Pharmacokinetics/pharmacodynamics of furosemide in man: a review

Design and in vitro evaluation of slow-release dosage form of piretanide: utility of beta-cyclodextrin:cellulose derivative combination as a modified-release drug carrier

To modify the release rate of piretanide, a potent loop diuretic, a double-layer tablet was designed, and in vitro release was evaluated. For a rapidly releasing portion, hydrophilic beta-cyclodextrin derivatives were employed to form a water-soluble complex with piretanide. For a sustained-release portion, cellulose derivatives were used to provide appropriate hydrophobicity. The release rate of piretanide in the pH range 1.2-6.8 was automatically monitored by a pH-changeable dissolution testing apparatus. The low solubility of piretanide in acidic medium was significantly improved by complexations with dimethyl-beta-cyclodextrin (DM-beta-CyD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CyD). The pH-independent slow release was attained by use of hydroxypropylcellulose (HPC):ethylcellulose (EC) matrices. Then, an optimal formulation of a double-layer tablet was obtained by the combination of each fraction. For example, the tablet consisting of the [DM-beta-CyD/(HPC:EC)] system in the weight ratio [1/3(1:3)] provided a sufficiently slow release of the drug over a period of 8 h in a wide pH region following an initial rapid dissolution.

Effects of aging on responses to furosemide

Furosemide causes both diuretic and non-diuretic changes in renal function. We compared responses to intravenous furosemide 0.5 mg.kg-1 in 38 subjects (30 males, 8 females) aged 18 to 30 with those in 14 subjects (9 males, 5 females) aged 50 and over. There were no consistent differences attributable to gender. Older persons showed greater natriuresis (47 percent in males and 26 percent in females) but their increment in plasma renin activity was markedly reduced. The urinary excretion of thromboxane B2 was elevated in older subjects (58 +/- 10 vs. 30 +/- 4 ng/4 h, p less than 0.05 for males; 48 +/- 7 vs. 29 +/- 4 ng/4 hr, p less than 0.05 for females) while that of 6-keto prostaglandin F1 alpha was not different. While differences in the diuretic response to furosemide may be due to pharmacokinetic differences, the non-diuretic response differences may reflect age related changes in renal prostaglandin synthesis.

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.

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.

Development of acute tolerance to bumetanide: bolus injection studies

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

Colloid osmotic pressure in pulmonary edema clearance with furosemide

After tripling of baseline lung water (EVLW), decreasing wedge pressure (PWP) alone for two hours did not decrease EVLW. In 11 of 16 dogs, triple baseline EVLW and a decrease in plasma colloid osmotic pressure (COP) from 21.1 +/- 0.8 to 17.8 +/- 0.8 mm Hg resulted from left atrial balloon inflation at PWP of 28 to 30 mm Hg. With subsequent lowering of PWP to 10 mm Hg, intravenously administered furosemide (1 mg/kg) was given to these 11 dogs. One half hour after furosemide, shunt decreased slightly without decreasing EVLW in all 11 dogs, but by two hours, seven dogs (group 1) decreased EVLW (from 23.2 +/- 1.8 to 11.1 +/- 1.4 ml/kg) and shunt (37.4 +/- 2.0 to 12.9 +/- 2.9 percent), while four dogs (group 2) did not (EVLW: 22.3 +/- 1.4 to 22.5 +/- 0.6 ml/kg: shunt, 36.8 +/- 1.7 to 36.5 +/- 1.9 percent). Group 1 had diuresis, maintained normal blood urea nitrogen and creatinine levels, and increased COP from 17.7 +/- 0.7 to 23.6 +/- 0.5 mm Hg while group 2 was oliguric with elevated BUN and creatinine values and showed no change in COP (17.9 +/- 0.9 to 18.3 +/- 0.6 mm Hg) after furosemide. After decreasing PWP in massive pulmonary edema (triple baseline EVLW), furosemide appeared to enhance edema clearance by changes in COP with diuresis.

Immediate hemodynamic response to furosemide in patients undergoing chronic hemodialysis

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

Plasma protein binding of furosemide in the elderly

The protein binding of furosemide was investigated in plasma from 22 old and 11 young subjects by equilibrium dialysis. The unbound fraction of furosemide was 3.16% in plasma from the elderly and 1.7% in plasma from the young. A significant correlation was found between the unbound fraction of furosemide and the plasma concentration of albumin. The average number of binding sites was 3.8 (elderly) and 2.7 (young) 10(-6) mol/g albumin. The average association constant (K) was 4.3 (elderly) and 4.2 (young) 10(5) M-1. By increasing the concentration of furosemide up to 200 micrograms/ml buffer the unbound fraction of the drug rose to 5.2% (elderly) and 3.5% (young).

Pharmacology and therapeutic use of low-dose dopamine

The renal pharmacologic effects of intravenous dopamine in doses of 0.5-3.0 micrograms/kg/min include increases in renal blood flow, glomerular filtration rate, solute excretion, and urine flow. Clinical studies revealed that low-dose dopamine can reverse oliguria, but these studies were poorly controlled, were confounded by the use of other diuretics, had small patient populations, and often did not evaluate mortality or long-term renal function. When used in low doses, side effects are rarely seen. Because of dopamine's effect on hepatic and renal function, changes in drug clearance may occur. Low-dose dopamine may be considered in the early course of oliguric patients; however, specific advantages over other diuretic therapy have not been established.

Effect of intravenous infusion time on the pharmacokinetics and pharmacodynamics of the same total dose of furosemide

The pharmacokinetics and pharmacodynamics of furosemide were evaluated after intravenous administration of the same total dose of furosemide in different lengths of infusion time (10 s, 30 min, 2 h, and 8 h) to 6 dogs. The fluid loss in urine was immediately replaced volume for volume with intravenous infusion of Lactated Ringer's solution. The pharmacokinetic parameters such as per cent of the dose excreted in urine, total body and renal clearances, and terminal half-life were not significantly different with four different infusion times. The volume of distribution at steady state and mean residence time based on venous data, on the other hand, appeared to increase with increasing infusion time. The mean values for Vss were 0.334, 0.478, 0.499, and 0.708 1 kg-1 for 10 s, 30 min, 2 h, and 8 h of infusion, respectively, and the corresponding values for MRT were 17.5, 22.2, 24.8, and 38.1 min. The diuretic effects (urine output and urinary excretion of sodium) were generally found to increase with increasing infusion times; the total mean 24 h urine outputs were 1102, 1464, 2190, and 3470 ml for 10 s, 30 min, 2 h, and 8 h of infusion, respectively, and the corresponding values for sodium excretion were 170, 175, 272, and 440 mmol. Furosemide plasma concentrations and hourly urinary excretion rates of furosemide, sodium, and potassium during the apparent steady state (between 2 and 8 h) in the 8 h infusion study were fairly constant.

Effects of the rate and composition of fluid replacement on the pharmacokinetics and pharmacodynamics of intravenous furosemide

Effects of differences in the rate and composition of intravenous fluid replacement for urine loss on the pharmacokinetics and pharmacodynamics of furosemide were evaluated using the dog as a model animal. Each of six dogs received 8-hr constant intravenous infusion of 20 mg (15 mg used in one dog) of furosemide with 0% replacement (treatment I), 50% replacement (treatment II), and 100% replacement (treatment III) with lactated Ringer's solution, as well as with 100% replacement with 5% dextrose in water (treatment IV). Most pharmacokinetic parameters, such as plasma clearance, steady-state volume of distribution, mean residence time, and terminal half-life, were essentially the same in all four treatments. Renal clearances and urinary excretion rates of the drug in treatments II-IV were essentially the same, but about 20% higher than those in treatment I. In spite of the similarities in kinetic properties, diuretic and/or natriuretic effects from furosemide were markedly different among the four treatments. For example, mean 10-hr urine outputs were 646, 1046, 3156, and 1976 ml and mean 10-hr sodium excretions were 87.0, 142, 383, and 97.2 mmole for treatments I-IV, respectively. Except for treatment III, diuresis and/or natriuresis were found to be time-dependent, generally decreasing with time until reaching a low plateau during later hours of infusion. The present findings also showed that no fluid replacement and 100% replacement with 5% dextrose solution both produced the same degree of severe acute tolerance in natriuresis, indicating the insignificance of water compensation in tolerance development; in treatment II, where neutral sodium balance was achieved, the development of acute tolerance in diuresis and natriuresis can mainly be attributed to negative water balance under this special condition; at steady state the hourly diuresis and natriuresis could differ up to about ten times between treatments. Some implications for the kinetic/dynamic relationship or modeling, in the clinical use, and in the bioequivalence evaluation of dosage forms are discussed.

Renal transport kinetics of furosemide in the isolated perfused rat kidney

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

Bioavailability of seven furosemide tablets in man

A seven-way crossover study was conducted in 14 healthy male volunteers to evaluate the relative bioavailability of seven different marketed 40 mg furosemide tablets. Each dose was administered as a single tablet after an overnight fast, and blood samples were obtained for 16 hours. Plasma was assayed by HPLC. There were no statistically significant differences among the seven products for the mean peak concentration (1.01-1.29 micrograms/ml), mean time of peak (1.2-2.1 h) or mean area under the plasma concentration-time curves, which differed by less than 14 per cent. However, one product exhibited greater intersubject variability, and on this basis was considered inequivalent to the other six products. Furosemide is a potent and widely used diuretic. Currently the United States Food and Drug Administration (USFDA) has granted approval to at least twelve manufacturers of 40 mg furosemide tablets, based in part on bioavailability data obtained in human subjects. In addition, the USFDA has granted an 'AB' therapeutic equivalence evaluation to each of these products, which is understood by many to indicate the therapeutic equivalence and interchangeability of these products. The objective of the present investigation was to directly compare the bioavailability of seven 40 mg furosemide tablet products which had previously been approved by the Food and Drug Administration.

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.

Cellular mechanism of action of loop diuretics: implications for drug effectiveness and adverse effects

The loop diuretics inhibit a transport system that moves sodium, potassium and chloride across cell membranes of many tissues, including the thick ascending loop of Henle. This inhibitory effect is responsible for their natriuretic effect. Of the agents available for clinical use, bumetanide is the most powerful; it has an in vitro transport inhibitory potency and an in vivo natriuretic effectiveness that is approximately 50-fold that of furosemide. This increased potency and the consequent decreased dose requirement give bumetanide the potential for increased effectiveness and decreased incidence of adverse effects.

Diuretic activity of torasemide and furosemide in chronic heart failure: a comparative double blind cross-over study

The diuretic effects of torasemide and of furosemide were compared in a double blind cross-over study in 13 patients with stable chronic heart failure. Single doses of 10 mg and 20 mg of torasemide and of 40 mg of furosemide were given orally, in a randomized order on 3 consecutive days. In addition, a placebo was administered on the day preceding the 3 active drug treatment days to obtain control data. Each experimental day was divided into three urine collection periods - 0 to 4 h, 4 to 12 h and 12 to 24 h. Urine output, ion excretion and clearance were measured during each of the 3 periods as well as for the 24-h period. Torasemide 20 mg was distinctly more active in each of the 3 collection periods and in the 24-h period than furosemide 40 mg, whereas no significant difference was found between furosemide 40 mg and torasemide 10 mg for most of the experimental data. From 0 to 4 h, both torasemide and furosemide significantly increased the urinary flow rate and the urinary excretion of sodium, chloride and calcium, while they decreased the urinary osmolality when compared to placebo. All the effects persisted in the 4 to 12 h period after torasemide 20 mg in contrast to furosemide, whose effects were limited to the 0 to 4 h period. In the third period (12-24 h), the urine volume fell below the placebo value after furosemide but not torasemide, and only torasemide 20 mg was followed by a persistent decrease in the urine osmolality.(ABSTRACT TRUNCATED AT 250 WORDS)

Study of the elimination kinetics of torasemide, a novel loop diuretic, in renal insufficiency

The plasma concentration of torasemide was determined as a function of time in 8 patients with impaired renal function (creatinine clearance less than or equal to 25 ml/min). The elimination half-life (1.3 to 3.8 h), the volume of distribution (0.12 to 0.29 l/kg), and the total body clearance (0.02 to 0.10 l/kg X h) were similar to those observed in normal volunteers.

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.

Liquid membrane phenomenon in diuretics

Surface activity and critical micelle concentrations are reported for two diuretic drugs, furosemide and triamterene. The drugs generate a liquid membrane on a supporting membrane. Transport of chloride, sodium, and potassium ions through the liquid membranes generated by the drugs was studied. The data suggest that the phenomenon of liquid membrane formation may contribute to the diuretic action.

Bumetanide and furosemide in heart failure

We assessed the handling of and response to oral bumetanide (1.0 and 2.0 mg) and to furosemide (40 and 80 mg) in 20 patients with stable, compensated congestive heart failure (CHF), comparing the two drugs and, in addition, examining differences from normal subjects. Bumetanide and furosemide were similar in time course of absorption, but patients with CHF had considerably prolonged absorption compared to normal subjects causing attainment of lower peak concentrations of drug. In both CHF and normal subjects, more bumetanide than furosemide was absorbed. The elimination half-life of furosemide was approximately twice that of bumetanide, and both were about two times longer than respective values in normal subjects. "Dose"-response curves were shifted downward from normal with both drugs. In patients with CHF, overall response did not differ between bumetanide and furosemide. The two drugs exhibit subtle differences, the clinical importance of which appears to be negligible from this study. Importantly, however, both drugs showed delayed absorption causing attainment of peak urinary excretion rates of diuretic two- to threefold lower than in normal subjects. This effect along with the abnormal responsivity of the tubule may contribute to the "resistance" to oral doses of diuretics observed clinically even though no quantitative malabsorption of drug occurs.

The influence of age on renal and extrarenal effects of frusemide

The effect of frusemide 80 mg i.v. was compared during 24 h in 10 young and eight elderly healthy male volunteers following a 24 h control period in the ward. During the 30 min following the injection the increments in excretion of urine, sodium, potassium and frusemide were significantly smaller in the elderly. The 24 h increase in sodium excretion was significantly larger in the 0 young and eight elderly healthy male volunteers following a 24 h control period in the ward. During the 30 min following the injection the increments in excretion of urine, sodium, potassium and frusemide were significantly smaller in the elderly. The 24 h increase in sodium excretion was significantly larger in the 0 young and eight elderly healthy male volunteers following a 24 h control period in the ward. During the 30 min following the injection the increments in excretion of urine, sodium, potassium and frusemide were significantly smaller in the elderly. The 24 h increase in sodium excretion was significantly larger in the elderly. The endogenous 24 h creatinine clearance was reduced by 12% (P less than 0.01) in both age groups. The frusemide induced changes in the 8 h serum concentration curves for albumin differed significantly between the two groups (analysis of variance, P less than 0.01). The drug induced increase in albumin concentration became significant in the young 5 min after the injection. In the elderly it took more than 15 min before the increase in serum albumin reached significance. The average maximal increase in albumin concentration was 14.3% in the young and 9.7% in the elderly (P less than 0.05). No difference was seen between the two age groups in the significant frusemide induced increases in the 24 h albumin excretion but in the elderly a significantly larger decrease in the 24 h excretion of beta 2-microglobulin was observed (P less than 0.05). No significant age difference was observed in the initial significant increases in diastolic blood pressure observed in both age groups or between the later changes in systolic blood pressure which was significantly reduced in the young only. The slower haemoconcentration response in the elderly seemed associated with the slower secretion rate of frusemide to the tubular lumen. We found no evidence of an age related difference in tubular cell response to frusemide. It is emphasized that a maximal initial frusemide response in the elderly, in contrast to what was found in the young, probably was not achieved by the 80 mg i.v.

Blood volume following diuresis induced by furosemide

Changes in blood volume were investigated following intravenous injection of a single dose of furosemide in 21 patients with pulmonary edema. In a subset of 10 patients in whom the blood urea nitrogen level was 11.4 +/- 2.2 mg/dl and the serum creatinine level was 1.3 +/- 0.1 mg/dl and in whom total urine output exceeded 1 liter over a four- to six-hour interval ("diuretic" group), no significant change in plasma or total blood volume was observed, nor were there any significant changes in hematocrit. In a "nondiuretic" group of 11 patients who had moderately decreased renal function (blood urea nitrogen level 59.3 +/- 13.0 mg/dl and serum creatinine level 2.3 +/- 0.3 mg/dl) and in whom total urine output was less than 1 liter over the four- to six-hour interval, there was a significant increase in blood volume with a concomitant decrease in hematocrit and hemoglobin levels. Furosemide-induced diuresis therefore did not deplete intravascular volume. To the contrary, actions of furosemide that were independent of its diuretic action were associated with an expansion of plasma volume in the absence of diuresis. This may be related to the venous capacitance effects of furosemide with lowering of venous resistance and, therefore, lowering of the capillary hydrostatic pressure. In addition, there was an increase in colloid osmotic pressure. Both mechanisms increase the effective oncotic pressure gradient, which favors reabsorption of extravascular (edema) fluid. It is concluded that intravascular volume was therefore replenished at a rate equal to or in excess of the volume removed by diuresis.

Methods in testing interrelationships between excretion of drugs via urine and bile

The liver and kidney are largely responsible for inactivating and eliminating drugs and other chemicals. As the excretory capabilities of the two organs overlap, a damage of one system might be compensated by the other. Because of the specificity of both renal and hepatic elimination mechanisms such an alternative excretion route is not possible generally. Several interferences are possible to characterize the relation between hepatic and renal excretion of drugs and xenobiotics. Firstly, the simultaneous assay of excreted drug amounts in urine and bile can give some information concerning the main transport routes of this drug. Thereafter the total interruption of liver or kidney function elucidates the general possibility of alternative excretion routes. But it is important for clinical practice to distinguish between different localizations of organ damages. Today some experimental possibilities exist to exclude partial functions of both kidney and liver separately. Thus it can be clarified why a compound might be excreted via liver or kidney. Moreover it can be characterized whether or not a compensation for the loss of one main excretion organ is possible or not. Such investigations are of some practical importance. Dosing guidelines for drug therapy must be completed for cases of renal or hepatic failure. Moreover the developmental pattern of both elimination routes has consequences for drug use in paediatrics as well as geriatrics. Beside this point of view such investigations are necessary for the prediction of changes in the toxicity of drugs after renal or hepatic insufficiency.

Pharmacokinetics of furosemide in man after intravenous and oral administration. Application of moment analysis

Furosemide 40 mg was administered to 8 healthy subjects as an i.v. bolus dose, as 1 tablet in the fasting state, and as 1 tablet and a solution after food intake. The i.v. data gave a total body clearance of 162 +/- 10.8 ml/min and a renal clearance of 117 +/- 11.3 ml/min; the volume of distribution at steady state was 8.3 +/- 0.61. Oral administration gave a bio-availability of the tablet (fasting) of 51%. Food intake slightly reduced the bioavailability, but not to a significant extent. There was no significant difference in availability between the tablet and the solution. Moment analysis gave a mean residence time after the i.v. dose, MRTi .v., of 51 +/- 1.5 min. The mean absorption times (MAT) for all oral doses were significantly longer than the MRTi .v., indicating absorption rate-limited kinetics of furosemide. On average, food delayed the absorption by 60 min. The MAT for the tablet in the postprandial state was significantly longer than for the solution, indicating dissolution rate-limited absorption of the tablet.

Implications of intraindividual variability in bioavailability studies of furosemide

Intrasubject variation in bioavailability (rate and extent) and disposition of furosemide 40 mg was investigated using a repeated, randomized, double-blind cross-over study in 8 healthy subjects. Two generic tablet formulations (Lasix and Furix) and intravenous furosemide were compared on 6 separate days. Extensive intrasubject variability after oral administration was observed in AUC, mean absorption time (MAT) and urinary excretion. The variability (error variance) within the dosage forms was as large as that between the two generics. These variations most probably depended on the absorption process, since the repeated i.v. doses showed only marginal intrasubject variability. Absolute bioavailability was 56% for Lasix and 55% for Furix (AUC). The range was 20 to 84% between individuals and the maximal range within one individual was 20 to 61%. Confidence interval and Bayesian analysis showed a high probability of non-equivalence not only between but also within the generics when the separate cross-over experiments were analyzed (8 observations). When extending the analysis to 16 observations, bioequivalence was demonstrated for the two generic tablets. Rate of absorption, quantified as MAT, was 128 min for Lasix and 98 min for Furix (16 observations). Since MAT was significantly longer (p less than 0.001) than the mean residence time after the i.v. dose (57 min), absorption was evidently the rate-limiting step in the overall kinetics of oral furosemide. Intraindividual variation in absorption is a confounding factor in bioavailability studies of furosemide using limited numbers of subjects. This is important to consider when designing and evaluating bioavailability studies for drugs showing these variations.

Evaluation of potential causes for the incomplete bioavailability of furosemide: gastric first-pass metabolism

Potential causes for reported incomplete (usually 40-60%) and often highly variable (e.g., 11-79%) bioavailability of furosemide in humans were investigated. The drug was found to be fairly stable in gastric fluids and its hepatic first-pass elimination (HFPE) was estimated to be much less than 6% based on published i.v. data. The rat was used as the main model for extensive evaluation. About 4% (n = 4) of dose was recovered unchanged in the GI tract after i.v. injection while about 40% (n = 12) was recovered after a 120-fold (0.05-6 mg) dose range of oral administration. In another study 70% of the oral dose eventually disappearing (presumably due to absorption and first-pass elimination) from the GI tract was estimated to occur in just 20 min. These data indicate an unsaturable, incomplete, site-specific absorption as well as a lack of dissolution-rate-limited absorption at the doses studied. Based on plasma data, oral bioavailability in four rats was only 30%, and the HFPE much less than 10%. After oral administration, 61% of the dose was absorbed and/or metabolized in the GI recovery study. Thus, 20-30% of oral dose in rats must be metabolized in the GI wall during absorption. The metabolic activity of stomach (homogenate) from 5 rats was found to be much (e.g., 5-10.5-fold) greater than those of liver and small intestine. This was also confirmed in preliminary studies with 3 rabbits and 1 dog. Large intersubject variability in enzyme activity was found in rats and rabbits. The phenomenon of a presystemic first-pass effect was also substantiated by urinary excretion data of a metabolite. It is postulated that variable gastric and intestinal first-pass metabolism may be a major factor causing incomplete and irregular absorption of furosemide in humans.

Bumetanide: a new loop diuretic (Bumex, Roche Laboratories)

Bumetanide is a recently introduced diuretic that inhibits sodium transport in the thick ascending limb of the loop of Henle. It is structurally and pharmacologically similar to furosemide, but is approximately 40 times as potent on a milligram-for-milligram basis. After oral administration, it is rapidly absorbed, with peak serum concentrations attained at approximately 30 minutes. Its pharmacokinetic parameters are similar to those of furosemide. Bumetanide has demonstrated efficacy in the management of edema associated with congestive heart failure, hepatic cirrhosis, and renal insufficiency. Bumetanide has demonstrated an adverse-reaction profile similar to that of furosemide, although the incidence of hypochloremia and hypokalemia is greater with bumetanide. The incidence of hyperglycemia and ototoxicity is greater with furosemide. The principal indication for bumetanide may be in patients with increased risk of ototoxicity. Cost considerations should relegate bumetanide to a secondary role for the treatment of sodium and fluid retention in most clinical settings.

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.

The pharmacokinetics of frusemide are influenced by age

After a 24 h control period 80 mg frusemide was given intravenously over 2 min to a group of young and a group of elderly healthy male volunteers. The serum concentration of frusemide and the excretion in urine of the drug and a glucuronidated metabolite were followed for 24 h. The elimination of the drug from serum was described by an open two compartment model. The serum clearance (CLs) was 170 +/- 19 ml min-1 in the young and 129 +/- 11 ml min-1 in the elderly (P less than 0.01) and the average renal clearance (CLr) was 67% of CLs in the young and 58% of CLs in the elderly (NS). The average amount of unchanged frusemide in the urine during the first 30 min was 30 +/- 6 mg in the young but only 20 +/- 4 mg in the elderly (P less than 0.01). The albumin concentration in serum was 15% lower in the elderly but on the average the protein bound fraction of frusemide was 98.6% in both groups. The Vd ss did not differ between the two age groups (0.130 1 kg-1) but the elimination half-life was 70 +/- 20 min in the young and 102 +/- 33 min in the elderly (P less than 0.05). In the young 11.4 +/- 5.0 mg frusemide was excreted as a glucuronidated compound whereas this figure was only 5.4 +/- 2.9 mg in the elderly (P less than 0.01). It is concluded that the age-related changes in the fate of unchanged frusemide in the organism mainly can be explained by a reduction in the tubular secretion of the drug which in turn may be caused by a reduction in renal plasma flow.

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.

The pharmacokinetics and pharmacodynamics of the diuretic bumetanide in hepatic and renal disease

1 Bumetanide (1 mg) was given orally and intravenously to a group of patients with chronic renal failure (n = 6) and to another group with cirrhosis of the liver (n = 8). 2 The pharmacokinetics, using a two-compartment model, and the pharmacodynamics of the drug in these patients were compared with those previously obtained for normal subjects. 3 In the renal group serum bumetanide concentrations were higher than for the normal subjects and the terminal half-lives were significantly prolonged (P less than 0.001). A decreased whole body clearance was attributable to a low renal clearance of drug, the non-renal clearance being significantly increased (P less than 0.01). 4 For the patients with liver disease, serum bumetanide concentrations were higher than for the renal group, and the terminal half-lives were significantly further prolonged (P less than 0.001). Both non-renal and renal clearances were significantly reduced (P less than 0.001). 5 Absorption rates were not significantly altered in either group and the values of F (bioavailability) were 0.82 and 0.95 for the patients with renal disease and hepatic disease, respectively. 6 A poor pharmacodynamic response and a reduced bumetanide excretion rate were observed for the patients with chronic renal failure, whereas with hepatic disease normal bumetanide excretion rates were observed with an impaired diuretic response.

Determinants of bumetanide response in the dog: effect of probenecid

The pharmacokinetics and pharmacodynamics of intravenous bumetanide (0.250 mg/kg), alone (treatment I) and after probenecid pretreatment (treatment II), were studied in four mongrel dogs. Lactated Ringer's solution was administered by vein throughout both treatments at a flow rate of 2 ml/min to avoid fluid and electrolyte depletion. Bumetanide and probenecid concentrations were analyzed by HPLC, sodium by flame photometry, and creatinine by colorimetry. Although the probenecid markedly reduced the plasma and renal clearances of bumetanide, as well as the fraction excreted unchanged in the urine, there was no significant difference between treatments I and II in the 4-hr natriuretic and diuretic responses. However, analysis of the dose-response curves between treatments I and II showed that sodium excretion was better correlated with bumetanide urinary excretion rate than with plasma concentration. The reasons for a poor correlation between treatments during the early time periods are discussed.

Clinical pharmacology of diuretics

Diuretics belong to the drugs most frequently used. Thiazide diuretics, loop diuretics and potassium sparing diuretics are the agents with practical significance. Many data concerning the pharmacokinetics of these drugs have been reported. Nevertheless, the metabolism of some diuretics is not yet fully elucidated. There are numerous pharmacodynamic drug interactions with diuretics which in general can be predicted from the spectrum of pharmacodynamic actions of the drugs involved.

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.

Biotransformation of furosemide in kidney transplant patients

The metabolic fate of furosemide was studied in kidney transplant patients after oral and intravenous administration of the diuretic at therapeutic doses. Serial urine samples were collected over a 24 h period and furosemide was analyzed by a specific high performance liquid chromatographic method using fluorescence detection. We found no evidence of the putative furosemide metabolite, 2-amino-4-chloro-5-sulfamoylanthranilic acid (CSA), in any of the samples analyzed. The amount of furosemide excreted as the glucuronide metabolite accounted for 8% of the available dose, whether administered orally or by intravenous infusion. In addition, the significant positive correlation observed between the percent of the available dose excreted as furosemide glucuronide and the renal clearance of furosemide (r = 0.581, p less than 0.02) suggests that the glucuronidation process for furosemide may be occurring in the kidney. Furosemide and its glucuronide metabolite accounted for only 45% of the intravenous dose recovered in the urine. Biliary excretion of unchanged furosemide and/or furosemide glucuronide into the feces probably accounts for the remainder of the dose not recovered.

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.

Disposition and absolute bioavailability of furosemide in healthy males

Furosemide (40 mg) was administered to 18 healthy adult males as an intravenous dose, an oral solution, and in tablet form. The pharmacokinetics of intravenous furosemide were studied, determining a total body clearance rate of 117.6 +/- 41.3 ml/min and a harmonic mean half-life of 78 min. The mean absolute bioavailability determined by ratio of areas under the plasma-time curves was 64 and 71% for the solution and tablet, respectively. The mean absolute bioavailability determined by the ratio of urinary cumulative excretion data was 61 and 66% for the solution and tablet, respectively. The absolute bioavailability of furosemide determined with plasma and urine data were not significantly different. Thus, urine data alone may be used to establish bioavailability of furosemide. Inspection of plasma-time curves revealed secondary maxima in several subjects, suggesting enterohepatic cycling.

The pharmacokinetics and pharmacodynamics of bumetanide in normal subjects

The pharmacokinetics and pharmacodynamics of bumetanide (1 mg) administered either orally or intravenously were studied in a group of normal subjects using high-pressure liquid chromatography. A two-compartment model adequately fitted the intravenous data. Renal clearance (85 ml min-1) contributed 65% to the total elimination of bumetanide irrespective of whether a model-dependent or model-independent method was used. Oral administration of bumetanide elicited a greater and a more prolonged pharmacological response than did intravenous bumetanide. An attempt is made to relate the pharmacokinetics of the drug to its pharmacodynamics.

Absorption and disposition of furosemide in congestive heart failure

Changes in response to furosemide and other diuretics in patients with congestive heart failure (CHF) could occur because of disease-induced changes in absorption of the drug or changes in disposition which affect its access to its site of action. A difference was not found in the bioavailability of forosemide in patients with CHF compared to normal volunteers, 31 +/- 12 vs. 38 +/- 20% (mean +/- sd), respectively. Both groups showed considerable interindividual variability, though serial analyses within individuals revealed consistency. Amounts of furosemide delivered into the urine after an intravenous dose correlated significantly to that after an oral dose implying that the interindividual variability is not caused primarily by variability in absorption in either group. Overall, disposition kinetics of furosemide did not differ between groups. Because of heterogeneity of renal and cardiac function among the patients, we were able to demonstrate correlations of plasma and renal clearance of furosemide with renal function; in turn, renal function correlated with left ventricular ejection fraction. Consequently, some patients had changes in furosemide disposition, but, for the most part, differences in response to furosemide were caused by abnormal responses to, rather than changed handling of the diuretic.

The time course of delivery of furosemide into urine: an independent determinant of overall response

After an oral or intravenous dose of furosemide, there is considerable interindividual variability in the amount of unchanged drug delivered into the urine. On average, approximately half as much reaches the intraluminal site of action with an oral compared to an intravenous dose. However, the natriuretic response to the same dose administered by either route is virtually the same. Similarly, after pretreatment with probenecid, the same total amount of furosemide in urine causes a greater overall response. It has been presumed that this paradox is accounted for by differences in rate of delivery of furosemide to the active site such that after an oral dose, or after pretreatment with probenecid, amounts of drug are for longer periods of time at the "steep" portion of the dose-response curve. Our analysis shows this not to be the case. For furosemide, the "slope factor" of the dose-response curve is such that the amount of diuretic delivered into the urine which is maximally efficient (21.5 micrograms/min) is considerably less than the amount causing half-maximal response (69.8 micrograms/min). Oral administration or pretreatment with probenecid maintains drug close to this maximally efficient amount more persistently than does intravenous administration. By so doing, total response to an oral dose approaches that of intravenous dosing despite delivering half the amount of drug to the active site, and after probenecid an intravenous dose causes a greater response than intravenous dosing alone despite delivering the same amount of drug to the active site. These data emphasize the importance of the time course of delivery of drug to the active site as an independent determinant of overall response.

The individual variation in pharmacokinetics and pharmacodynamics of furosemide in young normal male subjects

Following a 24 h control period in the ward 80 mg furosemide was injected intravenously to ten young healthy, male volunteers. The serum clearance of furosemide (Cls) was between 140 and 201 ml min-1 and on the average the renal clearance was 60% of Cls. During the initial 30 min period a maximum additional excretion rate of sodium of 3.3 mmol min-1 was reached at an excretion rate of 0.8 mg furosemide min-1. A marked initial drop in creatinine clearance (Clcr) was noted and Clcr(24 h) showed an average decrease of 12% after the drug administration. The serum concentration of potassium was decreased at 1 and 2 h after the injection and of sodium from 2 h and on. The concentration of albumin in serum increased by 3% (P less than 0.05) already after 5 min. After 2 h a maximum increase of 14% was reached. After 8 min diastolic blood pressure was increased by 13% (P less than 0.05), whereas systolic blood pressure reached a significant decrease gradually (7% after 3 h).

Variance comparison as a tool in clinical pharmacology: an example with two loop diuretics

Comparison of variances can be usefUl in assessing the regularity of drug effects. In order to compare the variances of the saluretic effects of piretanide and frusemide, two loop diuretics with different bioavailabilities, a double-blind cross-over study was carried out in 34 normal volunteers. The diuretics were given in randomized order, with an interval of 7 days, in single equipotent doses (frusemide 6.25 mg and piretanide 1.0 mg chosen from previous results) adjusted by body weight. The dispersion of individual values (comparison of variances from paired measures) for Na+, Cl- and Ca++ excretion, urine osmolality and excretion of the drugs, was significantly smaller for piretanide than for frusemide. It is concluded that the saluretic effect of a single dose of piretanide varies less than that of an equipotent dose of frusemide. The methodology may be useful in trials of drugs for which regularity of effect is important.

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

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

A comparison of antrafenine and aspirin on platelet aggregation and frusemide-induced diuresis

The effects of antrafenine were compared with aspirin and placebo on platelet aggregation and on the diuretic action of frusemide in normal volunteers. Aspirin significantly reduced platelet aggregation at 3 and 6 hr after administration, but antrafenine only at 3 hr. Only aspirin significantly reduced the increase in urine sodium and potassium produced by frusemide.

Variability in derived parameters of furosemide pharmacokinetics

The pharmacokinetics of furosemide in normal man reported from a number of investigators show great discrepancies. We have evaluated the effect on derived pharmacokinetic parameters of furosemide of using different weighting factors or fewer data points to fit the same set of data to an exponential equation, or using noncompartmental analysis. Terminal half-lives of furosemide differed vastly, as did the volume of distribution, but to a lesser extent. The plasma clearance was rather consistent with the different methods used. Thus the discrepancies of the pharmacokinetics of furosemide may, in large part, be due to different methods of analysis of the data. The terminal half-life was most subject to errors of method and the plasma clearance the least.