Phenobarbital Oral Solution

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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>> Phenobarbital Oral Solution contains not less than 90.0 percent and not more than 110.0 percent of the labeled amount of phenobarbital (C₁₂H₁₂N₂O₃).

1 Packaging and storage

Preserve in tight, light-resistant containers.

2 USP REFERENCE STANDARDS (11)

USP Phenobarbital RS

3 Identification

A: Place 10 mL of Oral Solution in a separator containing 20 mL of water, add 5 mL of 1 N sodium hydroxide, and extract with two 10-mL portions of chloroform, discarding the chloroform extracts. Add 5 mL of 3 N hydrochloric acid, and extract with two 25-mL portions of chloroform, filtering the extracts through paper into a beaker. Remove the chloroform by evaporation on a steam bath, and dry the residue at 105° for 2 hours: the residue so obtained meets the requirements for Identification test A under Phenobarbital.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, both relative to the internal standard, as obtained in the Assay.

4 ALCOHOL DETERMINATION, Method II (611)

Between 12.0% and 15.0% of C₂H₅OH.

5 Assay

5.1 pH 4.5 Buffer solution, Mobile phase, and Chromatographic system

Prepare as directed in the Assay under Phenobarbital.

5.2 Diluent

Prepare a mixture of methanol and pH 4.5 Buffer solution (2:1).

5.3 Internal standard solution

Dissolve a sufficient quantity of caffeine in Diluent to obtain a solution having a concentration of about 1.7 mg per mL.

5.4 Standard preparation

Transfer about 33 mg of USP Phenobarbital RS, accurately weighed, to a 25-mL volumetric flask containing 2.0 mL of Internal standard solution. Dilute with Diluent to volume, and mix.

5.5 Assay preparation

Transfer a quantity of Oral Solution, equivalent to about 33 mg of phenobarbital, to a 25-mL volumetric flask containing 2.0 mL of Internal standard solution. Dilute with Diluent to volume, and mix.

5.6 Procedure

Proceed as directed for Procedure in the Assay under Phenobarbital. Calculate the quantity, in mg, of phenobarbital (C₁₂H₁₂N₂O₃) in the portion of the Oral Solution taken by the formula:

W(R_U/R_S)

in which the terms are as defined therein.