Influence of hepatic cirrhosis and end-stage renal disease on pharmacokinetics and pharmacodynamics of furosemide

Effect of probenecid on blood levels and renal elimination of furosemide and endogenous compounds in rats: Discovery of putative organic anion transporter biomarkers

Transporter-mediated drug-drug interactions (DDIs) are assessed using probe drugs and in vitro and in vivo models during drug development. The utility of endogenous metabolites as transporter biomarkers is emerging for prediction of DDIs during early phases of clinical trials. Endogenous metabolites such as pyridoxic acid and kynurenic acid have shown potential to predict DDIs mediated by organic anion transporters (OAT1 and OAT3). However, these metabolites have not been assessed in rats as potential transporter biomarkers. We carried out a rat pharmacokinetic DDI study using probenecid and furosemide as OAT inhibitor and substrate, respectively. Probenecid administration led to a 3.8-fold increase in the blood concentrations and a 3-fold decrease in renal clearance of furosemide. High inter-individual and intra-day variability in pyridoxic acid and kynurenic acid, and no or moderate effect of probenecid administration on these metabolites suggest their limited utility for prediction of Oat-mediated DDI in rats. Therefore, rat blood and urine samples were further analysed using untargeted metabolomics. Twenty-one m/z features (out of >8000 detected features) were identified as putative biomarkers of rat Oat1 and Oat3 using a robust biomarker qualification approach. These m/z features belong to metabolic pathways such as fatty acid analogues, peptides, prostaglandin analogues, bile acid derivatives, flavonoids, phytoconstituents, and steroids, and can be used as a panel to decrease variability caused by processes other than Oats. When validated, these putative biomarkers will be useful in predicting DDIs caused by Oats in rats.

Contribution of Uptake and Efflux Transporters to Oral Pharmacokinetics of Furosemide

Furosemide is a widely used diuretic for treating excessive fluid accumulation caused by disease conditions like heart failure and liver cirrhosis. Furosemide tablet formulation exhibits variable pharmacokinetics (PK) with bioavailability ranging from 10 to almost 100%. To explain the variable absorption, we integrated the physicochemical, in vitro dissolution, permeability, distribution, and the elimination parameters of furosemide in a physiologically-based pharmacokinetic (PBPK) model. Although the intravenous PBPK model reasonably described the observed in vivo PK data, the reported low passive permeability failed to capture the observed data after oral administration. To mechanistically justify this discrepancy, we hypothesized that transporter-mediated uptake contributes to the oral absorption of furosemide in conjunction with passive permeability. Our in vitro results confirmed that furosemide is a substrate of intestinal breast cancer resistance protein (BCRP), multidrug resistance-associated protein 4 (MRP4), and organic anion transporting polypeptide 2B1 (OATP2B1), but it is not a substrate of P-glycoprotein (P-gp) and MRP2. We then estimated the net transporter-mediated intestinal uptake and integrated it into the PBPK model under both fasting and fed conditions. Our in vitro data and PBPK model suggest that the absorption of furosemide is permeability-limited, and OATP2B1 and MRP4 are important for its permeability across intestinal membrane. Further, as furosemide has been proposed as a probe substrate of renal organic anion transporters (OATs) for assessing clinical drug-drug interactions (DDIs) during drug development, the confounding effects of intestinal transporters identified in this study on furosemide PK should be considered in the clinical transporter DDI studies.

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.

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.

Pharmacokinetics and dosage adjustment in patients with hepatic dysfunction

The liver plays a central role in the pharmacokinetics of the majority of drugs. Liver dysfunction may not only reduce the blood/plasma clearance of drugs eliminated by hepatic metabolism or biliary excretion, it can also affect plasma protein binding, which in turn could influence the processes of distribution and elimination. Portal-systemic shunting, which is common in advanced liver cirrhosis, may substantially decrease the presystemic elimination (i.e., first-pass effect) of high extraction drugs following their oral administration, thus leading to a significant increase in the extent of absorption. Chronic liver diseases are associated with variable and non-uniform reductions in drug-metabolizing activities. For example, the activity of the various CYP450 enzymes seems to be differentially affected in patients with cirrhosis. Glucuronidation is often considered to be affected to a lesser extent than CYP450-mediated reactions in mild to moderate cirrhosis but can also be substantially impaired in patients with advanced cirrhosis. Patients with advanced cirrhosis often have impaired renal function and dose adjustment may, therefore, also be necessary for drugs eliminated by renal exctretion. In addition, patients with liver cirrhosis are more sensitive to the central adverse effects of opioid analgesics and the renal adverse effects of NSAIDs. In contrast, a decreased therapeutic effect has been noted in cirrhotic patients with beta-adrenoceptor antagonists and certain diuretics. Unfortunately, there is no simple endogenous marker to predict hepatic function with respect to the elimination capacity of specific drugs. Several quantitative liver tests that measure the elimination of marker substrates such as galactose, sorbitol, antipyrine, caffeine, erythromycin, and midazolam, have been developed and evaluated, but no single test has gained widespread clinical use to adjust dosage regimens for drugs in patients with hepatic dysfunction. The semi-quantitative Child-Pugh score is frequently used to assess the severity of liver function impairment, but only offers the clinician rough guidance for dosage adjustment because it lacks the sensitivity to quantitate the specific ability of the liver to metabolize individual drugs. The recommendations of the Food and Drug Administration (FDA) and the European Medicines Evaluation Agency (EMEA) to study the effect of liver disease on the pharmacokinetics of drugs under development is clearly aimed at generating, if possible, specific dosage recommendations for patients with hepatic dysfunction. However, the limitations of the Child-Pugh score are acknowledged, and further research is needed to develop more sensitive liver function tests to guide drug dosage adjustment in patients with hepatic dysfunction.

Pharmacokinetics and dosage adjustment in patients with hepatic dysfunction

The liver plays a central role in the pharmacokinetics of the majority of drugs. Liver dysfunction may not only reduce the blood/plasma clearance of drugs eliminated by hepatic metabolism or biliary excretion, it can also affect plasma protein binding, which in turn could influence the processes of distribution and elimination. Portal-systemic shunting, which is common in advanced liver cirrhosis, may substantially decrease the presystemic elimination (i.e., first-pass effect) of high extraction drugs following their oral administration, thus leading to a significant increase in the extent of absorption. Chronic liver diseases are associated with variable and non-uniform reductions in drug-metabolizing activities. For example, the activity of the various CYP450 enzymes seems to be differentially affected in patients with cirrhosis. Glucuronidation is often considered to be affected to a lesser extent than CYP450-mediated reactions in mild to moderate cirrhosis but can also be substantially impaired in patients with advanced cirrhosis. Patients with advanced cirrhosis often have impaired renal function and dose adjustment may, therefore, also be necessary for drugs eliminated by renal exctretion. In addition, patients with liver cirrhosis are more sensitive to the central adverse effects of opioid analgesics and the renal adverse effects of NSAIDs. In contrast, a decreased therapeutic effect has been noted in cirrhotic patients with beta-adrenoceptor antagonists and certain diuretics. Unfortunately, there is no simple endogenous marker to predict hepatic function with respect to the elimination capacity of specific drugs. Several quantitative liver tests that measure the elimination of marker substrates such as galactose, sorbitol, antipyrine, caffeine, erythromycin, and midazolam, have been developed and evaluated, but no single test has gained widespread clinical use to adjust dosage regimens for drugs in patients with hepatic dysfunction. The semi-quantitative Child-Pugh score is frequently used to assess the severity of liver function impairment, but only offers the clinician rough guidance for dosage adjustment because it lacks the sensitivity to quantitate the specific ability of the liver to metabolize individual drugs. The recommendations of the Food and Drug Administration (FDA) and the European Medicines Evaluation Agency (EMEA) to study the effect of liver disease on the pharmacokinetics of drugs under development is clearly aimed at generating, if possible, specific dosage recommendations for patients with hepatic dysfunction. However, the limitations of the Child-Pugh score are acknowledged, and further research is needed to develop more sensitive liver function tests to guide drug dosage adjustment in patients with hepatic dysfunction.

The influence of cardiovascular and antiinflammatory drugs on thiazide-induced hemodynamic and saluretic effects

OBJECTIVE

Thiazide diuretics are known to induce a transient fall of the glomerular filtration rate (GFR), which, in turn, reduces tubular Na(+) load. This tubuloglomerular feedback (TGF) curtails the natriuretic effect of this class of diuretics. Cardiovascular and antiinflammatory therapeutics may interfere with TGF and thereby influence the effect of thiazides once co-administration is clinically indicated.

METHODS

The effects on GFR and saluresis of hydrochlorothiazide (HCT; 25 mg) monotherapy were measured in healthy volunteers and compared to those obtained during co-administration of the thiazide and a second therapeutic.

RESULTS

In the presence of the ACE inhibitor enalapril (10 mg), the transient fall in the GFR induced by HCT was almost abolished, and Na(+) excretion increased by approximately 30 % as compared to HCT monotherapy. K(+) excretion, however, remained unchanged. Similar results were obtained with the AT II type 1 receptor antagonist candesartan (8 mg): GFR remained stable, Na(+) excretion rose by 35 % and K(+) excretion was not changed. The effect of the Ca(2+) channel blocker amlodipine (5 mg) on GFR and HCT-induced Na(+) excretion equalled that obtained with the AT(1) blocker, yet with this treatment K(+) excretion rose in proportion to Na(+) excretion. The beta-blockers propranolol (80 mg) or bisoprolol (5 mg) reduced GFR but maintained TGF. HCT-induced Na(+) excretion was significantly reduced in the presence of a beta-blocker, whereas K(+) excretion was not changed. The inhibition of cyclooxygenase by diclofenac (50 mg) or rofecoxib (25 mg) significantly reduced the diuretic/natriuretic effect of HCT, but K(+) excretion was unchanged, and TGF was still demonstrable.

CONCLUSION

In conclusion, AT(1) receptors, as well as the Ca(2+) channels in the smooth muscle cells of the afferent arteriole, are considered prerequisites for TGF function; their blockade increases the diuretic/natriuretic efficacy of thiazide diuretics. In contrast, beta-blockers and COX inhibitors do not interfere directly with TGF. These first dose effects reflect the primary response of the kidney to the drugs. They cannot, however, predict the benefits of long-term treatment.

Dose adjustment in patients with liver disease

Unfortunately, there is no endogenous marker for hepatic clearance that can be used as a guide for drug dosing. In order to predict the kinetic behaviour of drugs in cirrhotic patients, agents can be grouped according to their extent of hepatic extraction. For drugs with a high hepatic extraction (low bioavailability in healthy subjects), bioavailability increases and hepatic clearance decreases in cirrhotic patients. If such drugs are administered orally to cirrhotic patients, their initial dose has to be reduced according to hepatic extraction. Furthermore, their maintenance dose has to be adapted irrespective of the route of administration, if possible, according to kinetic studies in cirrhotic patients. For drugs with a low hepatic extraction, bioavailability is not affected by liver disease, but hepatic clearance may be affected. For such drugs, only the maintenance dose has to be reduced, according to the estimated decrease in hepatic drug metabolism. For drugs with an intermediate hepatic extraction, initial oral doses should be chosen in the low range of normal in cirrhotic patients and maintenance doses should be reduced as for high extraction drugs. In cholestatic patients, the clearance of drugs with predominant biliary elimination may be impaired. Guidelines for dose reduction in cholestasis exist for many antineoplastic drugs, but are mostly lacking for other drugs with biliary elimination. Dose adaptation of such drugs in cholestatic patients is, therefore, difficult and has to be performed according to pharmacological effect and/or toxicity. Importantly, the dose of drugs with predominant renal elimination may also have to be adapted in patients with liver disease. Cirrhotic patients often have impaired renal function, despite a normal serum creatinine level. In cirrhotic patients, creatinine clearance should, therefore, be measured or estimated to gain a guideline for the dosing of drugs with predominant renal elimination. Since the creatinine clearance tends to overestimate glomerular filtration in cirrhotic patients, the dose of a given drug may still be too high after adaptation to creatinine clearance. Therefore, the clinical monitoring of pharmacological effects and toxicity of such drugs is important. Besides the mentioned kinetic changes, the dynamics of some drugs is also altered in cirrhotic patients. Examples include opiates, benzodiazepines, NSAIDs and diuretics. Such drugs may exhibit unusual adverse effects that clinicians should be aware of for their safe use. However, it is important to realise that the recommendations for dose adaptation remain general and cannot replace accurate clinical monitoring of patients with liver disease treated with critical drugs.

Management of cirrhotic ascites: physiological basis of diuretic action

Ascites is a significant complication of cirrhosis that occurs in approximately 50% of patients. The mortality rate is high in patients with cirrhosis and ascites. Conventional interventions rest with dietary sodium restriction, diuretic use, large-volume paracentesis, peritoneovenous shunts and transjugular intrahepatic portosystemic shunts. The mainstay of therapy, however, is the judicious use of diuretics. This article reviews the physiological basis of diuretic use in patients with cirrhosis and ascites, as well as recent concepts on the pathogenesis of ascites formation. Through a better understanding of the pathophysiology of ascites formation and the mechanism of action of diuretics, improved extracellular fluid balance can be achieved in these patients.

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.

Furosemide: progress in understanding its diuretic, anti-inflammatory, and bronchodilating mechanism of action, and use in the treatment of respiratory tract diseases

Accumulated experimental and clinical data suggest that adrenocorticosteroids and/or endogenous ouabain-like substances may play an important role in the mechanism of furosemide diuretic action. It was reported that the drug is highly bound in the adrenals, lungs, kidney, spleen, and liver. In patients with liver cirrhosis, furosemide exerted a markedly decreased natriuretic effect compared with normal subjects, and the plasma levels of circulating endothelin and atrial natriuretic factor (ANF) were significantly elevated. In neonates, after administration of furosemide, the urinary excretion of endothelin-1 and aldosterone increased markedly, and it is known that endothelin may release ANF and aldosterone in a dose-dependent manner. Furosemide was used to stimulate zona glomerulosa, whereas ANF decreased the production of steroids in zona glomerulosa and fasciculata cell culture owing to stimulation by various factors. Because the concomitant use of ANF and furosemide appeared to be diuretically effective in newborns after cardiac surgery, one may suggest that furosemide competes with ANF for its effects on the adrenals. Furosemide administered by inhalation exerted a protective effect on allergic and perennial nonallergic rhinitis and was effective in preventing the postsurgical recurrence of nasal polyposis. The drug can also be used as an antiasthmatic agent. In preterm ventilator-dependent infants with chronic lung disease, aerosolized furosemide improved pulmonary function with no marked effect on diuresis. In adults and children with asthma, furosemide exerted a protective effect against bronchoconstriction induced by several indirect stimuli similar to that of disodium cromoglycate or nedocromil. Aerosolized furosemide had a preventive effect also on bronchoconstriction induced by inhaled lysine acetylsalicylate in patients with aspirin-sensitive asthma. In high-dose beclomethasone-dependent asthma, inhaled lysine acetylsalicylate and furosemide exerted a mutually potentiating antiasthmatic activity, allowing considerable sparing of the inhaled steroid. It is proposed that this effect may be explained by the corticosteroid-sparing action of lysine released from the lysine acetylsalicylate molecule because similar beneficial effects were also obtained after the concomitant use of epsilon-aminocaproic acid (whose chemical structure is almost the same as that of lysine) and prednisone. Furosemide exhibited an anti-inflammatory effect through inhibition of production and release of cytokines interleukin (IL)-6, IL-8, and tumor necrosis factor-alpha from peripheral mononuclear cells, which may have a beneficial effect on local inflamed tissue imbalance in the ratio of different cytokines, thus improving the sensitivity of target cells to endogenous glucocorticosteroids.

Clinical pharmacology of furosemide in children: a supplement

Furosemide is one of the most effective and least toxic diuretics used in pediatric practice. Experimental and clinical data suggest that adrenocorticosteroids and/or endogenous ouabain-like substances may play an important role in its diuretic effect. Also, the drug appears to have anti-inflammatory properties. In children with different diseases who received orally or intravenously 1 to 2 mg/kg doses of furosemide, a statistically significant positive linear relationship was found between the drug urinary excretion rate and the urine flow rate, but log dose-response curves to the drug were found to vary depending on the disease and the route of the drug administration. No sigmoid-shaped log dose-response curve (ie, one approaching a zero response at very low furosemide urinary excretion rates and a maximum response at very high excretion rates) was attained, which may suggest that the capacity of the kidney tubules to respond diuretically to the aforementioned doses of furosemide was not exceeded in these patients. However, in infants with different diseases and reasonably normal renal function who required administration of this diuretic, a very steep log dose-response curve to a 1 mg/kg intravenous dose of furosemide was found, which may suggest that higher doses may not result in a significant increase in diuretic response. The lowest mean furosemide urinary excretion rate and its concentration in urine associated with a significant diuresis were found to be 0.58 +/- 0.33 microg/kg/min and 24.2 +/- 10.5 microg/ml, respectively. Also, a significant correlation was found between the amount (in milligrams) of furosemide excreted in the urine during the first 6 hours after administration and the urine volume collected during that time. Patients with cystic fibrosis appeared to have a markedly more pronounced diuretic response to the average oral dose of 0.835 +/- 0.18 mg/kg than that reported in control children given 2 mg/kg. In children with acute renal failure caused by acute gastroenterocolitis or glomerulonephritis, a broad relationship was observed between a single intravenous dose and diuretic response after administration of furosemide (1.2 to 30.8 mg/kg). It was suggested that the total daily dose of the drug should not exceed 100 mg in these patients. Furosemide was found to be effective in management of bronchoconstriction accompanying chronic lung disease and narrowing of the upper respiratory airways; in hydrocephalus in infancy to avoid cerebrospinal fluid shunts; in some diagnostic procedures, such as an assessment of fetal and neonatal hydronephrosis; and in evaluation of different types of renal tubular acidosis. Among side effects accompanying clinical use of this drug were cholelithiasis in premature infants receiving total parenteral nutrition concomitantly with the diuretic; secondary hyperparathyroidism and bone disease in infants obtaining long-term furosemide treatment; and drug-induced fever.

Effect of hepatic insufficiency on pharmacokinetics and drug dosing

The liver plays a central role in the pharmacokinetics of many drugs. Liver dysfunction may not only reduce the plasma clearance of a number of drugs eliminated by biotransformation and/or biliary excretion, but it can also affect plasma protein binding which in turn could influence the processes of distribution and elimination. In addition, reduced liver blood flow in patients with chronic liver disease will decrease the systemic clearance of flow limited (high extraction) drugs and portal-systemic shunting may substantially reduce their presystemic elimination (first-pass effect) following oral administration. When selecting a drug and its dosage regimen for a patient with liver disease additional considerations such as altered pharmacodynamics and impaired renal excretion (hepatorenal syndrome) of drugs and metabolites should also be taken into account. Consequently, dosage reduction is necessary for many drugs administered to patients with chronic liver disease such as liver cirrhosis.

Sequential nephron blockade breaks resistance to diuretics in edematous states

Diuretic therapy in edematous diseases often yields an inadequate natriuretic response ("diuretic resistance"). To study the functional changes in patients with congestive heart failure, liver cirrhosis with ascites, and nephrotic syndrome, characterized by a reduced effective arterial blood volume (EABV), different diuretic strategies were studied. It was shown that monotherapy with hydrochlorothiazide or furosemide was followed by an inadequate natriuretic response. Correlation of diuretic response with pretreatment fractional sodium excretion of the patient revealed a clear-cut interdependency: Those patients were resistant whose FENa+ was greatly below normal (<0.2%). In addition, it was found that the coadministration of the carboanhydrase inhibitor acetazolamide to diuretic therapy was very effective. We therefore conclude that an increase in proximal-tubular Na+ reabsorption is the major ("pharmacodynamic") determinant for diuretic resistance in edematous diseases with functional "underfilling" of the vascular tree. This alteration of the kidney can easily be overcome by coadministration of a carboanhydrase inhibitor (e.g., acetazolamide).

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.

Drug dosage in patients during continuous renal replacement therapy. Pharmacokinetic and therapeutic considerations

The advantages of continuous haemofiltration and haemodialysis over intermittent haemodialysis for the treatment of acute renal failure are well recognised. In intensive care patients, 4 different continuous procedures, arteriovenous and venovenous haemofiltration (CAVH and CVVH) or haemodialysis (CAVHD and CVVHD), are employed. These effective detoxification treatments require knowledge of their influence on drug disposition. Data on kinetics of drugs during continuous treatment are scarce and limited almost exclusively to the oldest and least effective procedure (CAVH). Selected dialysis membranes may adsorb drugs, as in the case of aminoglycosides. In addition, elimination of substances with large molecular weights may vary depending on the pore size of the membrane, as in the case of vancomycin. Thus, even if drug dosages can be based on pharmacokinetic studies, selection of a dialysis membrane not studied may cause unpredictable drug concentrations. With these limitations in mind and considering the available literature on pharmacokinetics in patients with renal failure, general guidelines for drug dosage during continuous renal replacement therapy can be given. In haemofiltration, drug protein binding is the major factor determining sieving, i.e. the appearance of the drug in the ultrafiltrate. In haemodialysis, diffusion is added to ultrafiltration, and therefore the saturation of the combined dialysate and ultrafiltrate will decrease further with increasing dialysate flow rate. In continuous haemofiltration or haemodialysis the extracorporeal clearance can be calculated by multiplying the saturation value (estimated or, better, measured) with the ultrafiltrate and dialysate flow rate. Dividing the extracorporeal clearance by the total clearance (including the nonrenal clearance) gives the fraction of the dose removed due to extracorporeal elimination. Whether dosage recommendations available for anuric patients have to be modified or not can be decided on the basis of this value. In case of high nonrenal clearance, the degree of saturation is without clinical significance. Based on these considerations guidelines have been constructed for the effect of extracorporeal elimination on more than 120 different drugs commonly used in intensive care patients.

Low-dose segmental blockade of the nephron rather than high-dose diuretic monotherapy

The specific renal effect of diuretics is due to the fact that their concentrations is almost 100-fold greater in the renal tubule than in the plasma. The function of the different segments of the nephron may be altered following changes in the effective arterial blood volume (EABV) and the extracellular fluid volume (ECFV). In diseases with reduced EABV, e.g., congestive heart failure, decompensated cirrhosis of the liver, and the nephrotic syndrome, proximal tubular hyperreabsorption of sodium occurs, leaving only a low Na+ load in the distal segments of the nephron, the site of diuretic action. Clinically, the response to diuretics is reduced or resistance to diuretics may even ensue, which can be predicted by a FENa < 0.2%. Resistance to diuretics can be overcome by short-term comedication with acetazolamide, which increases Na+ delivery to the site of action of the other diuretics used concomitantly. In states with increased ECFV, e.g. in chronic renal failure, there is distal tubular Na+ rejection, leading to a greater increase in FENa the more GFR is reduced. The remaining intact nephrons present a relatively increased response to diuretics. The efficacy of diuretic treatment in renal failure can be optimised by combining loop diuretics with thiazides. In conclusion, low-dose combination therapy, inducing "segmental blockade of the nephron", meets the functional changes along the nephron. It is therefore more effective and safer than high-dose monotherapy.

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).

Pharmacodynamic and kinetic considerations on diuretics as a basis for differential therapy

Diuretics are classified according to their site of action in the nephron: loop diuretics, thiazides, and antikaliuretics. During peak diuresis the pattern of electrolyte excretion is constant and characteristic for a class of diuretics. The ratio of diuretic-induced excretion of K+ to Na+ is 0.12 for loop diuretics, 0.20 for thiazides, and -0.21 for antikaliuretics. The ratio of Ca2+ to Na+ is 0.02 for loop diuretics and 0.003 for thiazides. Mg2+ excretion follows K+ excretion in a ratio of 0.15. The natriuretic effect of a diuretic directly depends on the renal clearance of the drug and is proportionate to the number of intact nephrons. Not only loop diuretics but also thiazides and antikaliuretics were demonstrated to be effective natriuretic drugs down to end-stage renal disease. In renal failure FENa is doubled with every halfening of GFR. Loop diuretics increase FENa to a maximum of 24%, thiazides to 10-15%, and FENa is doubled by antikaliuretics. Comedication of loop diuretics with thiazides in renal failure may therefore be more effective than increasing monotherapy. In liver disease, nonrenal drug clearance is reduced the more the patient's direct bilirubin rises thus causing an increase in AUC and urinary excretion of parent drug and metabolites. Despite increased Ae, the cirrhotic patient may become resistant to diuretics as many patients with congestive heart failure or nephrotic syndrome. This is considered to be due to reduced Na+ load available at the diuretic's site of action following avid proximal Na+ reabsorption. In reduced EABV a short-term comedication of loop diuretics with carboanhydratase inhibitors is considered a more effective diuretic strategy than vigorously increasing monotherapy.

Saluretic effect of the loop diuretic torasemide in chronic renal failure. Interdependence of electrolyte excretion

The effects of torasemide have been studied in 7 healthy controls and 9 patients with stable chronic renal failure of various degrees. After a control period of 3 days torasemide 20 mg i.v. caused a dramatic increase in diuresis and electrolyte excretion without affecting the glomerular filtration rate. The duration of action of torasemide, tau, averaged 6 h and was independent of the creatinine clearance, CLCR. When related to tau the drug-induced excretion of Cl-, Na+, K+, Ca2+ and Mg2+ showed strong linear dependence on CLCR. Both the kaliuresis and the calciuresis during tau were tightly correlated with the natriuresis over the broad range of CLCR. Similarly, the excretion of Mg2+ was dependent on the kaliuresis. The torasemide-induced kaliuresis amounted to 12% of natriuresis, as after furosemide. The kaliuretic effect of loop diuretics is smaller than that of the thiazides. After tau, e.g. over a 24 h period, kaliuresis was not correlated with natriuresis. The magnitude of the rebound effect was diminished with increasing renal impairment.

Prediction of diuretic mobilization of cirrhotic ascites by pretreatment fractional sodium excretion

In a randomized prospective study the efficacy and side effects of xipamide versus the combination spironolactone/furosemide in the treatment of cirrhotic ascites were studied. Out of 27 patients four responded to a basic treatment consisting of salt and water restriction and one had to be excluded because of deterioration of kidney function. The remaining 22 patients were randomized to additional treatment with either 20 mg xipamide/day (group I) or 200 mg spironolactone/day combined with 40 mg of furosemide every other day (group II). A response to treatment during the first 4 days was seen in 7 of 11 patients of group I versus only 3 of 11 patients in group II. In the latter group 7 of 11 patients finally responded after 8 days of treatment. Responsiveness to either diuretic treatment strongly depended on pretreatment fractional Na excretion, FENa. The resistance to diuretic treatment can be predicted by a FENa less than 0.2%, and could be overcome by additional strategies known to reduce avid proximal Na reabsorption. Xipamide frequently induced hypokalemia, whereas hyperkalemia was seen following treatment with spironolactone/furosemide. Kidney function remained stable during either diuretic treatment.

Pharmacokinetics of diuretics in geriatric patients

Pharmacokinetics of three diuretics (furosemide, spironolactone, and triamterene) were investigated in 70 geriatric patients. Comparing the data with the corresponding values of young healthy volunteers, mean plasma concentrations of furosemide and spironolactone (and peak concentrations of triamterene) were markedly higher in the geriatric patients. Different concomitant diuretic therapy (hydrochlorothiazide vs. piretanide) seems to influence the kinetic parameters of triamterene and its active metabolite in the geriatric patients. In elderly patients reduction or correction of the dosage seems to be necessary for all three diuretics investigated in our studies.

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.

Urinary excretion and diuretic action of furosemide in rats: increased response to the urinary excretion rate of furosemide in rats with acute renal failure

A urinary excretion-response curve representing the urinary excretion rate of furosemide versus the urinary excretion rate of (Na+ + K+) was used to analyze furosemide action in rats with uranyl nitrate-induced acute renal failure (ARF) with and without dopamine coadministration. Urinary excretion of furosemide, but not its serum concentration, was the determinant for the diuretic action of furosemide. Increased diuretic response was observed in ARF rats, although the total diuretic response and urinary recovery of furosemide within 2 hr decreased. Dopamine enhanced furosemide-induced diuresis in ARF rats in terms of the total urine output and urinary electrolyte excretion, although the urinary excretion-response curves were not different. This enhancement by dopamine was found to be caused by the augmented urinary excretion of furosemide and the increased response to this drug in ARF rats. These findings suggest the contribution of decreased concentrating ability along the nephron and/or increased sensitivity of cells at the site of action to this drug.

A quantitative method of evaluating the diuretic response to furosemide in rats

Furosemide effects are usually evaluated by measuring the urinary excretion rate of Na+ (UVNa) in humans. In the present study, however, UVNa showed a nonlinear relationship with urine flow rate after intravenous injection of furosemide in rats. In contrast, when the urinary excretion rate of (Na+ + K+) (UVNa + K) was plotted against the urine flow rate, a linear regression line was observed, with small interindividual variations in normal rats and in rats with uranyl nitrate-induced acute renal failure (ARF). Piretanide, a loop diuretic, also showed a similar relationship, while other types of diuretics revealed different slope values for the relationship. Although the urinary excretion rate of Cl- (UVCl) vs UVNa + K is expected to show a linear relationship in normal rats, the correlation coefficient of the linear regression line was smaller than that of the urine flow rate vs UVNa + K. Further, the slope of UVCl vs UVNa + K was slightly different in ARF rats. Therefore, UVNa + K provides a better quantitative measure of diuretic response to loop diuretics than UVNa or UVCl.

On the mechanism of acute tolerance to furosemide diuresis

The renal response to continuous furosemide infusion (8 mg/h) and subsequent ECV changes was studied in 8 healthy volunteers. Furosemide increased urine flow from a basal flow of 4.3 ml/min to a maximum of 15.4 ml/min. During dehydration (-1.8 kg) the diuresis decreased to 8.4 ml/min. The sodium, chloride and potassium excretion likewise decreased. This reduction in diuretic effect (acute tolerance) was accompanied by significantly increased plasma levels of norepinephrine (1.38 to 2.14 nmol/l), PRA (0.52 to 1.13 ng/ml/h) and aldosterone (0.29 to 0.45 nmol/l). After rehydration the urine flow increased to 23.1 ml/min. The changes in diuretic response from initial effect to the dehydrated state and after rehydration were mainly a consequence of changed renal sensitivity to furosemide (urinary excretion of 21 to 14 to 35 mumol Na+ per microgram furosemide excreted). It is proposed that activation of the sympathetic nervous system and/or the renin-angiotensin-aldosterone system may play a role in mediating the acute tolerance to furosemide diuresis. The relative importance of each remains to be clarified.

Altered furosemide pharmacokinetics in chronic alcoholic liver disease with ascites contributes to diuretic resistance

Some patients with chronic alcoholic liver disease and ascites have an impaired natriuretic response to furosemide. To elucidate the mechanism of this diuretic resistance, we measured para-aminohippurate and inulin clearances and urinary excretion of electrolytes, prostaglandin E2, and furosemide after intravenous administration of 80 mg of furosemide in 26 patients. The natriuretic response was variable (3.3-172 mEq/h) and was unrelated to basal sodium excretion, renal clearances, or urinary prostaglandin E2. Natriuresis correlated negatively with plasma aldosterone (r = -0.54, p less than 0.01), and strongly with urinary furosemide (range 5.5-76 mg/h, r = 0.71, p less than 0.001). As urinary furosemide excretion reflects the amount of furosemide reaching the active site on the luminal side of the tubule, the data demonstrate markedly reduced amounts of furosemide at its primary site of action in patients with diuretic resistance. Plasma furosemide was higher in patients with reduced furosemide excretion and impaired natriuresis, suggesting that the defect was an impairment of furosemide transport into the tubule. Thus, a major factor in diuretic resistance is altered furosemide pharmacokinetics.

A decade of developments in diuretic drug therapy

New diuretics introduced into clinical medicine during the past decade include potent new loop diuretics such as bumetanide and piretanide, the uricosuric indanyloxyacetic acid derivative indacrinone, and a new generation of sulfamoyl diuretics such as indapamide and xipamide, which are recommended primarily for the treatment of hypertension. Pharmacokinetic studies of individual diuretics have demonstrated that the diuretic and natriuretic responses to the newer agents generally follow the plasma drug concentration-time curves and urinary drug excretion rates. Therapeutic monitoring can therefore be achieved in most patients with edema or hypertension by close clinical observation and laboratory analysis of plasma electrolyte and creatinine concentrations and urinary electrolyte excretion rates. Interest in the mechanisms involved in the renal and extrarenal vascular actions of the newer diuretics has led to a better understanding of how changes in venous compliance, peripheral vascular resistance, and renal blood flow distribution may contribute to the overall therapeutic response to these agents, especially in patients with severe congestive heart failure, renal insufficiency with low glomerular filtration rates, and hypertension with cardiorenal complications. Adverse reactions to modern diuretics, which are mainly an extension of their renal pharmacodynamic effects, have proved to be minimal, provided that the dosage is adjusted to meet but not exceed individual patient requirements. However, the long-term consequences of prolonged periods of diuretic-induced alterations in plasma potassium levels, and metabolic effects that include elevated blood lipids, are still under investigation.

Pharmacokinetics and pharmacodynamics of furosemide in geriatric patients

Twenty geriatric patients with multiple diseases were administered a single intravenous dose of 40 mg furosemide. Furosemide plasma and urine concentrations were measured using a thin-layer chromatography method and were fitted to an open 2-compartment model. Furosemide half-life was prolonged two-fold in the elderly patients compared with a control group of younger adults. In the same way renal clearance and total clearance were markedly reduced in the geriatric group. The non-renal clearance and the volume of distribution were not significantly altered. There were many significant correlations between clinical and biochemical data and pharmacokinetic parameters, especially between blood pressure and the area under the curve (AUC O-infinity), total clearance and non-renal clearance of furosemide. Our data suggest a special function of alpha-2-globulins in binding of furosemide. Renal function (i.e. creatinine clearance) was shown to be an important parameter for estimating the elimination rate of furosemide. In addition, pharmacodynamic action (volume of excreted urine) was closely correlated with the elimination rate: furosemide is apparently triggering its own elimination.

Disposition and response to bumetanide and furosemide

Bumetanide and furosemide are potent loop diuretics; the former is 40 to 50 times more potent than the latter on a weight basis. Bumetanide is absorbed more quickly than furosemide and is twice as bioavailable. Both drugs exhibit changes in elimination in the presence of renal insufficiency as well as changes in the time course of absorption in congestive heart failure. More data are needed to assess potential differences between them in various clinical conditions.

Bioavailability and diuretic effect of furosemide during long-term treatment of chronic respiratory failure

The bioavailability and diuretic effect of furosemide 40 mg administered orally for at least 6 months have been compared in patients with chronic respiratory failure and in healthy controls. The mean urinary recovery of unchanged drug was 11.5 mg and 9.41 mg in 24 h after pre- and postprandial administration to 10 patients, whereas the recovery was 14.4 mg in 10 healthy subjects. The diuretic effect, in terms of urine flow and sodium ion excretion in the 6 h after administration, was also less in patients than in healthy subjects. This was ascribed to the lower bioavailability of furosemide in patients, based on the urinary recovery of unchanged drug, and not to a lower level of response to furosemide than in healthy subjects. The mean absolute bioavailability of furosemide in 6 patients was 41.3% and 63.4%, respectively, calculated from unchanged drug and total drug (unchanged plus glucuronide conjugate). Approximately 53.9% of the dose of furosemide was excreted as the glucuronide conjugate after oral administration, and 34.2% after i.v. injection in the 6 patients. In 3 of the 6 patients studied, a distinct first-pass effect for glucuronidation of furosemide was observed after oral administration. In another study, the mean glucuronide fraction recovered in 24-h urine was 20.7% and 7.3% (p less than 0.01) in 38 patients and 12 healthy subjects, respectively. The fraction in urine was not affected by changing the dose of furosemide from 20 to 120 mg. The lower bioavailability in patients as compared to healthy subjects is ascribed to enhanced glucuronidation and incomplete drug absorption.

Pharmacodynamics and kinetics of etozolin/ozolinone in hypertensive patients with normal and impaired kidney function

The effect on urinary electrolyte excretion, renin release and plasma norepinephrine of single oral doses of 400 mg etozolin (E) and of 40 mg furosemide (F) were studied in hypertensive patients with normal (n = 6) and impaired kidney function (n = 6). E caused a marked saluresis up to 24 hours, showing its long duration of action. F, however, displayed a brief, brisk peak diuresis, followed by a rebound from the 4th to the 24th hours. The brisk peak diuresis induced by F was associated with pronounced release of renin, almost twice that induced by E. In chronic renal failure the renin release in relation to the magnitude of the diuresis was increased, i.e. the sensitivity of these patients to changes in water homeostasis was increased. E and F stimulated the sympathetic system to roughly the same extent. Patients with essential hypertension had higher plasma levels of norepinephrine than hypertensive patients with chronic renal failure. In addition, hypertensive patients with normal renal function (n = 4) and varying degrees of renal impairment (n = 11) were also given 400 mg daily for 2 weeks. Effects on blood pressure and electrolyte homeostasis were monitored, as well as the plasma kinetics of metabolite I, ozolinone. At the end of the 2 week treatment E had significantly lowered systolic (-12 mm Hg) and diastolic (-9 mm Hg) blood pressure, and had produced a significant loss of body weight, without altering plasma electrolytes or blood chemistry. There was no accumulation of the effective metabolite ozolinone under conditions of severe impairment of kidney function.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacodynamics and pharmacokinetics of xipamide in patients with normal and impaired kidney function

The effect of a single oral dose of 40 mg xipamide on urinary excretion of Na+, K+, Cl-, Ca2+ and Mg2+ in healthy subjects and in patients with varying degrees of renal impairment was compared with various conventional diuretics. Xipamide caused marked excretion of Na+ and Cl-, whereas the diuretic produced only moderate kaliuresis; urinary excretion of Ca2+ was increased in proportion to Na+, like the loop diuretics. Xipamide affected electrolyte excretion even in patients with a creatinine clearance below 30 ml/min, as do the loop diuretics, too. Therefore, the pharmacodynamic characteristics of xipamide are more like those of a loop diuretic than of a thiazide. Xipamide was good bioavailable, its t 1/2 beta was 7 h and urinary recovery of the undegraded drug was 40% of the given dose. In renal insufficiency, t 1/2 beta increased from 7 to only 9h, yielding a moderate increase in the AUC. Urinary recovery of the drug was reduced in proportion to the reduction in the creatinine clearance of the patient. Therefore, significant extrarenal elimination of the diuretic must be postulated, which suffices to prevent significant drug accumulation in renal failure.

Drug prescribing in renal failure: dosing guidelines for adults

The data base for rational guidelines to safe, efficacious drug prescribing in adults with renal insufficiency are presented in tabular form. Current medical literature was extensively surveyed to provide as much specific information as possible. When information is lacking, however, recommendations are based on pharmacokinetic variables in normal subjects. Nephrotoxicity, important adverse effects, and special considerations in renal patients are noted. Adjustments are suggested for hemodialysis and peritoneal dialysis when appropriate.

An intensive drug monitoring study suggesting possible clinical irrelevance of impaired drug disposition in liver disease

1 Liver disease can alter the disposition and clinical effects of drugs. However, even though altered drug disposition occurs, there is no clinical evidence relating it to an increased susceptibility to adverse drug reactions (ADRs). 2 An intensive prospective drug monitoring study of 2,582 hospitalized patients was conducted. The adverse drug reactions probability scale (APS) was used to assess ADRs. Only non-mild, definite or probable ADRs (APS greater than or equal to 5) were included. Severity of liver dysfunction was assessed by a composite clinical and laboratory index (CCLI). 3 The frequency of ADRs was higher in 402 patients with cirrhosis (27.4%) than in 661 with renal dysfunction (22.8%) and in 249 with other parenchymatous liver diseases (13.7%) or in 1,270 patients with neither liver diseases nor renal dysfunction (10.9%) (chi 2 3 = 85.53, P less than 0.001). The frequency of ADRs in cirrhotics was highly correlated with the severity of the liver dysfunction measured by CCLI (r = 0.82, P less than 0.001). 4 Drugs predominantly eliminated by liver metabolism were not among those most commonly inducing ADRs or those causing severe reactions in cirrhotics. Thus, frusemide caused the most common and the most severe ADRs, whereas reactions induced by sedatives were uncommon. Drug-induced hepatic encephalopathy was more common in cirrhotics receiving diuretics (13.3%) than in those receiving sedatives (1.8%) (chi 2 y.c. = 5.29, P less than 0.025). Patients with alcoholic liver disease had more drug-induced hepatic encephalopathy (7.7%) than those with non-alcoholic liver disease (1.2%) (chi 2 y.c. = 11.86, P less than 0.001). 5 These results indicate that susceptibility to ADRs is increased only in severe cirrhosis and that the most common and severe ADRs seem more likely related to enhanced pharmacodynamic action than to impaired drug disposition.

Bioavailability of two preparations of furosemide and their pharmacological activity in normal volunteers

The relative bioavailability and diuretic effect of 2 commercially available tablet preparations of furosemide 40 mg was examined in 10 healthy male volunteers. A close linear relationship between the urinary excretion rate of furosemide and the rate of sodium ion excretion in urine and/or flow rate of urine was demonstrated. There were no significant differences in the urinary excretion of furosemide, sodium and potassium ions or urinary volume following the oral doses. The difference in drug content affected the urinary recovery of furosemide over 24 h but had no effect on the pharmacological response. The analytical power of ANOVA using the various parameters of the responses to furosemide was no lower than when the parameters of urinary excretion of furosemide were used.

Changes in pharmacokinetics and in effect of furosemide in the elderly

In this paper the general changes in the pharmacokinetics of drugs in the elderly are summarized. The suggestion is proposed, that in the case of diuretics--which act after renal excretion--the results of these changes are totally different: contrary to other drugs the standard dose of a diuretic must have less saliuretic effect instead of more effect. This thesis is supported by the results of experiments with furosemide in old patients: the kinetics are changed as expected, leading to higher plasma levels and increased Area Under the (plasma level versus time) Curve (AUC), but the effects are--dependent on renal function--decreased. To a certain degree kinetics and dynamics of furosemide can be explained and predicted on the basis of simple patient parameters. If diuretics are used in old people to treat congestive heart failure, the normal adult dose has to be used, and occasionally a larger dose has to be given.

Delayed elimination of triamterene and its active metabolite in chronic renal failure

The kinetics of triamterene and its active phase II metabolite were studied in 32 patients with various degrees of impaired renal function; the creatinine clearances ranged from 135 to 10 ml/min. The area under the plasma concentration-time curves (AUC) for triamterene were not influenced by kidney function, but the AUCs for the effective metabolite OH-TA-ester were significantly elevated in renal failure, indicating accumulation of the metabolite. Urinary recovery of triamterene and its metabolite over a 48 h collection period was significantly reduced in renal failure. This is considered to be due to delayed urinary excretion, corresponding to reduced renal clearance. The renal clearance of the native drug exceeded that of the metabolite, because of their different protein binding, 55% for triamterene and 91% for the metabolite. The latter is eliminated almost exclusively via tubular secretion and extra-renal elimination is less important. Administration of this antikaliuretic is therefore considered hazardous in patients with impaired kidney function.

Dose-dependent pharmacokinetics of furosemide in the rat

The pharmacokinetics of furosemide were investigated in the rat at doses of 10 and 40 mg kg-1 corresponding to doses of 80 and 320 mg given to humans based on body surface area. A three-compartment open model with renal excretion taking place from the shallow peripheral compartment gave the best fit to the data. The terminal half-life of furosemide was found to change from 29 min for the 10 mg kg-1 dose to 49 min for the 40 mg kg-1 dose. This change could be detected as a change in the apparent volume of distribution caused by decreased protein binding at increasing plasma concentrations of furosemide. The total plasma clearance did not change significantly although metabolic and renal clearance both changed. The renal clearance was found to be dependent on the free fraction of furosemide in plasma and thus increased with increasing plasma concentrations. The metabolic clearance decreased with increasing dose indicating a saturable metabolism of furosemide.