Methenamine: a forgotten drug for preventing recurrent urinary tract infection in a multidrug resistance era

In the era of multidrug resistance, it is critical to utilize antibiotics in an appropriate manner and to identify new treatments or revisit the use of 'forgotten' drugs. Because urinary tract infections (UTIs) are common, particularly in an increasing elderly population, the 'forgotten' drug, methenamine, may become important as a preventive therapy for recurrent UTIs. Methenamine, a urinary antibacterial agent, can be used as methenamine hippurate or methenamine mandelate preparations and is United States Food and Drug Administration-approved. This article discusses the place of preventive therapy for recurrent UTIs, chemistry, mechanism of action, pharmacology, clinical uses, dosage, adverse reactions and safety, and drug interactions of methenamine. Because of its unique antiseptic property, the authors suggest that methenamine should be considered when more commonly used antibiotics fail to suppress recurrent UTIs.

Proteinuria-lowering effect of heparin therapy in diabetic nephropathy without affecting the renin-angiotensin-aldosterone system

Angiotensin-converting enzyme inhibitors and angiotensin II (AngII) type 1 receptor blockers lower proteinuria and preserve renal function in diabetic nephropathy (DN). The antiproteinuric effects are greater than their blood pressure reduction, involving the sieving properties of the glomerular filter. In DN, glomerular staining for heparan sulfate proteoglycans is decreased. AngII inhibits heparan sulfate synthesis. Also, heparins modulate AngII signaling in glomerular cells, inhibiting aldosterone synthesis and lowering proteinuria in DN. Is the antiproteinuric effect of heparins due to its interference with the renin-angiotensin-aldosterone system? Ten volunteers each with DN and glomerulonephritis and control subjects were examined before and after low-dosage enoxaparin. Renal hemodynamics were determined with (99m)Tc-DTPA and (131)I-hippurate clearance. Glomerular filtration rate (GFR), effective renal plasma flow, mean arterial pressure, and heart rate were measured at baseline and during AngII infusion before and after enoxaparin while on normal salt and salt restriction. Enoxaparin did not lower aldosterone levels. GFR remained stable in all groups. AngII caused a significant decrease in effective renal plasma flow, whereas mean arterial pressure and heart rate increased significantly. Enoxaparin did not influence the AngII-induced changes of renal hemodynamics during normal salt intake or salt restriction. All groups showed identical responses to AngII before and after enoxaparin. In patients with diabetes, enoxaparin caused a significant decrease in proteinuria. It is concluded that the antiproteinuric effect of heparins in DN cannot be explained via interaction with the renin-angiotensin-aldosterone system. The absence of hemodynamic changes combined with reduced proteinuria point to intrinsic alterations in the glomerular filter. The effects were seen only in DN, not in glomerulonephritis.

Renal Clearance of Endogenous Hippurate Correlates with Expression Levels of Renal Organic Anion Transporters in Uremic Rats

Hippurate (HA) is a harmful uremic toxin that accumulates during chronic renal failure, and failure of the excretion system for uremic toxins is thought to be responsible. Recently, we reported that rat organic anion transporter 1 (rOat1) is the primary mediator of HA uptake in the kidney, and so now we have studied the pharmacokinetics and tissue distribution of HA after a single i.v. dose of HA to normal and 5/6 nephrectomized rats (5/6Nx rats). In control rats, the renal and biliary clearances of HA were 18.1 and 0.1 ml/min/kg, respectively. Plasma clearance decreased as dosage increased from 0.1 to 5 mg/kg, which suggests that renal tubular secretion is the primary route for elimination of HA. The plasma clearance of HA was significantly decreased in 5/6 Nx rats compared with normal rats. In 5/6 Nx rats, renal clearance of endogenous HA correlated more closely with clearance of p-aminohippurate than with that of creatinine. Protein expression of rOat1 and rOat3, assessed by Western blot analysis, was decreased in 5/6 Nx rats. Furthermore, in 5/6 Nx rats, the renal secretory clearance of endogenous HA correlated closely with protein expression of renal rOats. Thus, HA is primarily eliminated from the plasma via the kidney by active tubular secretion. The renal clearance of endogenous HA seems to be a useful indicator of changes in renal secretion that accompany the reduced levels of OAT protein in chronic renal failure.

Differential contributions of rOat1 (Slc22a6) and rOat3 (Slc22a8) to the in vivo renal uptake of uremic toxins in rats

PURPOSE

Evidence suggests that uremic toxins such as hippurate (HA), indoleacetate (IA), indoxyl sulfate (IS), and 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF) promote the progression of renal failure by damaging tubular cells via rat organic anion transporter 1 (rOat1) and rOat3 on the basolateral membrane of the proximal tubules. The purpose of the current study is to evaluate the in vivo transport mechanism responsible for their renal uptake.

METHODS

We investigated the uremic toxins transport mechanism using the abdominal aorta injection technique [i.e., kidney uptake index (KUI) method], assuming minimal mixing of the bolus with serum protein from circulating serum.

RESULTS

Maximum mixing was estimated to be 5.8% of rat serum by measuring estrone sulfate extraction after addition of 0-90% rat serum to the arterial injection solution. Saturable renal uptake of p-aminohippurate (PAH, K(m) = 408 microM) and benzylpenicillin (PCG, K(m) = 346 microM) was observed, respectively. The uptake of PAH and PCG was inhibited in a dose-dependent manner by unlabeled PCG (IC(50) = 47.3 mM) and PAH (IC(50) = 512 microM), respectively, suggesting that different transporters are responsible for their uptake. A number of uremic toxins inhibited the renal uptake of PAH and PCG. Excess PAH, which could inhibit rOat1 and rOat3, completely inhibited the saturable uptake of IA, IS, and CMPF by the kidney, and by 85% for HA uptake. PCG inhibited the total saturable uptake of HA, IA, IS, and CMPF by 10%, 10%, 45%, and 65%, respectively, at the concentration selective for rOat3.

CONCLUSIONS

rOat1 could be the primary mediator of the renal uptake of HA and IA, accounting for approximately 75% and 90% of their transport, respectively. rOat1 and rOat3 contributed equally to the renal uptake of IS. rOat3 could account for about 65% of the uptake of CMPF under in vivo physiologic conditions. These results suggest that rOat1 and rOat3 play an important role in the renal uptake of uremic toxins and the induction of their nephrotoxicity.

Nuclear magnetic resonance spectroscopic based studies of the metabolism of black tea polyphenols in humans

Epidemiological studies indicate that a high intake of flavonoids is associated with an improved health status. Tea is one of the most abundant sources of flavonoids in the human diet. The bioavailability and biotransformation of tea flavonoids are, however, not clearly understood. The aim of the present study was to investigate the metabolism of black tea via a nonspecific screening method. (1)H nuclear magnetic resonance (NMR) spectroscopy was used to obtain nonselective profiles of urine samples collected from three human volunteers before and after a single dose of black tea. The complex spectroscopic profiles were interpreted with the use of pattern recognition techniques. Hippuric acid was confirmed as the major urinary black tea metabolite. One previously unknown metabolite was detected and identified as 1,3-dihydroxyphenyl-2-O-sulfate (sulfate conjugate of pyrogallol) using HPLC directly coupled to mass spectrometry and (1)H NMR spectroscopy. This study shows that NMR-pattern recognition studies can be used for the discovery of unknown flavonoid metabolites in humans.

Dynamic renal blood flow measurement by positron emission tomography in patients with CRF

BACKGROUND

Positron emission tomography (PET) is a functional imaging device that allows dynamic regional blood flow measurements. We performed a study to test whether PET could detect acute changes in renal blood flow (RBF) in patients with chronic renal failure (CRF).

METHODS

RBF was measured by means of PET (PET-RBF) using oxygen 15-labeled water (H2(15)O) in eight men with hypertension and moderate CRF before and 5, 40, 80, and 120 minutes after the injection of quinaprilat (10 mg intravenously). Effective renal plasma flow (ERPF) and glomerular filtration rate (GFR) were measured simultaneously by para-aminohippuric acid (PAH-ERPF) and inulin clearances before and 20, 60, 100, and 140 minutes after quinaprilat injection.

RESULTS

Baseline RBF and ERPF were decreased in all patients (221 +/- 20 mL/min/100 g and 225 +/- 38 mL/min/1.73 m2, respectively). PET-RBF increased significantly after quinaprilat injection (+15%, +26%, +19%, and +23% versus baseline; P < 0.003). PAH-ERPF did not increase significantly (-6%, +12%, +20%, and +15% versus baseline; P = 0.15). GFR (50.1 +/- 8.9 mL/min/1.73 m2 at baseline) did not change significantly after quinaprilat injection; however, filtration fraction (GFR-ERPF ratio) decreased significantly from 0.23% +/- 0.02% to 0.20% +/- 0.02% (P = 0.0004). Mean arterial pressure decreased significantly after quinaprilat injection (P < 0.005).

CONCLUSION

This study dynamically measured RBF by means of PET in patients with CRF for the first time. It showed that RBF rapidly increased after quinaprilat injection. PET using H2(15)O is a powerful method for the noninvasive measurement of dynamic changes in RBF that remain undetected by PAH clearance.

Polyphenols from alcoholic apple cider are absorbed, metabolized and excreted by humans

We determined the uptake and excretion of low doses of polyphenols in six subjects who each consumed 1.1 L of an alcoholic cider beverage. Over a 24-h period, no phloretin was detected in plasma (detection limit = 0.036 micromol/L), but 21 +/- 5% of the dose (4.8 mg) was excreted in the urine. In contrast, from a low dose of 1.6-mg quercetin equivalents, no quercetin was found in urine or plasma, but 3'-methyl quercetin was detected in plasma [C(max) (maximum concentration) = 0.14 +/- 0.19 micromol/L; range: 0 to 0.44 micromol/L]. No flavanol monomers (dose of free (+)-catechin and (-)-epicatechin = 3.5 mg) were detected in urine or plasma (detection limit: 0.01 micromol/L). Caffeic acid (total dose including esters = 11 mg) was detected only in plasma within 2 h, with C(max) = 0.43 +/- 0.3 micromol/L (range: 0.18 to 0.84 micromol/L). An almost 3-fold increase in hippuric acid was detected in 24-h urine (74 +/- 29 micromol/L; range: 38-116 micromol/L), compared with a prestudy value of 19 +/- 9 micromol/L. These data show that polyphenols are taken up from cider, that phloretin is excreted in the urine and suggest that low doses of quercetin are extensively methylated in humans.

Development of a physiologically based pharmacokinetic model of organic solvent in rats

A physiologically based pharmacokinetic model of the transfer of organic solvents in rat bodies was developed. The model has six compartments, i.e. lungs, vessel-rich tissue, muscles, fat tissue, tail, and liver, each being interconnected by the blood flow system. The transfer of organic solvents was expressed by simultaneous differential equations, which were then solved numerically by a personal computer using a simple spreadsheet program. m -xylene was used to represent organic solvents. The physiological parameters for rats (alveolar ventilation, cardiac output, tissue volume, tissue blood flow, etc.) and physicochemical or biochemical properties (blood/air partition coefficient, tissue/blood partition coefficients, metabolic constants, etc.) of m -xylene were based on the data obtained from the literature and our experiments. The partition coefficient of m -xylene for the tail and the blood flow and the volume of the rat tail were experimentally determined with adult rats. The results of simulation of rat exposure to m -xylene (50 and 500 ppm for 6 h) were essentially in good agreement with the experimental data on rats, i.e. the parent compound (m -xylene) concentration in the tail blood and the cumulative excretion of the metabolites in the urine were consistent.

Synthesis and in vitro/in vivo evaluation of 5-aminosalicyl-glycine as a colon-specific prodrug of 5-aminosalicylic acid

A simple synthetic route for the preparation of amino acid conjugate of 5-aminosalicylic acid (5-ASA) was exploited and prepared 5-aminosalicyl-glycine (5-ASA-Gly) in good yield. In vitro and in vivo properties of 5-ASA-Gly as a colon-specific prodrug of 5-ASA were investigated using rats as the test animal. Incubation of 5-ASA-Gly with cecal or colonic contents at 37 degrees C released 5-ASA in 65 or 27% of the dose in 8 h, respectively. No 5-ASA was detected from the incubation of 5-ASA-Gly with the homogenates of stomach or small intestine. Plasma concentration of 5-ASA-Gly decreased rapidly after intravenous administration of 5-ASA-Gly, and no 5-ASA was detected in the blood, which indicated 5-ASA-Gly was not degraded in the plasma. After oral administration of 5-ASA-Gly, about 50% of the administered dose was recovered as 5-ASA and N-acetyl-ASA and 3% as 5-ASA-Gly from feces and 14% as 5-ASA-Gly and 28% as 5-ASA and N-acetyl-ASA from urine in 24 h. These results suggested that a large fraction of 5-ASA-Gly was delivered to the large intestine and activated to liberate 5-ASA. For comparison, total recovery of 5-ASA and N-acetyl-5-ASA from feces after oral administration of 5-ASA-Gly was greater than that from sulfasalazine, which is one of the most commonly prescribed prodrugs of 5-ASA.

Effect of chlorophenoxyacetic acid herbicides on glycine conjugation of benzoic acid

1. 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) (0.1-0.5 mmol/kg i.p.) delayed the disappearance of injected benzoate from blood and diminished the urinary excretion of the formed benzoylglycine, but elevated the blood levels of benzoylglycine in rat, suggesting that these herbicides interfere with both the formation and the renal transport of benzoylglycine. 2. Inhibition of the renal excretion of benzoylglycine by 2,4-D or 2,4,5-T (0.5 mmol/kg i.p.) was directly demonstrated in rat injected with benzoylglycine. 3. Inhibition of benzoylglycine formation from benzoic acid by 2,4-D or 2,4,5-T (0.5 mmol/kg i.p.) was directly demonstrated in renal pedicles-ligated rats injected with benzoate. 4. Neither 2,4-D nor 2,4,5-T influenced the hepatic concentrations of ATP, coenzyme A (CoA) or glycine; therefore, it is unlikely that they inhibit glycine conjugation of benzoic acid by diminishing the availability of co-substrates. 5. Although the chlorophenoxyacetic acids did not appear to be a substrate for the mitochondrial acyl-CoA synthetases, both 2,4-D and 2,4,5-T diminished the activity of benzoyl-CoA synthetase (but not that of benzoyl-CoA:glycine N-acyltransferase) in solubilized hepatic mitochondria. These findings suggest that 2,4-D and 2,4,5-T impair benzoylglycine formation in rat by inhibiting benzoyl-CoA synthetase.

Influence of nutritional status on the pharmacokinetics of acetylsalicylic acid and its metabolites in children with autoimmune disease

BACKGROUND

It is unknown whether nutritional status associated with autoimmune disease alters the pharmacokinetics of acetylsalicylic acid (ASA) and its metabolites.

OBJECTIVE

We studied the effects of the nutritional status of children with autoimmune disease on the disposition of ASA and its metabolites.

DESIGN

A prospective, open-label study was performed with 21 children aged 3-15 y who required ASA therapy. Children received 25 mg ASA/kg orally. Blood samples were drawn before and 0.5, 1.0, 2.0, 4.0, 8.0, 12.0, and 24.0 h after ASA administration; urine samples were collected at different intervals. ASA and its metabolites were measured in plasma and urine. Nutritional status was assessed previously.

RESULTS

The ASA maximum plasma concentration, area under the curve, and total clearance were significantly lower in underweight children than in normal-weight children. The elimination rate constants of gentisic acid (GA), salicyluric acid (SUA), and salicylic acid (SA) in plasma were slower for underweight children than for normal-weight children. The distribution volume of SUA increased significantly (r = 0.92) when the deficit percentage in weight-for-height increased. Underweight children excreted less GA and SA, but more SUA, than did normal-weight children.

CONCLUSIONS

These observations suggest a decrease in the hydrolysis and oxidative reactions of the metabolic pathway of ASA and its metabolites in underweight children. The study illustrates the need for pharmacokinetic data to establish the individual doses of drugs, particularly in conditions that alter nutritional status.

Differences in excretion of hippurate, as a metabolite of benzoate and as an administered species, in the single-pass isolated perfused rat kidney explained

The extents of excretion of [14C]hippurate and [3H]hippurate were compared in the single-pass, constant flow (8 ml/min) isolated rat kidney which was perfused simultaneously with tracer concentrations of [14C]benzoate and [3H]hippurate. The steady-state renal extraction ratio of [14C]benzoate was 0.26 +/- 0.04 and was associated with a renal clearance of 1.13 +/- 0.17 ml/min/g. The urinary clearance of [14C]benzoic acid was low (0.011 +/- 0.01 ml/min/g), yielding a low fractional excretion [unbound urinary clearance/glomerular filtration rate (GFR)] value of 0.27 +/- 0.19 and suggesting that glycination of [14C]benzoate to [14C]hippurate accounted almost completely for the total renal clearance. Fractional excretion for preformed [3H]hippurate was eight times that of GFR, but the steady-state renal extraction ratio of preformed [3H]hippurate, E(pmi) (0.24 +/- 0.05) was much lower than the apparent extraction ratio of the renally formed [14C]hippuric acid [E(mi) = 0.39 +/- 0.09] (p <.05). The theoretical basis for the discrepancy was explored with mathematical formulations developed from a physiologically based model of the kidney. It was found that parent drug kinetic parameters (transport and metabolic intrinsic clearance of benzoate) were unimportant for E(mi) or E(pmi). Rather, the value of EK(mi) exceeded EK(pmi) because of the ratio of efflux clearances at the basolateral and luminal membranes for hippurate [corrected] was less than 26.089, a value determined by the GFR, plasma renal flow, and the unbound fraction of hippurate of the system that would render E(mi) to equal E(pmi) in the system. The influx clearance for hippurate to enter from plasma to cell at the basolateral membrane and the reabsorption clearance of hippurate to enter from tubular urine to cell at the luminal membrane failed to alter the ratio of EK(pmi)/EK(mi).

Disposition of 4-methylbenzoylglycine in rat isolated perfused kidney and effects of hippurates on renal mitochondrial metabolism

Hippurates tend to accumulate within proximal tubule cells during renal secretion. High intracellular concentrations can alter proximal tubular function or lead to tubular toxicity. In this study we examined the renal disposition of the hippurate 4-methylbenzoylglycine, a compound known for its high renal intrinsic clearance in-vivo. The effect of intracellular accumulation on mitochondrial respiration was also measured in-vitro and compared with that of the 2-methyl and 4-amino analogues. Experiments were performed with either 2.5% pluronic or a combination of 2.2% pluronic and 2% bovine serum albumin (BSA) as oncotic agents. Within the concentration range studied (1-200 microg mL(-1)) tubular secretion seemed to be a function of the amount of unbound drug in the perfusate. Renal excretion data were best fitted by a model in which a Michaelis-Menten term was used to describe active secretion. Parameters obtained after the analysis of renal excretion data were the maximum transport velocity (TM = 55+/-2 microg min(-1)) and the Michaelis-Menten constant for tubular transport (KT = 4.2+/-0.8 microg mL(-1)). The compound accumulated extensively in kidney tissue, ratios up to 600 times the perfusate concentration were reached. Accumulation could be explained by active tubular uptake and data were analysed best by a model similar to the model used to describe renal excretion. Calculated parameters were theoretical maximum capacity (RM =300+/-210 microg g(-1)) and affinity constant for renal accumulation (KA = 5.0+/-4.4 microg mL(-1)). The high intracellular concentrations of 4-methylbenzoylglycine had no effect on kidney function and mitochondrial oxygen consumption. The 2-methyl analogue reduced mitochondrial respiration slightly, but 4-aminobenzoylglycine (p-aminohippurate) caused a significant reduction. In conclusion, this study shows that renal accumulation of a hippurate is determined by the efficiency of its tubular secretion. Whether the high intracellular concentrations affect tubular cell functioning depends on the analogue involved.

Hepatic clearance models: comparison of the dispersion and Goresky models in outflow profiles from multiple indicator dilution rat liver studies

The multiple indicator dilution (MID) technique is often used for investigation of the kinetic behavior of substrates and metabolites in eliminating organs. The present study was a systematic comparison of the utility of the Goresky model (GM) (a structural model) and the mixed-boundary dispersion model (DM) (a stochastic model) in the interpretation of influx, efflux, and removal (sequestration) coefficients, with data generated from rat liver-perfusion/MID studies. Although the GM and the DM are equivalent in their descriptions of membrane transport, they differ in their classifications of the dispersion of blood-borne elements. For the DM, the dispersion is an inverse Gaussian distribution of vascular transit times; for the GM, it is accounted for by the dispersion observed among noneliminated reference indicators (e.g. labeled red blood cells, albumin, sucrose, and H2O) or the derived reference. In this study, previously published rat liver-perfusion/MID data obtained for the glutathione conjugate of bromosulfophthalein and hippuric acid, compounds that exhibit saturable carrier-mediated transport, with the GM were reanalyzed with the two-compartment DM. When the fitted values for volume and transfer coefficients were compared, good correlation was found between the fitted vascular volume for the DM and the vascular volume for the reference indicator for the GM. The influx coefficients were generally similar between the models, but improved correspondence was observed when the DM was modified to include the large-vessel transit time. In contrast, the efflux and sequestration coefficients obtained for the DM did not correspond well to those from the GM. The disagreement was due, in part, to differences in the interpretation of the late-in-time component of the reference transit time distribution curve, which was not described well by the DM. Consequently, the residence time distribution and the relative dispersion were underestimated by the DM.

Effect of diet on the urinary excretion of hippuric acid and other dietary-derived aromatics in rat. A complex interaction between diet, gut microflora and substrate specificity

1. A combined in vivo and in vitro study has been devised to investigate an observation, obtained by 1H NMR of urine, that Alp:AprSD (Wistar derived) rats kept under standard husbandry conditions did not excrete urinary hippuric acid (HA). meta-(hydroxyphenyl)-propionic acid ¿m-HPPA¿ was identified as the major aromatic component in urine samples lacking HA. 2. Examination of urine from Alp:APrSD and Zücker (obese negative) rats fed various diets showed that the lack of HA/presence of m-HPPA was due to diet and not to the strain of animal. This observation was reinforced by the demonstration that the administration of benzoic acid (BA) to rats not previously excreting urinary HA resulted in the return of this component to the urinary excretion profile. Thus rats receiving the standard diet were still capable of glycine conjugation. 3. Changing the diet of rats excreting m-HPPA led to the cessation of m-HPPA excretion and the return of HA urine excretion. Interestingly, switching back to the original diet did not cause the loss of HA and the re-emergence of m-HPPA. 4. In vitro studies on the two enzyme systems responsible for glycine conjugation (benzoyl CoA:synthetase and benzoyl CoA:glycine N-acyltransferase) in isolated liver mitochondria showed that m-HPPA did not inhibit either enzyme. However, m-HPPA was not found to be a substrate for the first reaction step explaining why it was found in the urine as the free acid and not as a glycine conjugate. 5. The absence and presence of m-HPPA and hippuric acid is suggested to be due to a combination of differences in dietary precursors of substrates for glycine conjugation and a dietary dependent redistribution of the intestinal microflora responsible for breakdown of plant phenolics and aromatic amino acids. Taken collectively this study emphasises how a simple diet change can cause a profound change in metabolism.

Synthesis and evaluation of 5-aminosalicyl-glycine as a potential colon-specific prodrug of 5-aminosalicylic acid

As a new colon-specific prodrug of 5-aminosalicylic acid (5-ASA), 5-aminosalicyl-glycine (5-ASA-Gly) was prepared by a simple synthetic route in good yield. Apparent partition coefficients of 5-ASA-Gly were lower than those of 5-ASA, which determined in CHCl3/pH 6.8 buffer or n-octanol/pH 6.8 buffer system. Stability of 5-ASA-Gly by peptidases was investigated by incubation of 5-ASA-Gly with the homogenates of tissue and contents of stomach, proximal small intestine or distal small intestine of rats at 37 degrees C. 5-ASA was not detected, indicating that the prodrug was stable in the upper intestine. The amount of 5-ASA liberated from incubation of the prodrug in cecal or colonic contents of rats was about 65% or 27% in 8 hrs, respectively, which indicated that the prodrug activation took place more readily in the rat cecum whose bacterial counts are high like human colon. Results from in vitro experiments suggested 5-ASA-Gly as a promising candidate of a colon-specific prodrug of 5-ASA.

Hepatic uptake of hippurate: a multiple-indicator dilution, perfused rat liver study

The hepatic transport of hippuric acid (HA), a glycine-conjugated metabolite of benzoic acid that exhibits only modest plasma albumin binding (binding association constant of 2.1 x 10(3) M-1), was studied in the single-pass perfused rat liver (12 ml/min), using the multiple indicator dilution (MID) technique. The venous recovery of [3H]HA on portal venous injection of a MID dose containing a mixture of a set of noneliminated reference indicators and [3H]HA revealed a survival fraction of unity, corroborating the lack of disappearance of bulk HA from plasma. When the outflow recovery was fitted to the barrier-limited model of Goresky et al. (C.A. Goresky, G. G. Bach, and B. E. Nadeau. J. Clin. Invest. 52: 991-1009, 1973), the derived influx (P(in)S) and efflux (P(out)S) permeability-surface area products were found to be dependent on the concentration of HA (1-930 microM); P(in)S and P(out)S were approximately 3.5 times the plasma flow rate at low HA concentration, but decreased with increasing HA concentration. All values, however, greatly exceeded the expected contribution from passive diffusion, because the equilibrium distribution ratio of chloroform to buffer for HA was extremely low (0.0001 at pH 7.4). The tissue equilibrium partition coefficient (P(in)/P(out), or ratio of influx to efflux rate constants, k1/k-1) was less than unity and decreased with concentration. The optimized apparent Michaelis-Menten constant and maximal velocity were 182 +/- 60 microM and 12 +/- 4 nmol.s-1.g-1, respectively, for influx and 390 +/- 190 microM and 29 +/- 13 nmol.s-1.g-1, respectively, for efflux. In the presence of L-lactate (20 mM), however, P(in)S for the uptake of HA (174 +/- 3 microM) was reduced. Benzoic acid (10-873 microM) was also effective in reducing hepatic uptake of HA (5.3 +/- 0.9 microM). These interactions suggest that MCT2, the monocarboxylate transporter that mediates the hepatic uptake of lactate and other monocarboxylic acids, may be involved in HA transport.

Direct analysis of salicylic acid, salicyl acyl glucuronide, salicyluric acid and gentisic acid in human plasma and urine by high-performance liquid chromatography

A method for the simultaneous direct determination of salicylate (SA), its labile, reactive metabolite, salicyl acyl glucuronide (SAG), and two other major metabolites, salicyluric acid and gentisic acid in plasma and urine is described. Isocratic reversed-phase high performance liquid chromatography (HPLC) employed a 15-cm C18 column using methanol-acetonitrile-25 mM acetic acid as the mobile phase, resulting in HPLC analysis time of less than 20 min. Ultraviolet detection at 310 nm permitted analysis of SAG in plasma, but did not provide sensitivity for measurement of salicyl phenol glucuronide. Plasma or urine samples are stabilized immediately upon collection by adjustment of pH to 3-4 to prevent degradation of the labile acyl glucuronide metabolite. Plasma is then deproteinated with acetonitrile, dried and reconstituted for injection, whereas urine samples are simply diluted prior to injection on HPLC. m-Hydroxybenzoic acid served as the internal standard. Recoveries from plasma were greater than 85% for all four compounds over a range of 0.2-20 micrograms/ml and linearity was observed from 0.1-200 micrograms/ml and 5-2000 micrograms/ml for SA in plasma and urine, respectively. The method was validated to 0.2 microgram/ml, thus allowing accurate measurement of SA, and three major metabolites in plasma and urine of subjects and small animals administered salicylates. The method is unique by allowing quantitation of reactive SAG in plasma at levels well below 1% that of the parent compound, SA, as is observed in patients administered salicylates.

Transdermal delivery of drugs with differing lipophilicities using azone analogs as dermal penetration enhancers

Six model drugs were selected for this study based on their degree of lipophilicity as represented by their log P values (range = -0.95 to 3.51). They included 2,4-dihydroxy-5-fluoropyrimidine (5-fluorouracil); 1,3,7-trimethylxanthine (caffeine); [(2-hydroxybenzoyl)amino]-acetic acid (salicyluric acid); 2-hydroxybenzoic acid (salicylic acid); 9 alpha-fluoro-16 alpha-hydroxyprednisolone 16 alpha, 17 alpha-acetonide (triamcinolone acetonide); and alpha-methyl-4-[2-methylpropyl]benzeneacetic acid (ibuprofen). Six dermal penetration enhancers [Azone or 1-dodecylhexahydro-2H-azepin-2-one (1), N-dodecyl-2-pyrrolidinone (2), N-dodecyl-2-piperidinone (3), N-dodecyl-N-(2-methoxyethyl)acetamide (4), N-(2,2-dihydroxyethyl)dodecylamine (5), and 2-(1-nonyl)-1,3-dioxolane (6)] were tested in vitro across full-thickness hairless mouse skin with each of the drugs. The relationship between lipophilicity (log P) and efficacy (represented by the enhancement ratio of flux) of the drugs when coadministered with the enhancers was examined using linear regression. The three cyclic enhancers (1-3) exhibited linear relationships, indicating that they were more effective at enhancing the penetration of hydrophilic drugs R2 = 0.8997 for 1, 0.8801 for 2, and 0.804 for 3) when evaluating all the model drugs except triamcinolone acetonide (TA). The two acyclic enhancers (4 and 5) showed a similar relationship, but their correlation coefficients were lower at 0.6463 for 4 and 0.6213 for 5. Studies with the dioxolane (6) yielded no relationship between the lipophilicity of the drug and the efficacy of the enhancer, with an R2 of 0.002. Overall, 6 was the least effective enhancer studied. The steroid TA was not included in the linear regression analysis. Of the six model drugs studied, TA exhibited the largest increase in transdermal delivery when enhancers 1-6 were used.

Drug-induced changes in renal hippurate clearance as a measure of renal blood flow

We studied the accuracy of the plasma 131I-hippurate clearance technique to monitor drug-induced changes in renal blood flow (RBF) by comparing it to a flow probe technique in six conscious, chronically instrumented dogs. Placebo caused no change in RBF, either established by hippurate clearance (ERPFhip) or by renal blood flow probe (RBFprobe). Enalaprilate induced a rise in ERPFhip and RBFprobe (+26 +/- 5 and 44 +/- 12%), as did dopamine (+16 +/- 4 and +33 +/- 5%). Intravenous infusion of norepinephrine induced a rise in ERPFhip (+2 +/- 6%, NS) and in RBFprobe (+18 +/- 3%), as did nitroprusside (+14 +/- 4% and +13 +/- 6%, NS). Indomethacin induced a fall in ERPFhip (-8 +/- 2%) and in RBFprobe (-7 +/- 3%, NS), as did angiotensin II (-19 +/- 1 and -26 +/- 3%). Renal hippurate extraction (Ehip) was affected by enalaprilate, dopamine, and angiotensin II (-5 +/- 2, -7 +/- 1, and +5 +/- 2%, respectively). Hematocrit (Hct) was affected by dopamine, norepinephrine, and nitroprusside (+2 +/- 1, +6 +/- 1, and -6 +/- 2%, respectively). Drug-induced changes in ERPFhip correlated well with changes in RBFprobe (r = 0.902, P < 0.01). Changes in Ehip did not independently affect this relation, whereas changes in Hct did: delta RBF(% of baseline) = 1.529 x delta ERPFhip(% of baseline) + 1.296 x delta Hct(% of baseline). These data indicate that drug-induced changes in plasma hippurate clearance can, even when changes in renal hippurate extraction are unknown, be used as a reliable indicator of changes in renal blood flow if changes in hematocrit are taken into account.

Benzoic acid glycine conjugation in the isolated perfused rat kidney

The fate of varying input concentrations (0.002-372 microM) of benzoic acid was examined in the single-pass isolated perfused rat kidney preparation under constant flow rate (8 ml min-1.organ-1). With an increasing concentration of benzoate, the steady-state renal extraction ratio decreased from 0.24 to 0.1. Little unchanged drug was found in the urine; the urinary clearance of benzoate was low (0.018 ml-1 min-1.g-1) and concentration-independent, yielding a rather constant fractional excretion of approximately 0.2. Metabolic clearance, due primarily to conjugation with glycine to form hippuric acid, constituted the majority of total renal clearance, and this decreased with concentration. These divergent trends for the metabolic and urinary clearance with concentration suggest that benzoate net influx across the basolateral membrane has not been saturated. Upon fitting of the hippurate formation rates vs. the plasma unbound logarithmic average concentrations of benzoate, overall kinetic constants (KM = 5.3 microM and Vmax = 195 nmol min-1.g-1) that likely reflect glycine conjugation were obtained. The formed hippurate either returned to the venous circulation or was excreted into urine without further biotransformation; the apparent renal extraction ratio (excretion rate/formation rate of hippurate) was quite high (approximately 0.48). Avid glycine conjugation and hippurate excretion thus occurred with administration of benzoic acid to the isolated perfused rat kidney.

Synthesis and preclinical evaluation of technetium-99m-labeled hippurate analogues

We have synthesized seven 99mTc-labeled hippurate analogues: 99mTc-hippurate. 99mTc-alpha-hydroxyhippurate, 99mTc-m-hydroxyhippurate. 99mTc-o-hydroxyhippurate [99m-salicylglycine (99mTc-SG)], 99mTc-p-hydroxyhippurate, 99mTc-salicylglycylglycine and 99mTc-salicylglycylglycylglycine. All of the 99mTc-hippurates were cleared rapidly from the rat blood and accumulated in the kidney. Of them 99mTc-SG has the desirable biological properties of two diagnostic agents. 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) and 99mTc-dimercaptosuccinate (99mTc-DMSA). A fraction of 99mTc-SG showed a transit time in the kidney and was excreted rapidly into the urine, being similar to 99mTc-MAG3. The binding ratio to the plasma proteins was 96.0% (91.1% in the albumin), being higher than that of 99mTc-DMSA, at 30 min. The lipophilicity revealed far less pH-dependent changes in a range of pH 4.0 to 7.4. 99mTc-SG distributed about 91% in the renal cortex, being similar to that of 99mTc-DMSA. From the present studies, the biological properties of 99mTc-SG suggest that it is a promising agent for measuring renal plasma flow and renal morphology.

Restricted diffusion of an 19F-labelled organic acid in human erythrocytes analyzed by 19F pulsed field gradient NMR

The diffusion coefficient of an 19F-labelled organic acid (3-trifluoromethylhippurate: TFMH) was measured in intact human red blood cells (RBCs) and sealed right-side-out ghosts at 22.5 +/- 0.05 degrees C. Diffusion coefficients were measured using stimulated echo and spin-echo pulsed field gradient sequences. The apparent diffusion coefficient (Da) of TFMH in the intracellular space was much smaller than in the extracellular medium. This was due to restricted diffusion of intracellular TFMH since i) the intracellular Da decreased when the diffusion time was increased, and ii) the smaller Da component disappeared when the membrane was permeabilized with saponin. From the intracellular Da values obtained over a range of diffusion times, from 5 ms to 1 s, the apparent radius of the diffusion barrier was estimated to be 3 +/- 1.1 micron assuming spherical geometry. Despite the high protein concentration in the intracellular space of the intact RBC, the intracellular values of Da were similar to the values obtained in the ghosts at the same diffusion times. We therefore conclude that the small diffusion coefficient of intracellular TFMH is mainly explained by the restricted diffusion due to the cell boundary.

Pharmacokinetics of acetylsalicylic acid and its metabolites at low doses: a compartmental modeling

The pharmacokinetics of acetylsalicylic acid (ASA) and its metabolites salicylic acid (SA) and salicyluric acid (SUA) were studied in 12 healthy young volunteers after oral administration of low (30 and 100 mg) and moderate (400 mg) doses. Plasma and urine were assayed for the above drugs by high-performance liquid chromatographic method. Individual pharmacokinetic parameters were estimated by compartmental modeling (ASA and SA) and by model-independent methods (SUA). ASA parameter values estimated in this study were in agreement with those reported by other authors after administration of higher doses, which confirms the linearity of ASA pharmacokinetics in a broad dose range. On the contrary, both metabolic and renal elimination routes for SA were found to be saturable. The relative changes in SA renal clearance with the dose were more pronounced than those in metabolic clearance. Particularly, there was no statistically significant difference in SA metabolic clearance between 30 and 100 mg doses, indicating the linear kinetics in this dose range. Further increase in the dose resulted in significant decrease in SA metabolic clearance. At the same time, both SA excretion rate constant and fraction excreted significantly diminished across the entire dose range studied. The dependence of SUA renal clearance upon the dose was shown to be complex, reflecting possible saturability of its excretion.

Effect of urinary pH on the pharmacokinetics of salicylic acid, with its glycine and glucuronide conjugates in human

We studied the effects of urinary pH on the kinetics of salicylic acid (SA) with its metabolites and assessed the contribution of alkaline hydrolysis of salicylic acid acyl glucuronide to the renal clearance of salicylic acid. Hydrolysis of SAAG in alkaline urine contributes marginally to the high renal clearance and excretion of salicylic acid, validating alkalinization of a patient with SA overdose. Under acidic urine conditions, salicylic acid (SA) had a terminal plasma t1/2 value of 3.29 +/- 0.52 hours while under alkaline urine conditions this t1/2 was significantly reduced to 2.50 +/- 0.41 hours (p = 0.0156). The total oral body clearance of salicylic acid under acidic conditions (1.38 +/- 0.43 l/h) is significantly lower than under alkaline urine conditions (2.27 +/- 0.83 l/h; p = 0.0410). The Km and Vmax values of SA, and its conjugates salicylic acid phenolic glucuronide (SAPG), salicyluric acid (SU) and salicyluric acid phenolic glucuronide (SUPG) did not differ statistically under acidic and alkaline urine conditions. The protein binding of SA was 93.8 +/- 1.0% and that of SU was 89.7 +/- 2.2% in vivo and in vitro. SUPG had a protein binding of 84.8 +/- 1.8%, while SAPG showed no protein binding at all. The renal excretion of salicylic acid depends strongly on the urinary pH. The percentage of the dose excreted unchanged increased from 2.3 +/- 1.5% under acidic conditions to 30.5 +/- 9.1% under alkaline conditions (p = 0.0006). Alkaline urine lowered by 50% the percentage of the dose excreted as SU (p = 0.0028), SAAG (p = 0.0013), and SUPG (p = 0.0296), while SAPG is only marginally lowered (p = 0.0589).(ABSTRACT TRUNCATED AT 250 WORDS)

Maleimidoethyl 3-(tri-n-butylstannyl)hippurate: a useful radioiodination reagent for protein radiopharmaceuticals to enhance target selective radioactivity localization

In pursuit of radiolabeled monoclonal antibodies (mAbs) with rapid urinary excretion of radioactivity from nontarget tissues, radioiodinated mAbs releasing a m-iodohippuric acid from the mAbs in nontarget tissues were designed. A novel reagent, maleimidoethyl 3-(tri-n-butylstannyl)hippurate (MIH), was synthesized by reacting N-(hydroxyethyl)maleimide with N-Boc-glycine before coupling with N-succinimidyl 3-(tri-n-butylstannyl)benzoate (ATE). MIH possessed a maleimide group for mAb conjugation and a butylstannyl moiety for high-yield and site-specific radioiodination, and the two functional groups were linked via an ester bond to release m-iodohippuric acid. To investigate the fate of radiolabels after lysosomal proteolysis, hepatic parenchymal cells were used as a model nontarget tissue and 131I-labeled MIH was conjugated with galactosyl-neoglycoalbumin (NGA). Further conjugation of [131I]MIH with a mAb against osteogenic sarcoma (OST7) after reduction of its disulfide bonds was followed up. In murine biodistribution studies, [131I]MIH-NGA exhibited rapid accumulation in the liver followed by radioactivity elimination from the liver at a rate that was identical to and faster than those of 131I-labeled NGA via direct iodination ([131I]NGA) and [131I]ATE-labeled NGA, respectively. While [131I]NGA indicated high radioactivity levels in the murine neck, stomach, and blood, such increases in the radioactivity count were not detectable by the administration of either [131I]MIH-NGA or [131I]ATE-NGA. At 6 h postinjection of [131I]MIH-NGA, 80% of the injected radioactivity was recovered in the urine. Analyses of urine samples indicated that m-iodohippuric acid was the sole radiolabeled metabolite. In biodistribution studies using [131I]-MIH-OST7 and [131I]ATE-OST7, while both 131I-labeled OST7s registered almost identical radioactivity levels in the blood up to 6 h postinjection, the former demonstrated a lower radioactivity level than [131I]ATE-OST7 in nontarget tissues throughout the experiment. Such chemical and biological characteristics of MIH would enable high target/nontarget ratios in diagnostic and therapeutic nuclear medicine using mAbs and other polypeptides.

Determination of 3,4-dimethylhippuric acid as a biological monitoring index for trimethylbenzene exposure in transfer printing workers

The relationship between exposure to 1,2,4-trimethylbenzene (1,2,4-TMB) and urinary concentration of 3,4-dimethylhippuric acid (3,4-DMHA), one of its metabolites, was studied in workers involved in transfer printing. Airborne TMBs were sampled by an organic vapor monitoring badge and analyzed by capillary gas chromatography. Urinary 3,4-DMHA and creatinine were analyzed under the same conditions of high-performance liquid chromatography. The exposure concentration of 1,2,4-TMB among workers was around 25 ppm, the threshold limit value (TLV). The urinary concentration of 3,4-DMHA was low at the start of each shift and high at the end. Exposure to the TLV (25 ppm) of 1,2,4-TMB results in a urinary 3,4-DMHA concentration of 410 mg/g creatinine (r = 0.897, P < 0.001). Urinary 3,4-DMHA concentration could be used as a biological monitoring index for 1,2,4-TMB exposure.

A newly designed radioimmunoconjugate releasing a hippurate-like radiometal chelate for enhanced target/non-target radioactivity

Target-to-non-target ratio of radioactivity can be enhanced by the injection of monoclonal antibodies (MoAbs) labeled with metallic radionuclides, if some modality to accelerate the urinary excretion of radioactivity accumulated in non-target tissues could be introduced. In this study, a radioimmunoconjugate chemically designed to release a hippurate-like radiometal chelate was synthesized and tested in vivo. A 67Ga chelate of succinyldeferoxamine (SDF) was conjugated with a MoAb against osteogenic sarcoma (OST7, IgG1) through an ester bond using a new metabolizable MESS linker, N-[I4-(maleimidoethoxy)succinyl]oxy]succinimide (67Ga-DFO-MESS-OST7). When injected into normal mice, 67Ga-DFO-MESS-OST7 exhibited faster clearance of radioactivity from circulation with less accumulation in the liver, kidney and spleen than those observed with 67Ga-DFO-EMCS-OST7, which was prepared under identical conditions to 67Ga-DFO-MESS-OST7 except for using a non-metabolizable linker holding no ester bond to release 67Ga-SDF. Size exclusion HPLC analysis of the liver homogenate obtained from mice 24 h after injection of 67Ga-DFO-MESS-OST7 indicated that all the radioactivity was eluted in the high molecular weight fraction with most of it being present as the 67Ga-DFO-MESS-OST7 fraction. Reverse-phase HPLC analysis of urine sample from the same mice showed a single radioactivity peak at the same retention time as that of 67Ga-SDF. In athymic mice bearing osteogenic sarcoma, 67Ga-DFO-MESS-OST7 exhibited higher tumor-to-blood and tumor-to-organ ratio of radioactivity when compared with 67Ga-DFO-EMCS-OST7. These results indicated that 67Ga-DFO-MESS-OST7 achieved enhanced target-to-non-target ratio of the radioactivity, due to preferential cleavage of the ester bond in non-target tissues, followed by rapid urinary excretion of the resulting chelate (probably as 57Ga-SDF). These results also suggest that the present design would become an applicable modality for enhancing the target-to-non-target ratio of radioactivity by MoAbs.

Application of 13C-labeling and nuclear magnetic resonance spectroscopy to pharmacokinetic research: measurement of metabolic rate of benzoic acid to hippuric acid in the rat

The use of 13C-labeling and nuclear magnetic resonance (NMR) spectroscopy to trace the biotransformation of benzoic acid (BA) to hippuric acid (HA) in the rat has been described. Novel [2,4,6,7-13C4]BA, which was labeled in the specific protonated carbons, was used in order to enhance the sensitivity of 13C NMR detection on the basis of the nuclear Overhauser enhancement and short spin-lattice relaxation time. The urinary excretion of [2,4,6,7-13C4]HA formed from intravenously administered [2,4,6,7-13C4]BA was followed by proton-decoupled 13C NMR spectroscopy (only 10 min accumulation time) without any separation procedures such as extraction and chromatography, using [2-13C]sodium acetate as an internal standard for quantitation. The heights of resonances for C2,6 of [2,4,6,7-13C4]HA and C2 of the internal standard were used to calculate [2,4,6,7-13C4]HA concentration. The lower limit of measurable amounts (ca. 40 nmol) was found to be improved about one order of magnitude over that of the method using commercially available [7-13C]BA. In general, this tracer technique has the potential for wide application to pharmacokinetic research since xenobiotic and endogenous metabolism can be followed by very simple and convenient procedures.

Hepatic metabolism of toluene after gastrointestinal uptake in humans

The metabolism of toluene and the influence of small doses of ethanol were measured in eight male volunteers after gastrointestinal uptake, the toluene concentration in alveolar air and the urinary excretion of hippuric acid and ortho-cresol being used as the measures of metabolism. During toluene exposure to 2 mg.min-1 for 3 h the alveolar toluene concentration was 0.07 (range 0-0.11) mg.m-3; exposure to 6 mg.min-1 for 30 min increased the alveolar concentration to 0.9 (range 0.03-2.6) mg.m-3. Ingestion of 0.08, 0.16, and 0.32 g of ethanol per kilogram of body weight during toluene exposure of 2 mg.min-1 increased the alveolar concentration within 10 min, and maximal alveolar concentrations of 5 (SD 3), 24 (SD 11), and 39 (SD 28) mg.m-3 were reached after 30, 60, and 90 min for the three doses, respectively. Hippuric acid excretion was only decreased by an ethanol dose of 0.32 g.kg-1. Very low doses of ethanol inhibit toluene metabolism, and the procedure is sensitive enough to measure metabolic interactions between solvents and other xenobiotics in humans.

Urinary excretion of 3,4-dimethylhippuric acid in workers exposed to 1,2,4-trimethylbenzene

The urinary excretion of 3,4-dimethylhippuric acid (34DMHA), a 1,2,4-trimethylbenzene (124TMB) metabolite, was investigated in workers exposed to 124TMB vapor. The time-weighted average of exposure to 124TMB was determined with a diffusive sampler. For biological monitoring of exposure, urine samples were collected from individual workers and analyzed for metabolites by high-pressure liquid chromatography. The concentration of urinary 34DMHA had a positive correlation with the level of exposure to 124TMB (r = 0.72). The data suggest that 34DMHA is one of the useful indicators for biological monitoring of 124TMB exposure.

Clinical significance of benzoate-metabolizing capacity in patients with chronic liver disease: pharmacokinetic analysis

Benzoate-metabolizing capacity was studied in control subjects and in liver disease patients after intra-venous loading of 15 mg benzoate per kg of body weight. In the 7 control subjects, the mean level (+/- SEM) of Cmax for serum benzoate was 104.1 +/- 6.8 micrograms/ml, AUC was 2.57 +/- 0.32 mg.min/ml, MRT was 21.5 +/- 1.5 min and T1/2 was 15.5 +/- 1.3 min. For serum hippurate, on the other hand, Tmax was 27.9 +/- 6.0 min, Cmax was 33.4 +/- 2.1 micrograms/ml, AUC was 1.96 +/- 0.13 mg.min/ml, MRT was 39.6 +/- 2.9 min and T1/2 was 30.7 +/- 2.4 min. In 12 patients with chronic hepatitis, Cmax, AUC, MRT and T1/2 for benzoate and Tmax, MRT and T1/2 for hippurate remained at control levels, but Cmax and AUC for hippurate were slightly decreased compared to controls. However, in 18 patients with liver cirrhosis, Cmax and AUC for benzoate were in the control range but MRT and T1/2 were significantly delayed (p less than 0.01 for both). Moreover, the MRT value was increased in proportion to the severity of liver disease (p less than 0.01). AUC for hippurate was not changed to any extent, and Tmax, MRT and T1/2 were slightly delayed, while Cmax was significantly reduced. AUC, MRT and T1/2 for benzoate and Tmax, MRT and T1/2 for hippurate showed significant correlation with serum albumin levels, prothrombin time and indocyanine green clearance rate. These results suggest that benzoate-metabolizing capacity, especially as indicated by the MRT value for serum benzoate, appears to be a better index than the indocyanine green clearance rate for determining hepatic functional reserve in chronic liver disease.

On pharmacokinetic evaluation of model drugs distribution into rat central lymph

Numerous experimental data obtained in the studies of factors influencing the transfer of model drugs (diazepam, inulin, hippurate) into the lymphatic system were evaluated using compartmental pharmacokinetic analysis. The selection of kinetic equations for lymphatic data analysis in respect to blood ones is specific. Lymphatic kinetic equations correspond in every case tested with those used generally in blood kinetic analysis of drugs administered perorally. The lag time parameter is useful in this lymphatic analysis, too.

Dose-dependent pharmacokinetics of benzoic acid following oral administration of sodium benzoate to humans

Plasma concentration-time data for benzoic and hippuric acids and urinary excretion-time data for hippuric acid were analyzed simultaneously after oral doses of 40, 80 or 160 mg/kg sodium benzoate administered at least one week apart to 6 healthy subjects. The mean AUCs of benzoic acid after the doses of 80 and 160 mg/kg of sodium benzoate were 3.7- and 12.0-times greater, respectively, than after 40 mg/kg. However, the mean AUC of hippuric acid was roughly proportional to the benzoate doses. The observed data were explained by a one-compartment model with first-order rate absorption and Michaelis-Menten elimination of benzoic acid, together with a one-compartment model with first-order elimination for hippuric acid. Although the maximum rate of biotransformation of benzoic acid to hippuric acid varied between 17.2 and 28.8 mg.kg-1.h-1 among the six individuals, the mean value (23.0 mg.kg-1.h-1) was fairly close to that provided by daily maximum dose (0.5 g.kg-1.day-1) recommended in the treatment of hyperammonaemia in patients with inborn errors of ureagenesis. The individual maximum rate of metabolism can be estimated from the urinary excretion rate of hippuric acid 1.5 to 3 h after the single oral dose of 80 to 160 mg.kg-1 sodium benzoate. The justification of this concept requires further studies in patients with inborn errors of urea synthesis.

Salicylic acid disposition in children with rheumatoid arthritis

The plasma level profile of SA and SUA after a single oral dose of ASA was studied in 8 children with juvenile rheumatoid arthritis, aged 3.5-15.0 years. Pharmacokinetic parameters were on average similar to those reported in the literature for adult subjects, although a somewhat larger intersubject variability was found.

The influence of age on salicylate pharmacokinetics in humans

The pharmacokinetics of salicylate after a single oral solution dose of 600 mg of sodium salicylate were investigated in 22 male subjects. Subjects were healthy nonsmokers and were not taking any regular medication. The plasma concentration and urinary excretion of salicylic acid and its metabolite, salicyluric acid, as well as the urinary excretion of salicyl glucuronides were determined. Urinary recovery essentially accounted for the administered dose and was not influenced by age, nor was the apparent oral clearance of salicylic acid. Assuming no presystemic elimination, it could be concluded that systemic availability is unaffected by age. An increase in the apparent volume of distribution, Varea, and a decrease in the maximum plasma salicylic acid concentration with age were observed. Renal clearance of salicyluric acid decreased significantly with age and was found to correlate significantly with creatinine clearance. The authors conclude that age does not have a major influence on salicylate disposition in healthy adult men.

Pharmacokinetics and elimination of salicylic acid in rabbits

Sodium salicylate was administered to rabbits in order to compare its disposition with that in other major and minor agricultural species. A dose of 44 mg/kg was given orally (p.o.) or intravenously (i.v.), and plasma and urine samples were collected for 36 h and 96 h, respectively. The majority of the drug was excreted as salicylic acid (SA) within 12 h. The major metabolites following an oral dose were salicyluric acid (SUA) and the glucuronide conjugates of SA and SUA. Following i.v. dosing, sulfate conjugates of both SA and SUA were also evident. Both SA and SUA were detected in plasma. Following i.v. administration, SA was distributed with a Vss of 0.249 +/- 0.082 l/kg and cleared at a rate of 0.0432 +/- 0.006 l/h/kg. The biological half-life, calculated from the terminal disposition-rate constant, was 4.3 h (i.v.) or 9.7 h (p.o.). The urinary elimination pattern of SA and metabolites in the rabbit was similar to that previously reported by our laboratories for cattle and goats, although total recovery of the administered dose was not as high as for the latter two species. However, the volume of distribution was larger than for cattle and goats, and rabbits cleared the drug more slowly than those species. As a consequence, the biological half-life was eight to ten times longer than in the ruminants studied previously.

A comparative study of renal scintigraphy and clearance with technetium-99m-MAG3 and iodine-123-hippurate in patients with renal disorders

The aim of this study was to compare kit prepared technetium-99m-mercaptoacetyltriglycine (99mTc-MAG3) with our routine radiopharmaceutical, iodine-123-hippurate our routine radiopharmaceutical, iodine-123-hippurate ([123I]OIH) for renal dynamic scintigraphy. Seventeen patients with different nephrologic disorders or hypertension were first studied with OIH and then reinvestigated with MAG3 2-8 days later. Renal MAG3 gamma camera images were almost identical with those of OIH except for higher (p less than 0.01) liver-to-background ratios at 20 min postinjection, irrespective of kidney function. Urinary peristalsis was visible longer and more clearly in the MAG3 studies. MAG3 and OIH renograms showed identical relative kidney uptake (r = 0.99), but elimination of MAG3 from the kidneys was slower (p less than 0.01). The plasma clearance of MAG3 was lower than that of OIH, but correlated (r = 0.92) significantly. The plasma distribution volume and content in blood cells was lower (p less than 0.01), but the binding of MAG3 to plasma proteins was higher, 90%, as compared with 74% for OIH, p less than 0.01. Urinary excretion expressed as a percent of the given dose 60 min after injection was the same for the two substances. Thus, there are some significant differences in the renal handling, plasma distribution, and cell penetration between MAG3 and [123I]OIH. MAG3, however, seems to have particular qualifications as a radionuclide for dynamic renal scintigraphy, especially in patients who require acute investigations or in those with low renal function.

Elimination of salicylic acid in goats and cattle

Sodium salicylate was administered to cattle and goats IV and PO according to a crossover design. Total urinary excretion of SA and its metabolites was measured for 3 days after dosing. Salicyluric acid (SUA) was the only metabolite detected in urine of either species. Recovery of sodium salicylate and SUA in goats amounted to 67.9 and 34.6% of the dose, respectively, after IV administration. After oral dosing, total recoveries were 30.2% (sodium salicylate) and 71.7% (SUA) of dose. By comparison, cattle excreted significantly (P less than 0.05) less sodium salicylate (54.0%) and more SUA (49.9%) after IV dosing. The same pattern was observed after oral administration, wherein cattle excreted less than 12% as sodium salicylate and more than 99% as SUA. In both species, almost 90% of the drug excreted as sodium salicylate was found in urine within the first 12 hours after an IV dose and within 24 hours after oral dosing. The excretion of SUA was somewhat slower in both species, especially after oral administration. The data suggested that there were only quantitative differences in the metabolism and elimination of sodium salicylate between the 2 species, with cattle excreting a higher proportion of the drug as the glycine conjugate SUA.

[Transport of drugs through human erythrocyte membranes. Change of transport by introduction of amino group or amino acids in benzoic acid]

The transporting properties of benzoic acid (BA) and its derivatives such as hippuric acid (HPA), p-aminohippuric acid (AHPA), N-benzoyl-beta-alanine (NBA), p-amino-N-benzoyl-beta-alanine (ANBA), N-benzoyl-6-aminocaproic acid (NBC), p-amino-N-benzoyl-6-amino-caproic acid (ANBC), o-, m- or p-hydroxybenzoic acid (o-, m- or p-HBA) and alpha- or gamma-resorcylic acid (alpha- or gamma-RA) through erythrocyte membranes were examined in two aspects of the inward direction from a drug-containing medium into the erythrocyte and the outward direction from the drug-containing erythrocyte to the drug-free medium. The significant difference in the rate of transport was observed between both directions. The introduction of a few methylene groups into the amino acid moieties of BA derivatives was slower in the rate of transport than that of more methylene groups. The rate of transport was slowed down by the introduction of amino group at p-position: NBC greater than NBA greater than HPA much greater than ANBC greater than ANBA greater than AHPA. The rate of transport in these drugs was correlated with the changes in partition coefficients. The same correlation was also observed in the drugs to which hydroxyl groups were introduced except alpha- or gamma-RA. This transport of alpha- or gamma-RA suggested the participation of the band 3 anion transporter protein.

Renal handling of salicyluric acid in the isolated perfused rat kidney: evidence for accumulation in tubular cells

The renal handling of salicyluric acid (SU) was studied over a broad concentration range (0-400 micrograms/ml) in the isolated perfused rat kidney (IPK). The accumulation of SU was determined by difference calculations between the SU dose given and the SU amount present in the perfusate and excreted into the urine. SU accumulates highly in the IPK and this accumulation is concentration-dependent. At low perfusate concentrations (5-20 micrograms/ml) there is a sharp increase in the accumulation (100-400 micrograms/g), whereas at higher concentrations (20-100 micrograms/ml) a small increase (400-500 micrograms/g) is seen. The largest part of the accumulation is probably caused by accumulation of SU in the tubular cells. This is a result of the active uptake of SU over the basolateral membrane followed by facilitated diffusion over the brush-border membrane. As a result of the saturation of the active SU uptake, accumulation reaches a maximal value. Excretion of SU in the IPK involves glomerular filtration, active secretion and reabsorption. Reabsorption is probably a passive process, dependent on the urinary flow and pH. The apparent Michaelis-Menten constant of the excretion is 18.7 +/- 1.8 micrograms/ml and the maximum transport capacity is 69.8 +/- 1.4 micrograms/min. The pharmacokinetic parameters of the excretion of SU were in good agreement with previously reported in vivo values.

Sustained blood concentration of salicylic acid following rectal administration of salicyluric acid in dogs

The blood concentrations of salicyluric acid and salicylic acid following rectal, intravenous and oral administrations of salicyluric acid (5, 10 and 60 mg/kg, respectively: salicylic acid equivalent) were determined in dogs. After rectal administration, a small amount of salicyluric acid was absorbed in intact form. The rest was hydrolyzed to salicylic acid, which was subsequently absorbed. The blood concentration of salicylic acid was maintained at 0.4-0.7 microgram/ml from 2 to 12 h. Following intravenous administration of salicyluric acid, salicyluric acid was detected in the blood but was rapidly eliminated. A trace amount of salicylic acid was detected, suggesting that systemic de-conjugation of glycine was involved. After oral administration of salicyluric acid, salicyluric acid was well absorbed. Salicylic acid was detected at low concentration for 12 h. Species difference in the metabolic fate of salicyluric acid in dogs, rabbits, rats and humans reported previously is discussed.

Protein binding of salicylic and salicyluric acid in serum from malnourished children: the influence of albumin, competitive binding and non-esterified fatty acids

The serum protein binding of salicylic and salicyluric acid has been determined by ultrafiltration in 60 children after administration of oral salicylate. The children were classified according to nutritional status: well-nourished (n = 12), underweight (n = 12), marasmic (n = 17) marasmic-kwashiorkor (n = 7) and kwashiorkor (n = 12). Salicylic acid free fractions were 0.106 +/- 0.026, 0.114 +/- 0.069, 0.141 +/- 0.037, 0.285 +/- 0.279 and 0.438 +/- 0.190 in the five groups, respectively. Salicyluric acid free fractions were 0.184 +/- 0.057, 0.280 +/- 0.282, 0.236 +/- 0.114, 0.484 +/- 0.497 and 0.646 +/- 0.261, respectively. The degree of binding was dependent on serum albumin levels, ligand concentrations and non-esterified fatty acids (NEFA). The NEFA/albumin ratio ranged from 0.05 to 6.6. The fitting of a one-site Scatchard binding model to the collective data was improved when a decrease was allowed for in the number of binding sites in proportion to NEFA concentrations. Salicyluric acid binding could be fitted only when inhibition of the parent compound was included. Binding was not affected by age or sex. The major determinants of salicylate binding in sera from malnourished children have thus been identified.

Renal clearance of substituted hippurates in the dog. II. 4-Amino-, hydroxy- and methoxy-substituted benzoylglycines

Plasma kinetics and renal excretion of 4-aminobenzoylglycine (p-aminohippurate), hydroxy- and methoxy-substituted benzoylglycines were studied in three Beagle dogs after rapid i.v. administration of about 1 g. Plasma protein binding of 4-amino-, 3-hydroxy- and 4-hydroxybenzoylglycine was low (less than 15%) and practically constant over a range of 5 to 450 micrograms/ml, whereas the 2-hydroxy analog showed concentration-dependent protein binding (40-80%). The excretory patterns of the 4-amino, 3- and 4-hydroxy analogs were essentially the same; rapid elimination from plasma into urine (greater than 80% of the dose), mainly by very efficient supply-limited tubular secretion. Conversely, the excretion of 2-hydroxybenzoylglycine was characterized by a lower plasma clearance and total renal excretion (64% of the dose), and a limited capacity of the tubular secretory system. The methoxybenzoylglycines showed nonlinear plasma protein binding varying between 10 and 70%, rapid clearance from plasma, largely by renal excretion (72-84% of the administered dose). Tubular secretion of 2- and 3-methoxybenzoylglycine was saturated, whereas complete saturation was not achieved for the 4-methoxy isomer. The kinetic parameters of tubular secretion were estimated with a physiologically based kidney model: 2-hydroxy, tubular transport maximum (TM) = 4.4 +/- 0.9 mg/min, Michael-Menten constant of the tubular secretion mechanism (KT) = 23 +/- 8 micrograms/ml; 2-methoxy-TM = 11.7 +/- 4.9 mg/min, KT = 42 +/- 9 micrograms/ml; 3-methoxy-TM = 8.8 +/- 1.0 mg/mn, KT = 27 +/- 20 micrograms/ml. Inasmuch as secretion of the other compounds was not saturated, only the intrinsic secretion clearance (CLint) = TM/KT could be estimated; 4-amino-CLint = 145 +/- 50 ml/min, 3-hydroxy-CLint = 194 +/- 21 ml/min, 4-hydroxy-CLint = 153 +/- 23 ml/min and 4-methoxy-CLint = 201 +/- 47 ml/min. The 4-methoxy isomer was metabolized to some extent by deconjugation of the glycine moiety and the resulting benzoate was found in plasma but not in urine.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal clearance of substituted hippurates in the dog. I. Benzoylglycine (hippurate) and methyl-substituted benzoylglycines

Plasma kinetics and renal excretion of benzoylglycine (hippurate) and methyl-substituted benzoylglycines were studied in three Beagle dogs, after rapid i.v. administration of about 1 g of glycine conjugate. Benzoylglycine and the 3- and 4-methyl analogs showed nonlinear plasma protein binding varying between 20 and 80% over a concentration range of 5 to 450 micrograms/ml. For 2-methylbenzoylglycine an extremely high protein binding, practically approaching 100%, was observed at low plasma levels (less than 50 micrograms/ml). All conjugates were cleared largely via the kidney (greater than 80% of the dose) and, except for the 2-methyl analog, eliminated rapidly from plasma. Plasma concentration and renal excretion rate data were analyzed simultaneously with a previously developed physiologically based kidney model. Tubular secretion appeared to be a function of the total drug concentration in renal plasma, except for 2-methylbenzoylglycine, presumably due to its tight protein binding. The average values of the parameters characterizing the tubular transport maximum (TM in milligrams per minute) and the apparent affinity for the secretory system (KT in micrograms per milliliter) were: benzoylglycine TM = 5.5 +/- 0.8, KT = 40 +/- 5; 3-methylbenzoylglycine TM = 7.1 +/- 3.3, KT = 49 +/- 1; 4-methylbenzoylglycine TM = 8.0 +/- 1.6, KT = 14 +/- 6. Secretion of 2-methylbenzoylglycine was not saturated. Accordingly, only the ratio TM/KT = 163 +/- 54 ml/min could be calculated. An interesting observation was the partial deconjugation of 4-methylbenzoylglycine to its corresponding benzoate.(ABSTRACT TRUNCATED AT 250 WORDS)

Further studies on the hydrolysis of salicyluric acid in intestinal microorganisms and prolonged blood concentration of salicylic acid following rectal administration of salicyluric acid in rabbits

The blood concentrations of salicyluric acid and salicylic acid following intracecal and rectal administration of salicyluric acid were determined in rabbits. Immediate and very extensive salicylic acid formation in the cecum was found following intracecal administration. After rectal administration, a small amount of salicyluric acid was absorbed in intact form. The rest was rapidly hydrolyzed to salicylic acid, which was subsequently absorbed. The blood concentration of salicylic acid was maintained at 1.3-1.8 micrograms/ml from 2 to 12 h. Three doses of salicyluric acid were administered rectally. The peak level of salicyluric acid increased with dose. However, salicylic acid concentration in the blood following administration of salicyluric acid at 10.0 mg/kg (salicylic acid equivalent) was not double that observed following administration of salicyluric acid at 5.0 mg/kg (salicylic acid equivalent). It appears that a larger amount of salicyluric acid in the rectal lumen may have saturated the glycine deconjugation system.

Physiologically based pharmacokinetic model for the renal clearance of salicyluric acid and the interaction with phenolsulfonphthalein in the dog

Plasma kinetics and renal excretion of salicyluric acid (SUA, 0.8 g) administered iv, with and without concomitant administration of phenolsulfonphthalein (PSP), were studied in the beagle dog. Pharmacokinetic analysis revealed that tubular secretion is the predominant route of excretion, and that secretion is inhibited by PSP. A physiologically based kidney model is presented comprising all the functional characteristics of the kidney that determine the excretion of SUA, i.e. renal plasma flow, urine flow, nonlinear protein binding, glomerular filtration, tubular secretion, and tubular accumulation. The model enabled an accurate description and analysis of the measured plasma levels and renal excretion rates. The interaction with PSP could be adequately described with the model by noncompetitive inhibition of the carrier-mediated uptake of SUA into the tubular cells. Furthermore, a small but significant reduction in nonrenal SUA clearance was observed. Model calculations showed that, in the control experiments, tubular secretion was accompanied by a pronounced accumulation of SUA within the cells, which was clearly diminished in the presence of PSP. The predicted accumulation ratios were in good agreement with previously reported in vitro values.

Disposition of aspirin and its metabolites in the semen of man

The study was undertaken to determine the distribution of aspirin and its metabolites in the semen of humans after an oral dose of aspirin. Each of seven healthy male volunteers was given a single oral dose of 975 mg of aspirin on an empty stomach together with 200 mL of water. Timed samples of blood and semen were obtained from each subject, and the concentrations of aspirin, salicylic acid, and salicyluric acid determined by a specific high-performance liquid chromatographic assay. The mean peak concentration of aspirin was 6.5 micrograms/mL in plasma (range, 4.9-8.9 micrograms/mL), reached in 26 minutes (range, 13-33 minutes). The half-life of aspirin was 31 minutes. The concentration ratio of aspirin (semen/plasma) was 0.12 (except for one subject in whom it was 0.025). The mean peak concentration of salicylate in plasma was 49 micrograms/mL (range, 42-62 micrograms/mL), reached in 2.5 hours (range, 2.0-2.8 hours). Salicylate distributed rapidly into semen and maintained a concentration ratio (semen/plasma) of 0.15. Salicyluric acid (the glycine conjugate of salicylic acid) was found in the semen. Its high concentration in some subjects' semen (four times the concurrent plasma concentration) was attributed to contamination of semen sample with residual urine, containing salicylurate, in the urethra of those who urinated after the dose of aspirin. Possible side effects of aspirin and salicylate in semen include adverse effects on fertility, male-medicated teratogenesis, dominant lethal mutations, and hypersensitivity reactions in the recipients.