Sulfamethoxazole Oral Suspension
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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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1 DEFINITION
Sulfamethoxazole Oral Suspension contains NLT 95.0% and NMT 110.0% of the labeled quantity of sulfamethoxazole (C10H11N3O3S).
2 IDENTIFICATION
A.
Standard solution: Dissolve 100 mg of USP Sulfamethoxazole RS in 5 mL of ammonium hydroxide. Dilute with methanol to 50.0 mL.
Sample solution: Transfer a quantity of Oral Suspension, equivalent to 100 mg of sulfamethoxazole, into a 50-mL centrifuge tube. Add 5 mL of ammonium hydroxide, and shake gently. Add 25 mL of methanol, shake thoroughly for 3 min, centrifuge, decant the supernatant into a 50-mL volumetric flask, and dilute with methanol to volume.
Chromatographic system
(See Chromatography 〈621〉, Thin-Layer Chromatography.)
Mode: TLC
Adsorbent: 0.25-mm layer of chromatographic silica gel
Application volume: 50 μL
Developing solvent system: Alcohol, n-heptane, chloroform, and glacial acetic acid (25:25:25:7)
Spray reagent: 0.10 g of p-dimethylaminobenzaldehyde in 1 mL of hydrochloric acid. Dilute with alcohol to 100 mL.
Analysis
Samples: Standard solution and Sample solution
Apply the Samples, and allow the spots to dry. Develop the chromatogram until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Locate the spots on the plate by lightly spraying with Spray reagent.
Acceptance criteria: The R value of the principal spot of the Sample solution corresponds to that of the Standard solution.
B.
Sample: Transfer a quantity of Oral Suspension, equivalent to 500 mg of sulfamethoxazole, into a 50-mL centrifuge tube. Add 25 mL of water, mix, and centrifuge. Decant and discard the supernatant, resuspend the residue in 25 mL of water, mix, and centrifuge again. Decant and discard the clear supernatant. Repeat the washing procedure an additional two times.
Analysis: Dissolve the residue from the Sample in 10 mL of hydrochloric acid, and add 15 mL of sodium nitrite solution (1 in 100) and 5 mL of sodium hydroxide solution (1 in 10) containing 10 mg of 2-naphthol.
Acceptance criteria: A red-orange precipitate is produced.
3 ASSAY
Procedure
Sample solution: Mix a volume of Oral Suspension, equivalent to 1 g of sulfamethoxazole, with 20 mL of glacial acetic acid and 40 mL of water.
Titrimetric system
Mode: Direct titration
Titrant: 0.1 M sodium nitrite VS
Endpoint detection: Potentiometric
Analysis: Add 15 mL of hydrochloric acid to the Sample solution. Cool to 15°, and titrate immediately with Titrant, using a calomel–platinum electrode system. Each mL of 0.1 M sodium nitrite is equivalent to 25.33 mg of sulfamethoxazole.
Acceptance criteria: 95.0%–110.0%
4 PERFORMANCE TESTS
Uniformity of Dosage Units 〈905〉: Meets the requirements for oral suspension packaged in single-unit containers
Deliverable Volume 〈698〉: Meets the requirements for oral suspension packaged in multiple-unit containers
5 ADDITIONAL REQUIREMENTS
Packaging and Storage: Preserve in tight, light-resistant containers.
USP Reference Standards 〈11〉
USP Sulfamethoxazole RS
