Sulfamethoxazole and Trimethoprim Oral Suspension

» Sulfamethoxazole and Trimethoprim Oral Suspension contains not less than 90.0 percent and not more than 110.0 percent of the labeled amounts of sulfamethoxazole (C10H11N3O3S) and trimethoprim (C14H18 N4O3).

Packaging and storage— Preserve in tight, light-resistant containers.

—

USP Sulfamethoxazole RS

USP Sulfamethoxazole N4-Glucoside RS

USP Sulfanilamide RS

USP Sulfanilic Acid RS

C6H7NO3S 173.19

USP Trimethoprim RS

Identification— In the Chromatographic purity test, the respective Test solutions exhibit spots whose RF values correspond to those spots produced by the Standard solutions of USP Trimethoprim RS and USP Sulfamethoxazole RS.

Uniformity of dosage units

905

—

for oral suspension packaged in single-unit containers: meets the requirements.

Deliverable volume

698

—

for oral suspension packaged in multiple-unit containers: meets the requirements.

791

: between 5.0 and 6.5.

Chromatographic purity—

limit of trimethoprim degradation product—

Test solution— Transfer an accurately measured volume of Oral Suspension, equivalent to about 40 mg of trimethoprim, to a separatory funnel. Extract with three 25-mL portions of a mixture of chloroform and methanol (8:2), collecting the extracts in a 125-mL conical flask. Evaporate the combined extracts with the aid of a current of air to dryness on a steam bath. Dissolve the residue in 2.0 mL of the mixture of chloroform and methanol (8:2), then centrifuge.

Standard solution A— Dissolve an accurately weighed quantity of USP Trimethoprim RS in a mixture of chloroform and methanol (8:2) to obtain a solution having a known concentration of about 20 mg per mL.

Standard solution B— Dilute an accurately measured volume of Standard solution A with a mixture of chloroform and methanol (8:2) to obtain a solution having a known concentration of about 0.1 mg per mL.

Procedure— Apply 5 µL each of the Test solution, Standard solution A, and Standard solution B to separate points on a thin-layer chromatographic plate (see Chromatography

621

) coated with a 0.25-mm layer of chromatographic silica gel. Place the plate in a saturated chromatographic chamber, and develop the chromatogram in a solvent system consisting of a mixture of chloroform, methanol, and ammonium hydroxide (80:20:3) until the solvent front has moved at least 15 cm. Remove the plate from the chamber, air-dry, and view under short-wavelength UV light: trimethoprim produces a spot at about RF 0.7, and the trimethoprim degradation product can be seen at RF 0.3 to 0.5. Any spot from the Test solution at about RF 0.3 to 0.5 is not greater in size and intensity than the spot produced by Standard solution B at about RF 0.7, corresponding to not more than 0.5%.

limit of sulfanilamide, sulfanilic acid, and sulfamethoxazole N4-glucoside)—

Alcohol–methanol mixture— Mix dehydrated alcohol and methanol (95:5).

Modified Ehrlich's reagent— Dissolve 100 mg of p-dimethylaminobenzaldehyde in 1 mL of hydrochloric acid, and dilute with alcohol to 100 mL.

Test solution— Using a syringe, transfer an accurately measured volume of Oral Suspension, equivalent to 200 mg of sulfamethoxazole, to a 100-mL volumetric flask containing 10 mL of ammonium hydroxide; and add 50 mL of methanol. Shake for 3 minutes, and dilute with methanol to volume. Centrifuge a portion of the solution for 3 minutes.

Standard solution A— Weigh 20 mg of USP Sulfamethoxazole RS into a 10-mL volumetric flask, dissolve in 1 mL of ammonium hydroxide, dilute with methanol to volume, and mix.

Standard solution B— Weigh 10 mg of USP Sulfanilamide RS into a 50-mL volumetric flask, dissolve in 5 mL of ammonium hydroxide, and dilute with methanol to volume. Pipet 5 mL of this solution into a 100-mL volumetric flask, add 10 mL of ammonium hydroxide, and dilute with methanol to volume.

Standard solution C— Weigh 10 mg of USP Sulfanilic Acid RS into a 50-mL volumetric flask, dissolve in 5 mL of ammonium hydroxide, and dilute with methanol to volume. Pipet 3 mL of this solution into a 100-mL volumetric flask, add 10 mL of ammonium hydroxide, and dilute with methanol to volume.

Standard solution D— Weigh 3.0 mg of USP Sulfamethoxazole N4-Glucoside RS into a 50-mL volumetric flask, dissolve in 5 mL of ammonium hydroxide, and dilute with methanol to volume.

Procedure— Apply 50 µL each of the Test solution and Standard solutions A, B, C, and D to separate points on a thin-layer chromatographic plate (see Chromatography

621

) coated with a 0.25-mm layer of chromatographic silica gel. Place the plate in an unsaturated chromatographic chamber, and develop the chromatogram in a solvent system consisting of a mixture of Alcohol–methanol mixture, heptane, chloroform, and glacial acetic acid (25:25:25:7) until the solvent front has moved at least 12 cm. Remove the plate from the developing chamber, air-dry, spray with Modified Ehrlich's reagent, and allow the plate to stand for 15 minutes: sulfamethoxazole produces a spot at about RF 0.7. Any spots from the Test solution at about RF 0.5, 0.1, and 0.3 are not greater in size and intensity than spots produced by Standard solutions B, C, and D, respectively, corresponding to not more than 0.5% of sulfanilamide, 0.3% of sulfanilic acid, and 3.0% of sulfamethoxazole N4-glucoside.

Alcohol content, Method II

611

: not more than 0.5% of C2H5OH.

Assay—

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 filter through a 0.45-µm membrane, making adjustments if necessary (see System Suitability under Chromatography

621

Standard preparation— Dissolve accurately weighed quantities of USP Trimethoprim RS and USP Sulfamethoxazole RS in methanol, and quantitatively dilute with methanol to obtain a solution containing, in each mL, about 0.32 mg and 0.32J mg, respectively, J being the ratio of the labeled amount, in mg, of sulfamethoxazole to the labeled amount, in mg, of trimethoprim in the dosage form. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix to obtain a Standard preparation having known concentrations of about 0.032 mg of USP Trimethoprim RS per mL and 0.032J mg of USP Sulfamethoxazole RS per mL.

Assay preparation— Transfer an accurately measured volume of Oral Suspension, equivalent to about 80 mg of Sulfamethoxazole, to a 50-mL volumetric flask with the aid of about 30 mL of methanol. Sonicate the mixture for about 10 minutes with occasional shaking. Allow to equilibrate to room temperature, dilute with methanol to volume, mix, and centrifuge. Transfer 5.0 mL of the supernatant to a second 50-mL volumetric flask, dilute with Mobile phase to volume, mix, and filter.

Chromatographic system (see Chromatography

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)— The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 1.0 for trimethoprim and 1.8 for sulfamethoxazole; the resolution, R, between sulfamethoxazole and trimethoprim is not less than 5.0; the tailing factor for the trimethoprim and sulfamethoxazole peaks is not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 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 quantities, in mg, of trimethoprim (C14H18N4O3) and sulfamethoxazole (C10H11N3O3S) in each mL of the Oral Suspension taken by the formula:

(500C/V)(rU / rS)

in which C is the concentration, in mg per mL, of the appropriate USP Reference Standard in the Standard preparation; V is the volume, in mL, of Oral Suspension taken; and rU and rS are the peak responses of the corresponding analyte obtained from the Assay preparation and the Standard preparation, respectively.

Auxiliary Information— Please check for your question in the FAQs before contacting USP.

Topic/Question	Contact	Expert Committee
Monograph	Leonel M. Santos, Ph.D. Senior Scientific Liaison 1-301-816-8168	(SM12010) Monographs - Small Molecules 1
Reference Standards	RS Technical Services 1-301-816-8129 rstech@usp.org

USP35–NF30 Page 4718

Pharmacopeial Forum: Volume No. 29(6) Page 1990