Determination of azosemide and its metabolite in plasma, blood, urine and tissue homogenates by high-performance liquid chromatography

A turn off-on fluorometric and paper based colorimetric dual-mode sensor for isoniazid detection

In the present study, Cobalt oxyhydroxide (CoOOH) nanosheets were applied for establishing a dual fluorometric and smartphone-paper-based colorimetric method to detect isoniazid. CoOOH nanosheets quenched the fluorescence emission of sulfur and nitrogen co-doped carbon dots (S,N-CDs) due to inner filter effect (IFE). The quenched fluorescence intensity of S,N-CDs restored in the presence of isoniazid due to destroying CoOOH nanosheets by this drug. Moreover, with adding isoniazid the solution color of CoOOH nanosheets altered from brownish yellow to pale yellow. We exploited these facts to design a turn off-on fluorometric and paper based colorimetric sensor for isoniazid measurement at the range of 0.5-10 and 5-100 μM with detection limits of 0.28 μM and 4.0 μM, respectively. The introduced dual sensor was used for pharmaceutical, environmental and biological analysis of isoniazid with satisfactory results. The paper based colorimetric sensor can be applied for isoniazid portable monitoring by smartphone as a detector and even nocked eyes.

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 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.

Determination of a new isoquinolinedione derivative, 7-anilino-5,8-isoquinolinedione, in plasma, urine and tissue homogenates by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method was developed for the determination of a new isoquinolinedione derivative, 7-anilino-5,8-isoquinolinedione (IQO4), in rat plasma, urine, blood and tissue homogenates using diazepam as an internal standard. A 2 volume of acetonitrile was added to deproteinize the biological sample. A 50 microl aliquot of the supernatant was injected onto a C(18) reversed-phase column. The mobile phase, 0.05 M acetate buffer (pH 3):acetonitrile:methanol (40:40:20, v/v/v), was run at a flow rate of 1.5 ml/min. The column effluent was monitored using an ultraviolet detector set at 298 nm. The retention times for IQO4 and the internal standard were approximately 5 and 7 min, respectively. The detection limits of IQO4 in rat plasma, urine and tissue homogenates (including blood) were 0.05, 0.1 and 0.1 microg/ml, respectively. The coefficients of variation of the assay were below 9.4% for rat plasma, urine and tissue homogenates. No interferences from endogenous substances were found.

Determination of a new reversible proton pump inhibitor, DBM-819, in human plasma and urine, and rat tissue homogenates by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method was developed for the determination of a new proton pump inhibitor, DBM-819, in human plasma and urine and rat tissue homogenates using KR-60461 as an internal standard. A 100-microl aliquot of acetonitrile (containing 0.5 microg/ml of the internal standard) and a 200-microl aliquot of 0.1 M Na(2)HPO(4) (adjusted pH 11 with 1 N NaOH) were added to a 100-microl aliquot of biological sample. After vortex-mixing, the mixture was extracted with 1 ml of ethylacetate. After centrifugation at 12000 x g for 3 min, the organic layer was collected and evaporated under nitrogen gas. The residue was then reconstituted with a 100-microl aliquot of mobile phase, and a 40-microl aliquot was injected onto the HPLC column. The mobile phase, 0.02 M phosphate buffer (pH 5): acetonitrile: methanol (46:44:10, v/v/v), was run at a flow rate of 0.5 ml/min and the column effluent was monitored by the fluorescence detector set at an excitation wavelength of 340 nm and an emission wavelength of 470 nm. The retention times for DBM-819 and the internal standard were approximately 10.5 and 12 min, respectively. The detection limits of DBM-819 in human plasma and urine, and rat tissue homogenates were 0.01, 0.02 and 0.02 (or 0.05) microg/ml. respectively. The coefficients of variation (CV) of the assay were below 11% for human plasma and urine, and rat tissue homogenates. No interferences from endogenous substances were found.

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.

Gastrointestinal absorption of a new reversible proton pump inhibitor, YJA-20379-8, and its pharmacokinetics after oral administration in acetic acid-induced gastric ulcer in rats

The absorption of YJA-20379-8 (3-butyryl-4-[5-(R)-(+)-methylbenzylamino]-8-ethoxy-1,7-naphthyrid ine) from various rat gastrointestinal segments was evaluated using in-situ closed-loops. The pharmacokinetics of the drug were also evaluated after oral administration to rats with acetic acid-induced gastric ulcer (AIURs). The concentrations of YJA-20379-8 in the biological samples were analyzed by HPLC. The absorption of YJA-20379-8 from stomach and jejunum was fast, but approximately 50% of the drug was recovered from each segment at 24 h. The total areas under the plasma concentration-time curves from time zero to 24h (AUC(0-24h)) were 161, 392, 233, 365, and 226 microg min mL(-1) for stomach, duodenum, jejunum, ileum, and colon, respectively. After oral administration of the drug, the plasma concentrations and the resultant AUC (0- 12h) were not significantly different between control and AIURs. The detection limits of YJA-20379-8 in human plasma and urine were 50 and 100 ng mL(-1), respectively. The results suggest that modification of the oral dose of YJA-20379-8 may not be required in gastric ulcer patients if the present rat pharmacokinetic data could be extrapolated to man.

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.

Determination of a chemoprotective agent, 2-(allylthio)pyrazine, in plasma, urine and tissue homogenates by high-performance liquid chromatography

A high-performance liquid chromatographic method was developed for the determination of a chemoprotective agent, 2-(allylthio)pyrazine (I), in human plasma and urine, and in rat blood and tissue homogenate using diazepam as an internal standard. The sample preparation was simple; 2.5 volumes of acetonitrile were added to the biological sample to deproteinize it. A 50-100 microl aliquot of the supernatant was injected onto a C18 reversed-phase column. The mobile phase employed was acetonitrile-water (55:45, v/v), and it was run at a flow-rate of 1.5 ml/min. The column effluent was monitored using an ultraviolet detector at 330 nm. The retention times for I and the internal standard were 4.0 and 5.1 min, respectively. The detection limits of I in human plasma and urine, and in rat tissue homogenate (including blood) were 20, 20 and 50 ng/ml, respectively. The coefficients of variation of the assay (within-day and between-day) were generally low (below 6.1%) in a concentration range from 0.02 to 10 microg/ml for human plasma and urine, and for rat tissue homogenate. No interferences from endogenous substances were found.

Liver and gastrointestinal first-pass effects of azosemide in rats

Since considerable first-pass effects of azosemide have been reported after oral administration of the drug to rats and man, first-pass effects of azosemide were evaluated after intravenous, intraportal and oral administration, and intraduodenal instillation of the drug, to rats. The total body clearances of azosemide after intravenous (5 mg kg-1) and intraportal (5 and 10 mg kg-1) administration of the drug to rats were considerably smaller than the cardiac output of rats suggesting that the lung or heart first-pass effect (or both) of azosemide after oral administration of the drug to rats was negligible. The total area under the plasma concentration-time curve from time zero to time infinity (AUC) after intraportal administration (5 mg kg-1) of the drug was significantly lower than that after intravenous administration (5 mg kg-1) of the drug (1000 vs 1270 micrograms min mL-1) suggesting that the liver first-pass effect of azosemide was approximately 20% in rats. The AUC from time 0 to 8 h (AUC0-8 h) after oral administration (5 mg kg-1) of the drug was considerably smaller than that after intraportal administration (5 mg kg-1) of the drug (27.1 vs 1580 micrograms min mL-1) suggesting that there are considerable gastrointestinal first-pass effects of azosemide after oral administration of azosemide to rats. Although the AUC0-8 h after oral administration (5 mg kg-1) of azosemide was approximately 15% lower than that after intraduodenal instillation (5 mg kg-1) of the drug (27.1 vs 32.0 micrograms min mL-1), the difference was not significant, suggesting that the gastric first-pass effect of azosemide was not considerable in rats. Azosemide was stable in human gastric juices and pH solutions ranging from 2 to 13. Almost complete absorption of azosemide from whole gastrointestinal tract was observed after oral administration of the drug to rats. The above data indicated that most of the orally administered azosemide disappeared (mainly due to metabolism) following intestinal first-pass in rats.

Determination of a new proton pump inhibitor, YH1885, in human plasma and urine by high-performance liquid chromatography

A high-performance liquid chromatographic method was developed for the determination of a new proton pump inhibitor, YH1885 (I), in human plasma and urine, and rat blood and tissue homogenate using fenticonazole as an internal standard. The sample preparation was simple: a 2.5 volume of acetonitrile was added to the biological sample to deproteinize it. A 50-microliter aliquot of the supernatant was injected onto a C8 reversed-phase column. The mobile phase employed was methanol-0.005 M tetrabutylammonium dihydrogenphosphate (77:23, v/v), and it was run at a flow-rate of 1.0 ml/min. The column effluent was monitored using an ultraviolet detector at 270 nm. The retention times for I and the internal standard were 9.0 and 10.3 min, respectively. The detection limits for I in human plasma and urine, and in rat tissue homogenate (including blood) were 50, 100 and 100 ng/ml, respectively. The coefficients of variation of the assay (within- day and between-day) were generally low (below 8.84%) for human plasma and urine, and for rat tissue homogenate. No interferences from endogenous substances were found.

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.

Stability, tissue metabolism, tissue distribution and blood partition of azosemide

Stability of azosemide after incubation in various pH solutions, human plasma, human gastric juice, and rat liver homogenates, metabolism of azosemide after incubation in 9000 g supernatant fraction of various rat tissue homogenates in the presence of NADPH, tissue distribution of azosemide and M1 after intravenous (i.v.) administration of azosemide, 20 mg kg-1, to rats, and blood partition of azosemide between plasma and blood cells from rabbit blood were studied. Azosemide seemed to be stable for up to 48 h incubation in various pH solutions ranging from two to 13 at an azosemide concentration of 10 micrograms mL-1; more than 93.4% of azosemide was recovered, and a metabolite of azosemide, M1, was not detected. However, the drug was unstable in pH1 solution: 75.8% of azosemide was recovered and 2.16 micrograms mL-1 of M1 (expressed in terms of azosemide) was formed after 48 h incubation in pH 1 solution at an azosemide concentration of 10 micrograms mL-1. Azosemide was stable in both human plasma and rat liver homogenates for up to 24 h incubation at an azosemide concentration of 1 microgram mL-1, and in human gastric juice for up to 4 h incubation at an azosemide concentration of 10 micrograms mL-1. However, all rat tissues studied had metabolic activity for azosemide in the presence of NADPH, with heart having a considerable metabolic activity: approximately 22% of azosemide disappeared and 9.32 micrograms of M1 was formed per gram of heart (expressed in terms of azosemide) after 30 min incubation of 50 micrograms of azosemide in 9000 g supernatant fraction of heart homogenates. The tissue to plasma ratios of azosemide (T/P) were greater than unity only in the liver (1.26) and kidney (1.74); however, M1 showed high affinity for all tissues studied except the brain and spleen when each tissue was collected at 30 min after i.v. administration of azosemide to rats. The equilibrium plasma to blood cell concentration ratios of azosemide were independent of azosemide blood concentrations: the values were 2.78-4.25 at azosemide blood concentrations of 1, 10, and 20 micrograms mL-1 in three rabbits. There was negligible 'blood storage effect' of azosemide, especially at low blood concentrations of azosemide, such as 1 and 10 micrograms mL-1.

Factors influencing the protein binding of azosemide using an equilibrium dialysis technique

Various factors most likely to influence the plasma protein binding of azosemide to 4% human serum albumin (HSA) were evaluated using equilibrium dialysis at the initial azosemide concentration of 10 micrograms mL-1. It took approximately 8 h of incubation to reach an equilibrium between 4% HSA and isotonic phosphate buffer of pH 7.4 containing 3% dextran (the 'buffer') using a Spectra/Por 2 membrane (molecular weight cut-off, 12000-14000) in a water bath shaker kept at 37 degrees C and a rate of 50 oscillations min-1. Azosemide was fairly stable both in 4% HSA and in the 'buffer' for up to 24 h. The binding of azosemide to 4% HSA was constant (95.5 +/- 0.142%) at azosemide concentrations ranging from 5 to 100 micrograms mL-1. However, the extent of binding was dependent on HSA concentration: the values were 88.4, 91.0, 92.2, 94.2, 94.9, 94.9, and 94.9% at albumin concentrations of 0.5, 1, 2, 3, 4, 5, and 6%, respectively. The binding was also dependent on incubation temperature: the binding values were 97.0, 94.9, and 94.9% when incubated at 6, 28, and 37 degrees C, respectively. The binding of azosemide was also influenced by buffers containing various chloride ion concentrations and buffer pHs. The binding values were 95.3, 94.9 and 93.6% for the chloride ion concentrations of 0, 0.249, and 0.546%, respectively, and the unbound values were 6.8, 5.1, 3.8, 3.4, and 3.3% for buffer pHs of 5.8, 6.4, 7.0, 7.4, and 8.0, respectively. The binding of azosemide was independent of the quantity of heparin (up to 40 U mL-1), AAG (up to 0.16%), sodium azide (NaN3, up to 5%), its metabolite, M1 (up to 10 micrograms mL-1), and anticoagulants (EDTA and citrate).