Glycerol phenylbutyrate binds with other substances in the liver and kidneys to help eliminate nitrogen from the body. Excess nitrogen can cause hyperammonemia (HYE-per-AM-moe-NEE-mee-a), a build-up of ammonia in the blood. Ammonia is very toxic when it circulates in blood and tissues and can cause permanent brain damage, coma, or death.

Glycerol phenylbutyrate helps prevent a build-up of ammonia in the blood in adults and children with urea cycle disorder. glycerol phenylbutyrate will not treat hyperammonemia.

Glycerol phenylbutyrate is usually given together with a low-protein diet and sometimes dietary supplements.

Glycerol phenylbutyrate may also be used for purposes not listed in this medication guide.

glycerol phenylbutyrate can affect your nervous system. Call your doctor right away if you have: confusion, headaches, memory problems, hearing problems, vomiting, an altered sense of taste, numbness or tingling in your hands or feet, or if you feel unusually sleepy or light-headed.

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

Glycerol phenylbutyrate is usually taken 3 times per day. Take with food or infant formula. If you are breastfeeding a baby who is taking glycerol phenylbutyrate, give each dose right before nursing.

Measure liquid medicine carefully. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).

Glycerol phenylbutyrate may be given through a nasogastric (NG) or gastric feeding tube as follows: Measure the correct dose in the oral syringe, attach it to the feeding tube and push the plunger down to empty the syringe into the tube. Flush the tube with 10 milliliters (mL) of water and allow the tube to drain. Follow this with 10 mL more of water to wash the contents down.

If you switch from sodium phenylbutyrate to glycerol phenylbutyrate, your dose will not be the same. Follow your doctor's dosing instructions very carefully.

Glycerol phenylbutyrate doses are based on body surface area (height and weight). Your dose needs may change if you gain or lose weight or if you are still growing.

You may need to follow a special diet while using glycerol phenlbutyrate. Follow all instructions of your doctor or dietitian. Learn about the foods to eat or avoid to help control your condition.

A buildup of ammonia in the blood can quickly cause brain injury or death. You will need frequent blood tests. Every person with a urea cycle disorder should remain under the care of a doctor.

Your name may be listed on a Urea Cycle Disorder registry. This is to collect information about people with these disorders and to evaluate the effects of treatment.

Store at room temperature away from moisture and heat.

You should not use glycerol phenylbutyrate if you are allergic to it.

Tell your doctor if you have ever had:

• liver or kidney disease;

• a pancreas disorder;

• stomach or intestinal disorder,

• a condition called NAGS (N-acetylglutamate synthase) deficiency; or

• if you use other medicines.

It is not known whether this medicine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

If you become pregnant, your name may be listed on a pregnancy registry. This is to track the outcome of the pregnancy and to evaluate any effects of glycerol phenylbutyrate on the baby.

You should not breastfeed while using this medicine.

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

Get emergency medical help if you have signs of an allergic reaction: hives; cough, wheezing, difficult breathing; feeling like you might pass out; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have any signs of high blood levels of ammonia (hyperammonemia):

• weakness, lack of energy;

• thinking problems, changes in behavior, feeling irritable;

• breathing problems;

• feeding problems; or

• seizure (convulsions).

Glycerol phenylbutyrate can affect your nervous system. Call your doctor at once if you have:

• drowsiness, unusual tiredness;

• memory problems;

• a light-headed feeling, like you might pass out;

• confusion, ongoing headache, vomiting;

• numbness, tingling, or burning pain in your hands or feet;

• altered sense of taste; or

• hearing problems.

Common side effects of glycerol phenylbutyrate may include:

• occasional headache;

• nausea, vomiting, diarrhea;

• loss of appetite, gas, stomach pain;

• dizziness, tiredness;

• rash; or

• (in children younger than 2 years) fever, cold or flu symptoms, cough, small bumps on the skin.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Sometimes it is not safe to use certain medications at the same time. Certain other drugs can affect your blood levels of ammonia, making glycerol phenylbutyrate less effective or causing hyperammonemia.

Many drugs can affect glycerol phenylbutyrate. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.