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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Other
Sodium Phenylbutyrate is a nitrogen-scavenging agent used as adjunctive therapy for the chronic management of patients with urea cycle disorders (UCDs) involving deficiencies of specific enzymes.
Name
Sodium Phenylbutyrate
Raw Name
SODIUM PHENYLBUTYRATE
Category
Other
Drug Count
4
Variant Count
7
Last Verified
February 17, 2026
RxCUI
199369, 2610128, 2610134, 213196, 984105, 984107
UNII
NT6K61736T
About Sodium Phenylbutyrate
Sodium Phenylbutyrate is a nitrogen-scavenging agent used as adjunctive therapy for the chronic management of patients with urea cycle disorders (UCDs) involving deficiencies of specific enzymes.
Detailed information about Sodium Phenylbutyrate
References used for this content
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Sodium Phenylbutyrate.
Urea cycle disorders are rare genetic conditions where the body lacks one of the enzymes necessary to convert nitrogen, a waste product of protein metabolism, into urea. In a healthy individual, nitrogen is converted into urea in the liver and excreted through urine. In patients with UCDs, nitrogen accumulates in the form of ammonia, a highly toxic substance that can lead to brain damage, coma, or death if left untreated. Sodium Phenylbutyrate belongs to a class of medications known as nitrogen scavengers, which provide an alternative pathway for the body to dispose of waste nitrogen, bypassing the defective urea cycle.
To understand how Sodium Phenylbutyrate works, one must understand the molecular biology of nitrogen disposal. Sodium Phenylbutyrate is a pro-drug; it is not the active moiety itself. Once ingested, it is rapidly metabolized (via beta-oxidation) into phenylacetate. Phenylacetate is the active metabolite that performs the "scavenging" work.
At the molecular level, phenylacetate undergoes enzymatic conjugation with the amino acid glutamine in the liver and kidneys. This reaction is catalyzed by the enzyme phenylacetyl-CoA:L-glutamine N-acetyltransferase. The result of this conjugation is a molecule called phenylacetylglutamine. Each molecule of phenylacetylglutamine contains two atoms of nitrogen. Unlike ammonia or free nitrogen, phenylacetylglutamine is easily filtered by the kidneys and excreted in the urine. By removing glutamine (which contains nitrogen), the body effectively lowers the overall nitrogen load, thereby preventing the formation of toxic ammonia. This "bypass" mechanism is critical for patients whose primary urea cycle is non-functional due to genetic mutations.
The pharmacokinetics of Sodium Phenylbutyrate are complex and highly dependent on the patient's metabolic state and liver function.
The primary, FDA-approved indication for Sodium Phenylbutyrate is the chronic management of urea cycle disorders. These include:
Beyond UCDs, Sodium Phenylbutyrate has been the subject of intense clinical research for other conditions. It has been investigated for its potential as a chemical chaperone in protein folding disorders and as a histone deacetylase (HDAC) inhibitor in certain cancers and neurodegenerative diseases. Notably, a combination of Sodium Phenylbutyrate and Taurursodiol was previously granted conditional approval for Amyotrophic Lateral Sclerosis (ALS), though its use in that context is subject to specific regulatory status and manufacturer programs (e.g., Relyvrio).
Sodium Phenylbutyrate is available in several formulations to accommodate different age groups and patient needs:
> Important: Only your healthcare provider can determine if Sodium Phenylbutyrate is right for your specific condition. Regular monitoring of plasma ammonia and amino acid levels is required to ensure the medication is working effectively.
The dosage of Sodium Phenylbutyrate is not "one size fits all." It must be meticulously calculated based on the patient's body surface area (BSA) or body weight and their individual protein tolerance. For adults and children weighing more than 20 kg (approximately 44 lbs), the standard recommended daily dose ranges from 9.9 to 13.0 grams per square meter (g/m²) per day.
This total daily dose is never taken all at once. It is typically divided into equal amounts and administered with each meal (e.g., three to six times per day) to coincide with the intake of dietary protein. The maximum daily dose is generally capped at 20 grams per day to avoid potential neurotoxicity from the phenylacetate metabolite.
In pediatric patients, particularly neonates and infants weighing less than 20 kg, dosing is even more critical. The recommended total daily dose for these small patients is 450 to 600 mg/kg/day.
As with adults, the dose must be divided into equal parts and given with each feeding. Because infants feed frequently, the medication may be administered 4 to 6 times in a 24-hour period. For very young infants, the powder formulation is typically mixed with formula or breast milk. Parents must be careful not to heat the mixture excessively, as this could potentially degrade the medication.
Sodium Phenylbutyrate should be used with extreme caution in patients with renal (kidney) impairment. Since the primary route of excretion for the nitrogen-scavenging product (phenylacetylglutamine) is the kidneys, a reduction in renal function can lead to the accumulation of metabolites. Healthcare providers may need to lower the dose or increase the frequency of monitoring for these patients.
Because the conversion of phenylbutyrate to phenylacetate and the subsequent conjugation with glutamine occur primarily in the liver, patients with hepatic (liver) impairment may have a reduced ability to process the drug. This can lead to increased plasma levels of phenylbutyrate and decreased production of the active scavenger. Close monitoring of ammonia levels is mandatory.
Clinical studies of Sodium Phenylbutyrate did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently than younger subjects. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function.
Proper administration is vital for the success of UCD management:
If a dose is missed, it should be taken as soon as the patient remembers, provided it is still close to the time of a meal. If it is almost time for the next scheduled dose, skip the missed dose and resume the regular schedule. Never double the dose to make up for a missed one, as this increases the risk of side effects and sodium overload.
An overdose of Sodium Phenylbutyrate can lead to a condition called metabolic acidosis or neurotoxicity. Symptoms of overdose may include extreme sleepiness, confusion, headache, taste disturbances, and lightheadedness. In the event of a suspected overdose, contact a poison control center or seek emergency medical attention immediately. Treatment is generally supportive and may include intravenous fluids to manage electrolyte imbalances.
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or stop the medication without medical guidance, as this could lead to a rapid and dangerous rise in ammonia levels.
Sodium Phenylbutyrate is associated with several common side effects that, while often manageable, can affect a patient's quality of life. According to clinical data published in the Journal of Pediatrics, the most frequently reported adverse reactions include:
While Sodium Phenylbutyrate is life-saving for UCD patients, it can cause severe reactions that require emergency care.
> Warning: Stop taking Sodium Phenylbutyrate and call your doctor immediately if you experience any of the following:
Long-term use of Sodium Phenylbutyrate requires constant vigilance. Prolonged use can lead to chronic nutritional deficiencies because the drug removes glutamine, an amino acid essential for various bodily functions. If glutamine levels fall too low, it can actually impair the body's ability to manage nitrogen, leading to a paradoxical increase in ammonia. Additionally, the high sodium load over many years can contribute to the development of hypertension (high blood pressure) or kidney strain.
As of 2026, there are no FDA black box warnings specifically for Sodium Phenylbutyrate monotherapy. However, there are significant "Warnings and Precautions" regarding its use in patients with heart failure or renal insufficiency due to the high sodium content.
Report any unusual symptoms or changes in your health to your healthcare provider immediately. Regular laboratory testing is the only way to ensure that the medication is not causing silent side effects like electrolyte imbalances or blood count changes.
Sodium Phenylbutyrate is a potent metabolic modifier. It must be used only under the supervision of a physician experienced in the treatment of inborn errors of metabolism. The most critical safety point is that this drug is not for the treatment of acute hyperammonemic coma. Acute episodes of high ammonia are life-threatening emergencies that require hemodialysis or other rapid-acting interventions. Sodium Phenylbutyrate is for long-term, maintenance therapy only.
No FDA black box warnings for Sodium Phenylbutyrate have been issued. However, the FDA emphasizes that it should be used as part of a comprehensive management plan that includes a low-protein diet and, in some cases, essential amino acid supplementation.
Each gram of Sodium Phenylbutyrate contains approximately 125 mg (5.4 mEq) of sodium. For a patient taking the maximum dose of 20 grams per day, this equates to 2,500 mg of sodium—more than the total daily recommended intake for a healthy adult. This is a major concern for patients with:
High levels of the metabolite phenylacetate have been associated with neurotoxicity in animal studies and some human clinical trials (particularly in cancer research where higher doses were used). Patients who experience unexplained sleepiness or confusion while their ammonia levels are normal should be evaluated for phenylacetate toxicity.
Sodium Phenylbutyrate works by removing glutamine. If glutamine levels are depleted too much, it can lead to a deficiency in essential nitrogen carriers. This is why patients must be monitored by a metabolic nutritionist to ensure they are receiving enough (but not too much) protein and amino acid supplements.
Patients taking Sodium Phenylbutyrate require frequent lab tests to ensure safety and efficacy. According to the American College of Medical Genetics and Genomics (ACMG) guidelines, monitoring should include:
Sodium Phenylbutyrate may cause dizziness, lightheadedness, or confusion in some patients. Patients should not drive or operate heavy machinery until they know how the medication affects them. If neurotoxicity symptoms occur, these activities must be avoided entirely.
Alcohol should be avoided while taking Sodium Phenylbutyrate. Alcohol can irritate the stomach lining, potentially worsening the gastrointestinal side effects of the drug. More importantly, alcohol metabolism can interfere with liver function, which is necessary for the drug to work correctly.
Never stop taking Sodium Phenylbutyrate suddenly. Discontinuing the medication can lead to a rapid and dangerous rise in ammonia levels (hyperammonemia), which can cause brain swelling and coma within hours or days. If the medication must be stopped, it must be done under strict medical supervision, usually in a hospital setting where ammonia levels can be monitored hourly.
> Important: Discuss all your medical conditions, especially heart or kidney problems, with your healthcare provider before starting Sodium Phenylbutyrate.
While there are few absolute contraindications regarding drug-drug interactions, certain combinations are highly dangerous for UCD patients:
Sodium Phenylbutyrate can interfere with certain laboratory tests:
For each major interaction, the management strategy involves:
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking. Even over-the-counter cold medicines can sometimes contain ingredients that affect nitrogen metabolism.
Sodium Phenylbutyrate must NEVER be used in the following circumstances:
These are conditions where the drug should only be used if the benefits clearly outweigh the risks, and under intense supervision:
Patients who have had allergic reactions to other phenylalkanoic acids (a chemical class of compounds) should be monitored closely for cross-sensitivity. While not common, the structural similarities between these compounds can occasionally trigger similar immune responses.
> Important: Your healthcare provider will evaluate your complete medical history, including heart and kidney function, before prescribing Sodium Phenylbutyrate. This medication requires a delicate balance between nitrogen scavenging and sodium management.
Sodium Phenylbutyrate is classified as Pregnancy Category C. There are no adequate and well-controlled studies in pregnant women. Animal reproduction studies have shown that phenylacetate (the active metabolite) can be neurotoxic to developing fetuses, potentially causing brain damage or developmental delays.
However, untreated urea cycle disorders in the mother are also extremely dangerous and can lead to fatal hyperammonemia during pregnancy or immediately after delivery (postpartum). Therefore, the use of Sodium Phenylbutyrate during pregnancy is a high-risk decision that must be made by a multidisciplinary team including a geneticist and a high-risk obstetrician. If used, the lowest effective dose should be employed, and ammonia levels must be monitored very frequently.
It is not known whether Sodium Phenylbutyrate or its metabolites are excreted in human milk. Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants (including neurotoxicity from phenylacetate), a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother. Most experts recommend formula feeding for infants if the mother must remain on Sodium Phenylbutyrate.
Sodium Phenylbutyrate is FDA-approved for use in children of all ages, including neonates, for the management of UCDs. In fact, the pediatric population is the primary user of this medication.
There is very little data on the use of Sodium Phenylbutyrate in patients over 65. Because elderly patients are more likely to have decreased renal function and cardiovascular disease (like hypertension or heart failure), they are at much higher risk for complications from the drug's high sodium content. If used in the elderly, doses should start low and kidney function should be checked frequently.
In patients with renal impairment, the clearance of phenylacetylglutamine (the final waste product) is reduced. This can lead to a "backlog" in the metabolic pathway, causing phenylacetate to build up in the blood. Phenylacetate levels above 3.5 mmol/L are associated with neurotoxicity. Patients with a GFR (Glomerular Filtration Rate) below 30 mL/min require significant dose reductions and potentially alternative therapies.
Patients with liver impairment (e.g., cirrhosis) may have difficulty converting phenylbutyrate to its active form. This reduces the drug's effectiveness as a nitrogen scavenger. In these patients, doctors may prefer using Glycerol Phenylbutyrate (Ravicti), which is processed slightly differently, or may increase the frequency of ammonia monitoring to ensure the drug is still working.
> Important: Special populations require individualized medical assessment and frequent laboratory monitoring to balance the risks of the medication against the risks of the underlying urea cycle disorder.
Sodium Phenylbutyrate is a pro-drug that functions as a nitrogen-scavenging agent. Its molecular mechanism involves the following steps:
By removing glutamine, the drug removes the nitrogen that would otherwise be converted into toxic ammonia. This provides an alternative to the urea cycle, which is defective in patients with UCDs.
The pharmacodynamic effect of Sodium Phenylbutyrate is the reduction of plasma ammonia and glutamine levels. The onset of action is relatively fast, with nitrogen excretion increasing within hours of the first dose. However, the full therapeutic effect on steady-state ammonia levels may take several days of consistent dosing to achieve. There is no evidence of tolerance development; the drug remains effective as long as it is taken consistently.
| Parameter | Value |
|---|---|
| Bioavailability | High (>80% in fasting state) |
| Protein Binding | 5% to 80% (variable for metabolites) |
| Half-life | Phenylbutyrate: 0.8 hours; Phenylacetate: 1.2 hours |
| Tmax | 1.0 hour (fasting) |
| Metabolism | Hepatic and Renal Beta-oxidation |
| Excretion | Renal (>80% as phenylacetylglutamine) |
Sodium Phenylbutyrate is classified as an Ammonia Detoxicant or Nitrogen Scavenger. It is part of a small group of drugs used for inborn errors of metabolism. Related medications include:
Medications containing this ingredient
Common questions about Sodium Phenylbutyrate
Sodium Phenylbutyrate is primarily used for the chronic management of patients with urea cycle disorders (UCDs). These are rare genetic conditions where the body cannot properly remove nitrogen, leading to toxic levels of ammonia in the blood. The drug works by providing an alternative pathway for nitrogen excretion, bypassing the defective urea cycle enzymes. It is typically prescribed for deficiencies in carbamylphosphate synthetase (CPS), ornithine transcarbamylase (OTC), or argininosuccinic acid synthetase (ASAS). It is not used for treating acute, emergency spikes in ammonia but rather as a daily maintenance therapy to prevent those spikes from occurring.
The most common side effects include menstrual irregularities in women (such as missed periods), a decrease in appetite, and a distinct body odor often described as smelling like 'sweaty feet' or 'locker rooms.' Many patients also experience gastrointestinal issues like nausea, abdominal pain, or a bitter taste in the mouth. Because the drug contains a large amount of sodium, it can also cause changes in electrolyte levels, such as high sodium or low potassium. Some patients may also experience skin rashes or headaches. Always report new or worsening symptoms to your healthcare provider, as they may indicate a need for dose adjustment.
It is strongly recommended that you avoid alcohol while taking Sodium Phenylbutyrate. Alcohol can irritate the stomach and gastrointestinal tract, which may worsen the nausea and stomach pain often caused by the medication. More importantly, alcohol can affect liver function and metabolic processes, potentially interfering with the drug's ability to clear ammonia from your system. Since patients with urea cycle disorders already have a compromised ability to process metabolic waste, adding alcohol creates an unnecessary and dangerous risk of a hyperammonemic crisis. Always consult your doctor before consuming any alcoholic beverages.
Sodium Phenylbutyrate is classified as Pregnancy Category C, meaning it should only be used if the potential benefit justifies the potential risk to the fetus. Animal studies have suggested that the drug's metabolites could be toxic to a developing baby's brain. However, a mother with an untreated urea cycle disorder faces a life-threatening risk of high ammonia levels during pregnancy and after childbirth. Because of this, the decision to use the drug involves a careful risk-benefit analysis by a specialist. If you are pregnant or planning to become pregnant, you must discuss a specialized management plan with your metabolic specialist and obstetrician.
Sodium Phenylbutyrate begins to work relatively quickly after the first dose, with its active metabolite appearing in the blood within an hour. You may see an increase in nitrogen excretion in the urine within the first 24 hours. However, it may take several days of consistent dosing and dietary management to see a stable reduction in your plasma ammonia levels. It is important to remember that this medication is a long-term treatment. It does not cure the underlying genetic disorder but manages the symptoms as long as the medication is taken exactly as prescribed every day.
No, you should never stop taking Sodium Phenylbutyrate suddenly unless specifically instructed by your doctor in a hospital setting. This medication is essential for keeping your ammonia levels within a safe range. If you stop taking it, nitrogen will quickly build up in your blood, which can lead to a hyperammonemic crisis. Symptoms of this crisis include confusion, vomiting, extreme sleepiness, and eventually coma or death. If you are having trouble taking the medication due to side effects or cost, talk to your doctor immediately so they can find an alternative way to manage your condition safely.
If you miss a dose of Sodium Phenylbutyrate, take it as soon as you remember, as long as it is near the time of a meal or feeding. If it is almost time for your next scheduled dose, skip the missed dose and continue with your regular schedule. Do not take two doses at once to make up for the one you missed, as this can increase the risk of sodium overload or side effects. Because missing doses can cause your ammonia levels to rise, it may be helpful to use a pill organizer or a phone alarm to help you remember your schedule.
Weight gain is not a commonly reported direct side effect of Sodium Phenylbutyrate. In fact, many patients experience a decrease in appetite (anorexia), which can lead to weight loss. However, the medication is a sodium salt, and high sodium intake can cause the body to retain water, which might look like weight gain or swelling (edema) in the legs or face. If you notice rapid weight gain over a few days or significant swelling, contact your doctor, as this could be a sign that the sodium in the medication is affecting your heart or kidneys.
Sodium Phenylbutyrate can interact with several other drugs, some of which are very dangerous. For example, valproic acid (an anti-seizure med) and corticosteroids (like prednisone) can cause ammonia levels to rise, making Sodium Phenylbutyrate less effective. Other drugs like probenecid can slow down the removal of the medication from your body, increasing the risk of toxicity. Because of these risks, you must provide your doctor with a complete list of all prescription drugs, over-the-counter medicines, and herbal supplements you are taking to ensure there are no dangerous interactions.
Yes, Sodium Phenylbutyrate is available as a generic medication in both tablet and powder forms. The brand name version of the tablets and powder is Buphenyl. Having a generic version available generally makes the medication more affordable for patients, although it is still considered a specialty drug. There are also newer, brand-only versions of phenylbutyrate, such as Pheburane (taste-masked pellets) and Olpruva (oral suspension), which may not have generic equivalents yet. Your pharmacist or insurance provider can help you determine which version is covered under your plan.