Sodium Phenylacetate and Sodium Benzoate (Page 3 of 5)

7 DRUG INTERACTIONS

Formal drug interaction studies have not been performed with sodium phenylacetate and sodium benzoate injection.

Some antibiotics such as penicillin may compete with phenylacetylglutamine and hippurate for active secretion by renal tubules, which may affect the overall disposition of the infused drug.

Probenecid is known to inhibit the renal transport of many organic compounds, including aminohippuric acid, and may affect renal excretion of phenylacetylglutamine and hippurate.

There have been reports that valproic acid can induce hyperammonemia through inhibition of the synthesis of N-acetylglutamate, a co-factor for carbamyl phosphate synthetase. Therefore, administration of valproic acid to patients with urea cycle disorders may exacerbate their condition and antagonize the efficacy of sodium phenylacetate and sodium benzoate injection.

Use of corticosteroids may cause a protein catabolic state and, thereby, potentially increase plasma ammonia levels in patients with impaired ability to form urea.

8 USE IN SPECIFIC POPULATIONS

8.1 Pregnancy

Risk Summary

Available data with sodium phenylacetate and sodium benzoate injection use in pregnant women are insufficient to identify a drug-associated risk of major birth defects, miscarriage or adverse maternal or fetal outcomes. Animal reproduction studies have not been conducted with sodium phenylacetate and sodium benzoate injection.

The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4%, and 15 to 20%, respectively.

8.2 Lactation

Risk Summary

There are no data on the presence of sodium phenylacetate, sodium benzoate in either human or animal milk, the effects on the breastfed infant, or the effects on milk production. The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for sodium phenylacetate and sodium benzoate injection and any potential adverse effects on the breastfed infant from sodium phenylacetate and sodium benzoate injection or from the underlying maternal condition.

8.4 Pediatric Use

Sodium phenylacetate and sodium benzoate injection has been used as a treatment for acute hyperammonemia in pediatric patients including patients in the early neonatal period [ see Dosage and Administration (2) ].

8.5 Geriatric Use

Clinical studies of sodium phenylacetate and sodium benzoate injection did not include any patients aged 65 and over to determine whether they respond differently from younger patients. Urea cycle disorders are presently diseases of the pediatric and younger adult populations. No pharmacokinetic studies of sodium phenylacetate and sodium benzoate injection have been performed in geriatric patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and concomitant disease or other drug therapy in this patient population.

8.6 Gender

Pharmacokinetic parameters of sodium phenylacetate and sodium benzoate injection were compared in healthy males and females. Bioavailability of both benzoate and phenylacetate was slightly higher in females than in males. However, conclusions cannot be drawn due to the limited number of subjects in this study.

8.7 Hepatic Insufficiency

Limited information is available on the metabolism and excretion of sodium phenylacetate and sodium benzoate in patients with impaired hepatic function. However, metabolic conjugation of sodium phenylacetate and sodium benzoate is known to take place in the liver and kidney. Therefore, caution should be used in administering sodium phenylacetate and sodium benzoate injection to patients with hepatic insufficiency.

8.8 Renal Impairment

The drug metabolites of sodium phenylacetate and sodium benzoate injection (phenylacetylglutamine and hippurate) and subsequently ammonia are primarily excreted by the kidney. Therefore, use caution and closely monitor patients with impaired renal function who receive sodium phenylacetate and sodium benzoate injection.

10 OVERDOSAGE

Overdosage has been reported during sodium phenylacetate and sodium benzoate injection treatment in urea cycle-deficient patients. All patients in the uncontrolled open-label study were to be treated with the same dose of sodium phenylacetate and sodium benzoate injection. However, some patients received more than the dose level specified in the protocol. In 16 of the 64 deaths, the patient received a known overdose of sodium phenylacetate and sodium benzoate injection. Causes of death in these patients included cardiorespiratory failure/arrest (6 patients), hyperammonemia (3 patients), increased intracranial pressure (2 patients), pneumonitis with septic shock and coagulopathy (1 patient), error in dialysis procedure (1 patient), respiratory failure (1 patient), intractable hypotension and probable sepsis (1 patient), and unknown (1 patient). Additionally, other signs of intoxication may include obtundation (in the absence of hyperammonemia), hyperventilation, a severe compensated metabolic acidosis, perhaps with a respiratory component, large anion gap, hypernatremia and hyperosmolarity, progressive encephalopathy, cardiovascular collapse, and death.

In case of overdose of sodium phenylacetate and sodium benzoate injection, discontinue the drug and institute appropriate emergency medical monitoring and procedures. In severe cases, the latter may include hemodialysis (procedure of choice) or peritoneal dialysis (when hemodialysis is unavailable).

11 DESCRIPTION

Sodium phenylacetate and sodium benzoate injection, 10% per 10% (a nitrogen binding agent) is a sterile, concentrated, aqueous solution of sodium phenylacetate and sodium benzoate. The pH of the solution is between 6 and 8. Sodium phenylacetate is a white to off-white powder. It is soluble in water. Sodium benzoate is a white to off-white powder that is readily soluble in water.

Sodium phenylacetate has a molecular weight of 158.14 and the molecular formula C ₈ H ₇ NaO ₂ . Sodium benzoate has a molecular weight of 144.10 and the molecular formula C ₇ H ₅ NaO ₂ .

Each mL of sodium phenylacetate and sodium benzoate injection contains 100 mg of sodium phenylacetate and 100 mg of sodium benzoate, and Water for Injection. Sodium hydroxide and/or hydrochloric acid may have been used for pH adjustment.

Sodium phenylacetate and sodium benzoate injection is a sterile, concentrated solution intended for intravenous administration via a central venous catheter only after dilution [ see Dosage and Administration (2) ].

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Urea cycle disorders can result from decreased activity of any of the following enzymes: N -acetylglutamate synthetase (NAGS), carbamyl phosphate synthetase (CPS), argininosuccinate synthetase (ASS), ornithine transcarbamylase (OTC), argininosuccinate lyase (ASL), or arginase (ARG).

Sodium phenylacetate and sodium benzoate are metabolically active compounds that can serve as alternatives to urea for the excretion of waste nitrogen. Figure 2 is a schematic illustrating how the components of sodium phenylacetate and sodium benzoate injection, phenylacetate and benzoate, provide an alternative pathway for nitrogen disposal in patients without a fully functioning urea cycle. Phenylacetate conjugates with glutamine in the liver and kidneys to form phenylacetylglutamine, via acetylation. Phenylacetylglutamine is excreted by the kidneys via glomerular filtration and tubular secretion. The nitrogen content of phenylacetylglutamine per mole is identical to that of urea (both contain two moles of nitrogen). Two moles of nitrogen are removed per mole of phenylacetate when it is conjugated with glutamine. Similarly, preceded by acylation, benzoate conjugates with glycine to form hippuric acid, which is rapidly excreted by the kidneys by glomerular filtration and tubular secretion. One mole of hippuric acid contains one mole of waste nitrogen. Thus, one mole of nitrogen is removed per mole of benzoate when it is conjugated with glycine.