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Glycerol phenylbutyrate (By mouth)

Glycerol Phenylbutyrate (GLI-ser-ol fen-il-BUE-ti-rate)

Treats urea cycle disorders to help remove nitrogen from the body.

Brand Name(s):


There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

This medicine is not right for everyone. Do not use it if you had an allergic reaction to glycerol phenylbutyrate.

How to Use This Medicine:


  • Take your medicine as directed. Your dose may need to be changed several times to find what works best for you.
  • It is best to take this medicine with food or milk.
  • Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup.
  • This medicine may be given through a feeding tube (nasogastric tube or gastrostomy tube).
    • Use an oral syringe to measure the dose. Place it on the tip of the feeding tube.
    • Inject the medicine into the tube.
    • Flush the tube with 10 milliliters (mL) of water to rinse all of the medicine into the stomach.
    • Rinse the tube again with another 10 mL of water to clear the tube.
  • Carefully follow your doctor's instructions about any special diet.
  • This medicine should come with a Medication Guide. Ask your pharmacist for a copy if you do not have one.
  • Missed dose: Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.
  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • Some medicines can affect how glycerol phenylbutyrate works. Tell your doctor if you are using any of the following:
    • Alfentanil, cyclosporine, haloperidol, midazolam, probenecid, quinidine, valproic acid
    • Steroid medicine (including dexamethasone, hydrocortisone, methylprednisolone, prednisolone, prednisone)

Warnings While Using This Medicine:

  • Tell your doctor if you are pregnant, or if you have kidney disease, liver disease, nerve problems, or digestive problems (including pancreas problems). Tell your doctor if you have used a phenylbutyrate medicine in the past.
  • Do not breastfeed during treatment with this medicine. But you may use this medicine just before breastfeeding.
  • Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
  • Burning, tingling, numbness or pain in the hands, arms, feet, or legs
  • Confusion, memory problems
  • Lightheadedness, headache, trouble hearing
  • Nausea, vomiting, seizures, yellow eyes or skin
  • Unusual sleepiness, tiredness, or weakness

If you notice these less serious side effects, talk with your doctor:

  • Decreased appetite
  • Diarrhea, gas, stomach pain

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088

Last Updated: 5/1/2020

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