Pharmacodynamic analysis of the furosemide-probenecid interaction in man

Drug repurposing for cardiovascular diseases: New targets and indications for probenecid

The available pharmacological options in the management of cardiovascular diseases such as ischaemic heart disease and subsequent heart failure are effective in slowing the progression of this condition. However, the long-term prognosis is still poor, raising the demand for new therapeutic strategies. Drug repurposing is a time- and cost-effective drug development strategy that offers approved and abandoned drugs a new chance for new indications. Recently, drugs used for the management of gout-related inflammation such as canakinumab or colchicine have been considered for drug repurposing in cardiovascular indications. The old uricosuric drug, probenecid, has been identified as a novel therapeutic option in the management of specific cardiac diseases as well. Probenecid can modulate myocardial contractility and vascular tone and exerts anti-inflammatory properties. The mechanisms behind these beneficial effects might be related inhibition of inflammasomes, and to modulation purinergic-pannexin-1 signalling and TRPV2 channels, which are recently identified molecular targets of probenecid. In this review, we provide an overview on repurposing probenecid for ischaemic heart disease and subsequent heart failure by summarizing the related experimental and clinical data and propose its potential repurposing to treat cardiovascular diseases.

Consideration of Fractional Distribution Parameter fd in the Chen and Gross Method for Tissue-to-Plasma Partition Coefficients: Comparison of Several Methods

PURPOSE

The tissue-to-plasma partition coefficient (K_p) describes the extent of tissue distribution in physiologically-based pharmacokinetic (PBPK) models. Constant-rate infusion studies are common for experimental determination of the steady-state K_p,ss, while the tissue-plasma concentration ratio (C_T/C_p) in the terminal phase after intravenous doses is often utilized. The Chen and Gross (C&G) method converts a terminal slope C_T/C_p to K_p,ss based on assumptions of perfusion-limited distribution in tissue-plasma equilibration. However, considering blood flow (Q_T) and apparent tissue permeability (f_upPS_in) in the rate of tissue distribution, this report extends the C&G method by utilizing a fractional distribution parameter (f_d).

METHODS

Relevant PBPK equations for non-eliminating and eliminating organs along with lung and liver were derived for the conversion of C_T/C_p values to K_p,ss. The relationships were demonstrated in rats with measured C_T/C_p and K_p,ss values and the model-dependent f_d for 8 compounds with a range of permeability coefficients. Several methods of assessing K_p were compared.

RESULTS

Utilizing f_d in an extended C&G method, our estimations of K_p,ss from C_T/C_p were improved, particularly for lower permeability compounds. However, four in silico methods for estimating K_p performed poorly across tissues in comparison with measured K_p values. Mathematical relationships between K_p and K_p,ss that are generally applicable for eliminating organs with tissue permeability limitations necessitates inclusion of an extraction ratio (ER) and f_d.

CONCLUSION

Since many different types/sources of K_p are present in the literature and used in PBPK models, these perspectives and equations should provide better insights in measuring and interpreting K_p values in PBPK.

Transporter-Mediated Drug-Drug Interactions and Their Significance

Drug transporters are considered to be determinants of drug disposition and effects/toxicities by affecting the absorption, distribution, and excretion of drugs. Drug transporters are generally divided into solute carrier (SLC) family and ATP binding cassette (ABC) family. Widely studied ABC family transporters include P-glycoprotein (P-GP), breast cancer resistance protein (BCRP), and multidrug resistance proteins (MRPs). SLC family transporters related to drug transport mainly include organic anion-transporting polypeptides (OATPs), organic anion transporters (OATs), organic cation transporters (OCTs), organic cation/carnitine transporters (OCTNs), peptide transporters (PEPTs), and multidrug/toxin extrusions (MATEs). These transporters are often expressed in tissues related to drug disposition, such as the small intestine, liver, and kidney, implicating intestinal absorption of drugs, uptake of drugs into hepatocytes, and renal/bile excretion of drugs. Most of therapeutic drugs are their substrates or inhibitors. When they are comedicated, serious drug-drug interactions (DDIs) may occur due to alterations in intestinal absorption, hepatic uptake, or renal/bile secretion of drugs, leading to enhancement of their activities or toxicities or therapeutic failure. This chapter will illustrate transporter-mediated DDIs (including food drug interaction) in human and their clinical significances.

Evidence for the Validity of Pyridoxic Acid (PDA) as a Plasma-Based Endogenous Probe for OAT1 and OAT3 Function in Healthy Subjects

Plasma pyridoxic acid (PDA) and homovanillic acid (HVA) were recently identified as novel endogenous biomarkers of organic anion transporter (OAT) 1/3 function in monkeys. Consequently, this clinical study assessed the dynamic changes and utility of plasma PDA and HVA as an initial evaluation of OAT1/3 inhibition in early-phase drug development. The study was designed as a single-dose randomized, three-phase, crossover study; 14 Indian healthy volunteers received probenecid (PROB) (1000 mg orally) alone, furosemide (FSM) (40 mg orally) alone, or FSM 1 hour after receiving PROB (40 and 1000 mg orally) on days 1, 8, and 15, respectively. PDA and HVA plasma concentrations remained stable over time in the prestudy and FSM groups. Administration of PROB significantly increased the area under the plasma concentration-time curve (AUC) of PDA by 3.1-fold (dosed alone; P < 0.05), and 3.2-fold (coadministered with FSM; P < 0.01), compared with the prestudy and FSM groups, respectively. The corresponding increase in HVA AUC was 1.8-fold (P > 0.05) and 2.1-fold (P < 0.05), respectively. The increases in PDA AUC are similar to those in FSM AUC, whereas those of HVA are smaller (3.1-3.2 and 1.8-2.1 vs. 3.3, respectively). PDA and HVA renal clearance (CL _R) values were decreased by PROB to smaller extents compared with FSM (0.35-0.37 and 0.67-0.73 vs. 0.23, respectively). These data demonstrate that plasma PDA is a promising endogenous biomarker for OAT1/3 function and that its plasma exposure responds in a similar fashion to FSM upon OAT1/3 inhibition by PROB. The magnitude and variability of response in PDA AUC and CL _R values between subjects is more favorable relative to HVA.

Optimization of a drug transporter probe cocktail: potential screening tool for transporter-mediated drug-drug interactions

AIMS

Previous pharmacokinetic characterization of a transporter probe cocktail containing digoxin (P-gp), furosemide (OAT1, OAT3), metformin (OCT2, MATE1, MATE2-K) and rosuvastatin (OATP1B1, OATP1B3, BCRP) in healthy subjects showed increases in rosuvastatin systemic exposure compared to rosuvastatin alone. In this trial, the doses of metformin and furosemide as putative perpetrators were reduced to eliminate their drug-drug interaction (DDI) with rosuvastatin.

METHODS

In a randomized, open-label, single-centre, five-treatment, five-period crossover trial, 30 healthy male subjects received as reference treatments separately 0.25 mg digoxin, 1 mg furosemide, 10 mg metformin and 10 mg rosuvastatin, and as test treatment all four drugs administered together as a cocktail. Primary pharmacokinetic endpoints were AUC_0-tz (area under the plasma concentration-time curve from time zero to the last quantifiable concentration) and C_max (maximum plasma concentration) of each probe drug.

RESULTS

Geometric mean ratios and 90% confidence intervals of test (cocktail) to reference (single drug) for AUC_0-tz were 96.4% (88.2-105.3%) for digoxin, 102.6% (93.8-112.3%) for furosemide, 97.5% (93.5-101.6%) for metformin and 105.0% (96.4-114.4%) for rosuvastatin, indicating lack of interaction. The same analysis for C_max and for pharmacokinetic parameters of urinary excretion of all cocktail components also indicated no DDI.

CONCLUSIONS

Digoxin (0.25 mg), furosemide (1 mg), metformin (10 mg) and rosuvastatin (10 mg) exhibit no mutual pharmacokinetic interactions and are well tolerated administered as a cocktail. The cocktail is thus optimized and has the potential to be used as a screening tool for clinical investigation of transporter-mediated DDI.

Discovery and Validation of Pyridoxic Acid and Homovanillic Acid as Novel Endogenous Plasma Biomarkers of Organic Anion Transporter (OAT) 1 and OAT3 in Cynomolgus Monkeys

Perturbation of organic anion transporter (OAT) 1- and OAT3-mediated transport can alter the exposure, efficacy, and safety of drugs. Although there have been reports of the endogenous biomarkers for OAT1/3, none of these have all of the characteristics required for a clinical useful biomarker. Cynomolgus monkeys were treated with intravenous probenecid (PROB) at a dose of 40 mg/kg in this study. As expected, PROB increased the area under the plasma concentration-time curve (AUC) of coadministered furosemide, a known substrate of OAT1 and OAT3, by 4.1-fold, consistent with the values reported in humans (3.1- to 3.7-fold). Of the 233 plasma metabolites analyzed using a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based metabolomics method, 29 metabolites, including pyridoxic acid (PDA) and homovanillic acid (HVA), were significantly increased after either 1 or 3 hours in plasma from the monkeys pretreated with PROB compared with the treated animals. The plasma of animals was then subjected to targeted LC-MS/MS analysis, which confirmed that the PDA and HVA AUCs increased by approximately 2- to 3-fold by PROB pretreatments. PROB also increased the plasma concentrations of hexadecanedioic acid (HDA) and tetradecanedioic acid (TDA), although the increases were not statistically significant. Moreover, transporter profiling assessed using stable cell lines constitutively expressing transporters demonstrated that PDA and HVA are substrates for human OAT1, OAT3, OAT2 (HVA), and OAT4 (PDA), but not OCT2, MATE1, MATE2K, OATP1B1, OATP1B3, and sodium taurocholate cotransporting polypeptide. Collectively, these findings suggest that PDA and HVA might serve as blood-based endogenous probes of cynomolgus monkey OAT1 and OAT3, and investigation of PDA and HVA as circulating endogenous biomarkers of human OAT1 and OAT3 function is warranted.

Renal Drug Transporters and Drug Interactions

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

Renal Drug Transport and Drug-Drug Interactions

The kidney plays a vital role in the elimination of xenobiotics including drugs, toxins, and endogenous metabolites. Renal drug elimination involves 3 major processes: glomerular filtration, tubular secretion, and tubular reabsorption. Although glomerular filtration is a simple unidirectional diffusion process, renal tubular secretion and/or reabsorption can involve saturable processes mediated by multiple highly specialized membrane transport systems. Current research has identified that these transport proteins play a significant role in the efficient removal and/or reabsorption of pharmacological agents. Since the majority of membrane transporters have broad substrate specificity, there is a significant risk for drug-drug interactions through competition for similar transport pathways. This article will focus on the cellular expression, localization, and transport properties of various renal drug transport systems (ie, organic anion, organic cation, nucleoside, and adenosine triphosphate [ATP]-dependent efflux transporters). Specific examples of drugs that are transported by each of these mechanisms will be provided. Clinically relevant drug-drug interactions involving renal drug transporters will be discussed to guide the clinician in understanding and preventing these interactions.

Goal-directed diuresis: A case - control study of continuous furosemide infusion in critically ill trauma patients

BACKGROUND

Excessive crystalloid administration is common and associated with negative outcomes in critically ill trauma patients. Continuous furosemide infusion (CFI) to remove excessive fluid has not been previously described in this population. We hypothesized that a goal-directed CFI is more effective for fluid removal than intermittent bolus injection (IBI) diuresis without excess incidence of hypokalemia or renal failure.

MATERIALS AND METHODS

CFI cases were prospectively enrolled between November 2011 and August 2012, and matched to historic IBI controls by age, gender, Injury Severity Score (ISS), and net fluid balance (NFB) at diuresis initiation. Paired and unpaired analyses were performed to compare groups. The primary endpoints were net fluid balance, potassium and creatinine levels. Secondary endpoints included intensive care unit (ICU) and hospital length of stay (LOS), ventilator-free days (VFD), and mortality.

RESULTS

55 patients were included, with 19 cases and 36 matched controls. Mean age was 54 years, mean ISS was 32.7, and mean initial NFB was +7.7 L. After one day of diuresis with CFI vs. IBI, net 24 h fluid balance was negative (-0.55 L vs. +0.43 L, P = 0.026) only for the CFI group, and there was no difference in potassium and creatinine levels. Cumulative furosemide dose (59.4mg vs. 25.4mg, P < 0.001) and urine output (4.2 L vs. 2.8 L, P < 0.001) were also significantly increased with CFI vs. IBI. There were no statistically significant differences in ICU LOS, hospital LOS, VFD, or mortality.

CONCLUSIONS

Compared to IBI, goal-directed diuresis by CFI is more successful in achieving net negative fluid balance in patients with fluid overload with no detrimental side effects on renal function or patient outcome.

Development and standardization of a furosemide stress test to predict the severity of acute kidney injury

Introduction

In the setting of early acute kidney injury (AKI), no test has been shown to definitively predict the progression to more severe stages.

Methods

We investigated the ability of a furosemide stress test (FST) (one-time dose of 1.0 or 1.5 mg/kg depending on prior furosemide-exposure) to predict the development of AKIN Stage-III in 2 cohorts of critically ill subjects with early AKI. Cohort 1 was a retrospective cohort who received a FST in the setting of AKI in critically ill patients as part of Southern AKI Network. Cohort 2 was a prospective multicenter group of critically ill patients who received their FST in the setting of early AKI.

Results

We studied 77 subjects; 23 from cohort 1 and 54 from cohort 2; 25 (32.4%) met the primary endpoint of progression to AKIN-III. Subjects with progressive AKI had significantly lower urine output following FST in each of the first 6 hours (p<0.001). The area under the receiver operator characteristic curves for the total urine output over the first 2 hours following FST to predict progression to AKIN-III was 0.87 (p = 0.001). The ideal-cutoff for predicting AKI progression during the first 2 hours following FST was a urine volume of less than 200mls(100ml/hr) with a sensitivity of 87.1% and specificity 84.1%.

Conclusions

The FST in subjects with early AKI serves as a novel assessment of tubular function with robust predictive capacity to identify those patients with severe and progressive AKI. Future studies to validate these findings are warranted.

Role of diuretics and ultrafiltration in congestive heart failure

Volume overload in heart failure (HF) results from neurohumoral activation causing renal sodium and water retention secondary to arterial underfilling. Volume overload not only causes signs and symptoms of congestion, but can impact myocardial remodeling and HF progression. Thus, treating congestion is a cornerstone of HF management. Loop diuretics are the most commonly used drugs in this setting. However, up to 30% of the patients with decompensated HF present with loop-diuretic resistance. A universally accepted definition of loop diuretic resistance, however, is lacking. Several approaches to treat diuretic-resistant HF are available, including addition of distal acting thiazide diuretics, natriuretic doses of mineralocorticoid receptor antagonists (MRAs), or vasoactive drugs. Slow continuous veno-venous ultrafiltration is another option. Ultrafiltration, if it is started early in the course of HF decompensation, may result in prominent decongestion and a reduction in re-hospitalization. On the other hand, ultrafiltration in HF patients with worsening renal function and volume overload after aggressive treatment with loop diuretics, failed to show benefit compared to a stepwise pharmacological approach, including diuretics and vasoactive drugs. Early detection of congested HF patients for ultrafiltration treatment might improve decongestion and reduce readmission. However, the best patient characteristics and best timing of ultrafiltration requires further evaluation in randomized controlled studies.

Diuretics in heart failure: practical considerations

This review discusses the role of diuretics in heart failure by focusing on different classifications and mechanisms of action. Pharmacodynamic and pharmacokinetic properties of diuretics are elucidated. The predominant discussion highlights the use of loop diuretics, which are the most commonly used drugs in heart failure. Different methods of using this therapy in different settings along with a comprehensive review of the side-effect profile are highlighted. Special situations necessitating adjustment and the phenomenon of diuretic resistance are explained.

The added-up albumin enhances the diuretic effect of furosemide in patients with hypoalbuminemic chronic kidney disease: a randomized controlled study

Background

Chronic kidney disease (CKD) with edema is a common clinical problem resulting from defects in water and solute excretion. Furosemide is the drug of choice for treatment. In theory, good perfusion and albumin are required for the furosemide to be secreted at the tubular lumen. Thus, in the situation of low glomerular filtration rate (GFR) and hypoalbuminemia, the efficacy of furosemide alone might be limited. There has been no study to validate the effectiveness of the combination of furosemide and albumin in this condition.

Methods

We conducted a randomized controlled crossover study to compare the efficacy of diuretics between furosemide alone and the combination of furosemide plus albumin in stable hypoalbuminemic CKD patients by measuring urine output and sodium. The baseline urine output/sodium at 6 and 24 hours were recorded. The increment of urine output/sodium after treatment at 6 and 24 hours were calculated by using post-treatment minus baseline urine output/sodium at the corresponding period.

Results

Twenty-four CKD patients (GFR = 31.0 ± 13.8 mL/min) with hypoalbuminemia (2.98 ± 0.30 g/dL) were enrolled. At 6 hours, there were significant differences in the increment of urine volume (0.47 ± 0.40 vs 0.67 ± 0.31 L, P < 0.02) and urine sodium (37.5 ± 29.3 vs 55.0 ± 26.7 mEq, P < 0.01) between treatment with furosemide alone and with furosemide plus albumin. However, at 24 hours, there were no significant differences in the increment of urine volume (0.49 ± 0.47 vs 0.59 ± 0.50 L, P = 0.46) and urine sodium (65.3 ± 47.5 vs 76.1 ± 50.1 mEq, P = 0.32) between the two groups.

Conclusion

The combination of furosemide and albumin has a superior short-term efficacy over furosemide alone in enhancing water and sodium diuresis in hypoalbuminemic CKD patients.

Trial registration

The Australian New Zealand Clinical Trials Registration (ANZCTR12611000480987)

Clinical pharmacology of the loop diuretics furosemide and bumetanide in neonates and infants

The loop diuretics furosemide and bumetanide are used widely for the management of fluid overload in both acute and chronic disease states. To date, most pharmacokinetic studies in neonates have been conducted with furosemide and little is known about bumetanide. The aim of this article was to review the published data on the pharmacology of furosemide and bumetanide in neonates and infants in order to provide a critical analysis of the literature, and a useful tool for physicians. The bibliographic search was performed electronically using PubMed and EMBASE databases as search engines and March 2011 was the cutoff point. The half-life (t(½)) of both furosemide and bumetanide is considerably longer in neonates than in adults and consequently the clearance (CL) of these drugs is reduced at birth. In healthy volunteers, plasma t(½) of furosemide ranges from 33 to 100 minutes, whereas in neonates it ranges from 8 to 27 hours. The volume of distribution (V(d)) of furosemide undergoes little variation during neonate maturation. The dose of furosemide, administered by intermittent intravenous infusion, is 1 mg/kg and may increase to a maximum of 2 mg/kg every 24 hours in premature infants and every 12 hours in full-term infants. Comparison of continuous infusion versus intermittent infusion of furosemide showed that the diuresis is more controlled with fewer hemodynamic and electrolytic variations during continuous infusion. The appropriate infusion rate of furosemide ranges from 0.1 to 0.2 mg/kg/h and when the diuresis is <1 mL/kg/h the infusion rate may be increased to 0.4 mg/kg/h. Treatment with theophylline before administration of furosemide results in a significant increase of urine flow rate. Bumetanide is more potent than furosemide and its dose after intermittent intravenous infusion ranges from 0.005 to 0.1 mg/kg every 24 hours. The t(½) of bumetanide in neonates ranges from 1.74 to 7.0 hours. Up to now, no data are available on the continuous infusion of bumetanide. Extracorporeal membrane oxygenation (ECMO) is used for a variety of indications including sepsis, persistent pulmonary hypertension, meconium aspiration syndrome, cardiac defects and congenital diaphragmatic hernia. There are two studies of furosemide in neonates undergoing ECMO and only one on the pharmacokinetics of bumetanide under ECMO. When ECMO was conducted for 72 hours, the total amount of furosemide administered was 7.0 mg/kg, and the urine production in the 3 days of treatment was about 6 mL/kg/h, which is the target value. The t(½) of bumetanide in neonates during ECMO was extremely variable. CL, t(½), and V(d) were 0.63 mL/min/kg, 13.2 hours, and 0.45 L/kg, respectively. Furosemide may be administered by inhalation and inhibits the bronco-constrictive effect of exercise, cold air ventilation and antigen challenge. However, inhaled furosemide is not active in infants with viral bronchiolitis and its effect on broncho-pulmonary dysplasia is still uncertain. Furosemide does not significantly increase the risk of failure of patent ductus arteriosus closure when indomethacin or ibuprofen have been co-administered. Infants with low birth weight treated long-term with furosemide are at risk for the development of intra-renal calcification. Furosemide therapy above 10 mg/kg bodyweight cumulative dose had a 48-fold increased risk of nephrocalcinosis. The use of furosemide in combination with indomethacin increased the incidence of acute renal failure. The maturation of the kidney governs the pharmacokinetics of furosemide and bumetanide in the infant. CL and t(½) are influenced by development, and this must be taken into consideration when planning a dosage regimen with these drugs.

Update in diuretic therapy: clinical pharmacology

All diuretics except spironolactone exert their effects from the lumen of the nephron. Thus, to exert an effect, they must reach the urine. Pharmacokinetics (PK) describes this access. Different edematous disorders can affect access to this site of action and therein affect response to a diuretic. In addition, once a diuretic reaches the site of action, a response ensues. The characteristics of this response that can be affected by a patient's clinical condition are described by the pharmacodynamics (PD) of a diuretic. To understand the mechanisms of abnormal response to a diuretic one must dissect its PK and PD in different edematous disorders. For example, in patients with renal insufficiency, the mechanism of poor diuretic response is PK. In contrast, in patients with cirrhosis or in those with congestive heart failure, it is PD. In patients with nephrotic syndrome, both PK and PD are operative. These different mechanisms mandate differences in therapeutic strategy, as explained in this article.

The effects of midodrine on the natriuretic response to furosemide in cirrhotics with ascites

BACKGROUND

Resistance to loop diuretics is common in patients with ascites. Diminished glomerular filtration rate (GFR) is thought to mediate resistance to loop diuretics. Midodrine, a commonly used alpha-1 agonist, has been shown to improve GFR in non-azotemic patients with cirrhosis.

AIM

To conduct a randomized, double-blind, placebo-controlled, cross-over study to test the hypothesis that midodrine significantly increases natriuretic response of IV furosemide in non-azotemic cirrhotics with ascites.

METHODS

All subjects participated in both phases, which were (i) furosemide IV infusion + oral midodrine 15 mg administered 30 min before furosemide (ii) furosemide IV infusion + oral placebo administered 30 min before furosemide. Primary outcomes were 6-h urine sodium excretion and 6-h total urine volume.

RESULTS

A total of 15 patients (men: 8; age: 52.7 ± 7.6 years; serum creatinine: 1.06 ± 0.2 mg/dL) were studied. Total 6-h urine sodium excretion was 109 ± 42 mmol in the furosemide + midodrine treatment phase and was not significantly different from that in the furosemide + placebo treatment phase (126 ± 69 mmol, P = 0.6). Similarly, mean 6-h total urine volume was not significantly different between two groups (1770 ± 262 mL vs. 1962 ± 170 mL, P = 0.25).

CONCLUSIONS

Oral midodrine does not increase the natriuretic response to furosemide in non-azotemic cirrhotic patients with ascites. Orally administered midodrine does not increase natriuretic response to furosemide in non-azotemic cirrhotic patients with ascites.

Diuretics in pediatrics : current knowledge and future prospects

This review summarizes current knowledge on the pharmacology, pharmacokinetics, pharmacodynamics, and clinical application of the most commonly used diuretics in children. Diuretics are frequently prescribed drugs in children. Their main indication is to reduce fluid overload in acute and chronic disease states such as congestive heart failure and renal failure. As with most drugs used in children, optimal dosing schedules are largely unknown and empirical. This is undesirable as it can potentially result in either under- or over-treatment with the possibility of unwanted effects. The pharmacokinetics of diuretics vary in the different pediatric age groups as well as in different disease states. To exert their action, all diuretics, except spironolactone, have to reach the tubular lumen by glomerular filtration and/or proximal tubular secretion. Therefore, renal maturation and function influence drug delivery and consequently pharmacodynamics. Currently advised doses for diuretics are largely based on adult pharmacokinetic and pharmacodynamic studies. Therefore, additional pharmacokinetic and pharmacodynamic studies for the different pediatric age groups are necessary to develop dosing regimens based on pharmacokinetic and pharmacodynamic models for all routes of administration.

Indomethacin decreases furosemide-induced natriuresis and diuresis on the neonatal kidney

Indomethacin is used to pharmacologically occlude patent ductus arteriosus in preterm infants. It induces renal untoward effects and furosemide is administered simultaneously to counteract them. The effect of furosemide is blunted by indomethacin. We analyzed comparatively the interactions of furosemide and indomethacin at the organic anion transport system in adult and newborn individuals. Adult and 5-day-old Wistar rats were allocated into three groups: (1) indomethacin (10 mg/kg, ip); (2) furosemide (2 mg/kg, ip); and (3) indomethacin/furosemide, at the same doses. Urinary flow, glomerular filtration rate (GFR), sodium and potassium fractional excretions, and free-water and osmolal clearances were estimated. Para-aminohippuric acid (PAH) uptake was measured in renal cortical slices to study the organic anion's secretory pathway. In adult and newborn rats, furosemide-induced increments in urinary fluxes and excretions of sodium and potassium were blunted by indomethacin administered simultaneously. PAH uptake was decreased to a further extent by indomethacin than by furosemide, suggesting that inhibition of the diuretic effect might be related to competition in the secretion of furosemide. Inhibitory interaction between indomethacin and furosemide was achieved at approximately 10-fold lower concentrations in the newborn than in the adult rats, suggesting that tubular secretion in the neonate is more sensitive to the action of these drugs than in the adult individual.

Drug-drug interactions involving membrane transporters in the human kidney

The kidneys play a critical role in the elimination of xenobiotics. Factors affecting the ability of the kidney to eliminate drugs may result in marked changes in the pharmacokinetics of a given compound. Drug-drug interactions due to competitive inhibition of renal organic anion or cation secretion systems have been noticed clinically for a long time. However, our understanding of the physical sites of interactions, that is, the specific transport proteins that the interacting drugs act on, has just begun very recently. This review summarises the latest progress in molecular identification and functional characterisation of major drug transporters in the human kidney. In particular, the review focuses on relating cloned renal drug transporters to clinically observed drug-drug interactions. The authors' opinion on the current status and future directions of research in these areas is also offered.

Furosemide Continuous Rate Infusion in the Horse: Evaluation of Enhanced Efficacy and Reduced Side Effects

Continuous rate infusion (CRI) of furosemide in humans is considered superior to intermittent administration (IA). This study examined whether furosemide CRI, compared with IA, would increase diuretic efficacy with decreased fluid and electrolyte fluctuations and activation of the renin-angiotensin-aldosterone system (RAAS) in the horse. Five mares were used in a crossover-design study. During a 24-hour period, each horse received a total of 3 mg/kg furosemide by either CRI (0.12 mg/kg/h preceded by a loading dose of 0.12 mg/kg IV) or IA (1 mg/kg IV q8h). There was not a statistically significant difference in urine volume over 24 hours between methods; however, urine volume was significantly greater after CRI compared with IA during the first 8 hours ([median 25th percentile, 75th percentile]: 9.6 L [8.9, 14.4] for CRI versus 5.9 L [5.3, 6.0] for IA). CRI produced a more uniform urine flow, decreased fluctuations in plasma volume, and suppressed renal concentrating ability throughout the infusion period. Potassium, Ca, and Cl excretion was greater during CRI than IA (1,133 mmol [1.110, 1,229] versus 764 mmol [709, 904], 102.7 mmol [96.0, 117.2] versus 73.3 mmol [65.0, 73.5], and 1,776 mmol [1,657, 2.378] versus 1,596 mmol [1,457, 1,767], respectively). Elimination half-lives of furosemide were 1.35 and 0.47 hours for CRI and IA, respectively. The area under the excretion rate curve was 1,285.7 and 184.2 mL x mg/mL for CRI and IA, respectively. Furosemide CRI (0.12 mg/kg/h) for 8 hours, preceded by a loading dose (0.12 mg/kg), is recommended when profound diuresis is needed acutely in horses.

Loop diuretics: from the Na-K-2Cl transporter to clinical use

The diuretic response to loop diuretics in various disease states has consistently been found to be subnormal. One of the key determinants of the degree of diuretic response is the functional integrity of the sodium-potassium-chloride transporter in the loop of Henle. Studies in animal models suggest that expression/activity of the transporter may be affected by factors such as altered natural splicing events of NKCC2 (the gene encoding for the renal transporter), renal prostanoids, vasopressin, and other autacoids. We have reviewed the pharmacokinetics and pharmacodynamics of loop diuretics in health and in edematous disorders for which they are used. On the basis of evidence reviewed in this paper, we propose that altered expression or activity of the sodium-potassium-chloride transporter in the loop of Henle, in conjunction with events occurring in other segments of the nephron, possibly accounts for the altered diuretic response to these agents. Thus the modulators of this altered expression/activity could serve as important therapeutic targets for alternative diuretic regimens in these conditions.

Transporter-mediated Drug Interactions

Since 1994, researchers have isolated various genes encoding transporter proteins involved in drug uptake into and efflux from tissues that play key roles in the absorption, distribution and secretion of drugs in animals and humans. The pharmacokinetic characteristics of drugs that are substrates for these transporters are expected to be influenced by coadministered drugs that work as inhibitors or enhancers of the transporter function. This review deals with recent progress in molecular and functional research on drug transporters, and then with transporter-mediated drug interactions in absorption and secretion from the intestine, secretion from the kidney and liver, and transport across the blood-brain barrier in humans. Although the participation of the particular transporters in observed drug-drug interactions can be difficult to confirm in humans, this review focuses mainly on pharmacokinetic interactions of clinically important drugs.

Mechanisms and clinical implications of renal drug excretion

The body defends itself against potentially harmful compounds like drugs, toxic compounds, and their metabolites by elimination, in which the kidney plays an important role. Renal clearance is used to determine renal elimination mechanisms of a drug, which is the result of glomerular filtration, active tubular secretion and reabsorption. The renal proximal tubule is the primary site of carrier-mediated transport from blood to urine. Renal secretory mechanisms exists for, anionic compounds and organic cations. Both systems comprises several transport proteins, and knowledge of the molecular identity of these transporters and their substrate specificity has increased considerably in the past decade. Due to overlapping specificities of the transport proteins, drug interactions at the level of tubular secretion is an event that may occur in clinical situation. This review describes the different processes that determine renal drug handling, the techniques that have been developed to attain more insight in the various aspects of drug excretion, the functional characteristics of the individual transport proteins, and finally the implications of drug interactions in a clinical perspective.

Effects of albumin/furosemide mixtures on responses to furosemide in hypoalbuminemic patients

Hypoalbuminemic patients often have sufficient fluid accumulation to mandate diuretic therapy but are often resistant to diuresis. Studies have suggested that hypoalbuminemia itself impairs delivery of effective amounts of diuretic agent into the urine, the site of action. Therefore, administration of mixtures of albumin and loop diuretics may enhance responses. Thirteen patients with biopsy-proven cirrhosis and ascites (age, 51.2 +/- 8.1 yr; Child-Pugh score, 8.5 +/- 1.0; serum albumin concentration, 3.0 +/- 0.6 g/dl) were studied in this randomized crossover study. Sodium balance was maintained throughout the study with a metabolic diet. All patients received spironolactone, but administration of all other diuretic agents was discontinued. Each patient received all of the following four treatments intravenously: (1) 40 mg of furosemide, (2) 25 g of albumin, (3) 40 mg of furosemide and 25 g of albumin premixed ex vivo, and (4) 40 mg of furosemide and 25 g of albumin infused simultaneously into different arms. Responses were assessed by measuring urinary sodium excretion and relating the urinary furosemide excretion rate to the sodium excretion rate. Additionally, the pharmacokinetics of furosemide were assessed. Furosemide pharmacokinetics were similar for all treatment arms. Albumin alone had negligible diuretic effects. Neither albumin regimen increased the response to furosemide. Moreover, the relationship between the urinary furosemide excretion rate and the sodium excretion rate was unaffected by albumin. In conclusion, albumin failed to enhance the diuretic effects of furosemide in cirrhotic patients with ascites. Therefore, the coadministration of albumin and furosemide for the treatment of cirrhosis, and likely other hypoalbuminemic conditions, should not be used clinically.

Urinary protein binding does not affect response to furosemide in patients with nephrotic syndrome

Response to loop diuretics in patients with nephrotic syndrome (NS) is subnormal. Studies in animal models of NS have suggested that binding of diuretic to urinary albumin is one of the mechanisms that may be operative in this diuretic resistance. To explore this hypothesis, 12 patients with NS were studied to determine whether displacement from urinary protein binding with sulfisoxazole would restore response to 120 mg of furosemide. The study was stopped after treating seven patients because it was clear that sulfizoxazole had no effect. Sodium excretion (mean +/- SD) from furosemide alone was 239 +/- 90 versus 240 +/- 115 mEq/8 h with sulfisoxazole. Sulfisoxazole had modest effects on serum pharmacokinetics of furosemide but had no effect on either the time course of furosemide urinary excretion or overall amount excreted: 49 +/- 15 mg versus 54 +/- 12 mg for furosemide alone and furosemide plus sulfisoxazole, respectively. It is concluded that urinary protein binding of loop diuretics is not a major mechanism for the diuretic resistance of NS. In turn, strategies aimed at displacing such binding are unlikely to be clinically helpful.

Pharmacology of diuretics

The diuretics in our therapeutic armamentarium have predictable effects based on their nephron sites of action. All but spironolactone must reach the lumen or urinary side of the nephron to exert their effects. Thus, in settings of decreased renal function, doses must be increased to deliver more diuretic into the urine. In other edematous disorders, such as congestive heart failure (CHF) and cirrhosis, adequate amounts of diuretic reach the site of action if renal function is satisfactory. Diminished response in these conditions is caused by a decrease in the sensitivity of the nephron to the diuretic, the mechanism of which is unknown. Rather than using large single doses of diuretic in CHF and cirrhosis, multiple doses and/or combinations of diuretics should be used. Therefore, thiazide diuretics coupled with loop diuretics are most logical because they affect different nephron sites and the thiazide counteracts distal nephron hypertrophy that may occur with loop diuretics alone. Ample studies have shown that such combinations can result in a truly synergistic response. Using pharmacokinetics and pharmacodynamics of diuretics, we can design therapeutic regimens in which satisfactory control of fluid and electrolyte homeostasis can be achieved in the vast majority of patients.

Clinical consequences of the biphasic elimination kinetics for the diuretic effect of furosemide and its acyl glucuronide in humans

This review discusses the possibility of whether furosemide acyl glucuronide, a metabolite of furosemide, contributes to the clinical effect of diuresis. First an analytical method (e.g. HPLC) must be available to measure both parent drug and furosemide acyl glucuronide. Then, with correctly treated plasma and urine samples (light protected, pH 5) from volunteers and furosemide-treated patients, the kinetic curves of both furosemide as well as its acyl glucuronide can be measured. The acyl glucuronide is formed in part by the kidney tubules and it is possible that the compound is pharmacologically active through inhibition of the Na+/2Cl-/K+ co-transport system; up to now the mechanism of action has been solely attributed to furosemide. The total body clearance of furosemide occurs by hepatic and renal glucuronidation (50%) and by renal excretion (50%). Enterohepatic cycling of furosemide acyl glucuronide, followed by hydrolysis, results in a second and slow elimination phase with a half-life of 20-30 h. This slow elimination phase coincides with a pharmacodynamic rebound phase of urine retention. After each dosage of furosemide, there is first a short stimulation of urine flow (4 h), which is followed by a 3-day recovery period of the body. The following clinical implications arise from study of the elimination kinetics of furosemide. Repetitive dosing must result in accumulation of the recovery period. Accumulation of furosemide and its acyl glucuronide in patients with end-stage renal failure results from infinite hepatic cycling. Impaired kidney function may result in impaired glucuronidation and diuresis. While kidney impairment normally requires a dose reduction for those compounds which are mainly eliminated by renal excretion, for diuretics, a dose increment is required in order to maintain a required level of diuresis. The full clinical impact of the accumulation of furosemide and its acyl glucuronide in patients with end-stage renal failure has to be determined.

Effects of recombinant human serum albumin on ascites in rats with puromycin aminonucleoside-induced nephropathy

1. Recombinant human serum albumin (rHSA) (1 g/kg) significantly decreased the weight of ascites in rats with puromycin aminonucleoside-induced nephropathy. 2. Furosemide (1-30 mg/kg) did not significantly reduce the weight of ascites in this model. 3. A combination of rHSA (1 g/kg) with furosemide (5 mg/kg) significantly decreased the weight of ascites in this model compared with furosemide alone. 4. In consideration of these results, rHSA can be a substitute for human serum albumin products prepared from human plasma in therapy for ascites or edema in furosemide-resistant nephrotic syndrome.

The pharmacokinetics of furosemide in anaesthetized horses after bilateral ureteral ligation

The pharmacokinetics of furosemide were investigated in anaesthetized horses with bilateral ureteral ligation (BUL) with (n = 5) or without (n = 5) premedication with phenylbutazone. Horses were administered an intravenous (i.v.) bolus dose of furosemide (1 mg/kg) approximately 60-90 min after BUL. Plasma samples collected up to 3 h after drug administration were analysed by a validated high performance liquid chromatography method. Median plasma clearance (CLp) of furosemide in anaesthetized horses with BUL was 1.4 mL/min/kg. Apparent steady state volume of distribution (Vd(ss)) ranged from 169 to 880 mL/kg and the elimination half life (t1/2) ranged from 83 min to 209 h. No differences in plasma concentration or kinetic parameter estimates were observed when phenylbutazone was administered before furosemide administration. BUL markedly reduces the elimination of furosemide in horses and models the potential effects that severe changes in kidney function may have on drug kinetics in horses.

Dose-ranging evaluation of bumetanide pharmacodynamics in critically ill infants

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Frusemide and its acyl glucuronide show a short and long phase in elimination kinetics and pharmacodynamic effect in man

The pharmacokinetics of 80 mg frusemide given orally were investigated in normal subjects using a direct HPLC method for parent drug and its acyl glucuronide conjugate. Two half-lives could be distinguished in the plasma elimination of both frusemide and its conjugate, with values of 1.25 +/- 0.75 and 30.4 +/- 11.5 h for frusemide and 1.31 +/- 0.60 and 33.2 +/- 28.0 h for the conjugate. The renal excretion rate-time profile showed two phases; the rapid elimination phase lasted from 0-15 h and the second and slow phase, from 15-96 h. During the first 15 h, 33.3 +/- 4.8% of the dosed frusemide was excreted; in the remaining period 15-96 h, 4.6 +/- 1.5% was excreted. In the same two periods the excretion of the glucuronide was 13.4 +/- 4.7 and 1.9 +/- 1.1%, respectively. The mean renal clearance of frusemide was 90.2 +/- 16.9 mL min-1 during the first period and 91.5 +/- 29.3 mL min-1 in the remaining period, during which the stimulation of urine production was absent. The renal clearance of the acyl glucuronide was 702 +/- 221 mL min-1 in the first period, but only 109 +/- 51.0 mL min-1 in the second period. The stimulated urine production in the first 6 h after administration amounted to 2260 +/- 755 mL (measured urine production minus baseline value of 1 mL min-1 (360 mL). During the second or rebound period (6-96 h after drug administration), the quantity of urine was 990 +/- 294 mL lower than what would have been expected from the baseline production of 5400 mL. This reduced production (0.82 mL min-1) is equivalent to an 18% reduction in the average urine flow rate of 1 mL min-1.

Furosemide dynamics in conscious rabbits: modulation by angiotensin II

The aim of this study was to investigate the effects of an infusion of angiotensin II (50 ng/kg/min) on furosemide pharmacodynamics and kinetics in the conscious rabbit. The protocol included a 90-minute phase to estimate the glomerular filtration rate and the renal plasma flow, followed by a 60-minute phase where 5 mg/kg (n = 12) or 10 mg/kg (n = 9) of furosemide were administered. During the pre-furosemide phase, compared to control rabbits, angiotensin II increased natriuresis and diuresis. In the presence of angiotensin II, the furosemide-induced natriuresis decreased, that is, it was 174 +/- 14 versus 95 +/- 25 mumol/min (p < 0.05) and 187 +/- 17 versus 89 +/- 21 mumol/min (p < 0.05) for the 5 and the 10 mg/kg doses, respectively. The infusion of angiotensin II decreased renal plasma flow without modifying the glomerular filtration rate, thus the filtration fraction was increased. Angiotensin II increased the area under the furosemide plasma concentrations as a function of time since it decreased its systemic clearance. However, furosemide urinary excretion rate was not altered and its renal clearance decreased slightly without reaching statistical significance. It is concluded that angiotensin II decreases the response to furosemide and the mechanism underlying this effect is related to the pharmacodynamics rather than the kinetics of the diuretic.

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.

The effects of probenecid on the excretion kinetics of stanozolol, an anabolic steroid, in rats

The pharmacokinetic behaviour and the mechanism of renal excretion of stanozolol (STZ), as affected by co-treatment with probenecid, were studied in male Sprague-Dawley rats. Pharmacokinetic parameters following intravenous (i.v.) administration of STZ (20 mg kg-1 body wt.) were measured in both STZ-treated (control) and STZ plus probenecid-treated (treatment) groups. In order to assess the renal clearance of STZ, bolus doses of STZ and inulin (40 mg kg-1 body wt.) were injected i.v. either in the presence or absence of probenecid (40 mg kg-1 body wt.). The blood and urine concentrations of STZ were determined by capillary gas chromatography-mass spectrometry (GC-MS). In the probenecid treatment group, the area under the plasma disappearance and urinary excretion curves (AUC) of STZ were significantly decreased (P < 0.01) and the volume of distribution (Vd) and total clearance (CLt) were significantly increased statistically (P < 0.05 and P < 0.01, respectively). No remarkable differences in the urine flow rate, urine pH values, glomerular filtration rate (GFR) or renal clearance were observed in the treatment group. However, the clearance ratio in the treatment group was significantly increased from 11.72 to 17.27. From these results, it is suggested that the significant decrease of AUC, i.e. increase of disappearance of STZ in plasma by co-administration with probenecid, is due to the increase of the clearance ratio.

Intermittent administration of furosemide vs continuous infusion preceded by a loading dose for congestive heart failure

Several reports have suggested that continuous intravenous administration of loop diuretics may be superior to intermittent administration. We performed a prospective randomized crossover study comparing intermittent intravenous administration (IA) of furosemide with continuous infusion following a single loading dose (LDCI) in nine patients with severe congestive heart failure. At the time of hospital admission, patients were randomly assigned to one of two treatment groups. One group (four patients) received an IV bolus injection of furosemide followed immediately by a continuous infusion for 48 h. The second group (five patients) was treated with three IV bolus injections a day for 48 h. Total doses of furosemide were equivalent in the two groups. After 48 h, each patient was crossed over to the other method and treated for an additional 48 h. LDCI produced significantly greater diuresis and natriuresis than IA (total urine output increased by 12 to 26 percent, total sodium excretion increased by 11 to 33 percent) (p less than 0.01). There were no significant differences in side effects between the two methods. These results indicate that LDCI may be a preferred method for administration of furosemide in patients with congestive heart failure.

The influence of co-administered organic acids on the kinetics and dynamics of frusemide

1. This study examines the effects of pretreatment with probenecid with and without pyrazinamide on the elimination kinetics and diuretic action of frusemide. 2. Six normal male volunteers received 40 mg frusemide i.v. on three occasions; i.e. once on its own and twice after pretreatment with 2 g probenecid with and without 3 g pyrazinamide. Both these latter drugs were administered orally 3 h before frusemide administration thereby attempting optimal suppression of proximal tubular secretion. Urinary losses were replaced i.v. with isovolumetric amounts of normal saline while insensible losses were compensated for by taking tap water orally. 3. The mean cumulative urinary frusemide excretion was significantly and similarly decreased by pretreatment with probenecid (34.9%) and probenecid plus pyrazinamide (33.6%), but the mean total volume of diuresis and the mean cumulative urinary sodium excretion did not differ significantly between treatments over the 5 h period. 4. The diuretic efficiency of frusemide was significantly increased with probenecid pretreatment during the first 90 min period after frusemide administration. Furthermore, in the first 30 min after administration the percent sodium fractional excretion was higher after pretreatment with probenecid even though the mean frusemide excretion rate was more than three times with frusemide alone than with probenecid-frusemide (374.4 micrograms min-1 vs 119.1 micrograms min-1). Pretreatment with probenecid results in a higher concentration on the peritubular or blood side of the tubules and these results lead us to question the unconditional acceptance of a luminal site of action for the loop diuretics. Alternatively, probenecid may act in some other way to increase the effects of frusemide.

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.

Analysis of the natriuretic action of a loop diuretic, piretanide, in man

1. The renal responses to a loop diuretic, piretanide, were investigated in a group of fourteen healthy volunteers. The effect of fluid replacement on the drug-response relationship was evaluated in the absence and in the presence of probenecid pretreatment following both oral and intravenous administration of piretanide. 2. Urinary excretion of piretanide was greater when volume losses were replaced than in the absence of volume replacement (i.v. dose: 3.32 +/- 0.15 vs 2.55 +/- 0.23 mg 6 h-1, P less than 0.01; oral dose: 2.57 +/- 0.09 vs 1.87 +/- 0.27 mg 6 h-1, P less than 0.01). With intravenous piretanide urinary excretion of sodium was likewise greater in the fluid replaced group (198 +/- 4 vs 141 +/- 10 mmol 6 h-1, P less than 0.01); these differences caused by fluid replacement did not however occur after oral dosing of piretanide (181 +/- 12 vs 167 +/- 14 mmol 6 h-1). 3. Probenecid pretreatment significantly decreased the renal excretion of piretanide in all subjects and consistently decreased the natriuretic response with the exception of intravenous piretanide challenge in subjects not undergoing fluid replacement. In this situation, despite probenecid causing a decrease in the amount of drug excreted (2.55 +/- 0.23 vs 1.63 +/- 0.15 mg 6 h-1, P less than 0.05) the sodium output was unaltered (141 +/- 10 vs 152 +/- 16 mmol 6 h-1, NS). 4. Complete replacement of the induced fluid losses resulted in the enhancement of the renal response, without affecting the shape of the diuretic response curve, of either the intravenous or orally administered piretanide.(ABSTRACT TRUNCATED AT 250 WORDS)

Furosemide kinetics and dynamics in rats and humans

1. Increasing doses of furosemide (F) were given intravenously to rats and humans and initial pharmacokinetics and pharmacodynamics were compared. 2. Weight-related initial renal excretion rate of F was twice as high in rats and serum concentration at 30 min was twice as high in humans (P less than 0.01). 3. Volume of distribution for F was 44% larger in rats (P less than 0.01). 4. Maximal weight-related diuretic and natriuretic responses were, like the theoretical maximal efficiency, 5-6 times higher in the rat. The potency was 230 times lower in the rats. 5. On a molecular basis species differences in kinetics disappeared when standardization was based on ERPF and species differences in dynamics disappeared when standardization was based on GFR.

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.

The in-vitro pH-dissolution dependence and in-vivo bioavailability of frusemide-PVP solid dispersions

The dependence of the dissolution rate on the pH of the buffered medium, using constant surface area discs, has been examined for crystalline frusemide, a semi-crystalline frusemide-polyvinylpyrrolidone (PVP) solid dispersion and an X-ray amorphous frusemide-PVP dispersion. The marked changes observed in the pH-dissolution profiles indicate that differing dissolution mechanisms operate in the amorphous regions. This conclusion was further supported by the comparison of pH-dissolution and pH-equilibrium solubility profiles that suggested a supersaturation effect to be the relevant term in describing the dissolution enhancing effects of amorphous regions. A marked dissolution enhancement, relative to crystalline frusemide, was shown by the X-ray amorphous solid dispersion in weakly acidic solutions. A similar effect was observed in the dissolution characteristics of gelatin capsule formulations in simulated gastric and intestinal media. In a human bioavailability study, the X-ray amorphous frusemide-PVP solid dispersion exhibited a significant reduction in the time for maximum effect in comparison to crystalline frusemide and a semi-crystalline solid dispersion. This effect, demonstrated by the primary end organ response in seven healthy subjects, concurred with the in-vitro prediction of dissolution enhancement in weakly acidic media.

Furosemide pharmacokinetics and pharmacodynamics in health and disease--an update

The literature on furosemide pharmacokinetics and pharmacodynamics is critically reviewed, concentrating on those papers published subsequent to the 1979 reviews of this topic. Intravenous and oral data are presented for healthy volunteers and for patients with various disease states. It is the latter populations about which the majority of the studies have been published since 1979. Inter- and intraindividual variations in bioavailability are discussed, as are data on the metabolism of furosemide to its glucuronide conjugate. Published studies examining the relationship between furosemide pharmacodynamics and pharmacokinetics are also evaluated. The literature is reviewed through June 1988.