Glycerol phenylbutyrate

Glycerol phenylbutyrate treats high blood levels of ammonia caused by urea cycle disorder. Take this medication with food.

Glycerol phenylbutyrate Overview

Reviewed: March 27, 2013

Glycerol phenylbutyrate is a prescription medication used to treat high blood levels of ammonia caused by a condition called urea cycle disorder (UCD). Glycerol phenylbutyrate belongs to a group of drugs called urea cycle disorder treatment agents. These work by lowering the amount of ammonia in the blood to a safe and normal level.

This medication comes in a liquid form (by mouth) and is usually taken 3 times a day with food.

Common side effects of glycerol phenylbutyrate include diarrhea, nausea, and vomiting.

Glycerol phenylbutyrate can also cause dizziness and drowsiness. Do not drive or operate heavy machinery until you know how glycerol phenylbutyrate affects you.

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Uses of Glycerol phenylbutyrate

Glycerol phenylbutyrate is a prescription medicine used along with a low-protein diet in adults and children 2 years of age and older for long-term management of high blood levels of ammonia (hyperammonemia) caused by a condition called urea cycle disorder (UCD). In people with UCD, the body does not get rid of a waste product called ammonia the way it should. When too much ammonia builds up in the body, it can be dangerous.

This medication may be prescribed for other uses.  Ask your doctor or pharmacist for more information.



Glycerol phenylbutyrate Brand Names

Glycerol phenylbutyrate may be found in some form under the following brand names:

Glycerol phenylbutyrate Drug Class

Glycerol phenylbutyrate is part of the drug class:

Side Effects of Glycerol phenylbutyrate

Serious side effects have been reported with glycerol phenylbutyrate. See the “Drug Precautions” section.

Common side effects of glycerol phenylbutyrate include the following:

  • diarrhea
  • gas
  • headache
  • nausea
  • vomiting
  • drowsiness
  • decreased appetite
  • high ammonia blood levels
  • dizziness
  • stomach pain

This is not a complete list of glycerol phenylbutyrate side effects. Ask your doctor or pharmacist for more information.

Tell your doctor if you have any side effect that bothers you or that does not go away.

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

Glycerol phenylbutyrate Interactions

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements. Especially tell your doctor if you take:

  • corticosteroid medications such as beclomethasone, budesonide, medrol, prednisolone, prednisone, fluticasone and others
  • valproic acid (Depakote, Depakene, Stavzor)
  • haloperidol (Haldol)
  • probenecid (Benemid, Probalan, in Colbenemid, and Proben-C)

This is not a complete list of glycerol phenylbutyrate drug interactions. Ask your doctor or pharmacist for more information. 

Glycerol phenylbutyrate Precautions

Glycerol phenylbutyrate may cause serious side effects, including:

Nervous system problems (Neurotoxicity). Phenylacetate, a breakdown product of glycerol phenylbutyrate, may cause nervous system side effects. Call your doctor or get medical help right away if you get any of these symptoms while taking glycerol phenylbutyrate:

  • sleepiness
  • weakness
  • lightheadedness
  • change in taste
  • problems with hearing
  • confusion
  • problems with memory
  • worsening neuropathy (numbness, tingling, or burning in your hands or feet)
  • headache

Do not take glycerol phenylbutyrate if you are:

  • less than 2 months of age because it may not be digested in babies less than 2 months of age.
  • allergic to phenylbutyrate. Call your doctor or go to the nearest hospital emergency room if you get wheezing, shortness of breath, cough, low blood pressure, flushing, nausea or a rash while taking glycerol phenylbutyrate.

Glycerol phenylbutyrate Food Interactions

Medicines can interact with certain foods. In some cases, this may be harmful and your doctor may advise you to avoid certain foods. In the case of glycerol phenylbutyrate there are no specific foods that you must exclude from your diet when receiving this medication.

Inform MD

Before you take glycerol phenylbutyrate, tell your doctor if you:

  • have liver or kidney problems
  • have pancreas or bowel (intestine) problems
  • have any other medical conditions
  • are pregnant or breastfeeding

Tell your doctor about all the medicines you take, including prescription and over-the-counter medicines, vitamins, dietary and herbal supplements.


Glycerol phenylbutyrate and Pregnancy

Tell your doctor if you are pregnant or plan to become pregnant.

The FDA categorizes medications based on safety for use during pregnancy. Five categories - A, B, C, D, and X, are used to classify the possible risks to an unborn baby when a medication is taken during pregnancy.

Glycerol phenylbutyrate falls into category C. There are no well-controlled studies that have been done in pregnant women. Glycerol phenylbutyrate should be used during pregnancy only if the possible benefit outweighs the possible risk to the unborn baby.

Glycerol phenylbutyrate and Lactation

It is not known if glycerol phenylbutyrate crosses into human milk. Because many medications can cross into human milk and because of the possibility for serious adverse reactions in nursing infants with use of this medication, a choice should be made whether to stop nursing or stop the use of this medication. Your doctor and you will decide if the benefits outweigh the risk of using glycerol phenylbutyrate.


Glycerol phenylbutyrate Usage

Take glycerol phenylbutyrate exactly as your doctor tells you.

  • Your doctor will tell you how much glycerol phenylbutyrate to take and when to take it.
  • Your doctor may change your dose if needed.
  • Take glycerol phenylbutyrate with food.
  • Glycerol phenylbutyrate is an oral liquid that is taken by mouth using an oral syringe or measuring cup. Ask your pharmacist for an oral syringe or measuring cup if you do not have one.
  • Stay on the diet that your doctor gives you.
  • Talk to your doctor about participating in a UCD registry. The purpose of this registry is to collect information about people with UCD to improve care. For more information about the registry program call 1-855-823-2595 or visit

For people who have a nasogastric or gastric tube in place, glycerol phenylbutyrate should be given as follows:

  • Use an oral syringe to withdraw the prescribed dose of glycerol phenylbutyrate from the bottle.
  • Place the tip of the syringe into the tip of the nasogastric or gastric tube and push the plunger of the syringe to give glycerol phenylbutyrate into the tube.
  • Flush the nasogastric or gastric tube with 30 mL of water and allow the flush to drain.
  • Flush the nasogastric or gastric tube a second time with an additional 30 mL of water.

Glycerol phenylbutyrate Dosage

The recommended glycerol phenylbutyrate dosage is different for people switching from sodium phenylbutyrate (Buphenyl) and for those who have never taken phenylbutyric acid.

Your doctor will determine the best starting glycerol phenylbutyrate dosage for you based on:

  • whether or not you have been taking sodium phenylbutyrate (Buphenyl) 
  • your height and weight
  • your dietary requirements 
  • other medications you are taking
  • liver function (if you have liver disease, you may receive a lower dose)

​Your doctor will monitor your fasting plasma ammonia levels and adjust your glycerol phenylbutyrate dose as necessary.

The maximum recommended glycerol phenylbutyrate dosage is 17.5 ml (19 g).

Glycerol phenylbutyrate Overdose

If you take too much glycerol phenylbutyrate, call your doctor or go to the nearest hospital emergency room right away.


Other Requirements

  • Store glycerol phenylbutyrate at room temperature between 68°F to 77°F (20°C to 25°C).
  • Keep glycerol phenylbutyrate and all medicines out of the reach of children.