Knowing when to modify the dose of RAVICTI® (glycerol phenylbutyrate)

Look over the patient treatment profile and important biomarkers, and order a metabolite testing kit.

Miranda, a 10-year-old female with carbamyl phosphate synthetase1 (CPS1) deficiency.Miranda, a 10-year-old female with carbamyl phosphate synthetase1 (CPS1) deficiency.

Using key biomarkers, RAVICTI dosing may be modified for targeted ammonia control1-3

Plasma ammonia

When plasma ammonia is elevated, increase the RAVICTI dosage to reduce the fasting ammonia level to less than half the upper limit of normal (ULN) in patients 6 years of age and older, or reduce the first ammonia level of the morning to below the ULN in infants and young children (generally less than 6 years of age).1,b

Plasma phenylacetate (PAA) and phenylacetylglutamine (PAGN)

PAA is the major metabolite of RAVICTI and may be associated with neurotoxicity. The PAA:PAGN ratio has been shown to be less than 1 in patients without significant PAA accumulation. A high PAA:PAGN ratio may indicate a slow or inefficient conjugation reaction to form PAGN, which may lead to increases in PAA without further conversion to PAGN.1,2,c

Urinary PAGN (U-PAGN)

If U-PAGN excretion is insufficient to cover daily dietary protein intake and the fasting ammonia is greater than half the ULN, the RAVICTI dosage should be increased.1

Chart showing how Phenylbutyrate (PBA) metabolites can be used to guide RAVICTI dosing decisions

The following factors should be considered when modifying RAVICTI dosage:

Change in body surface area

Periodic reassessment of BSA should be performed to ensure accurate dosing, particularly in pediatric patients who will experience significant changes in this parameter over time.1

Hepatic status

Be sure to consider any changes in hepatic capacity. For patients with moderate to severe hepatic impairment, the recommended starting dosage is at the lower end of the recommended dosing range, and the dosage should be kept at the lowest necessary to control the patient's plasma ammonia.1

Protein intake

Changes in a patient’s protein intake—either prescribed or through nonadherence to diet—may require altering the dosage to compensate for greater amounts of nitrogen that need to be excreted as waste.1

bInstruct patients to abstain from eating or drinking any foods or liquids before plasma ammonia levels are to be measured.1

cConsider a patient’s use of concomitant medications such as probenecid, when making dosing adjustment decisions based on U-PAGN and PAA. Probenecid may result in decrease of the urinary excretion of PAGN.1

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References: 1. RAVICTI (glycerol phenylbutyrate) Oral Liquid [prescribing information] Horizon. 2. Mokhtarani M, Diaz GA, Rhead W, et al. Elevated phenylacetic acid levels do not correlate with adverse reactions in patients with urea cycle disorders or hepatic encephalopathy and can be predicted based on the plasma PAA to PAGN ratio. Mol Genet Metab. 2013;110(4):446-453. 3. Mokhtarani M, Diaz GA, Rhead W, et al. Urinary phenylacetylglutamine as dosing biomarker for patients with urea cycle disorders. Mol Genet Metab. 2012;107(3):308-314.

INDICATION and IMPORTANT SAFETY INFORMATION

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INDICATION

RAVICTI (glycerol phenylbutyrate) Oral Liquid is indicated for use as a nitrogen-binding agent for chronic management of patients with urea cycle disorders (UCDs) who cannot be managed by dietary protein restriction and/or supplementation alone. RAVICTI must be used with dietary protein restriction and, in some cases, dietary supplements (e.g. essential amino acids, arginine, citrulline, protein-free calorie supplements).

LIMITATIONS OF USE
  • RAVICTI is not indicated for the treatment of acute hyperammonemia in patients with UCDs because more rapidly acting interventions are essential to reduce plasma ammonia levels.
  • The safety and efficacy of RAVICTI for the treatment of N-acetylglutamate synthase (NAGS) deficiency has not been established.

IMPORTANT SAFETY INFORMATION

CONTRAINDICATIONS
  • Patients with known hypersensitivity to phenylbutyrate: Reactions include wheezing, dyspnea, coughing, hypotension, flushing, nausea, and rash.
WARNINGS AND PRECAUTIONS
  • Neurotoxicity: Phenylacetate (PAA), the major metabolite of RAVICTI, may be toxic at levels of 500 micrograms/mL or greater. If symptoms of vomiting, nausea, headache, somnolence, or confusion, are present in the absence of high ammonia or other intercurrent illness which explains these symptoms, consider the potential for PAA neurotoxicity which may need reduction in the RAVICTI dosage.
  • Pancreatic Insufficiency or Intestinal Malabsorption: Low or absent pancreatic enzymes or intestinal disease resulting in fat malabsorption may result in reduced or absent digestion of RAVICTI and/or absorption of phenylbutyrate and reduced control of plasma ammonia. Monitor ammonia levels closely.
ADVERSE REACTIONS

The most common adverse reactions reported in clinical trials (at least 10% of patients) were:

  • Adult patients: diarrhea, flatulence, and headache occurred during 4-week treatment (n=45) with RAVICTI; nausea, vomiting, diarrhea, decreased appetite, dizziness, headache, and fatigue occurred during 12-month treatment (n=51) with RAVICTI.
  • Pediatric patients ages 2 to 17 years: upper abdominal pain, rash, nausea, vomiting, diarrhea, decreased appetite, and headache occurred during 12-month treatment (n=26) with RAVICTI.
  • Pediatric patients ages 2 months to less than 2 years: neutropenia, vomiting, constipation, diarrhea, pyrexia, hypophagia, cough, nasal congestion, rhinorrhea, rash, and papule occurred during 12-month treatment (n=17) with RAVICTI.
  • Pediatric patients less than 2 months of age: vomiting, rash, gastroesophageal reflux, increased hepatic enzymes, feeding disorder (decreased appetite, hypophagia), anemia, cough, dehydration, metabolic acidosis, thrombocytosis, thrombocytopenia, neutropenia, lymphocytosis, diarrhea, flatulence, constipation, pyrexia, lethargy, and irritability/agitation occurred during 24-month treatment (n=16) with RAVICTI.
DRUG INTERACTIONS
  • Corticosteroids, valproic acid, or haloperidol may increase plasma ammonia level. Monitor ammonia levels closely.
  • Probenecid may affect renal excretion of metabolites of RAVICTI, including phenylacetylglutamine (PAGN) and PAA.
  • CYP3A4 substrates with narrow therapeutic index (eg, alfentanil, quinidine, cyclosporine): RAVICTI may decrease exposure to the concomitant drug.
  • Midazolam: Use of RAVICTI decreased exposure of midazolam with concomitant use.
USE IN SPECIFIC POPULATIONS
  • Pregnancy: RAVICTI should be used with caution in patients who are pregnant or planning to become pregnant. Based on animal data, RAVICTI may cause fetal harm. Report pregnancies to Horizon at 1‐866‐479‐6742.
  • Lactation: breastfeeding is not recommended during treatment with RAVICTI. There are no data on the presence of RAVICTI in human milk, the effects on the breastfed infant, nor the effects on milk production.

Please see Full Prescribing Information.

INDICATION and IMPORTANT SAFETY INFORMATION

true

INDICATION

RAVICTI (glycerol phenylbutyrate) Oral Liquid is indicated for use as a nitrogen-binding agent for chronic management of patients with urea cycle disorders (UCDs) who cannot be managed by dietary protein restriction and/or supplementation alone. RAVICTI must be used with dietary protein restriction and, in some cases, dietary supplements (e.g. essential amino acids, arginine, citrulline, protein-free calorie supplements).

LIMITATIONS OF USE
  • RAVICTI is not indicated for the treatment of acute hyperammonemia in patients with UCDs because more rapidly acting interventions are essential to reduce plasma ammonia levels.
  • The safety and efficacy of RAVICTI for the treatment of N-acetylglutamate synthase (NAGS) deficiency has not been established.

IMPORTANT SAFETY INFORMATION

CONTRAINDICATIONS
  • Patients with known hypersensitivity to phenylbutyrate: Reactions include wheezing, dyspnea, coughing, hypotension, flushing, nausea, and rash.
WARNINGS AND PRECAUTIONS
  • Neurotoxicity: Phenylacetate (PAA), the major metabolite of RAVICTI, may be toxic at levels of 500 micrograms/mL or greater. If symptoms of vomiting, nausea, headache, somnolence, or confusion, are present in the absence of high ammonia or other intercurrent illness which explains these symptoms, consider the potential for PAA neurotoxicity which may need reduction in the RAVICTI dosage.
  • Pancreatic Insufficiency or Intestinal Malabsorption: Low or absent pancreatic enzymes or intestinal disease resulting in fat malabsorption may result in reduced or absent digestion of RAVICTI and/or absorption of phenylbutyrate and reduced control of plasma ammonia. Monitor ammonia levels closely.
ADVERSE REACTIONS

The most common adverse reactions reported in clinical trials (at least 10% of patients) were:

  • Adult patients: diarrhea, flatulence, and headache occurred during 4-week treatment (n=45) with RAVICTI; nausea, vomiting, diarrhea, decreased appetite, dizziness, headache, and fatigue occurred during 12-month treatment (n=51) with RAVICTI.
  • Pediatric patients ages 2 to 17 years: upper abdominal pain, rash, nausea, vomiting, diarrhea, decreased appetite, and headache occurred during 12-month treatment (n=26) with RAVICTI.
  • Pediatric patients ages 2 months to less than 2 years: neutropenia, vomiting, constipation, diarrhea, pyrexia, hypophagia, cough, nasal congestion, rhinorrhea, rash, and papule occurred during 12-month treatment (n=17) with RAVICTI.
  • Pediatric patients less than 2 months of age: vomiting, rash, gastroesophageal reflux, increased hepatic enzymes, feeding disorder (decreased appetite, hypophagia), anemia, cough, dehydration, metabolic acidosis, thrombocytosis, thrombocytopenia, neutropenia, lymphocytosis, diarrhea, flatulence, constipation, pyrexia, lethargy, and irritability/agitation occurred during 24-month treatment (n=16) with RAVICTI.
DRUG INTERACTIONS
  • Corticosteroids, valproic acid, or haloperidol may increase plasma ammonia level. Monitor ammonia levels closely.
  • Probenecid may affect renal excretion of metabolites of RAVICTI, including phenylacetylglutamine (PAGN) and PAA.
  • CYP3A4 substrates with narrow therapeutic index (eg, alfentanil, quinidine, cyclosporine): RAVICTI may decrease exposure to the concomitant drug.
  • Midazolam: Use of RAVICTI decreased exposure of midazolam with concomitant use.
USE IN SPECIFIC POPULATIONS
  • Pregnancy: RAVICTI should be used with caution in patients who are pregnant or planning to become pregnant. Based on animal data, RAVICTI may cause fetal harm. Report pregnancies to Horizon at 1‐866‐479‐6742.
  • Lactation: breastfeeding is not recommended during treatment with RAVICTI. There are no data on the presence of RAVICTI in human milk, the effects on the breastfed infant, nor the effects on milk production.

Please see Full Prescribing Information.