Diuretics. Clinical pharmacology and therapeutic use (Part I)

Diuretics: a review

Diuretics, in one form or another, have been around for centuries and this review sets out to chart their development and clinical use. Starting with the physiology of the kidney, it progresses to explain how diuretics actually work, via symports on the inside of the renal tubules. The different classes of diuretics are characterized, along with their mode of action. The clinical use of diuretics in conditions like congestive cardiac failure and hypertension, as well as some rarer, but clinically important, conditions is then examined. An account is given of the adverse effects of diuretics and how they come about. Common adverse effects like hypokalaemia and hyponatraemia are examined in some detail, and other electrolyte disturbances like hypomagnesaemia also gain a mention. Diuretic use in chronic kidney disease is examined and new guidelines that have been introduced are presented. A section on diuretic abuse is included as this is becoming an all too common clinical scenario, and the sometimes tragic consequences of this abuse are emphasized. Diuretics also find a role in the diagnosis of forms of renal tubular acidosis and this role is explored. Finally, a selection of some of the newer approaches to diuretic therapy are presented, often the consequence of the increasing development of molecular biology, and some of the novel compounds – which may be in drug formularies of the future – are revealed.

Does Smoking Act as a Friend or Enemy of Blood Pressure? Let Release Pandora's Box

In spite of the great number of observations which show the certainty of cardiovascular damage from smoking, the opinions on that are not yet unanimous. There is a discrepancy that could be attributed to the lack of reproducible data particularly in some epidemiological studies. On the contrary, experimental findings conducted on both animals and humans give evidence of exactly reproducible results of cardiovascular alterations and among these the course of Blood Pressure (BP). Findings identify an increase in BP of active smokers or non-smokers exposed to passive smoking, while a lot of others refer a lowering of BP due to smoking. This discrepancy could be explained as follows. Initially, a vasoconstriction mediated by nicotine causes acute but transient increase in systolic BP. This phase is followed by a decrease in BP as a consequence of depressant effects played chronically by nicotine itself. Simultaneously, carbon monoxide is acting directly on the arterial wall causing, in the long run, structurally irreversible alterations. At this time, there is a change in BP that increases again, and often constantly, its levels following chronic exposure. Changes in response to antihypertensive drugs have been observed in hypertensive smokers since smoking influences metabolic steps of the drugs.

Masking and manipulation

The list of prohibited substances in sports includes a group of masking agents that are forbidden in both in- and out-of-competition doping tests. This group consists of a series of compounds that are misused in sports to mask the administration of other doping agents, and includes: diuretics, used to reduce the concentration in urine of other doping agents either by increasing the urine volume or by reducing the excretion of basic doping agents by increasing the urinary pH; probenecid, used to reduce the concentration in urine of acidic compounds, such as glucuronoconjugates of some doping agents; 5alpha-reductase inhibitors, used to reduce the formation of 5alpha-reduced metabolites of anabolic androgenic steroids; plasma expanders, used to maintain the plasma volume after misuse of erythropoietin or red blood cells concentrates; and epitestosterone, used to mask the detection of the administration of testosterone. Diuretics may be also misused to achieve acute weight loss before competition in sports with weight categories. In this chapter, pharmacological modes of action, intended pharmacological effects for doping purposes, main routes of biotransformation and analytical procedures used for anti-doping controls to screen and confirm these substances will be reviewed and discussed.

Application of high-performance liquid chromatography-mass spectrometry to detection of diuretics in human urine

A rapid, sensitive and reliable high-performance liquid chromatographic-mass spectrometric method for the detection of 25 diuretics in human urine has been developed. Atmosphere pressure chemical ionization (APCI) and electrospray ionization (ESI) modes were evaluated. A 2-ml volume of urine was extracted under basic conditions and separated on an Agilent Zorbax SB-C(18) column (150 x 2.1 mm, 5 microm). The mobile phase consisted of formic ammonium-formic acid buffer (pH 3.5) and acetonitrile. The effects of capillary temperature, sheath gas pressure and compositions of mobile phase on the sensitivity were studied. The recoveries of most of the diuretics were 75-95%. In the full scan mode, the limits of detection of the 25 diuretics were 0.25-25 ng/ml for APCI and 0.6-250 ng/ml for ESI. Under the optimal conditions, 14 diuretics from authentic urine samples were detected successfully by LC-APCI-MS. To obtain more fragmentation information on the chemical structure for positive confirmation, tandem mass analysis was also investigated.

Effects of chloride transport inhibition and chloride substitution on neuron function and on hypoxic spreading-depression-like depolarization in rat hippocampal slices

Chloride fluxes play a crucial role in synaptic inhibition, cell pH regulation, as well as in cell volume control. In many neuropathological processes, cell swelling is a pivotal parameter, since cell volume changes and the dimension of the interstitial space critically modulate synchronized neuronal activity as well as the tissue's susceptibility to seizures or spreading depression. This study therefore focuses on the effects of different Cl(-) transport inhibitors and Cl(-) substitution on neuronal function and hypoxia-induced changes in rat hippocampal tissue slices. Orthodromically evoked focal excitatory postsynaptic potentials were depressed by furosemide (2mM), 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid (1mM) and Cl(-) substitution by methylsulfate, but were enhanced by 4,4'-dinitrostilbene-2,2'-disulfonic acid (1mM). All four treatments induced multiple population spike firing in response to single orthodromic volleys, suggesting reduced synaptic inhibition. Antidromic population spikes increased following Cl(-) withdrawal, were unaffected in the presence of furosemide and 4, 4'-dinitrostilbene-2,2'-disulfonic acid, but were abolished by 4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid. The amplitude of the hypoxic spreading-depression-like extracellular potential shift was reduced by furosemide, 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid and Cl(-) withdrawal, i.e. by the same treatments that depressed orthodromically evoked postsynaptic potentials. Furosemide prolonged the time to onset and the duration of the spreading-depression-like extracellular potential shift, while 4, 4'-dinitrostilbene-2,2'-disulfonic acid shortened the time to onset. Spreading-depression-related cell swelling was recorded as the shrinkage of relative interstitial space, which was measured as tetramethylammonium-chloride space. Neither the Cl(-) transport inhibitors nor Cl(-) withdrawal had any detectable effect on spreading-depression-related cell swelling. CA1 pyramidal neurons usually hyperpolarized during drug application and their input resistance decreased. Cl(-) withdrawal increased their input resistance and caused spontaneous burst firing. Hypoxia caused the expected spreading-depression-like rapid, near complete depolarization of single pyramidal neurons and drastically reduced their input resistance. The three Cl(-) transport inhibitors and Cl(-) withdrawal delayed the onset of the hypoxic depolarization. In low Cl(-) solutions, the apparent threshold potential at which spreading depression was triggered shifted to more positive membrane potentials. The final voltage of the hypoxic depolarization was, however, not affected. It appears from these results that the reduction in the hypoxic spreading-depression-like extracellular potential shifts by Cl(-) transport inhibitors is at least partially attributable to desynchronization of depolarization, not to decreased depolarization in individual cells. Other contributing factors could be changes in recording conditions, depression of swelling-induced amino acid release from glial cells and unspecific side-effects of the applied drugs. Desynchronization could also account for the delayed spreading-depression onset. It is concluded that Cl(-) fluxes play a role in the triggering of spreading depression, but the spreading-depression-like depolarization itself or its self-regenerative character is not mediated by Cl(-).

Detection of diuretic agents in doping control

Since the inclusion of diuretics in the list of banned substances in sports in 1988, a large number of screening and confirmation procedures to detect the presence of these substances in urine samples have been developed. In this paper, a review of the analytical methodology described to analyze diuretics is presented. The paper has been focused on the needs of doping control and mainly screening procedures including sample preparation and liquid or gas chromatographic separation have been considered. More relevant papers using capillary zone electrophoresis have been also considered. Mass spectrometry is mandatory in doping control for confirmation purposes, and finally, mass spectrometric techniques described for diuretics have been reviewed.

Non-steroidal anti-inflammatory agents, Part 20. Method for testing non-steroidal anti-inflammatories: the modified hen's egg chorioallantoic membrane test (HET-CAM test) compared to other procedures

The delay of onset of irritation phenomena at the chorioallantoic membrane of incubated hen's eggs, a parameter for anti-inflammatory activity, was determined for the pharmaceutical substances diclofenac, flufenamic acid, ibuprofen, indomethacin, ketoprofen, piroxicam, phenylbutazone, salicylic acid, and sodium salicylate. Alongside questions relating to the dose-effect ratio, metabolisation, recovery, and diffusion of the substances to their site of action were investigated. The reproducibility of the procedure and its selectivity with regard to substances with a different mechanism of action is proven. The method allows classification of the substances according to their anti-inflammatory potency. However, correlation with the results of enzyme inhibition or in vivo results is only possible to a limited extent.

Determination of piretanide and furosemide in pharmaceuticals and human urine by high-performance liquid chromatography with amperometric detection

A high-performance liquid chromatographic method with electrochemical detection (ED) has been developed for the determination of two diuretics: 4-phenoxy-3-(1-pyrrolidinyl)-5-sulfamoylbenzoic acid (piretanide) and 4-chloro-2-furfurylamino-5-sulfamoylbenzoic acid (furosemide). The chromatographic separation was performed on a mu Bondapak C18 column with a mobile phase of acetonitrile-water (40:60) containing 5 mM KH2PO4/K2HPO4 and with a flow-rate of 1 ml/min (69 bar). The temperature was optimized at 30 +/- 0.2 degrees C. The amperometric detector equipped with a glassy carbon electrode was operated at +1200 mV versus Ag/AgCl in the direct current mode. The method was applied to the determination of these compounds in two concentration ranges (ppm and ppb), obtaining a reproducibility in terms of relative standard deviations lower than 1% for within-day and 4% for day-to-day and determination limits of 15 ppb for both compounds. Recoveries greater than 90% were obtained for spiked urine samples, using a liquid-liquid extraction method in the sample clean-up procedure. The LC-ED method was applied to commercially available pharmaceuticals (Seguril, furosemide 40 mg, and Perbilén, piretanide 6 mg) and urine samples obtained from healthy volunteers and hypertensive patients.

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.

Furosemide, bumetanide, and ethacrynic acid

Furosemide and, less commonly, bumetanide and ethacrynic acid are potent diuretics administered to horses for a variety of reasons, including prophylaxis of exercise-induced pulmonary hemorrhage. These drugs affect urine volume and composition, and furosemide has marked effects on plasma volume and composition and on systemic hemodynamics at rest and during exercise.

Protective effect of inhaled piretanide on the bronchial obstructive response to ultrasonically nebulized H2O. A dose-response study

Inhaled furosemide prevents the obstructive response to several bronchoconstrictor stimuli in asthma. To verify whether this protective effect is also shared by other loop diuretics, we investigated the effect of inhaled piretanide on the bronchial obstructive response to ultrasonically nebulized distilled water (UNW) in ten patients with moderate, stable asthma. In a randomized, single-blind dose-response study, each subject performed an UNW test immediately after nebulization of different doses of piretanide between 12 and 48 mg or placebo. The effect of a single 40-mg dose of inhaled furosemide was also investigated in six subjects. Piretanide caused a significant, dose-dependent increase in UNW PD20 with respect to placebo, corresponding to 0.6 +/- 0.2 doubling doses (mean +/- SE) after 12 mg, 1.3 +/- 0.2 after 24 mg, and 2.0 +/- 0.2 after 48 mg, and had a remarkable diuretic effect; 40 mg of furosemide increased UNW PD20 by 2.3 +/- 0.3 doubling doses (p < 0.01), but showed only a modest diuretic activity. These data indicate that inhaled piretanide is as effective as furosemide in preventing UNW-induced asthma, and this effect is unrelated to their diuretic potency.

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.

Supraventricular tachycardia associated with continuous furosemide infusion

Three cases of supraventricular tachycardia (SVT) associated with the use of furosemide infusion (FI) in children following cardiac surgery are reported. The SVT occurred three to seven hours after starting an infusion at 1.0 mg.kg-1.hr-1. All three patients had a diuresis of 8-10 ml.kg-1.hr-1 compared with a mean average of 2.5 ml.kg-1.hr-1 in 22 other patients who had received a similar infusion. A rapid fluid shift was the most likely mechanism of the tachycardia. Sotalol was effective in controlling the tachycardia in the two patients in whom it was tried. We now recommend a starting dose of 0.3 mg.kg-1.hr-1 in using furosemide as a continuous infusion, with hourly increments of 0.1 mg.kg-1.hr-1 until the desired diuresis is obtained.

Drug-induced gout

A number of pharmacological agents can induce hyperuricaemia, and sometimes gout, usually by interfering with the renal tubular excretion of urate but also in some instances by increasing the formation of uric acid. Alcohol is well known to have this property and in recent years diuretic-induced hyperuricaemia has become a global phenomenon. Other drugs which can cause hyperuricaemia are salicylates, pyrazinamide, ethambutol, nicotinic acid, cyclosporin, 2-ethylamino-1,3,4-thiadiazole, fructose and cytotoxic agents. A special type of 'drug-induced gout' can follow the rapid lowering of serum uric acid by allopurinol or uricosuric drugs.

Effects of diuretics on outputs and flows of urine and urinary solutes in healthy subjects

The effects of single oral doses of common formulations of diuretics (i.e. formulations on the market or designed to be marketed) on 24-hour diuresis and natriuresis in healthy subjects are considered as a measure of the renal excretory potency of diuretics. Common formulations of distal tubular diuretics (e.g. hydrochlorothiazide 25mg, xipamide 10mg and 20mg) are more potent diuretics and natriuretics than common formulations of loop diuretics [e.g. furosemide (frusemide) 40mg, torasemide 2.5, 5 and 10mg]. Indeed, some common formulations of loop diuretics, such as torasemide 2.5, do not increase 24-hour diuresis or natriuresis in healthy subjects. 24-hour kaliuresis and magnesiuresis are elevated by common formulations of distal tubular diuretics, but they are only slightly increased or (more usually) not affected by common formulations of loop diuretics, when single doses are administered to healthy individuals. Common formulations of loop diuretics have lower diuretic and natriuretic potency and lower kaliuretic and magnesiuretic effects than common formulations of distal tubular diuretics, because the pronounced elevations in urinary excretions caused by loop diuretics during the first 6 hours after dosing are followed by rebounds, with respect to post-placebo excretions, between 6 and 24 hours after dosing. These rebounds, which affect the urinary flows of fluid, chloride, sodium, potassium and magnesium, do not occur after administration of common formulations of distal tubular diuretics, at least during the first 24 hours after administration of single doses to healthy subjects. The time courses of urinary excretions after loop diuretics are dose dependent. Higher doses produce more rapid changes in the urinary flows of fluid, chloride, sodium, potassium and magnesium than lower doses, to the extent that single administration of torasemide 2.5 or 5mg to healthy subjects is followed by urinary fluid and solute flows whose time courses resemble those after administration of hydrochlorothiazide 25mg.

Amiloride disposition in geriatric patients: importance of renal function

1. The absorption and disposition of the potassium sparing diuretic amiloride were determined in nine elderly patients aged 71 to 87 years and in eight young (25 to 38 years) subjects following oral administration of 5 mg amiloride HCl daily to steady-state. 2. The maximum and steady-state plasma amiloride concentrations were significantly (P less than 0.05 and P less than 0.001) higher in the elderly patients. The renal clearance of amiloride was lower in the elderly than in young subjects (102 +/- 36 ml min -1 vs 300 +/- 64 ml min-1, P less than 0.001) as was the urinary excretion of amiloride (36 +/- 13 vs 62 +/- 18% of the dose, P less than 0.01). 3. The steady-state plasma amiloride concentration correlated significantly (r2 = 0.61, P less than 0.001) with amiloride renal clearance and with creatinine clearance (r2 = 0.59, P less than 0.001). There was a very strong positive correlation between renal amiloride clearance and creatinine clearance (r2 = 0.76, P less than 0.001). The slope of the regression line was 2.5 indicating substantial proximal tubular secretion of amiloride. 4. Sodium and potassium excretion, along with urine volume were significantly (P less than 0.05) lower in the elderly (by 39, 45 and 34% respectively). 5. The disposition of amiloride was highly dependent on renal function, with higher plasma amiloride concentrations in the elderly reflecting diminished renal function. The dose of amiloride should be titrated to individual response, and the lower potassium excretion in the elderly patients suggests that the dose of amiloride could be reduced in this group of patients.

Effects of intravenous bumetanide administration on renal haemodynamics and proximal and distal tubular sodium reabsorption in conscious rats

The renal effects of 0.02-62.5 mg/kg bumetanide given as intravenous bolus injections were studied in water diuretic conscious rats. Clearances of 14C-tetraethylammonium, 3H-inulin and lithium were used as markers for renal plasma flow (RPF), glomerular filtion rate (GFR) and proximal tubular output, respectively. Bumetanide caused biphasic, transient and dose-independent changes in the renal haemodynamics without significant alterations of the filtration fraction. At dose-levels above 0.02 mg/kg bumetanide increased urine flow, absolute and fractional Na excretion as well as the indices for fractional output of Na from the proximal tubules (CLi/CIn) and the distal nephron segments (CNa/CLi). The changes in CLi/CIn became maximal at doses above 0.5 mg/kg, whereas CNa/CLi was increased with the dose up to 12.5 mg/kg. Paradoxically, doses above 12.5 mg/kg were less natriuretic due to a decrease of CNa/CLi. It is concluded that in rats bumetanide is an effective although short-acting diuretic when administered intravenously. When comparing peak responses bumetanide is equipotent to furosemide but has a lower maximal efficacy. Judged from the changes in fractional lithium excretion, the natriuretic effect of bumetanide is effected by inhibition of Na reabsorption in the proximal tubule in addition to the well-known effect on the distal nephron segment.

Acute and long-term renal and metabolic effects of piretanide in congestive cardiac failure

1. The renal and metabolic effects of the sulphamoylbenzoic acid diuretic, piretanide, have been studied, under controlled dietary conditions, in 39 patients with congestive cardiac failure. 2. In acute studies, peak saluresis occurred within 4 h of oral piretanide administration; saluresis was complete within 6 h, after which a significant antidiuretic effect was observed. Addition of triamterene, 50 mg, blunted the 0-6 h kaliuretic effect of piretanide. Over 24 h, piretanide, alone, caused insignificant urinary losses of potassium when compared with control. 3. In comparative studies, the piretanide dose-response curve was found to be parallel to that of frusemide over the dose range studied. The 0-6 h saluretic responses of piretanide, 6, 12 and 18 mg, were found to be equivalent to frusemide, 40, 80 and 120 mg respectively. The collective mean ratios of all the saluretic responses to each dose of piretanide with the corresponding dose of frusemide was observed to be 0.99 +/- 0.12, over 0-6 h period, and 0.86 +/- 0.09 over the 24 h period. The relative potency of piretanide, when compared with frusemide was found to be 6.18 (95% confidence limits 4.87-8.33), over the 0-6 h period, and 4.73 (95% confidence limits 3.65-6.14), over 24 h period. 4. In 15 patients in severe cardiac failure, urinary recovery of piretanide, over first 6 h, at the start of treatment was 21.2 +/- 2.1% while efficiency of the diuretic (mmol Na/mg drug) was 47.3 +/- 4.1. Long-term piretanide therapy was continued in the same group for up to and in some cases over 3 years. No other diuretics or potassium supplements were given. Piretanide dosage ranged from 6 to 24 mg day-1 according to clinical need. Plasma potassium fell significantly at 12 and 24 months, though remaining within the normal range. At these same times, significant elevations in both plasma urate and total fasting cholesterol were observed. Two patients developed overt gout on high dose piretanide therapy (24 mg day-1). Piretanide was well tolerated, and effective in the management of congestive cardiac failure without any other recognized metabolic or electrolyte changes.

Development of acute tolerance to bumetanide: constant-rate infusion studies

Bumetanide was administered intravenously to four mongrel dogs as a bolus of 8.7 micrograms/kg, immediately followed by a constant-rate infusion of 0.35 microgram/min/kg at 0.036 ml/min. Treatment A consisted of a 90-min equilibration period and first hour (Phase I) of study in which animals were maintained under euvolemic conditions. During the subsequent 3 hr of Treatment A (Phase II), animals were maintained under hydropenic conditions. These experiments were then repeated 1 week later (Treatment B) with the temporal aspects of hydration reversed (Phase III, hydropenia; Phase IV, euvolemia). Serial plasma and urine samples were assayed for bumetanide by high-performance liquid chromatography (HPLC) and for sodium by flame photometry. The bumetanide excretion rate was not significantly different during the 4 hr of Treatment A, although minor differences were observed between Phase III and Phase IV of Treatment B. The sodium excretion rate showed significant differences between euvolemic and hydropenic conditions of both treatments. A two- to threefold difference in the sodium excretion rate persisted even when slight differences (less than 20%) in bumetanide excretion rates were taken into account. These results demonstrate that an acute tolerance does develop to constant-rate infusions of bumetanide when inadequate fluid and electrolyte replacement occurs and that this tolerance can be reversed by rehydration.

Drug treatment of hypertension

There are several first choices for the treatment of mild and moderate hypertension. The selection of a drug may be influenced by concomitant pathology, with positive indications for particular drugs, e.g. coexistent angina, indicating use of a beta-receptor blocking drug or calcium antagonist; fluid retention indicating a diuretic; or contraindication e.g. asthma, and beta-adrenoceptor blocking drugs. beta-Adrenoceptor blocking drugs have the advantage of a long history and of possibly being cardioprotective following myocardial infarction, but they have not yet been established as primary preventive agents in hypertensive patients. The alpha-receptor blocking drugs have the advantage of favourably affecting lipid profile and blood pressure. Therefore, there may be advantages in the use of combined alpha- and beta-blockade. The diuretics, which have the advantage of being inexpensive, are widely used but long term metabolic effects, particularly hypokalaemia, cause concern. This is correctable by co-administration of a potassium sparing diuretic and often preventable by using low doses of the diuretic. Diet may be important as hypokalaemia appears to be less of a problem where potassium intake is high. Experience with calcium antagonists is widening but the use of converting enzyme inhibitors is more limited, and some physicians are less ready to use them as first choice in mild hypertension at present. Drugs like methyldopa, clonidine, the adrenergic neurone inhibitory drugs are now used more as reserve agents. More severe cases of hypertension may require drugs from 2 of the 3 major groups: beta-blocking drugs, vasodilators and diuretics. In some cases, drugs from each of these 3 groups will be required.

Development of acute tolerance to bumetanide: bolus injection studies

Bumetanide was administered intravenously to four mongrel dogs, in a random crossover fashion, at doses of 0.05 mg/kg (I), 0.15 mg/kg (II), and 0.5 mg/kg (III) where urinary losses were replaced with lactated Ringer's solution at 1.5 ml/min (hydropenic conditions) or at a dose of 0.5 mg/kg (IV) where urinary losses were replaced with lactated Ringer's solution isovolumetrically (euvolemic conditions). Serial plasma and urine samples were assayed for bumetanide by high-performance liquid chromatography (HPLC) and for sodium by flame photometry. There were no significant differences in the pharmacokinetic parameters of bumetanide among Treatments I-IV. The dynamic parameters Emax (maximum effect attributable to the drug) and s (slope factor) were not different between treatments. However, a consistent, demonstrable increase in ER50 (urinary excretion rate of drug producing 50% of Emax) was observed among Treatments I (2.34 micrograms/min), II (3.92 micrograms/min), and III (6.54 micrograms/min); also, a significant decrease in ER50 was observed between Treatment III (6.54 micrograms/min) and Treatment IV (2.66 micrograms/min). These results show that hydration status has a marked effect on natriuretic and diuretic response and that tolerance can rapidly develop within a single intravenous dose of bumetanide.

The effects of naproxen and sulindac on renal function and their interaction with hydrochlorothiazide and piretanide in man

We have studied the effect of a single dose challenge of naproxen (500 mg) and sulindac (200 mg) on renal function in five volunteers, and the effect of a single dose challenge of the thiazide, hydrochlorothiazide (100 mg), and loop diuretic, piretanide (6 mg) on renal function when the diuretics were given alone or when superimposed on chronic therapy of either naproxen or sulindac. None of the nonsteroidal anti-inflammatory drug (NSAID) or diuretic exposures significantly influenced glomerular filtration rate, as measured by creatinine clearance. Over the first 4 h of the study, both naproxen and sulindac reduced fractional excretion of sodium by approximately 50%. Sulindac also caused a significant uricosuria whilst naproxen promoted urate retention. Similar changes were observed over 8 h. Superimposition of either hydrochlorothiazide or piretanide on top of chronic sulindac therapy resulted in a blunting of the natriuresis by approximately 30% compared to when these diuretics were given alone: the action of the diuretics was unchanged by naproxen. Sulindac pretreatment did not alter the urinary excretion of either hydrochlorothiazide or piretanide; naproxen did not alter hydrochlorothiazide excretion. On the basis of these findings, it is concluded that NSAIDs exert direct tubular effects that do not necessarily interfere with the delivery of diuretics to their sites of action within the nephron.

Evolution of diuretics and ACE inhibitors, their renal and antihypertensive actions--parallels and contrasts

The emergence of diuretic drugs and angiotensin converting enzyme (ACE) inhibitors ranks amongst the major therapeutic advances of modern medicine. The discovery of these drug groups arose largely by chance, yet each has dramatically influenced the treatment of congestive cardiac failure and arterial hypertension. The central role which diuretics have had in the management of both oedema and hypertension hinges on their ability to induce a net renal excretion of solute and water by selective interference with either active or passive ion transport processes in different segments of the nephron. Irrespective of sites of action, the continued antihypertensive action of diuretics is characterized by a reduction in plasma volume and extracellular fluid (ECF) volume that lasts for as long as the diuretic is given. The mechanism of this effect remains unclear but may involve autoregulatory reactions that leave cardiac output unaltered but maintain a sustained reduction in total peripheral resistance. ACE inhibitors also lower blood pressure by decreasing total peripheral resistance, leaving cardiac output, plasma volume and ECF volume unchanged. The detailed way these haemodynamic changes are achieved remains unknown but inhibition of converting enzyme present not only in the kidney but also in many extrarenal tissue sites, appears important. In both hypertension and cardiac failure, however, the kidney acts as a key target organ for ACE inhibitors. The increased renal vascular resistance and inappropriate renal salt excretion are reversed with enhanced renal blood flow and saluresis. Both angiotensin II (AII) and vasopressin-mediated contraction of glomerular mesangial cells is inhibited, making glomerular filtration more efficient. Reduced aldosterone secondary to blockade of AII formation contributes to saluresis whilst encouraging positive potassium balance. ACE inhibition also impairs breakdown of kinins which may contribute to intrarenal and peripheral vasodilation either on their own or via release of prostaglandins and other vasoactive substances. The hypotensive actions of diuretics are potentiated by ACE inhibition primarily through blockade of AII formation and prevention of secondary aldosteronism. In combination, these drugs permit low doses to be used because of their synergistic effects. Caution has to be exercised whenever ACE inhibition is used, without and especially with diuretics, in the management of renovascular hypertension and other low-perfusion states. In these circumstances, AII plays an important autoregulatory role in preserving glomerular filtration through an increase in post-glomerular resistance.(ABSTRACT TRUNCATED AT 400 WORDS)

Chronopharmacological study of furosemide in rats

The present experiment was undertaken to determine whether or not the effects of furosemide depend upon the administration time and, if so, to study the mechanism(s) for these variations. After administration of furosemide (5 mg/kg) in Wistar rats at 10:00 or at 22:00, urine volume and urinary excretion of sodium, furosemide, and prostaglandin E2 (PGE2) were measured. Urine volume and urinary excretion of sodium and furosemide, but not PGE2, were significantly greater when furosemide was administered at 10:00 than when it was administered at 22:00. There was a good correlation between the urinary output of furosemide and the urine volume, or the urinary sodium. It is concluded that the effects of furosemide vary with the administration time and these variations depend upon the amount of furosemide secreted in urine.

Diuretic therapeutics in the pediatric patient

Careful management of fluid and electrolytes has long been an intrinsic part of pediatric practice. However, the augmentation of these manipulations through the rational use of diuretic agents requires considerable skill. In pediatric medicine, the regulation of pharmacokinetic processes and their interface with pharmacodynamic processes show dramatic age-related changes. These ontogenetic processes and their modification by various disease states must be considered carefully before selection and application of diuretic agents. The available data concerning the ontogeny of renal function and the attempts to apply diuretic therapy to pediatric disease are reviewed. It is concluded that results obtained to date suffer from the absence of a rigorous attempt to answer the fundamental therapeutic questions: What drug? What dose? What duration of therapy? A rational "target-effect" strategy is proposed for the application of diuretic agents to pediatric medicine.

Disposition of bumetanide in the isolated perfused rat kidney: effects of probenecid and dose response

The isolated perfused rat kidney was used to study the pharmacokinetic-pharmacodynamic relation of bumetanide and furosemide. Diuresis, as indicated by the concomitant increase in urine volume and fractional excretion of sodium, was produced with both drugs. The action of furosemide was dependent on a high clearance resulting from combined glomerular filtration and tubular secretion. The site of furosemide action was the luminal side of the nephron and a large amount of drug was required in the tubular lumen to produce diuresis. A bidirectional transport of bumetanide was indicated. Although tubular secretion of bumetanide was demonstrated, the action of bumetanide was not dependent on secretion and the highest response was achieved when bumetanide was filtered and partially reabsorbed. The lack of dependency on secretion to produce a response may be indicative of bumetanide reaching its site of action from the luminal as well as the vascular side of the nephron. In the isolated perfused rat kidney, although both drugs had the same pharmacodynamic endpoint, each drug had a different pharmacokinetic profile that characterized its response.