Phenylacetate and benzoate clearance in a hyperammonemic infant on sequential hemodialysis and hemofiltration

An infant with a suspected inborn metabolism error was treated with a metabolic cocktail of intravenous sodium phenylacetate (NaPh) and sodium benzoate (NaBz) for hyperammonemia. Sequential hemodialysis (HD) then hemofiltration (HF) was performed due to hyperammonemia. Dialytic and convective clearance (K; ml/min) of ammonia, NaPh, and NaBz was measured. The K of ammonia was 57 and 37 for HD and HF, respectively. The K of NaBz was 37 and 12 for HD and HF, respectively. The K of NaPh was 38 and 14 ml/min for HD and HF, respectively. Despite high clearance of both NaPh and NaBz by HD and HF, the hyperammonemia was corrected.

Conflicting demands on detoxification pathways influence how common brushtail possums choose their diets

Most herbivores eat more and survive better when they have access to a variety of foods. One explanation involves the detoxification of plant secondary metabolites (PSMs). By feeding from a variety of plants that contain different classes of PSMs, animals can use multiple detoxification pathways and presumably consume more food. Although popular, this theory is difficult to test because it requires knowledge of the detoxification pathways of each PSM in the diet. We established that common brushtail possums (Trichosurus vulpecula) use various combinations of oxidation, hydrolysis, and conjugation with glucuronic acid (GA) or glycine to detoxify six PSMs. Compared to their ingestion of a single PSM, possums ate more when offered a choice between two diets containing PSMs that require apparently independent detoxification pathways (benzoate and 1,8-cineole, benzoate and p-cymene, benzoate and orcinol, benzoate and salicin, or orcinol and 1,8-cineole). However, possums still did not eat as much of these diets as they did of a basal diet free of PSMs. This suggests that detoxification pathways are never independent, but are separated instead by degrees. In contrast, possums offered a choice of two PSMs that require competing detoxification pathways (1,8-cineole and p-cymene, 1,8-cineole and salicin, or orcinol and salicin) ate no more than when offered diets containing one of the compounds. There was an exception: even though both rutin and orcinol are detoxified via conjugation with GA, the feeding behavior of possums did not suggest competition for detoxification pathways. This implies that the supply of GA is not limiting. This study provides the first convincing evidence that herbivorous mammals can eat more by selecting mixed diets with a diversity of PSMs that make full use of their detoxification potential. It also emphasizes that other behavioral and physiological factors, such as transient food aversions, influence feeding behavior.

Sodium benzoate attenuates D-serine induced nephrotoxicity in the rat

D-Serine causes selective necrosis to the straight portion of the rat renal proximal tubules. The onset is rapid, occurring within 3-4 h and accompanied by proteinuria, glucosuria and aminoaciduria. The metabolism of D-serine by D-amino acid oxidase (D-AAO) may be involved in the mechanism of toxicity. D-AAO is localized within the peroxisomes of renal tubular epithelial cells, which is also the location of D-serine reabsorption. To address the role of D-AAO in D-serine-induced nephrotoxicity, we have examined the effect of sodium benzoate (SB) on the renal injury. SB has been shown to be a potent, competitive inhibitor of kidney D-AAO in vitro. Male Alderley Park rats were exposed to D-serine (500 mg/kg i.p.) 1 h after exposure to SB (125, 250, 500 or 750 mg/kg i.p.). Urine was collected for 0-6 h, then terminal plasma samples and kidneys were taken at 6.5 h. A second group of animals was given SB (500 mg/kg) followed by D-serine (500 mg/kg i.p.; 1 h later) and urine was collected after 0-6, 6-24 and 24-48 h. Terminal plasma samples and kidneys were taken at 48 h. 1H NMR spectroscopic analysis of urine, combined with principal component analysis, demonstrated that SB was able to prevent D-serine-induced perturbations to the urinary profile in a dose dependent manner. This was confirmed by measurement of plasma creatinine and urinary glucose and protein and histopathological examination of the kidneys. Assessment 48 h after D-serine administration revealed that nephrotoxicity was observed in animals pre-treated with SB (500 mg/kg) although the extent of injury was less pronounced than following D-serine alone. These results demonstrate that whilst prior exposure to SB prevents the initial onset of D-serine-induced nephrotoxicity, renal injury is still apparent at later time points. D-AAO activity in the kidney was decreased by 50% 1 h after dosing with SB suggesting that inhibition of this enzyme may be responsible for the observed protection.

Effect of alternative pathway therapy on branched chain amino acid metabolism in urea cycle disorder patients

Urea cycle disorders (UCDs) are a group of inborn errors of hepatic metabolism caused by the loss of enzymatic activities that mediate the transfer of nitrogen from ammonia to urea. These disorders often result in life-threatening hyperammonemia and hyperglutaminemia. A combination of sodium phenylbutyrate and sodium phenylacetate/benzoate is used in the clinical management of children with urea cycle defects as a glutamine trap, diverting nitrogen from urea synthesis to alternatives routes of excretion. We have observed that patients treated with these compounds have selective branched chain amino acid (BCAA) deficiency despite adequate dietary protein intake. However, the direct effect of alternative therapy on the steady state levels of plasma branched chain amino acids has not been well characterized. We have measured steady state plasma branched chain and other essential non-branched chain amino acids in control subjects, untreated ornithine transcarbamylase deficiency females and treated null activity urea cycle disorder patients in the fed steady state during the course of stable isotope studies. Steady-state leucine levels were noted to be significantly lower in treated urea cycle disorder patients when compared to either untreated ornithine transcarbamylase deficiency females or control subjects (P<0.0001). This effect was reproduced in control subjects who had depressed leucine levels when treated with sodium phenylacetate/benzoate (P<0.0001). Our studies suggest that this therapeutic modality has a substantial impact on the metabolism of branched chain amino acids in urea cycle disorder patients. These findings suggest that better titration of protein restriction could be achieved with branched chain amino acid supplementation in patients with UCDs who are on alternative route therapy.

Pharmacokinetics of sodium phenylacetate and sodium benzoate following intravenous administration as both a bolus and continuous infusion to healthy adult volunteers

BACKGROUND

Ammunol (sodium phenylacetate/sodium benzoate) is an intravenously administered, investigational drug used for the treatment of acute hyperammonemia in infants, children, and adults with urea cycle enzyme deficiencies. A pharmacokinetic study of sodium phenylacetate/sodium benzoate (NAPA/NABZ) was performed in two groups of normal healthy volunteers, following the dosing regimen used to treat hyperammonemia.

METHODS

The first group of subjects (n = 3) received a bolus dose of 5.5 g/m2 of NAPA/NABZ, over a period of 1.5 h. Following a seven-day washout, subjects then received the same bolus dose, followed by a continuous infusion of 5.5 g/m2 over 24h. A second group of different subjects (n = 17) received the same treatment regimen, but using doses of 3.75 g/m2. Phenylacetate (PA) and benzoate (BZ), and their respective metabolites, phenylacetylglutamine (PAG), and hippurate (HIP) were measured over a 24-h period. An HPLC method was used for the measurement of all analyte concentrations. Non-compartmental analysis and modeling was performed using WinNonlin Professional.

RESULTS

Both BZ and PA displayed saturable, non-linear elimination, with a decrease in clearance with increased dose. During the bolus dose with continuous infusion regimen, plasma levels of both BZ and PA peaked at the end of the priming dose, and PA levels remained near peak for 5-9h. In contrast, BZ plasma levels immediately fell following the priming dose, and became undetectable at 14.1+/-4.2 and 26.8+/-2.3h in the low- and high-dose group, respectively. The formation of HIP occurred more rapidly than that of PAG. For both PA and BZ, metabolite formation increased in a linear fashion with the dose.

CONCLUSION

These data describe the pharmacokinetics of PA and BZ, and their respective metabolites, as observed in healthy adult volunteers, with the higher dose studied equivalent to that used to treat hyperammonemia. Dose optimization is required to maximize nitrogen removal, while minimizing the risk of toxicity, especially due to PA. Because of the slower elimination of PA, and the non-linear pharmacokinetic behavior displayed by both PA and BZ, only investigational protocol-specific doses should be used, and higher doses should be avoided unless blood level monitoring can be done promptly and frequently.

Pediatric drug formulations of sodium benzoate: II. Coated granules with a lipophilic binder

Sodium benzoate is used as a therapeutic agent in the treatment of some rare disorders that predominantly affect children. In preliminary investigations, liquid and semi-solid formulations of sodium benzoate failed because children refuse the oral uptake due to the bad taste of the drug. Recently developed microcapsules with macrogol as a hydrophilic binder raise concern in high-dose treatment regimens because acceptable daily intake limits are exceeded. A novel microcapsule formulation was developed consisting of a lipophilic core with high sodium benzoate load and a saliva-resistant coating. A new powder quality of saturated triglycerides from plant origin was introduced which complies with the Ph. Eur. monograph 'Hard fat'. Sodium benzoate and the triglyceride were mixed and directly extruded at room temperature. The extrudates were spheronized and coated in a fluidized-bed process. The resulting coated granules are small-sized microcapsules and taste neutrally. They can be mixed with food before administration. As the amount of released sodium benzoate is negligible within the first minutes, children do not recognize the bad taste and accept the medication. Recently, sodium benzoate in this novel formulation has been designated by the European Community as an orphan drug in the treatment of non-ketotic hyperglycinemia.

Pediatric drug formulations of sodium benzoate: I. Coated granules with a hydrophilic binder

High doses of sodium benzoate are applied in the treatment of some rare metabolic disorders. In most cases children are affected who often refuse the oral uptake of sodium benzoate as a powder or in solution due to its bad taste. Therefore, small-sized, saliva-resistant microcapsules have been developed containing high doses of the drug substance. Granules were produced by roller compacting of sodium benzoate powder without any additives, by solvent-free cold extrusion and hot-melt extrusion adding poly(ethylene glycol)s of different grades. The granules with a diameter of less than 1 mm were film-coated by an ethanolic solution of Eudragit E 100. The microcapsules from hot-melt extrusion containing 25% Macrogol 4000 were most stable during the coating process and showed the highest yields. Sodium benzoate is completely released from the microcapsules within 9 min into 0.1 N HCl and 0.01 N HCl whereas dissolution into buffer pH 6.8 is different in the initial phase and completed after 14 min. The bad taste of sodium benzoate is not recognized in the buccal space for at least 5 min. The microcapsules are stable during storage for at least 6 months.

Effect of electric field on the enhanced skin permeation of drugs by electroporation

Electroporation (voltage; 200 V) was applied using an exponentially decaying electric pulse generator on hairless rat skin using different shapes of electrodes, and the in vitro skin permeation of benzoate was measured as an index of the effectiveness of electroporation. Despite the same voltage of application, the skin permeation of benzoate was markedly different by the electrode shapes. Several experiments hereafter suggest that this reason was probably due to different 2-dimensional electric fields in the skin barrier, stratum corneum, and the voltage decreasing pattern applied. To confirm whether this phenomenon was specific for benzoate, diclofenac having a similar pKa was selected to carry out the same kind of examination. As a result, the skin permeability of diclofenac was influenced by 2-dimensional electric fields in the stratum corneum and the voltage decreasing pattern, similar to the benzoate permeation. Next, a rectangular pulse generator, where no decaying pattern was obtained for the application voltage, was used to measure the effect of electroporation on the skin permeation of diclofenac. As expected, the enhanced skin permeation of diclofenac was dependent only on the electric field when using the rectangular pulse generator. These results suggest that the electric field and time profile of the voltage (or AUC of voltage against time) at electroporation are very important factors to increase the efficacy of electroporation, and that the efficacy can be optimized by the shape of electrodes in addition to the application conditions of electroporation.

[Kinetics of in vitro drug release from chitosan and N-alkyl chitosan membranes]

By using the so-called "lag-time" method, we studied the effect of membrane thickness(h), initial drug concentration(Co) and flow rate(V) on the difusion coefficient(D) of model drug in membranes. The experiment indicates that D increases as h and v increase; D Keeps constant when C0 changes; Under the same condition, the D value of N-alkyl chitosan membrane is bigger than that of pure chitosan membrane.

[Rationale for the use of sodium benzoate in clinical hepatology]

Sodium benzoate is widely used in the Alimentary Industry at low doses for its antimicrobial action. It has also been used as a liver function test. The principle is to evaluate the liver capacity for conjugation of glycine to benzoic acid and to form hippuric acid which is excreted in the urine. In hyperammonemic syndromes, secondary to enzymatic deficiency of the urea cicle, sodium benzoate has the property to act as an alternative way of nitrogen excretion to urinary hippurate instead of urea. Recently, it has been proposed as a therapeutic alternative in cirrhotic patients with portal systemic encephalopathy. Historical, biochemical and clinical data which constitute the principles to validate its clinical application in Hepatology are reviewed in this manuscript.