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Glycerol Phenylbutyrate Dosage

Applies to the following strength(s): 1.1 g/mL

The information at Drugs.com is not a substitute for medical advice. Always consult your doctor or pharmacist.

Usual Adult Dose for:

Usual Pediatric Dose for:

Additional dosage information:

Usual Adult Dose for Urea Cycle Disorders

Phenylbutyrate-Naive Patients:
-Initial dose: 4.5 to 11.2 mL/m2/day (5 to 12.4 g/m2/day) orally in 3 equally divided dosages
-Initial dose when residual enzyme activity is not adequately controlled with dietary restriction: 4.5 mL/m2/day
-Maintenance dose: Adjust dose to produce a fasting plasma ammonia level less than half the upper limit of normal according to age
-Maximum dose: 17.5 mL (19.5 g)

Comments:
-Doses should be rounded up to the nearest 0.5 mL.
- In determining the starting dose, consider the patient's residual urea synthetic capacity, dietary protein requirements, and diet adherence; may consider an initial estimated daily dose of 0.6 mL per gram of dietary protein ingested per 24 hour period.

Patients switching from Sodium Phenylbutyrate should use the following conversion:
-Total daily dose of glycerol phenylbutyrate (mL) should equal the total daily dose of sodium phenylbutyrate (g) x 0.86
Maximum dose: 17.5 mL (19.5 g)

Comments:
-Must use with dietary protein restriction and in some cases, with dietary supplements.
-Not indicated for the treatment of acute hyperammonemia as more rapid interventions should be used.
-Safety and efficacy for treatment of N-acetylglutamate synthase (NAGS) deficiency has not been established.

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 amino acid supplementation alone.

Usual Pediatric Dose for Urea Cycle Disorders

Aged 2 years or older:
Phenylbutyrate-Naive Patients:
-Initial dose: 4.5 to 11.2 mL/m2/day (5 to 12.4 g/m2/day) orally in 3 equally divided dosages
-Initial dose when residual enzyme activity is not adequately controlled with dietary restriction: 4.5 mL/m2/day
-Maintenance dose: Adjust dose to produce a fasting plasma ammonia level less than half the upper limit of normal according to age
-Maximum dose: 17.5 mL (19.5 g)

Comments:
-Doses should be rounded up to the nearest 0.5 mL.
- In determining the starting dose, consider the patient's residual urea synthetic capacity, dietary protein requirements, and diet adherence; may consider an initial estimated daily dose of 0.6 mL per gram of dietary protein ingested per 24 hour period.

Patients switching from Sodium Phenylbutyrate should use the following conversion:
-Total daily dose of glycerol phenylbutyrate (mL) should equal the total daily dose of sodium phenylbutyrate (g) x 0.86
Maximum dose: 17.5 mL (19.5 g)

Comments:
-Must use with dietary protein restriction and in some cases, with dietary supplements.
-Not indicated for the treatment of acute hyperammonemia as more rapid interventions should be used.
-Safety and efficacy for treatment of N-acetylglutamate synthase (NAGS) deficiency has not been established.

Use: As a nitrogen-binding agent for chronic management of pediatric patients 2 years or older with urea cycle disorders (UCDs) who cannot be managed by dietary protein restriction and/or amino acid supplementation alone.

Renal Dose Adjustments

Monitor ammonia levels closely when starting treatment.

Liver Dose Adjustments

Moderate to severe liver dysfunction: Starting dose should be at the lower end of the dose range; maintain at lowest dose necessary to control ammonia levels.

Dose Adjustments

Elderly: Start at the low end of the dosing range to account for decreased hepatic, renal, or cardiac function and concomitant disease or other drug therapies.

Therapeutic drug monitoring/range:
Dose adjustments should be made to produce fasting plasma ammonia levels that are less than half the upper limit of normal (ULN) according to age.
-Adjustment based on Urinary Phenylacetylglutamine (U-PAGN): If available, U-PAGN measurements may be used to guide therapy. Each g of U-PAGN excreted over 24 hours covers waste nitrogen generated from 1.4 g of dietary protein. If U-PAGN excretion is insufficient to cover daily dietary protein intake and the fasting ammonia level is greater than half the ULN, the dose should be adjusted upward. The amount of dose adjustment should factor in the amount of dietary protein that has not been covered (indicated by the 24 hour U-PAGN level), the estimated dose needed per gram of dietary protein ingested, and the maximum total daily dosage. Consider a patient's use of concomitant medications when making dosage adjustment decisions based on U-PAGN. Probenecid may decrease urinary excretion of PAGN.
-Adjustment based on Plasma Phenylacetate (PAA): If available, PAA levels may be useful to guide dosing if symptoms of vomiting, nausea, headache, somnolence, confusion, or sleepiness are present in the absence of high ammonia or intercurrent illness. The ratio of PAA to PAGN in plasma may provide additional information to assist in dose adjustment decisions. With a high PAA to PAGN ratio, a further increase in the dose may not increase PAGN formation, even if plasma PAA concentrations are increased, due to saturation of the conjugation reaction. The PAA to PAGN ratio has been observed to be generally less than 1 in patients without significant PAA accumulation.

Precautions

Safety and efficacy have not been established in patients younger than 18 years.

Consult WARNINGS section for dosing related precautions.

Dialysis

Data not available

Other Comments

Administration advice:
-Take with food
-Give in 3 equally divided doses, each rounded up to the nearest 0.5 mL
-Administer directly into mouth via oral syringe or dosing cup

Nasogastric Tube or Gastrostomy Tube Administration:
-Use oral syringe to withdraw dose from bottle
-Place tip of syringe into the tip of the nasogastric or gastrostomy tube
-Using the plunger of the syringe, administer drug into tube
-Flush once with 30 mL of water and allow the flush to drain
-Flush a second time with an additional 30 mL of water to clear tube

Storage requirements: Keep at 20 to 25C (68 to 77F); excursions permitted to 15 to 30C (59 to 86F)

General:
-This drug should be prescribed by a physician experienced in the management of urea cycle disorders.
-This drug should be used with dietary protein restriction, and possibly, dietary supplements (e.g. essential amino acids, arginine, citrulline, protein-free calorie supplements).
-A voluntary registry for urea cycle disorder (UCD ) patients has been established to better assess long-term outcomes including growth and neurocognitive outcomes and pregnancy outcomes. Patients and their caregivers are encouraged to participate; visit www.ucdregistry.com or call 1-855-823-2595.

Monitoring:
-Ammonia levels should be monitored closely during therapy
-If available, Urinary Phenylacetylglutamine (U-PAGN) and Plasma Phenylacetate (PAA) levels may be useful to guide therapy.

Patient advice:
-This drug may cause nervous system side effects and patients should be instructed to contact their healthcare professional promptly if these side effects occur.
-This drug is to be used in conjunction with dietary protein restriction, and in some cases, dietary supplements.
-Patients should talk to their health care provider if they are pregnant, planning on becoming pregnant, or are breastfeeding.

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