Sodium Phenylbutyrate (Oral)

Designed to be used as a treatment for urea cycle disorders alongside diet management, sodium phenylbutyrate works to prevent ammonia build up in the blood to reduce the life-threatening risk of excessive ammonia levels in the body.


Sodium phenylbutyrate is an orphan drug used alongside diet changes to treat urea cycle disorders. These disorders are hereditary and cause a deficiency of liver enzymes which are necessary for eliminating waste substances from the body. This can lead to a buildup of toxic ammonia (nitrogen) in the body which can cause serious health problems, including brain damage. In some cases, high ammonia levels can cause death.

Sodium phenylbutyrate works by helping the kidneys to eliminate waste substances from the body. It is these waste substances which produce ammonia. This helps to prevent a buildup of ammonia in the blood. However, the drug is not as effective if it is used as the only preventative method. Adjusting diet to minimize the production of ammonia is also essential for successful management of the condition.

In the US, sodium phenylbutyrate is available in tablet, enteric coated tablet, and powder forms and is known under the following brand names:

  • Buphenyl
  • SPB11

Condition(s) treated?

  • Urea cycle disorders

Type of medicine?

  • Orphan drug

Side Effects

There are a variety of side effects associated with sodium phenylbutyrate, some of which are serious and should be reported to a doctor immediately. The following are more common serious side effects associated with the drug:

  • Change in frequency of breathing
  • Irregular or lack of menstruation
  • Swelling in lower legs or feet
  • Pain in lower back, side or stomach
  • Nausea or vomiting
  • Unpleasant taste
  • Pain or twitching in muscles
  • Mood or mental changes
  • Nervousness or restlessness
  • Unusual tiredness or weakness

Less common but serious side effects include:

  • Chills
  • Fever
  • Sore throat
  • Joint pain
  • Abnormal bruising or bleeding

The following side effects are serious but rare:

  • Convulsion (seizures)
  • Fast, slow or irregular heartbeat
  • Increased blood pressure
  • Weak pulse
  • Dizziness
  • Swelling of the face
  • Dry mouth
  • Increased thirst
  • Muscle cramps
  • Rectal bleeding
  • Unusual weight gain

Some side effects of sodium phenylbutyrate are minor and do not require medical attention. In many instances, these effects go away once the body adjusts to the drug. However, if they persist and become very bothersome, you could discuss them with your doctor. They may be able to recommend lifestyle adjustments which could lessen or stop the unwanted effects. The following minor side effects are less common:

  • Changes in taste
  • Reduced appetite
  • Strong body odor

Rare minor side effects include:

  • Stomach or abdominal pain
  • Constipation
  • Headache
  • Mental depression
  • Skin rash
  • Fainting

If you notice any other side effects not listed here, discuss them with your doctor as soon as possible. You could also report new side effects to the FDA.


The amount of sodium phenylbutyrate taken will vary depending on the strength of the medicine, the number of doses given throughout the day, and the body weight of the patient. Usually, no more than 20 grams should be taken within one day. For the powder form of the medicine, this is usually split between 4 to 6 doses. For the tablet form, doses are usually taken three times each day. Always follow your doctor's directions and do not take more than the quantities prescribed to you.

Sodium phenylbutyrate should always be taken with food. The powder form is designed to be mixed with soft or liquid food, and it can be taken via a feeding tube. If you are taking the tablets, always consume them with a meal and swallow them whole with water if necessary. Do not crush or chew the tablets.

If you miss a dose of sodium phenylbutyrate, you should take it as soon as you remember, provided that it is with food. If it's almost time for your next dose when you realize you have missed a dose, simply skip that dose and continue your usual dosing schedule. Do not double doses to compensate for a missed dose.


You should make sure your doctor is aware of all medicines you are currently taking, including those purchased over the counter as well as those prescribed to you. In particular, your doctor should know if you take the following medications which are known to interact with sodium phenylbutyrate and could cause serious side effects:

  • Corticosteroids
  • Haloperidol
  • Probenecid
  • Valproic acid

You should also make sure your doctor knows about medicines you take which could cause drowsiness, since they may worsen the risk of drowsiness, sleepiness and dizziness associated with sodium phenylbutyrate. Examples of such medicines include:

  • Antihistamines
  • Anti-seizure medicines
  • Sleep medicines
  • Anti-anxiety medicines
  • Muscle relaxants
  • Narcotic pain relievers
  • Psychiatric medicines

Remember that some over the counter medicines, such as cold and flu treatments, can contain ingredients which induce drowsiness. Check with your doctor or a pharmacist if you plan to take medicines of this kind.

Interactions with medical conditions

The following conditions may be worsened by sodium phenylbutyrate:

  • Edema (excess bodily fluids and subsequent swelling)
  • Heart disease
  • Heart failure
  • Kidney disease

If you have any of these conditions, your doctor may choose not to prescribe you sodium phenylbutyrate, or they may adjust your dosage or adjust the treatments for the other conditions. Make sure your doctor knows about all medical conditions you have.

People with kidney disease or liver disease will process sodium phenylbutyrate at a slower rate than normal, which can lead to higher levels of sodium phenylbutyrate in the blood. This could increase the risk of side effects associated with the medicine. Your doctor may reduce your dosage to minimize these risks, or they may choose an alternative treatment.


Pediatric use

Sodium phenylbutyrate is not recommended for children weighing less than 44 pounds (20 kilograms). However, in some instances doctors may deem it a suitable treatment after carefully weighing up the potential risks and benefits of the medicine. Always follow your doctor's instructions.

Pregnancy and breastfeeding

The FDA have marked sodium phenylbutyrate in pregnancy category C, which means it can only be used if the benefits of the drug far outweigh potential risks to the fetus. There have not been adequate human studies performed to assess the safety of the drug during pregnancy, but animal studies have shown that the drug poses a risk to the unborn fetus.

It isn't known whether sodium phenylbutyrate is excreted in human breast milk, or in animal milk. It is also unknown what effects the drug could have on a nursing infant if it was excreted in breast milk. For this reason, breastfeeding is not recommended for women who are taking the medicine.

Managing urea cycle disorders

Your doctor will want to check your progress at regular intervals when you take sodium phenylbutyrate. You will probably be required to have blood tests on a regular basis. Not only are blood tests needed to check your ammonia levels, but they may also draw attention to unwanted effects of the sodium phenylbutyrate should they occur.

Sodium phenylbutyrate is usually used as a treatment in conjunction with strict diet management. Your doctor will probably make recommendations about your diet to limit the amount of sodium produced by the body. Protein is often limited as this is known to increase ammonia intake. Always follow your doctor's instructions to minimize the risk of complications associated with urea cycle disorders.

Urea cycle disorders can cause serious symptoms which could require emergency medical care. It is recommended that you wear a Medic Alert tag so that others can get emergency care for you should it be required. You should also carry an ID card which states that you have urea cycle disorder and lists all of your medicines, including sodium phenylbutyrate, so that healthcare professionals can provide you with the most suitable treatment as quickly as possible.

If you experience lightheadedness or sleepiness, consult your doctor immediately. These symptoms can be signs of more serious complications associated with urea cycle disorders.

Some medicines and supplements could increase the amount of ammonia produced by your body. Always check with your doctor that a medicine is safe for you before taking it. This includes prescribed medicines and those bought over the counter, as well as multivitamins and herbal supplements.

Risk of drowsiness or dizziness

Sodium phenylbutyrate can in some instances cause dizziness or drowsiness. Avoid driving or operating heavy machinery until you know how the medicine affects you. You should also limit alcohol intake, because alcohol may worsen drowsiness or dizziness.


Sodium phenylbutyrate may contain active ingredients which could cause allergic reaction. Make sure your doctor knows about all allergies you have, particularly if you've had an allergic reaction or sensitivity to a drug in the past.


Sodium phenylbutyrate should be stored at room temperature in a closed container. It should be kept from freezing and away from heat, direct light and moisture.

You should keep sodium phenylbutyrate away from children and pets by storing it up and away from the ground so that it is not within easy reach.

If you have leftover or outdated sodium phenylbutyrate, do not keep it. Instead, ask your healthcare provider how to dispose of it appropriately. Bear in mind that sodium phenylbutyrate normally has a strong, musty odor and this doesn't necessarily mean that it has expired or degraded. Check the expiry date on the packaging, or consult a doctor or pharmacist if you're in doubt about the safety of the drug.


Sodium phenylbutyrate is prescribed alongside strict dietary changes to manage ammonia buildup in individuals with urea cycle disorder. This disorder causes a deficiency in liver enzymes which are responsible for removing waste from the body. If the waste is not adequately removed, it can result in a buildup of ammonia which is toxic. If ammonia levels become too high, patients risk experiencing brain damage and, in some cases, death.

Sodium phenylbutyrate helps to remove waste in order to prevent a dangerous buildup of ammonia, but it is not a cure for urea cycle disorder. Generally speaking the drug is designed for long term use alongside diet changes. Different foods can lead to different levels of ammonia production, so it's important to limit those which are known to increase ammonia production.

This drug is designed to be taken orally and is available in two forms; powder and tablet. Tablets can be swallowed whole, while the powder should be mixed with soft or liquid foods and then eaten. Both the tablets and powder should be consumed at the same time as food. Usually, a patient takes three doses of the drug each day, but the powder form may be administered between three and six times each day. Your doctor will instruct on a dosing schedule most suitable for you.

Sodium phenylbutyrate can cause dizziness and drowsiness, so it's important to avoid alcohol and other medications which also induce these effects, such as antihistamines, cold and flu medicines and sleeping medicines. It can also cause taste changes and reduced appetite, but these are not usually side effects that require medical attention. If you experience changes in breathing, pain in the back or stomach, nausea or vomiting, changes in mood or mental state, fever, chills or convulsions, visit your doctor or the emergency room immediately.

Last Reviewed:
December 23, 2017
Last Updated:
April 05, 2018