Skip to main content

Sodium phenylbutyrate tablets


Take sodium phenylbutyrate at mealtimes.

It is important that you follow the special dietary advice given by your doctor or dietician.

Continue reading below

About sodium phenylbutyrate

Used for

Urea cycle disorders

Also called


Available as


Sodium phenylbutyrate is prescribed for people with urea cycle disorders. These are rare genetic disorders caused by a lack of an enzyme. Protein from the food you eat is usually broken down into nitrogen waste in your body. It is then converted into urea so that it can be removed from your body in your urine. Enzymes are involved in this breakdown process. If you have a lack of one of the enzymes your body needs, this means that nitrogen waste is not broken down. This leads to a build-up in your bloodstream of a nitrogen-containing substance called ammonia.

Sodium phenylbutyrate reduces the amount of ammonia in your blood by helping your body to get rid of nitrogen waste. You will also have to follow a special diet to help control your symptoms. You will be prescribed this medicine by a specialist doctor.

Before taking sodium phenylbutyrate tablets

Some medicines are not suitable for people with certain conditions, and sometimes a medicine can only be used if extra care is taken. For these reasons, before you (or your child, if appropriate) start taking sodium phenylbutyrate it is important that your doctor knows:

  • If you have any problems with the way your liver works or with the way your kidneys work.

  • If you have a condition where your heart is not working as well as it should (heart failure).

  • If you have difficulty swallowing food or drinks or your child has difficulty swallowing tablets.

  • If you have been advised to have a low-sodium diet.

  • If you are pregnant, trying for a baby or breastfeeding.

  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.

  • If you have ever had an allergic reaction to a medicine.

Continue reading below

How to take sodium phenylbutyrate

  • Before you start the treatment, read the manufacturer's printed information leaflet from inside your pack. It will give you more information about sodium phenylbutyrate, and it will provide you with a full list of side-effects which you could experience from taking it.

  • The dose you are prescribed will be tailored to your needs, so take the tablets exactly as your doctor tells you to. The directions will be printed on the label of the pack to remind you about what the doctor said to you.

  • You must take sodium phenylbutyrate tablets at each mealtime. This means it is usual for adults to take three doses every day. Doses in young children will be divided between their daily feeds, which can be 4 to 6 times daily.

  • Swallow the tablets with a large glass of water to make sure that they do not get lodged in your throat. If you have any difficulties swallowing the tablets, please let your doctor know.

  • If you forget to take a dose, make sure you remember to take one with your next meal and then continue as usual. Leave at least three hours between doses, and never take two doses together to make up for a forgotten dose.

Getting the most from your treatment

  • Try to keep your regular appointments with your doctor. This is so your doctor can check on your progress. Your doctor will want you to have blood tests to check on the levels of ammonia in your blood.

  • You should follow the dietary advice that your doctor or dietician has given you. It is important that you eat a special diet which is low in protein. Sodium phenylbutyrate tablets contain sodium which should be taken into account if you are following a low-sodium diet.

  • Treatment with sodium phenylbutyrate is usually long-term. Continue to take it unless you are told otherwise by your doctor.

  • You must avoid getting pregnant while you are taking sodium phenylbutyrate. If appropriate, make sure you have discussed with your doctor which types of contraception are suitable for you and your partner.

Continue reading below

Can sodium phenylbutyrate cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the most common ones associated with sodium phenylbutyrate. You will find a full list in the manufacturer's information leaflet supplied with the medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.

Common sodium phenylbutyrate side-effects

What can I do if I experience this?

Feeling sick (nausea) or being sick (vomiting), stomach discomfort

Stick to simple foods - avoid rich or spicy meals. Speak with your doctor about this as it may help for you to take smaller doses more frequently


Sit down if you feel faint; then try getting up and moving more slowly


Drink plenty of water and ask your doctor or pharmacist to recommend a suitable painkiller. If the headaches continue, let your doctor know

Irregular menstrual periods, loss of appetite, body odour, disturbed taste, swollen ankles or feet, changes in your mood such as feeling depressed or irritable, skin rash, increased weight

If any of these become troublesome, speak with your doctor for advice

Changes to the results of some blood tests

Your doctor will monitor these

Your doctor will discuss with you the possibility of other unwanted effects, such as blood disorders, and what symptoms to watch out for. If you experience any symptoms which you think may be due to the medicine, please speak with your doctor for advice as soon as possible.

How to store sodium phenylbutyrate

  • Keep all medicines out of the reach and sight of children.

  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines

Important information about all medicines

If you buy any medicines, check with a pharmacist that they are safe to take with your other medicines.

If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of the medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Report side effects to a medicine or vaccine

If you experience side effects, you can report them online through the Yellow Card website.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

symptom checker

Feeling unwell?

Assess your symptoms online for free