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

The search for brain-permeant NKCC1 inhibitors for the treatment of seizures: Pharmacokinetic-pharmacodynamic modelling of NKCC1 inhibition by azosemide, torasemide, and bumetanide in mouse brain

Because of its potent inhibitory effect on the Na⁺-K⁺-2Cl^- symporter isotype 1 (NKCC1) in brain neurons, bumetanide has been tested with varying results for treatment of seizures that potentially evolve as a consequence of abnormal NKCC1 activity. However, because of its physicochemical properties, bumetanide only poorly penetrates into the brain. We previously demonstrated that NKCC1 can be also inhibited by azosemide and torasemide, which lack the carboxyl group of bumetanide and thus should be better brain-permeable. Here we studied the brain distribution kinetics of azosemide and torasemide in comparison with bumetanide in mice and used pharmacokinetic-pharmacodynamic modelling to determine whether the drugs reach NKCC1-inhibitory brain concentrations. All three drugs hardly distributed into the brain, which seemed to be the result of probenecid-sensitive efflux transport at the blood-brain barrier. When fractions unbound in plasma and brain were determined by equilibrium dialysis, only about 6-17% of the brain drug concentration were freely available. With the systemic doses (10 mg/kg i.v.) used, free brain concentrations of bumetanide and torasemide were in the NKCC1-inhibitory concentration range, while levels of azosemide were slightly below this range. However, all three drugs exhibited free plasma levels that would be sufficient to block NKCC1 at the apical membrane of brain capillary endothelial cells. These data suggest that azosemide and torasemide are interesting alternatives to bumetanide for treatment of seizures involving abnormal NKCC1 functionality, particularly because of their longer duration of action and their lower diuretic potency, which is an advantage in patients with seizures.

Azosemide is more potent than bumetanide and various other loop diuretics to inhibit the sodium-potassium-chloride-cotransporter human variants hNKCC1A and hNKCC1B

The Na⁺–K⁺–2Cl⁻ cotransporter NKCC1 plays a role in neuronal Cl⁻ homeostasis secretion and represents a target for brain pathologies with altered NKCC1 function. Two main variants of NKCC1 have been identified: a full-length NKCC1 transcript (NKCC1A) and a shorter splice variant (NKCC1B) that is particularly enriched in the brain. The loop diuretic bumetanide is often used to inhibit NKCC1 in brain disorders, but only poorly crosses the blood-brain barrier. We determined the sensitivity of the two human NKCC1 splice variants to bumetanide and various other chemically diverse loop diuretics, using the Xenopus oocyte heterologous expression system. Azosemide was the most potent NKCC1 inhibitor (IC₅₀s 0.246 µM for hNKCC1A and 0.197 µM for NKCC1B), being about 4-times more potent than bumetanide. Structurally, a carboxylic group as in bumetanide was not a prerequisite for potent NKCC1 inhibition, whereas loop diuretics without a sulfonamide group were less potent. None of the drugs tested were selective for hNKCC1B vs. hNKCC1A, indicating that loop diuretics are not a useful starting point to design NKCC1B-specific compounds. Azosemide was found to exert an unexpectedly potent inhibitory effect and as a non-acidic compound, it is more likely to cross the blood-brain barrier than bumetanide.

The prediction of blood-tissue partitions, water-skin partitions and skin permeation for agrochemicals

BACKGROUND

There is considerable interest in the blood-tissue distribution of agrochemicals, and a number of researchers have developed experimental methods for in vitro distribution. These methods involve the determination of saline-blood and saline-tissue partitions; not only are they indirect, but they do not yield the required in vivo distribution.

RESULTS

The authors set out equations for gas-tissue and blood-tissue distribution, for partition from water into skin and for permeation from water through human skin. Together with Abraham descriptors for the agrochemicals, these equations can be used to predict values for all of these processes. The present predictions compare favourably with experimental in vivo blood-tissue distribution where available. The predictions require no more than simple arithmetic.

CONCLUSIONS

The present method represents a much easier and much more economic way of estimating blood-tissue partitions than the method that uses saline-blood and saline-tissue partitions. It has the added advantages of yielding the required in vivo partitions and being easily extended to the prediction of partition of agrochemicals from water into skin and permeation from water through skin.

Air to liver partition coefficients for volatile organic compounds and blood to liver partition coefficients for volatile organic compounds and drugs

Values of in vitro air to liver partition coefficients, K(liver), of VOCs have been collected from the literature. For 124 VOCs, application of the Abraham solvation equation to logK(liver) yielded a correlation equation with R(2)=0.927 and SD=0.26 log units. Combination of the logK(liver) values with logK(blood) values leads to in vitro blood to liver partition coefficients, as logP(liver) for VOCs; an Abraham solvation equation can correlate 125 such values with R(2)=0.583 and SD=0.23 log units. Values of in vivo logP(liver) for 85 drugs were collected, and were correlated with R(2)=0.522 and SD=0.42 log units. When the logP(liver) values for VOCs and drugs were combined, an Abraham solvation equation could correlate the 210 compounds with R(2)=0.544 and SD=0.32 log units. Division of the 210 compounds into a training set and a test set, each of 105 compounds, showed that the training equation could predict logP(liver) values with an average error of 0.05 and a standard deviation of 0.34 log units.

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.

Dose-independent pharmacokinetics of a candidate for diabetic neuropathy, SR-4668, after intravenous and oral administration to rats: Intestinal first-pass effect

Dose-independent pharmacokinetic parameters of SR-4668 were observed after intravenous (i.v.) administrations at doses of 25, 50, and 75 mg/kg and oral administrations at doses of 50, 100, and 150 mg/kg to rats. The hepatic, gastric, and intestinal first-pass effects of SR-4668 were also measured after i.v., intraportal (i.p.), intraduodenal (i.d.), and intragastric (i.g.) administrations at a dose of 50 mg/kg to rats. Although a considerable amount of orally administered SR-4668 was absorbed, the F was low--only 33%. This indicates considerable first-pass (gastric, intestinal, and/or hepatic) effects of SR-4668 in rats. After i.v. administrations, the total body clearances of SR-4668 were considerably slower than the reported cardiac output in rats, suggesting that the first-pass effects of SR-4668 in the lung and heart could be negligible, if any, in rats. The AUCs of SR-4668 were comparable between i.v. and i.p. administrations, suggesting that the hepatic first-pass effect of SR-4668 was not considerable in rats. The AUCs were also comparable between i.d. and i.g. administrations, suggesting that gastric first-pass effect was almost negligible in rats. However, the AUC after an i.d. administration was significantly smaller (approximately 55% decrease) than that after an i.p. administration, suggesting that the intestinal first-pass effect was approximately 55% of oral dose. The rests of the orally administered dose could be mainly due to degradation of SR-4668 in gastric juices; 77.3-95.6% of the spiked amount of SR-4668 were recovered after 4-h incubation in five human gastric juices. The above data suggested that the low F of SR-4668 could be mainly due to considerable intestinal first-pass effect in rats.

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.

Effects of acute renal failure induced by uranyl nitrate on the pharmacokinetics of intravenous theophylline in rats: the role of CYP2E1 induction in 1,3-dimethyluric acid formation

In rats with acute renal failure induced by uranyl nitrate, the hepatic microsomal cytochrome P450 (CYP) 2E1 and CYP3A23 increased 2-4- and 4-times, respectively, CYP2C11 decreased to 80% of control, but the levels of CYP1A2 and CYP2B1/2 were not changed. It has been reported that theophylline was metabolized to 1,3-dimethyluric acid by CYP1A2 and CYP2E1 and 1-methylxanthine via CYP1A2, which was metabolized further to 1-methyluric acid via xanthine oxidase in rats. Hence, it was expected that the formation of 1,3-dimethyluric acid would show an increase in rats with renal failure as a result of induction of CYP2E1. The pharmacokinetics of theophylline were compared in control rats and rats with renal failure after intravenous administration of aminophylline, 5 mg kg(-1) as theophylline. In rats with renal failure, the plasma concentrations of theophylline were considerably lower and the resultant total area under the plasma concentration-time curve from time zero to time infinity (AUC(0- infinity )) of theophylline was significantly smaller (2,200 vs 1,550 microg min mL(-1)) compared with control rats. In rats with renal failure, the plasma concentrations of 1,3-dimethyluric acid were considerably higher and the resultant AUC(0-6 h) of 1,3-dimethyluric acid was significantly greater (44.4 vs 456 microg min mL(-1)) compared with control rats. Moreover, the AUC(0-6 h, 1,3-dimethyluric acid)/AUC(0- infinity, theophylline) ratio increased from 2.02% in control rats to 29.4% in rats with renal failure. The in-vitro intrinsic 1,3-dimethyluric acid formation clearance was significantly faster in rats with renal failure (734 vs 529 10(-6) mL min(-1)) compared with control rats using hepatic microsomal fraction. The results led us to conclude that in rats with uranyl nitrate-induced renal failure after the administration of aminophylline, 5 mg kg(-1) as theophylline, there was an increase in the formation of 1,3-dimethyluric acid as a result of an increase in CYP2E1 expression.

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.

Pharmacokinetics and tissue distribution of ipriflavone, an isoflavone derivative, after intravenous administration to rabbits

Pharmacokinetic parameters of ipriflavone and its main metabolites, M1 and M5, after intravenous administration of spray-dried ipriflavone, SIP (10, 20, and 30 mg/kg as ipriflavone) and tissue distribution of ipriflavone, M1, and M5 after intravenous administration of SIP (20 mg/kg as ipriflavone) were evaluated in rabbits. Saturable metabolism of ipriflavone were observed after intravenous administration; at an ipriflavone dose of 30 mg/kg, the dose-normalized (based on 10 mg/kg) AUC was significantly greater (72.4 and 64.0 versus 103 microg min/mL), Cl was significantly slower (138 and 156 versus 97.6 mL/min/kg), and terminal half-life (94.8 and 129 versus 211 min) and mean residence time (91.3 and 116 versus 186 min) were significantly longer than those at 10 and 20 mg/kg. The AUC of M1 was also significantly greater at ipriflavone dose of 30 mg/kg. The terminal half-life, AUC, and renal clearance of M5 were also significantly different at ipriflavone dose of 30 mg/kg than those at 10 and 20 mg/kg. Ipriflavone was widely distributed in most rabbit tissues studied and the tissue-to-plasma (T/P) ratios of ipriflavone were greater than unity in all tissues (or organs) studied except spleen, indicating that ipriflavone has high affinity to rabbit tissues studied, and this could be supported by considerably high values of the apparent volume of distribution of ipriflavone at steady state (11 400-16 900 mL/kg). M1 and M5 were also detected in most rabbit tissues with considerable amount of M1 (T/P ratio of 9.43) and M5 (T/P ratio of 4.66) in the kidney.

Stability, blood partition and plasma protein binding of ipriflavone, an isoflavone derivative

It is generally recognized that the partition between plasma and blood cells, the immediate centrifugation of blood samples after collection for the measurement of 'true' in vivo concentrations and free drug concentrations in plasma are important determinants of the pharmacokinetics and/or pharmacodynamics of drugs. Therefore, the stability, blood partition between plasma and blood cells, and factors influencing the binding of ipriflavone to 4% human serum albumin (HSA) using an equilibrium dialysis technique were evaluated. Ipriflavone was unstable in rat liver homogenate and various pH solutions ranging from 1 to 13, except pH 8, rat blood and plasma and human plasma when incubated in a water-bath shaker for 24 h kept at 37 degrees C and at a rate of 50 oscillations/min. The recoveries of spiked amounts of ipriflavone at 24 h pH solutions ranging from 1 to 12 were 67.0, 78.1, 87.9, 89.6, 84.2, 87.4, 85.5, 99.3, 88.0, 76. 6, 79.4 and 81.5%, respectively. Ipriflavone was very unstable in pH 13 solution; only 0.814% of ipriflavone was recovered after 30 min incubation. Ipriflavone was stable for up to 3 h incubation in human gastric juices. Ipriflavone reached equilibrium fast (within 30 s of being mixed manually) between plasma and blood cells and the equilibrium plasma/blood cells partition ratios were independent of the initial rabbit blood concentrations of ipriflavone: 0.2, 2, and 10 microg/mL; the values were in the range of 0.900-2.45. The binding of ipriflavone to 4% HSA was 96.6+/-0.407% at ipriflavone concentrations ranging from 2 to 100 microg/mL, but it was dependent on HSA concentrations (0.5-6%), incubation temperature (4, 22 and 37 degrees C), 'the buffer' pHs (5.8, 6.4, 7.0, 7.4 and 8.0), and addition of salicylic acid (150-300 microg/mL) and sulphisoxazole (100-300 microg/mL). However, the binding was independent of buffers containing various concentrations of chloride ion (0-0.546%), glucose (0 and 5%), alpha-1-acid glycoprotein (0-0.32%) and heparin (0-40 U/mL), and addition of its metabolites (M1 and M5, 5 microg/mL).

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.

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 carbapenem derivative, DA-1131, in plasma and urine by high-performance liquid chromatography

A high-performance liquid chromatographic method was developed for the determination of a new carbapenem, DA-1131 (I), in human plasma and urine and in rat blood and tissue homogenates. The method involved deproteinization of the biological samples with 1 volume each of 0.04 M Ba(OH)2 and ZnSO4 aqueous solution. A 50-microliters aliquot of the supernatant was injected onto a C18 reversed-phase column. The mobile phase employed was 0.015 M KH2PO4-acetonitrile (9:1, v/v) with a pH of 5.0. The flow-rate was 0.8 ml/min. The column effluent was monitored by a ultraviolet detector at 300 nm. The retention time of I was 8.0 min. The detection limits of I in human plasma and urine were 0.1 and 0.5 micrograms/ml, respectively. The coefficients of variation of the assay were generally low (below 8.39%) for human plasma and urine, and rat blood and tissue homogenates. No interferences from endogenous substances were observed.

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.