Drug compounds have included stable heavy isotopes of carbon, hydrogen, and other elements, mostly as quantitative tracers while the drugs were being developed. Because deuteration may have an effect on a drug's pharmacokinetics and metabolic properties, it is a cause for concern [1].

Absorption, Distribution and Excretion
Following oral administration of a single 5g dose of sodium phenylbutyrate, the Cmax was 195-218 µg/mL under fasting conditions and the Tmax was one hour. The effect of food on drug absorption is unknown.
Approximately 80–100% of the dose was excreted by the kidneys within 24 hours as the conjugation product, phenylacetylglutamine. For each gram of sodium phenylbutyrate administered, it is estimated that between 0.12–0.15 grams of phenylacetylglutamine nitrogen are produced.

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Metabolism / Metabolites
The major sites for metabolism of sodium phenylbutyrate are the liver and kidney. Phenylbutyric acid is rapidly metabolized to phenylacetate via beta-oxidation. Phenylacetate is conjugated with phenylacetyl-CoA, which in turn combines with glutamine via acetylation to form phenylacetylglutamine.

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Biological Half-Life
Following oral administration of a single 5g dose of sodium phenylbutyrate, the elimination half-life of phenylbutyric acid ranged from 0.76 to 0.77 hours.

Hepatotoxicity
While the urea cycle disorders are caused by deficiencies of hepatic enzymes responsible for the elimination of nitrogen, patients generally present with hyperammonemia without other features or biochemical evidence of hepatic injury. Thus, serum aminotransferase, alkaline phosphatase and bilirubin levels are generally normal or only mildly elevated. Newborns presenting with hyperammonemia may have hepatomegaly but other, non-urea cycle, liver function is normal as is hepatic histology. Phenylbutyrate can help to lower ammonia levels acutely and manage to keep them in the normal or near normal range, but generally does not affect other liver functions. In open label studies, a small proportion of patients (particularly with ornithine transcarbamylase [OTC] deficiency) have had ALT or AST elevations, but these have generally been attributed to the underlying condition or its complications. Phenylbutyrate has not been linked to instances of clinically apparent liver injury with jaundice.
Likelihood score: E (unlikely cause of clinically apparent liver injury, but experience with its use is limited).

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Protein Binding
When co-administered with tauroursodeoxycholic acid as a combination product, the _in vitro_ plasma protein binding of phenylbutyric acid is 82%.

[1]. Impact of Deuterium Substitution on the Pharmacokinetics of Pharmaceuticals. Ann Pharmacother. 2019 Feb;53(2):211-216.

[2]. Enhanced growth inhibition by combination differentiation therapy with ligands of peroxisome proliferator-activated receptor-gamma and inhibitors of histone deacetylase in adenocarcinoma of the lung. Clin Cancer Res. 2002 Apr;8(4):1206-12.

[3]. Sodium phenylbutyrate abrogates African swine fever virus replication by disrupting the virus-induced hypoacetylation status of histone H3K9/K14. Virus Res. 2017 Oct 15242:24-29.

[4]. 4-Phenylbutyric acid protects against lipopolysaccharide-induced bone loss by modulating autophagy in osteoclasts. Biochem Pharmacol. 2018 May151:9-17.

4-phenylbutyric acid is a monocarboxylic acid the structure of which is that of butyric acid substituted with a phenyl group at C-4. It is a histone deacetylase inhibitor that displays anticancer activity. It inhibits cell proliferation, invasion and migration and induces apoptosis in glioma cells. It also inhibits protein isoprenylation, depletes plasma glutamine, increases production of foetal haemoglobin through transcriptional activation of the gamma-globin gene and affects hPPARgamma activation. It has a role as an EC 3.5.1.98 (histone deacetylase) inhibitor, an antineoplastic agent, an apoptosis inducer and a prodrug. It is functionally related to a butyric acid. It is a conjugate acid of a 4-phenylbutyrate.
Phenylbutyric acid is a fatty acid and a derivative of [butyric acid] naturally produced by colonic bacteria fermentation. It demonstrates a number of cellular and biological effects, such as relieving inflammation and acting as a chemical chaperone. It is used to treat genetic metabolic syndromes, neuropathies, and urea cycle disorders.
Phenylbutyric acid is a Nitrogen Binding Agent. The mechanism of action of phenylbutyric acid is as an Ammonium Ion Binding Activity.
Phenylbutyrate and sodium benzoate are orphan drugs approved for the treatment of hyperammonemia in patients with urea cycle disorders, a series of at least 8 rare genetic enzyme deficiencies. The urea cycle is the major pathway of elimination of excess nitrogen including ammonia, and absence of one of the urea cycle enzymes often causes elevations in serum ammonia which can be severe, life-threatening and result in permanent neurologic damage and cognitive deficiencies. Both phenylbutyrate and sodium benzoate act by promoting an alternative pathway of nitrogen elimination. Neither phenylbutyrate nor sodium benzoate have been linked to cases of liver injury either in the form of serum enzyme elevations during therapy or clinically apparent acute liver injury.
4-Phenylbutyric acid has been reported in Streptomyces with data available.
See also: Sodium Phenylbutyrate (active moiety of); Glycerol Phenylbutyrate (is active moiety of).

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Drug Indication
Phenylbutyric acid is used for the treatment of various conditions, including urea cycle disorders, neonatal-onset deficiency, late-onset deficiency disease in patients with a history of hyperammonemic encephalopathy. Phenylbutyric acid must be combined with dietary protein restriction and, in some cases, essential amino acid supplementation. Phenylbutyric acid, as sodium phenylbutyrate, is used in combination with [tauroursodeoxycholic acid] to treat amyotrophic lateral sclerosis (ALS) in adults.

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Mechanism of Action
Sodium phenylbutyrate is the most commonly used salt used in drug products of phenylbutyric acid. Sodium phenylbutyrate is a pro-drug that rapidly metabolizes to phenylacetate. Phenylacetate is conjugated with phenylacetyl-CoA, which in turn combines with glutamine via acetylation to form phenylacetylglutamine. Phenylacetylglutamine is then excreted by the kidneys, thus providing an alternate mechanism of waste nitrogen excretion to the urea cycle. Phenylacetylglutamine is comparable to urea, as each molecule contains two moles of nitrogen.

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Pharmacodynamics
Phenylbutyric acid decreases elevated plasma ammonia glutamine levels in patients with urea cycle disorders. It increases waste nitrogen excretion in the form of phenylacetylglutamine. In the intestines, phenylbutyric acid was shown to reduce mucosal inflammation, regulate transepithelial fluid transport, and improve oxidative status. Some studies report antineoplastic properties of phenylbutyric acid, showing that phenylbutyric acid can promote growth arrest and apoptosis of cancer cells. It is suggested that phenylbutyric acid can act as an ammonia scavenger, chemical chaperone, and histone deacetylase inhibitor.

C10H8D4O2

168.23

168.109

461391-24-2

4-Phenylbutyric acid;1821-12-1

4775

Typically exists as solid at room temperature

47 - 49 °C

2.093

1

2

4

12

137

0

C([2H])(CC1=CC=CC=C1)(C([2H])([2H])C(O)=O)[2H]

OBKXEAXTFZPCHS-UHFFFAOYSA-N

InChI=1S/C10H12O2/c11-10(12)8-4-7-9-5-2-1-3-6-9/h1-3,5-6H,4,7-8H2,(H,11,12)

4-phenylbutanoic acid

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)