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

A pharmacokinetic/pharmacodynamic model capturing the time course of torasemide-induced diuresis in the dog

A pharmacokinetic/pharmacodynamic modelling approach was used to determine a dosage regimen which maximizes diuretic efficiency of torasemide in dogs. Kinetic profiles of plasma concentration, torasemide excretion rate in urine (TERU) and diuresis were investigated in 10 dogs after single oral administrations at 3 dose levels, 0.2, 0.8 and 1.6 mg/kg, and an intravenous injection of 0.2 mg/kg. Endogenous regulation was evidenced by a proteresis loop between TERU and diuresis. To describe the diuresis-time profile, TERU served as input into a turnover model with inhibition of loss of response, extended by a moderator acting on both loss and production of response. Estimated maximum inhibition of loss of response, I_max , was 0.984 showing that torasemide is an efficacious diuretic able to suppress almost total water reabsorption. A TERU_50, value producing half of I_max , of 1.45 μg/kg/h was estimated from the model. Pharmacokinetic and pharmacodynamic parameters were used to simulate the torasemide dose-effect relationship after oral administration. Model predictions were in good agreement with diuresis measured in a validation study conducted in 10 dogs, which were administered oral doses of 0.15, 0.4, 0.75, 1.5 and 4.5 mg/kg for 5 days. Finally, oral dose associated with the highest daily diuretic efficiency was predicted to be 0.1 mg/kg.

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

The effects of differences in the rate and composition of intravenous fluid replacement for urine loss on the pharmacokinetics and pharmacodynamics of torasemide were evaluated in rabbits. Each rabbit received 2-h constant intravenous infusion of 1 mg kg−1 torasemide with 0% replacement (treatment 1, n = 6), 50% replacement (treatment 2, n = 9), 100% replacement with lactated Ringer's solution (treatment 3, n = 8), and 100% replacement with 5% dextrose in water (treatment 4, n = 6). Total body (4.53, 5.72, 10.0 and 4.45 mL min−1 kg−1 for treatments 1–4, respectively) and renal clearance (1.44, 1.87, 6.78 and 1.72 mL min−1 kg−1) of torasemide, and total amount of unchanged torasemide excreted in 8-h urine (Ae 0–8 h: 694, 780, 1310 and 1040 μg) in treatment 3 were considerably faster and greater compared with treatments 1, 2 and 4. Although the difference in Ae 0–8 h between treatments 1 and 3 was only 88.8%, the diuretic and/or natriuretic effects of torasemide were markedly different among the four treatments. For example, the mean 8-h urine output was 101, 185, 808 and 589 mL for treatments 1–4, respectively, and the corresponding values for sodium excretion were 10.1, 20.6, 89.2 and 29.9 mmol, and for chloride excretion were 14.5, 27.9, 94.0 and 37.2 mmol. Although full fluid replacement was used in both treatments 3 and 4, the 8-h diuretic, natriuretic and chloruretic effects in treatment 3 were significantly greater compared with treatment 4, indicating the importance of the composition of fluid replacement. Both treatments 1 and 4 received no sodium replacement, however, the 8-h diuretic, natriuretic and chloruretic effects were significantly greater in treatment 4 compared with treatment 1, indicating the importance of rate of fluid replacement for the diuretic effects. Therefore, the 8-h diuretic, natriuretic and chloruretic effects were significantly greater in treatment 3 compared with treatments 1, 2 and 4, indicating the importance of full fluid and electrolyte replacement. Some implications for the bioequivalence evaluation of dosage forms of torasemide are discussed.

A study of the pharmacodynamic differences between immediate and extended release bumetanide formulations

Optimized bumetanide extended (ER) and immediate release (IR) formulations were developed using fluid bed layering and coating techniques. We postulated that the ER bumetanide formulation would have more effective and sustained diuretic and saluretic effects than IR. The diuretic/saluretic effects of both formulations were measured in rabbits (n=8) for two days after dosing with 1mg/kg bumetanide. During the first day, both formulations produced 2-3 times more urine volume and sodium excretion than baseline. In the first 24h, despite less bumetanide excretion from the ER formulation (101+/-13.9microg/kg compared to 146+/-14.6microg/kg for the IR formulation; P<0.04); the ER formulation produced diuresis and natriuresis that was equivalent to that of the IR formulation. In contrast, urine production in the IR formulation group fell below that of placebo controls on day 2. During the second day, the ER formulation was noted to produce persistent bumetanide excretion; the diuretic and natriuretic effects were not statistically significant from baseline control. We speculate that the decrease in response to bumetanide observed especially for the IR formulation during the second day may be due to the activation of compensatory counter-regulatory homeostatic mechanism(s). We conclude that the ER formulation had similar diuretic/saluretic effects but better drug excretion to urine production efficiencies than the IR formulation in the healthy rabbit model. The ER formulation, while providing comparable diuretic/saluretic effect to the IR formulation, offers the advantage of avoiding the initial, rapid and robust diuretic effect experienced with the IR formulations. Taken together, the data provide sufficient basis to warrant further investigation and refinement of our ER bumetanide formulation in humans.

Pharmacokinetics and pharmacodynamics of azosemide

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

Gastrointestinal first-pass effect of furosemide in rats

The first-pass effect of furosemide was investigated in rats. Furosemide intravenous solution (20 mg kg(-1) Lasix), was administered via the jugular vein and the portal vein, orally, and instilled directly into the duodenum of rats. The first-pass effects of furosemide by lung, heart, and liver seemed to be negligible in rats. The absolute bioavailability of furosemide was 28.9 and 48.3% after oral and intraduodenal administration, respectively. Based on the gastrointestinal (GI) recovery study, 68.3 and 69.5% of furosemide were found to have disappeared mainly due to absorption and/or metabolism from rat GI tract after oral and intraduodenal administration, respectively. The results indicate that gastrointestinal and intestinal first-pass effects of furosemide were approximately 40% (68.3-28.9%) and 20% (69.5-48.3%) of the dose, respectively.

Considerations on pharmacodynamics and pharmacokinetics: Can everything be explained by the extent of drug binding to its receptor?

It is frequently assumed that pharmacological responses depend solely on the extent of drug binding to its receptor according to the occupational theory. It is therefore presumed that the intensity of the effect is determined by drug concentration at its receptor site, yielding a unique concentration-effect relationship. However, when dependence, abstinence, and tolerance phenomena occur, as well as for pharmacological responses in vivo that are modulated by homeostatic mechanisms, the rate of drug input shifts the concentration-effect relationship. Hence, such responses cannot be explained on the sole basis of the extent of drug binding to its receptor. Information on the cellular and molecular processes involved in the generation of abstinence, dependence, and tolerance will undoubtedly result in the development of pharmacodynamic models allowing a satisfactory explanation of drug effects modulated by these phenomena. Notwithstanding, integrative physiology concepts are required to develop pharmacokinetic-pharmacodynamic models allowing the description of drug effects in an intact organism. It is therefore important to emphasize that integrative physiology cannot be neglected in pharmacology teaching and research, but should be considered as an equally valuable tool as molecular biology and other biomedical disciplines for the understanding of pharmacological effects.Key words: pharmacodynamics, pharmacokinetics, drug-receptor binding, occupational theory.

Pharmacokinetics of torsemide in patients with decompensated and compensated congestive heart failure

Plasma pharmacokinetics of oral furosemide have been shown to be influenced by degree of decompensation in patients with congestive heart failure (CHF). This open-label, sequential comparison trial was conducted to determine whether CHF decompensation also alters the pharmacokinetics and pharmacodynamics of torsemide. Twelve patients with CHF, defined by either hemodynamic parameters or clinical signs and symptoms, were enrolled. On admission for treatment of their CHF, the patients were given 100 mg oral torsemide (phase A). A second dose of oral torsemide 100 mg was administered after hemodynamic parameters and clinical signs and symptoms of decompensated CHF resolved (phase B). Plasma and urine samples were collected over a 24-hour period for determination of torsemide concentrations and urine sodium. Hemodynamic measurements and physical signs and symptoms also were evaluated. During phase A, patients had significantly greater urine output and fractional sodium excretion compared with phase B. A significant increase in the area under the plasma concentration-time curve (AUC) was observed during phase B compared with phase A. However, no significant differences in maximal excretion rate of torsemide were noted between phase A and phase B. Heart failure status slightly affects the plasma pharmacokinetics of torsemide; however, this does not significantly alter the maximal urinary excretion rate of torsemide.

Pharmacokinetics and pharmacodynamics of azosemide after intravenous and oral administration to rats: absorption from various GI segments

Azosemide, 5, 10, 20, and 30 mg/kg, was administered both intravenously and orally to determine the pharmacokinetics and pharmacodynamics of azosemide in rats (n = 7-12). The absorption of azosemide from various segments of GI tract and the reasons for the appearance of multiple peaks in plasma concentrations of azosemide after oral administration were also investigated. After intravenous (iv) dose, the pharmacokinetic parameters of azosemide such as t1/2. MRT, VSS, CL, CLR, and CLNR were found to be dose-dependent in the dose ranges studied. The percentages of the iv dose excreted in 8-hr urine as azosemide, MI (a metabolite of azosemide), glucuronide of azosemide, and glucuronide of MI-expressed in terms of azosemide-were also dose-dependent in the dose ranges studied. The data above suggest saturable metabolism of azosemide in rats. The measurements taken after the iv administrations such as the 8 hr urine output, the total amount of sodium and chloride excreted in 8-hr urine per 100 g body weight, and diuretic, natriuretic, kaluretic, and chloruretic efficiencies were also shown to be dose-dependent. However, the total amount of potassium excreted in 8-hr urine per 100 g body weight was dose-independent. Similar dose-dependency was also observed following oral administration. Azosemide was absorbed from all regions of GI tract studied and approximately 93.5, 79.1, 86.1, and 71.5% of the doses (5, 10, 20, and 30 mg/kg, respectively) were absorbed between 1 and 24 hr after oral administration. The appearance of multiple peaks after oral administration is suspected to be due mainly to the gastric emptying pattern. The percentages of azosemide absorbed from the GI tract as unchanged azosemide for up to 24 hr after oral doses of 5, 10, 20, and 30 mg/kg were significantly different with doses (decreased with increasing doses), suggesting that the problem of azosemide precipitating in acidic gastric juices or dissolution may have at least partially influenced the absorption of azosemide after oral administration.

Pharmacokinetics and pharmacodynamics of azosemide after intravenous and oral administration to rats with alloxan-induced diabetes mellitus

Because physiological changes occurring in diabetes mellitus patients could alter the pharmacokinetics and pharmacodynamics of the drugs used to treat the disease, the pharmacokinetics and pharmacodynamics of azosemide were investigated after intravenous and oral administration of the drug (10 mg kg-1) to control and alloxan-induced diabetes mellitus rats (AIDRs). After intravenous administration of azosemide to the AIDRs, the area under the plasma concentration-time curve (AUC) increased considerably (3120 compared with 2520 micrograms min mL-1; P < 0.135) and the total body clearance decreased considerably (3.20 compared with 3.96 mL min-1 kg-1; P < 0.0593). The considerable reduction in time-averaged total body clearance in the AIDRs was a result of the significant decrease in renal clearance (1.01 compared with 1.55 mL min-1 kg-1) in the AIDRs, the non-renal clearance being comparable between the two groups of rats. After intravenous administration, the 8-h urinary excretion of azosemide (29.5 compared with 40% of intravenous dose; P < 0.0883) and one of its metabolites, M1 (2.15 compared with 2.60% of intravenous dose, expressed in terms of azosemide; P < 0.05) decreased in the AIDRs because of the impaired kidney function. The diuretic, natriuretic, kaliuretic and chloruretic efficiencies increased significantly in the AIDRs. After oral administration of azosemide, AUC decreased significantly in the AIDRs (115 compared with 215 micrograms min mL-1) possibly because of the reduced gastrointestinal absorption of azosemide in the AIDRs. After oral administration of azosemide, the 8-h urine output decreased significantly in the AIDRs (9.32 compared with 16.1 mL per 100 g body weight) because of the significantly reduced 8-h urinary excretion of azosemide (3.00 compared with 9.14% of oral dose). After both intravenous and oral administration some pharmacokinetic and pharmacodynamic parameters of azosemide were significantly different in AIDRs.

Pharmacodynamic modeling of furosemide tolerance after multiple intravenous administration

OBJECTIVE

Physiologic indirect-response models have been proposed to account for the pharmacodynamics of drugs with an indirect mechanism of action, such as furosemide. However, they have not been applied to tolerance development. The aim of this study was to investigate the development of tolerance after multiple intravenous dosing of furosemide in healthy volunteers.

METHODS

Three repetitive doses of 30 mg furosemide were given as rapid intravenous infusions at 0, 4, and 8 hours to eight healthy volunteers. Urine samples were collected for a period up to 14 hours after the first dose. Volume and sodium losses were isovolumetrically replaced with an oral rehydration fluid.

RESULTS

Tolerance was demonstrated as a significant decrease in diuretic and natriuretic response over time. Total mean diuresis was 35% lower (p < 0.01) and total mean natriuresis was 52% lower (p < 0.0001) after the third dose of furosemide compared with the first dose. However, there were considerable interindividual variations in the rate and extent of tolerance development for both diuresis and natriuresis. Pharmacokinetic-pharmacodynamic modeling of tolerance development was performed with use of an indirect-response model with an additional "modifier" compartment. This model gave an accurate description of the diuretic and natriuretic data after multiple dosing of furosemide and enabled the estimation of a lag-time for tolerance and a rate constant for tolerance development. Physiologic counteraction was demonstrated as a significant increase in plasma active renin levels (p < 0.00001) and a decrease in atrial natriuretic peptide levels (p < 0.005) during the day, concomitantly with the development of a negative sodium balance. This may be viewed as physiologic reflections of the modifier in our model.

CONCLUSION

Indirect-response models may be successfully applied for tolerance modeling of drugs after multiple dosing.

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

The effects of differences in the rate and composition of intravenous (i.v.) fluid replacement for urine loss on the pharmacokinetics and pharmacodynamics of bumetanide were evaluated with rabbit as the animal model. Each rabbit received a 4-h constant i.v. infusion of bumetanide at 1 mg/kg with 0% replacement (treatment I, n = 8), 50% replacement (treatment II, n = 6), and 100% replacement (treatment III, n = 7) with lactated Ringer's solution, in addition, another group of rabbits received 100% replacement with 5% dextrose in water (D-5-W, treatment IV, n = 4). Some pharmacokinetic parameters, such as the apparent volume of distribution at steady-state, mean residence time, and terminal half-life, remained relatively unchanged in all four treatments. Renal clearance and urinary excretion rate of the drug in treatments I-III were essentially the same, but were considerably higher than those in treatment IV. In spite of the similarities in kinetic properties (approximately 40% difference between lowest and highest values), the diuretic and/or natriuretic effects of bumetanide were markedly different among the four treatments. For example, the mean 8-h urine output values were 189, 317, 2170, and 306 mL for treatments I-IV, respectively, the corresponding 8-h sodium excretion values were 9.19, 16.5, 88.8, and 15.7 mmol, and the chloride excretion values were 10.8, 33.7, 77.4, and 11.7 mmol. Except for treatment III, diuresis and/or natriuresis were time dependent, generally decreasing with time until reaching a low plateau during later hours of infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

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

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

Arterial and venous blood sampling in pharmacokinetic studies: azosemide in rabbits

The pharmacokinetics of azosemide were evaluated simultaneously using both arterial and venous plasma data in six rabbits after a rapid 5 s intravenous bolus dosing. Initial arterial to venous ratios at 5 s after injection were the highest with values of 81.1, 67.3, 58.7, 530, 2660, and 10.5 for rabbits 1-6, respectively. Both curves decayed, paralleling each other at the terminal phase, with the venous levels higher than the arterial levels by 15.3, 31.9, 34.1, 40.7, 30.5, and 16.5% for rabbits 1-6, respectively. An exponential term with a negative coefficient was used to account for the short and steep rising phase of venous plasma levels after injection. Detailed analysis showed significant differences in various pharmacokinetic parameters, such as initial volume of distribution, apparent volume of distribution at steady state, and mean residence time based on arterial or venous data. A plot of 1/Q (urine flow rate) versus 1/CLR (renal clearance) of azosemide yielded a straight line in six rabbits, indicating that the CLR of azosemide is urine flow dependent in rabbits.

Pharmacokinetics and pharmacodynamics of furosemide after intravenous and oral administration to spontaneously hypertensive rats and DOCA-salt-induced hypertensive rats

The pharmacokinetics and pharmacodynamics of furosemide were investigated after intravenous (i.v.), 1 mg/100 g body weight, and oral administration, 2 mg per 100 g body weight, to spontaneously hypertensive rats (SHRs) and deoxycorticosterone acetate-salt-induced hypertensive rats (DOCA-salt rats). After i.v. administration, the 8 h urinary excretion of furosemide/g kidney (397 versus 572 micrograms) was significantly lower and the non-renal clearance (5.78 versus 3.94 ml min-1 kg-1) was significantly faster in SHRs of 16 weeks of age than in age-matched control Wistar rats. This suggested that the non-renal metabolism of furosemide could be faster in SHRs of 16 weeks of age than in age-matched control Wistar rats, and this could be supported by the significantly greater amount of 4-chloro-5-sulphamoyl anthranilic acid, a metabolite of furosemide, excreted in 8 h urine as expressed in terms of furosemide (11.1 versus 4.79% of the i.v. dose) in SHRs. It could also be supported at least in part by a study of liver homogenate; the amount of furosemide remaining per gram of liver after 30 min incubation of 50 micrograms of furosemide with the 9000g supernatant fraction of liver homogenate was significantly smaller (40.4 versus 43.7 micrograms) in SHRs of 16 weeks of age than in age-matched Wistar rats. The greater metabolic activity of furosemide in liver may also be supported by the result that the amount of hepatic cytochrome P-450 (0.7013 versus 0.5186 nmol/mg protein) and the weights of liver (3.52 versus 2.93% of body weight) were significantly greater in SHRs of 16 weeks of age than in age-matched Wistar rats. After i.v. administration of furosemide, the 8 h urine output (9.93 versus 16.5 ml) and 8 h urinary excretion of sodium (1.21 versus 2.05 mmol) and chloride (1.37 versus 2.17 mmol) per gram of kidney in SHRs of 16 weeks of age were lower than those in age-matched Wistar rats, this could be due to the significantly smaller amount of furosemide excreted in 8 h urine per gram of kidney. After oral administration, the pharmacokinetics and pharmacodynamics of furosemide were not significantly different between SHRs and the control Wistar rats of 16 weeks of age. After i.v. and oral administration of furosemide, there were no significant differences in the pharmacokinetics and pharmacodynamics between DOCA-salt rats and control SD rats of 16 weeks of age except for the significantly lower urinary excretion of potassium per gram of kidney in DOCA-salt rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of water deprivation on the pharmacokinetics and pharmacodynamics of bumetanide in rats

The effects of temporary water deprivation for 48 h on the pharmacokinetics and pharmacodynamics of bumetanide were examined after intravenous (i.v.) administration of bumetanide, 8 mg kg-1 to control and water deprived rats (n = 7). The values of AUC, t1/2 and MRT increased 79.0, 417, and 633 per cent, respectively, and CL and CLNR decreased 44.0 and 41.2 per cent, respectively, in water deprived rats. They were all significantly different. The decreased CLNR in water deprived rats could be due to decreased nonrenal metabolism of bumetanide; it could be supported that the amounts of glucuronide conjugate of bumetanide (52.5 vs 12.9 micrograms), desbutylbumetanide (170 vs 113 micrograms) and its glucuronide conjugation (191 vs 125 micrograms), and sum of the three metabolites (414 vs 229 micrograms), which are expressed in terms of bumetanide excreted in 24 h urine, decreased significantly in water deprived rats. The 8-h urine outputs per 100 g body weight (4.32 vs 1.34 ml) also reduced significantly in water deprived rats, and it might be due to significantly reduced amounts of bumetanide excreted in 8 h urine (90.9 vs 25.7 micrograms) and/or reduced kidney function in water deprived rats. The kidney function based on CLIot (9.87 vs 2.14 ml min-1 kg-1) reduced significantly in water deprived rats. The 8-h urinary excretions of sodium (0.430 vs 0.0818 mmol), potassium (0.567 vs 0.270 mmol), and chloride (0.549 vs 0.0624 mmol) per 100 g body weight also reduced significantly in water deprived rats.

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

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

Optimization of the therapeutic index by adjustment of the rate of drug administration or use of drug combinations: exploratory studies of diuretics

The purpose of this investigation was to explore theoretically certain strategies for optimizing the therapeutic index of drugs and to assess these strategies experimentally with two diuretics. Diuretic agents allow dosing rate flexibilities because the temporal profile of diuretic action can vary considerably as long as the total diuretic effect per day is the same. They can also be used in combination. Experiments were designed to determine if the therapeutic index of furosemide and hydrochlorothiazide can be optimized by administering one or the other at a certain rate or by administering the two drugs together in a certain ratio and at a certain rate. Male Lewis rats received one or the other drug, or combinations of the two, by i.v. infusion at different rates. Several timed urine collections were made under steady-state conditions, with excreted urine replaced volume for volume by i.v. lactated Ringer's solution. The urine flow rates and the urinary excretion rates of the diuretics and of Na+ and K+ were determined. The relationship between the diuretic effect of either of the two drugs given alone and the respective drug excretion rate could be described by the Hill equation. The ratio of urine flow rate to K+ excretion rate exhibited a marked dependence on hydrochlorothiazide excretion rate (highest ratio at high excretion rates), whereas the K+/Na+ excretion rate ratio was constant over a wide range of hydrochlorothiazide excretion rates. There was no significant change of these ratios with changing excretion rate of furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.