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What is Ammonaps (sodium phenylbutyrate) for?

Ammonaps (sodium phenylbutyrate) is an adjunctive therapy indicated for the chronic management of urea cycle disorders which involve deficiencies of the enzymes carbamylphosphate synthetase, ornithine transcarbamylase or argininosuccinate synthetase.^[1]

It is indicated for:^[1]

• ‘early-onset’ disease in babies who show a complete lack of one or more of these enzymes within the first 28 days after birth
• ‘late-onset’ disease in patients who show a partial lack of an enzyme after the age of one month and have had brain damage caused by high blood ammonia levels.

It is available in tablet form each containing 500 mg sodium phenylbutyrate.^[1]

How does Ammonaps (sodium phenylbutyrate) work?

The urea cycle is a process that helps the body remove waste nitrogen that is made from breaking down protein consumed through food. People with an urea cycle disorder are missing a gene that helps them get rid of this waste. As a result, there is a buildup of nitrogen levels in the form of ammonia, which is highly toxic, especially for the brain.^[2,3]

Sodium phenylbutyrate gives the body an alternative: it can bind to nitrogen to form a substance that can be removed from the body via the urine.^[1]

Besides this, sodium phenylbutyrate also works as a histone deacetylase inhibitor that can stimulate the survival of motor neurons. For this reason it is being studied for use in the treatment of amyotrophic lateral sclerosis (ALS).^[4]

Note: This medicine has not yet been approved for the treatment of ALS. Neurologists sometimes prescribe Ammonaps (sodium phenylbutyrate) for off-label treatment of people suffering from ALS.

Where has Ammonaps (sodium phenylbutyrate) been approved?

Ammonaps (sodium phenylbutyrate) was approved to treat urea cycle disorders involving deficiencies by:

• The Food and Drug Administration (FDA), USA, on May 13, 1995, under the brand name Buphenyl.^[1]
• The European Medicines Agency (EMA), Europe, on Dec 8, 1999.^[5]
• The Therapeutic Goods Administration (TGA), Australia, on May 19, 2017, under the brand name Pheburane.^[7]

Please note that this medicine may have also been approved in other regions than the ones we’ve listed. If you have a question about its approval in a specific country feel free to contact our support team.

How is Ammonaps (sodium phenylbutyrate) taken?

The daily dosage of Ammonaps (sodium phenylbutyrate) will be calculated from the patient’s protein tolerance, diet and body weight or body surface. Regular blood tests should be performed to determine the correct daily dose.^[1,6]

Tablets should be taken by mouth (orally) in equally divided doses with each meal (for example three to six times per day). Ammonaps (sodium phenylbutyrate) should be taken with a large volume of water.^[1]

Tablets should be taken with a special diet low in protein.^[1]

Complete information about Ammonaps (sodium phenylbutyrate) dosage and administration can be found in the official prescribing information listed in our references section.^[1]

Note: Please consult with your treating doctor for personalised dosing.

Are there any known adverse reactions or side effects of Ammonaps (sodium phenylbutyrate)?

Common adverse reactions

The most common side effects (≥20% of patients) listed in the prescribing information include:^[1]

• Irregular menstruation (irregular periods)
• Amenorrhoea (absence of periods)
• Too much acid in the body fluids (acidosis)
• Low blood levels of albumin (hypoalbuminemia)
• Allergic reactions

Use in a specific population

It is not yet known whether Ammonaps (sodium phenylbutyrate) can cause fetal harm when administered to a pregnant woman. Please ask for medical advice before taking this medicine.^[1]

For a comprehensive list of side effects and adverse reactions please refer to the official prescribing information.^[1,6]

References

1. Full prescribing information [FDA]: Ammonaps (sodium phenylbutyrate) [PDF] FDA, cited on Oct 16, 2020

2. Urea Cycle Disorder (UCD)
Cincinnati Children’s Hospital Medical Center, cited on Oct 16, 2020

3. What is the urea cycle?
News Medical Life Sciences, cited on Oct 16, 2020

4. Phase 2 study of sodium phenylbutyrate in ALS
Cudkowicz M., Amyotroph Lateral Scler., Apr 2009

5. Ammonaps (sodium phenylbutyrate)
EMA product overview, cited on Oct 16, 2020

6. Full prescribing information [EMA]: Ammonaps (sodium phenylbutyrate) [PDF] EMA, cited on Oct 16, 2020

7. Sodium Phenulbutyrate
Australian Public Assessment Report