Effect of inhaled furosemide on the bronchial response to methacholine and cold-air hyperventilation challenges

Chloride channel blockade relaxes airway smooth muscle and potentiates relaxation by β-agonists

Severe bronchospasm refractory to β-agonists continues to cause significant morbidity and mortality in asthmatic patients. We questioned whether chloride channels/transporters are novel targets for the relaxation of airway smooth muscle (ASM). We have screened a library of compounds, derivatives of anthranilic and indanyloxyacetic acid, that were originally developed to antagonize chloride channels in the kidney. We hypothesized that members of this library would be novel calcium-activated chloride channel blockers for the airway. The initial screen of this compound library identified 4 of 20 compounds that relaxed a tetraethylammonium chloride-induced contraction in guinea pig tracheal rings. The two most effective compounds, compounds 1 and 13, were further studied for their potential to either prevent the initiation of or relax the maintenance phase of an acetylcholine (ACh)-induced contraction or to potentiate β-agonist-mediated relaxation. Both relaxed an established ACh-induced contraction in human and guinea pig ex vivo ASM. In contrast, the prevention of an ACh-induced contraction required copretreatment with the sodium-potassium-chloride cotransporter blocker bumetanide. The combination of compound 13 and bumetanide also potentiated relaxation by the β-agonist isoproterenol in guinea pig tracheal rings. Compounds 1 and 13 hyperpolarized the plasma cell membrane of human ASM cells and blocked spontaneous transient inward currents, a measure of chloride currents in these cells. These functional and electrophysiological data suggest that modulating ASM chloride flux is a novel therapeutic target in asthma and other bronchoconstrictive diseases.

Exhaled breath condensate pH decreases during exercise-induced bronchoconstriction

BACKGROUND AND OBJECTIVE

Exercise-induced bronchoconstriction (EIB) is the temporary narrowing of the airways caused by physical exercise. Its exact pathophysiology is unclear; however, acute changes in airways pH may play a role. Exhaled breath condensate (EBC) pH was suggested as a surrogate indicator for airway acid-base status, but its value is also affected by volatile molecules and respiratory droplet dilution. The aim of the study was to assess changes in EBC pH during EIB.

METHODS

Twenty-two asthmatics who reported breathlessness following exercise and 16 healthy individuals participated in the study. Lung function test was performed and exhaled breath samples were collected for pH, dilution factor and volatile compound pattern measurements (Cyranose 320) pre-exercise and at 0, 10, 20 and 30 min after physical exercise challenge. Fractional exhaled nitric oxide was measured before exercise.

RESULTS

EIB developed in 13 asthmatic subjects. In these participants, but not in the EIB-negative asthmatics (P = 0.51), EBC pH reduced significantly during exercise (P = 0.01). In addition, changes in EBC pH were related to the degree of bronchospasm in the EIB-positive group (P = 0.01, r = 0.68). Exhaled volatile pattern became altered (P < 0.05) during exercise in all subjects (asthmatics and controls). EBC pH changes were not related to EBC dilution or volatile compound pattern alterations (P > 0.05).

CONCLUSIONS

The development of EIB was related to acute changes of EBC pH, which suggest the role of airway pH decrease in the pathophysiology of EIB. Exercise-induced changes in exhaled biomarkers suggest methodological precautions to avoid physical exercise before performing exhaled breath tests.

Effectiveness of nebulized furosemide added to nebulized salbutamol in children with acute asthma

BACKGROUND

Nebulized furosemide has been shown to be protective against bronchoconstricting stimuli.

METHODS

To investigate whether inhaled furosemide would exhibit an additional therapeutic effect in children with acute asthma we performed a double-blind, placebo-controlled study in which patients with acute asthma attack were randomized to receive either nebulized salbutamol (0.15 mg/kg) plus nebulized furosemide (10 mg/m(2)) or nebulized salbutamol (0.15 mg/kg) plus nebulized saline as placebo. In all patients, clinical asthma scores (CAS) were determined before and after drug administration. Peak expiratory flow rates (PEFR) were measured by a peak flow meter.

RESULTS

CAS and PEFR improved in both groups with nebulized salbutamol treatment. The CAS changed from 3.56 +/- 2.13 to 2.06 +/- 1.84 (p = 0.0001) in the study group and from 4.44 +/- 2.63 to 2.56 +/- 1.86 (p = 0.0003) in the control group. PEFR increased from 177.50 +/- 65.88 to 221.88 +/- 66.05 L/min in the first group (p = 0.0001) and from 183.13 +/- 51.73 to 218.13 +/- 60.25 in the second group (p = 0.0001).

CONCLUSION

Adding nebulized furosemide to nebulized salbutamol in pediatric patients experiencing an acute asthma attack did not produce greater improvement in clinical (p = 0.3829) or spirometric (p = 0.3839) parameters than nebulized salbutamol alone.

The Effect of Furosemide Infusion on Serum Epidermal Growth Factor Concentration After Acute Lung Injury

Acute lung injury and its more severe form, acute respiratory distress syndrome, are clinical syndromes of progressive hypoxemia and ventilation-perfusion mismatch with decreasing pulmonary compliance in the absence of congestive heart failure. Epidermal growth factor is involved in the pathogenesis of airway inflammation as well as a proinflammatory effect in other tissues. Furosemide has been shown to improve pulmonary gas exchange and intrapulmonary shunt by a nondiuretic mechanism in animal models of acute respiratory distress syndrome. The current study was undertaken to clarify whether furosemide attenuates the inflammatory response by changing the epidermal growth factor level in patients with acute lung injury. A prospective, randomized clinical trial involving 30 patients with acute lung injury was designed and conducted over 7 days. The measured outcomes included hemodynamics, acute physiology and chronic health evaluation (APACHE II) scores, and oxygenation. The serum specimens were analyzed with enzyme-linked immunoassay (ELISA) for epidermal growth factor at baseline, then 3 and 7 days after acute lung injury. The ratio of partial pressure of arterial oxygen (PaO2) to fraction of inspired oxygen (FIO2) improved in the furosemide-treated group within 24 hours (from 180 to 264; P = .01). The mean arterial pressure and heart rate was greater in this group than in the control group (that received no furosemide) on day 7 (P = .027). The mean arterial pressure increased and the heart rate decreased over time in the treatment group, but not significantly. Serum epidermal growth factor levels also were not significantly different between the furosemide treatment group and the control group (P > .05). Continuous furosemide infusion improves oxygenation and hemodynamics in patients with acute lung injury, but not through a change in the serum epidermal growth factor level. Further study is needed to determine the exact mechanism of furosemide action in patients with acute lung injury and acute respiratory distress syndrome.

Effects of hyperosmolarity and airway epithelial ion transport inhibitors on sodium nitroprusside-induced relaxation of guinea pig trachea

Increased airway surface osmolarity has been shown to abolish the airway relaxant effects of inhaled nitric oxide. We have investigated the effects of increased airway surface osmolarity on airway relaxation induced by nitric oxide. The physiological responses, obtained by a guinea pig tracheal perfusion method, were compared to the ion content of the tracheal tissues, and the effects of amiloride or furosemide were studied. Hyperosmolarity decreased the ability of sodium nitroprusside (SNP) to relax carbachol-constricted trachea. Light microscopy showed shrinkage of the epithelial cells and X-ray microanalysis showed increased epithelial ion content under conditions of intraluminal hyperosmolarity, suggesting dehydration of the epithelium. Amiloride treatment reduced the increase in epithelial ion content but had no effect on shrinkage or SNP-induced relaxation. Furosemide had no effect on the altered ion content, shrinkage, or on SNP-induced relaxation. In conclusion, neither amiloride nor furosemide can counteract the shrinkage of the airway wall induced by increased osmolarity in the lumen of guinea pig trachea in vitro, nor can they affect the reduction in relaxing response to the NO-donor SNP.

Differential effects of furosemide on porcine bronchial arterial and airway smooth muscle

Furosemide attenuates airway obstruction in asthmatic subjects when administered as an aerosol pretreatment. This protective effect of furosemide could be related to relaxation of bronchial smooth muscle or to increased bronchial blood flow. To determine whether furosemide dilates bronchial smooth muscle, isometric contractile responses in distal bronchi from young pigs were studied. In bronchial smooth muscle rings that were precontracted with 10(-5) M acetylcholine, significant relaxation occurred with 10(-8) to 3 x 10(-6) M isoproterenol but not with 10(-8) to 10(-3) M furosemide. In contrast, bronchial arteries that were precontracted with either 10(-4) M norepinephrine or 10(-8) M vasopressin significantly relaxed in response to 10(-4) to 3 x 10(-3) M and 10(-3) to 3 x 10(-3) M furosemide, respectively. We conclude that furosemide, under the described experimental conditions, relaxes airway vascular smooth muscle but not bronchial smooth muscle. These results are consistent with previous suggestions that inhaled furosemide increases blood flow to airway tissues (Gilbert IA, Lenner KA, Nelson JA, Wolin AD, and Fouke JM. J Appl Physiol 76: 409-415, 1994).

Aerosolized furosemide in the treatment of acute respiratory distress and possible bronchopulmonary dysplasia in preterm neonates

OBJECTIVE

To review the efficacy and safety of inhaled furosemide in the treatment of acute respiratory distress and possible bronchopulmonary dysplasia (BPD) in preterm neonates receiving ventilator and oxygen support.

DATA SOURCES

A MEDLINE search was performed from January 1966 to December 1998 using the key words inhaled or aerosolized furosemide, BPD, preterm, neonate, and infant newborn.

STUDY SELECTION AND DATA EXTRACTION

All clinical trials involving the use of inhaled furosemide in ventilator- and oxygen-dependent preterm neonates with acute respiratory distress and possible BPD were evaluated.

DATA SYNTHESIS

Inhaled furosemide 1 and 2 mg/kg has improved pulmonary function in preterm neonates without significant adverse effects. However, only a single dose of inhaled furosemide was used in these trials, and pulmonary functions were monitored for only two or four hours after administration.

CONCLUSIONS

Inhaled furosemide may be effective, but studies are needed to determine the optimal dosage regimen and long-term risks and benefits of its use in these patients.

Immunosuppressive and cytotoxic effects of furosemide on human peripheral blood mononuclear cells

BACKGROUND

We have previously shown that children with mild asthma have a modest improvement in their pulmonary function tests after aerosolized furosemide. The mechanism of action is not known. The observation that furosemide possesses a similar profile of protection as sodium cromoglycate and nedocromil sodium suggests that furosemide may inhibit mediator production and release.

OBJECTIVE

We studied the in vitro effects of furosemide on cytokine release from normal human peripheral blood mononuclear cells (PBMC) induced by E. coli lipopolysaccharide (LPS).

METHODS

Peripheral blood mononuclear cells were isolated by density gradient centrifugation, stimulated with LPS and incubated at 37 degrees C with varying concentrations of furosemide, hydrocortisone, sodium cromoglycate, and nedocromil sodium for 24 hours. Supernatants were extracted and study for levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and interleukin-8 (IL-8). Intracellular IL-6 and TNF-alpha concentrations were also measured by cell cytometry. Cell viability was examined using XTT cell proliferation test and-measuring the release of lactate dehydrogenase (LDH).

RESULTS

There was a significant reduction in levels of TNF-alpha and IL-6 at a furosemide concentration of 0.5 x 10(-2) M and a reduction in IL-8 levels at 10(-2) M. This inhibition was comparable to that found with equivalent molar concentrations of hydrocortisone. These findings were also confirmed with measurements of intracellular IL-6 and TNF-alpha by cell cytometry. High concentration of furosemide at 10(-2) M caused significant cellular cytotoxicity.

CONCLUSION

These data suggest that furosemide may exhibit an anti-inflammatory effect. Specifically, the addition of furosemide resulted in decreased production of cytokines. This effect may be due to an immunosuppressive activity on monocytes as well as a direct cytotoxic effect at high furosemide concentrations.

Effect of pre-treatment with inhaled furosemide on allergen nasal challenge

The inhalation of furosemide has been reported to inhibit the bronchospasm induced by several agents. In the present study, we evaluated the effect of inhaled furosemide on the specific nasal challenge test in patients with allergic rhinitis. A total of 21 consecutive patients with allergic rhinitis (positive skin test and RAST) and a positive basal nasal provocation test (NPT) with the specific allergen were investigated. In each patient, we compared the changes in nasal air-flow (anterior rhinomanometry) during NPT after inhalation of placebo and 20 mg furosemide. The previously positive NPT response to the inhalation of the specific allergen became negative after the furosemide pretreatment in 16 patients (76.2%, p < 0.001, chi-square test). The nasal air flows during NPT were significantly increased after furosemide treatment with respect to placebo inhalation (F = 17.2, d.f. = 1 and 3; p < 0.03; covariance analysis). Our results suggest that the pretreatment with inhaled furosemide in atopic subjects is able to exert a protective effect on the nasal mucosa reactivity to the specific allergen. Therefore, the anti-reactive effect of the drug on the airways is not confined to the bronchial asthmatic response.

Changes in neurokinin A (NKA) airway responsiveness with inhaled frusemide in asthma

BACKGROUND

Inhaled frusemide exerts a protective effect against bronchoconstriction induced by several indirect stimuli in asthma which could be due to interference of airway nerves. A randomised, double blind, placebo controlled study was performed to investigate the effect of the potent loop diuretic, frusemide, administered by inhalation on the bronchoconstrictor response to neurokinin A (NKA) and histamine in 11 asthmatic subjects.

METHODS

Subjects attended the laboratory on four separate occasions to receive nebulised frusemide (40 mg) or matched placebo 10 minutes prior to bronchial challenge with NKA and histamine in a randomised, double blind order. Changes in airway calibre were followed as forced expiratory volume in one second (FEV1) and responsiveness to the agonists was expressed as the provocative concentration causing a 20% fall in FEV1 from baseline (PC20).

RESULTS

Compared with placebo, inhaled frusemide reduced the airway responsiveness to NKA in all the subjects studied, the geometric mean (range) values for PC20NKA increasing significantly (p < 0.001) from 130.3 (35.8-378.8) to 419.9 (126.5-1000) micrograms/ml after placebo and frusemide, respectively. Moreover, a small but significant change in airway responsiveness to histamine was recorded after frusemide, their geometric mean (range) PC20 values being 0.58 (0.12-3.80) and 1.04 (0.28-4.33) mg/ml after placebo and frusemide, respectively.

CONCLUSIONS

The decrease in airway responsiveness to NKA after administration of frusemide by inhalation suggests that this drug may interfere with the activation of neurotransmission in human asthma.

Dilatory effect of furosemide on rat tracheal arterioles and venules

Furosemide pretreatment greatly reduces the severity of an asthmatic response to several types of bronchoconstrictor challenge. Indirect evidence suggests that furosemide exerts its protective effects by dilating the airway vasculature during thermal stress. To test the hypothesis that furosemide dilates airway microvessels, the tracheas of anesthetized rats were surgically exposed and continuously suffused with Krebs Ringer bicarbonate warmed to 37 degrees C. Tracheal adventitial arterioles (13.0 to 41.0 microns initial diameter, n = 47) and venules (50.0 to 99.0 microns initial diameter, n = 46) were visualized with a videomicroscope, and vessel diameters were measured using videocalipers. When vessels were preconstricted with 10(-4) M phenylephrine, a selective alpha 1-adrenergic agonist, and then treated with 10(-4) M furosemide, significant (p < 0.05) dilation was observed in both arterioles (from 64.6 to 79.5% of their initial diameter) and venules (from 52.1 to 65.4% of their initial diameter). When vessels were preconstricted with 10(-4) phenylephrine, after pretreatment with the cyclooxygenase inhibitor indomethacin (5.0 mg/kg), 10(-4) M furosemide significantly dilated arterioles (from 77.5 to 93.0% of their initial diameter) and venules (from 58.5 to 80.1% of their initial diameter). In vessels preconstricted with 10(-3) M L-NAME, an inhibitor of nitric oxide synthesis, addition of 10(-4) M furosemide to the suffusion still caused significant dilation in arterioles, from 77.4 to 88.8% of their initial diameter, and in venules from 79.5 to 86.7% of their initial diameter. These data confirm that furosemide, when applied topically, dilates tracheal arterioles and venules by cyclooxygenase- and nitric oxide-independent mechanisms.

Furosemide given by inhalation ameliorates acute exacerbation of asthma

Previous studies have suggested that inhaled furosemide may have a protective effect against a wide variety of bronchoconstrictor agents, but a therapeutic effect has not been established in acute exacerbation of asthma. The purpose of this study was to investigate whether inhaled furosemide would exhibit any therapeutic benefit in acute asthma. We conducted a double-blind, placebo-controlled, randomized study in 40 patients with acute mild or moderate exacerbation of asthma. All patients received intravenous (i.v.) aminophylline 250 mg for 90 min and i.v. hydrocortisone 100 mg at entry. After randomization, 3 patients were excluded from the final analysis. At 30 min after starting i.v. aminophylline, 20 patients were given inhaled furosemide 20 mg and 17 patients received normal saline as placebo-control. Both inhalations were given by a jet nebulizer. The baseline forced expiratory volume at 1 sec (FEV1), peak expiratory flow rate (PEFR), and serum concentration of theophylline did not differ between the two groups. An increase in FEV1 in the furosemide group by 28.2 +/- 5.9% (mean +/- SE) was noted at 60 min, and this was significantly higher than in the control group. PEFR at 60 min was also significantly higher in the furosemide group than in control group. We conclude that inhaled furosemide has a bronchodilator effect on mild to moderate exacerbation of asthma when it is used with i.v. theophylline. Inhaled furosemide may benefit certain acute asthma patients, especially those suffering complications from the adverse effects of beta 2-agonists.

Pulmonary effect of inhaled furosemide in ventilated infants with severe bronchopulmonary dysplasia

BACKGROUND

When administered parenterally, furosemide, a loop diuretic, results in improved lung compliance and decreased airway resistance in infants with bronchopulmonary dysplasia (BPD). However, furosemide-induced diuresis results in hypokalemia, chloride deficiency, hypercalciuria, nephrocalcinosis, and rickets. In patients with asthma, inhaled furosemide has recently been demonstrated to inhibit the bronchoconstrictive effects of exercise, cold air hyperventilation, and antigen challenge. We hypothesized that inhaled furosemide will result in improved pulmonary mechanics in ventilated infants with BPD and will prevent the systemic complications of parenteral furosemide.

OBJECTIVE

To determine the efficacy and safety of a single dose of inhaled furosemide on pulmonary mechanics in infants with severe BPD who are ventilator dependent at 21 days of age.

DESIGN AND METHODS

A randomized, double-blind, crossover study was performed on 9 infants with BPD, each serving as his own control. Each patient was randomized to receive an aerosol dose of furosemide (1 mg/kg in 2 mL of saline) or placebo (2 mL of saline) on the first day of the study and the other agent the following day of the study. Pulmonary mechanics were measured before and 1 and 2 hours after the inhalation using the Pulmonary Evaluation and Diagnostics System.

RESULTS

Gestational age (mean +/- SEM) was 29 +/- 1 weeks; birth weight was 1.1 +/- 0.1 kg; age at study was 47 +/- 6 days; and weight at study was 1.8 +/- 0.2 kg. There was no significant change in the pulmonary function measurements before treatment and 1 or 2 hours after treatment with either placebo or furosemide. Baseline and 2-hour values were: dynamic compliance (mL/ cm H2O per kilogram): 0.46 +/- .03 to 0.50 +/- .03 (placebo) and 0.50 +/- 0.02 to 0.51 +/- 0.02 (furosemide); dynamic resistance (cm H2O/L per second): 118 +/- 9 to 106 +/- 7 (placebo) and 111 +/- 8 to 105 +/- 7 (furosemide); and tidal volume (mL/kg): 8.6 +/- 0.5 to 8.9 +/- 0.5 (placebo) and 8.9 +/- 0.2 to 9.4 +/- 0.3 (furosemide).

CONCLUSION

We conclude that, under the conditions of our study, a single dose of 1 mg/kg inhaled furosemide does not improve the pulmonary mechanics in ventilator-dependent infants with severe BPD.

Effect of inhaled frusemide and oral indomethacin on the airway response to hypertonic saline challenge in asthmatic subjects

BACKGROUND

Inhaled frusemide inhibits airway narrowing and causes a transient increase in forced expiratory volume in one second (FEV1) during hypertonic saline challenge. This inhibitory effect could be secondary to prostaglandin release during challenge. The involvement of prostaglandins in the inhibitory action of frusemide during challenge with 4.5% NaCl was investigated by premedicating with indomethacin, a prostaglandin synthetase inhibitor.

METHODS

Fourteen asthmatic subjects (eight women) aged 26.6 (range 18-56) years participated in a double blind, placebo controlled, crossover study. The subjects attended five times and inhaled 4.5% NaCl for 0.5, 0.75, 1, 1.5, 2, 4, 8, 8, and 8 minutes, or part thereof, or until a provocative dose causing a 20% fall in FEV1 (PD20 FEV1) was recorded. Indomethacin (100 mg/day) or placebo were taken three days before all visits, except control day. The FEV1 was measured and frusemide (38.0 (6.4) mg, pH = 9) or vehicle (0.9% NaCl, pH = 9) were inhaled 10 minutes before the challenge. Bronchodilation was calculated as the percentage rise in FEV1 from the prechallenge FEV1 to the highest FEV1 recorded during the challenge.

RESULTS

Frusemide caused a fold increase in PD20 FEV1 compared with the vehicle which was similar in the presence of both indomethacin and placebo (3.7 (95% CI 2.0 to 7.3) versus 3.3 (2.0 to 5.4)). Frusemide, but not vehicle, also caused a transient percentage rise in FEV1 during challenge with 4.5% NaCl which was not blocked by indomethacin (3.6% (1.2 to 6.0)) or placebo (3.1% (1.0 to 5.2)).

CONCLUSIONS

Inhaled frusemide inhibited airway narrowing and caused a transient increase in FEV1 during challenge with 4.5% NaCl. These effects were not blocked by indomethacin, which suggests that the inhibitory action of frusemide is not secondary to prostaglandin release.

Breathlessness and exercise capacity in heart failure: the role of bronchial obstruction and responsiveness

The cause of the breathlessness and reduced exercise capacity that occur in patients with chronic heart failure remains obscure. We examined the hypothesis that airway obstruction and bronchial hyper-responsiveness, which are recognised features of chronic heart failure, might contribute to the breathlessness and reduced exercise capacity in this condition. We studied 37 patients (7 female) with chronic heart failure, of mean age 61 years. Each patient underwent: (i) lung function testing with spirometry and expiratory flow volume loops. (ii) Measurement of bronchial responsiveness to methacholine. (iii) Symptom-limited treadmill exercise capacity using both incremental and fixed workload protocols, with measurement of Borg scores for breathlessness. Lung function was not significantly related to either exercise time, or Borg symptom scores in either exercise protocol. Bronchial hyper-responsiveness to methacholine was demonstrated in 12 patients. Exercise time did not correlate with the degree of bronchial hyper-responsiveness in these 12 patients. Group mean exercise time and Borg scores were not significantly different in these 12 patients when compared to the 25 patients in whom bronchial hyper-responsiveness was not found. We conclude that airway obstruction and bronchial hyper-responsiveness are not likely to be important determinants of reduced exercise capacity and breathlessness in chronic heart failure.

Effect of furosemide on hyperpnea-induced airway obstruction, injury, and microvascular leakage

Furosemide attenuates hyperpnea-induced airway obstruction (HIAO) in asthmatic subjects via unknown mechanism(s). We studied the effect of furosemide on dry air-induced bronchoconstriction, mucosal injury, and bronchovascular hyperpermeability in a canine model of exercise-induced asthma. Peripheral airway resistance (Rp) was recorded before and after a 2-min dry-air challenge (DAC) at 2,000 ml/min. After pretreatment with aerosolized saline containing 0.75% dimethyl sulfoxide, DAC increased Rp 72 +/- 11% (SE, n = 7) above baseline; aerosolized furosemide (10(-3) M) reduced this response by approximately 50 +/- 6% (P < 0.01). To assess bronchovascular permeability, colloidal carbon was injected (1 ml/kg i.v.) 1 min before DAC, and after 1 h, the vehicle- and furosemide-treated airways were prepared for morphometric analysis. Light microscopy confirmed previous studies showing that DAC damaged the airway epithelium and enhanced bronchovascular permeability. Furosemide did not inhibit dry air-induced mucosal injury or bronchovascular hyperpermeability and in fact tended to increase airway damage and vascular leakage. This positive trend toward enhanced bronchovascular permeability in DAC canine peripheral airways is consistent with the hypothesis that furosemide inhibits HIAO in part by enhancing microvascular leakage and thus counterbalancing the evaporative water loss that occurs during hyperpnea.

Inhaled furosemide is not effective in acute asthma

As previous studies have suggested that inhaled furosemide may have a protective effect against certain types of provocative challenges in asthmatic subjects, we investigated the role of furosemide in treating acute asthma exacerbations. Twenty-four patients (n = 24) with acute asthma were entered into the study on presenting to the emergency department. They were blindly randomized to receive one of three drug regimens: (1) inhaled furosemide (40 mg) (n = 8); (2) inhaled metaproterenol (15 mg) (n = 7); or (3) the combination of furosemide (40 mg) and metaproterenol (15 mg) (n = 9). We measured FEV1 at entry (time 0) and 15, 30, 45, and 60 min after inhalation of the individual drugs or the combination from a face mask nebulizer. At entry, the three groups did not differ significantly in age (mean +/- SEM = 37.6 +/- 3.6, 38.5 +/- 3.6, and 41.0 years, respectively; p = 0.770), baseline FEV1 (1.01 +/- 0.27, 1.04 +/- 0.27, and 1.25 +/- 0.14 L, respectively; p = 0.620), or theophylline levels (2.87 +/- 1.8, 7.39 +/- 2.8, and 5.29 +/- 2.6 micrograms/ml, respectively; p = 0.498). Pretreatment and posttreatment potassium levels were similar among the three groups. Inhalation of furosemide alone resulted in a 14.9 +/- 10.5 percent change in FEV1 percent from baseline, which was not statistically significant. In contrast, metaproterenol alone resulted in a 42.9 +/- 15.2 percent increase in FEV1 percent (F ratio = 6.226; p = 0.0028). The combination of furosemide and metaproterenol resulted in a change in FEV1 percent that was not statistically different compared with metaproterenol alone (FEV1 percent = 41.9 +/- 12 percent). No significant adverse effects occurred in any of the groups.

Reversal of bronchial obstruction in children with mild stable asthma by aerosolized furosemide

Aerosolized furosemide has been shown to prevent the worsening of different variables in pulmonary function testing, following exercise or bronchial provocation with numerous agents. To investigate if aerosolized furosemide has a bronchodilator effect, we performed two prospective, randomized, placebo-controlled, double-blinded and crossover studies of four aerosol regimens in children with mild chronic asthma. In a pilot study examining three different doses of furosemide in 11 children, the dose of 1.0 mg/kg resulted in a mean maximum increase of 30.0 +/- 6.8% in forced expiratory flow between 25 and 75% vital capacity (FEF25-75), compared with a 3.1 +/- 6.8% increase after aerosolized normal saline. The effect was observed after 10 minutes with a mean percent change of 17.7 +/- 1.7% from baseline, that persisted to 30 minutes (19.3 +/- 3.7%) and was significantly greater than that seen following aerosolized placebo (1.4 +/- 2.9% and 0.7 +/- 3.4%, respectively; P < 0.05). We then compared the effect of furosemide with that of aerosolized albuterol (0.15 mg/kg) in 18 patients. There was no statistically significant difference in the improvement observed in forced expiratory volume in 1 second (FEV1) for albuterol (15.0 +/- 2.7%) compared with furosemide (12.1 +/- 2.9%) or in FEF25-75 (42.9 +/- 9.0% versus 26.3 +/- 6.7%). The addition of albuterol to furosemide resulted in a 17.2 +/- 5.9% increase in FEV1 and a 51.1 +/- 13.9% increase in FEF25-75. Our results indicate that aerosolized furosemide has a bronchodilator effect in children with mild stable asthma.

Effect of loop diuretics on cholinergic neurotransmission in human airways in vitro

BACKGROUND

Frusemide can inhibit various indirectly acting bronchoconstrictor stimuli in asthmatic patients. Both frusemide and bumetanide also modulate airway neurotransmission in some species but there are no data on the effect of loop diuretics on neurotransmission in man. An in vitro study was performed in human airways to investigate the possible neuromodulatory action of two loop diuretics, frusemide and bumetanide, and to elucidate whether a cyclooxygenase inhibitor such as indomethacin could modulate the effect of frusemide. The effect of acetazolamide, a carbonic anhydrase inhibitor, was also investigated.

METHODS

Electrical field stimulation (EFS; 40 V, 0.5 ms, 0.5-32 Hz for 15 seconds) in human airways with or without epithelium was used to induce a cholinergic contraction (n = 5 in all experiments). Indomethacin was present throughout. After obtaining a control frequency-response curve, different concentrations of diuretic were added to the organ bath and another frequency-response curve was constructed. To determine whether the effect of the diuretic was prejunctional or postjunctional a cumulative concentration-response curve to exogenous acetylcholine (Ach, 0.3 mumol/l to 10 mmol/l) was constructed in the presence of a diuretic (frusemide 1 mmol/l or bumetanide 0.1 mmol/l) or its vehicle. In some experiments indomethacin was omitted from the organ bath to investigate the possible involvement of cyclooxygenase products.

RESULTS

Both frusemide (10 mumol/l to 1 mmol/l) and bumetanide (1 mumol/l to 0.1 mmol/l) produced a concentration-dependent inhibition of the EFS-induced cholinergic contraction in human airways in vitro but only in epithelium denuded tissues. Frusemide (1 mmol/l) produced a maximum inhibition of 46.3% (SE 9.9%) at 0.5 Hz and bumetanide (0.1 mmol/l 39.6 (6.2)% at 0.5 Hz. Without indomethacin in the organ bath the frusemide-induced inhibition was enhanced at 4, 8, and 16 Hz, but bumetanide-induced inhibition was not enhanced at any frequency when indomethacin was omitted. Frusemide (1 mmol/l) and bumetanide (0.1 mmol/l) had no effect on the cumulative concentration-response curve to exogenous Ach (0.3 mumol/l to 10 mmol/l). Acetazolamide (100 mumol/l) had no effect on the EFS-induced cholinergic contraction in tissues with or without epithelium.

CONCLUSIONS

In human airways in vitro both frusemide and bumetanide produced a concentration-dependent inhibition of the EFS-induced cholinergic contraction. This inhibition is mediated through a prejunctional mechanism. Epithelium removal was necessary to achieve this effect. The mechanism of action of frusemide and bumetanide on airway nerves remains unclear: inhibition of the Na-K-Cl cotransporter is a possibility and, for frusemide, release of endogenous cyclooxygenase products may be involved. Carbonic anhydrase inhibition, on the other hand, is unlikely to be a factor.

Effect of inhaled frusemide on responses of airways to bradykinin and adenosine 5'-monophosphate in asthma

BACKGROUND

Inhaled frusemide exerts a protective effect against bronchoconstriction induced by several indirect stimuli in asthma. This effect could be caused by interference with neural pathways. The effect of inhaled frusemide on bronchoconstriction induced by inhaled bradykinin, which is thought to cause bronchoconstriction via neural mechanisms, was studied and compared with the effects of adenosine 5'-monophosphate (AMP) which probably produces its airway effects by augmenting mast cell mediator release and interfering with neural pathways.

METHODS

Patients first underwent AMP and bradykinin challenges. They were then studied in a randomised, placebo controlled, double blind fashion. Ten atopic asthmatic subjects, studied on four days, were pretreated with inhaled frusemide (40 mg) or placebo for 10 minutes, five minutes before challenge with increasing concentrations of nebulised AMP or bradykinin.

RESULTS

On the open visit days the provocative concentrations required to reduce forced expiratory volume in one second (FEV1) by 20% from baseline (PC20) for AMP and bradykinin were 16.23 (1.42-67.16) and 2.75 (0.81-6.6) mg/ml. There was a significant correlation between baseline AMP and bradykinin PC20 values. For AMP the geometric mean PC20 values following pretreatment with inhaled frusemide and matched placebo were 80.97 (9.97- > 400.0) and 14.86 (2.6-104.6) mg/ml respectively (95% CI 0.49 to 0.98). For bradykinin the geometric mean PC20 values following pretreatment with inhaled frusemide and matched placebo were 13.22 (2.53- > 16.0) and 2.52 (0.45-5.61) mg/ml respectively (95% CI 0.43 to 1.01). Frusemide afforded 5.45 and 5.24 fold protection against AMP and bradykinin-induced bronchoconstriction respectively. Furthermore, there was a significant correlation between protection afforded to the airways against AMP and bradykinin.

CONCLUSIONS

These data suggest that inhaled frusemide affords protection against bradykinin-induced bronchoconstriction which is comparable to that against AMP, supporting a common mechanism of action for frusemide.

Evaluation of cold air challenge data in a population sample using a model of bronchial hyperreactivity and disposition to bronchial obstruction

To explore the role of bronchial hyperreactivity and obstruction after cold air challenge, data from a cross-sectional study of more than 7,000 10-year-old children were used. Current knowledge of hyperreactivity is primarily based on pharmacological provocation tests with variable prechallenge flow rates and their decrease relative to baseline. Using forced expiratory volume (FEV) in 1 sec values before and after cold air challenge, however, it is possible to define a subsample of children with predominant hyperreactivity and a subsample with predominant obstruction after challenge. The prevalence of respiratory symptoms and the diagnoses in the two subsamples were compared. The analysis showed that children with bronchial obstruction have nearly the same frequency of respiratory symptoms as those with bronchial hyperreactivity. A combined model of bronchial obstruction and hyperreactivity was, therefore, more predictive of symptoms than a model of hyperreactivity alone.

The effect of inhaled frusemide on airway sensitivity to inhaled 4.5% sodium chloride aerosol in asthmatic subjects

BACKGROUND

Frusemide inhaled by asthmatic subjects before a variety of indirect bronchial challenges inhibits the airway response to these challenges. Since inhalation of hyperosmolar saline is an indirect bronchial challenge, the effect of inhaled frusemide and its vehicle on airway sensitivity to a 4.5% sodium chloride (NaCl) aerosol challenge was investigated.

METHODS

Eleven asthmatic subjects (five females, six males) who had a 20% fall in forced expiratory volume in one second after 4.5% NaCl challenge were enrolled in this double blind controlled crossover trial. Sensitivity was measured as the dose of aerosol required to provoke a 20% fall in FEV1. Frusemide (33.2 mg) or its vehicle was delivered through a Fisoneb ultrasonic nebuliser and inhaled 10 minutes before challenge with 4.5% NaCl. A Mistogen ultrasonic nebuliser was used to generate the 4.5% NaCl aerosol and FEV1 was measured before and one minute after each challenge period of 0.5, one, two, four, eight, eight and eight minutes. The doubling dose difference for PD20 was calculated.

RESULTS

Frusemide or vehicle had no effect on baseline lung function. The geometric mean PD20 after vehicle was 1.3 ml with a 95% confidence interval of 0.7-2.3 and after frusemide was 8.2 ml with a 95% confidence interval of 4.7-14.1. This represented a 2.6 doubling dose increase in PD20 after frusemide inhalation. In five of the 11 subjects an increase from baseline FEV1 occurred after exposure to 4.5% NaCl challenge in the presence of frusemide. This transient bronchodilatation may be caused by the release of prostaglandin E2.

CONCLUSION

Inhalation of frusemide is very effective in delaying airway narrowing induced by an aerosol of 4.5% NaCl in asthmatic subjects.

Effect of inhaled amiloride on the bronchial response to methacholine and cold air hyperventilation challenges

Inhaled amiloride has been recently demonstrated to have an effect on the decline of pulmonary function in patients with cystic fibrosis. Other diuretics have been demonstrated to provide protection against bronchoconstriction in asthmatic subjects. We report on the effect of inhaled amiloride on cold air hyperventilation challenge (CAHC) and methacholine challenge in asthmatics. We studied nine subjects with mild-moderate asthma in a double-blind, placebo-controlled, crossover study. Our results showed amiloride did not significantly protect against the bronchoconstriction induced by CAHC. Inhaled amiloride did not affect FEV1 in the hour after inhalation, and there was no significant difference between placebo or amiloride on the dose of methacholine causing a 20 percent fall in FEV1. Inhaled amiloride appears not to have a profile of action as previously seen with inhaled furosemide.

Effect of inhaled furosemide on the bronchial response to lysine-aspirin inhalation in asthmatic subjects

It has been demonstrated recently that inhaled furosemide inhibits bronchoconstriction induced by cold air, physical exercise, various antigens, and metabisulfite. The goal of the present study was to determine if the inhalation of furosemide would inhibit the bronchoconstriction resulting from the inhalation of lysine-aspirin in aspirin-sensitive asthmatics. Six female subjects with known hypersensitivity to aspirin participated in this crossover study comparing 20 mg of inhaled furosemide and placebo. The volunteers inhaled increasing concentrations of lysine-aspirin after the inhalation of furosemide or placebo. The geometric mean provocative dose causing a 20 percent decrease in the FEV1 (PD20) after the inhalation of placebo was 30.4 mg/ml and the PD20 was equal or below 90 mg/ml in all patients. In contrast, the FEV1 did not decrease by 20 percent in any of the patients pretreated with furosemide when the inhaled concentration was increased to 360 mg/ml. From this study, we conclude that the administration of furosemide blocks the bronchospasm induced by the inhalation of lysine-aspirin in aspirin-sensitive asthmatics.

Inhaled frusemide against cold air induced bronchoconstriction in asthmatic children

Inhaled frusemide prevents bronchoconstriction in asthmatic adults induced by various triggers. To determine if frusemide provides similar protection in children, whether this is age dependent and equally effective for central and peripheral airways, we performed a double blind, placebo controlled, randomised, crossover study on the effect of inhaled frusemide on lung function changes induced by cold air challenge in 21 asthmatic children. In addition, we measured diuresis before and after inhalation. Bronchodilatation after frusemide was not observed. However, deterioration in lung function after frusemide, compared with placebo, was significantly diminished: forced expiratory volume in one second (FEV1) was -5.7% v -11.5%, peak expiratory flow (PEF) -7.7% v -23.3%, maximum expiratory flow at 50% of vital capacity (MEF50VC) -16.0% v -35.2%, and at 60% of total lung capacity (MEF60TLC) -32.4% v -61.6%, and specific airways conduction -42.0% v -57.7%, respectively. This effect was not age dependent. Diuresis was significantly increased from a mean (SEM) of 198 (34) ml/3 hours before inhaled frusemide to 379 (62) ml/3 hours after nebulisation. We conclude that inhaled frusemide prevents cold air induced bronchoconstriction in asthmatic children and that increased diuresis can be expected with a dose as low as 28 mg of frusemide given by nebuliser.