological features of autophagy, necrosis, and apoptosis were apparent. In addition to damage to the organ of Corti, there was a significant and progressive decrease in strial thickness beginning as early as 7 days posttreatment. This was due predominantly to degeneration of marginal cells. The strial pathology resembled that reported after noise damage and with aging. This in vivo protocol provides a robust model in which to obtain extensive OHC loss in the mature cochleae of mice and is a means with which to examine different aspects of cochlear pathology in transgenic or mutant strains.

Investigation of the photochemical properties and in vitro phototoxic potential of bumetanide.

The photophysical and photochemical properties of bumetanide, a sulfonamide diuretic drug, have been investigated and the photodegradation of the drug on exposure to UV-B and UV-A radiation monitored by fluorimetric and chromatographic (HPLC) methods. The main photoproducts were isolated by solid-phase extraction and liquid chromatographic procedures, and their structure elucidated by 1H-NMR and mass spectrometry. Bumetanide generates only extremely small quantities of singlet oxygen (1O2) upon irradiation in the presence of oxygen. The in vitro 3T3 N RU phototoxicity test yielded no evidence of phototoxic action.

Comparative acute ototoxicity of loop diuretic compounds.

A microelectrode was used to measure endocochlear potentials (EP) in adult chinchillas and to study the effects of a series of loop diuretics. EP was measured before, during and for several hours after the intravenous injection of the following loop diuretics: furosemide, piretanide, bumetanide, ethacrynic acid, indacrinone stereoisomers and ozolinone. The first four loop diuretics caused a substantial dose-related reduction of EP. The (-) isomer of indacrinone was found to cause a dose-related reduction of EP to a moderate degree. The (+) isomer of indacrinone and ozolinone caused very little change of EP, even in very high doses. Findings are consistent with data on the mechanism of action of these agents in the kidney.

Evidence for diabetogenic action of bumetanide in mice.

The effect of bumetanide on carbohydrate metabolism was studied in mice. Intraperitoneal injection of 50 or 100 mg bumetanide/kg body weight resulted in an acute and transient hyperglycaemia. Pretreatment with 240 mg probenecid/kg body weight reduced the diuretic effect but potentiated the hyperglycaemic effect of bumetanide (50 mg/kg body weight). The glucose tolerance was impaired, and there was an elevated serum glucose and glucose/insulin ratio 2 h after a single injection of bumetanide (100 mg/kg body weight). It is suggested that bumetanide has an acute effect on carbohydrate metabolism in mice that is not secondary to diuresis and that the reduced glucose tolerance may, at least in part, be due to a reduced capacity to secrete insulin.

Quantitative evaluation of ototoxic side effects of furosemide, piretanide, bumetanide, azosemide and ozolinone in the cat--a new approach to the problem of ototoxicity.

A new method for the quantitative assessment of acute ototoxic side effects of drugs is described. It is suitable for screening purposes. The method is based on the determination of the toxic dose (TD50) which causes a defined hearing loss in 50% of the animals tested. The hearing loss is defined as a complete suppression of the compound action potential (CAP) of the auditory nerve, elicited by clicks 30 dB above threshold. This is approximately equivalent to a clinical hearing loss of 30 dB. The TD50 is used to estimate the therapeutic range. With this approach ototoxic side effects of furosemide, piretanide and bumetanide were compared quantitatively in cats. The TD50 values for CAP suppression were 18.37 mg/kg for furosemide; 4.29 mg/kg for piretanide and 2.21 mg/kg for bumetanide. As equipotent diuretic doses are 2.61 mg/kg for furosemide, 0.26 mg/kg for piretanide and 1.16 mg/kg for bumetanide, it appears that the relative ototoxicity is least for piretanide and highest for bumetanide. Plasma concentrations, determined initially and when recovery of CAP to 50% of control had occurred, indicate that bumetanide may be more slowly eliminated from the cochlear spaces than furosemide and piretanide. In addition azosemide and ozolinone were tested. The TD50 for azosemide was less than 10 mg/kg. With ozolinone where there are two isomers, only the diuretic (-)ozolinone was ototoxic; the TD50 was less than 100 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Bumetanide. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic use.

Bumetanide is a potent 'loop' diuretic for the treatment of oedema associated with congestive heart failure, hepatic and renal diseases, acute pulmonary congestion and premenstrual syndrome and in forced diuresis during and after surgery. Bumetanide may be given orally, intravenously or intramuscularly and produces a rapid and marked diuresis, and increased urinary excretion of sodium, chloride and other electrolytes (within 30 minutes) which persists for 3 to 6 hours. Its principal site of action is on the ascending limb of the loop of Henle, with a secondary action on the proximal tubule. Pharmacologically, bumetanide is about 40-fold more potent than frusemide (furosemide), with the exception of its effects on urinary potassium excretion where its potency is lower. Studies in patients with oedema due to congestive heart failure, pulmonary oedema or hepatic disease show that oral or intravenous bumetanide 0.5 to 2 mg/day produces results comparable to those with frusemide 20 to 80 mg/day. In acute pulmonary oedema, intravenous bumetanide produces a very rapid diuresis. Higher doses of bumetanide may be required (up to 15 mg/day) in patients with chronic renal failure or nephrotic syndrome. In these patients muscle cramps are not uncommon with bumetanide, but glomerular filtration rates are unaffected. In most studies, diuretic effects were accompanied by decreased bodyweight, abdominal girth and improvements in a variety of haemodynamic parameters. Comparison of bumetanide with frusemide at a dose ratio of 1 : 40 reveals no significant differences in clinical response with the exception of renal disease, where patients with oedema appear to respond better to bumetanide. Combination with thiazide diuretics enhances the clinical response to bumetanide. Potassium supplements and spironolactone may be beneficial additions to bumetanide where patients at risk of hypokalaemia can be identified. Clinically important side effects are infrequent, with audiological impairment occurring to a lesser extent than with frusemide. Bumetanide thus offers an important alternative to frusemide when a 'loop' diuretic is indicated.

Comparative ototoxicity of bumetanide and furosemide when used in combination with kanamycin.

The ototoxicity of bumetanide and furosemide was compared in Topeka strain guinea pigs pretreated with kanamycin. The animals, anesthetized with pentobarbital, received a single dose of 400 mg/kg kanamycin subcutaneously and the diuretics via indwelling catheter in the jugular vein 2 hours later. Ototoxic drug effects were determined by measuring the electrophysiological responses of the cochlea to sound stimuli and by determining the presence or absence of cochlear sensory hair cells from the organ of Corti. Both bumetanide and furosemide produced permanent alteration of cochlear activity in the kanamycin-pretreated animals. The ototoxic effect of bumetanide is five times that of furosemide on a milligram-for-milligram basis. The ototoxic potential of bumetanide is one eighth that of furosemide when the doses are adjusted for diuretic potency difference between the two diuretics.

Comparative acute cochlear toxicity of intravenous bumetanide and furosemide in the purebred beagle.

Comparisons were made of the effects of various doses of intravenous bumetanide and furosemide on the primary auditory afferent activity (N1) and cochlear microphonics (CM) of beagles. The dose-response relationships of the N1 depressions to bumetanide and furosemide are parallel; those of the CM depressions are also parallel but have a much shallower slope than those of the N1 depressions. With both drugs, N1 depression occurs at lower doses than does CM depression. The N1 depression produced by a particular dose of bumetanide or furosemide bore a linear relationship to the CM depression produced. This finding supports the postulate that the cochlear site and mechanism of ototoxic action of the loop diuretics are directed at an earlier step of the cochlear transduction process than N1. Using N1 depression as the gross electrophysiologic index of ototoxicity, the acute ototoxic potency of bumetanide in beagles is approximately 6.5 times that of furosemide, whereas its diuretic potency is 40 to 60 times that of furosemide. Therefore, when clinical dosages of the two drugs are considered, the relative acute ototoxic potency of bumetanide in the beagle is 0.11 to 0.16 that of furosemide. This range is identical to the relative ototoxic potency of 0.11 to 0.16 previously obtained in the cat. Serum concentrations of bumetanide and furosemide increased linearly with the doses of the two drugs, except for the highest dose given (100 mg/kg for both drugs). The serum concentrations at that dose of both drugs are less than the mathematically predicted values. Histologic (light-microscopic) examination of the cochleas did not reveal any significant pathology.

Comparative efficacy and safety of bumetanide and furosemide in long-term treatment of edema due to congestive heart failure.

Bumetanide and furosemide were compared for efficacy in reducing edema due to congestive heart failure in 28 patients (21 receiving bumetanide and seven receiving furosemide) in a long-term study for periods from one week to 18 months. In both groups the patients showed decreases in body weight, abdominal girth, edema, hepatomegaly, blood pressure, and heart rate. Commonly observed decreases frequently achieved statistical significance, more often with bumetanide, but the differences between treatments were rarely statistically significant. Both drugs were generally well tolerated. A breast nodule and gynecomastia were each reported once in the bumetanide group as was gynecomastia in one patient who had been on furosemide, all remotely related to test drugs. Soft stools, flatulence, mild constipation, and diminished vision each reported once in the bumetanide group were judged to be unrelated or remotely related to the drug therapy. Tendencies toward hypokalemia, hypochloremia, alkalosis, and hyperuricemia without clinical gout were deemed the result of the pharmacologic action of the diuretics. Others were attributable to the underlying disease state of these patients. Both diuretics proved to be effective in the treatment of cardiac edema and other manifestations of heart failure. Bumetanide treatment beyond six months in 11 patients indicated continued safety as well as efficacy.

Toxicologic evaluation of bumetanide, potent diuretic agent.

The studies reported represent the preclinical toxicologic evaluation of bumetanide. Toxicity testing in rats, rabbits, dogs, and baboons indicate that bumetanide is well tolerated in various species. The toxicity that was observed is, for the most part, the direct consequence of its potent diuretic activity and is similar to that produced by other "loop" diuretics. Bumetanide was fetotoxic at maternal toxic doses in the rabbit, but no evidence of teratogenic effects was observed in rabbits, rats, mice, or hamsters. The compound was devoid of mutagenic activity by the Ames test and was found to be noncarcinogenic in long-term rat studies.

Bumetanide: a new diuretic. Results of clinical efficacy and safety in patients with congestive heart failure.

A clinical study of bumetanide, a new diuretic, was conducted in outpatients of a cardiology clinic to determine its long-term effectiveness and safety in the treatment of peripheral edema due to congestive heart failure. The drug was administered for at least 24 weeks on a selected group of 34 patients. The patients were monitored for clinical response, evidenced by changes in cardiac signs and symptoms, and by laboratory tests, as well as by slit-lamp ophthalmic examination, electrocardiogram, and chest x-ray. Based on the clinical evaluation of effects on body weight, chronic edema, functional physical capacity, and results of selected laboratory data, it was concluded that bumetanide is as effective as other diuretics and can be used as an initial diuretic for maintenance of body weight for long-term use in patients with peripheral edema due to congestive heart failure. Bumetanide mobilizes peripheral edema effectively in most patients and leads to improvement in functional physical capacity. Safety and adverse reactions during treatments are discussed.