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The pharmacokinetics and pharmacodynamics of furosemide were compared after an oral administration or a direct administration of Lasix into the duodenum in humans (40 mg). Furosemide was absorbed quickly after a direct administration of Lasix into the duodenum; the peak plasma concentration of furosemide was reached within 1 h in both routes of administration, and the peak concentration was higher in all four subjects after a direct administration into the duodenum than after an oral administration. Furosemide was absorbed considerably after a direct administration of Lasix into the duodenum; the values of the area under the plasma concentration-time curves of furosemide from time zero to 4 h (AUC0-4 h, 93.6 versus 122 micrograms min mL-1, p < 0.123) and the cumulative amounts of the dose excreted in 8 h (10,600 versus 15,000 micrograms, p < 0.0185) and 24 h (11,300 versus 15,400 micrograms, p < 0.0192) urine as unchanged furosemide were significantly higher after a direct administration into the duodenum than after an oral administration. However, the amounts excreted in urine as glucuronide conjugates, a metabolite of furosemide, tended to increase after an oral administration (4030 versus 1670 micrograms as expressed in terms of furosemide, p < 0.0858) when compared to a direct administration into the duodenum, possibly due to the increased gastric first-pass metabolism of furosemide. The 8 h urine output and 8 h urinary excretion of sodium did not increase significantly after a direct administration of Lasix into the duodenum, despite the significantly greater amount of the drug delivered to the active site after a direct administration into the duodenum. This could be explained by the fact that the urinary excretion rates of furosemide after a direct administration into the stomach were closer to the values of maximally efficient urinary excretion rate of furosemide during the 8 h experimental period than after a direct administration into the duodenum.

Aims: The aim of the present study was to investigate the influence of the rate of delivery of frusemide to its site of action on the effect and efficiency of the drug., Methods: Frusemide 30 mg was administered as a bolus dose, a slow-rate infusion and a bolus dose in combination with 2 g of probenecid in a three way cross-over design to seven healthy volunteers. Urinary volume and contents of frusemide and sodium were measured in samples collected over 10 h., Results: Total natriuretic response was 40% higher (P < 0.001) after the infusion and 20% higher (P < 0.05) after the combined treatment with probenecid, as compared with the bolus dose. Total natriuretic efficiency did not differ between the infusion (0.013 mmol microg(-1)) and the combined treatment with probenecid (0.015 mmol microg(-1)), but was significantly higher as compared with the bolus dose (0.009 mmol microg(-1)). Natriuretic effect data were modeled according to the sigmoid Emax model and the frusemide excretion rate with maximum efficiency (ER(effmax)) was calculated from the estimated parameters. For both the frusemide infusion and the combined treatment with probenecid, the time course of delivery of frusemide into the urine consistently approached ER(effmax) more closely than was the case for the bolus dose. The natriuretic effect vs frusemide excretion rate curves were shifted to the right, and the estimated values of the sigmoid Emax model were higher for EC50 and lower for the slope factor after the bolus dose, which may indicate tolerance development for this treatment., Conclusions: Slowing the delivery of frusemide to the site of action increased the efficiency of the drug, leading to an increased natriuretic response.

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

The tubular site of furosemide (F) action was studied by the technique of diuretic microinjection (MIJ) into proximal tubules of the rat nephron. F was injected into the last proximal superficial loop of 51 proximal tubules, at the concentration of 3 x 10(-4) mol/l in an infusate that contained 14C-inulin. Collections were performed at the early distal tubule before and after MIJ. Single nephron filtration rate (SNGFR) remained unchanged, while the percent of filtered volume reabsorbed up to the site of collection was 85+/-2 before, 79+/-2% after MIJ, p < 0.005. The calculated concentration of F in the collected distal tubular fluid during the post-MIJ measurements averaged 3 x 10(-5) mol/l. This experiment was repeated by injecting F into the early proximal convolutions of 43 nephrons, while the collections were performed at the last proximal segments. In these studies of proximal volume absorption, SNGFR was 34+/-3 before, 35+/-4 nl/min after F (p > 0.6). The respective percent reabsorptions were 70+/-3 and 73+/-3% (p +/- 0.3). In order to determine whether the technique per se was suitable to detect changes in reabsorption, the proximal MIJ study was repeated by using the carbonic anhydrase inhibitor dichlorphenamide 3 x 10(-5) mol/l in the microinjectate: while SNGFR remained unchanged, percent reabsorption fell from 63+/-5 to 45+/-7% during injection of the diuretic, p < 0.03. We conclude that the technique is adequate to examine the effects of drugs, and that F does not reduce proximal volume absorption at concentrations of 3 x 10(-5) mol/l. The loop diuretic decreases distal volume absorption by abolishing the osmotic gradient between blood and tubular fluid along the early distal convoluted tubule.

Furosemide is a problematic drug in a prolonged-release product because its absorption is site specific, taking place mainly in the upper parts of the alimentary tract. The aim of the study reported here was to develop prolonged-release furosemide formulations for dogs. The type of preparation selected was a hydroxypropyl methylcellulose (HPMC) matrix tablet. Evaluation was based on dissolution studies, on in vivo disintegration studies in the canine stomach and on bioavailability studies in Beagle dogs. The variables tested were the viscosity grade of the polymer, the amount of polymer and presence or absence of an alkaline compound (potassium carbonate) in the formulation. When potassium carbonate was included, furosemide was absorbed so slowly that drug administration once daily would give plateau drug plasma concentrations, even though the elimination half-life of furosemide is only about one hour. In vitro dissolution tests gave a wrong indication of the in vivo behaviour of the products. Thus, in vivo studies are important from the very beginning in the development of new drug products for dogs.

We describe a 39 years old patient with a history of chronic symptomatic hypokalemia. She denied taking any drugs. She satisfied the clinical criteria for Bartter's syndrome and more precisely for Gitelman's syndrome: hypokalemia in the presence of inappropriately high potassium excretion, metabolic alkalosis, hyperreninemic hyperaldosteronism, hypomagnesemia with inappropriately high magnesium excretion, normocalcemia, hypocalciuria and normal blood pressure. A HPLC analysis detected the presence of furosemide in urine and chlorthalidone in urine and plasma samples. After the self administration of diuretics was stopped, the above alterations came back to normality. Prior to the verification of a self administration of diuretics, the patient showed clinical and biochemical parameters that oriented to surreptitious diuretic ingestion (Pseudo-Bartter's syndrome) not to Bartter's syndrome or Gitelman's syndrome, particularly the plasma potassium readily restored to normal by the administration of potassium chloride supplements, the increased plasma uric acid with low uric acid fractional clearance, the widely different urine and plasma electrolyte levels and the presence psychiatric disorders. The literature is reviewed and differential diagnosis, among this three syndromes, is made.

The separation and determination of amiloride, metoprolol, deacetylmetipranolol, labetalol and furosemide in human serum and urine by capillary isotachophoresis were investigated. Amiloride and beta-blockers were separated by cationic isotachophoresis in the electrolyte system sodium morpholinoethanesulfonate buffer (pH 5.5) (cL = 10 mM)-glutamic acid. Furosemide was separated using the anionic electrolyte system histidine hydrochloride buffer (pH 6.2) (cL = 10 mM)-morpholinopropanesulfonic acid. Endogenous and the possible exogenous compounds were almost totally removed from serum and urine by solid-phase extraction using a Separon SGX C18 cartridge. The recovery of compounds varied from 98.2 to 103.2%. The linearity range for the compounds was 50-1000 ng/ml. The relative standard deviations varied from 0.1 to 5.6%. The overall limits of determination ranged from 32 to 46 ng/ml of urine and from 39 to 46 ng/ml of serum, depending of the type of drugs.

To test the hypothesis that renal sympathetic nerves influence the renal and renin responses to furosemide in conscious newborn animals, experiments were carried out in chronically instrumented lambs with either bilateral renal denervation (denervated, n = 7, age = 13 +/- 3 (SD) days) or intact renal sympathetic nerves (intact, n = 6, age = 13 +/- 4 (SD) days), at least 4 days after surgery. Basal glomerular filtration rate (GFR), urinary flow, and sodium excretion rates were similar in intact and denervated lambs (p > 0.5). A prompt diuretic and natriuretic response and a decrease in GFR occurred after i.v. furosemide (2 mg/kg); these responses were similar in intact and denervated lambs. Basal plasma renin activity (PRA) was not altered by renal denervation. PRA increased 10 min after furosemide (p < 0.001) and remained elevated at 90 min; the response was similar in both groups of lambs. Basal plasma aldosterone levels were elevated in denervated (191 +/- 232 (SD) pg/mL) compared with intact lambs (62 +/- 24 (SD) pg/mL). Plasma aldosterone levels increased after furosemide administration in both groups of animals. These data provide evidence to suggest that renal sympathetic nerves do not appear to modulate the renal and endocrine responses to furosemide, at least at a dose of 2 mg/kg. Our observations also support the premise that early in life, aldosterone counteracts the effects of renal denervation on fluid and electrolyte homeostasis.

The plasma concentration profile, urinary excretion rate and diuretic response were studied in anaesthetized dogs after an intravenous administration of torasemide or furosemide. The urinary excretion rate of furosemide decreased rapidly after administration. The plasma concentration, which is related to the urinary excretion profile, also decreased rapidly. The diuretic response, which reflected the excretion rate, occurred rapidly after administration but lasted for a short time. The urinary excretion rate of torasemide was much lower than that of furosemide and decreased slowly after administration. The plasma concentration also decreased slowly. The diuretic response to torasemide occurred more slowly but lasted longer than the response to furosemide. These results suggest that the diuretic response profile of either diuretic depends on their urinary excretion rate, and that the difference in the diuretic response between torasemide and furosemide may be explained by the different transfer rate of the drugs from the plasma to the nephron.

Two kinds of dosage forms (tablets and retarded capsules) of furosemide (F) were compared in vitro dissolution profile and in vivo absorption studies. The dissolution of F from retarded capsules was extremely restricted in the first fluid of the JP XII disintegration test (within 0.8%), while the dissolution of F from tablets and retarded capsules in the second fluid of JP XII disintegration test were both complete. Metabolite specific assay of F showed F, conjugation of F with glucuronic acid (FG) and acyl migration isomers of FG (FG-iso) in urine or plasma. The mean cumulative urinary excretion of F following administration of the tablets during 24 h was twice that of retarded capsules. The mean area under the plasma concentration-time curve (AUC) of F following administration of tablets was 1.5 times that of retarded capsules. The mean cumulative urine volume during 24 h, however, was not significantly different between the two dosage forms. Clockwise hysteresis relationships between the diuretic response and the urinary excretion rate of F was observed after administration of retarded capsules. A straight relation between logarithm of the diuresis and logarithm of the urinary excretion of F was observed after maximum excretion rate of F following administration of both dosage forms.

The site where furosemide is metabolized and the location where probenecid reduces furosemide metabolism remain poorly defined. The liver appears to play a minor role, and there is indirect evidence suggesting that the kidneys could be responsible for the metabolism of furosemide. To assess the role of the kidneys in the metabolism of furosemide, its intravenous kinetics have been studied in control and anephric rabbits, after the ligation of the renal pedicles. Two additional groups of rabbits, control and anephric, have received probenecid before the administration of furosemide. In the control group, the total clearance of furosemide was 18.65 +/- 1.01 mL/ min per kg; urinary and metabolic clearances of furosemide were 7.95 +/- 0.65 and 10.70 +/- 1.11 mL/min per kg, respectively. In anephric rabbits, total clearance was reduced by 85% to 2.69 +/- 0.26 mL/min per kg (P < 0.001), secondary to the abolition of furosemide renal excretion and to the reduction in metabolic clearance from 10.70 +/- 1.11 to 2.69 +/- 0.26 mL/min per kg (P < 0.001). The pretreatment with probenecid reduced the total clearance of furosemide by 80%, to 3.62 +/- 0.24 mL/min per kg (P < 0.001), because of a reduction of 90 and 75% in urinary and metabolic clearances, respectively. The administration of probenecid to anephric rabbits did not reduce further the metabolic clearance. It is concluded that the kidneys are responsible for 85% of furosemide total clearance, either via excretion (43%) or biotransformation (42%), and that probenecid inhibits both processes.

A high-performance liquid chromatographic method with electrochemical detection (ED) has been developed for the determination of two diuretics: 4-phenoxy-3-(1-pyrrolidinyl)-5-sulfamoylbenzoic acid (piretanide) and 4-chloro-2-furfurylamino-5-sulfamoylbenzoic acid (furosemide). The chromatographic separation was performed on a mu Bondapak C18 column with a mobile phase of acetonitrile-water (40:60) containing 5 mM KH2PO4/K2HPO4 and with a flow-rate of 1 ml/min (69 bar). The temperature was optimized at 30 +/- 0.2 degrees C. The amperometric detector equipped with a glassy carbon electrode was operated at +1200 mV versus Ag/AgCl in the direct current mode. The method was applied to the determination of these compounds in two concentration ranges (ppm and ppb), obtaining a reproducibility in terms of relative standard deviations lower than 1% for within-day and 4% for day-to-day and determination limits of 15 ppb for both compounds. Recoveries greater than 90% were obtained for spiked urine samples, using a liquid-liquid extraction method in the sample clean-up procedure. The LC-ED method was applied to commercially available pharmaceuticals (Seguril, furosemide 40 mg, and Perbilén, piretanide 6 mg) and urine samples obtained from healthy volunteers and hypertensive patients.

A 4.5-year-old boy was admitted to three different hospitals because of a tendency towards dehydration and polyuria, along with normal blood pressure, hypochloraemia, hypokalaemia, metabolic alkalosis and an impaired urinary concentrating ability. A renal biopsy failed to reveal juxtaglomerular hyperplasia. The clinical and laboratory findings failed to improve despite supplementation with potassium chloride and treatment with indomethacin. The urine was found to contain frusemide. The parents denied any drug administration to the boy. The child is now doing well more than 1 year after separation from his mother. Since ingestion of diuretic cannot be differentiated from true Bartter syndrome by blood and urinary electrolyte measurements alone, a diuretic screen is warranted in children with findings consistent with Bartter syndrome.

To examine the diuretic and natriuretic synergism between bendroflumethiazide (BFTZ) and furosemide (FUR), the acute diuretic and natriuretic response to BFTZ was compared when given alone, during acute and during chronic FUR infusion. Responses to diuretics were assessed in conscious, chronically instrumented rats and, to avoid confounding influences of diuretic-induced volume contraction, extracellular fluid volume was kept constant by a computer-driven servo-control technique. Two groups were pretreated with osmotic minipumps chronically infusing either FUR (0.25 mg/hr; group CF; n = 9) or vehicle (8% ethanolamine; group CV; n = 8) i.p. for 7 days before the experiment. During the experiment, two other groups received either acute infusion with FUR (0.25 mg/hr; group AF; n = 16) or acute infusion with vehicle (150 mM glucose; group AV; n = 11). After a 60-min control period, BFTZ (0.083 mg; 0.25 mg/hr) was administered for 90 min to all four groups. Whereas the diuretic and natriuretic response to BFTZ was similar in groups AF, AV and CV, a supra-additive response was observed in the CF group (vs. group CV: delta urine flow rate: +78%; delta urinary Na excretion: +69%). BFTZ had no effect on the fractional excretion of Li, which suggests that the supra-additive effect was due to inhibition of an enhanced distal tubular Na reabsorption induced by chronic FUR administration. Because before BFTZ administration urinary Na excretion was 3-fold higher during acute than during chronic FUR infusion, an increased delivery of NaCl to the thiazide segment cannot by itself explain the exaggerated BFTZ response during chronic FUR treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of oral probenecid (1 g) on the pharmacokinetics of frusemide (80 mg p.o.) and its acyl glucuronide was studied in nine healthy subjects. Probenecid significantly increased the t1/2,z of frusemide from 2.01 +/- 0.68 to 3.40 +/- 1.48 h (P = 0.0015) and significantly decreased oral clearance from 164 +/- 67.0 to 58.3 +/- 28.1 ml min-1 (P = 0.0001). No effect of probenecid on the plasma protein binding of frusemide was detected. Probenecid significantly increased the tmax of the metabolite frusemide acyl glucuronide from 1.4 to 2.6 h, but had no effect on the tlag, Cmax, t1/2,z and plasma protein binding. The urinary recoveries of unchanged frusemide (39.2 +/- 10.2 vs 34.4 +/- 8.6%, P = 0.28) and its acyl glucuronide (12.1 +/- 2.7 vs 11.8 +/- 3.7%, P > 0.8) were not altered by probenecid. However, probenecid decreased the renal clearance of both frusemide (128 +/- 49 vs 44.0 +/- 18.6 ml min-1, P = 0.0002) and the acyl glucuronide (552 +/- 298 vs 158 +/- 94.0 ml min-1, P < 0.0001). The non-renal clearance of frusemide (36.7 +/- 21.0 vs 15.2 +/- 13.4 ml min-1, P = 0.0068) was also decreased. The clinical relevance of the study relates to the possible conjugation of frusemide in the kidney and the role of the conjugate in the pharmacodynamic effect.

Diuretic drugs have been reported to alter the glomerular filtration rate and possibly the creatinine excretion by the kidneys. We evaluated the effects of single doses of diuretic drugs on creatinine clearance determination. Ten healthy volunteers were randomized to receive either oral hydrochlorothiazide, oral furosemide, intravenous furosemide, or no treatment in a cross-over fashion during four separate test days with 6-day washout periods. Urine and blood specimens were collected during 24 h after the treatments. Specimens were assayed for creatinine, and the creatinine clearance corresponding to the 4-, 6-, 12-, and 24-h urine collections were calculated. Analysis of variance did not show a statistically significant effect of the diuretic regimens on creatinine clearance over these periods. This study demonstrates that single doses of diuretic drugs do not have significant effect on creatinine clearance determination using urine collected during 4-24-h periods.

The gastrointestinal absorption of furosemide preadsorbed onto activated charcoal was studied in 8 healthy volunteers using a randomized cross-over design with 3 phases. The 3 experimental furosemide formulations were capsules containing 40 mg furosemide only (reference) or 100 mg furosemide preadsorbed onto 160 mg or 200 mg charcoal. Timed plasma samples were taken and urine was collected for 24 hours for determination of drug concentrations and diuretic response. The release of furosemide from the formulations was also studied in vitro. Furosemide was found to dissolve rapidly from the reference formulation, whereas it was slowly desorbed from charcoal with the cumulative release reaching 50-60% in 24 hours (pH 5.3). The absorption rate of furosemide was smaller after intake of the charcoal formulations that after intake of the reference formulation. However, also the amounts of furosemide found in plasma and urine were clearly decreased due to preadsorption onto charcoal. The dose-adjusted relative bioavailabilities of the furosemide-charcoal formulations (compared to the reference formulation) remained less than 10%. The release mechanism of furosemide from charcoal is sensitive to physiological factors of the gastrointestinal tract. The large variability known to be typical for furosemide absorption was further increased when the drug was preadsorbed onto charcoal.

Carbonic anhydrase (CA)-immobilized aminopropyl silica precolumn was developed for direct injection determination of certain sulphonamide drugs in biological fluids by column-switching (CS) high-performance liquid chromatography. Under the optimized conditions, only the sulphonamide drugs with an unsubstituted sulphonamide group were retained on the CA precolumn and separated on a reversed-phase analytical column. Of these, the retention of hydrochlorothiazide (HCT), chlorothiazide, acetazolamide, furosemide (FS) and chlorthalidone was almost quantitative. The peak area of HCT was proportional to the concentration in the range of 1-100 nmol/mL with relative standard deviations of 3.7% (5 nmol/mL) and 0.7% (100 nmol/mL). This CS system was applied to urine and plasma samples spiked with HCT and FS. Endogenous components of these were effectively removed, and HCT and FS were selectively retained on the CA precolumn. Almost quantitative recoveries and reproducibility were obtained.

Analytical procedures were developed to monitor furosemide concentrations in post-race serum and urine samples obtained from horses participating in an exercise-induced pulmonary haemorrhage (EIPH) program. High performance liquid chromatography with ultraviolet light detection proved a reliable, sensitive method for measuring urinary furosemide concentrations up to 12 h after administration of either 150 or 250 mg of the drug to race horses. However, this method was unreliable for determination of serum furosemide concentration. High performance liquid chromatography with fluorescence detection proved a reliable, sensitive method for measuring serum furosemide concentration in horses administered 250 mg of the diuretic, permitting detection of approximately 5-10 ng/ml 6 h after treatment. This method was applied to field conditions where furosemide was administered to horses (between 150 and 250 mg intravenously) 4 h prior to the race. Analytical results assisted in establishing a threshold concentration of 85 ng/ml for serum furosemide. It was found that serum furosemide concentrations are a valid measure of compliance with furosemide administration in the EIPH program.

The influence of age on the time-dependent difference in urinary excretion of furosemide, a loop diuretic agent, was examined in this longitudinal study. Male Wistar rats were maintained under conditions of light from 07:00 to 19:00 h and dark from 19:00 to 07:00 h. Furosemide (30 mg/kg) was given orally at 12:00 h (day trial) or 00:00 h (night trial) to rats at 3 months of age, and urine was collected for 8 h after dosage. Thereafter, the identical protocol was repeated using the same animals at 6, 9, 12, 15, 18, and 21 months of age. The urinary excretion of furosemide was significantly greater in the day than in the night trial at 3 months of age. Such a time-dependent difference was observed for up to 15 months, but disappeared at 18 and 21 months of age. The time-dependent difference in urinary excretion of furosemide (day trial - night trial) decreased gradually throughout the observation period of the study. These results suggest that the time-dependent difference in the urinary excretion of furosemide diminishes during the aging process and disappears by 18 months of age in male Wistar rats.

We have recently demonstrated that the time-dependent difference in urinary excretion of furosemide, a loop diuretic, diminishes during the aging process and disappears by 18 months of age in rats. The present study was undertaken to examine whether the amplitude of the daily variations in the urinary excretion of furosemide or their pattern, or both, are influenced in aged animals. Young (3 months of age) and aged (30 months of age) Wistar rats were maintained under conditions of light from 7 am to 7 pm and dark from 7 pm to 7 am. Furosemide (30 mg/kg) was given orally at 4 am, 8 am, 12 am, 4 pm, 8 pm or 12 pm. Urine was collected for 8 hours after furosemide administration and urinary excretion of furosemide was determined. There were significant daily variations in the urinary furosemide and the urine volume with the peak at 8 am and the trough at 12 pm in both groups of rats. The differences in these parameters between the 8 am and 12 pm trials were significantly smaller in the aged than in the young rats. These results suggest that the age-related alteration in the time-dependent phenomenon of furosemide is caused by the decreased amplitude of the daily variation in the urinary furosemide excretion and its diuretic effect.

Circadian variations in the adrenergic nervous system have been reported to be altered by chronic treatment with clorgyline, a monoamine-oxidase inhibitor. In the present study, the influence of clorgyline on the chronopharmacology of furosemide, a loop diuretic agent, was examined in rats maintained under conditions of light from 7 am to 7 pm and dark from 7 pm to 7 am. Clorgyline (4 mg/kg/day) or its vehicle alone was infused subcutaneously by osmotic minipumps for 14 days. Furosemide (30 mg/kg) was given orally at 12 am [noon (N)] or 12 pm [midnight (M)]. Urine was collected for 8 hours after the agent, and urinary excretions of sodium and furosemide were determined. Urine volume and urinary excretions of sodium and furosemide were significantly greater at 12 N than at 12 M in the vehicle-infused group of rats. However these administration time-dependent changes in the effects of furosemide and its urinary excretion disappeared in the clorgyline-infused animals. These results suggest that the mode of the diurnal variation in the effects of furosemide is altered by chronic treatment with clorgyline. As chronic clorgyline is considered to disturb the adrenergic nervous system, the present findings are compatible with the hypothesis that this system is involved in the mechanism responsible for the time-dependent change in the effects of furosemide.

Daily variation in the effects of furosemide, a loop diuretic agent, was examined in Wistar rats maintained under conditions of light from 7 a.m. to 7 p.m. and dark from 7 p.m. to 7 a.m. Furosemide (30 mg/kg) was given orally at 12 p.m., 4 a.m., 8 a.m., 12 a.m., 4 p.m. or 8 p.m. Urine was collected for 8 hr after furosemide administration, and urinary excretions of sodium and furosemide were determined. There were significant daily variations in the urine volume and urinary excretions of sodium and furosemide with a peak at 8 a.m. and a trough at 12 p.m. Significant correlations were observed between the urinary amount of furosemide and its diuretic effects (urine volume and urinary sodium excretion). These results suggest that the diuretic effects of furosemide show daily variations which are, at least in part, caused by the daily variation in the urinary excretion of furosemide.

The use of micellar liquid chromatography for the determination of diuretics in urine by direct injection of the sample into the chromatographic system is discussed. The retention of the urine matrix at the beginning of the chromatograms was observed for different sodium dodecyl sulphate (SDS) mobile phases. The eluent strengths of a hybrid SDS-methanol micellar mobile phase for several diuretics were compared and related to the stationary phase/water partition coefficient with a purely micellar mobile phase. The urine band was appreciably narrower with a mobile phase of 0.05 M SDS-5% methanol (v/v) at 50 degrees C (pH 6.9). With this mobile phase the determination of bendroflumethiazide and chlorthalidone was adequate. Acetazolamide, ethacrynic acid, furosemide, hydrochlorothiazide and probenecid were overlapped by the urine matrix, and the retention of amiloride and triamterene was too long.

The authors have previously reported the time-dependent change in the diuretic effects of furosemide, a loop diuretic agent, in young and middle-aged subjects. The current study was undertaken to examine an influence of aging on this chronopharmacologic phenomenon. Ten milligrams furosemide was given intravenously to 12 elderly subjects (greater than 70 years of age) at 9:00 AM (day trial) or at 9:00 PM (night trial) by a cross-over design. One-hour urine samples were collected for 3 hours after each administration, and urine volume and urinary excretions of sodium and furosemide were determined. Urine volume and urinary sodium excretion increased after furosemide administration. Contrary to the findings in the young and middle-aged subjects, no significant differences were observed in these parameters at any observation period between the day and night trials in the elderly subjects. Urinary furosemide excretion of the day and night trials did not significantly differ. These results suggest that the chronopharmacologic profiles of furosemide are altered in the elderly.

This study was undertaken to determine the applicability of plasma concentration of furosemide and specific gravity (SG) of urine in regulating the use of furosemide administered 4 hours prior to race time in Exercise-Induced Pulmonary Hemorrhage (EIPH) race horses. Nonbleeders (CTL) and certified bleeders (FUR) actively racing in Illinois (IL) and Pennsylvania (PA) were used in the study. Various doses (less than 250, 250, 300, 350, 400 and 500 mg) were administered either as a single intravenous (IV) dose or as a combination (IV-IM) of IV and intramuscular (IM) administrations 4 hours before race time. Plasma and urine samples were obtained post race for determination of furosemide concentration in plasma and measurement of SG of the urine in both CTL and FUR groups. Plasma samples were analyzed for furosemide using High Performance Liquid Chromatography with Fluorescence Detection. SG was measured using a digital refractometer. The results indicate a significant difference (p less than 0.0001) in the SG of the urine samples between the CTL and FUR groups irrespective of the route of administration (IV versus IV-IM). However, SG values of the urine in some CTL samples were lower than those in some FUR samples and vice versa. Thus, the use of SG alone is not reliable for predicting either the dose or the administration of furosemide to race horses. The plasma concentrations of furosemide following the administration (IV) of 250 mg or 500 mg 4 hours prior to race time were indistinguishable (25.91 +/- 4.45 versus 28.12 +/- 6.99 ng/ml, respectively); the majority of the horses in the groups had a plasma concentration of less than 40 ng/ml. When taken in total, plasma concentration of furosemide can only be used as a guide in regulating the administration of furosemide to race horses.

1. The effect of variability of gastric emptying and oro-caecal transit on the absorption of a multicomponent solution of frusemide, atenolol, hydrochlorthiazide and salicylic acid has been studied in six healthy subjects. Each subject was studied on five separate occasions: three times under basal conditions, once following metoclopramide and once following codeine pretreatment in an attempt to speed and slow transit respectively. 2. Inter-subject variability of gastric emptying, oro-caecal transit and the rate and extent of drug absorption was considerable. 3. The absorption of salicylic acid appeared rate-limited by gastric emptying but the rate and extent of frusemide, atenolol and hydrochlorthiazide absorption were unrelated to measures of gastric emptying or oro-caecal transit. 4. Codeine phosphate caused a two-fold delay in oro-caecal transit but did not influence gastric emptying while metoclopramide had no significant effect on either function. 5. Metoclopramide and codeine had no significant effect on the rate or extent of absorption of any of the study drugs. 6. Within the limits of this experiment, oro-caecal transit time did not appear to be an important determinant of frusemide, atenolol, hydrochlorothiazide or salicylic acid absorption. Other factors must account for the observed variability in drug absorption.

1. We have studied the effects of a non-absorbable osmotic load on the absorption of a multicomponent solution of frusemide, atenolol, hydrochlorothiazide and salicylic acid in six healthy volunteers. 2. Each subject was studied on up to four separate occasions. The drugs were administered in one of four solutions: a) a mannitol/electrolyte solution, b) a double-strength mannitol/electrolyte solution, c) a glucose/electrolyte solution and d) water. Lactulose or sulphasalazine were added as oro-caecal transit markers. Lactulose was included in the mannitol- and glucose-based solutions, adding a further non-absorbable osmotic load, and sulphasalazine was added to the water, adding little osmotic load. 3. The absorption of atenolol and hydrochlorothiazide was two- to three-times less from all lactulose-containing solutions than from the sulphasalazine-containing solution. The absorption of frusemide and salicylic acid was similar from all four solutions. 4. The largest non-absorbable osmotic load impaired the absorption of atenolol and hydrochlorothiazide most and the incorporation of glucose only partly restored absorption. 5. These results suggest that transmucosal water movement is an important determinant of atenolol and hydrochlorothiazide absorption but is less relevant for the absorption of frusemide and salicylic acid. Furthermore, these data demonstrate a previously unrecognised interaction between a commonly prescribed laxative--lactulose, and atenolol and hydrochlorothiazide.

1. Frusemide was given at a dose of 60 mg as two oral controlled release (CR) formulations and as plain tablets in a randomised, balanced, three way cross over design to 26 healthy volunteers. Urinary volume, and contents of frusemide, sodium, chloride and potassium were measured in samples taken over 24 h. 2. There was a marked difference between the CR formulations on one hand and the plain tablets on the other, in excretion of frusemide and diuresis vs time. The total diuretic/saluretic effect was only marginally lower (19 and 28% respectively, P less than 0.05) after CR compared with plain tablets although the fraction absorbed was markedly decreased (39 and 51% lower, respectively, P less than 0.05), estimated as urinary recovery of frusemide. The total diuresis of the two CR formulations did not differ although the urinary recovery was significantly different (P less than 0.05). 3. The diuretic effect vs frusemide excretion rate showed minimal counter-clockwise hysteresis after plain tablets while the CR formulations produced clockwise hysteresis indicating tolerance. 4. In agreement with the concept of efficiency, the higher diuretic/saluretic effect per amount of excreted frusemide may be a consequence of the slower output of frusemide in urine with the CR formulations compared with plain tablets. The major part of the pharmacological effect was produced with a higher efficiency after CR compared with plain tablets. It should be noted that the pharmacokinetics of a drug and its pharmacodynamic potency independently determine the total response.(ABSTRACT TRUNCATED AT 250 WORDS)

A rapid and simple external-standard high-performance liquid chromatographic (HPLC) method has been developed for the determination of the concentration of furosemide in plasma. The analyte is extracted with a C-2 ethyl sorbent. On-line elution of the analyte into the HPLC system is accomplished with an advanced automated sample processor (Varian). Furosemide is quantified by fluorescence detection within a linear range of 25 to 1000 ng/mL (average correlation coefficient, 0.9998), with a limit of detection of 1.8 ng/mL. Both internal- and external-standard procedures were evaluated, and the external-standard procedure demonstrated superior characteristics. The external-standard procedure was precise to within a relative standard deviation of 8% and accurate with less than 3% error throughout the concentration range studied. The external-standard HPLC method was used to analyze the concentration of furosemide in greater than 1000 plasma samples obtained from patients with either normal kidney function or renal failure who had received furosemide either orally or intravenously in an experimental setting.

To investigate the influence of the presence of oedema on the pharmacokinetics and pharmacodynamics of furosemide (frusemide) we selected 9 hospitalised patients (mean age 70.3 years, range 59 to 84 years) with severe congestive heart failure (NYHA III to IV) and an assessed amount of peripheral oedema of at least 5 kg. In these patients the absorption of a single oral dose of furosemide 250 mg was studied when their heart failure was decompensated and again, after intensive therapy, when it was clinically compensated. The mean (+/- SEM) weight loss after clinical treatment was 12.0 +/- 2.2 kg. Individual furosemide plasma concentration-time curves could be fitted adequately to a 1-compartment model with 1 first-order absorption and elimination process, in which absorption took place in 2 parts with different lag times. Comparing the decompensated state with the compensated state we did not find significant differences in pharmacodynamics, absorption half-life, elimination half-life, time to peak serum concentration, peak serum concentration itself and area under the plasma concentration-time curve. However, the relative amount of furosemide absorbed in the first fraction was significantly increased after compensation. We conclude that the presence of massive oedema in patients with congestive heart failure has a minor influence on the pharmacokinetics and pharmacodynamics of high dose oral furosemide.

The role of adrenal corticoids in the time-dependent changes in the effects of furosemide was examined. Furosemide (30 mg/kg) was given orally to adrenalectomized or sham-operated rats at 12 a.m. or 12 p.m. Urine volume and urinary excretion of sodium and furosemide for 8 hr were significantly greater at 12 a.m. than at 12 p.m. in the sham-operated rats. However, such time-dependent changes in these parameters disappeared in the adrenalectomized animals. These findings indicate that adrenal corticoids are directly or indirectly involved in this event.

Six acyloxymethyl esters of Furosemide were synthesized and the structures were determined by chemical and spectroscopic methods. Lipophilicity parameters were analysed by high performance liquid chromatography (HPLC). Hydrolysis performances in human plasma and intestinal fluids anticipate their properties as absorption prodrugs of Furosemide. A bioavailability study carried out with 8 male Wistar rats with one of the synthesized prodrug (acetyloxymethyl 4-chloro-N-furfuryl-5-sulfamoylanthranilate) showed a greater absorption in relation to Furosemide. The percentages of mean urinary recovery of Furosemide for the prodrug and for the standard solution of the drug were 20.84 and 14.36 respectively. The doses were 10 mg/Kg in Furosemide. The analytical determinations of Furosemide in biological fluids were done by HPLC.

Our previous studies have suggested that the adrenergic nervous system is involved in the mechanism responsible for the time-dependent change in the urinary excretion of furosemide in rats. To examine a potential role of renal nerves in this phenomenon, renal denervation or sham operation was performed using unilaterally nephrectomized rats. Furosemide (30 mg/kg) was given orally at 12 am or 12 pm. Urine was collected for 8 hours after furosemide dosing, and urinary excretions of furosemide and sodium were determined. Urinary furosemide excretion and diuretic effects of the agent (urine volume and urinary sodium) were significantly greater at 12 am than at 12 pm in the sham-operated group of rats. However these administration time-dependent changes in urinary furosemide and its diuretic effects disappeared in the renal-denervated group of animals. These results suggest that the renal nerves contribute to the time-dependent changes in the urinary excretion of furosemide and its subsequent diuretic effects.

To examine the influence of mercuric chloride (HgCl2)-induced acute renal damage on urinary excretion of furosemide, HgCl2 (1 mg/kg) or its vehicle alone was given intraperitoneally to Wistar rats. The following two experiments were done. Study I: Three percent body weight (b.w.) of 1% NaCl solution or furosemide (30 mg/kg) in 3% b.w. of 1% NaCl solution was given orally before and after HgCl2 treatment, and an 8-hour urine was collected. Study II: Furosemide (30 mg/kg) was given orally, and blood samples were obtained at 1, 2, 3, 4, 6 and 8 hours after administration. Urinary excretion of N-acetyl-beta-D-glucosaminidase increased, and urine volume and urinary excretions of furosemide and sodium decreased in the HgCl2-treated rats. There were significant correlations between the urinary furosemide and its diuretic effects. Regression lines after HgCl2 were significantly different from those before treatment. The values of absorption as well as elimination rate constant were smaller, while the time to maximum concentration and the elimination half-life were longer in the HgCl2-treated rats compared to vehicle-treated animals. These results suggest that the urinary excretion of furosemide and the responsiveness of renal tubular cells to this agent are impaired in rats with HgCl2-induced acute renal damage.

Our previous studies have suggested that the adrenergic nervous system is involved in the mechanisms responsible for the time-dependent changes in the effects of furosemide in rats. To examine this hypothesis further, norepinephrine (150 micrograms/kg/hr) or its vehicle alone was infused subcutaneously by osmotic minipumps. Furosemide (30 mg/kg) was given orally at 12 am or 12 pm. Urine was collected for 8 hours after the agent, and urinary excretions of sodium and furosemide were determined. Urine volume and urinary excretion of sodium and furosemide were significantly greater at 12 am than at 12 pm in the vehicle-infused group of rats. However these administration-time-dependent changes in the effects of furosemide and its urinary amount disappeared in the norepinephrine-infused group of animals. Since chronic norepinephrine infusion is considered to disturb the axis of adrenergic nervous system, these data support the hypothesis concerning the mechanisms of this chronopharmacological phenomenon of furosemide.

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).

The present study was undertaken to examine whether the urinary amount of furosemide is influenced by chronic lithium treatment. LiCl at 2 mEq/kg/day in 1 ml vehicle (5% glucose solution) or 1 ml of vehicle alone was injected intraperitoneally for 8 days into Wistar rats. On day 8, 30 mg/kg of furosemide in 3% body weight of 1% NaCl was given orally, and urine was collected for 6 hr after dosage. The urinary amount of furosemide in the Li-treated rats was significantly lower than that in the control animals [Li group (n = 12): 514 +/- 75 (mean +/- S.E.) vs. control group (n = 12): 916 +/- 85 micrograms/kg/6 hr, P less than 0.01]. This finding indicates that pharmacokinetic alterations of furosemide might occur during chronic treatment with lithium.

Furosemide (FD: Lasix) is a loop diuretic which strongly increases both urine flow and electrolyte urinary excretion. Healthy volunteers were administered 40 mg orally (dissolved in water) and concentrations of FD were determined in serum and urine for up to 6 h for eight subjects, who absorbed water at a rate of 400 ml/h. Quantification was performed by HPLC with fluorescence detection (excitation at 233 nm, emission at 389 nm) with a limit of detection of 5 ng/ml for a 300-microliters sample. The elution of FD was completed within 4 min using a gradient of acetonitrile concentration rising from 30 to 50% in 0.08 M phosphoric acid. The delay to the peak serum concentration ranged from 60 to 120 min. FD was still easily measurable in the sera from all subjects 6 h after administration. In urine, the excretion rates reached their maximum between 1 and 3 h. The total amount of FD excreted in the urine averaged 11.2 mg (range 7.6-14.0 mg), with a mean urine volume of 3024 ml (range 2620-3596 ml). Moreover, the urine density was lower than 1.010 (recommended as an upper limit in doping analysis to screen diuretics) only for 2 h. An additional volunteer was administered 40 mg of FD and his urine was collected over a longer period. FD was still detectable 48 h after intake. Gas chromatography-mass spectrometry with different types of ionization was used to confirm the occurrence of FD after permethylation of the extract. Negative-ion chemical ionization, with ammonia as reactant gas, was found to be the most sensitive method of detection.

Fourteen normotensive patients with chronic glomerulonephritis and well-preserved renal function and thirteen healthy control subjects were studied. Glomerular filtration rate (GFR), proximal and distal absolute and fractional tubular reabsorption (PAR, PFR, DARNa, DFRNa), evaluated by the lithium clearance technique, were determined before and in four 30-60-min periods after intravenous injection of frusemide 0.5 mg/kg body weight (Study 1) and 1.0 mg/kg body weight (Study 2). Plasma concentrations of angiotensin II (Ang II), aldosterone (Aldo), atrial natriuretic peptide (ANP) and arginine vasopressine (AVP) were measured before, and 60 and 180 min after frusemide. GFR decreased and UNa and FENa increased significantly in patients and controls after frusemide in both studies, but in study 2 GFR decreased significantly more in patients than in controls, and UNa and FENa increased significantly less above baseline in patients compared to controls. PAR, PFR, DARNa, and DFRNa were reduced in patients and controls in both studies. In study 2 the reduction in PAR was significantly (P less than 0.05) less pronounced in patients (23%) than in controls (43%), whereas DARNa was reduced significantly more (P less than 0.05) in patients (36%) than in controls (21%). The efficiency of frusemide with regard to renal sodium excretion was significantly reduced in patients compared to controls in both studies. Angiotensin II and aldosterone increased, ANP decreased, and AVP was unchanged in patients and controls in both studies. It is concluded that in comparison to control subjects, patients with chronic glomerulonephritis and well-preserved GFR respond to frusemide with an exaggerated reduction in GFR, a lesser decrease in absolute proximal tubular reabsorption, and a larger reduction in absolute distal tubular reabsorption. Thus, primary glomerular disease with well-preserved glomerular function may be accompanied by a distinctly disturbed tubular function.

A high-performance liquid chromatographic method using electrochemical detection is described for the determination of furosemide in serum and urine. Serum proteins were precipitated with acetonitrile containing the internal standard and the clear supernatant was separated. Urine was diluted with water to 50 times. Furosemide was chromatographed on a reversed-phase column, 8MBC18 column, using 35% ethanol solution containing 5 mmol/L tetrabutylammonium phosphate (pH 7.50) as the mobile phase (1.0 ml/min) and detected at 0.90 volts. FD-Val-OH synthesized was used as internal standard in the furosemide assay. The retention times for furosemide and internal standard were 10 min and 15 min, respectively. The amount of furosemide was determined by measuring peak height ratio. The detection limit of furosemide was 16 and 9 ng per ml serum and urine respectively. The calibration curve was linear in the range from 0.25 ng/microliters to 5 ng/microliters (serum) and from 0.5 ng/microliters to 10 ng/microliters (urine). The recovery of furosemide was 100.5% (serum) and 100.6% (urine). Coefficient of variation was less than 4.6%.

Selectivity was optimized for the determination of drugs in urine by direct injection micellar chromatography through changes in specific mobile phase parameters. The rôle of mobile phase pH and the type of surfactant used for mobile phase preparation was investigated. The retention of the urine matrix was found to be minimal between pH 5.5 and 7.5. The non-ionic surfactant, polyoxyethylene 23 lauryl ether (Brij 35), was found to be the surfactant of choice for the separation of drugs from urine. Favourable retention of both the urine background and the analyte was achieved with this surfactant. Micellar mobile phases of optimal composition were used to develop chromatographic procedures for the determination of furosemide, hydrochlorothiazide and propranolol in urine. Good accuracy (98-102% of drug recovered), precision (1-4% RSD) and linearity were obtained for all methods. Limits of detection for all drugs were adequate.

We have previously reported that a time-dependent variation is observed in the diuretic effect of furosemide and the light-dark cycle is a potent zeitgeber for this chronopharmacological phenomenon of the agent in rats. The present study was undertaken to examine whether a time of food intake is another zeitgeber for this event. In study I, rats were maintained with free access to food for 3 weeks. Furosemide (30 mg/kg) was given orally at 12 am or 12 pm. Urine was collected for 8 hours after the agent and urinary excretion of sodium and furosemide were determined. Thereafter, these rats were maintained under a daytime-restricted feeding schedule (9 am-11 am) for 3 weeks (study II) and a night-time-restricted feeding schedule (9 pm-11 pm) for 3 weeks (study III). The identical protocol of study I was repeated at the end of study II and III. Diuretic effect of furosemide and its urinary excretion were significantly greater at 12 am than at 12 pm in study I and III. However such an administration time-dependent change in the effect of furosemide and its urinary amount disappeared in study II. These data indicate that a time of food intake is another potent zeitgeber for the time-dependent variation in the diuretic effect of furosemide.

To characterize the postural effect on the pharmacodynamic response to furosemide, seven healthy female subjects received the drug (30 mg i.v.), and the diuretic response and urinary drug excretion were monitored either in the supine or upright posture more than 5 h after dose. Six days later the same procedure was repeated, each subject being assigned to the other posture. Diuresis, chlor- and natriuresis were about 50% greater (P less than .01) in the supine than in the upright posture up to 45 min after dose, despite no significant difference in urinary drug excretion between the postures. Creatinine clearance and fractional sodium excretion were also significantly (P less than .05) greater in the supine posture. Pharmacodynamic analysis with the Emax model revealed that the maximum drug response (Emax) to furosemide in the upright posture was significantly (P less than .01) attenuated by about 65% of that in the supine posture, with no significant difference in either ER50 (urinary drug excretion rate producing 50% of Emax) or slope between the postures. Plasma norepinephrine concentration was significantly (P less than .05) greater, whereas urinary kallikrein excretion was significantly (P less than .05) less in the upright posture. There were no significant differences in blood pressure, plasma renin activity and atrial natriuretic peptide as well as in urinary excretion of prostaglandin E2, dopamine and adenosine between the postures.(ABSTRACT TRUNCATED AT 250 WORDS)

Equine plasma and urine samples were analyzed by using a high-performance liquid chromatography (HPLC), enzyme-linked immunosorbent assay (ELISA) and particle concentration fluorescence assay (PCFIA). Although ELISA and PCFIA were rapid, simple and sensitive for the screening of furosemide, they did not give reproducible quantitative results. The HPLC method, which required relatively longer analysis time, provided simple and reproducible quantitative analysis of furosemide in plasma and urine. The performance of the three methods was compared for the quantitation of furosemide in plasma obtained from thoroughbred mares dosed intravenously with furosemide (500 micrograms/kg (n = 7) and 1.0 mg/kg (n = 5)). Although the plasma furosemide profiles determined by ELISA, PCFIA and HPLC were similar, ELISA and PCFIA methods exhibited considerable variation in values. At high furosemide concentrations, the PCFIA method gave better quantitative values than ELISA. However, at trace furosemide concentrations the PCFIA method gave false positive values which were not confirmed by HPLC or ELISA. The pharmacokinetic values obtained from the HPLC data and the pharmacokinetic values obtained previously from the gas chromatographic data were comparable. The data obtained by ELISA and PCFIA were not suitable for the pharmacokinetic calculations.

Influence of captopril on urinary excretion of furosemide was examined in a placebo-controlled, crossover design. Furosemide (20 mg) was injected intravenously in eight hypertensive subjects with pretreatment with captopril (25 mg) or matching placebo. Urine samples for furosemide and sodium were collected during the following intervals: -60-0, 0-60, 60-120, and 120-180 minutes after furosemide. Blood samples for plasma renin activity (PRA) and angiotensin II (AII) were obtained, and blood pressure was measured at -60, 0, 60, 120, and 180 minutes after furosemide. No significant difference was observed in urinary excretion of furosemide, volume or sodium between these trials. Although PRA increased following furosemide with captopril, as predicted plasma AII did not increase. Blood pressure significantly decreased following the combined therapy, but not furosemide alone. These data indicate that the urinary excretion of furosemide and its subsequent diuretic effects are not influenced by captopril.

The pharmacokinetics and the biliary and urinary excretions following intravenous administration of furosemide (5 mg/kg) were investigated in the anesthetized dogs with normal and experimentally reduced renal function. After the administration, furosemide caused diuretic and choleretic response, and was excreted into urine and bile at almost similar rate to plasma concentration decay in normal dogs. Half maximum diuretic response was obtained at 1.5 micrograms/ml of plasma concentration and 100 micrograms/min of urinary excretion rate of furosemide. Acute renal failure was produced in dogs by the intravenous administration of mercuric chloride (HgCl2, 2 mg/kg). In HgCl2-treated dogs, the prolongation of half life (T1/2 beta) and the decrease in plasma clearance were noted with the decreased diuretic response. These changes in parameters appeared to be associated with the decrease in excretion of furosemide into the urine, but not into the bile. Plasma level-diuretic response relationship was extensively shifted to the right in HgCl2-treated dogs, while urinary dose-response relationship did not change significantly between two groups. These results suggest that the decreased response to furosemide in HgCl2-treated dogs seems to be due to the decreased renal clearance rather than to the subsensitivity to furosemide on the site of action.

Our previous indirect evidences suggested that the adrenergic nervous system is involved in the mechanisms responsible for the time-dependent changes in the effects of furosemide in Wistar rats. In the present study, the role of this system was examined more directly by means of 6-hydroxydopamine-induced sympathectomy. Thirty mg/kg of 6-hydroxydopamine hydrobromide (6-OH-DA) (n = 9) or its vehicle alone (n = 9) was injected intra-arterially (i.a.) twice in Wistar rats. Furosemide (5 mg/kg) was administered i.a. at 1000 hrs (03HALO*) or at 2200 hrs (15HALO). Urine was collected for 60 min after the drug and urinary excretion of sodium and furosemide were determined respectively. Urine volume and urinary excretion of sodium and furosemide were significantly greater at 1000 hrs (03HALO) than at 2200 hrs (15HALO) in the vehicle-injected rats as observed in the previous study. However these administration-time-dependent changes in the effects of furosemide disappeared in the rats with 6-OH-DA. Thus, the present study provides more direct evidence and supports our original hypothesis concerning the mechanisms of this chronopharmacological phenomenon of the agent. Since 6-OH-DA does not penetrate the central nervous system from the blood stream, the present data also indicate that the peripheral adrenergic system is involved in this event.

The pharmacokinetics and metabolism of orally administered bumetanide were studied in five healthy subjects and in five patients with renal insufficiency. Healthy subjects excreted 51% of the dose as unchanged drug in the urine, whilst the patients with renal insufficiency excreted only 11% of the dose as bumetanide. Similarly the urinary excretion of the gamma-hydroxybutyl metabolite was reduced from 6% in healthy subjects to 2.3% in patients with renal impairment. In both groups of subjects the mean elimination half-life of the metabolite was greater than for bumetanide. The results indicate a possible accumulation of bumetanide and metabolite in patient with renal failure.

We have previously reported that a time-dependent variability is observed in the diuretic effects of furosemide in young Wistar rats. The present study was undertaken to examine the influence of ageing on chronopharmacological profiles of furosemide in rats. Furosemide (5 mg/kg) was injected intra-arterially in young (10-11 week old) and aged (21-22 month old) Wistar rats at 1000 hrs or at 2200 hrs. Urine was collected for 60 min after the drug and urinary excretion of sodium and furosemide were determined respectively. Urine volume and urinary excretion of sodium and furosemide following the drug injection were significantly greater at 1000 hrs than at 2200 hrs in the young rats as observed in the previous study. However these administration time-dependent changes in the effects of furosemide and its urinary amount disappeared in the aged rats. These findings indicate that the mode of the time-dependent changes in the effects of furosemide is altered in aged Wistar rats.