SODIUM PHENYLBUTYRATE: 300 Adverse Event Reports & Safety Profile

DESCRIPTION BUPHENYL (sodium phenylbutyrate) Tablets for oral administration and BUPHENYL (sodium phenylbutyrate) Powder for oral, nasogastric, or gastrostomy tube administration contain sodium phenylbutyrate. Sodium phenylbutyrate is an off-white crystalline substance which is soluble in water and has a strong salty taste. Sodium phenylbutyrate also is freely soluble in methanol and practically insoluble in acetone and diethyl ether. It is known chemically as 4-phenylbutyric acid, sodium salt with a molecular weight of 186 and the molecular formula C 10 H 11 O 2 Na.

Chemical

Structure: Each tablet of BUPHENYL contains 500 mg of sodium phenylbutyrate and the inactive ingredients microcrystalline cellulose NF, magnesium stearate NF, and colloidal silicon dioxide NF. Each gram of BUPHENYL Powder contains 0.94 grams of sodium phenylbutyrate and the inactive ingredients calcium stearate NF, and colloidal silicon dioxide NF.

Chemical

Structure

INDICATIONS AND USAGE Sodium Phenylbutyrate Tablets is indicated as adjunctive therapy in the chronic management of patients with urea cycle disorders involving deficiencies of carbamylphosphate synthetase (CPS), ornithine transcarbamylase (OTC), or argininosuccinic acid synthetase (AS). It is indicated in all patients with neonatal-onset deficiency (complete enzymatic deficiency, presenting within the first 28 days of life). It is also indicated in patients with late-onset disease (partial enzymatic deficiency, presenting after the first month of life) who have a history of hyperammonemic encephalopathy. It is important that the diagnosis be made early and treatment initiated immediately to improve survival. Any episode of acute hyperammonemia should be treated as a life-threatening emergency.

Sodium Phenylbutyrate

Tablets must be combined with dietary protein restriction and, in some cases, essential amino acid supplementation. (See Nutritional Supplementation subsection of the DOSAGE AND ADMINISTRATION section.) Previously, neonatal-onset disease was almost universally fatal within the first year of life, even when treated with peritoneal dialysis and essential amino acids or their nitrogen-free analogs. However, with hemodialysis, use of alternative waste nitrogen excretion pathways (sodium phenylbutyrate, sodium benzoate, and sodium phenylacetate), dietary protein restriction, and, in some cases, essential amino acid supplementation, the survival rate in newborns diagnosed after birth but within the first month of life is almost 80%. Most deaths have occurred during an episode of acute hyperammonemic encephalopathy. Patients with neonatal-onset disease have a high incidence of mental retardation. Those who had IQ tests administered had an incidence of mental retardation as follows: ornithine transcarbamylase deficiency, 100% (14/14 patients tested); argininosuccinic acid synthetase deficiency, 88% (15/17 patients tested); and carbamylphosphate synthetase deficiency, 57% (4/7 patients tested). Retardation was severe in the majority of the retarded patients. In patients diagnosed during gestation and treated prior to any episode of hyperammonemic encephalopathy, survival is 100%, but even in these patients, most subsequently demonstrate cognitive impairment or other neurologic deficits. In late-onset deficiency patients, including females heterozygous for ornithine transcarbamylase deficiency, who recover from hyperammonemic encephalopathy and are then treated chronically with Sodium Phenylbutyrate Tablets and dietary protein restriction, the survival rate is 98%. The two deaths in this group of patients occurred during episodes of hyperammonemic encephalopathy. However, compliance with the therapeutic regimen has not been adequately documented to allow evaluation of the potential for Sodium Phenylbutyrate Tablets and dietary protein restriction to prevent mental deterioration and recurrence of hyperammonemic encephalopathy if carefully adhered to. The majority of these patients tested (30/46 or 65%) have IQ's in the average to low average/borderline mentally retarded range. Reversal of pre-existing neurologic impairment is not likely to occur with treatment and neurologic deterioration may continue in some patients. Even on therapy, acute hyperammonemic encephalopathy recurred in the majority of patients for whom the drug is indicated.

Sodium Phenylbutyrate

Tablets may be required life-long unless orthotopic liver transplantation is elected. (See CLINICAL PHARMACOLOGY , Pharmacodynamics subsection for the biochemical effects of Sodium Phenylbutyrate Tablets).

DOSAGE AND ADMINISTRATION For Oral Use Only. The use of sodium phenylbutyrate tablets is indicated for children weighing more than 20 kg and for adults. The usual total daily dose of sodium phenylbutyrate powder for patients with urea cycle disorders is 450 to 600 mg/kg/day in patients weighing less than 20 kg, or 9.9 to 13 g/m 2 /day in larger patients. The powder is to be taken in equally divided amounts with each meal or feeding (i.e., three to six times per day). Sodium phenylbutyrate powder is indicated for oral use (via mouth, gastrostomy, or nasogastric tube) only. The powder is to be mixed with food (solid or liquid) for immediate use; however, when dissolved in water, sodium phenylbutyrate powder has been shown to be stable for up to one week at room temperature or refrigerated. Sodium phenylbutyrate, USP is very soluble in water (5 grams per 10 mL). When sodium phenylbutyrate powder is added to a liquid, only sodium phenylbutyrate, USP will dissolve, the excipients will not. The effect of food on sodium phenylbutyrate, USP has not been determined. Each level yellow teaspoon (enclosed) dispenses 3.2 grams of powder and 3 grams of sodium phenylbutyrate, USP. Each level blue tablespoon (enclosed) dispenses 9.1 grams of powder and 8.6 grams of sodium phenylbutyrate, USP. Shake lightly before use. The safety or efficacy of doses in excess of 20 grams per day has not been established.

Nutritional Management

To promote growth and development, plasma levels of ammonia, arginine, branched-chain amino acids, and serum protein should be maintained within normal limits while plasma glutamine is maintained at levels less than 1,000 µmol/L. Minimum daily protein intake for a patient of a particular age should be taken from, for example, "Recommended Dietary Allowances", 10th ed., Food and Nutrition Board, National Academy of Sciences, 1989. The allocation of dietary nitrogen into natural protein and essential amino acids is a function of age, residual urea-cycle enzyme activity, and the dose of sodium phenylbutyrate. At the recommended dose of sodium phenylbutyrate, it is suggested that infants with neonatal-onset CPS and OTC deficiencies initially receive a daily dietary protein intake limited to approximately 1.6 g/kg/day for the first 4 months of life. If tolerated, the daily protein intake may be increased to 1.9 g/kg/day during this period. Protein tolerance will decrease as the growth rate decreases, requiring a reduction in dietary nitrogen intake.

From

4 months to 1 year of age, it is recommended that the infant receive at least 1.4 g/kg/day, but 1.7 g/kg/day is advisable.

From

1 to 3 years of age, the protein intake should not be less than 1.2 g/kg/day; 1.4 g/kg/day is advisable during this period. For neonatal-onset patients with carbamylphosphate synthetase deficiency or ornithine transcarbamylase deficiency who are at least 6 months of age, it is recommended that the daily protein intake be equally divided between natural protein and supplemental essential amino acids. Patients with argininosuccinic acid synthetase deficiency and those with late-onset disease (partial deficiencies, including females heterozygous for ornithine transcarbamylase), initially may receive a diet containing the age-determined minimal daily natural protein allowance. The protein intake may be increased as tolerated and determined by plasma glutamine and other amino acid levels. However, many patients with partial deficiencies avoid dietary protein. Citrulline supplementation is required and recommended for patients diagnosed with neonatal-onset deficiency of carbamylphosphate synthetase or ornithine transcarbamylase; citrulline daily intake is recommended at 0.17 g/kg/day or 3.8 g/m 2 /day. The free-base form of arginine may be used instead of citrulline in patients with milder forms of carbamylphosphate synthetase and ornithine transcarbamylase deficiency (daily intake is recommended at 0.17 g/kg/day or 3.8 g/m 2 /day). Arginine supplementation is needed for patients diagnosed with deficiency of argininosuccinic acid synthetase; arginine (free base) daily intake is recommended at 0.4 to 0.7 g/kg/day or 8.8 to 15.4 g/m 2 /day. If caloric supplementation is indicated, a protein-free product is recommended. Caloric intake should be based upon the "Recommended Dietary Allowances", 10th ed., Food and Nutrition Board, National Research Council, National Academy of Sciences, 1989.

CONTRAINDICATIONS Sodium phenylbutyrate tablets should not be used to manage acute hyperammonemia, which is a medical emergency.

ADVERSE REACTIONS The assessment of clinical adverse events came from 206 patients treated with sodium phenylbutyrate. Adverse events (both clinical and laboratory) were not collected systematically in these patients, but were obtained from patient-visit reports by the 65 co-investigators. Causality of adverse effects is sometimes difficult to determine in this patient population because they may result from either the underlying disease, the patient's restricted diet, intercurrent illness, or Sodium Phenylbutyrate Powder. Furthermore, the rates may be under-estimated because they were reported primarily by parent or guardian and not the patient.

Clinical Adverse

Events In female patients, the most common clinical adverse event reported was amenorrhea/menstrual dysfunction (irregular menstrual cycles), which occurred in 23% of the menstruating patients. Decreased appetite occurred in 4% of all patients. Body odor (probably caused by the metabolite, phenylacetate) and bad taste or taste aversion were each reported in 3% of patients. Other adverse events reported in 2% or fewer patients were: Gastrointestinal: abdominal pain, gastritis, nausea and vomiting; constipation, rectal bleeding, peptic ulcer disease, and pancreatitis each occurred in one patient. Hematologic: aplastic anemia and ecchymoses each occurred in one patient. Cardiovascular: arrhythmia and edema each occurred in one patient. Renal: renal tubular acidosis Psychiatric: depression Skin: rash Miscellaneous: headache, syncope, and weight gain Neurotoxicity was reported in cancer patients receiving intravenous phenylacetate, 250–300 mg/kg/day for 14 days, repeated at 4-week intervals. Manifestations were predominately somnolence, fatigue, and lightheadedness; with less frequent headache, dysgeusia, hypoacusis, disorientation, impaired memory, and exacerbation of a pre-existing neuropathy. These adverse events were mainly mild in severity. The acute onset and reversibility when the phenylacetate infusion was discontinued suggest a drug effect.

Laboratory Adverse

Events In patients with urea cycle disorders, the frequency of laboratory adverse events by body system were: Metabolic: acidosis (14%), alkalosis and hyperchloremia (each 7%), hypophosphatemia (6%), hyperuricemia and hyperphosphatemia (each 2%), and hypernatremia and hypokalemia (each 1%). Nutritional: hypoalbuminemia (11%) and decreased total protein (3%). Hepatic: increased alkaline phosphatase (6%), increased liver transaminases (4%), and hyperbilirubinemia (1%). Hematologic: anemia (9%), leukopenia and leukocytosis (each 4%), thrombocytopenia (3%), and thrombocytosis (1%). The clinician is advised to routinely perform urinalysis, blood chemistry profiles, and hematologic tests. To report SUSPECTED ADVERSE REACTIONS , contact Sigmapharm Laboratories, LLC, Pharmacovigilance at 1-855-332-0731 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

AND PRECAUTIONS Neurotoxicity of Phenylacetate : Increased exposure to phenylacetate, the major metabolite of PHEBURANE, may be associated with neurotoxicity in patients with UCDs. Consider reducing the dose if neurotoxicity symptoms are present. ( 5.1 ) Hypokalemia : Renal excretion of phenylacetylglutamine may induce urinary loss of potassium. Monitor serum potassium during therapy and initiate appropriate treatment when necessary. ( 5.2 )

Conditions

Associated with Edema : Calculate the total amount of sodium patients will be exposed to based on their weight or body surface area. If a patient develops new-onset edema or worsening edema while on treatment, discontinue administration of PHEBURANE and initiate appropriate therapy. ( 5.3 )

Diabetes

Mellitus, Hereditary Fructose Intolerance, Glucose-Galactose Malabsorption or Sucrase-Isomaltase Insufficiency : Avoid use of PHEBURANE in patients with rare hereditary problems of fructose intolerance, glucose-galactose malabsorption or sucrase-isomaltase insufficiency. ( 5.4 )

5.1 Neurotoxicity of Phenylacetate Increased exposure to phenylacetate, the major metabolite of PHEBURANE, may be associated with neurotoxicity in patients with UCDs. In a study of adult cancer patients receiving intravenous phenylacetate, 250-300 mg/kg/day for 14 days, repeated at 4-week intervals, signs and symptoms of neurotoxicity, which were reversible upon discontinuation, were seen at plasma concentrations ≥ 3.5 mmol/L, and included somnolence, fatigue, and light headedness <span class="opacity-50 text-xs">[see Adverse Reactions ( 6 ) ]</span> . PHEBURANE is not approved for intravenous use or for treatment of patients with cancer. If symptoms of vomiting, nausea, headache, somnolence or confusion are present in the absence of high ammonia levels or other intercurrent illnesses, consider reducing the dose of PHEBURANE <span class="opacity-50 text-xs">[see Dosage and Administration ( 2.2 )]</span> . Phenylacetate caused neurotoxicity when given subcutaneously in rat pups <span class="opacity-50 text-xs">[see Use in Specific Populations ( 8.4 )]</span> .

5.2 Hypokalemia Renal excretion of phenylacetylglutamine may induce urinary loss of potassium. Monitor serum potassium during therapy and initiate appropriate treatment when necessary.

5.3 Conditions Associated with Edema PHEBURANE contains 124 mg (5.4 mmol) of sodium per gram of sodium phenylbutyrate, corresponding to 2.5 g (108 mmol) of sodium in the maximum daily dose of 20 g of sodium phenylbutyrate. In order to decide if administration of PHEBURANE is appropriate in patients with diseases that involve edema such as heart failure, cirrhosis, or nephrosis, calculate the total amount of sodium patients will be exposed to based on their weight or body surface area (BSA) <span class="opacity-50 text-xs">[see Dosage and Administration ( 2.1 )]</span> . If a patient develops new-onset edema or worsening edema while on treatment, discontinue administration of PHEBURANE and initiate appropriate therapy.

5.4 Diabetes Mellitus, Hereditary Fructose Intolerance, Glucose-Galactose Malabsorption or Sucrase-Isomaltase Insufficiency PHEBURANE contains 768 mg of sucrose per gram of sodium phenylbutyrate, corresponding to 15.4 g of sucrose in the maximum daily dose of 20 g of sodium phenylbutyrate. This should be considered in patients with diabetes mellitus. Avoid use of PHEBURANE in patients with rare hereditary problems of fructose intolerance, glucose-galactose malabsorption or sucrase-isomaltase insufficiency.

General: Sodium Phenylbutyrate Powder should not be administered to patients with known hypersensitivity to sodium phenylbutyrate or any component of this preparation. There have been published reports of hyperammonemia being induced by haloperidol and by valproic acid. Neurotoxicity of phenylacetate in animals: When given subcutaneously to rat pups, 190–474 mg/kg phenylacetate caused decreased proliferation and increased loss of neurons, and it reduced CNS myelin. Cerebral synapse maturation was retarded, and the number of functioning nerve terminals in the cerebrum was reduced, which resulted in impaired brain growth. Prenatal exposure of rat pups to phenylacetate produced lesions in layer 5 of the cortical pyramidal cells; dendritic spines were longer and thinner than normal and reduced in number. Information for Patients: The full text of the separate insert of information for patients is reprinted at the end of the labeling.

Laboratory

Tests: Plasma levels of ammonia, arginine, branched-chain amino acids, and serum proteins should be maintained within normal limits, and plasma glutamine should be maintained at levels less than 1,000 µmol/L. Serum drug levels of phenylbutyrate and its metabolites, phenylacetate and phenylacetylglutamine, should be monitored periodically. Carcinogenesis, Mutagenesis, Impairment of Fertility: Carcinogenicity, mutagenicity, and fertility studies of sodium phenylbutyrate have not been conducted. Pregnancy: Pregnancy Category C. Animal reproduction studies have not been conducted with Sodium Phenylbutyrate Powder. It is also not known whether Sodium Phenylbutyrate Powder can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity.

Sodium Phenylbutyrate

Powder should be given to a pregnant woman only if clearly needed.

Nursing

Mothers: It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when Sodium Phenylbutyrate Powder is administered to a nursing woman.

Pediatric

Use: The use of tablets for neonates, infants and children to the weight of 20 kg is not recommended. ( See Dosage and Administration ).

INTERACTIONS Valproic Acid, Haloperidol, or Corticosteroids : May increase plasma ammonia level; monitor ammonia levels closely. ( 7.1 ) Probenecid : May inhibit renal excretion of metabolites of PHEBURANE including phenylacetate and phenylacetylglutamine; monitor for potential neurotoxicity. ( 7.2 )

7.1 Potential for Other Drugs to Affect Ammonia Corticosteroids Use of corticosteroids may cause the breakdown of body protein and increase plasma ammonia levels.

Valproic

Acid and Haloperidol Hyperammonemia may be induced by haloperidol and by valproic acid. Monitor plasma ammonia levels closely when corticosteroids, valproic acid, or haloperidol is used concomitantly with PHEBURANE.

7.2 Potential for Other Drugs to Affect PHEBURANE Probenecid Probenecid may inhibit renal excretion of the metabolites of PHEBURANE including phenylacetate and phenylacetylglutamine. Monitor patients for potential neurotoxicity and measure plasma phenylacetate and phenylacetylglutamine levels when probenecid is used concomitantly with PHEBURANE <span class="opacity-50 text-xs">[see Dosage and Administration ( 2.2 )]</span> .