Sulfadimethoxine

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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Sulfadimethoxine contains not less than 98.0 percent and not more than 102.0 percent of C₁₂H₁₄N₄O₄S, calculated on the dried basis.

1 Packaging and storage

Preserve in tight, light-resistant containers, and store at controlled room temperature.

2 Labeling

Label it to indicate that it is for veterinary use only.

USP Reference standards 〈11〉—

USP Sulfadimethoxine RS

3 Identification

Change to read:

A: Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K (CN 1-May-2020) .

Change to read:

B: Spectroscopic Identification Tests 〈197〉, Ultraviolet-Visible Spectroscopy: 197U (CN 1-May-2020) —

Solution: 1 in 100,000.

Medium: alcohol.

Absorptivities, calculated on the dried basis, at 272 nm do not differ by more than 3.0%.

C: To about 100 mg, add 3 mL of 2.5 N sodium hydroxide and 50 mL of water, mix until dissolved, and dilute with water to 100 mL. To about 5mL of this solution, add 100 mg of phenol, and heat to boiling. Cool the solution, and add 0.5 mL of sodium hypochlorite TS and 3 drops of 2.5 N sodium hydroxide: a yellow color is produced.

D: To about 10 mg dissolved in 2 mL of diluted hydrochloric acid, add 3 drops of sodium nitrite solution (1 in 100), and dilute with water to 4 mL: the solution turns yellow. Add 1 mL of 2.5 N sodium hydroxide containing 10 mg of 2-naphthol: a red-orange precipitate is formed.

Melting range 〈741〉: between 197° and 202°.

Loss on drying 〈731〉: Dry it at 105° for 3 hours: it loses not more than 0.5% of its weight.

Residue on ignition 〈281〉: not more than 0.1%.

4 Assay

Mobile phase—Dissolve 6 g of monobasic sodium phosphate in water to make 1000 mL. Adjust with 50% (w/v) sodium hydroxide solution to a pH of 7.0. Prepare a mixture of this solution and methanol (300:100). Make adjustments if necessary (see System Suitability under

Chromatography 〈621〉).

Standard preparation—Quantitatively dissolve an accurately weighed quantity of USP Sulfadimethoxine RS in Mobile phase to obtain a solution having a known concentration of about 0.2 mg per mL. Protect this solution from light.

Assay preparation—Transfer about 20 mg of Sulfadimethoxine, accurately weighed, to a 100-mL volumetric flask, add about 75 mL of Mobile phase, and swirl to dissolve. Dilute this solution with Mobile phase to volume, and mix. Protect this solution from light.

Chromatographic system (see Chromatography 〈621〉)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 1.5; and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure—Separately inject equal volumes (about 10 μL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C₁₂H₁₄N₄O₄S in the portion of

Sulfadimethoxine taken by the formula:

100C(r_U/r_S)

in which C is the concentration, in mg per mL, of USP Sulfadimethoxine RS in the Standard preparation; and r_U and r_S are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.