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

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.

Mechanism of enhanced bioavailability and diuretic effect of azosemide by ascorbic acid in rats

To increase the extent of comparative oral bioavailability (F) value and the diuretic and natriuretic effects of orally administered azosemide, ascorbic acid was coadministered to rats. The rationales for this study are that ascorbic acid might inhibit intestinal first-pass effect of azosemide and might increase the unionized fraction of azosemide at the receptor sites. After oral administration of azosemide (20 mg/kg) with 100 mg of ascorbic acid, the F value (138% vs. 100%), 8-h urinary excretion of azosemide (5.18% vs. 1.32% of oral dose), 8-h urine output (41.3 vs. 23.0 ml), and 8-h urinary excretion of sodium (24.6 vs. 15.3 mmol/kg) were greater than controls (without ascorbic acid). The amount of spiked azosemide remaining after 30 min incubation of 50 mug of azosemide with the 9000 g supernatant fraction of rat small intestine was significantly greater by 100 microg of ascorbic acid (45.3 vs. 40.9 microg) than controls (without ascorbic acid). After oral administration of azosemide with NH4Cl, the urine pH decreased by 0.5 U, and 8-h urine output (25.8 vs. 11.0 ml) and 8-h urinary excretion of sodium (13.3 vs. 6.89 mmol/kg) were significantly greater than controls (without NH4Cl). The increase in F value and diuretic and natriuretic effects of azosemide with coadministration of ascorbic acid seemed to be due to reduced intestinal first-pass metabolism of azosemide, increased urinary excretion of azosemide, and increased unionized fraction of azosemide at the renal tubular receptor sites.

Pharmacokinetics and pharmacodynamics of intravenous azosemide in mutant Nagase analbuminemic rats

This paper reports 1) the increase in expression of CYP1A2 in mutant Nagase analbuminemic rats (NARs), 2) the role of globulin binding of azosemide in circulating blood in its urinary excretion and hence its diuretic effects in NARs, and 3) the significantly faster renal (CL(R)) and nonrenal (CL(NR)) clearances of azosemide in NARs. Azosemide (mainly metabolized via CYP1A2 in rats), 10 mg/kg, was intravenously administered to control rats and NARs. Northern and Western blot analyses revealed that the expression of CYP1A2 increased approximately 3.5-fold in NARs as compared with control. The plasma protein binding of azosemide in control rats and NARs was 97.9 and 84.6%, respectively. In NARs, plasma protein binding (84.6%) was due to binding to alpha- (82.6%) and beta- (68.9%) globulins. In NARs, the amount of unchanged azosemide excreted in 8-h urine was significantly greater (37.7 versus 21.0% of intravenous dose) than that in control rats due to an increase in intrinsic renal active secretion of azosemide. Accordingly, the 8-h urine output was significantly greater in NARs. The area under the plasma concentration-time curve of azosemide was significantly smaller (505 versus 2790 microg. min/ml) in NARs because of markedly faster CL(R) (7.36 versus 0.772 ml/min/kg, secondary to a significant increase in urinary excretion of azosemide and intrinsic renal active secretion). Additionally, CL(NR) was significantly faster (12.4 versus 3.05 ml/min/kg, because of approximately 3.5 fold increase in CYP1A2) in NARs compared with control. Based on in vitro hepatic microsomal studies, the intrinsic M1 [a metabolite of azosemide; 5-(2-amino-4-chloro-5-sulfamoylphenyl)-tetrazole] formation clearance was significantly faster (67.0% increase) in NARs than that in control rats, and this supports significantly faster CL(NR) in NARs. Renal sensitivity to azosemide was significantly greater in NARs than in control rats with respect to 8-h urine output (385 versus 221 ml/kg) and 8-h urinary excretions of sodium, potassium, and chloride. This study supports that in NARs, binding of azosemide to alpha- and beta-globulins in circulating blood play an important role in its diuretic effects.

Pharmacokinetics and pharmacodynamics of intravenous trasemide in mutant Nagase analbuminemic rats

The importance of plasma protein binding of intravenous furosemide in circulating blood for its urinary excretion and hence its diuretic effects in mutant Nagase analbuminemic rats (NARs, an animal model for human familial analbuminemia) was reported. Based on the furosemide report, the diuretic effects of another loop diuretic, torasemide, could be expected in NARs if plasma protein binding of torasemide is considerable in the rats. This was proven by this study. After intravenous administration of torasemide, 10 mg/kg, to NARs, the plasma protein binding of torasemide was 23.3% in the rats due to binding to alpha- and beta-globulins (this value, 23.3%, was greater than only 12% for furosemide), and hence the percentages of intravenous dose of torasemide excreted in 8-h urine as unchanged drug was 14.9% in the rat (this value was considerably greater than only 7% for furosemide). After intravenous administration of torasemide to NARs, the AUC (301 versus 2680 microg/min/ml) was significantly smaller [due to significantly faster both Cl(r) (4.81 versus 0.386 ml/min/kg) and Cl(nr) (28.3 versus 3.33 ml/min/kg)], terminal half-life (18.3 versus 73.5 min) and mean residence time (6.97 versus 61.8 min) were significantly shorter (due to faster Cl, 33.2 versus 3.74 ml/min/kg), and amount of 8-h urinary excretion of unchanged torasemide (446 versus 323 microg, due to increase in intrinsic renal excretion) was significantly greater than those in control rats. The 8-h urine output and 8-h urinary excretions of sodium and chloride were comparable between two groups of rats although the 8-h urinary excretion of torasemide was significantly greater in NARs. This could be explained by the following. The amount of urinary excretion of torasemide was significantly greater in NARs than that in control rats only between 0 and 30 min urine collection. In both groups of rats, the urinary excretion rate of torasemide during 0-30 min reached an upper plateau with respect to urine flow rate as well urinary excretion rates of sodium and chloride. Therefore, the diuretic effects (8-h urine output and 8-h urinary excretions of sodium and chloride) were not significantly different between the two groups of rats.

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.

Influence of 4-week and 8-week exercise training on the pharmacokinetics and pharmacodynamics of intravenous and oral azosemide in rats

Cytochrome P450 expression was determined in the livers of control, 4-week exercised (4WE) and 8-week exercised (8WE) rats. Even though the 4-week and 8-week exercise training caused 53 and 25% increases, respectively, in total cytochrome P450 contents in the liver, exercise training did not cause any changes in the levels of P450 1A2 (which primarily metabolizes azosemide), 2E1 and 3A23 in the liver, as assessed by both Western and Northern blot analyses. Also, exercise training failed to alter the activity of NADPH-dependent cytochrome P450 reductase. The plasma concentrations of norepinephrine and epinephrine were significantly (2 to 3 folds) higher in 4WE rats than in controls, presumably due to physical stress, but the catecholamine levels in 8 WE rats returned to control levels. After intravenous administration (10 mg/kg of azosemide), the amount of unchanged azosemide excreted in 8-h urine (Ae(Azo, 0-8 h)) was significantly greater (46% increase) in 4WE rats than that in control rats. This resulted in a significantly faster (82% increase) renal clearance of azosemide. However, the nonrenal clearances were not significantly different between control and 4WE rats. The significantly greater Ae(Azo, 0-8 h) in 4WE rats was mainly due to a significant increase in intrinsic active secretion of azosemide in renal tubules and not due to a decrease in the metabolism of azosemide. After oral administration (20 mg/kg), Ae(Azo, 0-8 h) was also significantly greater (264%) in 4WE rats and this again was due to a significant increase in intrinsic active renal secretion of azosemide and not due to an increase in gastrointestinal absorption. After both intravenous and oral administration, the 8-h urine output was not significantly different between control and 4WE rats although Ae(Azo, 0-8 h) increased significantly in 4WE rats. This could be due to the fact that the urine output reached a plateau at 10 mg/kg after intravenous administration and 20 mg/kg after oral administration of azosemide to rats and possibly due to increase in plasma antidiuretic hormone levels and aldosterone production in 4WE rats.

Suppression of rat hepatic cytochrome P450s by protein-calorie malnutrition: complete or partial restoration by cysteine or methionine supplementation

Pharmacokinetic profiles of therapeutic agents are altered by protein-calorie malnutrition (PCM). The current study was designed to determine the expression of hepatic cytochrome P450s in rats after protein restriction and to investigate its molecular basis. Western blot analysis revealed that rats with protein restriction for 4 weeks exhibited marked suppression in the hepatic P450 1A2, 2C11, 2E1, and 3A1/2 levels. Northern blot analysis showed that hepatic P450 1A2, 2C11, and 3A1/2 mRNAs were significantly decreased in the state of PCM. The P450 2E1 mRNA level was slightly decreased in PCM rats, suggesting the possibility that expression of P450 2E1 affected by PCM might result from the transcriptional and/or posttranscriptional regulation. PCM-induced changes in most P450 expression completely or partially returned to control levels by a week of cysteine supplementation. Cysteine also prevented decreases in P450 1A2, 2C11, 2E1, and 3A1/2 mRNA levels by PCM. Methionine was minimally active in restoring the P450 expression. A metabolic change in hepatic ethoxyresorufin dealkylase activity in PCM rats was consistent with the P450 apoprotein and mRNA levels. Although the plasma concentrations of azosemide, a loop diuretic, primarily metabolized by cytochrome P450 1A, increased in protein-deprived rats, cysteine supplementation significantly reduced the increased plasma concentrations of the drug. The altered pharmacokinetic parameters of azosemide in PCM rats returned to those of control after cysteine supplementation, corroborating the conclusion that cysteine was effective in restoring cytochrome P450 expression and metabolic activities.

Gender differences in pharmacokinetics and pharmacodynamics of azosemide in rats

Gender differences in pharmacokinetics and pharmacodynamics of azosemide were evaluated after intravenous, 10 mg kg(-1), and oral, 10 mg kg(-1), administration to male and female rats. After intravenous administration to male rats, the percentages of intravenous dose of azosemide recovered from entire gastrointestinal tract at 24 h (13.2 versus 3.93%) was significantly greater than those in female rats. In male rats, the nonrenal clearance of azosemide tended (p<0.066) to be faster and kidney weight tended (p<0.068) to be greater than those in female rats. After oral administration of azosemide to male rats, the 8-h urinary excretion of potassium (0.395 versus 0.766 mmol g(-1) kidney) and 8-h kaluretic efficiency (55.9 versus 284 mmol mg(-1)) decreased significantly compared with female rats.

Circadian changes in the pharmacokinetics and pharmacodynamics of azosemide in rats

The circadian changes in the pharmacokinetics and pharmacodynamics of azosemide were investigated after intravenous and oral administration of the drug (10 mg kg(-1)) to rats at 1000 or 2200 h. After intravenous administration of azosemide the percentage of the dose excreted in 8-h urine as unchanged azosemide was significantly higher in the 1000 h group than in the 2200 h group (41.7 compared with 28.9%) and this resulted in a significant increase in 8-h urine output (84.7 compared with 36.6 mL/100 g). After intravenous administration the time-averaged renal clearance (CLR) of azosemide was significantly faster (2.86 compared with 1.76 mL min(-1) kg(-1)) and urinary excretion of sodium (46.4 compared with 25.9 mmol/100 g) and chloride (35.6 compared with 18.8 mmol/100 g) increased significantly in the 1000 h group. However, after oral administration, the percentages of oral dose of azosemide excreted in 8-h urine as unchanged azosemide were significantly higher (1.88 compared with 0.67%) and the CL(R) of azosemide was significantly faster (3.64 compared with 0.79 mL min(-1) kg(-1)) in the 2200 h group. This could be at least partly because of increased absorption of azosemide from the gastrointestinal tract in the 2200 h group; the percentages of oral dose of azosemide recovered from the gastrointestinal tract in 8 h as unchanged azosemide was significantly smaller (5.7 compared with 13.2%) in the 2200 h group. The pharmacodynamic parameters of azosemide were not significantly different after oral administration of the drug to both groups of rats. If these data could be extrapolated to man, the intravenous dose of azosemide could be modified on the basis of circadian time.