Pharmacokinetics/pharmacodynamics of furosemide in man: a review

Sleep Disorders, Comorbidities, Actions, Lower Urinary Tract Dysfunction, and Medications ("Sleep C.A.L.M.") in the evaluation and management of nocturia: A simple approach to a complex diagnosis

INTRODUCTION

Nocturia arises from a fundamental mismatch between nocturnal urine production, storage capacity, and sleep architecture, which may be driven by abnormalities of the genitourinary tract, but also by sleep disorders, medical diseases, patient actions/lifestyle factors, or medications. This article introduces a novel system for organizing the complex differential diagnosis for nocturia, as proposed by an international collective of practicing urologists, physician specialists, and sleep experts: "Sleep CALM"-Sleep Disorders, Comorbidities, Actions, Lower Urinary Tract Dysfunction, and Medications.

METHODS

Narrative review of current evidence regarding the relevance of each "Sleep CALM" factor to nocturia pathogenesis, evaluation, and management.

RESULTS

Nocturia and sleep disorders are highly intertwined and often bidirectional, such that nocturnal awakenings for reasons other than a sensation of bladder fullness should not be used as grounds for exclusion from nocturia treatment, but rather leveraged to broaden therapeutic options for nocturia. Nocturia is an important potential harbinger of several serious medical conditions beyond the genitourinary tract. Urologists should have a low threshold for primary care and medical specialty referral for medical optimization, which carries the potential to significantly improve nocturnal voiding frequency in addition to overall health status. Adverse patient actions/lifestyle factors, lower urinary tract dysfunction, and medication use commonly coexist with disordered sleep and comorbid medical conditions, and may be the primary mediators of nocturia severity and treatment response, or further exacerbate nocturia severity and complicate treatment.

CONCLUSION

"Sleep CALM" provides a memorable and clinically relevant means by which to structure the initial patient history, physical exam, and clinical testing in accordance with current best-practice guidelines for nocturia. Although not intended as an all-encompassing diagnostic tool, the "Sleep CALM" schema may also be useful in guiding individualized ancillary testing, identifying the need for specialty referral and multidisciplinary care, and uncovering first-line treatment targets.

An Insight into the Degradation Processes of the Anti-Hypertensive Drug Furosemide

Furosemide (FUR), an active pharmaceutical ingredient (API) belonging to a group of drugs known as loop diuretics, has widespread use, but, is characterized by a strong instability to light, which causes chemical transformations that could give a yellowing phenomenon and have a significant impact from a health and marketing point of view. Many studies have tried to explain this phenomenon under different experimental conditions, but no detailed explanation of the yellowing phenomenon has been provided. This work, unlike the others, provides an overall view and explanation of the behavior of FUR in relation to the yellowing phenomenon, both in the solution and in solid state, considering several aspects, such as light exposure, presence of oxygen, and moisture effects.

Pharmacokinetics and diuretic effect of furosemide after single intravenous, oral tablet, and newly developed oral disintegrating film administration in healthy beagle dogs

Background

Furosemide, a diuretic that acts on the loop of Henle, is commonly used to treat congestive heart failure in veterinary medicine. Some owners have difficulty in administering oral tablet medication to animal patients, which leads to noncompliance, especially during long-term administration. Oral disintegrating film (ODF) has the advantages of easy administration via a non-invasive route, rapid dissolution, and low suffocating risk. The objective of this study was to research the pharmacokinetic (PK) profiles and diuretic effect of furosemide after intravenous (IV), orally uncoated tablet (OUT), and newly developed ODF administration in healthy beagle dogs. In this study, a furosemide-loaded ODF (FS-ODF) formulation was developed and five beagle dogs were administered a single dose (2 mg/kg) of furosemide via each route using a cross-over design.

Results

The most suitable film-forming agent was sodium alginate; thus, this was used to develop an ODF for easy drug administration. No significant differences were detected in the PK profiles between OUT and FS-ODF. In the blood profiles, the concentration of total protein was significantly increased compared to the baseline (0 h), whereas no significant difference was detected in the concentration of creatinine and hematocrit compared to the baseline. FS-ODF resulted in a similar hourly urinary output to OUT during the initial 2 h after administration. The urine specific gravity was significantly decreased compared to the baseline in each group. The peak times of urine electrolyte (sodium and chloride) excretion per hour were 1 h (IV), 2 h (OUT), and 2 h (FS-ODF).

Conclusions

These results suggest that the PK/PD of furosemide after administration of newly developed FS-ODF are similar to those of OUT in healthy dogs. Therefore, the ODF formulation has the benefits of ease and convenience, which would be helpful to owners of companion animals, such as small dogs (< 10 kg), for the management of congestive heart failure.

Transformation of 3-(Furan-2-yl)-1,3-di(het)arylpropan-1-ones to Prop-2-en-1-ones via Oxidative Furan Dearomatization/2-Ene-1,4,7-triones Cyclization

The approach to 3-(furan-2-yl)-1,3-di(het)arylprop-2-en-1-ones based on the oxidative dearomatization of 3-(furan-2-yl)-1,3-di(het)arylpropan-1-ones followed by an unusual cyclization of the formed di(het)aryl-substituted 2-ene-1,4,7-triones has been developed. The cyclization step is related to the Paal-Knorr synthesis, but the furan ring formation is accompanied in this case by a formal shift of the double bond through the formation of a fully conjugated 4,7-hydroxy-2,4,6-trien-1-one system or its surrogate.

Understanding Mechanisms of Food Effect and Developing Reliable PBPK Models Using a Middle-out Approach

Over the last 10 years, 40% of approved oral drugs exhibited a significant effect of food on their pharmacokinetics (PK) and currently the only method to characterize the effect of food on drug absorption, which is recognized by the authorities, is to conduct a clinical evaluation. Within the pharmaceutical industry, there is a significant effort to predict the mechanism and clinical relevance of a food effect. Physiologically based pharmacokinetic (PBPK) models combining both drug-specific and physiology-specific data have been used to predict the effect of food on absorption and to reveal the underlying mechanisms. This manuscript provides detailed descriptions of how a middle-out modeling approach, combining bottom-up in vitro-based predictions with limited top-down fitting of key model parameters for clinical data, can be successfully used to predict the magnitude and direction of food effect when it is predicted poorly by a bottom-up approach. For nefazodone, a mechanistic clearance for the gut and liver was added, for furosemide, an absorption window was introduced, and for aprepitant, the biorelevant solubility was refined using multiple solubility measurements. In all cases, these adjustments were supported by literature data and showcased a rational approach to assess the factors limiting absorption and exposure.

BCS Class IV Oral Drugs and Absorption Windows: Regional-Dependent Intestinal Permeability of Furosemide

Biopharmaceutical classification system (BCS) class IV drugs (low-solubility low-permeability) are generally poor drug candidates, yet, ~5% of oral drugs on the market belong to this class. While solubility is often predictable, intestinal permeability is rather complicated and highly dependent on many biochemical/physiological parameters. In this work, we investigated the solubility/permeability of BCS class IV drug, furosemide, considering the complexity of the entire small intestine (SI). Furosemide solubility, physicochemical properties, and intestinal permeability were thoroughly investigated in-vitro and in-vivo throughout the SI. In addition, advanced in-silico simulations (GastroPlus^®) were used to elucidate furosemide regional-dependent absorption pattern. Metoprolol was used as the low/high permeability class boundary. Furosemide was found to be a low-solubility compound. Log D of furosemide at the three pH values 6.5, 7.0, and 7.5 (representing the conditions throughout the SI) showed a downward trend. Similarly, segmental-dependent in-vivo intestinal permeability was revealed; as the intestinal region becomes progressively distal, and the pH gradually increases, the permeability of furosemide significantly decreased. The opposite trend was evident for metoprolol. Theoretical physicochemical analysis based on ionization, pK_a, and partitioning predicted the same trend and confirmed the experimental results. Computational simulations clearly showed the effect of furosemide’s regional-dependent permeability on its absorption, as well as the critical role of the drug’s absorption window on the overall bioavailability. The data reveals the absorption window of furosemide in the proximal SI, allowing adequate absorption and consequent effect, despite its class IV characteristics. Nevertheless, this absorption window so early on in the SI rules out the suitability of controlled-release furosemide formulations, as confirmed by the in-silico results. The potential link between segmental-dependent intestinal permeability and adequate oral absorption of BCS Class IV drugs may aid to develop challenging drugs as successful oral products.

Comparison between Branded and Generic Furosemide 40 mg Tablets Using Thermal Gravimetric Analysis and Fourier Transform Infrared Spectroscopy

Background and Purpose

There has been a long-standing belief that generic drugs are of lower value in comparison to their branded name counterparts. They are in particular under scrutiny due to their low market price. Even though the reduction in costs is largely based on skipping expensive preclinical studies and clinical trials for generic drugs, the purity and quality of the raw materials in the production of generic drugs is debatable. Thus, the objective of the study was to analyze and assess the quality comparability of generic furosemide 40 mg (FSD) tablets to branded product available in the market.

Materials and Methods

Quality control tests, in vitro drug release assessments, and thermal analysis investigations for both analog products of FSD were performed. Various physical parameters related to the tablet quality, such as hardness, weight variation, and friability tests, were examined. In vitro drug release behavior evaluations were conducted according to United States Pharmacopeia (USP) specifications and guidelines, whereas thermal analysis was carried out using thermal gravimetric analysis (TGA), and tablets were further evaluated by Fourier transform infrared (FTIR) spectroscopy.

Results

The results indicated a significant variation between the two products in terms of hardness, weight variation, and friability. This could be correlated to variation appeared in thermal and spectroscopic spectra between the two products using TGA and FTIR. Drug release of FSD was slightly different between both products following incubation in different pH media (1.2, 3.0, and 6.5; 120 min), however, this was in accordance with USP dissolution requirements as < 80% of drug release was obtained within the first 30 min from each product.

Conclusion

This study is a useful example for the independent investigations using thermal and spectroscopic analysis to confirm potential hidden variations between generic and branded products that could not be obtained by the bioequivalence studies.

Is Inhaled Furosemide a Potential Therapeutic for COVID-19?

The potentially lethal infection caused by the novel Severe Acute Respiratory Disease Coronavirus-2 (SARS-CoV-2) has evolved into a global crisis. Following the initial viral infection is the host inflammatory response that frequently results in excessive secretion of inflammatory cytokines (e.g., IL-6 and TNFα), developing into a self-targeting, toxic "cytokine storm" causing critical pulmonary tissue damage. The need for a therapeutic that is available immediately is growing daily but the de novo development of a vaccine may take years. Therefore, repurposing of approved drugs offers a promising approach to address this urgent need. Inhaled furosemide, a small molecule capable of inhibiting IL-6 and TNFα, may be an agent capable of treating the Coronavirus Disease 2019 cytokine storm in both resource-rich and developing countries. Furosemide is a "repurpose-able" small molecule therapeutics, that is safe, easily synthesized, handled, and stored, and is available in reasonable quantities worldwide.

Modeling, design and manufacture of innovative floating gastroretentive drug delivery systems based on hot-melt extruded tubes

The problem of many gastroretentive systems is the mechanistic connection of drug release and gastric retention control. This connection could be successfully separated by formulating hollow tubes via hot-melt extrusion and sealing both tube ends, which led to immediately floating devices. The tube wall consisted of metformin crystals embedded in an inert polymer matrix of Eudragit® RS PO and E PO. Very high drug loadings of up to 80% (w/w) were used without generating a 'burst release'. Sustained release profiles from four to more than twelve hours were achieved by varying the polymer proportions without affecting the floatability. Buoyancy was found to mainly depend on the cylinder design, i.e. the outer to inner diameter ratio. This allowed the polymer/metformin composition to be changed without affecting buoyancy, i.e. a separation of floatability and release control was achieved. A prediction model was implemented that allowed for the buoyancy force to be determined with high accuracy by selecting a suitable ratio of outer to inner diameter of the modular tube die. Wall thickness and mass normalized surface area were identified as geometric parameters that mainly influenced the release properties. Conclusively, this study offers a highly flexible and rational manufacturing approach for the development of gastroretentive floating drug delivery systems.

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.

Development of a Whole-Body Physiologically Based Pharmacokinetic Approach to Assess the Pharmacokinetics of Drugs in Elderly Individuals

Background

Because of the vulnerability and frailty of elderly adults, clinical drug development has traditionally been biased towards young and middle-aged adults. Recent efforts have begun to incorporate data from paediatric investigations. Nevertheless, the elderly often remain underrepresented in clinical trials, even though persons aged 65 years and older receive the majority of drug prescriptions. Consequently, a knowledge gap exists with regard to pharmacokinetic (PK) and pharmacodynamic (PD) responses in elderly subjects, leaving the safety and efficacy of medicines for this population unclear.

Objectives

The goal of this study was to extend a physiologically based pharmacokinetic (PBPK) model for adults to encompass the full course of healthy aging through to the age of 100 years, to support dose selection and improve pharmacotherapy for the elderly age group.

Methods

For parameterization of the PBPK model for healthy aging individuals, the literature was scanned for anthropometric and physiological data, which were consolidated and incorporated into the PBPK software PK-Sim^®. Age-related changes that occur from 65 to 100 years of age were the main focus of this work. For a sound and continuous description of an aging human, data on anatomical and physiological changes ranging from early adulthood to old age were included. The capability of the PBPK approach to predict distribution and elimination of drugs was verified using the test compounds morphine and furosemide, administered intravenously. Both are cleared by a single elimination pathway. PK parameters for the two compounds in younger adults and elderly individuals were obtained from the literature. Matching virtual populations—with regard to age, sex, anthropometric measures and dosage—were generated. Profiles of plasma drug concentrations over time, volume of distribution at steady state (V_ss) values and elimination half-life (t_½) values from the literature were compared with those predicted by PBPK simulations for both younger adults and the elderly.

Results

For most organs, the age-dependent information gathered in the extensive literature analysis was dense. In contrast, with respect to blood flow, the literature study produced only sparse data for several tissues, and in these cases, linear regression was required to capture the entire elderly age range. On the basis of age-informed physiology, the predicted PK profiles described age-associated trends well. The root mean squared prediction error for the prediction of plasma concentrations of furosemide and morphine in the elderly were improved by 32 and 49 %, respectively, by use of age-informed physiology. The majority of the individual V_ss and t_½ values for the two model compounds, furosemide and morphine, were well predicted in the elderly population, except for long furosemide half-lifes.

Conclusion

The results of this study support the feasibility of using a knowledge-driven PBPK aging model that includes the elderly to predict PK alterations throughout the entire course of aging, and thus to optimize drug therapy in elderly individuals. These results indicate that pharmacotherapy and safety-related control of geriatric drug therapy regimens may be greatly facilitated by the information gained from PBPK predictions.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-016-0422-3) contains supplementary material, which is available to authorized users.

Hypertonic Saline in Conjunction with High-Dose Furosemide Improves Dose-Response Curves in Worsening Refractory Congestive Heart Failure

INTRODUCTION

Diuretic responsiveness in patients with chronic heart failure (CHF) is better assessed by urine production per unit diuretic dose than by the absolute urine output or diuretic dose. Diuretic resistance arises over time when the plateau rate of sodium and water excretion is reached prior to optimal fluid elimination and may be overcome when hypertonic saline solution (HSS) is added to high doses of furosemide.

METHODS

Forty-two consecutively hospitalized patients with refractory CHF were randomized in a 1:1:1 ratio to furosemide doses (125 mg, 250 mg, 500 mg) so that all patients received intravenous furosemide diluted in 150 ml of normal saline (0.9%) in the first step (0-24 h) and the same furosemide dose diluted in 150 ml of HSS (1.4%) in the next step (24-48 h) as to obtain 3 groups as follows: Fourteen patients receiving 125 mg (group 1), fourteen patients receiving 250 mg (group 2), and fourteen patients receiving 500 mg (group 3) of furosemide. Urine samples of all patients were collected at 30, 60, and 90 min, and 3, 4, 5, 6, 8, and 24 h after infusion. Diuresis, sodium excretion, osmolality, and furosemide concentration were evaluated for each urine sample.

RESULTS

After randomization, 40 patients completed the study. Two patients, one in group 2 and one in group 3 dropped out. Patients in group 1 (125 mg furosemide) had a mean age of 77 ± 17 years, 43% were male, 6 (43%) had heart failure with a preserved ejection fraction (HFpEF), and 64% were in New York Heart Association (NYHA) class IV; the mean age of patients in group 2 (250 mg furosemide) was 80 ± 8.1 years, 15% were male, 5 (38%) had HFpEF, and 84% were in NYHA class IV; and the mean age of patients in group 3 (500 mg furosemide) was 73 ± 12 years, 54% were male, 6 (46%) had HFpEF, and 69% were in NYHA class IV. HSS added to furosemide increased total urine output, sodium excretion, urinary osmolality, and furosemide urine delivery in all patients and at all time points. The percentage increase was 18,14, and 14% for urine output; 29, 24, and 16% for total sodium excretion; 45, 34, and 20% for urinary osmolarity; and 27, 36, and 32% for total furosemide excretion in groups 1, 2, and 3, respectively. These findings were translated in an improvement in the furosemide dose-response curves in these patients.

CONCLUSION

These results may serve as new pathophysiological basis for HSS use in the treatment of refractory CHF.

Prehospital use of furosemide for the treatment of heart failure

INTRODUCTION

The diagnosis and management of acute decompensated heart failure (HF) in the prehospital setting can be challenging. The objectives of this study are to evaluate the appropriateness of furosemide use by Emergency Medical Services (EMS) and its association with adverse outcomes.

METHODS

This study was a multi-centre health records review of EMS patients who received prehospital furosemide or had an emergency department (ED) diagnosis of HF. We included acutely ill patients ≥50 years of age with shortness of breath transported by land EMS. Univariate and logistic regression analyses were performed to determine associations between furosemide use and serious adverse outcomes (acute renal failure, intubation, vasopressors or death).

RESULTS

The study population consisted of 330 patients (N=58, furosemide given by EMS but no HF diagnosed in ED; N=110, furosemide given, HF diagnosed; N=162, no furosemide given, HF diagnosed). The median dose of intravenous furosemide was 80 mg (range 20-80 mg). Serious adverse outcomes occurred in 61 patients (19.0%, 23.6% and 14.8% of the three groups, respectively; p=0.18). The adjusted ORs for adverse events with furosemide use was 0.62 (95% CI 0.33 to 1.43) in patients with a diagnosis of HF and 1.14 (95% CI 0.58 to 2.23) in those without.

CONCLUSIONS

More than a third of patients who received prehospital furosemide did not have an HF diagnosis, suggesting that the prehospital diagnosis of HF can be challenging. Serious adverse outcomes were identified in all patient groups and we found no statistically significant associations between furosemide use and adverse events.

Effects of cytochrome P450 inducers and inhibitors on the pharmacokinetics of intravenous furosemide in rats: involvement of CYP2C11, 2E1, 3A1 and 3A2 in furosemide metabolism

Objectives

It has been reported that the non-renal clearance of furosemide was significantly faster in rats pretreated with phenobarbital but was not altered in rats pretreated with 3-methylcholanthrene. However, no studies on other cytochrome P450 (CYP) isozymes have yet been reported in rats.

Method

Furosemide 20 mg/kg was administered intravenously to rats pretreated with various CYP inducers –3-methylcholanthrene, orphenadrine citrate and isoniazid, inducers of CYP1A1/2, 2B1/2 and 2E1, respectively, in rats – and inhibitors – SKF-525A (a nonspecific inhibitor of CYP isozymes), sulfaphenazole, cimetidine, quinine hydrochloride and troleandomycin, inhibitors of CYP2C6, 2C11, 2D and 3A1/2, respectively, in rats.

Key findings

The non-renal clearance of furosemide was significantly faster (55.9% increase) in rats pretreated with isoniazid, but slower in those pretreated with cimetidine or troleandomycin (38.5% and 22.7% decreases, respectively), than controls. After incubation of furosemide with baculovirus-infected insect cells expressing CYP2C11, 2E1, 3A1 or 3A2, furosemide was metabolized via CYP2C11, 2E1, 3A1 and 3A2.

Conclusions

These findings could help explain possible pharmacokinetic changes of furosemide in various rat disease models (where CYP2C11, 2E1, 3A1 and/or CYP3A2 are altered) and drug–drug interactions between furosemide and other drugs (mainly metabolized via CYP2C11, 2E1, 3A1 and/or 3A2).

Increased serum bilirubin levels coincident with heart failure decompensation indicate the need for intravenous inotropic agents

We have reported that chronic heart failure (HF) patients with increased serum bilirubin coincident with acute decompensation have a poor prognosis, indicating severe congestion and low tissue perfusion. The aim of this study was to analyze the possibility of increased bilirubin coincident with acute decompensation as a parameter which indicates the need for intravenous inotropic agents. We stratified 131 decompensated chronic HF patients with a LVEF <or= 40% and systolic blood pressure between 90 and 120 mmHg, based on total bilirubin levels on admission. In patients with high bilirubin (T-Bil >or= 1.2 mg/dL), intravenous inotropics contributed to significantly more abundant diuresis, body weight reduction, and decreases in bilirubin and serum creatinine in the first 5 in-hospital days compared to those without (group A: inotropics +; n = 24 versus group B: -; n = 38: 1726 +/- 418 versus 1458 +/- 424 mL/day: P < 0.05, -3.1 +/- 1.6 versus -2.1 +/- 2.2 kg: P < 0.05, -0.74 +/- 0.51 versus -0.04 +/- 0.60 mg/dL: P < 0.01, -0.29 +/- 0.89 versus -0.01 +/- 0.24 mg/dL: P < 0.01), in spite of no significant difference in the doses of diuretics between the 2 groups. On the contrary, patients with low bilirubin (T-Bil < 1.2 mg/dL) recovered from decompensation equally irrespective of inotropic administration (group C: inotropics +; n = 15 versus group D: -; n = 54: 1557 +/- 329 versus 1507 +/- 406 mL/day, -2.9 +/- 1.7 versus -2.8 +/- 1.5 kg, -0.01 +/- 0.25 versus -0.08 +/- 0.23 mg/dL, 0.02 +/- 0.24 versus 0.47 +/- 0.19 mg/dL; NS, respectively). Inotropics were administered after all because of unimproved hemodynamics in 26% of group B patients, compared to 4% of group D patients (P < 0.01). Increased bilirubin coincident with HF decompensation can be a useful marker indicating the need for intravenous inotropic agent administration.

Renal accumulation of [111In]DOTATOC in rats: influence of inhibitors of the organic ion transport and diuretics

AIM

Radiation exposure to the kidney limits therapy with radiometal labelled DOTATOC. This study evaluates the organic anion and cation transport (inhibitors: probenecid and cimetidine/dexamethasone) as well as diuresis (furosemide and mannitol) regarding renal uptake of [(111)In]DOTATOC.

METHODS

One hundred eight male Fisher rats were injected with [(111)In]DOTATOC via the tail vein. Prior to activity injection a total of 84 rats underwent injection with probenecid vs. sodium chloride 0.9% (48 rats), cimetidine vs. dexamethasone vs. sodium chloride 0.9% (18 rats), and furosemide vs. mannitol vs. sodium chloride 0.9% (18 rats). Rats were sacrificed at predetermined time points up to 48 h after activity injection. Kidneys, adrenal glands, pancreas, spleen, blood, liver, and muscle were harvested and injected activity per gram tissue was determined. Autoradiographic images of the kidneys were acquired in a total of 24 rats.

RESULTS

Probenecid led to a reduction in renal uptake by up to 30% while not significantly changing the activity accumulation in the other organs investigated. This reduction was attributable to the renal cortex (ratio cortex/medulla 1.72 vs. 1.99; p = 0.006). Cimetidine and dexamethasone had no effect in any of the organs. Furosemide led to a 44% increase in renal activity accumulation attributable to enhanced renal medullary uptake (ratio cortex/medulla 1.44 versus 1.69; p = 0.006). Mannitol had no effect on renal activity uptake.

CONCLUSION

Inhibition of the organic anion transport by probenecid may help reduce renal uptake regarding therapy with radiometal labelled DOTATOC. The enhancing effect of furosemide may be unfavourable for therapy. The results must be confirmed by human studies.

The Metabolism and Toxicity of Furosemide in the Wistar Rat and CD-1 Mouse: a Chemical and Biochemical Definition of the Toxicophore

Furosemide, a loop diuretic, causes hepatic necrosis in mice. Previous evidence suggested hepatotoxicity arises from metabolic bioactivation to a chemically reactive metabolite that binds to hepatic proteins. To define the nature of the toxic metabolite, we examined the relationship between furosemide metabolism in CD-1 mice and Wistar rats. Furosemide (1.21 mmol/kg) was shown to cause toxicity in mice, but not rats, at 24 h, without resulting in glutathione depletion. In vivo covalent binding to hepatic protein was 6-fold higher in the mouse (1.57 +/- 0.98 nmol equivalent bound/mg protein) than rat (0.26 +/- 0.13 nmol equivalent bound/mg protein). In vivo covalent binding to mouse hepatic protein was reduced 14-fold by a predose of the cytochrome P450 (P450) inhibitor, 1-aminobenzotriazole (ABT; 0.11 +/- 0.04 nmol equivalent bound/mg protein), which also reduced hepatotoxicity. Administration of [(14)C]furosemide to bile duct-cannulated rats demonstrated turnover to glutathione conjugate (8.8 +/- 2.8%), gamma-ketocarboxylic acid metabolite (22.1 +/- 3.3%), N-dealkylated metabolite (21.1 +/- 2.9%), and furosemide glucuronide (12.8 +/- 1.8%). Furosemide-glutathione conjugate was not observed in bile from mice dosed with [(14)C]furosemide. The novel gamma-ketocarboxylic acid, identified by nuclear magnetic resonance spectroscopy, indicates bioactivation of the furan ring. Formation of gamma-ketocarboxylic acid was P450-dependent. In mouse liver microsomes, a gamma-ketoenal furosemide metabolite was trapped, forming an N-acetylcysteine/N-acetyl lysine furosemide adduct. Furosemide (1 mM, 6 h) became irreversibly bound to primary mouse and rat hepatocytes, 0.73 +/- 0.1 and 2.44 +/- 0.3 nmol equivalent bound/mg protein, respectively, which was significantly reduced in the presence of ABT, 0.11 +/- 0.03 and 0.21 +/- 0.1 nmol equivalent bound/mg protein, respectively. Furan rings are part of new chemical entities, and mechanisms underlying species differences in toxicity are important to understand to decrease the drug attrition rate.

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.

Evaluation of renal functional parameters in different settings of isolated organ hemoperfusions

Isolated porcine kidneys are commonly used to study physiological and pathophysiological aspects of renal homeostasis but standardized evaluation procedures of renal function in this model do not exist so far. A double-logarithmical nomogram is established for filtration and reabsorption functions in isolated and hemoperfused porcine kidneys using different perfusion settings. Model validity was demonstrated by the levels of urine flow and sodium excretion showing expected alteration levels of lowering in the ADH-group and increasing in the furosemide-group of isolated kidneys. Creatinine-clearance values were in constant ranges within each specific perfusion group as indicated by the nomogram procedure. The present studies used a nomogram method to analyze the effects of different renal perfusion settings in a porcine model of kidney perfusion. The method may be of use to differentiate various kidney perfusion parameters both at the experimental and clinical levels.

Determination of furosemide in plasma and urine using monolithic silica rod liquid chromatography

In the present study we developed a fast and reliable HPLC assay for the determination of the loop diuretic furosemide in plasma and urine, using a Chromolith RP 18e (100 mm x 4.6 mm) monolithic silica rod HPLC column. After liquid-liquid extraction with diethylether plasma or urine samples were separated with a gradient consisting of solvent A (20% acetonitrile) and solvent B (80% acetonitrile), both in 0.25% acetic acid. The flow rate was 3.5 ml/min and the effluent was monitored by fluorescence with excitation at 230 nm and emission at 410 nm. The retention times for the internal standard (naproxen) and for furosemide were 2.1 and 3.7 min, respectively, and total run time was 8 min. The calibration curves were linear between 7.8 and 1000 ng/ml, and within-assay and between-assay coefficients of variation were <6.5% and <10%, respectively. The proposed assay for furosemide in plasma and urine using monolithic silica rod chromatography is fast, sensitive, and reliable, and, thus, well suited for pharmacokinetic studies.

Furosemide responsiveness, non-adherence and resistance during the chronic treatment of heart failure: a longitudinal study

BACKGROUND AND METHODS

Loop diuretic therapy is an essential part of chronic systolic heart failure (CH)F management, yet response to treatment can be variable. We analysed diuretic responsiveness in 39 stable patients with CHF in the community over 2 years. We measured serum ACE as a marker of adherence to ACE inhibitor therapy and urinary furosemide as a marker of diuretic adherence and action. Patients' clinical outcome was stable and not hospitalized (Group 0); alive but hospitalized (Group 1); or dead during follow up (Group 2).

RESULTS

Prescribed furosemide dose was variable (range 20-370 mg generally once daily) and progressive dose increments were common. Failed furosemide adherence (defined as < 10% of a dose excreted in 24 h urine where normal average excretion = 50% of an oral dose) during static prescribed dosing was infrequent relative to all days of therapy; yet was equally common across all outcome groups. Furosemide non-adherence appeared to be independent of non-adherence with ACE inhibitor (as marked by serum ACE activity > 20 U l(-1)) treatment. Furosemide responsiveness (mm of sodium excreted per mg furosemide in urine) showed no relationship to prescribed dose and paradoxically tended to rise in patients with higher basal aldosterone concentrations. Furosemide responsiveness fell by outcome class despite increased dose. Within-patient responsiveness remained relatively constant although highly variable between individuals.

CONCLUSIONS

Furosemide responsiveness varied greatly between individuals but was constant within an individual. Non-adherence with furosemide was less common among those who died and appeared to occur at different time points from non-adherence with ACE inhibitor treatment, which was slightly more common in all outcome groups. Patients who died were prescribed higher furosemide doses and had greater furosemide excretion yet had similar sodium excretion. The main factor in response to chronic furosemide therapy was intrarenal diuretic resistance. Gross non-adherence was less important.

Food: An Unrecognized Source of Loop Diuretic Resistance

Food significantly affects the pharmacokinetics of oral loop diuretics in healthy individuals, but studies have not been performed in patients with edema. Because of this omission, food's effect on pharmacokinetics has been overlooked and may decrease the pharmacodynamic response in patients who rely on diuretics. Despite this potential interaction, reference manuals do not provide warnings about the effects of food on loop diuretic absorption. We reviewed the published human studies investigating the effects of food on loop diuretics. Peak plasma concentrations and urinary recovery were significantly decreased when taken with food, but only one study showed a corresponding decrease in total urine output, which is likely related to the diuretic threshold effect. These healthy subjects probably were always above the diuretic threshold under both fed and fasting conditions and thus could not augment their urine output. Based on these data in healthy subjects, the special implications for patients who routinely take diuretics are discussed. Therefore, food is more likely to have a clinical effect on the diuretic threshold given its effect in healthy subjects and the special considerations for patients with edema. Additional studies are needed to help answer these questions. Until such data are available, the most conservative, effective clinical approach is to administer oral loop diuretics without food.

Pharmacokinetics and pharmacodynamics of azosemide

Azosemide is used in the treatment of oedematous states and hypertension. The exact mechanism of action is not fully understood, but it mainly acts on both the medullary and cortical segments of the thick ascending limb of the loop of Henle. Delayed tolerance was demonstrated in humans by homeostatic mechanisms (principally an increase in aldosterone secretion and perhaps also an increase in the reabsorption of solute in the proximal tubule). After oral administration to healthy humans in the fasting state, the plasma concentration of azosemide reached its peak at 3-4 h with an absorption lag time of approximately 1 h and a terminal half-life of 2-3 h. The estimated extent of absolute oral bioavailability in humans was approximately 20.4%. After oral administration of the same dose of azosemide and furosemide, the diuretic effect was similar between the two drugs, but after intravenous administration, the effect of azosemide was 5.5-8 times greater than that in furosemide. This could be due to the considerable first-pass effect of azosemide. The protein binding to 4% human serum albumin was greater than 95% at azosemide concentrations ranging from 10 to 100 microg/ml using an equilibrium dialysis technique. The poor affinity of human tissues to azosemide was supported by the relatively small value of the apparent post-pseudodistribution volume of distribution (Vdbeta), 0.262 l/kg. Eleven metabolites (including degraded products) of azosemide including M1, glucuronide conjugates of both M1 and azosemide, thiophenemethanol, thiophencarboxylic acid and its glycine conjugate were obtained in rats. Only azosemide and its glucuronide were detected in humans. In humans, total body clearance, renal clearance and terminal half-life of azosemide were 112 ml/min, 41.6 ml/min and 2.03 h, respectively. Azosemide is actively secreted in the renal proximal tubule possibly via nonspecific organic acid secretory pathway in humans. Thus, the amount of azosemide that reaches its site of action could be significantly modified by changes in the capacity of this transport system. This capacity, in turn, could be predictably changed in disease states, resulting in decreased delivery of the diuretic to the transport site, as well as in the presence of other organic acids such as nonsteroidal anti-inflammatory drugs which could compete for active transport of azosemide. The urinary excretion rate of azosemide could be correlated well to its diuretic effects since the receptors are located in the loop of Henle. The diuretic effects of azosemide were dependent on the rate and composition of fluid replacement in rabbits; therefore, this factor should be considered in the evaluation of bioequivalence assessment.

Evaluation of human intestinal absorption data and subsequent derivation of a quantitative structure–activity relationship (QSAR) with the Abraham descriptors

The human intestinal absorption of 241 drugs was evaluated. Three main methods were used to determine the human intestinal absorption: bioavailability, percentage of urinary excretion of drug-related material following oral administration, and the ratio of cumulative urinary excretion of drug-related material following oral and intravenous administration. The general solvation equation developed by Abraham's group was used to model the human intestinal absorption data of 169 drugs we considered to have reliable data. The model contains five Abraham descriptors calculated by the ABSOLV program. The results show that Abraham descriptors can successfully predict human intestinal absorption if the human absorption data is carefully classified based on solubility and administration dose to humans.

Improvement in site-specific intestinal absorption of furosemide by Eudragit L100-55

Furosemide (frusemide) is a weakly acidic diuretic drug. Its absorption is poor and variable, in part due to its restricted sites of absorption, mainly the stomach. The narrow absorption window of this drug can be explained by pH partition theory. The purpose of this study was to investigate the feasibility of widening the absorption window of furosemide by controlling the pH in distal portions of the gastrointestinal tract with officially used additives. Methacrylate copolymer (Eudragit L100-55), hydroxypropylmethylcellulose phthalate (HP-55) and hydroxypropylmethylcellulose acetate succinate (AS-MF) were selected as additives. The pH of suspensions of these additives was about 4, and the pH was adjusted to about 6-7 by the addition of NaOH. The Eudragit L100-55 suspension was found to be the most resistant to NaOH titration. When Eudragit L100-55 was used in an in-situ ileal loop experiment in rats, the pH of the intestinal contents was significantly reduced, from 7.9+/-0.1 to 5.7+/-0.1, and the plasma concentration of furosemide 15 min after administration was about 3 times higher than that in controls, 1.81+/- 0.42microg mL(-1) vs 0.63+/-0.08 microg mL(-1). However, the plasma concentration of [14C] mannitol was not changed by the co-administration of Eudragit L100-55. Furthermore, the AUC of furosemide was significantly increased by a factor of about 1.6 relative to that in controls by the co-administration of Eudragit L100-55, to 21.4+/-4.0 microg h mL(-1) from 13.3+/- 3.9 microg h mL(-1), and the gastrointestinal pH in the midgut and ileum was significantly reduced, with most of the furosemide remaining in these segments at 2 h following the oral administration of furosemide with Eudragit L100-55 to rats. These findings clearly demonstrate that the addition of Eudragit L100-55 can increase the absorption of furosemide in distal portions of the gastrointestinal tract. In conclusion, it is feasible to widen the absorption window of furosemide by controlling the pH in distal portions of the gastrointestinal tract by the co-administration of Eudragit L100-55.

Evaluation of using dog as an animal model to study the fraction of oral dose absorbed of 43 drugs in humans

PURPOSE

To conduct a retrospective evaluation of using dog as an animal model to study the fraction of oral dose absorbed (F) of 43 drugs in humans and to briefly discuss potential factors that might have contributed to the observed differences in absorption.

METHODS

Mean human and dog absorption data obtained under fasted state of 43 drugs with markedly different physicochemical and pharmacological properties and with mean F values ranging from 0.015 to 1.0 were obtained from the literature. Correlation of F values between humans and dogs was studied. Based on the same references, additional F data for humans and rats were also obtained for 18 drugs.

RESULTS

Among the 43 drugs studied, 22 drugs were virtually completely absorbed in both dogs and humans. However, the overall correlation was relatively poor (r2 = 0.5123) as compared to the earlier rat vs. human study on 64 drugs (r2 = 0.975). Several drugs showed much better absorption in dogs than in humans. Marked differences in the nonliner absorption profiles between the two species were found for some drugs. Also, some drugs had much longer Tmax values and prolonged absorption in humans than in dogs that might be theoretically predicted. Data on 18 drugs further support great similarity in F between humans and rats reported earlier from our laboratory.

CONCLUSIONS

Although dog has been commonly employed as an animal model for studying oral absorption in drug discovery and development, the present study suggests that one may need to exercise caution in the interpretation of data obtained. Exact reasons for the observed interspecies differences in oral absorption remain to be explored.

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.

Prediction of human intestinal absorption of drug compounds from molecular structure

The absorption of a drug compound through the human intestinal cell lining is an important property for potential drug candidates. Measuring this property, however, can be costly and time-consuming. The use of quantitative structure-property relationships (QSPRs) to estimate percent human intestinal absorption (%HIA) is an attractive alternative to experimental measurements. A data set of 86 drug and drug-like compounds with measured values of %HIA taken from the literature was used to develop and test a QSPR mode. The compounds were encoded with calculated molecular structure descriptors. A nonlinear computational neural network model was developed by using the genetic algorithm with a neural network fitness evaluator. The calculated %HIA (cHIA) model performs wells, with root-mean-square (rms) errors of 9.4%HIA units for the training set, 19.7%HIA units for the cross-validation (CV) set, and 16.0%HIA units for the external prediction set.

Micellar electrokinetic chromatography as a fast screening method for the determination of the doping agents furosemide and piretanide in urine

The possibility of using micellar electrokinetic chromatography for the screening of the loop diuretics piretanide and furosemide in urine was studied. A fast and simple method with good repeatability is described. The method was applied to urine samples collected from a healthy volunteer after oral administration of therapeutic doses of each compound. Positive identification in the urine matrix was possible through recording diode array spectra.

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.

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 dynamics in conscious rabbits: modulation by arginine vasopressin

The aims of this study were to assess the influence of arginine-vasopressin (AVP) on the pharmacodynamics and kinetics of furosemide. To this purpose, the response and the kinetics of furosemide (5 mg/kg i.v.) were studied in two groups of rabbits, one control and one receiving an infusion of AVP (2.5 ng/kg/min). The infusion of AVP generated mean plasma levels of 35 pg/ml, and in these rabbits osmolal clearance was increased, free water clearance was reduced, and renal plasma flow was reduced by 25% (p < 0.05). High AVP plasma levels increased the natriuresis (p < 0.01) and the urinary excretion of prostaglandin E2 (UPgE2V; p < 0.01). The increase in UPgE2V was associated with AVP plasma concentrations (r = 0.8248; p < 0.001). AVP reduced the increment in natriuresis and diuresis elicited by furosemide from 163 +/- 20 to 87 +/- 20 mumol/min (p < 0.05) and from 1.22 +/- 0.11 to 0.83 +/- 0.13 ml/min (p < 0.05). The infusion of AVP enhanced furosemide metabolic clearance but diminished its renal clearance, resulting in a decrease in the rate of furosemide urinary secretion. It was concluded that high plasma levels of AVP reduce furosemide natriuresis, presumably because of a decrease in furosemide urinary secretion.

Effects of water deprivation for 48 hours on the pharmacokinetics and pharmacodynamics of furosemide in rats

The effects of water deprivation for 48 h on the pharmacokinetics and pharmacodynamics of furosemide were examined after intravenous, 8 mg/kg body weight, and oral administration, 16 mg/kg body weight, of furosemide to control and water deprived rats. After i.v. administration, the total body and nonrenal clearances decreased significantly in water-deprived rats. The urine output, urinary excretion of sodium, potassium and chloride based on grams of kidney weight, and the diuretic, natriuretic and chloruretic efficiencies decreased significantly in water-deprived rats after both intravenous and oral administration of furosemide, suggesting that the dose of furosemide for water-deprived patients may require modification.

Determination of furosemide with its acyl glucuronide in human plasma and urine by means of direct gradient high-performance liquid chromatographic analysis with fluorescence detection. Preliminary pharmacokinetics and effect of probenecid

Furosemide is metabolized in humans by acyl glucuronidation to the 1-O-glucuronide (Fgluc). Furosemide (F) and the conjugate can be measured directly by gradient high-performance liquid chromatographic analysis without enzymic deglucuronidation. The glucuronide conjugate was isolated by preparative HPLC from human urine samples. Furosemide and its acyl glucuronide were present in plasma. No isoglucuronides were present in acidic urine of a volunteer. Calibration curves were constructed by enzymic deconjugation of samples containing different concentrations of isolated F-acyl glucuronide. The limit of quantitation of F in plasma is 0.007 microgram/ml, Fgluc 0.010 microgram/ml. The limits of quantitation in urine are respectively: F 0.10 microgram/ml, Fgluc 0.15 microgram/ml. A pharmacokinetic profile of furosemide is shown, and some preliminary pharmacokinetic parameters of furosemide obtained from one human volunteer are given. Probenecid does not inhibit the formation of the acyl glucuronide of F, but inhibits the renal clearance of both compounds.

Influence of protein and calorie malnutrition on the pharmacokinetics and pharmacodynamics of bumetanide in rats

Bumetanide is a loop diuretic that is used for the treatment of edema and hypertension. The rapidly developing syndrome of extracellular fluid overload in some malnourished children has been successfully treated with furosemide, another loop diuretic, and digoxin; however, similar studies with bumetanide have not been conducted to date. Therefore, in the present study, the influence of dietary protein deficiency on the pharmacokinetics and pharmacodynamics of bumetanide was investigated after intravenous (i.v.) bolus and oral administration of bumetanide to male Sprague-Dawley rats fed on 23% (control rats) or 5% [protein and calorie malnutrition (PCM) rats] protein diet ad libitum for 4 weeks. After an i.v. dose of bumetanide, 1 mg/100 g body weight, the mean values of renal clearance and percentages of dose excreted as unchanged bumetanide in an 8-h urine sample were 166 and 154% higher, respectively, in PCM than control rats; however, nonrenal clearance (CLNR) was 28% lower. The decrease in nonrenal clearance in PCM rats might be because of the decrease in nonrenal metabolism of bumetanide in PCM rats. The urine output per 100 g of body weight was not significantly different between the two groups of rats after i.v. administration, although the amount of bumetanide excreted in the 8-h urine sample per 100 g body weight increased significantly in PCM rats. These results could be explained by the fact that the dose of bumetanide used results in urinary excretion rate of bumetanide at the plateau of the concentration-effect relationship.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and pharmacodynamics of furosemide in protein-calorie malnutrition

The influence of dietary protein deficiency on pharmacokinetics and pharmacodynamics of furosemide was investigated after i.v. bolus (1 mg/100 g) and oral (2 mg/100 g) administration of furosemide to male Sprague-Dawley rats fed on a 23% (control) or a 5% (protein-calorie malnutrition: PCM) protein diet ad lib. for 4 weeks. After i.v. administration, the mean values of CLR, Vss, and the percentages of dose excreted in 8-hr urine as furosemide were increased 81, 31, and 61%, respectively, in PCM rats when compared with those in control rats, however, CLNR was 54% decreased in PCM rats. The decreased CLNR in PCM rats suggested the significantly decreased nonrenal metabolism of furosemide. The urine volume per g kidney after i.v. administration was not significantly different between the two groups of rats although the amount of furosemide excreted in 8-hr urine per g kidney increased significantly in PCM rats. The diuretic, natriuretic, kaliuretic, and chloruretic efficiencies reduced significantly in PCM rats after i.v. administration. After oral administration, the extent of bioavailability increased considerably from 27.6% in control rats to 47.0% in PCM rats, probably as a result of decreased gastrointestinal and hepatic first-pass metabolism. This was supported by a tissue homogenate study; the amount of furosemide remaining per g tissue after 30-min incubation of 50 micrograms of furosemide with the 9000 x g supernatant fraction of stomach (42.4 vs. 47.9 micrograms) and liver (41.4 vs. 45.9 micrograms) homogenates increased significantly in PCM rats. No significant differences in CLR and t1/2 were found between the control and the PCM rats after oral administration. The 24-hr urine volume and the amount of sodium excreted in 24-hr urine per g kidney increased significantly in PCM rats, and this might be due to a significantly increased amount of furosemide reaching the kidney excreted in urine per g kidney.

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.

Pharmacokinetics of terfenadine in healthy elderly subjects

The pharmacokinetics of the terfenadine active metabolite, metabolite I, was examined in ten healthy elderly adults and ten younger adults after single-dose oral administration of 120-mg terfenadine. All subjects successfully completed the study without reporting sedation or other adverse events. Absorption was rapid in both the young and elderly. The mean Cmax was the same for both groups, 501 ng/mL, and occurred at 2.3 hours in the young subjects and 2.5 hours in elderly subjects. However, the apparent clearance was reduced by about 25% in the elderly. After correcting clearance for bodyweight, this difference was not statistically significant.

Combination of long-acting furosemide and instant-acting amiloride: pharmacokinetics and pharmacodynamics in human subjects

The pharmacokinetics and pharmacodynamics of the combination of amiloride (2 x 2.5 mg) and long-acting furosemide (2 x 10 mg) were compared with amiloride (5 mg) and furosemide (20 mg) in 12 healthy male volunteers aged 26.2 +/- 1.6 years and weighing 68.8 +/- 6.2 kg, after random order administration. Furosemide and amiloride plasma or urine concentrations were determined by HPLC with fluorimetric detection. The rate of absorption (tmax = 3 h) and the bioavailability of the two diuretics were not significantly modified by their combination. Furosemide plasma half-life was 2.77 +/- 1.04 h after the combination treatment and 2.76 +/- 0.98 h alone, amiloride plasma half-life was respectively 15.7 +/- 4.6 h and 14.6 +/- 3.7 h. The urinary elimination of furosemide was significantly higher in the 2-4 h interval in the combination treatment, accompanying its delayed maximum effect of diuresis. A synergistic effect was observed after the combination administration of the two diuretics; between the 2nd and the 8th hour, the sodium elimination was significantly increased (P less than 0.01) and the potassium excretion was significantly decreased (P = 0.05). After a single dose, no modification of plasma or erythrocyte magnesium levels was observed. This study shows that the combination of the two drugs entails a synergy of their activities which does not involve pharmacokinetic changes.

Multiple linear regression modeling of furosemide renal clearance and urinary excretion rate

Multiple linear regression techniques were utilized to determine models for the renal clearance and urinary excretion rate of furosemide. Models for the renal clearance were formulated based on data collected from the literature. The best model predicted that the weight-normalized renal clearance was a function of the weight-normalized creatinine clearance, with coefficient values dependent on the presence or absence of heart, liver, and/or kidney failure. The predictive performance of this model was evaluated using a separate verification data set, and, prospectively, for a group of cardiac patients. The urinary excretion rate of furosemide is the primary determinate of response. Models for the furosemide excretion rate were formulated from data collected prospectively from a group of patients with cardiac disease. The best model predicted that the dose-normalized morning urinary excretion rate was a function of the blood urea nitrogen concentration (BUN), with modifications for the presence of liver failure and/or decompensated heart failure. The oral dosage required to produce a clinically optimal furosemide excretion rate in cardiac patients without liver disease was dose (mg) = 42.1/(0.925-0.0151 BUN).

Effects of phenobarbital and 3-methylcholanthrene pretreatment on the pharmacokinetics and pharmacodynamics of furosemide in rats

The effects of pretreatment with the enzyme inducers phenobarbital (PB) and 3-methylcholanthrene (3-MC) on the pharmacokinetic and pharmacodynamic parameters of furosemide were examined in rats. The nonrenal clearance (4.58 versus 6.18 mL/min/kg) increased significantly in PB-treated rats. This suggested that the nonrenal metabolism of furosemide increased by pretreatment with PB. This relationship was supported by the results of a tissue homogenate study; the amounts of furosemide remaining per gram of tissue after 30 min of incubation of 50 micrograms of furosemide with the 9000 x g supernatant fraction of liver, stomach, and kidney tissue homogenates decreased significantly in PB-treated rats. The contents of hepatic cytochrome P-450 (1.29 versus 2.15 nmol/mg protein) and the weights of liver and stomach increased significantly in PB-treated rats, suggesting that the metabolizing enzymes for furosemide are induced by pretreatment with PB. The 8-h urine output per 100 g of body weight increased significantly in PB-treated rats; however, the 8-h urinary excretion of furosemide per 100 g of body weight (797 versus 635 micrograms) decreased significantly in PB-treated rats. Alterations in the urine output might be due to the hormonal alterations in the concentration-effect relationship for furosemide in PB-treated rats. In 3-MC-treated rats, pharmacokinetic and pharmacodynamic parameters of furosemide were not significantly different, indicating that the metabolizing enzymes for furosemide were not induced by pretreatment with 3-MC. However, the contents of hepatic cytochrome P-450 and the weights of liver and stomach increased significantly.

Pharmacokinetic, biliary excretion, and metabolic studies of 14C-furosemide in the rat

1. Partition of furosemide into organic solvents at pH 3.8 was greatest for ethyl acetate (33:1) greater than 2-ethyl-1-hexanol (10:1) greater than ethyl ether (6:1). 2. Furosemide was highly bound to human, bovine, rabbit, and rat plasma or albumin (97.4-98.4%). 3. Furosemide was highly bound to rat tissues. One hour after i.p. injection of the drug, tissue to plasma concentration ratios were: adrenals (10:1), lung (4:1), kidney (4:1), spleen (3:1). 4. In rats with ligated renal pedicles, furosemide was excreted in bile, at least in part, by active transport. Hepatic clearance of a 1 mg/kg i.v. dose contributed 20% to total body clearance. Large doses (50 mg/kg and more) of furosemide exerted a choleretic effect. 5. Chromatography of bile showed that i.v. administration of 50 mg/kg and higher doses of furosemide to rats resulted in saturation of hepatic drug metabolism. 6. The bile of rats contained the parent drug, 4-chloro-5-sulphamoyl-anthranilic acid, and at least two unknown metabolites with the furan ring intact.

The pharmacology and therapeutics of diuretics in the pediatric patient

Selection of appropriate diuretic therapy in children is hampered by a lack of age-specific pharmacokinetic and pharmacodynamic data, especially in premature neonates. Well-designed clinical trials in neonates, infants, and younger children are necessary prerequisites to safer and more efficacious diuretic therapy.