Clinical pharmacology of furosemide and ethacrynic acid

Renal lymphatic vessel dynamics

Similar to other organs, renal lymphatics remove excess fluid, solutes, and macromolecules from the renal interstitium. Given the kidney's unique role in maintaining body fluid homeostasis, renal lymphatics may be critical in this process. However, little is known regarding the pathways involved in renal lymphatic vessel function, and there are no studies on the effects of drugs targeting impaired interstitial clearance, such as diuretics. Using pressure myography, we showed that renal lymphatic collecting vessels are sensitive to changes in transmural pressure and have an optimal range of effective pumping. In addition, they are responsive to vasoactive factors known to regulate tone in other lymphatic vessels including prostaglandin E₂ and nitric oxide, and their spontaneous contractility requires Ca²⁺ and Cl^-. We also demonstrated that Na⁺-K⁺-2Cl^- cotransporter Nkcc1, but not Nkcc2, is expressed in extrarenal lymphatic vessels. Furosemide, a loop diuretic that inhibits Na⁺-K⁺-2Cl^- cotransporters, induced a dose-dependent dilation in lymphatic vessels and decreased the magnitude and frequency of spontaneous contractions, thereby reducing the ability of these vessels to propel lymph. Ethacrynic acid, another loop diuretic, had no effect on vessel tone. These data represent a significant step forward in our understanding of the mechanisms underlying renal lymphatic vessel function and highlight potential off-target effects of furosemide that may exacerbate fluid accumulation in edema-forming conditions.

Drug repositioning and pharmacophore identification in the discovery of hookworm MIF inhibitors

The screening of bioactive compound libraries can be an effective approach for repositioning FDA-approved drugs or discovering new pharmacophores. Hookworms are blood-feeding, intestinal nematode parasites that infect up to 600 million people worldwide. Vaccination with recombinant Ancylostoma ceylanicum macrophage migration inhibitory factor (rAceMIF) provided partial protection from disease, thus establishing a "proof-of-concept" for targeting AceMIF to prevent or treat infection. A high-throughput screen (HTS) against rAceMIF identified six AceMIF-specific inhibitors. A nonsteroidal anti-inflammatory drug (NSAID), sodium meclofenamate, could be tested in an animal model to assess the therapeutic efficacy in treating hookworm disease. Furosemide, an FDA-approved diuretic, exhibited submicromolar inhibition of rAceMIF tautomerase activity. Structure-activity relationships of a pharmacophore based on furosemide included one analog that binds similarly to the active site, yet does not inhibit the Na-K-Cl symporter (NKCC1) responsible for diuretic activity.

Review of furosemide in horse racing: its effects and regulation

Furosemide has been used empirically and has been legally approved for many years by the US racing industry for the control of exercise-induced pulmonary haemorrhage (EIPH) or bleeding. Its use in horses for this purpose is highly controversial and has been criticized by organizations outside and inside of the racing industry. This review concentrates on its renal and extra-renal actions and the possible relationship of these actions to the modification of EIPH and changes in performance of horses. The existing literature references suggest that furosemide has the potential of increasing performance in horses without significantly changing the bleeding status. The pulmonary capillary transmural pressure in the exercising horse is estimated to be over 100 mmHg. The pressure reduction produced by the administration of furosemide is not of sufficient magnitude to reduce transmural pressures within the capillaries to a level where pressures resulting in rupture of the capillaries, and thus haemorrhage, would be completely prevented. This is substantiated by clinical observations that the administration of furosemide to horses with EIPH may reduce haemorrhage but does not completely stop it. The unanswered question is whether the improvement of racing times which have been shown in a number of studies are due to the reduction in bleeding or to other actions of furosemide. This review also discusses the difficulties encountered in furosemide regulation, in view of its diuretic actions and potential for the reduction in the ability of forensic laboratories to detect drugs and medications administered to a horse within days or hours before a race. Interactions between nonsteroidal anti-inflammatory drugs (NSAIDs) and furosemide have also been examined, and the results suggest that the effects of prior administration of NSAID may partially mitigate the renal and extra-renal effects which may contribute to the effects of furosemide on EIPH.

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.

Pharmacology of furosemide in the horse: a review

Furosemide, a diuretic, is frequently administered to horses for the prophylaxis of exercise-induced pulmonary hemorrhage and the treatment of a number of clinical conditions, including acute renal failure and congestive heart failure. Furosemide increases the rate of urinary sodium, chloride, and hydrogen ion excretion. Plasma potassium concentration decreases after furosemide administration but urinary potassium excretion in horses is minimally affected. Renal blood flow increases after furosemide administration. Systemically, furosemide increases venous compliance and decreases right atrial pressure, pulmonary artery pressure, pulmonary artery wedge pressure, and pulmonary blood volume. The systemic hemodynamic effects of furosemide are only manifest in the presence of a functional kidney, but can occur in the absence of diuresis, emphasizing the importance of the renal-dependent extra-renal effects of furosemide. The renal and systemic hemodynamic effects of furosemide are modified by prior administration of nonsteroidal anti-inflammatory drugs. Furosemide administration attenuates exercise-induced increases in right atrial, aortic, and pulmonary artery pressures in ponies. Furosemide prevents exercise and allergen-induced bronchoconstriction in humans and decreases total pulmonary resistance in ponies with recurrent obstructive airway disease. These pharmacologic effects are frequently used to rationalize its questionable efficacy in the prevention of exercise-induced pulmonary hemorrhage. Neither the effect of furosemide on athletic performance nor its efficacy in the prevention of exercise-induced pulmonary hemorrhage has been convincingly demonstrated.

Lack of a modifying effect by the diuretic drug furosemide on the development of neoplastic lesions in rat two-stage urinary bladder carcinogenesis

The effect of the diuretic drug furosemide on two-stage urinary bladder carcinogenesis in F344 rats initiated by N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) was investigated with regard to possible promoting activity. BBN was administered at 2 doses, 0.01 or 0.05%, in drinking water for 4 wk, and thereafter furosemide was given by gavage 3 times weekly for 32 wk, 250 mg/kg body weight. Furosemide ingestion induced diuresis with an alkaline, hypotonic urine. No significant difference with regard to incidences of bladder lesions were apparent between furosemide and control groups. The present investigation indicated that neither furosemide nor its related polyuria acted as a promoter in two-stage urinary bladder carcinogenesis.

Immediate hemodynamic response to furosemide in patients undergoing chronic hemodialysis

To evaluate the effect of furosemide on cardiovascular hemodynamics in patients with end-stage renal failure, we studied ten patients undergoing hemodialysis three times a week. Arterial pressure, heart rate, and cardiac output (indocyanine green dye) were measured in triplicate; total peripheral resistance and central blood volume were calculated by standard formulas. Hemodynamics were determined at baseline and 5, 10, 15, and 30 minutes after intravenous (IV) bolus injection of furosemide 60 mg. Furosemide produced a decrease in central blood volume of -13% +/- 2.2% from pretreatment values (P less than .01) that was most pronounced five minutes after injection, together with a fall in cardiac output (from 6.76 +/- 0.59 to 6.17 +/- 0.52 L/min, P less than .10). Stroke volume decreased with a maximum fall occurring after 15 minutes (from 84 +/- 7 to 79 +/- 7 mL/min, P less than .05), and total peripheral resistance increased (from 15.8 +/- 2.1 to 17.8 +/- 2.3 units, P less than .05) after furosemide. Arterial pressure and heart rate did not change. The decrease in central blood volume reflects a shift of the total blood volume from the cardiopulmonary circulation to the periphery, suggesting dilation of the peripheral venous bed. Thus, even in patients undergoing hemodialysis, furosemide acutely decreases left ventricular preload by venous dilation and should therefore prove to be beneficial in acute volume overload.

Renal transport kinetics of furosemide in the isolated perfused rat kidney

Direct quantitative data and corresponding theory are provided for the effect of protein binding on the renal transport of furosemide. Drug studies were performed with various combinations of bovine serum albumin and dextran. This resulted in a percent unbound (fu) of furosemide ranging from 0.785 to 85.8%. The corrected renal (CLr/GFR) and secretion (CLs/GFR) clearances of furosemide were observed to increase with percent free, but in a nonproportional manner. Plots of CLr/GFR or CLs/GFR vs. fu appeared to have a prominent y intercept as well as a convex ascending curve. In addition, the excretion ratio [ER = CLr/(fu . GFR)] was reduced from 60.8 to 8.72 as fu increased. Overall, the data were best fitted to a model in which two Michaelis-Menten terms were used to describe renal tubular transport, and secretion was dependent upon free drug concentrations in the perfusate. The results demonstrate that the renal mechanisms of furosemide excretion are more complex than previously reported and that active secretion may involve two different transport systems over the concentration range studied.

Drug-drug and drug-disease interactions with nonsteroidal anti-inflammatory drugs

Nonsteroidal anti-inflammatory drugs may cause a number of drug interactions. They can displace other drugs from serum proteins, and some can affect the metabolism or decrease the renal elimination of other drugs. In addition, they can attenuate the pharmacologic effect of other drugs, such as diuretic and antihypertensive agents, without affecting their disposition. Lastly, many disease states and aging can affect the handling of nonsteroidal anti-inflammatory drugs, mandating dose adjustment of some of these agents in certain clinical conditions. Some drugs may require more of these adjustments than others.

Urinary protein binding, kinetics, and dynamics of furosemide in nephrotic patients

The urinary protein binding, kinetics, and dynamics of furosemide were studied in five nephrotic patients after intravenous dosing. Serial plasma and urine samples containing furosemide were analyzed by HPLC, and drug binding to plasma and urinary proteins was determined using equilibrium dialysis techniques. In comparison to data reported previously in healthy subjects, the steady-state volumes of distribution and nonrenal plasma clearances were significantly increased in nephrotic patients, reflecting the reduced binding of furosemide to plasma proteins. Although there was no significant difference in renal clearance between these two groups, the unbound renal clearance of furosemide was significantly reduced in nephrotic patients even when compensated for by the number of functioning nephrons. Furosemide was extensively bound to urinary protein (19.6-78.4%), and the binding was dependent on the degree of proteinuria. Nevertheless, dose-response analyses, in which the response was represented by sodium excretion rate and the dose by urinary excretion rate of unbound drug, demonstrated that nephrotic patients were less responsive to equivalent amounts of unbound diuretic as compared to healthy subjects.

Comparative pharmacokinetics of frusemide in female rhesus monkeys, cynomolgus monkeys and baboons

1. The pharmacokinetics of frusemide have been compared in 3 non-human primate species after single intravenous dose of 3 mg/kg of the drug. 2. Peak mean plasma concentrations of frusemide were 31.6, 33.6, 43.6 micrograms/ml in the rhesus monkey, cynomolgus monkey and baboon respectively, and concentrations declined with a half-life of about 20 min. 3. There were no notable differences in the pharmacokinetic parameters estimated from either a one-compartment or two-compartment open model. 4. There were statistically significant species-related differences in clearance, half-lives and volumes of distribution adjusted for bodyweight. 5. The pharmacokinetics of frusemide in the cynomolgus monkey are closer to those in man than are those in the rhesus monkey, the baboon or other commonly used laboratory animal species.

Intracranial hypertension and brain oedema in albino rabbits. Part 2: Effects of acute therapy with diuretics

Increased intracranial pressure due to brain oedema was produced in albino rabbits by combining a cryogenic lesion in the left hemisphere with the intraperitoneal administration of 6-aminonicotinamide (cytotoxic agent). The most effective reduction in ICP (74%) was achieved when furosemide and mannitol were used in combination. When either mannitol or furosemide was employed alone, the average ICP reduction was approximately 53%. Peak ICP reduction occurred at 45 minutes with furosemide, 30 minutes with mannitol and furosemide combined, and at 60 minutes with a combination of mannitol and acetazolamide. Also studied simultaneously in these animals were investigated elastance (Em), brain water content, hemispheric water volume content, electrolytes, EEG, and gross pathology. Following therapy there was a statistically significance reduction of water content in the left hemisphere (cryogenic lesion) by all therapeutic modalities except with furosemide alone. In the right hemisphere the water content was reduced by furosemide and the furosemide-mannitol combination but not by the association of mannitol with acetazolamide. A significant decrease of brain sodium was noted only for the combination of mannitol and furosemide. This study indicates that effective reduction of cytotoxic-cryogenic brain oedema and intracranial hypertension can be obtained with a variety of diuretic agents. From the standpoint of tissue dehydration, restoration of tissue electrolyte balance, and rate of ICP reduction, the combination of furosemide-mannitol appears to offer advantages over furosemide alone, or acetazolamide-mannitol.

Preliminary evaluation of furosemide-probenecid interaction in humans

The pharmacokinetics and pharmacodynamics of intravenous furosemide, 40 mg, were studied in four healthy male subjects in a crossover fashion with and without probenecid pretreatment. In each study, 16 plasma and 10 urine samples were collected over 24 hr. Fluid and electrolyte urinary losses were replaced orally throughout the study. Unchanged furosemide and probenecid were measured using high-pressure liquid chromatography; urinary sodium was measured by flame photometry. Although probenecid caused marked changes in the pharmacokinetic parameters of furosemide (increased area under the curve, decreased plasma and renal clearance, increased half-life, and decreased fraction excreted unchanged in the urine), there was no significant difference in its gross 8-hr natriuretic and diuretic effect. However, analysis of the time course of natriuresis showed a pattern similar to that of the urinary furosemide excretion rate, whereas the plasma concentration was poorly correlated over the entire dose-response curve.

Pharmacokinetics/pharmacodynamics of furosemide in man: a review

The pharmacokinetics of furosemide and the attempt to correlate biological fluid measurements with diuretic response have been the subject of a large number of studies since the original reports of Hajdú, Rupp, and coworkers in the mid-1960s. This article attempts to critically review these studies under seven different sections: furosemide pharmacokinetics in normal volunteers, furosemide pharmacokinetics in patients with decreased renal function, furosemide pharmacokinetics in patients with congestive heart failure, furosemide metabolism and assay methods, furosemide bioavailability, dose-response relationships, and the role of inhibitors and mediators on furosemide effects. The literature is reviewed through August 1978.

Evaluation of a new diuretic, diapamide, in congestive heart failure

The diuretic response of patients with congestive heart failure to establish doses of diapamide (750 mg) and furosemide (80 mg) was compared in an open, crossover study. Peak urine output occurred in the first 6 hours after administration of furosemide but somewhat later (12 to 18 hours) with diapamide. Both agents produced active diuresis and natriuresis in most patients. Comparisons of drug effect during the first days of each treatment period and analysis of the entire first treatment period indicated that urine output with furosemide was significantly greater than with diapamide. Urinary sodium excretion on the first day of treatment was not significantly greater with furosemide than with diapamide, nor were the differences significant on subsequent days. The observed differences between drugs on urinary potassium and chloride excretion were not statistically significant. The most frequently occurring adverse reaction was mild to moderate nausea, which was reported by five patients receiving diapamide and two patients receiving furosemide. Diarrhea and vomiting were also more frequent with diapamide. Diapamide would appear to serve a role between the milder thiazide diuretics and the more effective furosemide.

Formation of a cyclic derivative of ethacrynic acid with diazomethane

Samples of ethacrynic acid were treated with methanol-hydrochloric acid or with diazomethane. GLC and mass spectrometric analysis indicated that the methanol-hydrochloric acid reaction gave the expected methyl ester, whereas diazomethane treatment gave a compound containing an additional 14 mass units. Accurate mass measurement and PMR and IR spectra showed that this product was a cyclic derivative of the methyl ester of ethacrynic acid, methyl 4-(2,3-dihydro-4-ethyl-5-furyl)-2,3-dichlorophenoxyacetate. Either derivatization method can be used for development of an assay for ethacrynic acid.

Clinical toxicity of furosemide in hospitalized patients. A report from the Boston Collaborative Drug Surveillance Program

Of 17,068 hospitalized medical patients monitored in a drug surveillance program, 2,367 (13.9 per cent) received furosemide. Of these patients, 53 per cent were hospitalized with a primary (first) diagnosis of cardiovascular disease; many other patients had cardiovascular disorders coincident with other diseases. In 78 per cent of cases the indication for furosemide therapy was congestive heart failure. Adverse reactions were attributed to furosemide in 239 patients (10.1 per cent), but in only 14 instances were the unwanted effects considered life-threatening. The most common adverse reactions were: intravascular volume depletion (4.6 per cent of furosemide recipients), hypokalemia (3.6 per cent), and other eletrolyte disturbances (1.5 per cent). Many patients experienced more than one manifestation of toxicity. The over-all frequency of adverse reactions increased progressively with higher daily doses of furosemide, but was not correlated with total furosemide dose. Among furosemide recipients who also recieved potassium-supplements or potassium-sparing diuretics, hypokalemia was less frequent, less severe, and of slower onset. Coadministration of other diuretics with furosemide was associated with a higher frequency of volume depletion. The findings indicate that furosemide is a relatively safe diuretic in a wide range of clinical situations. Serious adverse reactions are uncommon, and occur primarily in the seriously ill.