Sulfamethoxazole and Trimethoprim Oral Suspension

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

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

DOWNLOAD PDF HERE

1 DEFINITION

Sulfamethoxazole and Trimethoprim Oral Suspension contains NLT 90.0% and NMT 110.0% of the labeled amounts of sulfamethoxazole (C₁₀H₁₁N₃O₃S) and trimethoprim (C₁₄H₁₈N₄O₃).

2 IDENTIFICATION

A. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

3 ASSAY

Procedure

Mobile phase: Mix 1400 mL of water, 400 mL of acetonitrile, and 2.0 mL of triethylamine in a 2000-mL volumetric flask. Allow to equilibrate to room temperature, and adjust with 0.2 N sodium hydroxide or dilute glacial acetic acid (1 in 100) to a pH of 5.9 ± 0.1. Dilute with water to volume, and pass through a filter of 0.45-μm pore size.

Standard stock solution: 0.32 mg/mL of USP Trimethoprim RS and 0.32J mg/mL of USP Sulfamethoxazole RS in methanol, where J is the ratio of the labeled amount, in mg, of sulfamethoxazole to the labeled amount, in mg, of trimethoprim in the dosage form

Standard solution: 0.032 mg/mL of USP Trimethoprim RS per mL and 0.032J mg/mL of USP Sulfamethoxazole RS per mL in Mobile phase from Standard stock solution

Sample stock solution: Transfer a volume of Oral Suspension, equivalent to 80 mg of sulfamethoxazole, to a 50-mL volumetric flask with the aid of 30 mL of methanol. Sonicate the mixture for 10 min with occasional shaking. Allow to equilibrate to room temperature, dilute with methanol to volume, and centrifuge. Use the filtrate in the preparation of the Sample solution.

Sample solution: Nominally 0.16 mg/mL of sulfamethoxazole in Mobile phase from Sample stock solution. Filter the solution.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 254 nm

Column: 3.9-mm × 30-cm; 10-μm packing L1

Flow rate: 2 mL/min

Injection volume: 20 μL

System suitability

Sample: Standard solution

[Note—The relative retention times for trimethoprim and sulfamethoxazole are 1.0 and 1.8, respectively.]

Suitability requirements

Resolution: NLT 5.0 between sulfamethoxazole and trimethoprim

Tailing factor: NMT 2.0 for sulfamethoxazole and trimethoprim

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of trimethoprim (C₁₄H₁₈N₄O₃) and sulfamethoxazole (C₁₀H₁₁N₃O₃S) in the portion of Oral

Suspension taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of trimethoprim or sulfamethoxazole from the Sample solution

r_S = peak response of trimethoprim or sulfamethoxazole from the Standard solution

C_S = concentration of the USP Trimethoprim RS or USP Sulfamethoxazole RS in the Standard solution (mg/mL)

C_U = nominal concentration of trimethoprim or sulfamethoxazole in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0% each of sulfamethoxazole (C H N O S) and trimethoprim (C H N O )

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 IMPURITIES

Organic Impurities

Solution A: Triethylamine and water (2.5:2000). Adjust with glacial acetic acid to a pH of 5.9.

Solution B: Acetonitrile

Mobile phase: See Table 1.

Table 1

Diluent: Solution A and Solution B (75:25)

System suitability solution: 1 mg/mL of USP Sulfamethoxazole RS; 0.2 mg/mL of USP Trimethoprim RS; 1 μg/mL each of USP

Sulfamethoxazole N4-Glucoside RS, USP Sulfamethoxazole Related Compound C RS, and 0.3 μg/mL each of USP Trimethoprim Related

Compound A RS, USP Trimethoprim Related Compound B RS, and USP Diaveridine RS in Diluent

Standard stock solution A: 0.3 mg/mL of USP Sulfamethoxazole N4-Glucoside RS, and 0.05 mg/mL each of USP Sulfamethoxazole Related

Compound C RS and USP Sulfamethoxazole RS in Diluent. Sonicate for 5 min to dissolve.

Standard stock solution B: 0.03 mg/mL each of USP Trimethoprim RS, USP Trimethoprim Related Compound A RS, USP Trimethoprim

Related Compound B RS, and USP Diaveridine RS in Diluent. Sonicate for 5 min to dissolve.

Standard solution: 0.03 mg/mL of USP Sulfamethoxazole N4-Glucoside RS; 5 μg/mL each of USP Sulfamethoxazole Related Compound C RS and USP Sulfamethoxazole RS from Standard stock solution A; and 1 μg/mL each of USP Trimethoprim RS, USP Trimethoprim Related

Compound A RS, USP Trimethoprim Related Compound B RS, and USP Diaveridine RS from Standard stock solution B in Diluent

Sample solution: Nominally 1 mg/mL of sulfamethoxazole and 0.2 mg/mL of trimethoprim from a volume of Oral Suspension in Diluent.

Sonicate for 15 min in Diluent before diluting to fnal volume.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 240 nm

Column: 4.6-mm × 25-cm; 5-μm packing L1

Flow rate: 0.8 mL/min

Injection volume: 20 μL

System suitability

Sample: System suitability solution

Suitability requirements

Resolution: NLT 1.5 between trimethoprim and trimethoprim related compound A; and NLT 1.5 between sulfamethoxazole and trimethoprim related compound B

Relative standard deviation: NMT 2.0% for sulfamethoxazole related compound C, sulfamethoxazole N -glucoside, diaveridine, trimethoprim, trimethoprim related compound A, sulfamethoxazole, and trimethoprim related compound B

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of sulfanilic acid and sulfanilamide in the portion of Oral Suspension taken:

Result = (r_U/r_S) × (C_S/C_U) × (1/F) × 100

r_U = peak response of sulfanilic acid or sulfanilamide from the Sample solution

r_S = peak response of sulfamethoxazole from the Standard solution

C_S = concentration of USP Sulfamethoxazole RS in the Standard solution (mg/mL)

C_U = nominal concentration of sulfamethoxazole in the Sample solution (mg/mL)

F = relative response factor

Calculate the percentage of sulfamethoxazole related compound C and sulfamethoxazole N₄-glucoside in the portion of Oral Suspension taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of sulfamethoxazole related compound C or sulfamethoxazole N₄-glucoside from the Sample solution

r_S = peak response of sulfamethoxazole related compound C or sulfamethoxazole N₄-glucoside from the Standard solution

C_S = concentration of USP Sulfamethoxazole Related Compound C RS or USP Sulfamethoxazole N₄-Glucoside RS in the Standard solution (mg/mL)

C_U = nominal concentration of sulfamethoxazole in the Sample solution (mg/mL)

Calculate the percentage of diaveridine, trimethoprim related compound A, trimethoprim related compound B, and any other unspecified degradation product in the portion of Oral Suspension taken:

Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of diaveridine, trimethoprim related compound A, trimethoprim related compound B, or any other unspecified degradation product from the Sample solution

r_S = peak response of diaveridine, trimethoprim related compound A, trimethoprim related compound B, or trimethoprim (for any other unspecified degradation product) from the Standard solution

C_S = concentration of USP Diaveridine RS, USP Trimethoprim Related Compound A RS, USP Trimethoprim Related Compound B RS, or USP Trimethoprim RS (for any other unspecified degradation product) in the Standard solution (mg/mL)

C_U = nominal concentration of trimethoprim in the Sample solution (mg/mL)

Acceptance criteria: See Table 2. Disregard limit: 0.01%.

Table 2

^a Process related impurities monitored in the drug substance.

6 SPECIFIC TESTS

pH 〈791〉: 5.0–6.5

Alcohol Determination, Method II〈611〉: NMT 0.5% of alcohol (C H OH)

7 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, light-resistant containers. Store at controlled room temperature. Protect from light.

USP Reference Standards 〈11〉

USP Alcohol Determination–Acetonitrile RS

USP Alcohol Determination–Alcohol RS

USP Diaveridine RS